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Purpose To image multidimensional flow in fetuses using golden-angle radial phase contrast cardiovascular magnetic resonance (PC-CMR) with motion correction and retrospective gating. Methods A novel PC-CMR method was developed using an ungated golden-angle radial acquisition with continuously incremented velocity encoding. Healthy subjects (n = 5, 27 ± 3 years, males) and pregnant females (n = 5, 34 ± 2 weeks gestation) were imaged at 3 T using the proposed sequence. Real-time reconstructions were first performed for retrospective motion correction and cardiac gating (using metric optimized gating, MOG). CINE reconstructions of multidimensional flow were then performed using the corrected and gated data. Results In adults, flows obtained using the proposed method agreed strongly with those obtained using a conventionally gated Cartesian acquisition. Across the five adults, bias and limits of agreement were − 1.0 cm/s and [− 5.1, 3.2] cm/s for mean velocities and − 1.1 cm/s and [− 6.5, 4.3] cm/s for peak velocities. Temporal correlation between corresponding waveforms was also high (R~ 0.98). Calculated timing errors between MOG and pulse-gating RR intervals were low (~ 20 ms). First insights into multidimensional fetal blood flows were achieved. Inter-subject consistency in fetal descending aortic flows (n = 3) was strong with an average velocity of 27.1 ± 0.4 cm/s, peak systolic velocity of 70.0 ± 1.8 cm/s and an intra-class correlation coefficient of 0.95 between the velocity waveforms. In one fetal case, high flow waveform reproducibility was demonstrated in the ascending aorta (R = 0.97) and main pulmonary artery (R = 0.99). Conclusion Multidimensional PC-CMR of fetal flow was developed and validated, incorporating retrospective motion compensation and cardiac gating. Using this method, the first quantification and visualization of multidimensional fetal blood flow was achieved using CMR. Electronic supplementary material The online version of this article (10.1186/s12968-018-0498-z) contains supplementary material, which is available to authorized users.

Structural remodeling in lung disease is progressive and heterogeneous, making temporally and spatially explicit information necessary to understand disease initiation and progression. While mouse models are essential to elucidate mechanistic pathways underlying disease, the experimental tools commonly available to quantify lung disease burden are typically invasive (e.g., histology). This necessitates large cross-sectional studies with terminal endpoints, which increases experimental complexity and expense. Alternatively, magnetic resonance imaging (MRI) provides information noninvasively, thus permitting robust, repeated-measures statistics. Although lung MRI is challenging due to low tissue density and rapid apparent transverse relaxation (T(2)*

PURPOSE To test the feasibility of cardiac real-time MRI in combination with retrospective gating by MR-compatible spirometry, to improve motion control, and to allow quantification of respiratory-induced changes during free-breathing. METHODS Cross-sectional real-time MRI (1.5T; 30 frames/s) using steady-state free precession contrast during free-breathing was combined with MR-compatible spirometry in healthy adult volunteers (n = 4). Retrospective binning assigned images to classes that were defined by electrocardiogram and spirometry. Left ventricular eccentricity index as an indicator of septal position and ventricular volumes in different respiratory phases were calculated to assess heart-lung interactions. RESULTS Real-time MRI with MR-compatible spirometry is feasible and well tolerated. Spirometry-based binning improved motion control significantly. The end-diastolic epicardial eccentricity index increased significantly during inspiration (1.04 ± 0.04 to 1.19 ± 0.05; P < .05). During inspiration, right ventricular end-diastolic volume (79 ± 17 mL/m2 to 98 ± 18 mL/m2 ), stroke volume (41 ± 8 mL/m2 to 59 ± 11 mL/m2 ) and ejection fraction (53 ± 3% to 60 ± 1%) increased significantly, whereas the end-systolic volume remained almost unchanged. Left ventricular end-diastolic volume, left ventricular stroke volume, and left ventricular ejection fraction decreased during inspiration, whereas the left ventricular end-systolic volume increased. The relationship between stroke volume and end-diastolic volume (Frank-Starling relationship) based on changes induced by respiration allowed for a slope estimate of the Frank-Starling curve to be 0.9 to 1.1. CONCLUSION Real-time MRI during free-breathing combined with MR-compatible spirometry and retrospective binning improves image stabilization, allows quantitative image analysis, and importantly, offers unique opportunities to judge heart-lung interactions.

Purpose: Is to compare the role of 128 MDCT in quantitative evaluation of left ventricle function in patients with coronary artery disease compared to 2D echocardiography. Patients and methods: Fifty patients with suspected coronary artery disease underwent contrast enhanced MDCT using retrospective gating without dose modulation. Ten phases of cardiac cycle were processed to assess end-systolic and end-diastolic phase at LV short-axis view. 2DSE was performed in the same day. LVSV, LVDV, LFEF, LVSV were calculated using the Simpson's method in MDCT and modified Simpson's method in echocardiography. Results: LVSV, LVDV, LVSV, LFEF were 74.30 ± 24.92, 185.46 ± 56.25, 84.15 ± 33.16, 48.88 ± 13.32 respectively on MSCT and 71.43 ± 21.93, 182.31 ± 56.49, 81.74 ± 32.88, 47.82 ± 13.64 respectively on echocardiography with excellent correlation between the modalities (P

