Christopher G. Roth

Optimizing abdominal MR imaging: approaches to common problems.

Abdominal magnetic resonance (MR) imaging involves many challenges and is complicated by physiologic motion not encountered to the same degree in other regions of the body. Problems that uniquely affect abdominal MR imaging include motion artifact (from respiratory, cardiac, gastrointestinal, and voluntary movement), susceptibility artifact, conductive and dielectric effects, and wraparound artifact. Techniques to minimize these artifacts often need to be addressed within the time constraints of a single breath hold. Patient motion during image acquisition is minimized by using physical restraint, respiratory gating, and reduction of acquisition time. Correction of motion-induced dephasing (through gradient moment nulling), signal averaging, and suppression of signal in moving structures all address unavoidable motion (eg, cardiac pulsation). Acquisition time is minimized by obtaining fewer phase-encoding steps, decreasing repetition time, and increasing efficiency with use of parallel imaging and multiecho acquisitions. Adjusting the echo time does not directly affect scanning time, but it does allow more time for section sampling per repetition time interval in multisection acquisitions by means of closer echo spacing and it plays a pivotal role in optimizing image quality. Familiarity with basic MR imaging principles and the ability to minimize the effects of motion and other artifacts are essential to optimizing abdominal MR imaging protocols and improving efficiency.

Exophytic Renal Masses: Angular Interface with Renal Parenchyma for Distinguishing Benign from Malignant Lesions at MR Imaging

PURPOSE To retrospectively determine whether benign exophytic renal masses can be distinguished from renal cell carcinoma (RCC) on the basis of angular interface at single-shot fast spin-echo (SE) T2-weighted magnetic resonance (MR) imaging. MATERIALS AND METHODS This retrospective study was compliant with HIPAA and was approved by the institutional review board. Patient informed consent was waived. A total of 162 exophytic (2 cm or greater) renal masses in 152 patients (103 men, 49 women; mean age, 58 years; age range, 23-85 years) were included. Two radiologists independently recorded the mass size and angular interface on single-shot fast SE T2-weighted MR images. Surgical pathologic report and MR follow-up were used as reference standards. Logistic regression analysis was used to examine the usefulness of these variables for differentiating benign masses from RCCs. Diagnostic performance was analyzed by comparing values for area under receiver operating characteristic curve (A(z)). Sensitivity, specificity, positive predictive value (PPV), and negative predictive value (NPV) of angular interface for diagnosing benign masses were calculated. Reader agreement was assessed with kappa-weighted statistics and intraclass correlation coefficients (ICCs). RESULTS Of 162 masses, 65 were benign, and 97 were RCCs. The sensitivity, specificity, PPV, NPV, and A(z) of angular interface for diagnosing benign masses were 78%, 100%, 100%, 87%, and 0.813, respectively. Angular interface (P < .001) was a significant predictor of benign renal mass but mass size (P = .66) was not. There was almost perfect interobserver agreement for mass size (ICC = 0.96) and angular interface (kappa = 0.91). CONCLUSION The presence of an angular interface with the renal parenchyma at single-shot fast SE T2-weighted MR imaging is a strong predictor of benignity in an exophytic renal mass 2 cm or greater in diameter with high specificity and diagnostic accuracy.

Hepatocellular carcinoma and other hepatic malignancies: MR imaging.

Magnetic resonance (MR) imaging surpasses all other imaging modalities in characterizing liver lesions by virtue of the exquisite tissue contrast, specificity for various tissue types, and extreme sensitivity to contrast enhancement. In addition to differentiating benign from malignant lesions, MR imaging generally discriminates between the various malignant liver lesions. Hepatocellular carcinoma constitutes most primary malignant liver lesions and usually arises in the setting of cirrhosis. Intrahepatic cholangiocarcinoma is a distant second and features distinctly different imaging features. Overall, metastases are the most common malignant liver lesions and arise from several primary neoplasms; most commonly gastrointestinal, lung, breast, and genitourinary.

