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OBJECTIVES: The purpose of this study was to evaluate the effect of placing small lead shields on the temple region of the skull to reduce radiation dose to the lens of the eye during interventional fluoroscopically-guided procedures and cone-beam computed tomography (CBCT) scans of the head. METHODS: EGSnrc Monte-Carlo code was used to determine the eye lens dose reduction when using lateral lead shields for single x-ray projections, CBCT scans with different protocols, and interventional neuroradiology procedures with the Zubal computational head phantom. A clinical C-Arm system was used to take radiographic projections and CBCT scans of anthropomorphic head phantoms without and with lead patches, and the images were compared to assess the effect of the shields. RESULTS: For single lateral projections, a 0.1 (0.3) mm thick lead patch reduced the dose to the left-eye lens by 40% to 60% (55% to 80%) from 45° to 90° RAO and to the right-eye lens by around 30% (55%) from 70° to 90° RAO. For different CBCT protocols, the reduction of lens dose with a 0.3 mm thick lead patch ranged from 20% to 53% at 110 kVp. For CBCT scans of the anthropomorphic phantom, the lead patch introduced streak artifacts that were mainly in the orbital regions but were insignificant in the brain region where most neuro-interventional activity occurs. CONCLUSION: The dose to the patient’s eye lens can be reduced considerably by placing small lead shields over the temple region of the head without substantially compromising image quality in neuro-imaging procedures.

Skin dose is dependent on the incident beam angle and corrections are needed for accurate estimation of the risk of deterministic effects of the skin. Angular-correction factors (ACF) were calculated and incorporated into our skin-dose-tracking system (DTS) and the results compared to Monte-Carlo simulations for a neuro-interventional procedure. To obtain the ACF's, EGSnrc Monte-Carlo (MC) software was used to calculate the dose averaged over 0.5, 1, 2, 3, 4 and 5 mm depth into the entrance surface of a water phantom at the center of the field as a function of incident beam to skin angle from 90-10 degrees for beam field sizes from 5-15 cm and for beam energies from 60-120 kVp. These values were normalized to the incident primary dose to obtain the ACF. The angle of incidence at each mesh vertex in the beam on the surface of the DTS patient graphic was calculated as the complement of the angle between the normal vector and the vector of the intersecting ray from the tube focal spot; skin dose at that vertex was calculated using the corresponding ACF. The skin-dose values with angular correction were compared to those calculated using MC with a matching voxelized phantom. The results show the ACF decreases with decreasing incident angle and skin thickness, and increases with increasing field size and kVp. Good agreement was obtained between the skin dose calculated by the angular-corrected DTS and MC, while use of the ACF allows the real-time performance of the DTS to be maintained.

The patient’s eye-lens dose changes for each projection view during fluoroscopically-guided neuro-interventional procedures. Monte-Carlo (MC) simulation can be done to estimate lens dose but MC cannot be done in real-time to give feedback to the interventionalist. Deep learning (DL) models were investigated to estimate patient-lens dose for given exposure conditions to give real-time updates. MC simulations were done using a Zubal computational phantom to create a dataset of eye-lens dose values for training the DL models. Six geometric parameters (entrance-field size, LAO gantry angulation, patient x, y, z head position relative to the beam isocenter, and whether patient’s right or left eye) were varied for the simulations. The dose for each combination of parameters was expressed as lens dose per entrance air kerma (mGy/Gy). Geometric parameter combinations associated with high-dose values were sampled more finely to generate more high-dose values for training purposes. Additionally, dose at intermediate parameter values was calculated by MC in order to validate the interpolation capabilities of DL. Data was split into training, validation and testing sets. Stacked models and median algorithms were implemented to create more robust models. Model performance was evaluated using mean absolute percentage error (MAPE). The goal for this DL model is that it be implemented into the Dose Tracking System (DTS) developed by our group. This would allow the DTS to infer the patient’s eye-lens dose for real-time feedback and eliminate the need for a large database of pre-calculated values with interpolation capabilities.

BACKGROUND AND PURPOSE: Quality of visualization of treatment devices during critical stages of endovascular interventions, can directly impact their safety and efficacy. Our aim was to compare the visualization of neurointerventional procedures and treatment devices using a 194-μm pixel flat panel detector mode and a 76-μm pixel complementary metal oxide semiconductor detector mode (high definition) of a new-generation x-ray detector system using a blinded-rater study. MATERIALS AND METHODS: Deployment of flow-diversion devices for the treatment of internal carotid artery aneurysms was performed under flat panel detector and high-definition-mode image guidance in a neurointerventional phantom simulating patient cranium and tissue attenuation, embedded with 3D-printed intracranial vascular models, each with an aneurysm in the ICA segment. Image-sequence pairs of device deployments for each detector mode, under similar exposure and FOV conditions, were evaluated by 2 blinded experienced neurointerventionalists who independently selected their preferred image on the basis of visualization of anatomic features, image noise, and treatment device. They rated their selection as either similar, better, much better, or substantially better than the other choice. Inter- and intrarater agreement was calculated and categorized as poor, moderate, and good. RESULTS: Both raters demonstrating good inter- and intrarater agreement selected high-definition-mode images with a frequency of at least 95% each and, on average, rated the high-definition images as much better than flat panel detector images with a frequency of 73% from a total of 60 image pairs. CONCLUSIONS: Due to their higher resolution, high-definition-mode images are sharper and visually preferred compared with the flat panel detector images. The improved imaging provided by the high-definition mode can potentially provide an advantage during neurointerventional procedures.

Skin dose is dependent on the incident beam angle and corrections are needed for accurate estimation of the risk of deterministic effects of the skin. To obtain the angular correction factors (ACF’s), EGSnrc Monte Carlo (MC) software was used to calculate the skin dose as a function of incident x-ray beam angle at the center of the field for beam energies from 60 to 120 kVp, field sizes from 5 to 15 cm, and thicknesses of Cu beam filters from 0.2 to 0.5 mm. All MC simulations used 3×10(10) incident photons. The dose was averaged over a 1 mm depth on the entrance surface of a 40×40 cm by 20 cm thick water phantom and was then normalized to the incident primary dose which was calculated using NIST mass energy absorption coefficients and by integrating over the beam energy spectrum. The Matlab tool, ‘cftool’, was used to fit these normalized dose values to power law equations as a function of incident beam angle, with coefficients that were fit to polynomials as a function of kVp. Separate fitting was done for different beam sizes and beam filters. The skin dose values calculated using the ACF determined from the fitted functional formulas agreed with that calculated by MC with a mean absolute percentage error (MAPE) less than 3% over the entire range of incident angles and kVp values. This fitting technique allows an ACF to be quickly determined for accurate skin dose calculation.

Staff-dose management in fluoroscopic procedures is a continuing concern due to insufficient awareness of radiation dose levels. To maintain dose as low as reasonably achievable (ALARA), we have developed a software system capable of monitoring the procedure room scattered radiation and the dose to staff members in real-time during fluoroscopic procedures. The scattered-radiation display system (SDS) acquires imaging-system signal inputs to update technique and geometric parameters used to provide a color-coded mapping of room scatter. We have calculated a discrete look-up-table (LUT) of scatter distributions using Monte-Carlo (MC) software and developed an interpolation technique for the multiple parameters known to alter the spatial shape of the distribution. However, the file size for the LUT’s can be large (~2GB), leading to long SDS installation times in the clinic. Instead, this work investigated the speed and accuracy of a regressional neural network (RNN) that we developed for predicting the scatter distribution from imaging-system inputs without the need for the LUT and interpolation. This method greatly reduces installation time while maintaining real-time performance. Results using error maps derived from the structural similarity index indicate high visual accuracy of predicted matrices when compared to the MC-calculated distributions. Dose error is also acceptable with a matrix element-averaged percent error of 31%. This dose-monitoring system for staff members can lead to improved radiation safety due to immediate visual feedback of high-dose regions in the room during the procedure as well as enhanced reporting of individual doses post-procedure.