Background and aim: We hypothesised that small differences in the anatomy of the coronary venous tree might be one of the factors responsible for the differences in the response for cardiac resynchronisation depending on a patient’s gender. Methods: Cardiac computed tomography scans with retrospective gating were performed on 315 subjects (aged 58.3 ± 11.6 years; 117 women) according to the clinical criteria. The standard protocol for coronary arteries was used during scanning. Additional reconstructions that were focused on the coronary veins during post processing were used to analyse the data. Gender-related anatomical variants were identified. Results: The average of 3.6 ± 1.4 veins per case were visualised. The posterolateral vein was visualised more frequently in men than in women (p < 0.05). Eight variants were identified as being more frequent — they were found in 237 out of 315 cases (75.24%). Those variants occurred in 95 (81.19%) of the women and in 142 (71.72%) of the men, p = 0.080. Six variants occurred more frequently in women; however, the differences were not significant. Conclusions: In women a more frequent presence of favourable coronary vein variants in the target area for cardiac resynchronisation can be seen. Anatomical findings may help to explain why women more frequently respond to cardiac resyn­chronisation therapy compared to men.

Background Respiratory motion is a major limiting factor for spectral quality and duration of in vivo proton MR spectroscopy of the heart. Prospective navigator gating is frequently applied to minimize the effects of respiratory motion, but scan durations are subject-dependent and hence difficult to predict. Purpose To implement cardiac proton MRS with fixed scan time by employing retrospective phase-based gating and to compare the proposed method to conventional navigator-gated MRS. Study type Prospective. Subjects Eighteen healthy volunteers (29.7 ± 7.8 years). Field strength/sequence 1.5, navigator-gated (16 averages without, 96 with water suppression [WS]) data acquisition as reference and navigator-free data acquisition with a fixed scan time (48 without WS, 304 with WS), cardiac-triggered point-resolved spectroscopy (PRESS). Assessment Navigator-free data acquisition with retrospective phase-based gating was compared with prospective navigator-gating. Navigator-free acquisition was repeated in 10 subjects to assess reproducibility. Scan time was assessed for prospective and retrospective gating. Retrospective phase-based gating was performed using a threshold based on the standard deviation (SD) of individual water (W) and triglyceride (TG) phases. Statistical tests T-tests and Bland-Altman analysis. Results The duration of the prospective navigator-gated scans ranged from 6:09 minutes to 21:50 minutes (mean 10:05 ± 3:46 min, gating efficiency 40.4 ± 10.5%), while data acquisition for retrospective phase-based gating had a fixed scan time of 11:44 minutes. Retrospective phase-based gating using a threshold of 1 × SD yielded a gating efficiency of 72.7 ± 4.3% and a coefficient of variation (CoV) of triglyceride-to-water ratios of 9.8% compared with the navigated reference. The intrasubject reproducibility of retrospective gating revealed a CoV of 9.5%. Data conclusion Cardiac proton MRS employing retrospective phase-based gating is feasible and provides reproducible assessment of TG/W in a fixed scan time. Since scan time is independent of respiratory motion, retrospective phase-based gating offers an approach to motion compensation with predictable exam time for proton MRS of the heart. Level of evidence 2 Technical Efficacy: Stage 2 J. Magn. Reson. Imaging 2019;50:1973-1981.

Cardiac computed tomography angiography (CCTA) is a commonly used diagnostic imaging tool for cardiovascular disease. Despite constant improvements to imaging technologies, the radiation dose to patients remains a concern when using this procedure. Diagnostic reference levels (DRLs) are used as a trigger to identify and alert individual facilities that are using high doses during CT. This study aims to assess patient radiation dose and establish new national DRLs (NDRL) associated with CCTA in Saudi clinical practices. A structured booklet survey was designed for recording patient and scanning protocols during CCTA procedures. The data were collected retrospectively from the participating centres. NDRLs for CCTA were defined as the 75th and 25th of volumetric CT dose index (CTDIvol) and dose length product (DLP). Specific DRLs based on two main ECG-gating modes were also proposed. Data sets related to 197 CCTAs with a mean weight of 77 kg were analysed in detail. The DRL values for CTDIvol and DLP for prospective gating mode and retrospective gating mode were 29 and 62 mGy and 393 and 1057 mGy cm, respectively. NDRLs for CCTA in Saudi Arabia are comparable or slightly lower than European DRLs due to the current use of dose-saving technology. There are major variations in patient doses during CCTA due to differences in CT scanners, scanning modes and departmental CCTA protocols.

Retrospective gating on animal studies with microCT has gained popularity in recent years. Previously, we use ECG signals for cardiac gating and breathing airflow or video signals of abdominal motion for respiratory gating. This method is adequate and works well for most applications. However, through the years, researchers have noticed some pitfalls in the method. For example, the additional signal acquisition step may increase failure rate in practice. X-Ray image-based gating, on the other hand, does not require any extra step in the scanning. Therefore we investigate imagebased gating techniques. This paper presents a comparison study of the image-based versus signal-based approach to retrospective gating. The two application areas we have studied are respiratory and cardiac imaging for both rats and mice. Image-based respiratory gating on microCT is relatively straightforward and has been done by several other researchers and groups. This method retrieves an intensity curve of a region of interest (ROI) placed in the lung area on all projections. From scans on our systems based on step-and-shoot scanning mode, we confirm that this method is very effective. A detailed comparison between image-based and signal-based gating methods is given. For cardiac gating, breathing motion is not negligible and has to be dealt with. Another difficulty in cardiac gating is the relatively smaller amplitude of cardiac movements comparing to the respirational movements, and the higher heart rate. Higher heart rate requires high speed image acquisition. We have been working on our systems to improve the acquisition speed. A dual gating technique has been developed to achieve adequate cardiac imaging.