Erratum to: Identifying decreased peristalsis of abnormal small bowel segments in Crohn’s disease using cine MR enterography: the frozen bowel sign

AbstractPurpose The purpose of this study was to evaluate whether affected bowel in Crohn’s disease patients can be identified by observing decreased peristalsis (frozen bowel sign) using cine balanced steady-state free precession (cine BSSFP) images.Materials and methods5 radiologists independently reviewed cine BSSFP sequences from randomized MR Enterography (MRE) exams for 30 normal and 30 Crohn’s disease patients, graded overall small bowel peristalsis from slowest to fastest, and graded peristalsis for the most abnormal small bowel segment. Sensitivity and specificity of the frozen bowel sign for diagnosing Crohn’s disease were calculated. T tests of the peristalsis difference between abnormal segments and overall small bowel were conducted.ResultsFor 5 readers, the sensitivity and specificity of cine BSSFP of the frozen bowel sign for diagnosing Crohn’s disease ranged from 70% to 100% and 87% to 100%, respectively. There were significant differences in peristalsis between abnormal small bowel segments and the overall small bowel for Crohn’s patients, but not in the overall small bowel between normal-MRE patients and Crohn’s disease patients.ConclusionAbnormal Crohn’s small bowel segments have significantly decreased peristalsis compared to normal small bowel, which can be identified using cine BSSFP sequences as the frozen bowel sign.

Hepatic MR Imaging Techniques, Optimization, and Artifacts

This article describes a basic 1.5-T hepatic magnetic resonance (MR) imaging protocol, strategies for optimizing pulse sequences while managing artifacts, the proper timing of postgadolinium 3-dimensional gradient echo sequences, and an effective order of performing pulse sequences with the goal of creating an efficient and high-quality hepatic MR imaging examination. The authors have implemented this general approach on General Electric, Philips, and Siemens clinical scanners.

Contrast-enhanced or noncontrast CT for renal colic: utilizing urinalysis and patient history of urolithiasis to decide

PurposeIn the emergency setting, flank pain commonly leads to a noncontrast CT despite a significant percentage of patients having alternative diagnoses, often difficult to characterize without contrast. We investigated the combined utility of urinalysis and history of urolithiasis in identifying patients who are unlikely to have urolithiasis and may benefit from a contrast-enhanced study.MethodsRetrospective review of 350 patients from May 2013 to May 2016 was performed for patients in the emergency department with renal colic that underwent noncontrast CT and urinalysis testing.ResultsUrolithiasis was present in 282 of the 350 patients reviewed (81%), of which 175 (62%) had an obstructing calculus. RBC-positive urinalysis was present in 231 patients with calculi on CT (sensitivity 82%). Patient history of urolithiasis plus urinalysis had a sensitivity of 94% for detecting calculi. Thirty-five patients (10%) had alternative diagnoses, 33 of which were in patients without obstructing calculi. Sixty-seven patients underwent noncontrast CT despite no history of urolithiasis and a negative urinalysis, 10 of which (15%) had alternative diagnoses. Only three cases in this subset (4%) had nonobstructing 1–2-mm calculi, potentially missed with contrast. In this subset, the projected proportion of optimally characterized cases with intravenous contrast is 96%, compared to 85% without contrast (p = .03).DiscussionGiven the high combined sensitivity of urinalysis and patient history (94%), this simple analysis can confidently direct clinicians to a contrast-enhanced CT in “rule-out” cases of flank pain in patients with a negative history and negative urinalysis, particularly given that 15% of these patients had alternative diagnoses.

Hepatocellular carcinoma after locoregional therapy: Magnetic resonance imaging findings in falsely negative exams.

AIM To elucidate causes for false negative magnetic resonance imaging (MRI) exams by identifying imaging characteristics that predict viable hepatocellular carcinoma (HCC) in lesions previously treated with locoregional therapy when obvious findings of recurrence are absent. METHODS This retrospective institutional review board-approved and Health Insurance Portability and Accountability Act-compliant study included patients who underwent liver transplantation at our center between 1/1/2000 and 12/31/2012 after being treated for HCC with locoregional therapy. All selected patients had a contrast-enhanced MRI after locoregional therapy within 90 d of transplant that was prospectively interpreted as without evidence of residual or recurrent tumor. Retrospectively, 2 radiologists, blinded to clinical and pathological data, independently reviewed the pre-transplant MRIs for 7 imaging features. Liver explant histopathology provided the reference standard, with clinically significant tumor defined as viable tumor ≥ 1.0 cm in maximum dimension. Fishers exact test was first performed to identify significant imaging features. RESULTS Inclusion criteria selected for 42 patients with 65 treated lesions. Fourteen of 42 patients (33%) and 16 of 65 treated lesions (25%) had clinically significant viable tumor on explant histology. None of the 7 imaging findings examined could reliably and reproducibly determine which treated lesion had viable tumor when the exam had been prospectively read as without evidence of viable HCC. CONCLUSION After locoregional therapy some treated lesions that do not demonstrate any MRI evidence of HCC will contain viable tumor. As such even patients with a negative MRI following treatment should receive regular short-term imaging surveillance because some have occult viable tumor. The possibility of occult tumor should be a consideration when contemplating any action which might delay liver transplant.

