CT Acquisition Research Articles

Development of an ultrafast brain MR neuronavigation protocol for ventricular shunt placement.

Advancements in MRI technology have provided improved ways to acquire imaging data and to more seamlessly incorporate MRI into modern pediatric surgical practice. One such situation is image-guided navigation for pediatric neurosurgical procedures, including intracranial catheter placement. Image-guided surgery (IGS) requires acquisition of CT or MR images, but the former carries the risk of ionizing radiation and the latter is associated with long scan times and often requires pediatric patients to be sedated. The objective of this project was to circumvent the use of CT and standard-sequence MRI in ventricular neuronavigation by investigating the use of fast MR sequences on the basis of 3 criteria: scan duration comparable to that of CT acquisition, visualization of ventricular morphology, and image registration with surface renderings comparable to standard of care. The aim of this work was to report image development, implementation, and results of registration accuracy testing in healthy subjects. The authors formulated 11 candidate MR sequences on the basis of the standard IGS protocol, and various scan parameters were modified, such as k-space readout direction, partial k-space acquisition, sparse sampling of k-space (i.e., compressed sensing), in-plane spatial resolution, and slice thickness. To evaluate registration accuracy, the authors calculated target registration error (TRE). A candidate sequence was selected for further evaluation in 10 healthy subjects. The authors identified a candidate imaging protocol, termed presurgical imaging with compressed sensing for time optimization (PICO). Acquisition of the PICO protocol takes 25 seconds. The authors demonstrated noninferior TRE for PICO (3.00 ± 0.19 mm) in comparison with the default MRI neuronavigation protocol (3.35 ± 0.20 mm, p = 0.20). The developed and tested sequence of this work allowed accurate intraoperative image registration and provided sufficient parenchymal contrast for visualization of ventricular anatomy. Further investigations will evaluate use of the PICO protocol as a substitute for CT and conventional MRI protocols in ventricular neuronavigation.

Abstract WMP60: Eliminating False Positive Detections Of Intracranial Hemorrhage (ICH) Using RAPID ICH 3

Introduction: Prompt detection of intracranial hemorrhage (ICH) on a non-contrast head CT (NCCT) is critical to initial patient triage. Several ICH detection and notification programs now exist, but none presently generate locations or segmentations of suspected ICH, and false-positive notifications are not easily identified. We investigated an enhanced ICH detection tool with heightened immunity to false-positive diagnosis. Methods: NCCT scans from 3 large databases were evaluated for the presence of an ICH (IPH, IVH, SAH or SDH) of >0.4 ml by the automated RAPID ICH 3.0 software module and compared to a consensus detection from 3 neuroradiology experts. Scans were excluded for (1) severe CT acquisition artifacts, (2) prior neurosurgical procedures or (3) intravenous contrast administration. ICH detection accuracy, sensitivity, specificity, positive predictive value, negative predictive value, and positive and negative likelihood ratios by RAPID ICH 3 were determined. Results: A total of 790 studies were included. RAPID ICH 3.0 correctly identified 399/411 ICH-positive cases and 378/379 ICH-negative cases, resulting in a sensitivity of 98.08% and specificity 99.74%, positive predictive value 99.75%, and negative predictive value 96.92% for ICH detection. The positive and negative likelihood ratios for ICH detection were similarly favorable at 367.93 and 0.03 respectively. Mean processing time was <40 seconds. Conclusions: In this large data set of nearly 800 patients, the RAPID ICH 3.0 automated software maintained a high sensitivity for detection of ICH, while essentially eliminating false positive identifications, leading to very high positive predictive value.

Abstract TP91: Automated Cerebral Hemorrhage Volume Calculation And Stability Detection Using RAPID Software

Introduction: The measurement of intraparenchymal hemorrhage (IPH) volume is important for management, particularly in evaluating expansion on subsequent imaging. However manual volumetric analysis is time-consuming, especially in busy hospital settings. We aimed to use automated RAPID hyperdensity software to accurately measure IPH volume across repeated imaging. Methods: We identified primary IPH cases, without evidence of IVH, SDH, or SAH, from two randomized ICH trials where enrollment was not based on IPH volume. Scans were excluded if (1) there was CT acquisition artifact, (2) measured IPH volume was < 0.4ml, or (3) patient underwent a neurosurgical procedure. Repeat imaging, conducted within 12h, was included in a secondary stability analysis. Manual IPH measurements were conducted by one neuroimaging expert using MIPAV software and compared to the performance of the RAPID hyperdensity module. Results: 149 scans were included with median IPH volume manually measured at 13.3ml (IQR 3.2-27.5) compared to RAPID detection of 18.0ml (IQR 5.1-36.8). The two modalities were highly correlated (Figure 1, r = 0.948, p < 0.001) with a median absolute difference of 3.4ml (IQR 0.2-9.4) and standard error of 0.655. Repeat imaging was available in 65 patients, with a median absolute difference of 0ml (IQR: -2.6-1.5) compared to RAPID detection at 0.1ml (IQR: -2.3-2.7). These absolute differences were also highly correlated (r = 0.878, p < 0.001), with the ability of RAPID to detect a 5ml IPH expansion with a Sensitivity of 98.1% and Specificity 72.7%. Processing time for the software was < 3 minutes. Conclusion: In our pilot data, the RAPID hyperdensity module has high reliability in its ability to quickly automatically detect IPH volume and high sensitivity to detect expansion on subsequent imaging.