Digital Subtraction Angiography (DSA) is considered the gold standard for imaging and guiding treatment of neurovascular lesions, such as cerebral aneurysms and carotid stenoses. Though DSA can show high-resolution morphology, it remains difficult to extract temporal physiological information, because higher frame-rates are necessary to accurately quantify neurovascular flow details. Recent advances in photon-counting detector technology have led us to develop High-Speed Angiography (HSA), where X-ray images are acquired at 1000 fps for more accurate visualization and quantification of blood flow. Blood flow was imaged using HSA under constant flow conditions within various 3D printed patient-specific phantoms. Blood velocity was quantified using an open source Optical Flow algorithm, OpenOpticalFlow, to perform velocity estimation based on the spatio-temporal intensity changes of iodinated contrast wavefronts. The results of these algorithms are then compared with Computational Fluid Dynamics (CFD) simulations, using the same inlet boundary conditions and model geometries. The performance of these algorithms at lower temporal resolution was then also assessed by simulating lower frame rates from the acquired 1000 fps data. It is important to ascertain the hemodynamic effect of abnormal neurovascular conditions, as well as their effect on treatment of such conditions during the actual clinical interventional procedure. While theoretical CFD results requiring considerable computer capability are delayed for hours or more, it is expected that clinical results from multiple HSA sequences will be available almost immediately while the patient is still under treatment, and even right after flow conditions are changed beneficially by the intervention.

Staff dose management is a continuing concern in fluoroscopically-guided interventional (FGI) procedures. Being unaware of radiation scatter levels can lead to unnecessarily high stochastic and deterministic risks due to the effects of absorbed dose by staff members. Our group has developed a scattered-radiation display system (SDS) capable of monitoring system parameters in real-time using a controller-area network (CAN) bus interface and displaying a color-coded mapping of the Compton-scatter distribution. This system additionally uses a time-of-flight depth sensing camera to track staff member positional information for dose rate updates. The current work capitalizes on our body tracking methodology to facilitate individualized dose recording via human recognition using 16-bit grayscale depth maps acquired using a Microsoft Kinect V2. Background features are removed from the images using a depth threshold technique and connected component analysis, which results in a body silhouette binary mask. The masks are then fed into a convolutional neural network (CNN) for identification of unique body shape features. The CNN was trained using 144 binary masks for each of four individuals (total of 576 images). Initial results indicate high-fidelity prediction (97.3% testing accuracy) from the CNN irrespective of obstructing objects (face masks and lead aprons). Body tracking is still maintained when protective attire is introduced, albeit with a slight increase in positional data error. Dose reports are then able to be produced which contain cumulative dose to each staff member at the eye lens level, waist level, and collar level. Individualized cumulative dose reporting through the use of a CNN in addition to real-time feedback in the clinic will lead to improved radiation dose management.

The imaging parameters used in neurointerventional procedures were evaluated to better understand the exposure techniques used clinically and their impact on patient dose. All parameters are available on the imaging system’s network bus in real time for each exposure pulse during a procedure. The Canon Dose Tracking System (DTS), which we developed, records the parameters of each exposure event in a raw data log file of controller area network (CAN) packets. We have collected such log files for 120 neurointerventional cases. Parameters are extracted by converting the raw data log file to a reformatted text file using a MATLAB script. The text file is input into a Microsoft Visual Studio project which outputs a new text file, which, with a reference table, allows the parameters to be identified. A written Python script is used to extract the specific parameters that were to be evaluated and output a .csv file. These were then input into MATLAB for analysis. The parameters extracted were the kVp, beam filter type, mAs, and the cranial/caudal angle as well as the RAO/LAO angle for the frontal and lateral gantries for DA and pulsed fluoroscopy (PF) modes. The gantry angles ranged from 34⁰ CRA to 42⁰ CAU and from 114⁰ RAO to 91⁰ LAO for DA and PF, respectively. The median kVp was 84 and 73 and the average per frame mAs was about 11 and 1.8 for DA and PF, respectively. This analysis should allow a better understanding of clinical practice in order to relate technique to patient and staff dose.

A new imaging x-ray detector with 194μm pixel conventional FPD imaging mode for large area visualization with detector field-of-views (FOV) ranging from 12 inch to 6 inch and a 76μm pixel high resolution high-definition (Hi-Def) zoom mode for smaller region-of-interest (ROI) visualization with FOV’s from 3 to 1.5 inches in one detector panel was built to improve visualization of endovascular devices during neurovascular interventions. In this work we investigate the effect of simultaneous use of both imaging modes on entrance kerma area product (KAP) and scatter at the detector. The entrance KAP and the scatter reaching the detector during simultaneous acquisition is the same as the large FOV FPD mode acquisitions, both higher than just Hi-Def mode acquisition. When a 0.7mm thick differential ROI Cu attenuator with a circular 10mm hole was aligned to the Hi-Def detector area, the entrance air kerma is reduced by 70%. To study the effect of scatter on image quality, Hi-Def images of the devices such as guide catheter and stents placed on a head equivalent phantom were acquired with the x-ray field opened to 8inch FOV, with and without the grid. Compared to the 3 inch Hi-Def FOV, with the grid the contrast of the guide catheter tip was reduced by 11% when the FOV was opened to 8 inch; however, without the grid the reduction in contrast was 36%. With the ROI attenuator and no grid the contrast was reduced by 16% when the FOV was opened to 8inch.

Angiographic parametric imaging (API) is a quantitative imaging method which uses digital subtraction angiography (DSA) to calculate biomarkers related to hemodynamics. This method has been used for neurovascular disease diagnosis and treatment outcome predictions in clinical settings but results are regarded with caution since derived biomarkers are strongly correlated with contrast injection parameters. This study aimed to assess utilization of truncated singular value decomposition (TSVD) in correcting API maps across various injection rates. Digital angiography data was collected using two neurovascular phantoms embedded in a simulated flow loop. Contrast volumes of 5 and 10 mL along with injection rates of 5, 10, 15, and 20 mL/sec were utilized during testing. API maps were generated with baseline and stenosis models using gamma variate fitting along with TSVD of the arterial input of the phantom. Surrogate regional blood flow (sRBF) and regional blood volume (sRBV) maps indicate consistent values across varying injection rates along with decreases in flow and volumes following introduction of a stenosis (Baseline: sRBF=53.3±4.20 arbitrary volume units (AVU)/min, sRBV=2.66±0.14 AVU, Stenosis: sRBF=28.6±3.78 AVU/min, sRBV=1.75±0.45 AVU). Mean transit time (MTT) and time of maximal residue function (Tmax) maps indicate consistent and decreasing parameter values respectively as injection rates increase along with increases in each parameter in the presence of a stenosis (Baseline: MTT=0.72±0.14 sec, Tmax=1.36±0.14 sec, Stenosis: MTT=0.94±0.13 sec, Tmax=1.71±0.18 sec). This study indicates TSVD has the potential to normalize API parameter maps across various injection rates potentially allowing for the implementation of API in ischemic stroke diagnosis and treatment.

We have developed a prototype scatter-display system (SDS) which includes a top-down view, virtual reality (VR) representation of an interventional room containing a color-coded scatter dose rate distribution in real-time. To represent various attenuating objects of interest in the room, such as the C-Arm gantry and ceiling mounted shield, the STL toolbox in Matlab was implemented to produce a 3D VR description of the objects. Attenuation by objects in the room will alter the dose distribution and may lead to shielding of individual staff members, and thus representation of those objects in the software is needed for precise dose rate estimations. Determination of the spatial regions of attenuation requires accurate specification of object position. To retain identification of a ceiling mounted shield, we implemented an open-source package which maintains object recognition using the depth camera feed of a Microsoft Kinect V2 and the features-from-accelerated-segment- test (FAST) algorithm in OpenCV for a dense sampling of salient features. The depth information from the identified object is transferred to an open-source robot operating system (ROS) wrapper for specification of the 3D position to be fed into the SDS. To compute the C-Arm gantry position, we take advantage of a controller area network (CAN) bus interfaced with the angiography system’s application programming interface (API). Methods for computing gantry and ceiling mounted shield shadow regions are discussed and demonstrated. FAST was applied to the ceiling-shield assembly’s flange with reliable recognition. Including object attenuation of room scatter in the SDS will facilitate accurate dose rate computation.

