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Objective: Image-guided percutaneous needle biopsies are essential in the workup of musculoskeletal (MSK) lesions. While helical CT (HCT) is well established, intermittent CT fluoroscopy (iCTF) is an increasingly used alternative. The purpose of this study is to establish whether differences in subject radiation exposure, procedure time, yield, or adverse events exist between HCT and iCTF guidance.Materials and Methods: This retrospective cohort study included consecutive MSK needle biopsies performed on a single-CT scanner over a 12-month period at a tertiary academic center. Subject demographics, radiation dose, and outcomes were abstracted from the medical record. Comparisons between the two cohorts were performed using Student's t-test for continuous data and using Fisher's exact test for categorical data and a two-tailed p value less than 0.05 was considered significant.Results: Two hundred sixteen adults (115 (53.2%) females) with a mean age of 58.8 ± 18.4 years, underwent 216 biopsies (109 (50.5%) HCT guided, 107 (49.5%) iCTF guided) between June 2017 and June 2018. Dose-length product (DLP) and volume CT dose index (CTDIvol) were significantly higher for the HCT cohort (HCT 698.9 ± 400.8 mGycm vs iCTF 312.8 ± 170.8 mGycm; p < 0.005 and HCT 19.1 mGy ± 8.8 vs iCTF 6.9 mGy ± 1.5, p < 0.001). No significant difference in diagnostic yield, procedure time, or adverse event rate was identified.Conclusion: For CT-guided MSK needle biopsies, iCTF decreases subject radiation dose compared to HCT without negatively affecting outcomes. iCTF should be strongly considered by radiologists performing MSK biopsies given the reduced patient radiation exposure. [ABSTRACT FROM AUTHOR]

Helical computed tomography (CT) scans are often performed to obtain three-dimensional images of an object that is longer than the detector. However, the existing quasi-exact and exact reconstruction methods, such as re-binning and Katsevich algorithm, generate interpolation errors or require high computational power. In this work, we propose a method to reconstruct helical CT projections by iteratively reducing helical artifacts. In each iteration, a convolutional neural network (CNN)-based denoising technique is used to accurately segment the prior image (bone and soft tissue image). The results indicate that the proposed algorithm reduces helical artifacts to a significantly greater extent than the existing single slice re-binning (SSR) and weighted filtered backprojection (W-FBP) methods.

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Objectives: To present a new method to assess the cervical lymph nodes status in head and neck cancer patients. Methods: Twenty-five oral and maxillofacial cancer patients underwent preoperative CT imaging. The cervical lymph node features on CT scan were examined. Each parameter was given a score, and the total scores in each case was calculated and referred to as metastatic score (MS). Then, patients underwent neck dissection, and all dissected lymph nodes were sent for histopathology. Results: All cases with MS ≥ 6 were histopathologically positive, and all cases with MS ≤ 3 were histopathologically negative. All cases of nodal sizes > 3 cm were histopathologically positive, 82% of cases of nodal sizes between 2.1 and 3 cm were histopathologically positive, 40% of cases of nodal sizes between 1 and 2 cm were histopathologically positive, and all cases of lymph nodes sizes < 1 cm were histopathologically negative. Seventy-seven percent of cases which had a group of lymph nodes ≥ 3 nodes/region were histopathologically positive, while 79% of cases with rounded nodes were histopathologically positive, and all cases with necrotic lymph nodes were positive for malignancy. Conclusion: The proposed formula is a good assessment tool for cervical lymph nodes evaluation using helical CT scan in head and neck cancer patients. [ABSTRACT FROM AUTHOR]

Sparse-view scanning has great potential for realizing ultra-low-dose computed tomography (CT) examination. However, noise and artifacts in reconstructed images are big obstacles, which must be handled to maintain the diagnosis accuracy. Existing sparse-view CT reconstruction algorithms were usually designed for circular imaging geometry, whereas the helical imaging geometry is commonly adopted in the clinic. In this paper, we show that the sparse-view helical CT (SHCT) images contain not only noise and artifacts but also severe anatomical distortions. These troubles reduce the applicability of existing sparse-view CT reconstruction algorithms. To deal with this problem, we analyzed the three-dimensional (3D) anatomical structure sparsity in SHCT images. Based on the analyses, we proposed a tensor decomposition and anisotropic total variation regularization model (TDATV) for SHCT reconstruction. Specifically, the tensor decomposition works on nonlocal cube groups to exploit the anatomical structure redundancy; the anisotropic total variation works on the whole volume to exploit the structural piecewise-smooth. Finally, an alternating direction method of multipliers is developed to solve the TDATV model. To our knowledge, the paper presents the first work investigating the reconstruction of sparse-view helical CT. The TDATV model was validated through digital phantom, physical phantom, and clinical patient studies. The results reveal that SHCT could serve as a potential solution for reducing HCT radiation dose to ultra-low level by using the proposed TDATV model.