Several recent technical advances in cardiac ultrasound allow data to be acquired at a very high frame rate. Retrospective gating, plane/diverging wave imaging, and multiline transmit imaging all improve the temporal resolution of the conventional ultrasound system. The main drawback of such high frame rate data acquisition is that it typically has reduced image quality. However, for given clinical applications, the acquisition of temporally-resolved data might outweigh the reduction in image quality. It is the aim of this paper to provide an overview of the technical principles behind these new ultrasound imaging modalities, to review the current evidence of their potential clinical added value, and to forecast how they might influence daily clinical practice.

Assessment of patients with left ventricular assist devices (LVADs) can be challenging, and multiple modalities are sometimes necessary to arrive at the accurate diagnosis. We describe two patients with persistent heart failure symptoms after HeartMate II LVAD placement. After initial evaluation was unrevealing, retrospectively gated computed tomographic angiography (CTA) was used to diagnose partial inflow obstruction, leading to important changes in management. We describe the techniques and role of retrospective gating and discuss functional assessment by CT as well as future applications.

We propose a new method for PET/MR respiratory motion compensation, which is based on strongly undersampled measured MR data and a) runs in parallel with the PET acquisition, b) can be interlaced with clinical MR sequences, and c) can be acquired with measurement times as short as 0.5 min per bed position. An MR dataset covering the free-breathing thorax and abdomen of a volunteer was acquired with a Siemens Biograph mMR system. We applied a 3D encoded radial stack-of- stars sequence with a golden angle radial spacing (acquisition time: 5.0 min). Respiratory motion amplitudes were estimated from measured k-space centers allowing for a retrospective gating into 20 overlapping motion phase bins with a width of 10%. In addition, two highly undersampled datasets consisting of 300 and 600 spokes were created corresponding to acquisition times of 0.5 min and 1.0 min, respectively. 4D gated MR images of the three datasets (0.5, 1.0 and 5.0 min acquisition time) were reconstructed iteratively. For each of the three resulting image sets, MVFs were estimated. A 4D PET volume of the volunteer with four artificial hot lesions in the lungs and abdomen was simulated. 3D PET and MoCo 4D PET images based on the three sets of motion vector fields derived from MR were reconstructed and compared to a reference gated 4D reconstruction with ten-fold acquisition time. Visual inspection of the reconstructed PET images showed that blurring was reduced in MoCo 4D images for all acquisition times compared to the 3D reconstruction. A quantitative evaluation in the end-exhale and a mid-ventilation motion phase demonstrated that MoCo 4D reconstructions outperformed the 3D reconstruction in terms of SUVmean values for all lesions and acquisition times compared to the reference gated 4D reconstruction.

The aim of our work was to compare image quality and radiation dose in a group of patients who underwent cardiac dual-source computed tomography (DSCT) with prospective electrocardiographic (ECG) gating with those of a control group studied with retrospective gating.Sixty patients were randomly assigned to two groups of 30 individuals each. Patients with heart rates70 bpm and body mass index (BMI)30 kg/m(2) were excluded. Group A was examined with prospective ECG gating and group B with retrospective gating. The dose-length product (DLP) was recorded to calculate the radiation dose, whereas the effective dose was normalised to a standard 12-cm scan of the heart.Applying the best reconstruction interval, 98.6% of segments in the prospective group and 99.3% in the retrospective group were diagnostic. No significant difference (p0.05) in image quality was observed between groups. Mean normalised radiation dose was 4.91 ± 0.4 mSv in the prospective-gating group and 14.62 mSv ± 4.36 in the retrospective-gating group (p0.01).Coronary CT with prospective ECG gating, a standard feature on new scanners, allows for a significant reduction in radiation dose without causing any significant decrease in image quality or in the number of segments assessed. The prospective technique is thus recommended for patients with heart rates £70 bpm and BMI £30 kg/m(2).

Cardiac MDCT is here to stay. And, it is more than just imaging coronary arteries. Understanding the differ- ences in and the benefits of one CT scanner from another will help you to optimize the capabilities of the scanner, but re- quires a basic understanding of the MDCT imaging physics. This review provides key information needed to understand the differences in the types of MDCT scanners, from 64 - 320 detectors, flat panels, single and dual source configurations, step and shoot prospective and retrospective gating, and how each factor influences radiation dose, spatial and temporal resolution, and image noise.