The functionality of a real-time, top-down view virtual reality (VR) display of scattered radiation during fluoroscopic interventional procedures is being expanded to incorporate automatic input of staff member locations. Microsoft Kinect V2 depth sensing camera input was integrated into an open-source Robot Operating System (ROS) wrapper to facilitate automatic extraction of relative landmark body feature coordinates. Coordinates for the torso are selected to represent the staff member location in the selected plane of scatter; these coordinates are stored in a text file to be input into the real-time scatter display system (SDS). Accuracy of the depth sensing camera was evaluated using a pinhole camera model. This model was also implemented in an ROS wrapper to calibrate the Microsoft Kinect V2. Calibrated values were then implemented within a coordinate transformation algorithm which converts the physical distance measurements in the frame of the Kinect to normalized coordinates used in Matlab for visualization of the top-down horizontal plane of the interventional suite. Impact on real-time performance was evaluated for both staff member position update on-screen as well as for the update of SDS image frames.

It is important to determine the patient’s skin dose accurately for fluoroscopic interventional procedures in order to estimate the risk of deterministic injury. The purpose of this study is to investigate how the patient’s skin dose changes as a function of x-ray beam incident angle for flat and curved surfaces. The primary and scatter dose was calculated averaged over a 2.0 mm depth at the surfaces of both cubic and cylindrical water phantoms to simulate different patient curvature. The total skin dose was calculated using EGSnrc Monte-Carlo (MC) software with 1010 photons incident and the primary dose was calculated at the central axis using the mass energy absorption coefficients published by NIST and integrated over the beam-energy spectrum. Simulations were done for incident angles from 90 to 10 degrees, beam field sizes from 5 to 15 cm, cylinder diameters from 20 to 30 cm, and beam energies from 60 to 120 kVp. The results show the scatter-plus-primary to incident-primary dose ratio decreases with decreasing incident angle due to increased primary attenuation and decreases from cubic to cylindrical phantom and with decreasing cylinder diameter at all angles due to reduced backscatter. These results can be used to determine angular correction factors needed to accurately estimate patient skin dose when the beam is not normal to the entrance surface during fluoroscopic procedures.

The eye lens is a very radiosensitive organ and is at risk for cataractogenesis during neuro-interventional procedures. It is paramount that the lens is exposed to the x-ray beam as little as possible while still being able to complete the clinical task. In this preliminary investigation, a convolutional neural network (CNN) has been created in order identify if the lens is within the x-ray projection image and where it is located with the intent to facilitate lens dose estimation. The model was trained using a database of patient cases of radiographic skull images, which had different views, in order to generalize the data. The size of the dataset was increased by rotating the images at various angles and masks were created for each corresponding image by hand-contouring the eye socket in the image. For image segmentation, a U-Net model was used which consisted of a down-block, bottleneck, and up-block. Different network parameters were tested and receiver operating curves (ROCs), with Jaccard indices, were assessed to identify the best model. The end goal of this project is model implementation into the real-time Canon Dose Tracking System (DTS) during interventional fluoroscopic procedures. This will allow the DTS to have a more accurate identification of where the lens is, whether fully in the beam or only partially. With this information, a more accurate calculation of the eye lens dose can be done which allows for patients’ dose to be more carefully monitored.

Purpose: 3D printed Patient-Specific Neurovascular Phantoms (3DP-PSNP) containing significant portions of the neurovasculature can be used to develop and test new diagnostic tools. The purpose of this research is to assess the use of 3DP-PSNP to study the correlation between Angiographic Parametric Imaging (API) features and the severity of carotid artery disease. Materials and Methods: We developed 3DP-PSNP for twenty patients with carotid atherosclerosis and performed two studies. In the first study, we used three phantoms with complete Circle of Willis (COW) with none, moderate and severe stenosis respectively. In the second experiment, all phantoms regardless of the COW structure were used. 3DP-PSNPs were connected in a simulated physiological pulsatile flow loop and Digital Subtractive Angiography (DSA) was performed by injecting 10 ml of contrast at 10 mL/s. An API software calculated imaging biomarkers: time-to-peak TTP, mean transit time MTT, time to arrival TTA, peak height PH, and area under the curve AUC for both carotids. Results: For none, moderate, and severe stenosis respectively, absolute mean percent differences between diseased vs. contralateral carotids were: 1.9%, 8.1%, 32.3% TTP; 6.8%, 7.5%, 41.0% TTA; 13.2%, 12.4%, 6.4% MTT; 8.7%, 11.3%, 97.6% PH; and 10.3%, 22.6%, 100% AUC. Injection parameters did not cause significant change to the difference between diseased and contralateral carotids. The second experiment showed strong correlation between the TTA and location of the stenosis, regardless of COW configuration. Conclusions: Overall, API was assessed in 3DP-PSNPs and shown to have increasing differences between diseased and contralateral carotid arteries with increasing severity.

Purpose: 3D-printing of patient-specific phantoms such as the mitral valve (MV) is challenging due to inability of current imaging systems to reconstruct fine moving features and 3D printing constraints. We investigated methods to 3D-print MV structures using ex-vivo micro-CT. Materials and Methods: A dissected porcine MV was imaged using micro-CT in diastole, using a special fixation holder. The holder design was based on a patient ECG gated cardiac CT scan using as reference points the papillary muscles and annulus. Next the micro-CT volume was segmented and 3D-printed in various elastic materials. We tested different postprocessing techniques for support material removal and surface coatings to preserve the MV integrity. To test the error a Cloud Comparison of the porcine valve-mesh file and the valve-mesh file from the patient ECG gated cardiac CT scan was performed. Results: Best results for the 3D-printed models were achieved using TangoPlus poly-jet material with a Objet Eden printer. The error computation yielded a 2.6mm deviation-distance between the two aligned valves indicating adequate alignment. The post-processing methods for support removal were challenging and required 24+ hours sample-emersion in slow agitating sodium hydroxide baths. Conclusions: The most challenging part for MV manufacturing is 3D volume acquisition and the post-printing methods during support cleaning. We developed methods to circumvent both, the imaging and the 3D-printing challenges and to ensure that the final phantom includes the fine chordae and valve geometry. Using these solutions, we were able to create complete MV structures which could benefit medical research and device testing.

Vascular pathologies such as stenosis cause changes in blood flow patterns and rates in patient vasculature. These changes are difficult to observe using conventional x-ray imaging techniques that typically operate at no more than 30 fps. However, 1000 fps High-Speed Angiography (HSA) provides sufficient temporal resolution to observe flow patterns in patient vasculature. The Actaeon detector from XCounter provides 1000 fps HSA with high spatial resolution (100 μm pixel pitch) enabling observation of detailed blood flow in 3D printed phantoms. To observe the effects of stenosis on flow, three carotid artery phantoms beginning 7.6 cm proximal to the bifurcation of the common carotid and extending 6.9 cm into the internal and external carotids with different degrees of stenosis (0%, 33%, and 66% stenosis) in the internal carotid were printed. Iodine contrast was injected into the phantom proximal to the bifurcation and images were recorded at 1000 fps. Time-density curves were generated for ROIs distal and proximal to the location of the stenosis for both branches of the carotid artery. The curves for the control phantom (no stenosis) showed little difference between the branches of the carotid while the stenotic phantoms showed an increased velocity in the flow of contrast and a lower maximum signal intensity for the stenosed internal carotid. 1000 fps HSA could be used during treatment of vascular pathologies to observe changes in flow patterns following an endovascular treatment.

While angiography may be considered the gold standard for evaluating diseases of the human vasculature, vascular flow details are unavailable due to the low temporal resolution of flat panel detectors (FPDs) which operate at a maximum of 15 – 30 fps. Higher frame rates are necessary to extract any meaningful flow detail, which may act as additional information that can be used to characterize flow-dependent disease states. These higher rates have become available with recent advances in photon-counting detector (PCD) technology. The XCounter Actaeon was used to perform high frame rate imaging at 1000 fps. The Actaeon also provides superior spatial resolution due to its 100 um pixel size and electronic charge sharing correction, making it a good candidate for small ROI imaging. With this detector, “High Speed Angiography” (HSA) was performed on a variety of 3D printed patient-specific vasculature and interventional devices, using a simulated flow loop and iodinated contrast media. The images, which illustrate pathology-dependent flow detail, were recorded in a sequence of 1 ms frames. In addition, the energy discrimination capabilities of the Actaeon were used such that with a lower energy threshold, instrumentation noise was virtually negligible. The per frame noise quality and overall patient dose were acceptable as compared to standard angiography dose rates using FPDs. The previously unseen flow detail may give new insight into the diagnosis, progression, and treatment of neuro and cardiovascular pathologies.