Objectives: Early recognition of coronavirus disease 2019 (COVID-19) severity can guide patient management. However, it is challenging to predict when COVID-19 patients will progress to critical illness. This study aimed to develop an artificial intelligence system to predict future deterioration to critical illness in COVID-19 patients. Methods: An artificial intelligence (AI) system in a time-to-event analysis framework was developed to integrate chest CT and clinical data for risk prediction of future deterioration to critical illness in patients with COVID-19. Results: A multi-institutional international cohort of 1,051 patients with RT-PCR confirmed COVID-19 and chest CT was included in this study. Of them, 282 patients developed critical illness, which was defined as requiring ICU admission and/or mechanical ventilation and/or reaching death during their hospital stay. The AI system achieved a C-index of 0.80 for predicting individual COVID-19 patients' to critical illness. The AI system successfully stratified the patients into high-risk and low-risk groups with distinct progression risks (p < 0.0001). Conclusions: Using CT imaging and clinical data, the AI system successfully predicted time to critical illness for individual patients and identified patients with high risk. AI has the potential to accurately triage patients and facilitate personalized treatment. Key Point: • AI system can predict time to critical illness for patients with COVID-19 by using CT imaging and clinical data. [ABSTRACT FROM AUTHOR]

Objective: In X‐raycomputed tomography (CT), many important clinical applications may benefit from a fast acquisition speed. The helical scan is the most widely used acquisition mode in clinical CT, where a fast helical pitch can improve the acquisition speed. However, on a typical single‐source helical CT (SSCT) system, the helical pitch p typically cannot exceed 1.5; otherwise, reconstruction artifacts will result from data insufficiency. The purpose of this work is to develop a deep convolutional neural network (CNN) to correct for artifacts caused by an ultra‐fast pitch, which can enable faster acquisition speed than what is currently achievable. Methods: A customized CNN (denoted as ultra‐fast‐pitch network (UFP‐net)) was developed to restore the underlying anatomical structure from the artifact‐corrupted post‐reconstruction data acquired from SSCT with ultra‐fast pitch (i.e., p ≥ 2). UFP‐net employed residual learning to capture the features of image artifacts. UFP‐net further deployed in‐house‐customized functional blocks with spatial‐domain local operators and frequency‐domain non‐local operators, to explore multi‐scale feature representation. Images of contrast‐enhanced patient exams (n = 83) with routine pitch setting (i.e., p < 1) were retrospectively collected, which were used as training and testing datasets. This patient cohort involved CT exams over different scan ranges of anatomy (chest, abdomen, and pelvis) and CT systems (Siemens Definition, Definition Flash, Definition AS+, Siemens Healthcare, Inc.), and the corresponding base CT scanning protocols used consistent settings of major scan parameters (e.g., collimation and pitch). Forward projection of the original images was calculated to synthesize helical CT scans with one regular pitch setting (p = 1) and two ultra‐fast‐pitch setting (p = 2 and 3). All patient images were reconstructed using the standard filtered‐back‐projection (FBP) algorithm. A customized multi‐stage training scheme was developed to incrementally optimize the parameters of UFP‐net, using ultra‐fast‐pitch images as network inputs and regular pitch images as labels. Visual inspection was conducted to evaluate image quality. Structural similarity index (SSIM) and relative root‐mean‐square error (rRMSE) were used as quantitative quality metrics. Results: The UFP‐net dramatically improved image quality over standard FBP at both ultra‐fast‐pitch settings. At p = 2, UFP‐net yielded higher mean SSIM (> 0.98) with lower mean rRMSE (< 2.9%), compared to FBP (mean SSIM < 0.93; mean rRMSE > 9.1%). Quantitative metrics at p = 3: UFP‐net—mean SSIM [0.86, 0.94] and mean rRMSE [5.0%, 8.2%]; FBP—mean SSIM [0.36, 0.61] and mean rRMSE [36.0%, 58.6%]. Conclusion: The proposed UFP‐net has the potential to enable ultra‐fast data acquisition in clinical CT without sacrificing image quality. This method has demonstrated reasonable generalizability over different body parts when the corresponding CT exams involved consistent base scan parameters. [ABSTRACT FROM AUTHOR]

Objectives: To determine whether imaging features and severity indices using low monoenergetic DECT images improve diagnostic conspicuity and outcome prediction in acute pancreatitis compared to conventional images. Methods: A retrospective study of patients with clinical and radiographic signs of acute pancreatitis who underwent 50 contrast-enhanced CT exams conducted on a single-source DECT was performed. Representative conventional and 50 keV-monoenergetic images were randomized and presented to four abdominal radiologists to determine preferred imaging for detecting fat stranding and parenchymal inflammation. Contrast and signal-to-noise ratios were constructed for necrotic, hypoattenuated, inflamed, and healthy parenchyma. These parameters and the CT severity index (CTSI) were compared between conventional and low monoenergetic images using paired t tests and correlated to clinical outcome. Results: Although preference for conventional images was noted for subtle peri-pancreatic fat stranding (169/200 (85%) reads), there was clear preference for low monoenergetic images among all readers for pancreatic inflammation evaluation (188/200 (94%) reads). Moreover, identification of small, hypoattenuating inflammatory foci on monoenergetic images alone in 13/50 (26%) cases resulted in upstaged CTSI from mild to moderate in 7/50 (14%), associated with longer hospitalization (16 ± 17 days vs. 5 ± 2 days; p < 0.05), ICU admission, and drainage. Quantitatively, a twofold difference between normal and inflamed parenchyma attenuation was identified for monoenergetic (44.8 ± 27.6) vs. conventional (25.1 ± 14.7) images (p < 0.05). Significant increases were seen in the monoenergetic SNR and CNR compared to the conventional images (p < 0.05). Conclusions: DECT low monoenergetic images afford better tissue assessment and demarcation of inflamed pancreatic parenchyma. Additionally, they provide improved characterization of the extent parenchymal necrosis, enabling better classification that may better predict severe clinical outcomes. Key Points: • DECT low monoenergetic images afford better tissue assessment and demarcation of inflamed pancreatic parenchyma and provide improved characterization of the extent parenchymal necrosis. • Qualitatively, low monoenergetic images were preferred over conventional DECT images for the evaluation of pancreatic inflammation; and quantitatively, there is a twofold difference between normal and inflamed parenchyma attenuation, SNR, and CNR between monoenergetic vs. conventional images. • Monoenergetic imaging identified additional small, hypoattenuating inflammatory foci in 26% resulting in an upstaged CT severity index in 14% associated with longer hospitalization, ICU admission, and drainage, thereby enabling better classification and better prediction of severe clinical outcomes. [ABSTRACT FROM AUTHOR]