Ultra-Low Dose CT Chest in Acute COVID-19 Pneumonia: A Pilot Study from India.

The rapid increase in the number of CT acquisitions during the COVID-19 pandemic raised concerns about increased radiation exposure to patients and the resultant radiation-induced health risks. It prompted researchers to explore newer CT techniques like ultra-low dose CT (ULDCT), which could improve patient safety. Our aim was to study the utility of ultra-low dose CT (ULDCT) chest in the evaluation of acute COVID-19 pneumonia with standard-dose CT (SDCT) chest as a reference standard. This was a prospective study approved by the institutional review board. 60 RT-PCR positive COVID-19 patients with valid indication for CT chest underwent SDCT and ULDCT. ULDCT and SDCT were compared in terms of objective (noise and signal-to-noise ratio) and subjective (noise, sharpness, artifacts and diagnostic confidence) image quality, various imaging patterns of COVID-19, CT severity score and effective radiation dose. The sensitivity, specificity, positive and negative predictive value, and diagnostic accuracy of ULDCT for detecting lung lesions were calculated by taking SDCT as a reference standard. The mean age of subjects was 47.2 ± 10.7 years, with 66.67% being men. 90% of ULDCT scans showed no/minimal noise and sharp images, while 93.33% had image quality of high diagnostic confidence. The major imaging findings detected by SDCT were GGOs (90%), consolidation (76.67%), septal thickening (60%), linear opacities (33.33%), crazy-paving pattern (33.33%), nodules (30%), pleural thickening (30%), lymphadenopathy (30%) and pleural effusion (23.33%). Sensitivity, specificity and diagnostic accuracy of ULDCT for detecting most of the imaging patterns were 100% (p < 0.001); except for GGOs (sensitivity: 92.59%, specificity: 100%, diagnostic accuracy: 93.33%), consolidation (sensitivity: 100%, specificity: 71.43%, diagnostic accuracy: 93.33%) and linear opacity (sensitivity: 90.00%, specificity: 100%, diagnostic accuracy: 96.67%). CT severity score (range: 15-25) showed 100% concordance on SDCT and ULDCT, while effective radiation dose was 4.93 ± 1.11 mSv and 0.26 ± 0.024 mSv, respectively. A dose reduction of 94.38 ± 1.7% was achieved with ULDCT. Compared to SDCT, ULDCT chest yielded images of reasonable and comparable diagnostic quality with the advantage of significantly reduced radiation dose; thus, it can be a good alternative to SDCT in the evaluation of COVID-19 pneumonia.

Chlamydia trachomatis Seropositivity and Associated Risk Factors Among Women Attending A Northern Nigerian Tertiary Hospital.

Genital Chlamydia trachomatis (Ct) is the commonest bacterial sexually transmitted infection globally. Acquisition of Ct infection is affected by biological and behavioural factors. Determine the prevalence of Ct infection and identify risk factors associated with Ct infection in sexually active fertile women in Northern Nigeria. One hundred and fifty sexually active women presenting to the Obstetrics and Gynaecology department of Ahmadu Bello University Teaching Hospital, Zaria were studied. Socio-demographic characteristics and history of risk factors for acquisition of genital Ct were obtained from the participants using a questionnaire. Their sera were tested for the presence of Ct immunoglobulin G using Enzyme-Linked Immunosorbent Assay. The mean ages ± standard deviation of seropositive and seronegative women were 29.1 ± 7.3 years and 28.9 (SD 6.7) years respectively (P = 0.438). The prevalence of Ct infection was 6.7% (10/150). Occupation was associated with Ct seropositivity (P = 0.02). Number of sexual partners, age at coitarche; duration of sexual exposure and previous history suggestive of sexually transmitted infection were not associated with Ct seropositivity (P > 0.05). A low prevalence of Ct was found among fertile women. Lack of regular source of personal income was associated with Ct infection but the sexual behavioural factors studied were not.