[Abstract] The 22nd International Congress and Exhibition, Barcelona, Spain, June 25-28, 2008

Background Prospectively gated coronary computed tomographic angiography (CCTA) with dual-source CT allows substantial reduction of radiation exposure but requires prospective single-phase selection and assessment of likelihood of adequate image quality. Objective We developed and tested the model for predicting success of prospectively gated CCTA. Methods Retrospectively gated CCTA was acquired with dual-source CT in 162 patients. Two cardiologists assessed by consensus whether diagnostic quality images could have been obtained in a single predefined phase, 70% of R-R interval (70P), thereby identifying patients in whom a prospectively gated scan at 70P would have been successful. Logistic regression models were built with and without a coronary calcium scan. The obtained criteria were applied on 42 additional patients. Results By logistic regression, heart rate before CCTA of ≥70 beats/min, maximal heart rate variation before CCTA of ≥10 beats/min, coronary calcium score ≥ 400 U, and body mass index (in kg/m 2 ) ≥ 30 were independent predictors of unsuccessful prospectively gated CCTA using 70P. Excluding coronary calcium score from the model, these same variables in addition to age > 65 years were found to be predictors of unsuccessful prospectively gated CCTA. Applying this model to 42 additional patients, using prospective gating, only 5 segments in 4 patients were nondiagnostic. Mean radiation dose for prospectively gated CCTA was 2.2 ± 0.8 mSv. Conclusion Prospectively gated CCTA with dual-source CT can be successfully implemented with consideration of prescan heart rate, heart rate variability, body mass index, and coronary calcium score.

Cardiac MR imaging in small animals presents some difficulties due to shorter cardiac cycles and smaller dimensions than in human beings, but prospectively gated techniques have been successfully applied. As with human imaging, there may be certain applications in animal imaging for which retrospective gating is preferable to prospective gating. For example, cardiac imaging in multiple mice simultaneously is one such application. In this work we investigate the use of retrospective gating for cardiac imaging in a mouse. Using a three-dimensional imaging protocol, we show that image quality with retrospective gating is comparable to prospectively gated imaging. We conclude that retrospective gating is applicable for small animal cardiac MRI and show how it can be applied to the problem of cardiac MRI in multiple mice.

Most MRI centers currently use prospective ECG triggering and fast gradient-echo sequences for image acquisition. Retrospectively gated sequences allow the coverage of the entire cardiac cycle. There is concern about whether ventricular volumes and ejection fraction (EF) differ according to the gating method used for image acquisition. We sought to evaluate the impact of the gating method on measurements of right and left ventricular volumes and EF in normal subjects.Fifteen subjects with no cardiovascular disease were investigated by MRI using a 1.5 Tesla scanner. Images were acquired with a gradient-echo sequence with steady-state free precession (SSFP) using the standard short-axis method for volume and EF measurements. Images were acquired with 6-mn-thick slices using both prospective triggering and retrospective gating. Left and right ventricular volumes (EDV, ESV, SV) and EF were determined with a commercially available software package (Argus, Siemens).EDV and SV calculated from short-axis images were significantly smaller with the prospectively triggered SSFP sequence (mean difference: EDV left: 13.9 +/- 4.4 mL, p0.0001; SV left: 13.5 +/- 4.8 mL, p0.0001; EDV right: 14.2 +/- 3.9 mL, p0.0001; SV right: 14.7 +/- 5.9 mL, p0.0001). EF was significantly smaller for the right ventricle (mean difference -3.6 +/- 3.3%, p = 0.0008) and the left ventricle (mean difference -2.3 +/- 3.3%, p = 0.02). ESV remained unchanged (mean difference: ESV left: 0.47 +/- 3.5 mL, p = 0.6179; right ESV: 0.5 +/- 3.7 mL, p = 0.6083).The gating method has a significant impact on volume and EF measurements. The global ventricular EF is underestimated by using the prospective triggering technique. However, the difference in the left ventricle is small and might not be of clinical relevance.

We review the scanning techniques for cardiac CT imaging with single slice and multislice scanners. Combined with prospective triggering for transaxial scanning and retrospective gating for helical scanning the potential advantages and the basic limitations are discussed. Based on those theoretical considerations, the major conclusion is that high resolution data sets with isotropic spatial resolution can be acquired with quadslice, spiral scanning, only. First clinical results support this conclusion.

Aim. To determine absorbed radiation dose (ARD) in radiosensitive organs during prospective and full phase dose modulation using ECG-gated MDCTA scanner under 64- and 320-row detector modes.Methods. Female phantom was used to measure organ radiation dose. Five DP-3 radiation detectors were used to measure ARD to lungs, breast, and thyroid using the Aquilion ONE scanner in 64- and 320-row modes using both prospective and dose modulation in full phase acquisition. Five measurements were made using three tube voltages: 100, 120, and 135 kVp at 400 mA at heart rate (HR) of 60 and 75 bpm for each protocol. Mean acquisition was recorded in milligrays (mGy).Results. Mean ARD was less for 320-row versus 64-row mode for each imaging protocol. Prospective EKG-gated imaging protocol resulted in a statistically lower ARD using 320-row versus 64-row modes for midbreast (6.728 versus 19.687 mGy,P<0.001), lung (6.102 versus 21.841 mGy,P<0.001), and thyroid gland (0.208 versus 0.913 mGy;P<0.001). Retrospective imaging using 320- versus 64-row modes showed lower ARD for midbreast (10.839 versus 43.169 mGy,P<0.001), lung (8.848 versus 47.877 mGy,P<0.001), and thyroid gland (0.057 versus 2.091 mGy;P<0.001). ARD reduction was observed at lower kVp and heart rate.Conclusions. Dose reduction to radiosensitive organs is achieved using 320-row compared to 64-row modes for both prospective and retrospective gating, whereas 64-row mode is equivalent to the same model 64-row MDCT scanner.