OBJECTIVES: This study used the data from patients with congenital sensorineural hearing loss (CSNHL) and those with normal hearing to measure and compare the length of the cochlea with high-resolution computed tomography (HRCT). MATERIALS and METHODS: HRCT images of patients who were diagnosed with CSNHL and were candidates for cochlear implantation were evaluated retrospectively. Sixty-three ears of 33 patients were included in the study. The control group comprised 66 ears of 33 individuals. The measurements were conducted by an experienced radiologist, using three-dimensional curved multiplanar reconstruction. All the measurements were performed thrice, and the average was calculated. RESULTS: The data were distributed normally. The lengths of the cochlear components for the CSNHL and control groups were as follows: basal turn 21.66±1.01 (21.30-22.02) and 22.57±0.68 (22.32-22.81) mm, middle turn 11.58±0.69 (11.34-11.83) and 12.39±0.46 (12.23-12.56) mm, and apical turn 6.45±0.92 (6.12-6.77) and 7.12±0.65 (6.89-7.35) mm, respectively. The mean cochlear lateral wall (LW) length was significantly shorter in the CSNHL patients [39.71±1.32 (39.25-40.18) mm] than in the controls [42.09±1.17 (41.67-42.51) mm], (p<0.001). The intra-rater reliability was 0.878 (confidence interval 95%: 0.841-0.908 p<0.001). The cut-off value was 40.81 mm (sensitivity: 0.91, specificity: 0.94, and accuracy: 0.90). CONCLUSION: There were microanatomic dissimilarities between the length of the cochlea in subjects from the CSNHL group and those from the control group. [ABSTRACT FROM AUTHOR]

To investigate the effect of scan projection radiography (SPR) coverage on tube current modulation in pediatric and adult thoracic CT examinations. Sixty pediatric and 60 adult chest CT examinations were retrospectively studied to determine the incidence rate of examinations involving SPRs that did not include the entire image volume (IV) or the entire primarily exposed body volume (PEBV). The routine chest CT acquisition procedure on a modern 64-slice CT system was imitated on five anthropomorphic phantoms of different size. SPRs of varying length were successively acquired. The same IV was prescribed each time and the computed tube current modulation plan was recorded. The SPR boundaries were altered symmetrically by several steps of ±10 mm with respect to the IV boundaries. The upper IV boundary was found to be excluded from SPR in 52% of pediatric and 40% adult chest CT examinations. The corresponding values for the lower boundary were 15% and 20%, respectively. The computed tube current modulation was found to be considerably affected when the SPR did not encompass the entire IV. SPR deficit of 3 cm was found to induce up to 46% increase in the computed tube current value to be applied during the first tube rotations over lung apex. The tube current modulation mechanism functions properly only if the IV set by the operator is entirely included in the localizing SPR image. Operators should cautiously set the SPR boundaries to avoid partial exclusion of prescribed IV from SPRs and thus achieve optimum tube current modulation. [ABSTRACT FROM AUTHOR]

Objectives: To investigate the diagnostic impact and performance of spectral dual-layer detector CT in the detection and characterization of cancer compared to conventional CE-CT.Methods: In a national workup program for occult cancer, 503 patients (286 females and 217 males) were prospectively enrolled for a contrast-enhanced spectral CT scan. The readings were performed with and without spectral data available. A minimum of 3 months between interpretations was implemented to minimize recall bias. The sequence of reads for the individual patient was randomized. Readers were blinded for patient identifiers and clinical outcome. Two radiologists with 9 and 33 years of experience performed the readings in consensus. If disagreement, a third radiologist with 11 years of experience determined the outcome of the reading RESULTS: Significantly more cancer findings were identified on the spectral reading. In 73 cases of proven cancer, we found a sensitivity of 89% vs 77% and a specificity of 77% vs 83% on spectral CT compared to conventional CT. A slight increase in reading time in spectral images of 82 s was found (382 vs 300, p < 0.001). For all cystic lesions, the perceived diagnostic certainty increased from 30% being completely certain to 96% most pronounced in the kidney, liver, thyroid, and ovaries. And adding the spectral information to the reading gave a decrease in follow-up examination for diagnostic certainty (0.25 vs 0.81 per reading, p < 0.001).Conclusion: The use of contrast-enhanced spectral CT increases the confidence of the radiologists in correct characterization of various lesions and minimizes the need for supplementary examinations.Key Points: • Spectral CT is associated with a higher sensitivity, but a slightly lower specificity compared to conventional CT. • Spectral CT increases the confidence of the radiologists. • The need for supplementary examinations is decreased, with only a slight increase in reading times. [ABSTRACT FROM AUTHOR]

