Publications

PURPOSE: We constructed a 13C/31P surface coil at 3 T for studying cancer metabolism and bioenergetics. In a single scan session, hyperpolarized 13C-pyruvate MRS and 31P MRS was carried out for a healthy rat brain.

METHODS: All experiments were carried out at 3 Tesla. The multinuclear surface coil was designed as two coplanar loops each tuned to either the 13C or 31P operating frequency with an LCC trap on the 13C loop. A commercial volume proton coil was used for anatomical localization and B0 shimming. Single tuned coils operating at either the 13C or 31P frequency were built to evaluate the relative performance of the multinuclear coil. Coil performance metrics consisted of measuring Q factor ratio, calculating system input power using a single-pulse acquisition, and acquiring SNR and flip angle maps using 2D CSI sequences. To observe in vivo spectra, a bolus of hyperpolarized [1-13C] pyruvate was administered via tail vein. In vivo13C and endogenous 31P spectra were obtained in a single scan session using 1D slice selective acquisitions.

RESULTS: When compared with single tuned surface coils, the multinuclear coil performance showed a decrease in Q factor ratio, SNR, and transmit efficiency. Flip angle maps showed adequate flip angles within the phantom when the transmit voltage was set using an external phantom. Results show good detection of 13C labeled lactate, alanine, and bicarbonate in addition to ATP from 31P MRS.

CONCLUSIONS: The coil enables obtaining complementary information within a scan session, thus reducing the number of trials and minimizing biological variability for studies of metabolism and bioenergetics.

INTRODUCTION: Morphometric assessment of Chiari malformation type I (CMI) is typically performed on a midsagittal MRI. However, errors arising from an imprecise selection of the midsagittal plane are unknown. We define absolute parasagittal error as the absolute difference between morphometric measurements at the midsagittal and parasagittal planes. Our objective was to determine the absolute parasagittal error at various lateral distances for morphometric parameters commonly used in CMI research.

METHODS: Sagittal T1-weighted MRI scans of 30 CMI adult female subjects were included. Image sets were evaluated to assess 14 CMI morphometric parameters in the midsagittal plane and four parasagittal planes located 1 and 2 mm lateral (left and right). Comparisons between measurements at the midsagittal and parasagittal planes were conducted to determine the mean individual absolute and mean group parasagittal errors for all 14 parameters.

RESULTS: The mean individual absolute parasagittal error was > 1 unit (1 mm for lengths and 1 degree for angles) for 9/14 parameters within a lateral distance of 2 mm. No significant group parasagittal errors were seen in 14/14 parameters, including tonsillar position within a lateral distance of 2 mm.

CONCLUSION: Our results show that the absolute errors for imprecise midsagittal plane selection may impact the clinical assessment of an individual patient. However, the impact on group measurements, such as in a research setting, will be minimal.

BACKGROUND: Exercise cardiovascular magnetic resonance (Ex-CMR) is a promising stress imaging test for coronary artery disease (CAD). However, Ex-CMR requires accelerated imaging techniques that result in significant aliasing artifacts. Our goal was to develop and evaluate a free-breathing and electrocardiogram (ECG)-free real-time cine with deep learning (DL)-based radial acceleration for Ex-CMR.

METHODS: A 3D (2D + time) convolutional neural network was implemented to suppress artifacts from aliased radial cine images. The network was trained using synthetic real-time radial cine images simulated using breath-hold, ECG-gated segmented Cartesian k-space data acquired at 3 T from 503 patients at rest. A prototype real-time radial sequence with acceleration rate = 12 was used to collect images with inline DL reconstruction. Performance was evaluated in 8 healthy subjects in whom only rest images were collected. Subsequently, 14 subjects (6 healthy and 8 patients with suspected CAD) were prospectively recruited for an Ex-CMR to evaluate image quality. At rest (n = 22), standard breath-hold ECG-gated Cartesian segmented cine and free-breathing ECG-free real-time radial cine images were acquired. During post-exercise stress (n = 14), only real-time radial cine images were acquired. Three readers evaluated residual artifact level in all collected images on a 4-point Likert scale (1-non-diagnostic, 2-severe, 3-moderate, 4-minimal).

RESULTS: The DL model substantially suppressed artifacts in real-time radial cine images acquired at rest and during post-exercise stress. In real-time images at rest, 89.4% of scores were moderate to minimal. The mean score was 3.3 ± 0.7, representing increased (P < 0.001) artifacts compared to standard cine (3.9 ± 0.3). In real-time images during post-exercise stress, 84.6% of scores were moderate to minimal, and the mean artifact level score was 3.1 ± 0.6. Comparison of left-ventricular (LV) measures derived from standard and real-time cine at rest showed differences in LV end-diastolic volume (3.0 mL [- 11.7, 17.8], P = 0.320) that were not significantly different from zero. Differences in measures of LV end-systolic volume (7.0 mL [- 1.3, 15.3], P < 0.001) and LV ejection fraction (- 5.0% [- 11.1, 1.0], P < 0.001) were significant. Total inline reconstruction time of real-time radial images was 16.6 ms per frame.