BackgroundA new dual resolution imaging x-ray detector system (Canon Medical Systems Corporation, Tochigi, Japan) has a standard resolution 194 µm pixel conventional flat-panel detector (FPD) mode and a high-resolution 76 µm high-definition (Hi-Def) mode in a single unit. The Hi-Def mode enhances the visualization of the intravascular devices.ObjectiveWe report the clinical experience and physician evaluation of this new detector system with Hi-Def mode for the treatment of intracranial aneurysms using a Pipeline embolization device (PED).MethodsDuring intervention at our institute, under large field of view (FOV) regular resolution FPD mode imaging, the catheter systems and devices were first guided to the proximity of the treatment area. Final placement and deployment of the PED was performed under Hi-Def mode guidance. A post-procedure 9-question physician survey was conducted to qualitatively assess the impact of Hi-Def mode visualization on physicians’ intraoperative decision-making. One-sample t-test was performed on the responses from the survey. Dose values reported by the x-ray unit were also recorded.ResultsTwenty-five cases were included in our study. The survey results indicated that, for each of the nine questions, the physicians in all cases indicated that the Hi-Def mode improved visualization compared with the FPD mode. For the 25 cases, the mean cumulative entrance air kerma was 2.35 Gy, the mean dose area product (DAP) was 173.71 Gy.cm2, and the mean x-ray exposure time was 39.30 min.ConclusionsThe Hi-Def mode improves visualization of flow diverters and may help in achieving more accurate placement and deployment of devices.

BACKGROUND AND PURPOSE: Visualization of structural details of treatment devices during neurointerventional procedures can be challenging. A new true 2-resolution imaging x-ray detector system (Canon Medical Systems Corporation, Tochigi, Japan) features a 194μm pixel conventional flat-panel detector (FPD) mode and a 76μm pixel high-resolution high-definition (Hi-Def) zoom mode in 1 detector panel. The Hi-Def zoom mode was developed for use in interventional procedures requiring superior image quality over a small field-of-view (FOV). We report successful use of this imaging system during intracranial aneurysm treatment in 1 patient with a Pipeline-embolization device (PED; Medtronic, Dublin, Ireland) and 1 patient with a low-profile visualized intramural support (LVIS Blue) device (MicroVention-Terumo, Somerset, New Jersey) plus adjunctive coiling. METHODS: A guide catheter was advanced from the femoral artery insertion site to the proximity of each lesion using standard FPD mode. Under magnified small FOV Hi-Def imaging mode, an intermediate catheter and microcatheters were guided to the treatment site, and the PED and LVIS Blue plus coils were deployed. Radiation doses were tracked intraprocedurally. RESULTS: Critical details, including structural changes in the PED and LVIS Blue and position and movement of the microcatheter tip within the coil mass, were more readily apparent in Hi-Def mode. Skin-dose mapping indicated that Hi-Def mode limited radiation exposure to the smaller FOV of the treatment area. CONCLUSIONS: Visualization of device structures was much improved in the high-resolution Hi-Def mode, leading to easier, more controlled deployment of stents and coils than conventional FPD mode.

Traditional digital subtraction angiography provides rather limited evaluation of contrast flow dynamics when studying and treating intracranial brain aneurysms. A 1000-frames-per-second photon-counting x-ray detector was used to image detailed iodine-contrast flow patterns in an internal carotid artery aneurysm of a 3D-printed vascular phantom. High-speed imaging revealed differences in vortex and inflow patterns with and without a Pipeline Embolization Device flow diverter in more detail and clarity than could be seen in standard pulsed angiography. Improved temporal imaging has the potential to impact the outcomes of endovascular interventions by allowing clinicians to better understand and act on flow dynamics in real-time.

Temporal and spatial details of vascular flow patterns and rates in neuro and cardio vascular pathology are difficult to evaluate even with so-called “real-time” 15 or 30 fps x-ray imaging using flat panel detectors (FPDs). Higher frame rates of 1000 fps with high spatial resolution of 100 um pixels can demonstrate vascular flow details previously unseen by any other means. A new ultra-high temporal and spatial resolution detector with the above capabilities, the XCounter’s Actaeon, is a direct conversion photon counting detector (PCD) with built-in electronic charge sharing correction and dual energy threshold settings. This PCD was used to image a 3D-printed realistic aneurysm flow phantom injected with both iodine and gas bubble contrast media. The flow patterns, including details of the vortex flow and velocities of individual gas bubbles, were recorded in a sequence of 1 ms images and compared with frames from standard 30 fps angiographic imaging where flow patterns were blurred and individual gas bubble movement could not be observed. Because of the low-energy threshold capability of the PCD, instrumentation noise was virtually negligible enabling quantum limited performance such that, at standard angiography dose rates for FPDs, the per frame noise quality for the 1 ms frames of the PCD sequences was acceptable. This resulted in a combination of temporal, spatial, and contrast resolution unseen previously.

Photon counting detectors (PCDs) with their low noise, high spatial and contrast resolution, and dual energy imaging capabilities are shown to be prospective candidates for Cone-Beam CT (CBCT) vascular imaging. The ultra-high frame rate capability of such detectors can enable CBCT at scan speeds far greater than that of current CBCT scanners which can only go up to about 0.14 rev/s (50 degrees/sec) compared to current multislice CT scanners that can achieve 3-4 rev/s. XCounter’s Actaeon PCD with frame rates up to 1000 fps can achieve CBCT scans at multi-slice CT scanner rates. The CdTe Actaeon PCD with pixel pitch of 100 μm and dual energy direct acquisition capability has built-in electronic anti-charge sharing correction. CBCT of a moving wire was demonstrated with the Actaeon PCD at these higher speeds and shown to be able to eliminate the effect of acquisition system image motion blur. Also a patient-specific 3D printed vascular phantom with a stent deployed was imaged at high frame rates using the Actaeon for CBCT acquisition with reconstruction using an FDK algorithm and the maximum intensity projection images clearly showed individual strut detail. This feasibility study will lead to exploration of new possibilities of high frame-rate imaging with PCDs and their potential applications.

Purpose: Various CT-FFR methods are being proposed as a non-invasive method to estimate cardiac disease severity. 3D printed patient specific cardiovascular models with high geometric accuracy can be used to simulate blood flow conditions and perform precise and repeatable benchtop flow experiments for validation of such methods. Materials and Methods: Twelve patient-specific 3D printed cardiac phantoms were created from CT Angiography (CTA) scans using a compliant 3D printing material. Pressure sensors were connected to the aortic root and distal ends of the three main coronary arteries to measure benchtop pressure gradients for each stenosed vessel. The patient geometries were used in Canon Medical Systems 1D fluid dynamics algorithm to calculate the CT- FFR. In addition, a 3D computational fluid dynamics simulation was done using ANSYS to estimate pressure gradients across the coronary arteries. Experimental data and 1D and 3D flow simulations were compared to the standard catheter lab FFR measurement (Invasive-FFR). Results: The average percent difference in Benchtop FFR/Invasive FFR, CT-FFR/Invasive FFR, and CFDFFR/Invasive FFR was 0.05, 0.06, and 0.07 respectively. The average time it took for the CT-FFR simulation was ~35 minutes and it took ~15 hours for the CFD-FFR simulation but can vary based on the number of iterations the user defines the software to run. Conclusions: Benchtop FFR proved to be highly accurate when compared to both 1D and 3D CFD software and therefore, 3D printing of patient specific coronary phantoms is a quality tool for CT-FFR software validation.