The relationship between heart rate (HR) and computed tomography dose index (CTDI) was evaluated using an electrocardiogram (ECG) gate scan for scan applications such as prospective triggering, Ca scoring, target computed tomography angiography (CTA), prospective CTA and retrospective gating, continuous CTA/CFA (cardiac functional analysis) and CTA/CFA modulation. Even in the case of a volume scan, doses for the multiple scan average dose were similar to those for CTDI. Moreover, it was found that the ECG gate scan yields significantly different doses. When selecting the optimum scan, the doses were dependent on many factors such as HR, scan rotation time, active time, prespecified cardiac phase and modulation rate. Therefore, it is necessary to take these results into consideration when selecting the scanning parameters.

PURPOSE Aim of this study was to evaluate whether phase contrast MR angiography (PC-MRA) could provide additional functional information besides morphology in the assessment of haemodialysis fistulae. MATERIAL AND METHOD Twenty-two patients (11 male, 11 female), aged 22-77 years, were examined. MR images were obtained with a 1.5 T Gyroscan ACS-NT (Philips, Best, Netherlands) using a high-resolution wrap-around coil. In addition to MRA blood-flow measurements were performed with a gradient-echo sequence (TR 14 ms, TE 5-5.5 ms, flip-angle 15 degrees, 6 mm slice thickness, retrospective gating, matrix 96:128) in the venous and arterial section of the fistulae. Doppler flow measurements were performed at the same position with a Sonoline Elegra (Siemens AG, Erlangen) using a 7.5 MHz transducer. RESULTS Both methods of flow-volume measurements showed a good correlation (r = 0.94 in the arterial section, r = 0.90 in the venous section, p < 0.001). The average calculated blood flow was measured 11% (arterial section) and 12.8% (venous section) higher with Pulsed Waved Doppler as compared to PC-MRA. CONCLUSION PC-MRA with a high-resolution wrap-around coil is a reliable method for measuring functional parameters like flow-volume and flow velocity in haemodialysis fistulae and a useful complement to the visualisation capabilities of MRA.

Motion artifacts continue to present a major challenge to single cell imaging in cardiothoracic organs such as the beating heart, blood vessels, or lung. In this study, we present a new water-immersion suctioning stabilizer that enables minimally invasive intravital fluorescence microscopy using water-based stick objectives. The stabilizer works by reducing major motion excursions and can be used in conjunction with both prospective or retrospective gating approaches. We show that the new approach offers cellular resolution in the beating murine heart without perturbing normal physiology. In addition, because this technique allows multiple areas to be easily probed, it offers the opportunity for wide area coverage at high resolution.

Performing cardiac CT on Philips scanners is described. 10c.1 Preparing and Starting the Examination....... 123 10c.2 Prospective Axial Acquisition (“Step & Shoot”) 123 10c.2.1 Scan Protocol 126 10c.2.2 Dose Indication Box 126 10c.2.3 Injection Protocol 126 10c.3 Retrospective Helical Image Acquisition ....... 126 10c.3.1 Scan Protocol 127 10c.4 Reconstruction 128 124 Chapter 10c • Philips Brilliance 64 and iCT

To date, there have been >1000 implantations of temporary total artificial hearts (TAH-t). As expected, complications related to the use of the TAH-t can occur.1 A noninvasive imaging modality that would be capable of diagnosing mechanical failure, surgical complications, and thromboembolic phenomena related to the TAH-t is desirable. Echocardiography is not suitable to evaluate a TAH-t because ultrasound cannot penetrate air and the polyurethane components in the TAH-t assembly. Cardiac magnetic resonance imaging is likewise unsuitable because of the susceptibility to artifacts that the titanium valve components in the TAH-t would create. Conventional computed tomography (CT) is limited by motion artifact.2 Cardiac CT (CCT) can produce motion-artifact–free images of the heart. If performed with retrospective gating, CCT can also be used to acquire time-resolved images. However, CCT requires simultaneous recording of the patient’s ECG, and patients who have a TAH-t do not generate an ECG. Consequently, a variation in technique is necessary to image patients with TAH-t with this modality. Detailed below …

Computed tomography (CT) technology has undergone major advances over the last decade, with no advance being more important than the development of 64-slice multidetector CT (MDCT) scanners. In parallel, the contraindications to coronary CT angiography (CCTA) have decreased, although there are still several absolute contraindications to this procedure. This chapter addresses the absolute contraindications to CCTA with respect to the medical/technical aspects of the exam, as well as the clinical absolute contraindications.

Background Time-resolved three-dimensional phase contrast CMR (4D flow) is a powerful tool for hemodynamic assessment in the cardiovascular system. However, long scan times have hindered the application of the method in many cases. By using spiral readout trajectories, improved efficiency provides a means of reducing scan times without decreasing SNR. Furthermore, spiral acquisition offers increased robustness in areas with accelerating flow. Spiral readouts have previously been used for rapid 4D flow measurements in the aorta using prospective gating [1]. Using retrospective gating, the entire cardiac cycle is covered, which allows analysis of late diastole and tracking of blood over a complete cardiac cycle. These are crucial for cardiac 4D flow studies, and allow for pathline based data quality assessment. The aim of this work is to develop a retrospectively gated 4D flow sequence using a stack of spiral readouts for the measurement of intra-cardiac velocities.