Abdominal atherosclerosis is not a risk factor of nonocclusive mesenteric ischemia among critically ill patients: a propensity matching study

BackgroundAlthough risk factors of occlusive acute mesenteric ischemia are well known, triggering factors of nonocclusive mesenteric ischemia (NOMI) remain unclear. Alongside to the known risk factors for NOMI, the role of atherosclerosis is not fully elucidated. The purpose of our study was to evaluate whether abdominal atherosclerosis is a risk factor for NOMI.MethodsFrom January 2018 to December 2021, all consecutive patients admitted to the intensive care unit who underwent contrast-enhanced CT for suspicion of NOMI were evaluated for inclusion. Clinical and biological data at the time of the CT scan were retrospectively extracted from medical charts and reviewed by a single radiologist. The cohorts were matched by a 1:1 propensity score based on the patient clinical, biological data, and abdominal CT features associated with NOMI. Noncontrast CT acquisitions were used to calculate calcium scores of the abdominal aorta, celiac trunk, superior mesenteric artery (SMA), and common iliac artery according to the Agatston method. Analyses were performed before and after propensity score matching.ResultsAmong the 165 critically ill patients included, 59 (36%) had NOMI. Before matching analysis, the SMA and total abdominal Agatston calcium scores were not different between patients without and with NOMI (52.00 [IQR = 0, 473] vs. 137.00 [IQR = 0, 259], P = 0.857, respectively, and 7253 [IQR = 1220, 21738] versus 5802 [IQR = 2075, 15,084]; P = 0.723). The results were similar after matching 38 patients with NOMI and 38 without: 153 [IQR = 0, 665] versus 85 [IQR = 0, 240] (P = 0.312) for the SMA calcium score, and 7915 [IQR = 1812, 21561] versus 4139 [IQR = 1440, 9858] (P = 0.170) for the total abdominal Agatston calcium score.ConclusionOur results suggest that atherosclerosis is not a risk factor for NOMI in critically ill patients.

11 PRINTING 3D MODELS OF THE HEART: CAN IT HELP IN UNDERSTANDING THE COMPLEX ANATOMY?

Abstract The use of 3D printing in the medical field is widespread especially in the dental clinic as a support to orthodontic / implant therapy. In the training of personnel relating to cardiological diagnostic methods, can it be useful to shorten the learning curve of human anatomy? A light-curing liquid resin 3D printer was used to obtain anatomical models that faithfully reproduce the real anatomy of the individual patient. The starting model was obtained from CT with contrast medium performed on patients. Depending on the diagnostic question, CT may contain complete information on both the arterial circulation and the venous circulation of the heart and the epiaortic vessels. From this information a 3D surface reconstruction is obtained which, once reworked, can be used directly for printing. The model size is limited by the print volume of the printer which may vary depending on the printer model. The model to be printed obtained from CT acquisitions the 3D model will be the representation of the lumen of the vessels and cavities of the heart. The models obtained faithfully represent the anatomical reality of the patient who underwent CT with contrast medium. Actual size is affected by the print volume size of the printer model. In my experience in university teaching, the models obtained with 3D printing have been found to be very useful for understanding the complex spatial configuration of the anatomy of the heart and great vessels

The use of dynamic CT imaging for tracking mandibular movements in a phantom

Purpose. The objective of this study was to analyse the possibilities of using 4D CT scanning for the tracking of patients’ mandibles. Methods. A clinical 256-slice Revolution CT was used in obtaining 4D CT scans without table movement, with a novel mandibular phantom, mounted on a programmable six degrees-of-freedom Stewart Platform in motion. The phantom was used to simulate mandibular motions which are combinations of rotations with translations (depression, elevation, protrusion, retrusion and laterotrusion). The phantom was scanned five times during identical motion patterns with a dynamic CT acquisition protocol. An image processing workflow consisting of a pairwise rigid registration and semi-automatic segmentation was developed to extract kinematic parameters (cardan angles and point-of-interest displacements) from the dynamic sequences. Reproducibility was investigated by the 95% confidence interval and the absorbed organ dose to organs of interest in the primary beam were also estimated and compared to those of a standard CT scan of the brain Results. The maximum average 95% confidence interval for the displacement across all time points for the five repetitions was 0.61 mm (Y axis). In terms of rotations, the maximum average 95% confidence interval across all time points for the five repetitions was 1.39° (X axis). The effective dose for the dynamic scan was found to be 1.3 mSv, for a CTDIvol of 63.95 mGy and a DLP of 1023.14 mGycm. The absorbed organ doses were similar to organ doses during a clinical head CT scan. Conclusions. A framework is proposed to use 4D CT scanning as a possible methodology to evaluate the motion of the temporomandibular joint. The scanning protocol allows to visualise the motion by applying a semi-automated segmentation and registration. A graphical representation of all displacements in the three spatial dimensions can depict multiple points-of-interest at once during the same acquisition. A novel type of phantom was also introduced which simulates mandibular movement with six degrees-of-freedom (three translations and three rotations).