Exact histological clot composition remains unknown. The purpose of this study was to identify the best imaging variables to be extrapolated on clot composition and clarify variability in the imaging of thrombi by non-contrast CT. Using a CT-phantom and covering a wide range of histologies, we analyzed 80 clot analogs with respect to X-ray attenuation at 24 and 48 h after production. The mean, maximum, and minimum HU values for the axial and coronal reconstructions were recorded. Each thrombus underwent a corresponding histological analysis, together with a laboratory analysis of water and iron contents. Decision trees, a type of supervised machine learning, were used to select the primary variable altering attenuation and the best parameter for predicting histology. The decision trees selected red blood cells (RBCs) for correlation with all attenuation parameters (p < 0.001). Conversely, maximum attenuation on axial CT offered the greatest accuracy for discriminating up to four groups of clot histology (p < 0.001). Similar RBC-rich thrombi displayed variable imaging associated with different iron (p = 0.023) and white blood cell contents (p = 0.019). Water content varied among the different histologies but did not in itself account for the differences in attenuation. Independent factors determining clot attenuation were the RBCs (β = 0.33, CI = 0.219–0.441, p < 0.001) followed by the iron content (β = 0.005, CI = 0.0002–0.009, p = 0.042). Our findings suggest that it is possible to extract more and valuable information from NCCT that can be extrapolated to provide insights into clot histological and chemical composition. [ABSTRACT FROM AUTHOR]

Purpose: To describe CT features of parathyroid carcinomas (PCs) by comparison with benign parathyroid lesions (BPs).Methods: This retrospective study comprised 82 patients with 76 BPs (62 adenomas and 14 hyperplastic lesions) and 6 PCs. CT features (size, short-to-long axis ratio, shape, peritumoral infiltration, homogeneity, calcification, attenuation values on unenhanced CT, and contrast enhancement during arterial and venous phases) were compared between PCs and BPs. The diagnostic performance of CT features for diagnosing PCs was calculated for these individual parameters.Results: Short-to-long axis ratio was significantly larger in PCs (0.7 ± 0.1) than in BPs (0.5 ± 0.1, p = 0.004). Irregular shape (33%), the presence of peritumoral infiltration (50%), and calcification (33%) were significantly more common in PCs than BPs. The contrast enhancement value was significantly lower in PCs than BPs during arterial (p = 0.004) and venous phases (p = 0.044). The 100% sensitivity criterion for the short-to-long axis ratio (≥ 0.53), enhancement during arterial phase (≤ 56.6HU), and venous phase (≤ 59.5HU) yielded accuracies (62.1%, 71.9%, and 75.4%, respectively). Irregular shape, peritumoral infiltration, and calcification showed high specificity (98.7%) and accuracy (93.9%, 95.1%, and 93.9%, respectively).Conclusions: CT features of high short-to-long axis ratio, irregular shape, the presence of peritumoral infiltration and calcification, and low contrast enhancement may aid in distinguishing PCs from BPs. [ABSTRACT FROM AUTHOR]

The diagnostic accuracy of contrast‐enhanced CT for detection of cervical lymph node metastasis in dogs is unknown. The purpose of this retrospective, observational, diagnostic accuracy study was to assess the efficacy of CT for detection of mandibular and medial retropharyngeal lymph node metastasis in dogs. Histopathology of dogs with cancer of the head, CT and bilateral mandibular and medial retropharyngeal lymphadenectomy was reviewed. A single radiologist measured lymph nodes to derive short axis width and long‐short axis ratios. Two blinded radiologists separately assessed lymph node margins, attenuation and contrast enhancement and each provided a final subjective interpretation of each node site as benign or neoplastic. Where radiologists' opinions differed, a consensus was reached. Sensitivity, specificity and accuracy were calculated for mandibular and medial retropharyngeal sites. Agreement between radiologists was assessed. Fisher's exact test and the Kruskal‐Wallis H‐test were used to assess associations between variables. Forty‐one primary tumours were recorded in 40 dogs. Metastasis to mandibular or retropharyngeal lymph nodes occurred in 16 out of 40 dogs (43/160 nodes). Agreement between radiologists was almost perfect for margination, attenuation and enhancement, strong for interpretation of mandibular lymph node metastasis, and weak for interpretation of medial retropharyngeal lymph node metastasis. Sensitivity of CT was 12.5% and 10.5%, specificity was 91.1% and 96.7%, and accuracy was 67.5% and 76.3% for mandibular and medial retropharyngeal lymph nodes respectively. No individual CT findings were predictive of nodal metastasis. Given the low sensitivity of CT, this modality cannot be relied upon alone for assessment of cervical lymph node metastasis in dogs. [ABSTRACT FROM AUTHOR]