Image-guided neuro-endovascular interventional studies often require a high resolution image quality which requires the use of small focal-spot sizes. There is always a tradeoff while choosing focal-spot sizes. The use of small- focal-spots gives better spatial resolution but limits x-ray tube output and tube loading. The use of larger- focal-spots provides better heat dissipation capacity and higher x-ray output but gives rise to geometric blurring hence loss of spatial resolution. A method has been proposed which incorporates the use of the line-focus principle that can achieve a smaller projected focal-spot while keeping the actual focal-spot size as the medium focal-spot. Here the gantry is tilted to reduce the effective anode angle, hence the central axis is tilted producing a smaller projected focal-spot. This was tested by acquiring images of a Pipeline stent in the right jugular vein and a guidewire of a rabbit using a high-resolution CMOSbased fluoroscopic detector with 75um pixels. Also the gantry was tilted in the anode-cathode direction shifting the central axis to the anode side of the beam and the rabbit was aligned with the new perpendicular ray. Acquired images, for small focal-spot, medium focal-spot, and 7-degree tilted medium focal-spot were compared. While small focal-spot images demonstrated superior resolution, and both tilted and untilted medium focal spot images demonstrated lower noise due to the increased tube output the tilted medium focal spot images exhibited improved resolution. Line profiles and quantitative measures of generalized relative object detectability confirmed the advantage of the tilted medium focalspot method above all.

A new image receptor has recently been introduced that has a standard flat-panel detector (FPD) mode as well as a highdefinition (Hi-Def) zoom mode. The Dose Tracking System (DTS), which our group has developed, has been expanded in functionality to allow for the analysis of the skin-dose contribution of the Hi-Def mode during fluoroscopic interventional procedures. A clinical version of the DTS records all geometric and exposure technique parameters from a digital interface on the Canon Biplane Angiography System during interventional procedures in log files. Previous work on the enhancement of our group’s DTS led to the development of a replay function which facilitates playback of the log files. Within the replay feature, modifications have been made to allow for separate evaluation of exposures from each detector mode as identified by signals for the magnification (MAG) mode being used. The current work utilizes this separation method for neuro-interventional cases performed with the new image receptor to retrospectively analyze dose related contributions from the Hi-Def mode as compared to FPD usage. Peak skin dose (PSD) and dose area product (DAP) were evaluated for six clinical cases under IRB approval. Three de-identified log files were also included in order to demonstrate the method for separation of PSD as well as the variation with procedure types. Ratios of FPD PSD and DAP to Hi-Def values were determined for a subset of three cases during which the new image receptor was implemented.

Region-of-Interest (ROI) fluoroscopy uses a differential x-ray attenuator to reduce the dose to the patient in the periphery region while maintaining regular dose within the ROI treatment area, resulting in an image with differential brightness regions. The brightness difference can be corrected by subtracting a mask of the ROI attenuator from the dose-reduced image. The purpose of this work is to implement a Convolutional-Neural-Network (CNN) capable of deriving a mask of the ROI attenuator from the dose-reduced images, which can be used to equalize the brightness in the dose-reduced images without a pre-acquired mask. A data set of 10,000 ROI dose reduced images of various objects including anthropomorphic head and chest phantoms were generated with different ROI positions and sizes. A 22 layer CNN was developed to derive a mask of the ROI attenuator from the dose reduced image. The network was trained on 30% and tested on 15% of the images from the ROI image data set. The trained CNN was used on the remaining 55% of the data set to generate the ROI mask, and the average computation time for each image was calculated to be 70 ms. The Mean-Square-Error (MSE) for the testing data set was calculated to be 2.03e-05. For the remaining data set of 5500 images the average MSE between the network output and the corresponding expected ROI mask was calculated to be 2.21e-05. The masks generated by the CNN were successfully used to restore and equalize the brightness of the dose reduced images.

Neuro-endovascular image-guided interventions (EIGIs) are aided by use of detectors with improved spatial resolution. A new detector is capable of switching between standard resolution, flat-panel detector (FPD) zoom and high-definition (Hi-Def) zoom modes, with 194 and 76 μm pixels respectively. The relative performance of the two zoom modes to image specific, high-resolution objects was quantitatively investigated. Detector DQEs were measured for both zoom modes and used to determine the Relative Object Detectability (ROD), which compares two imaging detectors’ relative abilities to image a simulated object by integrating the DQE of one detector with the square of the Fourier transform of the simulated object function and dividing the result by a similar integral for a second reference detector. Initial evaluations used a pre-whitened matched filter (PWMF) ideal-observer model. Comparisons were also made using the generalized-ROD (G-ROD) which uses the generalized-DQE (GDQE) that includes the effects of clinically relevant parameters such as magnification, focal-spot size, and scatter and the generalized-measured-ROD (GM-ROD) which uses the square of the Fourier transform of the actual images of the object acquired with the detectors. Each of the metrics demonstrated improved performance of the Hi-Def zoom mode over the standard FPD mode in imaging a wide array of objects such as stents, wires, and spheres. Of particular note is the greater performance of the Hi-Def when considering the high spatial frequencies necessary for visualizing fine image details of a pipeline stent. These initial investigations demonstrate the great potential of the Hi-Def zoom mode during neuro-interventions.

We have been working on the development of a Scatter Display System (SDS) for monitoring and displaying scatterrelated dose to staff members during fluoroscopic interventional procedures. We have considered various methods for such a display using augmented reality (AR) and computer-generated virtual reality (VR). The current work focuses on development of the VR SDS display, which shows the color-coded scattered dose distribution in a horizontal plane at a selected height above the floor in a top-down view of the interventional suite. Reported is the first development of the methodology for real-time functionality of this software via integration of controller area network (CAN) bus digital signals from the Canon C-Arm Biplane System. Importing the CAN bus information allows immediate selection of the appropriate pre-calculated scatter dose distribution consistent with the x-ray beam orientation and characteristics as well as selection of the proper gantry and table graphic for the display. The Python CAN interface module was used for streamlining the integration of the CAN bus interface. Development of real-time functionality for the SDS allows it to provide feedback to staff during clinical procedures for informed dose management; the SDS can work alongside the patient skin dose tracking system (DTS) for complete clinical monitoring of staff and patient dose.

Purpose: The purpose of this study is to apply targeted Parametric Imaging on aneurysms to quantitatively investigate contrast flow changes at pre-, post-treatment and follow-up with outcome scoring. Methods: The angiograms for 50 patients were acquired, 25 treated with coil embolization and 25 treated using a flow diverter. API was performed by synthesizing the time density curve (TDC) at every pixel. Based on the TDCs, we calculated various parameters for the quantitative characterization of contrast flow through the vascular network and aneurysms and displayed them using color encoded maps. The parameters included were : Time to Peak (TTP), Mean Transit Time (MTT), Time of Arrival (TTA), Peak Height (PH) and Area Under the Curve (AUC). Two Regions of Interest (ROI) were manually marked over the aneurysm dome and the main artery. Average aneurysm parameter values were normalized to those values recorded in the main artery and recorded pre-/post-treatment and follow-up and compared to Raymond Roy scores and flow diverter stent scoring. Results: The normalized mean values were as follows (pre and post treatment): TTP (1.09+/-0.14, 1.55+/-1.36), MTT (1.07+/-0.23, 1.27+/-0.42), TTA (0.14+/-0.15, 0.26+/-0.23), PH (1.2+/-0.54, 0.95+/-0.83) and AUC (1.29+/-0.69, 1.44+/- 1.92). The neural network gave a validation accuracy of 0.8036 with a loss of 0.0927. A receiver operating characteristic curve with an AUC of 0.866 was obtained. Conclusions: API can quantitatively describe the flow in the aneurysm for initial investigation of the radiomics of intracranial aneurysms. It also shows a clear demarcation between pre and post treatment. Statistical modelling and a machine learning network is used to prove the success of our model.