A new upper limit for effective dose in patient administered with 18F-FDG for PET/CT whole-body imaging with diagnostic CT parameters

IntroductionThe aim of present study is to estimate effective dose in patient undergoing 18F-FDG for whole body PET/CT imaging with diagnostic CT parameters and identify the lowest achievable total effective dose. MethodA total of 2247 PET/CT patients with normal glucose level underwent 18F-FDG-whole body imaging procedures. The 18F-FDG dose of 3.7MBq per kg of patient weight administered via intravenous infusion. For CT parameters, kilovoltage of 140keV and current of 40 mAs were used for all studies. All the acquired images collected retrospectively and the effective dose was calculated for each patient using algorithm adapted from ICRP Publication 106, modified for patient weight and patient blood volume. The estimated effective doses were evaluated for patients’ body weight and BMI. ResultsThe mean of total effective dose and standard deviation is approximately 15.08(4.52) mSv using ICRP algorithm. 56% of total patient has normal BMI and their average total effective dose is 13.6mSv. Underweight patients’ effective dose can be as low as 9.6mSv even using diagnostic CT protocols. ConclusionThe effective dose of PET/CT procedure in present study is one of the lowest although using diagnostic parameters for CT acquisition compared to published data worldwide. This is due to the improved sensitivity of PET and complex reconstruction technique that maintains the image quality. A significant association between body weight, BMI and effective dose is reported in present study. Therefore, it is suggested that attention must be given for underweight and ideal BMI patients while prescribing FDG activity and CT imaging parameters in order to minimize the effective dose. The effective dose reported in present study can be considered as an upper limit for effective dose in PET/CT patients with normal BMI. This upper limit can be treated as a standard limit when optimizing imaging parameters, developing algorithm for image reconstruction and prescribing activity for patients. This practice could fulfill ALARA principle that could reduce cancer risk.

Initial experience, feasibility, and technical development with an electromagnetic navigation assistance in percutaneous pelvic bone cementoplasty: retrospective analysis.

To assess the feasibility and technical outcomes of pelvic bone cementoplasty using an electromagnetic navigation system (EMNS) in standard practice. Monocentric retrospective study of all consecutive patients treated with cementoplasty or reinforced cementoplasty of the pelvic bone with EMNS-assisted procedures. The endpoints were periprocedural adverse events, needle repositioning rates, procedure duration, and radiation exposure. A detailed description of the technical steps is provided. Thirty-three patients (68 years ± 10) were treated between February 2016 and February 2020. Needle repositioning was required for 1/33 patients (3%). The main minor technical adverse event was soft tissue PMMA cement leaks. No major adverse event was noted. The median number of CT acquisitions throughout the procedures was 4 (range: 2 to 8). Radiation exposure and mean procedure duration are provided. Electromagnetic navigation system-assisted percutaneous interventions for the pelvic bone are feasible and lead to low rates of minor technical adverse events and needle repositioning. Procedure duration and radiation exposure were low. • Initial experience for 33 patients treated with an electromagnetic navigation assistance for pelvic cementoplasty shows feasibility and safety. • The use of an electromagnetic navigation system does not expose to high procedure duration or radiation exposure. • The system is efficient in assisting the radiologist for extra-axial planes in challenging approaches.

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.

Assessment of patients radiation doses associated with computed tomography coronary angiography