Purpose: The noise power spectrum (NPS) in computed tomography (CT) images potentially varies with the X-ray tube angle in a spiral orbit of the helical scan. The purpose of this study was to propose a method for measuring the NPS for each angle of the X-ray tube., Methods: Images of the water phantom were acquired using a helical scan. As a conventional method, we measured the two-dimensional (2D) NPS from each image and averaged them; the obtained 2D-NPS was referred to as NPS conventional . In the proposed method, we made the X-ray tube angle θ (0°≤θ<360°) to correspond to the image according to each slice position of the images that located within the travel distance of the CT scan table per 360° rotation of the X-ray tube. We obtained the 2D-NPS from each image and assigned the θ (0°, 30°, 60°, 90°, 120°, 150°, 180°); the obtained 2D-NPS was referred to as NPSs θ . The NPSs θ was compared to the NPS conventional . Also, we investigated the dependency of the NPSs θ on the θ., Results: The NPS conventional was found to be isotropic, and in contrast, the NPSs θ was anisotropic. The NPSs θ showed a continuously rotational change while increasing the θ. There was an excellent correlation (R 2 >0.999) between the rotation angle of NPS θ and the θ., Conclusion: The proposed method was demonstrated to be effective for evaluating anisotropic noise characteristics depending on the X-ray tube angle.

Objectives: The aim of this study was to assess the CT findings that characterise haemoptysis in patients with chronic pulmonary aspergillosis (CPA).Methods: We retrospectively identified 120 consecutive patients with CPA (84 men and 36 women, 17-89 years of age, mean age 68.4 years) who had undergone a total of 829 CT examinations between January 2007 and February 2017. In the 11 patients who underwent surgical resection, CT images were compared with the pathological results.Results: The scab-like sign was seen on 142 of the 829 CT scans, specifically, in 87 of the 90 CT scans for haemoptysis and in 55 of the 739 CT scans obtained during therapy evaluation. In 48 of those 55 patients, haemoptysis occurred within 55 days (mean 12.0 days) after the CT scan. In the 687 CT scans with no scab-like sign, there were only three instances of subsequent haemoptysis in the respective patients over the following 6 months. Patients with and without scab-like sign differed significantly in the frequency of haemoptysis occurring after a CT scan (p<0.0001). Pathologically, the scab-like sign corresponded to a fibrinopurulent mass or blood crust.Conclusions: The scab-like sign should be considered as a CT finding indicative of haemoptysis.Key Points: • Haemoptysis is commonly found in patients with CPA. • A CT finding indicative of haemoptysis in CPA patients is described. • Scab-like sign may identify CPA patients at higher risk of haemoptysis. [ABSTRACT FROM AUTHOR]

Abstract: The goal of this project is to investigate quantitatively the performance of different deformable image registration algorithms (DIR) with helical (HCT), axial (ACT), and cone‐beam CT (CBCT). The variations in the CT‐number values and lengths of well‐known targets moving with controlled motion were evaluated. Four DIR algorithms: Demons, Fast‐Demons, Horn‐Schunck and Lucas‐Kanade were used to register intramodality CT images of a mobile phantom scanned with different imaging techniques. The phantom had three water‐equivalent targets inserted in a low‐density foam with different lengths (10–40 mm) and moved with adjustable motion amplitudes (0–20 mm) and frequencies (0–0.5 Hz). The variations in the CT‐number level, volumes and shapes of these targets were measured from the spread‐out of the CT‐number distributions. In CBCT, most of the DIR algorithms were able to produce the actual lengths of the mobile targets; however, the CT‐number values obtained from the DIR algorithms deviated from the actual CT‐number of the targets. In HCT, the DIR algorithms were successful in deforming the images of the mobile targets to the images of the stationary targets producing the CT‐number values and lengths of the targets for motion amplitudes <20 mm. Similarly in ACT, all DIR algorithms produced the actual CT‐number values and lengths of the stationary targets for low‐motion amplitudes <15 mm. The optical flow‐based DIR algorithms such as the Horn‐Schunck and Lucas‐Kanade performed better than the Demons and Fast‐Demons that are based on attraction forces particularly at large motion amplitudes. In conclusion, most of the DIR algorithms did not reproduce well the CT‐number values and lengths of the targets in images that have artifacts induced by large motion amplitudes. The deviations in the CT‐number values and variations in the volume of the mobile targets in the deformed CT images produced by the different DIR algorithms need to be considered carefully in the treatment planning for accurate dose calculation dose coverage of the tumor, and sparing of critical structures. [ABSTRACT FROM AUTHOR]

Time-lapse X-ray computed tomography is used to image the evolution of calcite precipitation during flow through microporous quartz over the course of 400 h. The growth rate decreases by more than seven times, which is linked to the clogging of flow paths that restricts flow to some regions of the column. Fewer precipitates are observed as a function of column depth, which is found to be related to a differential nucleation density along the sample. A higher nucleation density closer to the inlet implies more crystal volume increase per unit of time without affecting the rate if normalized to the surface area of crystals. Our overall growth rates measured in porous media are orders of magnitude slower than growth rates derived from traditional precipitation experiments on free surfaces. Based on our time-lapse results we hypothesize a scenario where the evolving distribution of precipitates within a pore structure during precipitation progressively modifies the local transport through the pores. Within less permeable regions the saturation index may be lower than along the main flow paths. Therefore, the reactive crystal surfaces within those regions grow at a slower rate than that expected from the bulk fluid composition. Since the amount of reactive surface area within these less permeable regions increases over time, the overall growth rate decreases without a necessary significant change of the bulk fluid composition along more permeable flow paths. In conclusion, the overall growth rates in an evolving porous media expected from bulk fluid compositions alone can be overestimated due to the development of stagnant sub-regions where the reactive surface area is bath by a solution with lower saturation index. In this context we highlight the value of time-lapse 3D studies for understanding the dynamics of mineral precipitation in porous media. [ABSTRACT FROM AUTHOR]