Purpose: Neurovascular interventional procedures using biplane fluoroscopic imaging systems can lead to increased risk of radiation-induced skin injuries. The authors developed a biplane dose tracking system (Biplane-DTS) to calculate the cumulative skin dose distribution from the frontal and lateral x-ray tubes and display it in real-time as a color-coded map on a 3D graphic of the patient for immediate feedback to the physician. The agreement of the calculated values with the dose measured on phantoms was evaluated. Methods: The Biplane-DTS consists of multiple components including 3D graphic models of the imaging system and patient, an interactive graphical user interface, a data acquisition module to collect geometry and exposure parameters, the computer graphics processing unit, and functions for determining which parts of the patient graphic skin surface are within the beam and for calculating dose. The dose is calculated to individual points on the patient graphic using premeasured calibration files of entrance skin dose per mAs including backscatter; corrections are applied for field area, distance from the focal spot and patient table and pad attenuation when appropriate. The agreement of the calculated patient skin dose and its spatial distribution with measured values was evaluated in 2D and 3D for simulated procedure conditions using a PMMA block phantom and an SK-150 head phantom, respectively. Dose values calculated by the Biplane-DTS were compared to the measurements made on the phantom surface with radiochromic film and a calibrated ionization chamber, which was also used to calibrate the DTS. The agreement with measurements was specifically evaluated with variation in kVp, gantry angle, and field size. Results: The dose tracking system that was developed is able to acquire data from the two x-ray gantries on a biplane imaging system and calculate the skin dose for each exposure pulse to those vertices of a patient graphic that are determined to be in the beam. The calculations are done in real-time with a typical graphic update time of 30 ms and an average vertex separation of 3 mm. With appropriate corrections applied, the Biplane-DTS was able to determine the entrance dose within 6% and the spatial distribution of the dose within 4% compared to the measurements with the ionization chamber and film for the SK150 head phantom. The cumulative dose for overlapping fields from both gantries showed similar agreement. Conclusions: The Biplane-DTS can provide a good estimate of the peak skin dose and cumulative skin dose distribution during biplane neurointerventional procedures. Real-time display of this information should help the physician manage patient dose to reduce the risk of radiation-induced skin injuries.

The purpose of this study was to evaluate the effect of patient head size on radiation dose to radiosensitive organs, such as the eye lens, brain and spinal cord in fluoroscopically guided neuro-interventional procedures and CBCT scans of the head. The Toshiba Infinix C-Arm System was modeled in BEAMnrc/EGSnrc Monte-Carlo code and patient organ and effective doses were calculated in DOSxynrc/EGSnrc for CBCT and interventional procedures. X-ray projections from different angles, CBCT scans, and neuro-interventional procedures were simulated on a computational head phantom for the range of head sizes in the adult population and for different pediatric ages. The difference of left-eye lens dose between the mean head size and the mean ± 1 standard deviation (SD) ranges from 20% to 300% for projection angles of 0° to 90° RAO. The differences for other organs do not vary as much and is only about 10% for the brain. For a LCI-High CBCT protocol, the difference between mean and mean ± 1 SD head size is about 100% for lens dose and only 10% for mean and peak brain dose; the difference between 20 and 3 year-old mean head size is an increase of about 200% for the eye lens dose and only 30% for mean and peak brain dose. Dose for all organs increases with decreasing head size for the same reference point air kerma. These results will allow size-specific dose estimates to be made using software such as our dose tracking system (DTS).

As neuro-endovascular image-guided interventions (EIGIs) make use of higher resolution detectors, gantry rotational motion-induced blur becomes more noticeable in acquired projections as well as reconstructed images by reducing the visibility of vascular and device features whose visualization could be critical in the treatment of vascular pathology. Motion-induced blur in projections views is a function of an object's position in the field-of-view (FOV), gantry rotational speed, and frame capture or exposure time. In this work different frame rates were used to investigate the effects of blurring from individual projections on the reconstructed image. To test the effects of these parameters on reconstructed images, a regular pattern phantom of small objects was simulated and projection views were generated at various different frame rates for a given simulated rotational velocity. The reconstruction was made using a linear interpolation of filtered backprojections. Images reconstructed from lower frame rates showed significant blurring in the azimuthal direction, increasingly worse towards the periphery of the image. However, those reconstructed from higher frame rates showed significantly less blur throughout the entire FOV. While lower frame rates could be used with slower gantry speeds this would increase the risk of voluntary or involuntary patient motion contributing to blur over the entire FOV. A high frame rate used with high gantry speeds could reliable provide images without gantry-motion blur while reducing the risk of patient-motion blur. Frame rates exceeding 2000 fps available with photon counting detectors such as the X-counter Actaeon1 are available.

The forward-scatter dose distribution generated by the patient table during fluoroscopic interventions and its contribution to the skin dose is studied. The forward-scatter dose distribution to skin generated by a water table-equivalent phantom and the patient table are calculated using EGSnrc Monte-Carlo and Gafchromic film as a function of x-ray field size and beam penetrability. Forward scatter point spread function's (PSFn) were generated with EGSnrc from a 1×1 mm simulated primary pencil beam incident on the water model and patient table. The forward-scatter point spread function normalized to the primary is convolved over the primary-dose distribution to generate scatter-dose distributions. The utility of PSFn to calculate the entrance skin dose distribution using DTS (dose tracking system) software is investigated. The forward-scatter distribution calculations were performed for 2.32 mm, 3.10 mm, 3.84 mm and 4.24 mm Al HVL x-ray beams for 5×5 cm, 9×9 cm, 13.5×13.5 cm sized x-ray fields for water and 3.1 mm Al HVL x-ray beam for 16.5×16.5 cm field for the patient table. The skin dose is determined with DTS by convolution of the scatter dose PSFn's and with Gafchromic film under PMMA "patient-simulating" blocks for uniform and for shaped x-ray fields. The normalized forward-scatter distribution determined using the convolution method for water table-equivalent phantom agreed with that calculated for the full field using EGSnrc within ±6%. The normalized forward-scatter dose distribution calculated for the patient table for a 16.5×16.5 cm FOV, agreed with that determined using film within ±2.4%. For the homogenous PMMA phantom, the skin dose using DTS was calculated within ±2 % of that measured with the film for both uniform and non-uniform x-ray fields. The convolution method provides improved accuracy over using a single forward-scatter value over the entire field and is a faster alternative to performing full-field Monte-Carlo calculations.

The prospect of improved low noise, high speed, and dual-energy imaging that may be associated with the use of photon-counting imaging detectors (PCD) has motivated this evaluation of a newly upgraded version of a prototype PCD. The XCounter Actaeon was evaluated in its four acquisition modes each based upon varying signal processing firmware including a mode with charge sharing correction that enables neighboring pixels that share the energy from one incident x-ray photon detection to be counted only once at the proper summed energy in the pixel with the largest charge deposition. Since this PCD is a CdTe-based direct detector with 100 μm pixels, such charge sharing for typical medical x-ray energy photons may occur frequently and must be corrected to achieve more accurate counts. This charge sharing correction is achieved with an Anti-Coincidence Circuit (ACC) which prevents double pixel counting from one event as well as prevents counting from either event if they are below a preset threshold. Various physical parameters of the PCD were evaluated including linearity, sensitivity, pulse pile-up effects, dark noise, spatial resolution, noise power spectrum, and detective quantum efficiency.

The imaging of objects using high-resolution detectors coupled to CT systems may be made challenging due to the presence of ring artifacts in the reconstructed data. Not only are the artifacts qualitatilvely distracting, they reduce the SNR of the reconstructed data and may lead to a reduction in the clinical utility of the image data. To address these challenges, we introduce a multistep algorithm that greatly reduces the impact of the ring artifacts on the reconstructed data through image processing in the sinogram space. First, for a single row of detectors corresponding to one slice, we compute the mean of every detector element in the row across all projection view angles and place the reciprocal values in a vector with length equal to the number of detector elements in a row. This vector is then multiplied with each detector element value for each projection view angle, obtaining a normalized or corrected sinogram. This sinogram is subtracted from the original uncorrected sinogram of the slice to obtain a difference map, which is then blurred with a median filter along the row direction. This blurred difference map is summed back to the corrected sinogram, to obtain the final sinogram, which can be back projected to obtain an axial slice of the scanned object, with a greatly reduced presence of ring artifacts. This process is done for each detector row corresponding to each slice. The performance of this algorithm was assessed using images of a mouse femur. These images were acquired using a micro-CT system coupled to a high-resolution CMOS detector. We found that the use of this algorithm led to an increase in SNR and a more uniform line-profile, as a result of the reduction in the presence of the ring artifacts.

