[Method for Measuring Noise Power Spectrum Depending on X-ray Tube Angle in Spiral Orbit of Helical CT Scan].

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 NPSconventional. 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 NPSsθ. The NPSsθ was compared to the NPSconventional. Also, we investigated the dependency of the NPSsθ on the θ. RESULTS: The NPSconventional was found to be isotropic, and in contrast, the NPSsθ was anisotropic. The NPSsθ showed a continuously rotational change while increasing the θ. There was an excellent correlation (R2>0.999) between the rotation angle of NPSθ and the θ. CONCLUSION: The proposed method was demonstrated to be effective for evaluating anisotropic noise characteristics depending on the X-ray tube angle.

Computed tomographic evaluation of the distal limb in the standing sedated horse: Technique, imaging diagnoses, feasibility, and artifacts.

In several veterinary institutions, adjustments of CT machines have been made that allow for imaging of the standing horse. The risk of general anesthesia is eliminated and the shorter scan completion time reduces cost to clients. The objective of this retrospective, analytical study was to evaluate the technique, imaging diagnoses, feasibility, and image artifacts of multi-slice helical CT of horses' distal limbs acquired under standing sedation. The CT images of 250 horses of various breeds, aged 3-23 years, that underwent standing distal limb CT were evaluated. Three observers assessed the CT images for artifacts and inter-observer agreement was calculated. Eighty-six percent (95% confidence interval (CI), 81-90) of the scans were carried out on the forelimbs, while 14% (95% CI, 10-19) were of the hindlimbs. A total of 65% (95% CI, 59-71) of horses that underwent standing sedated CT had single imaging diagnoses. Seventy-one percent (95% CI, 65-77) of the cases had unilateral lesions, 27% (95% CI, 22-33) had bilateral lesions and 2% (95% CI, 1-4) had no diagnosed lesions. The average CT acquisition time was 17.5 minutes (range = 15-20). The average number of acquisitions per horse was 1.7 (median = 1; range = 1-4). There was good to excellent agreement between all three observers for the presence of motion artifact in the metacarpo/metatarsophalangeal joints, identification of marked beam hardening artifact, mild solar/ skin dirt, and photon starvation artifact (kappa 0.61-0.80). No complications were encountered. Standing examination of the distal limb achieved diagnostic image quality that was obtained with minimal acquisition attempts and in a timely manner.

Helical CT versus intermittent CT fluoroscopic guidance for musculoskeletal needle biopsies: impact on radiation exposure, procedure time, diagnostic yield, and adverse events.

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.

A Proposed Method for Cervical Lymph Node Evaluation in Head and Neck Cancer Patients: A Radiological Study.

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.

Artificial intelligence for prediction of COVID-19 progression using CT imaging and clinical data.

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.

Ultrasound intervention combined with multi-slice spiral CT has excellent diagnostic value in lymph node metastasis of gastric cancer.

OBJECTIVE: To investigate the diagnostic value of contrast-enhanced ultrasound (CEUS) combined with multi-slice helical CT (MSCT) for gastric carcinoma and its lymph node metastasis (LNM). METHODS: 150 patients with gastric carcinoma diagnosed in our hospital from July 2017 to July 2020 were enrolled for this retrospective study. The patients were all confirmed with gastric carcinoma by biopsy pathology. CEUS and MSCT were performed within one week before surgery. Logistic regression analysis was conducted to analyze the risk factors for LNM of gastric carcinoma. The diagnostic efficiency of CEUS and MSCT in gastric carcinoma and the screening efficiency of LNM were compared, and the sensitivity and specificity were calculated with the postoperative pathologic finding as the gold standard. The scores of lymph node reinforcement were compared. RESULTS: There were 115 cases diagnosed with LNM while 35 were diagnosed without it by CEUS. MSCT results confirmed that there were 112 cases with LNM while 38 without. CEUS combined with MSCT confirmed that there were 116 cases with LNM while 34 cases were without. The sensitivity, specificity, and diagnostic coincidence rate of CEUS for LNM of gastric carcinoma were 89.07%, 70.96% and 85.33%, respectively. Those of MSCT were 84.87%, 64.51% and 80.66%, respectively. Those of CEUS combined with MSCT were 94.11%, 87.10%, and 92.67%, respectively. The reinforcement of CEUS combined with MSCT was better than either alone. CONCLUSION: CEUS combined with MSCT is more effective in the diagnosis of LNM in gastric carcinoma patients. Hence, the combination of the two is helpful to enhance the accuracy of LNM diagnosis before operation.