Cardiovascular emergencies have one of the worst prognosis for a patient. In the acute stages they can lead to death in a matter of minutes. Aortic dissection is no exception from the rule, thus it must be quickly diagnosed and treated. Studies have shown that helical computed tomography (CT) has a specificity and sensibility of nearly 100% in detecting acute aortic dissection. Once diagnosed, there are a couple of steps that need to be solved: the first one would be separating the dissection in one that requires surgical repair or one in which medical management would be enough. This is obtained using either the Stanford classification or DeBakey classification, both assessing the level at which the aorta was affected (ascending aorta, aortic arch or descending aorta beyond the left subclavian artery). In the next step, the radiologist must determine the luminal origins of vessel braches in patients who may need surgical repair. As an imaging method, helical CT is useful in follow-up of postoperative complications, aneurysms of the true and false lumen and monitoring ischemic complications of abdominal branch vessels. The purpose of this article is to present certain CT imaging indicators that can detect the true or false lumen in an aortic dissection, with the help of microscopic anatomy knowledge. [ABSTRACT FROM AUTHOR]

Understanding the fatigue damage mechanisms in composite materials is of great importance in the wind turbine industry because of the very large number of loading cycles rotor blades undergo during their service life. In this paper, the fatigue damage mechanisms of a non-crimp unidirectional (UD) glass fibre reinforced polymer (GFRP) used in wind turbine blades are characterised by time-lapse ex-situ helical X-ray computed tomography (CT) at different stages through its fatigue life. Our observations validate the hypothesis that off-axis cracking in secondary oriented fibre bundles, the so-called backing bundles, are directly related to fibre fractures in the UD bundles. Using helical X-ray CT we are able to follow the fatigue damage evolution in the composite over a length of 20 mm in the UD fibre direction using a voxel size of (2.75 µm)3. A staining approach was used to enhance the detectability of the narrow off-axis matrix and interface cracks, partly closed fibre fractures and thin longitudinal splits. Instead of being evenly distributed, fibre fractures in the UD bundles nucleate and propagate locally where backing bundles cross-over, or where stitching threads cross-over. In addition, UD fibre fractures can also be initiated by the presence of extensive debonding and longitudinal splitting, which were found to develop from debonding of the stitching threads near surface. The splits lower the lateral constraint of the originally closely packed UD fibres, which could potentially make the composite susceptible to compressive loads as well as the environment in service. The results here indicate that further research into the better design of the positioning of stitching threads, and backing fibre cross-over regions is required, as well as new approaches to control the positions of UD fibres.

Objectives: Radiographic examinations have clinical validation/relevance in dental practice. Dentists pay strong attention to absorbed doses to the eye lens, which is located near or inside the irradiation field. Recently, the ICRP recommended a new threshold dose for the eye lens. Therefore, we carried out eye lens dose measurements using a head phantom. Methods: We affixed fluorescence glass dosimeters to a head phantom and measured the absorbed doses during intraoral radiography, panoramic radiography, cephalography, helical scan computed tomography (helical CT), and dental cone beam computed tomography (dental CBCT). Results: The mean absorbed dose to the eye lens in intraoral radiography examinations for maxillary incisor teeth and molar teeth was 0.11 ± 0.09 and 0.08 ± 0.04 mGy, respectively. Corresponding values in occlusal method examinations for the maxillary (craniocaudal angulation 70° parallel to the occlusal plane) and mandibular (craniocaudal angulation 90°) regions were 0.19 ± 0.01 and 0.19 ± 0.07 mGy, respectively. The mean value for panoramic radiography examinations was 0.07 ± 0.02 mGy, while that for cephalography examinations in the posteroanterior projection and left lateral projection was 0.02 ± 0.00 and 0.18 ± 0.02 mGy, respectively. The corresponding value for helical CT was 11.87 ± 1.12 mGy, while those for dental CBCT of the front teeth and molar teeth were 0.07 ± 0.02 and 0.12 ± 0.09 mGy, respectively. Conclusions: Eye lens doses ranged between 0.02 and 0.19 mGy in individual radiographic examinations, including CBCT. Although helical CT recorded 11.87 mGy, it was still lower than the recent ICRP-recommended threshold (500 mGy). [ABSTRACT FROM AUTHOR]

