Peter S. Liu

Comparison of Acute Transient Dyspnea after Intravenous Administration of Gadoxetate Disodium and Gadobenate Dimeglumine: Effect on Arterial Phase Image Quality

PURPOSE To determine whether acute transient dyspnea and/or arterial phase image degradation occurs more or less often after intravenous administration of gadoxetate disodium than with intravenous administration of gadobenate dimeglumine. MATERIALS AND METHODS Institutional review board approval and patient consent were obtained for this prospective observational study. One hundred ninety-eight gadolinium-based contrast media administrations (99 with gadoxetate disodium [10 mL, n = 97; 8 mL, n = 1; 16 mL, n = 1] and 99 with gadobenate dimeglumine [0.1 mmol per kilogram of body weight, maximum dose, 20 mL]) for hepatobiliary indications were assessed in 192 patients. Subjective patient complaints were assessed. Objective respiratory motion degradation on T1-weighted precontrast and dynamic postcontrast (arterial, venous, or late dynamic or extracellular) magnetic resonance (MR) imaging datasets were independently assessed in a randomized, blinded fashion by five readers using a five-point scale, with mean scores of 4 or greater indicating severe motion. Comparisons between agents were made by using χ(2) or Fisher exact test, where appropriate. RESULTS Significantly more patient complaints of acute transient dyspnea occurred after gadoxetate disodium administration than gadobenate dimeglumine (14% [14 of 99] vs 5% [five of 99], P = .05). There were significantly more severely degraded arterial phase data sets for gadoxetate disodium than for gadobenate dimeglumine for both the general population (17% [17 of 99] vs 2% [two of 99], P = .0007) and the subpopulation with cirrhosis (19% [14 of 72] vs 3% [one of 37], P = .02). This effect did not extend to venous (1% [one of 99] vs 2% [two of 99], P > .99 [overall population]) or late dynamic or extracellular (2% [two of 99] vs 0% [zero of 99], P = .5 [overall population]) phases. No patient required treatment for self-limited dyspnea. CONCLUSION Intravenous gadoxetate disodium can result in acute self-limiting dyspnea that can have a deleterious effect on arterial phase MR image quality and occurs significantly more often than with intravenous gadobenate dimeglumine.

Imaging of the Placenta: A Multimodality Pictorial Review

The placenta is often overlooked in the routine evaluation of a normal gestation, receiving attention only when an abnormality is detected. Although uncommon, abnormalities of the placenta are important to recognize owing to the potential for maternal and fetal morbidity and mortality. Pathologic conditions of the placenta include placental causes of hemorrhage, gestational trophoblastic disease, retained products of conception, nontrophoblastic placental tumors, metastases, and cystic lesions. Sonography remains the imaging modality of choice for evaluation of the placenta. Magnetic resonance (MR) imaging can be of added diagnostic value when further characterization is required, particularly in the setting of invasive placental processes such as placenta accreta and gestational trophoblastic disease. Computed tomography (CT) has a limited role in the evaluation of placental disease owing to limited tissue characterization, compared with that of MR imaging, and the radiation risk to the fetus; this risk often outweighs the benefit. The primary role for CT is in the evaluation of trauma and gestational trophoblastic disease, for which it allows characterization of the primary lesion and distant metastases.

MR Imaging and CT of the Biliary Tract

Magnetic resonance (MR) imaging and computed tomography (CT) can be useful in the diagnosis of biliary disease, with both modalities allowing detailed evaluation of the biliary tract. Careful interrogation of the images is critical, regardless of modality. The identification of dilated bile ducts necessitates evaluation for strictures or filling defects, which is best performed with thin-section imaging. Smooth, concentric short-segment strictures favor a benign cause, whereas abrupt, eccentric long-segment strictures favor a malignancy. At MR imaging, extrabiliary entities such as crossing vessels or metallic clip artifact may mimic strictures and should not be mistaken for disease. A stone is the most common biliary filling defect and may occur in the absence of dilated ducts. Stones commonly have a lamellated, geometric shape and are found in a dependent portion of the duct. Identification of bile duct wall thickening raises concern for cholangitis or malignancy. Improved diagnosis of biliary disease can be achieved with a knowledge of the benefits and limitations of modern MR and CT cholangiographic techniques, including the use of biliary-excreted contrast material and of various postprocessing techniques. Familiarity with the radiologic appearances of the duct lumen, wall, and surrounding structures is also important for accurate image interpretation. The rapidly evolving technology for both MR imaging and CT of the biliary tract will continue to present radiologists with opportunities as well as challenges.