CONCLUSIONS: Our proof-of-concept study demonstrated the feasibility of inline real-time cine with DL-based radial acceleration for Ex-CMR.

PURPOSE: To describe the feasibility and outcomes of filter-assisted shunt embolization in patients with acquired large portosystemic shunts.

METHODS: Two-center HIPAA compliant retrospective study of all patients who underwent filter-assisted shunt embolization between 03/2015-03/2021. Initial clinical evaluation, including demographic information, shunt sizing, and procedural details, was reviewed. Technical success was defined as successful occlusion of the targeted shunt.

RESULTS: Eight patients (55 ± 10 years/88% male) had a large acquired portosystemic shunt which was suitable for filter-assisted shunt embolization. Indications for the procedure: 3 = pre-transplantation optimization, 2 = overt hepatic encephalopathy (HE), 1 = post-transplant thrombosis, 1 = portal vein thrombosis and encephalopathy, 1 = encephalopathy and variceal bleeding. Portosystemic shunts occurred between splenic and renal veins, inferior mesenteric and gonadal veins, and coronary veins. Mean shunt diameter was 27 ± 5 mm. The technical success of the procedure was 8/8 (100%). In 7 patients, a transjugular intrahepatic portosystemic shunt (TIPS) was also placed at the time of the shunt embolization due to either pre-transplant indication or sluggish portal flow. There were no intraprocedural complications from filter placement.

OUTCOMES: 3 = currently listed for transplant, 2 = resolution of HE, 1 = made CMO, 1 patient with patent post-transplant vasculature. 1 = died as a complication related to TIPS placement (SIR Class F Complication).

CONCLUSION: Filter-assisted shunt embolization is a technically feasible and safe technique to reduce or embolize large portosystemic shunts.

RATIONALE AND OBJECTIVES: In response to COVID-19, our institution implemented three virtual readout systems: a commercial HIPAA compliant web-based video conferencing platform used for screen-sharing (Starleaf), an interactive control sharing system integrated into PACS allowing simultaneous multi-user mouse control over images (Collaborate), and the telephone. Our aim was to assess overall satisfaction with and perceived effectiveness of these virtual readout methods to optimize best practices for the future.

MATERIALS AND METHODS: An IRB-exempt survey was electronically distributed to 64 trainees and 76 attendings at one tertiary-care institution via Survey Monkey. Questions focused on overall satisfaction, perceived effectiveness, technical difficulties, and continued future use of the three virtual readout strategies. Answers were collected with Likert scales, tick boxes, and open-ended questions.

RESULTS: 32/64 trainees (50%) and 32/76 attendings (42%) completed the survey. Trainees and attendings were more satisfied with screen sharing (Starleaf) and perceived it more effective than control sharing (Collaborate) or the telephone (p < 0.0001). Respondents experienced more technical difficulties with control sharing versus screen sharing (p = 0.0004) with a negative correlation between level of technical difficulties and satisfaction with screen sharing (r = -0.50, p < 0.0001) and control sharing (r = -0.38, p = 0.0006). Trainees and faculty supported a combination of in-person and virtual readouts in the future (p < 0.0001).

CONCLUSION: Platforms mirroring in-person readouts, such as Starleaf, are preferred by both trainees and attendings over non-screen sharing platforms such as the telephone. However, technical stability determines satisfaction between similar platforms. Both trainees and attendings support incorporation of virtual readout methods in combination with traditional in-person readouts in the post-COVID-19 era.

BACKGROUND: Routine management after abscess drainage includes CT or fluoroscopic imaging to assess for residual abscess cavity prior to catheter removal. It is unclear whether this practice is necessary in patients without residual infection signs and symptoms.

PURPOSE: To evaluate safety of abscess catheter removal without follow-up imaging in patients without residual clinical or laboratory signs of infection and catheter output < 10 cc/day for 2 consecutive days.

MATERIALS AND METHODS: In this IRB-approved, HIPAA compliant, retrospective study, consecutive patients that underwent percutaneous CT-guided drainage of a single abdominal or pelvic abscess between 01/2015 and 12/2017 in a single tertiary academic institution with or without follow-up imaging prior to catheter removal were included. In our institution, catheters are routinely removed without imaging if there are no clinical (fever, pain) or laboratory (elevated WBC count) signs of infection and catheter output is < 10 cc/day for 2 consecutive days. Patients' and abscess's characteristics, repeat imaging data, and need for re-interventions were obtained through medical records review. Statistical analysis was performed with Fisher's exact test for independent data and Student's t-test for comparison of group means.