Deep learning enabled ultra-fast-pitch acquisition in clinical X-ray computed tomography.

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.

CT severity indices derived from low monoenergetic images at dual-energy CT may improve prediction of outcome in acute pancreatitis.

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.

Effect of scan projection radiography coverage on tube current modulation in pediatric and adult chest CT.

PURPOSE: To investigate the effect of scan projection radiography (SPR) coverage on tube current modulation in pediatric and adult thoracic CT examinations. METHODS: 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 ±10mm with respect to the IV boundaries. RESULTS: 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 3cm 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. CONCLUSIONS: 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.

Impact of spectral body imaging in patients suspected for occult cancer: a prospective study of 503 patients.

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.

Clot Analog Attenuation in Non-contrast CT Predicts Histology: an Experimental Study Using Machine Learning.

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 (ß = 0.33, CI = 0.219-0.441, p < 0.001) followed by the iron content (ß = 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.

[Sparse-view helical CT reconstruction based on tensor total generalized variation minimization].

OBJECTIVE: We propose a sparse-view helical CT iterative reconstruction algorithm based on projection of convex set tensor total generalized variation minimization (TTGV-POCS) to reduce the X-ray dose of helical CT scanning. METHODS: The three-dimensional volume data of helical CT reconstruction was viewed as the third-order tensor. The tensor generalized total variation (TTGV) was used to describe the structural sparsity of the three-dimensional image. The POCS iterative reconstruction framework was adopted to achieve a robust result of sparse-view helical CT reconstruction. The TTGV-POCS algorithm fully used the structural sparsity of first-order and second-order derivation and the correlation between the slices of helical CT image data to effectively suppress artifacts and noise in the image of sparse-view reconstruction and better preserve image edge information. RESULTS: The experimental results of XCAT phantom and patient scan data showed that the TTGVPOCS algorithm had better performance in reducing noise, removing artifacts and maintaining edges than the existing reconstruction algorithms. Comparison of the sparse-view reconstruction results of XCAT phantom data with 144 exposure views showed that the TTGV-POCS algorithm proposed herein increased the PSNR quantitative index by 9.17%-15.24% compared with the experimental comparison algorithm; the FSIM quantitative index was increased by 1.27%-9.30%. CONCLUSIONS: The TTGV-POCS algorithm can effectively improve the image quality of helical CT sparse-view reconstruction and reduce the radiation dose of helical CT examination to improve the clinical imaging diagnosis.

Comparison of Achievable Contrast Features in Computed Tomography Observing the Growth of a 4H-SiC Bulk Crystal.

Today the physical vapor transport process is regularly applied for the growth of bulk SiC crystals. Due to the required high temperature of up to 2400 °C, and low gas pressure of several Mbar inside the crucible, the systems are encapsulated by several layers for heating, cooling and isolation inhibiting the operator from observing the growth. Also, the crucible itself is fully encapsulated to avoid impurities from being inserted into the crystal or disturbing the temperature field distribution. Thus, once the crucible has been set up with SiC powder and the seed crystal, the visible access to the progress of growth is limited. In the past, X-ray radiography has allowed this limitation to be overcome by placing the crucible in between an X-ray source and a radiographic film. Recently these two-dimensional attenuation signals have been extended to three-dimensional density distribution by the technique of computed tomography (CT). Beside the classic X-ray attenuation signal dominated by photoelectric effect, Compton effect and Rayleigh scattering, X-ray diffraction resulting in the crystalline structure of the 4H-SiC superimposes the reconstructed result. In this contribution, the achievable material contrast related to the level of X-ray energy and the absorption effects is analyzed using different CT systems with energies from 125 kV to 9 MeV. Furthermore the X-ray diffraction influence is shown by the comparison between the advanced helical-CT method and the classical 3D-CT.