Purpose Iterative image reconstruction is often time-consuming, especially for helical CT. The calculation of X-ray projections and backprojections are computationally expensive. Although they can be significantly accelerated by parallel computing (e.g., via graphics processing unit (GPU)), they have to be calculated numerous times on-the-fly (OTF) during iterative image reconstruction due to insufficient memory storage. In this work, the memory-efficient algorithm for stored system matrix (SSM) is developed for both projections and backprojections to avoid repeated OTF computations of system matrices. Methods The SSM algorithm is based on the shift-invariance for projection and backprojection under a rotating coordinate. As a result, the size of projection and backprojection matrices can be significantly reduced and fully stored in memory. The proposed method can be readily incorporated into iterative reconstruction algorithm with minor modification, i.e., by replacing OTF for SSM. Rigorous mathematical analysis is carried out to establish the shift-invariance for ray-driven projection and pixel-driven backprojection. Results Numerical results via GPU suggest that the proposed SSM method has improved computational efficiency from the OTF method, i.e., by three- to sixfold acceleration for the projection and 3- to 16-fold acceleration for the backprojection respectively for helical CT. Conclusions We propose a memory-efficient SSM algorithm for projections and backprojections so that system matrices can be fully stored on the state-of-the-art GPU to facilitate the rapid iterative helical CT image reconstruction. [ABSTRACT FROM AUTHOR]

Objective: To assess the relationship between proximal femoral cortical bone thickness and radiological hip osteoarthritis using quantitative 3D analysis of clinical computed tomography (CT) data.Methods: Image analysis was performed on clinical CT imaging data from 203 female volunteers with a technique called cortical bone mapping (CBM). Colour thickness maps were created for each proximal femur. Statistical parametric mapping was performed to identify statistically significant differences in cortical bone thickness that corresponded with the severity of radiological hip osteoarthritis. Kellgren and Lawrence (K&L) grade, minimum joint space width (JSW) and a novel CT-based osteophyte score were also blindly assessed from the CT data.Results: For each increase in K&L grade, cortical thickness increased by up to 25 % in distinct areas of the superolateral femoral head-neck junction and superior subchondral bone plate. For increasing severity of CT osteophytes, the increase in cortical thickness was more circumferential, involving a wider portion of the head-neck junction, with up to a 7 % increase in cortical thickness per increment in score. Results were not significant for minimum JSW.Conclusions: These findings indicate that quantitative 3D analysis of the proximal femur can identify changes in cortical bone thickness relevant to structural hip osteoarthritis.Key Points: • CT is being increasingly used to assess bony involvement in osteoarthritis • CBM provides accurate and reliable quantitative analysis of cortical bone thickness • Cortical bone is thicker at the superior femoral head-neck with worse osteoarthritis • Regions of increased thickness co-locate with impingement and osteophyte formation • Quantitative 3D bone analysis could enable clinical disease prediction and therapy development. [ABSTRACT FROM AUTHOR]

Computed tomography (CT) scanning has recently been introduced into forensic medicine and dentistry. However, the presence of metal restorations in the dentition can adversely affect the quality of three-dimensional reconstruction from CT scans. In this study, we aimed to evaluate the reproducibility of a “high-precision, reconstructed 3D model” obtained from a conebeam CT scan of dentition, a method that might be particularly helpful in forensic medicine. We took conebeam CT and helical CT images of three dry skulls marked with 47 measuring points; reconstructed three-dimensional images; and measured the distances between the points in the 3D images with a computer-aided design/computer-aided manufacturing (CAD/CAM) marker. We found that in comparison with the helical CT, conebeam CT is capable of reproducing measurements closer to those obtained from the actual samples. In conclusion, our study indicated that the image-reproduction from a conebeam CT scan was more accurate than that from a helical CT scan. Furthermore, the “high-precision reconstructed 3D model” facilitates reliable visualization of full-sized oral and maxillofacial regions in both helical and conebeam CT scans. [ABSTRACT FROM AUTHOR]

Evaluation of the posterior fossa (PF) on 5-mm-thick helical CT images (current default) has improved diagnostic accuracy compared to 5-mm sequential CT images; however, 5-mm-thick images may not be ideal for PF pathology due to volume averaging of rapid changes in anatomy in the Z-direction. Therefore, we sought to determine if routine review of 1.25-mm-thin helical CT images has superior accuracy in screening for nontraumatic PF pathology. MRI proof of diagnosis was obtained within 6 h of helical CT acquisition for 90 consecutive ED patients with, and 88 without, posterior fossa lesions. Helical CT images were post-processed at 1.25 and 5-mm-axial slice thickness. Two neuroradiologists blinded to the clinical/MRI findings reviewed both image sets. Interobserver agreement and accuracy were rated using Kappa statistics and ROC analysis, respectively. Of the 90/178 (51 %) who were MR positive, 60/90 (66 %) had stroke and 30/90 (33 %) had other etiologies. There was excellent interobserver agreement ( κ > 0.97) for both thick and thin slice assessments. The accuracy, sensitivity, and specificity for 1.25-mm images were 65, 44, and 84 %, respectively, and for 5-mm images were 67, 45, and 85 %, respectively. The diagnostic accuracy was not significantly different ( p > 0.5). In this cohort of patients with nontraumatic neurological symptoms referred to the posterior fossa, 1.25-mm-thin slice CT reformatted images do not have superior accuracy compared to 5-mm-thick images. This information has implications on optimizing resource utilizations and efficiency in a busy emergency room. Review of 1.25-mm-thin images may help diagnostic accuracy only when review of 5-mm-thick images as current default is inconclusive. [ABSTRACT FROM AUTHOR]