Recently, we developed the streak-mode Fourier domain optical coherence tomography (OCT) technique in which an area-scan camera is used in a streak-mode to record the OCT spectrum. Here we report the application of this technique to in ovo imaging HH18 embryonic chick hearts with an ultrahigh speed of 1,016,000 axial scans per second. The high-scan rate enables the acquisition of high temporal resolution 2D datasets (1,000 frames per second or 1 ms between frames) and 3D datasets (10 volumes per second), without use of prospective or retrospective gating technique. This marks the first time that the embryonic animal heart has been 4D imaged using a megahertz OCT.

Summary To investigate how disequilibrium of spoiling affects background offset errors in phase-contrast velocity images. Background Phase-contrast imaging normally uses gradient-echoes with RF spoiling and phase-encode rewinding with a fixed dephasing by gradient “spoiler” pulses in each TR (time between RF pulses) studied in detail (1) where effective artifact suppression in magnitude images required >≈ 8PI dephasing over the slice thickness, with >≈ 2PI dephasing over an FE pixel. However, the effectiveness of spoiling depends on establishing a steadystate. In phase-contrast imaging, background offsets are known to stabilise in continuous scanning such as retrospective gating, but sequence interruptions can be necessary eg in navigator-gating or slice-tracking. Unsteady background offsets are generally ascribed to disturbed equilibrium in eddy-current effects. This

ically indicated CCT. Methods: All patients were scanned using retrospective gating on a 64-slice CCT, for clinically indicated reasons, where coronary CT angiogram and calcium score measurements were performed. The amount of radiation was calculated from different parameters in millisievert (mSv). Results: 1287 patients were scanned with mean age of 52 ± 13.2 y, 65% males, and 35% females. Chest pain was the indication in 80% of cases. There mean radiation dose was 15 ± 10.4 (mSv). Patients with body mass index (BMI) P 35 received more radiation compared to those with BMI < 30 was, 15.3 ± 9.3 vs. 14.6 ± 7.4 (mSv), p< 0.002. Patients who had coronary bypass surgery (CABG) received significantly higher dose of radiation, 22.2 ± 9.3 vs. 14.4 ± 10.4 (mSv), P < 0.0001. Conclusion: Overweight patients and patients who underwent CABG are exposed to significantly higher radiation dose during CCT. Measures have to be applied to minimize the radiation dose during CCT.

We aimed testing feasibility of identification of regional left ventricular (LV) endocardial motion abnormalities in mice undergoing coronary ligation (MI), using cine magnetic resonance with retrospective gating and computation of regional fractional area change (RFAC), by comparison with histological "gold standard" evaluation. ROC analysis determined the optimal RFAC cut-off values for detecting regional ischemic injury. This approach was tested on 18 MI and 10 sham mice. Automated regional LV motion interpretation and bull's eye display allowed non-invasive localization of the induced infarction. Possible applications to future studies assessing the effectiveness of pharmacological treatments or regenerative medicine are expected.

Proper post-processing of cardiac CT images is crucial to obtain high-quality diagnostic images of the coronary arteries. The design of acquisition protocols take into account scan-related factors such as the temporal and spatial resolution of the scanner as well as patient-relate factors such as the patient weight and ECG tracing. ECG gating can be performed with either prospective or retrospective gating, with each method having distinct advantages. The next phase of post-processing involves the layout of images on the cardiac CT workstation. These reconstruction techniques enable the interpreting physician to reliably identify the anatomy and course of the coronary arteries and interpret coronary artery plaque and luminal obstruction.

A prospective, electrocardiographically gated technique was recently adapted for use with coronary and cardiac multidetector row CT studies. The most widely available form of prospective gating uses "step-and-shoot" axial data acquisition, an incrementally moving table, adaptive electrocardiographic triggering, an improved image reconstruction algorithm, and multiphase reconstruction capability. Studies have shown a 77%-87% effective radiation dose reduction compared with retrospective gating and equal to significantly improved image quality. Comparison with conventional angiography has proven it to be as accurate as retrospective gating for coronary stenosis detection. The technique is not applicable to all patients because there are some restrictions for clinical use, including a limited number of reconstructed phases and a maximum scan heart rate of 68-75 beats/min. However, with careful patient selection and effective heart rate control, prospective gating can be used in a high percentage of cardiac CT examinations. This article reviews the scanning and patient selection protocols for prospective gating and discusses how it may be used in clinical practice.

Our aim was to test, in a murine myocardial infarction (MMI) model, the feasibility of a new MRI protocol with no ECG/respiratory gating, and compare normal mice versus MMI, in terms of global and regional LV function. A control group (C, 10 mice) and a MMI group (18 mice) were studied. MRI with retrospective gating was performed. End-diastolic (EDV) and end-systolic (ESV) LV volumes with ejection fraction (EF) were computed. In addition, regional fractional area change (RFAC) was used as index of regional wall motion. In MMI, LV size (in muL) was larger compared to C (EDV: 92plusmn25 vs 36plusmn4, ESV: 66plusmn27 vs 10plusmn3), with a significant decrease in EF (31plusmn10 vs 72plusmn7%). RFAC in C showed heterogeneous values. In MMI, RFAC decreased from LV base to apex, with a min (26%) in the anterior segment, in agreement with the occluded LAD. MRI with retrospective gating is feasible in mice, and regional LV function analysis allows the localization of the induced infarction.