Interpreting body MRI cases: what you need to know to get started.

Interpreting body MRI cases can seem overwhelming to an uninitiated radiologist. The standard study includes a variety of pulse sequences, the names of which vary depending on the MR vendor. Pulse sequences may be displayed haphazardly on the picture archiving and communication system (PACS), frequently not synchronized with the imaging protocol. Adding to the complexity is the use of different gadolinium-based contrast agents, which may affect the timing and diagnostic yield of each sequence. The following introductory primer for interpreting body MRI cases is meant to create a basic framework for efficiently reviewing body MRI cases to provide high quality interpretations, fully utilizing the diagnostic information of the modality. There are 4 components that need to be mastered when interpreting body MRI cases including: (1) recognizing the key sequences in a basic body MRI protocol, (2) learning how to best display the key pulse sequences on PACS, (3) understanding the technique and clinical utility of each sequence and learning how to utilize sequences to be an “MR Pathologist”, and (4) understanding the key features of the different gadolinium based contrast agents.

Does transitioning from computed radiography (CR) to direct radiography (DR) with portable imaging systems affect workflow efficiency

In digital radiography, computed radiography (CR) technology is based on latent image capture by storage phosphors whereas direct radiography (DR) technology is based either on indirect conversion using a scintillator or direct conversion using a photoconductor. DR-based portable imaging systems may enhance workflow efficiency. The purpose of this work was to investigate changes in workflow efficiency at a tertiary healthcare center after transitioning from CR to DR technology for imaging with portable x-ray units. An IRB exemption was obtained. Data for all inpatient-radiographs acquired with portable x-ray units from July-2014 till June-2015 (period 1) with CR technology (AMX4 or AMX4+ portable unit from GE Healthcare, NX workstation from Agfa Healthcare for digitization), from July-2015 till June-2016 (period 2) with DR technology (Carestream DRX-Revolution x-ray units and DRX-1C image receptors) and from July-2016 till January-2017 (period 3; same DR technology) were extracted using Centricity RIS-IC (GE Healthcare). Duration between the imaging-examination scheduled time and completed time (timesch-com) was calculated and compared using non-parametric tests (between the three time periods with corrections for multiple comparisons; three time periods were used to identify if there were any other potential temporal trends not related to transitioning from CR to DR). IBMs SPSS package was used for statistical analysis. Overall data was obtained from 33131, 32194, and 18015 cases in periods 1, 2 and 3, respectively. Independent-Samples Kruskal-Wallis test revealed a statistically significant difference in timesch-com across the three time periods (χ2(2, n= 83,340) = 2053, p < 0.001). The timesch-com was highest for period 1 i.e., radiographs acquired with CR technology (median: 64 minutes) and it decreased significantly for radiographs acquired with DR technology in periods 2 (median: 49 minutes; p < 0.001) and 3 (median∶ 44 minutes; p < 0.001). Overall, adoption of DR technology resulted in a drop in timesch-com by 27% relative to the use of CR technology. Transitioning from CR to DR was associated with improved workflow efficiency for radiographic imaging with portable x-ray units.

Contrast-Enhanced Chest Computed Tomography Reveals Treatable Causes of Cerebral Abscesses in Patients without Antecedent Surgery or Trauma

OBJECTIVE Brain abscesses cause substantial morbidity and mortality even after appropriate therapy, and no underlying cause is found in 25% of cases. We investigated the added utility of contrast-enhanced chest computed tomography (CT) in the diagnostic work-up of patients presenting with cerebral abscesses and no history or prior trauma or cranial surgery. METHODS All patients presenting to a single institution with a surgically proven brain abscess were reviewed. Concurrent contrast-enhanced chest CT imaging results were reviewed when available to identify treatable predisposing causes of intracranial suppuration. RESULTS This study included 31 patients with biopsy-proven abscesses. Multiple abscesses were present in 8 patients (26%). Contrast-enhanced CT was performed in 15 patients (48%). Of these 15 patients, 2 had pulmonary arteriovenous malformations, 1 had an intrapulmonary shunt, and 3 had empyemas. Definitive therapy for the chest findings was provided to 6 of the 15 patients (40%). In the remaining 9 patients, 3 had pulmonary abscesses, for which diagnostic aspiration was requested. Another patient had an incidental pulmonary embolism, resulting in same-day placement of an inferior vena caval filter (not included in chest analysis, given that the finding was incidental). CONCLUSIONS Contrast-enhanced chest CT is useful for identifying treatable causes of cerebral abscesses in patients with a cerebral abscess and no history of surgery or trauma.