Computed tomography coronary angiography (CTCA) has generated tremendous interest over the past 20 years by using multidetector computed tomography (MDCT) because of its high diagnostic accuracy and efficacy in assessing patients with coronary artery disease. This technique is related to high radiation doses, which has raised serious concerns in the literature. Effective dose (E, mSv) may be a single parameter meant to reflect the relative risk from radiation exposure. Therefore, it is necessary to calculate this quantity to point to relative radiation risk. The objectives of this study are to evaluate patients' exposure during diagnostic CCTA procedures and to estimate the risks. Seven hundred ninety patients were estimated during three successive years. The patient's exposure was estimated based on a CT device's delivered radiation dose (Siemens Somatom Sensation 64 (64-MDCT)). The participating physicians obtained the parameters relevant to the radiation dose from the scan protocol generated by the CT system after each CCTA study. The parameters included the volume CT dose index (CTDIvol, mGy) and dose length product (DLP, mGy × cm). The mean and range of CTDIvol (mGy) and DLP (mGy × cm) for three respective year was (2018):10.8 (1.14–77.7) and 2369.8 ± 1231.4 (290.4–6188.9), (2019): 13.82 (1.13–348.5), and 2180.5 (501.8–9534.5) and (2020) 10.9 (0.7–52.9) and 1877.3 (149.4–5011.1), respectively. Patients' effective doses were higher compared to previous studies. Therefore, the CT acquisition parameter optimization is vital to reduce the dose to its minimal value.

The use of cardiac CT acquisition mode for dynamic musculoskeletal imaging

ObjectivesTo quantitatively evaluate the impact of a cardiac acquisition CT mode on motion artifacts in comparison to a conventional cine mode for dynamic musculoskeletal (MSK) imaging. MethodsA rotating PMMA phantom with air-filled holes drilled at varying distances from the disk center corresponding to linear hole speeds of 0.75 cm/s, 2.0 cm/s, and 3.6 cm/s was designed. Dynamic scans were obtained in cardiac and cine modes while the phantom was rotating at 48°/s in the CT scanner. An automated workflow to compute the Jaccard distance (JD) was established to quantify degree of motion artifacts in the reconstructed phantom images. JD values between the cardiac and cine scan modes were compared using a paired sample t-test. In addition, three healthy volunteers were scanned with both modes during a cyclic flexion–extension motion of the knee and analysed using the proposed metric. ResultsFor all hole sizes and speeds, the cardiac scan mode had significantly lower (p-value <0.001) JD values.(0.39 [0.32–0.46]) i.e less motion artifacts in comparison to the cine mode (0.72 [0.68–0.76]). For both modes, a progressive increase in JD was also observed as the linear speed of the holes increased from 0.75 cm/s to 3.6 cm/s. The dynamic images of the three healthy volunteers showed less artifacts when scanned in cardiac mode compared to cine mode, and this was quantitatively confirmed by the JD values. ConclusionsA cardiac scan mode could be used to study dynamic musculoskeletal phenomena especially of fast-moving joints since it significantly minimized motion artifacts.

Prospective Multireader Evaluation of Photon-counting CT for Multiple Myeloma Screening.

Purpose To determine whether photon-counting CT (PCCT) acquisition of whole-body CT images provides similar quantitative image quality and reader satisfaction for multiple myeloma screening at lower radiation doses than does standard energy-integrating detector (EID) CT. Materials and Methods Patients with monoclonal gammopathy of undetermined significance prospectively underwent clinical noncontrast whole-body CT with EID and same-day PCCT (August-December 2021). Five axial scan locations were evaluated by seven radiologists, with 11% (eight of 70) of images including osteolytic lesions. Images were shown in randomized order, and each reader rated the following: discernibility of the osseous cortex and osseous trabeculae, perceived image noise level, and diagnostic confidence. Presence of lytic osseous lesions was indicated. Contrast-to-noise ratio (CNR) and signal-to-noise ratio (SNR) were calculated. Comparisons were made using paired t tests and mixed linear effects models. Results Seven participants (four women) were included (mean age, 66 years ± 9 [SD]; body mass index, 30.1 kg/m2 ± 5.2). Mean cortical definition, trabecular definition, image noise, and image quality scores were 83, 67, 75, and 78 versus 84, 66, 74, and 76 for EID and PCCT, respectively (P = .65, .11, .26, and .11, respectively). PCCT helped identify more lesions (79% [22 of 28]) than did EID (64% [18 of 28]). CNRs and SNRs were similar between modalities. PCCT had lower radiation doses than EID (volume CT dose index: EID, 11.37 ± 2.8 vs PCCT, 1.8 ± 0.6 [P = .06]; dose-length product: EID, 1654.1 ± 409.6 vs PCCT, 253.4 ± 89.6 [P = .05]). Conclusion This pilot investigation suggests that PCCT affords similar quantitative and qualitative scores as EID at significantly lower radiation doses. Keywords: CT, CT-Spectral, Skeletal-Axial, Spine, Hematologic Diseases, Whole-Body Imaging, Comparative Studies Supplemental material is available for this article. © RSNA, 2022.