We propose a retrospective respiratory gating algorithm to generate dynamic CT studies. To this end, we compared three different methods of extracting the respiratory signal from the projections of small-animal cone-beam computed tomography (CBCT) scanners. Given a set of frames acquired from a certain axial angle, subtraction of their average image from each individual frame produces a set of difference images. Pixels in these images have positive or negative values (according to the respiratory phase) in those areas where there is lung movement. The respiratory signals were extracted by analysing the shape of the histogram of these difference images: we calculated the first four central and non-central moments. However, only odd-order moments produced the desired breathing signal, as the even-order moments lacked information about the phase. Each of these curves was compared to a reference signal recorded by means of a pneumatic pillow. Given the similar correlation coefficients yielded by all of them, we selected the mean to implement our retrospective protocol. Respiratory phase bins were separated, reconstructed independently and included in a dynamic sequence, suitable for cine playback. We validated our method in five adult rat studies by comparing profiles drawn across the diaphragm dome, with and without retrospective respiratory gating. Results showed a sharper transition in the gated reconstruction, with an average slope improvement of 60.7% This project was supported by the CENIT Programme (Ministerio de Industria), CIBER CB07/09/0031 (Ministerio de Sanidad y Consumo) and TEC2007-64731/TCM (Ministerio de Educación y Ciencia) Publicado

Cardiac C-arm CT is a promising technique that enables 3D cardiac image acquisition and real-time fluoroscopy on the same system. Retrospective ECG gating techniques have already been adapted from clinical cardiac CT that allow 3D reconstruction using retrospectively gated projection images of a multi-sweep C-arm CT scan according to the desired cardiac phase. However, it is known that retrospective gating of projection data does not provide an optimal signal-to-noise-ratio (SNR) since the measured projection data is only partially considered during the reconstruction. In this work we introduce a new reconstruction technique for cardiac C-arm CT that provides increased SNR by including additional corrected and resampled filtered back-projections (FBP) from temporal windows outside of the targeted reconstruction phase. We take advantage of several motion corrected FDK-like reconstructions of the subject to increase SNR. In the presented results, using in vivo data from an animal model, the SNR could be increased by approximately 30 percent.

Current implementations of k-t Broad-use Linear Acqusition Speed-up Technique (BLAST) require the sampling in k-t space to conform to a lattice. To permit the use of k-t BLAST with non-Cartesian sampling, an iterative reconstruction approach is proposed in this work. This method, which is based on the conjugate gradient (CG) method and gridding reconstruction principles, can efficiently handle data that are sampled along non-Cartesian trajectories in k-t space. The approach is demonstrated on prospectively gated radial and retrospectively gated Cartesian imaging. Compared to a sliding window (SW) reconstruction, the resulting image series exhibit lower artifact levels and improved temporal fidelity. The proposed approach thus allows investigators to combine the specific advantages of non-Cartesian imaging or retrospective gating with the acceleration provided by k-t BLAST.

Effective suppression of cardiac motion is crucial for MR coronary angiography (MRCA). Thus, we evaluated a new technique for rapid and automatic detection of the cardiac rest period in comparison to the conventional visual assessment of the coronary artery rest periods.One hundred and thirty-five consecutive cardiac patients were examined (Philips Intera CV 1.5 T, Best, The Netherlands). Visual assessment of the left and right coronary rest periods was done using a cine-SSFP scan with a transversal slice orientation (retrospective gating, 40 phases/cardiac cycle); the coronary rest period was defined as the duration of the coronary artery being completely within a region of interest placed on the outer edge of the cross-section of the vessel. Common coronary rest period as determined from visual assessment was defined as the intersection of both coronary artery rest periods. For comparison, an automatic technique was applied: using the position of the shim volume to define a correlation kernel, the cross-correlations of consecutive cine images were registered and displayed in a graph. Based on these cross-correlation values, the cardiac rest period was detected. The correlation between the visual and automated analysis was assessed.A high correlation between the automatically and visually determined starting points for the coronary artery rest periods and the cardiac rest period was found. The automatically assessed cardiac rest period was significantly shorter in comparison to the visually assessed left and right coronary artery rest period (103 +/- 46 ms vs. 158 +/- 72 ms and 117 +/- 52 ms, respectively; p0.001). However, the common coronary rest period demonstrated excellent agreement with the cardiac rest period (r = 0.93, p0.001) without a significant difference in duration (109 +/- 52 ms vs. 103 +/- 46 ms).Automated analysis of the cardiac rest period yielded similar results compared to the visual analysis. This rapid assessment of a cardiac acquisition window may be most helpful for MRCA, especially when aiming at 3-dimensional coverage of the whole coronary arterial tree during a single scan.