RESULTS: 310 consecutive patients (age 56 ± 16 years, 48% female) were included in the study. In 265/310 (85%) patients, no routine follow-up imaging prior to catheter removal was obtained. In 2/265 (0.8%, 95% CI 0.02-0.27%) patients without routine pre-removal imaging, repeat abscess drainage was required 6 and 15 days after catheter removal in patient with perforated appendicitis and after laparoscopic renal cyst decortication, respectively. No patients, 0/45 (0%, 95% CI 0-0.07), that underwent routine imaging without clinical or laboratory signs infection needed to undergo a repeat abscess drainage.

CONCLUSION: There is a low rate (0.8%) of abscess recurrence if percutaneous abscess catheter is removed at the time cessation of drainage without routine imaging in clinically well patient.

Soft tissue lesions are commonly encountered and imaging is an important diagnostic step in the diagnosis and management of these lesions. While some of these lesions are true neoplasms, others are not. These soft tissue tumor mimickers can be due to a variety of conditions including traumatic, iatrogenic, inflammatory/reactive, infection, vascular, and variant anatomy. It is important for the radiologist and clinician to be aware of these common soft tissue tumor mimickers and their characteristic imaging features to avoid unnecessary workup and provide the best treatment outcome.

Biopsies of the lung, pleura, and mediastinum play a crucial role in the workup of thoracic lesions. Percutaneous image-guided biopsy of thoracic lesions is a relatively safe and noninvasive way to obtain a pathologic diagnosis which is required to direct patient management. This article reviews how to safely perform image-guided biopsies of the lung, pleura, and mediastinum, from the preprocedural assessment to reviewing intraprocedural techniques, and how to avoid and manage complications.

RATIONALE AND OBJECTIVES: To ascertain the perceived obstacles that medical students and Interventional Radiology (IR) residents face performing IR research during training and incorporating research into their future careers.

MATERIALS AND METHODS: The study was reviewed and exempt from Institutional Review Board review. Participants' attitudes and perceived barriers toward performing IR research, and experience with mentorship in IR were assessed using a 27-item survey sent to all members of the Society of Interventional Radiology Resident, Fellow and Student (SIR-RFS, n = 445), and Medical Student Council (SIR-MSC, n = 267) sections between July and September 2020. Descriptive statistics were computed for all assessed categorical variables. Fisher's exact tests were performed to measure the significance of association between categorical variables.

RESULTS: Of the 712 students and residents surveyed, 151 (∼21%) responded. Of respondents, 100% reported that conducting research is important to advancing the field of IR. The highest ranked factors and obstacles to performing IR research were increased clinical demands (67.9%), lack of time (46.2%), lack of institutional support (41.5%), and lack of research experience (35.8%). Interestingly, those with a mentor were more likely to report an interest in pursuing a career in IR compared to those without a mentor (98.6% vs 41.0%, p < 0.0001). Furthermore, those with a mentor were more likely to report an interest in pursuing IR research compared to those without a mentor (32.5% vs 14.4%, p < 0.0001).

CONCLUSION: There are many obstacles to performing IR research. Strong mentorship is an avenue to address these deterrents. The deployment of mentorship programs in IR is needed to ensure trainees can overcome the barriers outlined in this study and successfully pursue research careers in IR.

BACKGROUND AND PURPOSE: Templates are a hallmark of image analysis in neuroimaging. However, while numerous structural templates exist and have facilitated single-subject and large group studies, templates based on functional contrasts, such as arterial spin labeling (ASL) perfusion, are scarce, have an inherently low spatial resolution, and are not as widely distributed. Having such tools at one's disposal is desirable, for example, in the case of studies not acquiring structural scans. We here propose an initial development of an ASL adult template based on high-resolution fast spin echo acquisitions.

METHODS: High-resolution single-delay ASL, low-resolution multi-delay ASL, T1 -weighted magnetization prepared rapid acquisition 2 gradient echoes, and T2 fluid attenuated inversion recovery data were acquired in a cohort of 10 healthy volunteers (6 males and 4 females, 30± 7 years old). After offline reconstruction of high-resolution perfusion arterial transit time (ATT) and T1 maps, we built a multi-contrast template relying on the Advanced Normalization Toolbox multivariate template nonlinear construction framework. We offer examples for the registration of ASL data acquired with different sequences. Finally, we propose an ASL simulator based on our templates and a standard kinetic model that allows generating synthetic ASL contrasts based on user-specified parameters.

RESULTS: Boston ASL Template and Simulator (BATS) offers high-quality, high-resolution perfusion-weighted and quantitative perfusion templates accompanied by ATT and different anatomical contrasts readily available in the Montreal Neurological Institute space. In addition, examples of use for data registration and as a synthetic contrast generator show various applications in which BATS could be used.

CONCLUSIONS: We propose a new ASL template collection, named BATS, that also includes a simulator allowing the generation of synthetic ASL contrasts. BATS is available at http://github.com/manueltaso/batsasltemplate.