PHSPP03 Presentation Time: 2:50 PM: Dosimetric Considerations of the Use of Synthetic MRI for Prostate HDR Brachytherapy

<h3>Purpose</h3> In prostate HDR brachytherapy, MRI, while providing exquisite soft-tissue contrast and anatomic delineation, its acquisition slows the treatment workflow and the image registration between CT and MRI adds uncertainty to the treatment planning process. Deep learning-based MRI synthesis from CT is possible but has yet to be clinically validated. To address this, we assessed the dosimetric and workflow impact of synthetic MRI (sMRI) use in prostate HDR brachytherapy. <h3>Materials and Methods</h3> 58 paired pelvis CT and T2-weighted MRI datasets from patients treated with HDR brachytherapy to either a prescription dose of 13.5 Gy or 15 Gy were collected. A deep learning-based framework was developed to synthesize MRI data from CT and was validated using 17 additional patient datasets. The prostate was contoured on the sMRI, which was used to create a new planning target volume (PTV) with a 3 mm isotropic expansion and removal of the urethra, bladder, and rectum. New brachytherapy treatment plans were generated to cover the sMRI PTV with the catheter positions visible in the CT scans by adjusting the source dwell times from the original treatments. This dose was overlaid onto a second PTV, created from the prostate contour by the same observer on real MRI (rMRI). This observer is different from the one who contoured the prostate for the clinically delivered treatment, so the inter-observer variability of the prostate contour on rMRI can be compared with the inter-modality variability between the prostate contour on sMRI and rMRI using the dice similarity coefficient (DSC). The impact of sMRI use was assessed with dosimetric volume histogram (DVH) parameters PTV V100%, V150%, V200%, bladder D1cc, urethra D1cc, and rectum D1cc (percent of prescription dose averaged over 17 test cases ± standard deviation, institutional constraints based on ABS prostate high-dose rate task group). The sMRI PTV DVH metrics were compared with the rMRI DVH metrics, such that we assessed how delivering dose to the sMRI PTV would cover the ground truth rMRI PTV. The bladder, rectum, and urethra DVH metrics were compared with those of the original treatment. The workflow impact was assessed by comparison of the time for sMRI generation with the time from the end of the CT acquisition to the end of the MRI acquisition during the clinically delivered plan. <h3>Results</h3> The inter-modality variability of the prostate contour between sMRI and rMRI was found to be statistically similar to the inter-observer variability of the prostate contour on rMRI assessed with DSC, indicating that the prostate contour is similarly sensitive to observer as it is to sMRI (table a). Target coverage of sMRI PTV was not statistically different to that of rMRI PTV (table b). While there were statistical increases (p<0.05) in bladder, rectum, and urethra doses in the sMRI-planned cases (table c), in no case did this lead to an increase above the constraint for D1cc. Lastly, a full sMRI volume can be generated from the corresponding CT in approximately 10 seconds, compared to the 73.6 minutes on average between the completion of the CT and rMRI scans during the clinically delivered treatment workflow, not including image registration which will add further time to the procedure. <h3>Conclusions</h3> To our knowledge, this is the first report which details the dosimetric similarity and workflow advantages from the use of synthetic MRI for prostate HDR brachytherapy.

Chronic cavitary pulmonary aspergillosis: Serial clinical and CT findings correlated with antifungal treatment and patient response.

Chronic cavitary pulmonary aspergillosis (CCPA) is the most common form of chronic pulmonary aspergillosis. We hypothesise that by observing serial clinical and CT findings of CCPA patients with antifungal therapy, factors helping predict responses to antifungal therapy could be withdrawn. A total of 31 patients with CCPA who received antifungal therapy for greater than six months and who had serial CT studies were included. Clinical finding analyses were performed at initial and last follow-up CT acquisition dates. Clinical characteristics and CT features were compared between clinically improving or stable and deteriorating groups. With antifungal therapy, neutrophil-to-lymphocyte ratio (2.66 vs. 5.12, p= .038) and serum albumin (4.40 vs. 3.85 g/dl, p= .013) and CRP (1.10 vs. 42.80 mg/L, p= .007) were different between two groups. With antifungal therapy, meaningful CT change, regardless of clinical response grouping, was decrease in cavity wall thickness (from 13.70 mm to 8.28 mm, p< .001). But baseline (p= .668) and follow-up (p= .278) cavity wall thickness was not different between two groups. In univariate analysis, initial maximum diameter of cavity (p= .028; HR [0.983], 95% CI [0.967-0.998]) and concurrent NTM infection (p= .030; HR [0.20], 95% CI [0.05-0.86]) were related factors for poor clinical response. With antifungal therapy, cavities demonstrate wall thinning. Of all clinical and radiological findings and their changes, initial large cavity size and concurrent presence of NTM infection are related factors to poor response to antifungal therapy.