CT features of parathyroid carcinomas: comparison with benign parathyroid lesions.

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.

Sparse-view helical CT reconstruction based on tensor total generalized variation minimization / 南方医科大学学报

OBJECTIVE@#We propose a sparse-view helical CT iterative reconstruction algorithm based on projection of convex set tensor total generalized variation minimization (TTGV-POCS) to reduce the X-ray dose of helical CT scanning.@*METHODS@#The three-dimensional volume data of helical CT reconstruction was viewed as the third-order tensor. The tensor generalized total variation (TTGV) was used to describe the structural sparsity of the three-dimensional image. The POCS iterative reconstruction framework was adopted to achieve a robust result of sparse-view helical CT reconstruction. The TTGV-POCS algorithm fully used the structural sparsity of first-order and second-order derivation and the correlation between the slices of helical CT image data to effectively suppress artifacts and noise in the image of sparse-view reconstruction and better preserve image edge information.@*RESULTS@#The experimental results of XCAT phantom and patient scan data showed that the TTGVPOCS algorithm had better performance in reducing noise, removing artifacts and maintaining edges than the existing reconstruction algorithms. Comparison of the sparse-view reconstruction results of XCAT phantom data with 144 exposure views showed that the TTGV-POCS algorithm proposed herein increased the PSNR quantitative index by 9.17%-15.24% compared with the experimental comparison algorithm; the FSIM quantitative index was increased by 1.27%-9.30%.@*CONCLUSIONS@#The TTGV-POCS algorithm can effectively improve the image quality of helical CT sparse-view reconstruction and reduce the radiation dose of helical CT examination to improve the clinical imaging diagnosis.

Time-Lapse Helical X-ray Computed Tomography (CT) Study of Tensile Fatigue Damage Formation in Composites for Wind Turbine Blades.

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.

Diagnostic accuracy of contrast-enhanced computed tomography for assessment of mandibular and medial retropharyngeal lymph node metastasis in dogs with oral and nasal cancer.

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.

Wide volume versus helical acquisition using 320-detector row computed tomography for computed tomography urography in adults.

PURPOSE: To evaluate the best collimation used in wide volume (WV) mode to cover the abdomen in computed tomography (CT) urography in terms of radiation dose and image quality. MATERIALS AND METHODS: This study was performed on a 320×0.5mm detector row CT unit. The first part identified the lowest volume CT dose index (CTDIvol) by using the topograms data of 25 medium size patients (13 men and 12 women; mean age: 52±9 [SD] years; age range: 46-68 years) using different collimations on WV from 6cm to 16cm and the one of the helical mode for the same coverage length. The second part consisted of a clinical evaluation of this result including 45 medium size patients (32 men and 13 women; mean age: 68±14 [SD] years; age range: 45-72 years). The qualitative evaluation included several items based on a 5-point Likert scale. RESULTS: The first part of the study indicated that a collimation of 10cm (200×0.5mm) in WV mode with 5 volumes had the lowest CTDIvol (2.78±0.35mGy; range: 2.35-3.21mGy) compared to helical mode (4.38±0.48mGy, range: 3.75-4.95mGy). In the second part, the mean radiation dose reduction by comparison with helical mode was 44.03%±0.36% (P<0.001) and 51.16%±1.22% (P<0.005) for CTDIvol and DLP, respectively. CONCLUSION: Wide volume mode of the abdomen can be performed with a significant radiation dose reduction with a collimation of 10cm (200×0.5mm) and five volumes.

The scab-like sign: A CT finding indicative of haemoptysis in patients with chronic pulmonary aspergillosis?

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.

Quantitative evaluation of the performance of different deformable image registration algorithms in helical, axial, and cone-beam CT images using a mobile phantom.

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.