Digitally reconstructed radiographs (DRRs) play a vital role for verifying patient position for many radiotherapy treatments. As DRRs are generated from CT scans, image quality may be affected by the scanning mode (axial or helical). The aim of this study was to investigate the high and low contrast resolution and the spatial linearity in DRRs as a function of CT scanning mode and to highlight the significance of this variation, if any. A commercial CT phantom (Fluke Biomedical Model 76-417) was scanned with a Siemens Somatom Sensation 4 CT scanner using six variations of field of view, scanning mode and helical pitch. The image quality of the DRR's produced from the scans was evaluated in terms of high contrast resolution using the modulation transfer function, low contrast resolution using Image Quality Score method and spatial linearity. The results indicated that the high contrast resolution for the axial mode was comparable to that for the helical modes. The low contrast resolution with axial scanning was comparable to scans performed with a helical pitch of 1 but deteriorated at pitches greater than 1. The field of view was not found to impact the low contrast resolution. When changing scanning parameters the impact on DRR quality should be considered. For DRRs, particularly where visualisation of low contrast structures is desired, a helical scan with a pitch of 1 is recommended. [ABSTRACT FROM AUTHOR]

PURPOSE: To investigate variations in mobile target length induced by sinusoidal motion in helical (HCT) and axial CT (ACT) imaging. A mathematical model was derived that predicts the measured broadening of the apparent lengths of mobile targets and its dependence on motion parameters, target size, and imaging couch speed in CT images. MATERIALS AND METHODS: Three mobile targets of differing lengths and sizes were constructed of tissue-equivalent gel material and embedded into artificial lung phantom. Respiratory motion was mimicked with a mobile phantom that moves in one-dimension along the superior-inferior direction with sinusoidal motion patterns. A mathematical model was derived to predict quantitatively the variations of apparent lengths for mobile targets and its dependence on phantom and imaging couch motion parameters in HCT and ACT. The model predictions were verified by length measurements of the mobile phantom targets that were imaged with the different motion patterns using CT imaging. RESULTS: The measured lengths of mobile targets enlarged or shrunk depending on the phantom motion parameters that include phantom speed, amplitude, frequency, phase and speed of the imaging couch. The target length variations were significant where some targets doubled lengths or shrunk to less than half of their actual length. The apparent lengths of mobile targets decreased if the target was moving in the same direction as the imaging couch motion and increased if the mobile target was moving opposed to imaging couch in both HCT and ACT. The model predicts well the variations in the mobile target apparent lengths and their dependence on the motion parameters. CONCLUSION: The measured and model variations of apparent lengths of mobile targets are considerable and may affect the accuracy of tumor volumes obtained from HCT and ACT. This mathematical model provides a method to quantitatively assess the length variations of mobile targets and their dependence on motion parameters of the phantom and imaging system which may have potential applications in the fields of diagnostic imaging and radiotherapy. [ABSTRACT FROM AUTHOR]

Abstract: The current state-of-the-art of tree-ring analysis and densitometry is still mainly limited to two dimensions and mostly requires proper treatment of the surface of the samples. In this paper we elaborate on the potential of helical X-ray computed tomography for 3D tree-ring analysis. Microdensitometrical profiles are obtained by processing of the reconstructed volumes. Correction of the structure direction, taking into account the angle of growth rings and grain, results in very accurate microdensity and precise ring width measurements. Both a manual as well as an automated methodology is proposed here, of which the MATLAB© code is available. Examples are given for pine (Pinus sylvestris L.), oak (Quercus robur L.) and teak (Tectona grandis L.). In all, the methodologies applied here on the 3D volumes are useful for growth related studies, enabling a fast and non-destructive analysis. [Copyright &y& Elsevier]

Objectives: The aim of this study was to determine the incidence of posterior maxillary fractures involving the posterior maxillary sinus wall, pterygoid plate or both, unrelated to major midface fractures in patients with mandibular fractures, and to characterize associated fractures. Methods: A CT study was performed in patients with mandibular fractures to identify posterior maxillary fractures. Patients aged under 16 years, those with mandibular fractures involving only dentoalveolar components and those with concurrent major midfacial fractures were excluded. Results: 13 (6.7%) of 194 patients with mandibular fractures also had posterior maxillary fractures (case group). The injury pattern correlated with the external force directed to the lateral side of the mandible (p < 0.001), alcohol consumption (p = 0.049), the presence of multifocal fractures (p = 0.002) and the fracture regions in the symphysis/parasymphysis (p = 0.001) and the angle/ramus (p = 0.001). No significant difference between the case and non-case groups was seen for age, sex or cause of trauma. Non-displaced fractures in the ipsilateral posterior mandible occurred with significant frequency (p = 0.001) when the posterior maxillary fractures involved only the sinus. Conclusions: Mandibular fractures accompanied by posterior maxillary fractures are not rare. The finding of a unilateral posterior maxillary fracture on CT may aid the efficient radiological examination of the mandible based on possible patterns of associated fractures, as follows: in the ipsilateral posterior region as a direct fracture when the impact is a medially directed force, and in the symphysis/parasymphysis or contralateral condylar neck as an indirect fracture. [ABSTRACT FROM AUTHOR]