Deep Learning-Based Synthetic CT Generation for MR-Only Adaptive Radiation Therapy on MR-Linacs

<h3>Purpose/Objective(s)</h3> In existing MR-guided on-table adaptive radiation therapy (MRgRT) workflows, electron density of the target and organs-at-risk are obtained by deforming a simulation CT scan to the current MR setup scan. CT acquisition adds significant time to MRgRT workflows and imaging dose to the patient. Registrations have inherent limitations, particularly for air and tissue overriding, which frequently require manual corrections. We hypothesize that synthetically generated CTs (SynCTs) via deep learning could be utilized to accurately predict electron density directly from the MR setup scan for subsequent adaptive planning and dose computation. <h3>Materials/Methods</h3> Simulation MR/CT scans from 20 patients undergoing MRgRT were used to train a generative encoder-decoder network that predicts SynCTs from MR setup scans. All patients underwent a standard CT simulation followed by an MR simulation scan on the MR-Linac approximately 1 hour later. The trained network then predicted electron density for a different setup scan acquired at subsequent treatment fractions. These SynCT volumes were directly compared to the deformed CT volumes using mean absolute error in Hounsfield units (HU). SynCT volumes were also exported as DICOM sequences and re-imported to the MR-Linac treatment planning system to recalculate dose and assess differences in resulting dose distributions, dose volume histograms and clinical dose prescriptions. <h3>Results</h3> The trained network achieved good accuracy on both training and testing datasets (mean absolute error in HU ± standard deviation, train: 38.4 ± 19.1 HU, test: 45.9 ± 24.5 HU). Average time required to generate a SynCT for a single MR volume using the trained model was 0.63 ± 0.06 seconds. Using the SynCT volumes for dose re-optimization did not result in any clinically meaningful differences in doses calculated to the primary treatment volumes in all 20 plans. <h3>Conclusion</h3> Accuracy of deep learning based synthetic CT generation using low-field MR setup scans on MR-Linacs was sufficient for accurate dose calculation/optimization. This approach can enable MR-only treatment planning workflows on MR-Linacs, thereby increasing the efficiency of simulation and adaptive planning for MRgRT.

Narrowing the Differential Diagnosis of Cystic Lesions in Smokers with Expiratory CT Acquisition Using the Cyst-Airway Communication Hypothesis.

The aim of this study was to assess percentage respiratory changes (δ) in the size of pulmonary cysts of different smoking-related etiologies. Retrospectively, we measured the cystic lesions due to histopathological-confirmed honeycombing from interstitial pulmonary fibrosis, pulmonary Langerhans cell histiocytosis (PLCH), and paraseptal emphysema, using paired inspiratory and expiratory CT scans. In a sample of 72 patients and 216 lesions, the mean diameter of PLCH and honeycombing decreased during expiration (PLCH, δ = 60.9%; p = 0.001; honeycombing, δ = 47.5%; p = 0.014). Conversely, paraseptal emphysema did not show any changes (δ = 5.2%; p = 0.34). In summary, our results demonstrated that cysts in smokers with PLCH and honeycombing fibrosis get smaller during expiratory CT scans, whereas the size of cystic-like lesions due to paraseptal emphysema and bullae tend to remain constant during respiratory cycles. These results support the hypothesis of cyst-airway communication in some cystic diseases, which could assist in the differential diagnosis in smoking-related lung diseases.

A Multi-Centric Evaluation of AI-Driven Synthetic CT Generation Form Low Field Magnetic Resonance Imaging