Repeatability of Diagnostic Features and Scoring Systems for Hepatocellular Carcinoma by Using MR Imaging

PURPOSE To determine for expert and novice radiologists repeatability of major diagnostic features and scoring systems (ie, Liver Imaging Reporting and Data System [LI-RADS], Organ Procurement and Transplantation Network [OPTN], and American Association for the Study of Liver Diseases [AASLD]) for hepatocellular carcinoma (HCC) by using magnetic resonance (MR) imaging. MATERIALS AND METHODS Institutional review board approval was obtained and patient consent was waived for this HIPAA-compliant, retrospective study. The LI-RADS discussed in this article refers to version 2013.1. Ten blinded readers reviewed 100 liver MR imaging studies that demonstrated observations preliminarily assigned LI-RADS scores of LR1-LR5. Diameter and major HCC features (arterial hyperenhancement, washout appearance, pseudocapsule) were recorded for each observation. LI-RADS, OPTN, and AASLD scores were assigned. Interreader agreement was assessed by using intraclass correlation coefficients and κ statistics. Scoring rates were compared by using McNemar test. RESULTS Overall interreader agreement was substantial for arterial hyperenhancement (0.67 [95% confidence interval {CI}: 0.65, 0.69]), moderate for washout appearance (0.48 [95%CI: 0.46, 0.50]), moderate for pseudocapsule (0.52 [95% CI: 050, 0.54]), fair for LI-RADS (0.35 [95% CI: 0.34, 0.37]), fair for AASLD (0.39 [95% CI: 0.37, 0.42]), and moderate for OPTN (0.53 [95% CI: 0.51, 0.56]). Agreement for measured diameter was almost perfect (range, 0.95-0.97). There was substantial agreement for most scores consistent with HCC. Experts agreed significantly more than did novices and were significantly more likely than were novices to assign a diagnosis of HCC (P < .001). CONCLUSION Two of three major features for HCC (washout appearance and pseudocapsule) have only moderate interreader agreement. Experts and novices who assigned scores consistent with HCC had substantial but not perfect agreement. Expert agreement is substantial for OPTN, but moderate for LI-RADS and AASLD. Novices were less consistent and less likely to diagnose HCC than were experts.

CT Enterography at 80 kVp With Adaptive Statistical Iterative Reconstruction Versus at 120 kVp With Standard Reconstruction: Image Quality, Diagnostic Adequacy, and Dose Reduction

OBJECTIVE The objective of our study was to evaluate the image quality and diagnostic adequacy of the following two CT enterography protocols in patients weighing less than 160 lb (72 kg): 80-kVp imaging with the adaptive statistical iterative reconstruction (ASIR) in comparison with 120-kVp imaging with the filtered back projection reconstruction. MATERIALS AND METHODS We retrospectively reviewed 133 CT enterography examinations of 127 patients weighing less than 160 lb, 64 80-kVp examinations, and 69 120-kVp examinations. Image quality for evaluation of the bowel wall, mesenteric vessels, and hepatic parenchyma and the overall image quality were graded on a scale of 1-5 (1 = poor, 2 = acceptable, 3 = good, 4 = very good, 5 = excellent). Diagnostic accuracy for the detection of inflammatory bowel disease was evaluated. The volume CT dose index (CTDI(vol)) was recorded and effective dose was calculated from scanner-generated dose-length product. RESULTS There was a statistically significant decrease in the mean image quality scores for 80-kVp examinations compared with 120-kVp examinations for evaluation of the bowel wall (3.19 vs 3.70, respectively) and liver (3.12 vs 3.81) and for overall image quality (3.23 vs 3.68), but there was no significant decrease in score for evaluation of the mesenteric vessels (3.63 vs 3.67). None of the 80-kVp examinations was graded as poor, and all were considered to be of acceptable quality. Both techniques had comparable diagnostic accuracy for the detection of inflammatory bowel disease. Interobserver agreement was fair to moderate for qualitative image grading and was substantial for the detection of features of inflammatory bowel disease. The mean CTDI(vol) and effective dose for the 80-kVp examinations were 6.15 mGy and 4.60 mSv, respectively, and for the 120-kVp examinations, 20.79 mGy and 15.81 mSv. CONCLUSION In patients weighing less than 160 lb, CT enterography examinations at 80 kVp with 30% ASIR produce diagnostically acceptable image quality with an average CTDI(vol) of 6.15 mGy and an average effective dose of 4.60 mSv.