ECG-gated cardiac MRI in the mouse is hindered by many technical difficulties in ECG signal recording inside static and variable high magnetic scanner fields. The present study proposes an alternative robust method of acquiring auto-gated cine images in mouse heart. In our approach, a motion synchronization signal is extracted from the echo peak MR signal of a non-triggered radial acquisition. This signal is then used for both cardiac and respiratory retrospective gating before cine image reconstruction. Highly asymmetric echoes were acquired to achieve the radial k-space sampling, in order to avoid radial acquisition related artifacts and to increase auto-gating robustness. In vivo experiments demonstrated the feasibility and robustness of self-gated cine-MRI in the mouse heart at 7T

In recent years, there has been an important increase of interest in the use of noninvasive measurement of coronary arterial calcification as a screening test for coronary atherosclerosis. Until the introduction of subsecond mechanical CT scanners, coronary calcium measurement remained a domain of electron beam CT (EBCT). Due to the limited number of EBCT scanners available in dedicated imaging centers, access to coronary CT scanning was restricted. Many of the whole body multi-detector-row CT (MDCT) systems installed today are equipped with the necessary hard- and software to perform examinations of the heart using either prospective triggering of sequential scans or retrospective gating of spiral CT scans. This development opens CT scanning of the heart for a larger patient population. There is a continuous debate about possible indications for coronary calcium scans. In the light of the new availability of heart scanners, the role of coronary calcium scanning in the clinical setting should be defined.

Intracoronary ultrasound (ICUS) provides high-resolution tomographic images of selected segments of coronary arteries. Series of cross-sectional images are acquired with motorized pullback imaging catheters and used for quantitative analysis in intracoronary ultrasound studies (ICUS). Due to catheter displacement in the vascular lumen during the cardiac cycle the images that are typically acquired at 0.5 mm/s are anatomically shuffled. This results in a saw-tooth shaped appearance of the coronary segment in longitudinal reconstructed views (L-views) used frequently in quantitative coronary ultrasound (QCU) software. This paper describes a novel image-based gating method called "Intelligate", which overcomes this problem by automatic retrospective selection of end-diastolic frames from pre-recorded ICUS studies. Our evaluation shows that there are no quantitative differences between analysis results of hardware ECG-gated and intelligated ICUS studies.

This paper presents the experimental part of an investigation on tracking and eliminating organ motion artifacts in x-ray CT cardiac applications with emphasis on imaging coronary calcification. The system methodology consists of a software implementation of the spatial overlap correlator (SSOC) concept in x-ray CT scanners to track the net amplitude and phase of organ motion during the CT data acquisition process. A coherent sinogram synthesis (CSS) method is then used to identify the repeated phases of a periodic organ motion from the information provided by the SSOC process and hence synthesize a new sinogram with no motion effects. Since the SSOC scheme is capable of tracking cardiac motion, it identifies also the projection points associated with minimum amplitude cardiac motion effects. These points are used to identify a 180 degrees plus the fan angle sinogram for image reconstruction. This leads to a retrospective gating (RG) scheme that is based on the output of the SSOC process. Performance comparison of the proposed methodology with the retrospective ECG gating using real data sets with phantoms and human patients provides a performance assessment of the merits of the proposed methods. Real results demonstrate that the new methodology eliminates the requirement for ECG gating. Moreover, the CSS and the new RG methods do not require breath holding and they can be implemented in x-ray CT scanners to image coronary calcification and the heart's ventricles.

When we first applied retrospective gating on the singleslice scanner Siemens SOMATOM Plus 4 for improvement of cardiac imaging in 1997, we did not expect the tremendous possibilities of this new, fast evolving tool for spiral computed tomography (CT). By now, we have greatly enhanced our thoughts on possible clinical settings and indications for cardiac spiral CT, and learned about some possible inherent new artifacts not known in standard CT.

The sections in this article are 1 Introduction 2 Requirement of Cardiac Gating 3 Methods of Cardiac Monitoring 4 Artifacts on the Electrocardiogram 5 Electrocardiogram Electrode and Lead Positioning 6 Prospective and Retrospective Gating 7 Implications of the Gating Type on the Accuracy of Blood Flow Mapping 8 Biographical Sketch Related Articles

An analysis of the effect of respiratory function on MR flow measures of the internal jugular vein (IJV) is presented. A novel 2D radial acquisition and reconstruction method allows for retrospective gating to both the cardiac and respiratory cycle. In-vivo scans of human volunteers verify the efficacy of the algorithm, showing increased IJV flow during inspiration and decreased flow during expiration for each cardiac time frame.

A new “wireless” method of cardiac imaging is introduced, which, unlike ECG triggering, allows imaging the heart at end-diastole, and greatly reduces smearing artifacts in the phase-encoding direction. It is an improvement over ECG-driven retrospective gating, in that patients with poor ECGs can be imaged. This method extends the applicability of cardiac imaging, and since it requires no physiological monitoring hardware, can be implemented easily on any MR imager. The images produced by this method are superior to those from ECG triggering, especially when viewed in a “cine” loop. The technique described herein is, furthermore, extendable to any area where periodic or quasi-periodic motion is a problem.

In this paper we propose a method to overcome the effects of cardiac and respiratory motion in coronary subtraction imaging. We present the ideas of retrospective gating of masks, where both cardiac and respiratory phases are measured for a set of masks, and are subsequently used in a functional decomposition of motion. Through retrospective gating of masks, we are able to select appropriate images and to perform temporal and spatial processing on them to produce computed masks, subtraction of which should lead to motion-artifact-free images. The computed masks are built from two components: the first includes the time-variant structures related to respiration, such as ribs and soft tissues of the chest wall, and the second incorporates the time-variant structures related to cardiac motion. A preliminary study of the method in the area of digital subtraction angiography produced images which are comparable to but not better than those produced by techniques in current clinical practice: we discuss the reasons for this.