2D and 3D scatter dose display options are evaluated for usefulness and ease of interpretation for real-time feedback to staff to facilitate changes in individual positioning for dose reduction purposes, as well as improving staff consciousness of radiation presence. Room-sized scatter dose 3D matrices are obtained utilizing Monte Carlo simulations in EGSnrc. These distributions are superimposed on either a ceiling-view 2D graphic of the patient and table for reference or a 3D augmented reality (AR) display featuring a real-time video feed of the interventional room. A slice of the scatter dose matrix, at a selectable distance above the floor, is color-coded and superimposed on the computer graphic or AR display. The 3D display obtains depth information from a ceiling mounted Microsoft Kinect camera, which is equipped with a 1080p visual camera, as well as an IR emitter/receiver to generate a depth map of the interventional suite and persons within it. The 3D depth information allows parts of objects above the 2D dose map to pass through the map without being colorized by it so the height perspective of the dose map can be maintained. The 2D and 3D displays incorporate network information from the imaging system to scale the scatter dose with exposure factors and adjust rotation of the distribution to match the gantry. Demonstration images were displayed to neurosurgery interventional staff and survey responses were collected. Results from the survey indicated that scatter distribution displays would be desirable and helpful in managing staff dose.

Real-time visualization of fine details ranging to 100 um or less in neuro-vascular imaging guided interventions is important. A separate high-resolution detector mounted on a standard flat panel detector (FPD) was previously reported. This device had to be rotated mechanically into position over the FPD for high resolution imaging. Now, the new detector reported here has a high definition (Hi-Def) zoom capability along with the FPD built into one unified housing. The new detector enables rapid switching, by the operator between Hi-Def and FPD modes. Standard physical metrics comparing the new Hi-Def modes with those of the FPD are reported, demonstrating improved imaging resolution and noise capability at patient doses similar to those used for the FPD. Semi-quantitative subjective studies involving qualitative clinician feedback on images of interventional devices such as a Pipeline Embolization Device (PED) acquired in both Hi-Def and FPD modes are presented. The PED is deployed in a patient specific 3D printed neuro-vascular phantom embedded inside realistic bone and with tissue attenuating material. Field-of-view (FOV), exposure and magnification were kept constant for FPD and Hi-Def modes. Static image comparisons of the same view of the PED within the phantom were rated by expert interventionalists who chose from the following ratings: Similar, Better, or Superior. Generally, the Hi-Def zoomed images were much preferred over the FPD, indicating the potential to improve endovascular procedures and hence outcomes using such a Hi-Def feature.

The spectroscopic capabilities of a newly upgraded version of a prototype imaging photon counting detector (PCD) was investigated. The XCounter Actaeon has four acquisition modes in which signal processing is varied including one mode having a charge sharing correction so that neighboring pixels that share a detected event will not be erroneously counted twice, hence it is designated the Anti-Coincidence Circuit On or ACC On mode. Since this CdTe-based direct conversion PCD has 100 μm pixels, such charge sharing may frequently occur for typical medical x-ray energies. Each pixel of this PCD has two scalers and two energy discriminators that enable counting without instrumentation noise of events above each threshold level; hence, a spectrum can be obtained by sequentially moving the thresholds of both discriminators. It became evident from the spectra for the various acquisition modes that only those obtained with the charge sharing correction enabled, compared favorably with theoretically predicted spectra. After verifying the energy calibration using the mono-energetic emissions from an Am-241 source, spectra at various kVps from a standard medical x-ray generator were obtained. The spectra generated by ACC On mode for 70 kVp and 110 kVp were the closest match to the theoretical spectra generated by SpekCal. For dual energy applications, ACC On mode with charge sharing correction circuitry would be the best choice among various acquisition modes. Also investigated was the dual energy imaging capability of the Actaeon PCD with ACC On mode to separate Aluminum and Iodine while imaging an artery stenosis phantom.

Modern 3D printing technology allows rapid prototyping of vascular phantoms based on an actual human patient with a high degree of precision. Using this technology, we present a platform to accurately simulate clinical views of neuro-endovascular interventions and devices. The neuro-endovascular interventional phantom has a 3D printed cerebrovasculature model derived from a patient CT angiogram and embedded inside a human skull providing bone attenuation. Acrylic layers were placed underneath and on top of the skull, simulating entrance and exit tissue attenuation and also simulating forward scatter. The 3D model was connected to a pulsatile flow loop for simulating interventions using clinical devices such as catheters and stents. To validate the x-ray attenuation and establish clinical accuracy, the automatic exposure selection by a clinical c-arm system for the phantom was compared with that for a commercial anthropomorphic head phantom (SK-150, Phantom Labs). The percentage difference between automatic exposure selection for the neuro-intervention phantom and the SK-150 phantom was under 10p. By changing 3D printed models, various patient diseased anatomies can be simulated accurately with the necessary x-ray attenuation. Using this platform various interventional procedures were performed using new imaging technologies such as a high-resolution x-ray fluoroscope and a dose-reduced region-of-interest attenuator and differential temporally filtered display for enhanced interventional imaging. Simulated clinical views from such phantom-based procedures were used to evaluate the potential clinical performance of such new technologies.

Purpose: 3D printed patient specific vascular models provide the ability to perform precise and repeatable benchtop experiments with simulated physiological blood flow conditions. This approach can be applied to CT-derived patient geometries to determine coronary flow related parameters such as Fractional Flow Reserve (FFR). To demonstrate the utility of this approach we compared bench-top results with non-invasive CT-derived FFR software based on a computational fluid dynamics algorithm and catheter based FFR measurements. Materials and Methods: Twelve patients for whom catheter angiography was clinically indicated signed written informed consent to CT Angiography (CTA) before their standard care that included coronary angiography (ICA) and conventional FFR (Angio-FFR). The research CTA was used first to determine CT-derived FFR (Vital Images) and second to generate patient specific 3D printed models of the aortic root and three main coronary arteries that were connected to a programmable pulsatile pump. Benchtop FFR was derived from pressures measured proximal and distal to coronary stenosis using pressure transducers. Results: All 12 patients completed the clinical study without any complication, and the three FFR techniques (Angio-FFR, CT-FFR, and Benchtop FFR) are reported for one or two main coronary arteries. The Pearson correlation among Benchtop FFR/ Angio-FFR, CT-FFR/ Benchtop FFR, and CT-FFR/ Angio-FFR are 0.871, 0.877, and 0.927 respectively. Conclusions: 3D printed patient specific cardiovascular models successfully simulated hyperemic blood flow conditions, matching invasive Angio-FFR measurements. This benchtop flow system could be used to validate CTderived FFR diagnostic software, alleviating both cost and risk during invasive procedures.

This project investigated the signal thresholding effectiveness at reducing the instrument noise of an electron multiplying charged coupled device (EMCCD) based micro-CT system at low x-ray exposure levels. Scans of a mouse spine and an iodine phantom were taken using an EMCCD detector coupled with a micro-CT system. An iodine filter of 4 mg/cm2 area density was placed in the beam. The output signal was thresholded using some multiple of the inherent background noise. For each threshold, 100, 200, and 300 frames were summed for each projection to evaluate the effect on the reconstructed image. The projection images from the scans were compared using line profiles and their SNR. Our results indicate that, as the threshold was increased, the line profiles of the projection images showed less statistical variation, but also lower signal levels, so that the SNR of the projection images decreased as the threshold increased. When the line profile of a projection image obtained using a signal threshold is compared with one obtained using energy integrating mode, the profile obtained using thresholding had less variation than that obtained using energy integration, which indicates less instrument noise. The SNR at the edges of the scan object is higher in the thresholded images when compared with the energy integrated projection images. We conclude that thresholding the output signal from an EMCCD detector at low x-ray exposure levels is an effective method to reduce the instrument noise of an EMCCD detector.