Rectal Imaging: Part 2, Perianal Fistula Evaluation on Pelvic MRI???What the Radiologist Needs to Know

OBJECTIVE The purpose of this article is to provide an overview of pelvic MRI for the evaluation of perianal fistulas, with a description of the technique, illustration of relevant normal anatomy, and examples of various fistula types. CONCLUSION MRI evaluation of perianal fistulas can be challenging, and knowledge of relevant pelvic anatomy and fistula classification remains crucial in the diagnosis. MRI is highly accurate for fistula depiction and, by providing an accurate assessment of disease status and extension, can help surgical planning to minimize recurrence and detect clinically unapparent disease.

“Sweet spot” for endoleak detection: Optimizing contrast to noise using low keV reconstructions from fast-switch kVp dual energy CT

Objective To assess endoleak detection and conspicuity using low–kiloelectron volt (keV) monochromatic reconstructions of single-source (fast-switch kilovolt [peak]) dual-energy data sets. Methods With approval of the institutional review board, multiphasic dual-energy computed tomographic (CT) scans for aortic endograft surveillance were retrospectively reviewed for 39 patients. Two abdominal radiologists each performed 2 separate reading sessions, at 55-keV and standard 75-keV reconstruction, respectively. The readers tabulated endoleak presence, conspicuity on 1-to-5 scale, and type overall and in arterial and venous phases. Originally, dictated reports in medical records were used as criterion standard. Results Original dictations identified 19 endoleaks (9 abdominal and 10 thoracic), 13 of which were type II. The blinded readers (R1 and R2) exhibited good to very good intraobserver and interobserver agreement. Endoleak detection was higher at 55 keV than at 75 keV (sensitivity, 100% (95% confidence interval [CI], 82.4%–100.0%) and 84.2% (95% CI, 60.4–96.6%) at 55 keV vs 79% (95% CI, 54.4–94.0%) and 68.4% (95% CI, 43.5%–87.4%) at 75 keV in venous phase). Further, endoleak conspicuity ratings (where original dictation showed positive leak) were higher at 55 keV than at 75 keV, which was a significant difference for R2 in the overall ratings (P = 0.03) and for both readers in the venous phase ratings (R1, P = 0.01; R2, P = 0.004). There was no difference in endoleak type characterization between the kiloelectron volt levels. Conclusion Sensitivity for endoleak detection and overall endoleak conspicuity ratings were both higher at 55 keV than 75 keV, favoring the inclusion of a lower-energy monochromatic reconstruction for endoleak surveillance protocols with dual-energy computed tomography.

CT angiography of the renal circulation.

Although catheter angiography remains the accepted gold standard for imaging of the renal vascular system, rapid progress in cross-sectional imaging techniques has caused a paradigm shift in many diagnostic algorithms toward noninvasive techniques such as computed tomographic angiography (CTA). CTAs cross-sectional imaging techniques provide an opportunity for comprehensive renal investigation that would be impossible with angiography alone. While other competing noninvasive technologies such as ultrasound and magnetic resonance angiography can be used successfully in renal imaging, the benefits of CTA are substantial, including high spatial and temporal resolution, widespread availability, implantable device compatibility, and easy technical reproducibility. This article describes the technical considerations relevant to CTA of the renal vascular system, postprocessing algorithms for volumetric data, and numerous specific applications.

Abdominal applications of diffusion-weighted magnetic resonance imaging: Where do we stand

Diffusion-weighted imaging (DWI) is one of the magnetic resonance imaging (MRI) sequences providing qualitative as well as quantitative information at a cellular level. It has been widely used for various applications in the central nervous system. Over the past decade, various extracranial applications of DWI have been increasingly explored, as it may detect changes even before signal alterations or morphological abnormalities become apparent on other pulse sequences. Initial results from abdominal MRI applications are promising, particularly in oncological settings and for the detection of abscesses. The purpose of this article is to describe the clinically relevant basic concepts of DWI, techniques to perform abdominal DWI, its analysis and applications in abdominal visceral MR imaging, in addition to a brief overview of whole body DWI MRI.

Multidetector CT imaging in mesenteric ischemia—pearls and pitfalls

Mesenteric ischemia is a complex and devastating disease which still remains a diagnostic challenge to the clinicians due to non-specific clinical and laboratory findings. Several imaging features have been described with multidetector computed tomography which allows the diagnosis of mesenteric ischemia with high sensitivity and specificity. However, there are imaging features which overlap with other pathologies including benign inflammation and infection. Knowledge of imaging findings in mesenteric ischemia and its potential mimics is important in early and definitive diagnosis.