<h3>Purpose/Objective(s)</h3> Magnetic Resonance is an essential modality in the context of radiotherapy primarily for providing additional information with respect to tumor functional information leading to better target delineation (brain, prostate, etc.) and secondary in the context of emergence of magnetic resonance guided radiotherapy. However, in both cases computed tomography acquisition remains necessary for dosimetric purposes hampering the workflow, introducing additional cost and dose simulation/optimization discrepancies (due to the registration issues between MR & CT) while being associated with additional patient toxicity. This study aims to investigate in a retrospective manner the relevance deep learning synthetic CT generation as an alternative for simulation and planning for pelvic tumors treated with low field (0.35T) MRgRT. <h3>Materials/Methods</h3> In the context of this study, a cycle generative adversarial neural network (GAN) deep learning architecture was trained to determine a bijective transformation between a low field (0.35T) MR and the associated computed tomography scan acquisition. The training set involved 350 pairs of weakly aligned data of pelvis cases. A retrospective cohort involving 20 test cases coming from eight different institutions (US: 2, EU: 5, AS: 1) involving different CT vendors was considered for testing. <h3>Results</h3> Reconstruction performance was assessed using the OARs used for treatment. The observed average scaled (between maximum and minimum HU values of the CT) difference between the reconstructed and the CT used for planning was 35.08 with significant discrepancies across organs. Femoral heads were the most reliably reconstructed (4.51 & 4.77) while rectum and sigmoid were the less precise ones (53.13 & 51.48). In terms of qualitative evaluation, the presence of fiducial markers heavily penalizes the reconstruction due to the implicit propagation of errors associated with the "convolution" nature of deep learning. The presence of air bubbles visible on the CT (sigmoid and rectum) is also an issue since these elements are marginally perceptible in the MR and therefore can hardly be predicted from generator. Detailed reconstruction results per organ are appended. <h3>Conclusion</h3> This retrospective multi-centric study is a first step toward assessing the potential of a fully low field MR-based treatment planning workflow that eliminates the need of CT acquisition. Integration of the synthetic CT in the simulation/optimization and assessment of the induced dosimetric errors are necessary steps to determine the clinical relevance of our preliminary findings.

Impact of First Metatarsal Hyperpronation on First Ray Alignment: A Cadaveric Study

Category: Midfoot/Forefoot; Bunion Introduction/Purpose: Hyperpronation of the first metatarsal (M1) is present in Hallux Valgus (HV) but its impact is still unknown. A previous biomechanical study showed that an increase in hallucal pronation might lead to a medial soft tissue failure of the first metatarsophalangeal joint (MTP1). Conversely, an increase in supination and adduction of the first ray when weight-bearing is present in case of HV. The objective of our study was to sequentially answer the following questions: (1) Does an increase in M1 pronation cause an increase in hallucal pronation? (2) Can a combination of intrinsic M1 hyperpronation and MTP1 medial soft tissue failure induce a supination motion of the first ray during weight-bearing? (3) Can a first ray supination motion during weight- bearing be accompanied by an increase in IMA and HVA? Methods: A cadaveric model allowing a simulated standing position was developed and secured with a radiolucent frame (Figure 1). A midshaft osteotomy of M1 was performed allowing either 0° or 30° in pronation. MTP1 medial soft tissue release was performed to simulate failure. Twelve specimens underwent 6 Weight-Bearing CT acquisitions under different conditions listed below. The first 3 acquisitions had 0° pronation of M1:1. Simulated non-weight-bearing condition (Figure 2a) 2. Simulated weight- bearing condition (Figure 2b) 3. Simulated weight-bearing condition with medial soft tissue failure (Figure 2c). The next 3 WBCT acquisitions followed the same sequence but with 30° pronation of M1 (Figure 2d to 2f). On each WBCT acquisition, the HVA, IMA, Metatarsal Pronation Angle (MPA, M1 head pronation relative to the ground) and the hallucal pronation (HP) were measured (Figure 3). Motions were indirectly calculated from the differential values of these angular measurements produced by these 6 different conditions. Results: 1.The increase in MPA and HP induced by the 30° pronation osteotomy of M1 in simulated non weight bearing- conditions were respectively 27.6+/-4.1 and 25.5+/-5.6 degrees (p=0.202). 2.The first ray motion induced by weight-bearing without pronation osteotomy combined with a MTP1 medial soft tissue failure was 3.7+/-3.6 degrees pronation (differential value on MRA between Figure 2a and 2c) compared to 11+/-7.5 degrees supination after the 30 degrees pronation osteotomy of M1 combined with a MTP1 medial soft tissue failure (p&lt;0.01) (differential value on MPA between Figure 2d and 2f). 3.Regarding the static angular measurements, the HVA and the IMA presented fair positive linear correlations with the MPA (respectively ρ=0.2 and ρ=0.22). Regarding the motions, the increase of the HVA and the IMA during weight-bearing presented respectively a very strong negative (ρ=-0.82) and a strong negative (ρ=-0.77) linear correlations with the pronation motion of the first ray during weight-bearing. Conclusion: The combination of M1 intrinsic hyperpronation and MTP1 medial soft tissue failure led to an HV deformity in our cadaveric study. The static measurement of M1 head pronation relative to the ground (MPA) does not reflect the real intrinsic pronation of the first ray and foot and ankle specialists should be careful when interpreting these measures. HV is a dynamic condition, and the deformity could be more correlated with motions when WB than with plain static measurements. The first ray supination motion compensating a M1 intrinsic hyperpronation might be an important factor in the HV pathogenesis.