Purpose: Accurate patient-specific phantoms for device testing or endovascular treatment planning can be 3D printed. We expand the applicability of this approach for cardiovascular disease, in particular, for CT-geometry derived benchtop measurements of Fractional Flow Reserve, the reference standard for determination of significant individual coronary artery atherosclerotic lesions. Materials and Methods: Coronary CT Angiography (CTA) images during a single heartbeat were acquired with a 320x0.5mm detector row scanner (Toshiba Aquilion ONE). These coronary CTA images were used to create 4 patientspecific cardiovascular models with various grades of stenosis: severe

The purpose of this work is to evaluate methods for producing a library of 2D-radiographic images to be correlated to clinical images obtained during a fluoroscopically-guided procedure for automated patient-model localization. The localization algorithm will be used to improve the accuracy of the skin-dose map superimposed on the 3D patient- model of the real-time Dose-Tracking-System (DTS). For the library, 2D images were generated from CT datasets of the SK-150 anthropomorphic phantom using two methods: Schmid’s 3D-visualization tool and Plastimatch’s digitally-reconstructed-radiograph (DRR) code. Those images, as well as a standard 2D-radiographic image, were correlated to a 2D-fluoroscopic image of a phantom, which represented the clinical-fluoroscopic image, using the Corr2 function in Matlab. The Corr2 function takes two images and outputs the relative correlation between them, which is fed into the localization algorithm. Higher correlation means better alignment of the 3D patient-model with the patient image. In this instance, it was determined that the localization algorithm will succeed when Corr2 returns a correlation of at least 50%. The 3D-visualization tool images returned 55-80% correlation relative to the fluoroscopic-image, which was comparable to the correlation for the radiograph. The DRR images returned 61-90% correlation, again comparable to the radiograph. Both methods prove to be sufficient for the localization algorithm and can be produced quickly; however, the DRR method produces more accurate grey-levels. Using the DRR code, a library at varying angles can be produced for the localization algorithm.

Beam shaping devices like ROI attenuators and compensation filters modulate the intensity distribution of the x-ray beam incident on the patient. This results in a spatial variation of skin dose due to the variation of primary radiation and also a variation in backscattered radiation from the patient. To determine the backscatter component, backscatter point spread functions (PSF) are generated using EGS Monte-Carlo software. For this study, PSF's were determined by simulating a 1 mm beam incident on the lateral surface of an anthropomorphic head phantom and a 20 cm thick PMMA block phantom. The backscatter PSF's for the head phantom and PMMA phantom are curve fit with a Lorentzian function after being normalized to the primary dose intensity (PSFn). PSFn is convolved with the primary dose distribution to generate the scatter dose distribution, which is added to the primary to obtain the total dose distribution. The backscatter convolution technique is incorporated in the dose tracking system (DTS), which tracks skin dose during fluoroscopic procedures and provides a color map of the dose distribution on a 3D patient graphic model. A convolution technique is developed for the backscatter dose determination for the non-uniformly spaced graphic-model surface vertices. A Gafchromic film validation was performed for shaped x-ray beams generated with an ROI attenuator and with two compensation filters inserted into the field. The total dose distribution calculated by the backscatter convolution technique closely agreed with that measured with the film.

The aim of this work is to develop a method to calculate lens dose for fluoroscopically-guided neuro-interventional procedures and for CBCT scans of the head. EGSnrc Monte Carlo software is used to determine the dose to the lens of the eye for the projection geometry and exposure parameters used in these procedures. This information is provided by a digital CAN bus on the Toshiba Infinix C-Arm system which is saved in a log file by the real-time skin-dose tracking system (DTS) we previously developed. The x-ray beam spectra on this machine were simulated using BEAMnrc. These spectra were compared to those determined by SpekCalc and validated through measured percent-depth-dose (PDD) curves and half-value-layer (HVL) measurements. We simulated CBCT procedures in DOSXYZnrc for a CTDI head phantom and compared the surface dose distribution with that measured with Gafchromic film, and also for an SK150 head phantom and compared the lens dose with that measured with an ionization chamber. Both methods demonstrated good agreement. Organ dose calculated for a simulated neuro-interventional-procedure using DOSXYZnrc with the Zubal CT voxel phantom agreed within 10% with that calculated by PCXMC code for most organs. To calculate the lens dose in a neuro-interventional procedure, we developed a library of normalized lens dose values for different projection angles and kVp's. The total lens dose is then calculated by summing the values over all beam projections and can be included on the DTS report at the end of the procedure.

Following new trends in precision medicine, Juxatarenal Abdominal Aortic Aneurysm (JAAA) treatment has been enabled by using patient-specific fenestrated endovascular grafts. The X-ray guided procedure requires precise orientation of multiple modular endografts within the arteries confirmed via radiopaque markers. Patient-specific 3D printed phantoms could familiarize physicians with complex procedures and new devices in a risk-free simulation environment to avoid periprocedural complications and improve training. Using the Vascular Modeling Toolkit (VMTK), 3D Data from a CTA imaging of a patient scheduled for Fenestrated EndoVascular Aortic Repair (FEVAR) was segmented to isolate the aortic lumen, thrombus, and calcifications. A stereolithographic mesh (STL) was generated and then modified in Autodesk MeshMixer for fabrication via a Stratasys Eden 260 printer in a flexible photopolymer to simulate arterial compliance. Fluoroscopic guided simulation of the patient-specific FEVAR procedure was performed by interventionists using all demonstration endografts and accessory devices. Analysis compared treatment strategy between the planned procedure, the simulation procedure, and the patient procedure using a derived scoring scheme. Results: With training on the patient-specific 3D printed AAA phantom, the clinical team optimized their procedural strategy. Anatomical landmarks and all devices were visible under x-ray during the simulation mimicking the clinical environment. The actual patient procedure went without complications. Conclusions: With advances in 3D printing, fabrication of patient specific AAA phantoms is possible. Simulation with 3D printed phantoms shows potential to inform clinical interventional procedures in addition to CTA diagnostic imaging.

Apodized Aperture Pixel (AAP) design, proposed by Ismailova et. al, is an alternative to the conventional pixel design1. The advantages of AAP processing with a sinc filter in comparison with using other filters include non-degradation of MTF values and elimination of signal and noise aliasing, resulting in an increased performance at higher frequencies, approaching the Nyquist frequency3. If high resolution small field-of-view (FOV) detectors with small pixels used during critical stages of Endovascular Image Guided Interventions (EIGIs) could also be extended to cover a full field-of-view typical of flat panel detectors (FPDs) and made to have larger effective pixels, then methods must be used to preserve the MTF over the frequency range up to the Nyquist frequency of the FPD while minimizing aliasing. In this work, we convolve the experimentally measured MTFs of an Microangiographic Fluoroscope (MAF) detector, (the MAF-CCD with 35μm pixels) and a High Resolution Fluoroscope (HRF) detector (HRF-CMOS50 with 49.5μm pixels) with the AAP filter and show the superiority of the results compared to MTFs resulting from moving average pixel binning and to the MTF of a standard FPD. The effect of using AAP is also shown in the spatial domain, when used to image an infinitely small point object. For detectors in neurovascular interventions, where high resolution is the priority during critical parts of the intervention, but full FOV with larger pixels are needed during less critical parts, AAP design provides an alternative to simple pixel binning while effectively eliminating signal and noise aliasing yet allowing the small FOV high resolution imaging to be maintained during critical parts of the EIGI.

A novel amorphous selenium (a-Se) direct detector with CMOS readout has been designed, and relative detector performance investigated. The detector features include a 25μm pixel pitch, and 1000μm thick a-Se layer operating at 10V/μm bias field. A simulated detector DQE was determined, and used in comparative calculations of the Relative Object Detectability (ROD) family of prewhitening matched-filter (PWMF) observer and non-pre-whitening matched filter (NPWMF) observer model metrics to gauge a-Se detector performance against existing high resolution micro-angiographic fluoroscopic (MAF) detectors and a standard flat panel detector (FPD). The PWMF-ROD or ROD metric compares two x-ray imaging detectors in their relative abilities in imaging a given object by taking the integral over spatial frequencies of the Fourier transform of the detector DQE weighted by an object function, divided by the comparable integral for a different detector. The generalized-ROD (G-ROD) metric incorporates clinically relevant parameters (focal- spot size, magnification, and scatter) to show the degradation in imaging performance for detectors that are part of an imaging chain. Preliminary ROD calculations using simulated spheres as the object predicted superior imaging performance by the a-Se detector as compared to existing detectors. New PWMF-G-ROD and NPWMF-G-ROD results still indicate better performance by the a-Se detector in an imaging chain over all sphere sizes for various focal spot sizes and magnifications, although a-Se performance advantages were degraded by focal spot blurring. Nevertheless, the a-Se technology has great potential to provide break- through abilities such as visualization of fine details including of neuro-vascular perforator vessels and of small vascular devices.