Multimodality Imaging of a Mass Arising from a Cor Triatriatum Sinister Membrane.

Cor triatriatum sinister is a rare entity characterized by a membrane within the left atrium and posterior to the atrial appendage. This defect may cause obstructive symptoms analogous to mitral stenosis. The authors present a case of an incidentally detected enhancing mass originating from a cor triatriatum sinister membrane, with imaging characteristics most suggestive of myxoma. Keywords: MR Imaging, Cardiac, Left Atrium, Congenital, CT Angiography, Echocardiography Supplemental material is available for this article.

Non-Contrast Magnetic Resonance Angiography: Techniques, Principles, and Applications.

Several non-contrast magnetic resonance angiography (MRA) techniques have been developed, providing an attractive alternative to contrast-enhanced MRA and a radiation-free alternative to computed tomography (CT) CT angiography. This review describes the physical principles, limitations, and clinical applications of bright-blood (BB) non-contrast MRA techniques. The principles of BB MRA techniques can be broadly divided into (a) flow-independent MRA, (b) blood-inflow-based MRA, (c) cardiac phase dependent, flow-based MRA, (d) velocity sensitive MRA, and (e) arterial spin-labeling MRA. The review also includes emerging multi-contrast MRA techniques that provide simultaneous BB and black-blood images for combined luminal and vessel wall evaluation.

Multimodality imaging evaluation of arteriovenous fistulas and grafts: a clinical practice review.

Arteriovenous fistulas (AVFs) and grafts (AVGs) are the preferred forms of vascular access for hemodialysis in patients with severe renal dysfunction. Multimodality imaging plays an important role in the pre-procedural evaluation of these patients. Ultrasound is often used for pre-procedural vascular mapping in preparation for the creation of an AVF or AVG. Pre-procedural mapping includes a comprehensive evaluation of the arterial and venous vasculature including evaluation of vessel diameter, stenosis, course, presence of collateral veins, wall thickness and wall abnormalities. Computed tomography (CT), magnetic resonance imaging (MRI) or catheter angiography are used when sonography is not available or when further characterization of sonographic abnormalities is required. Following the procedure, routine surveillance imaging is not recommended. If there are any clinical concerns or if physical examination is inconclusive, further evaluation with ultrasound is warranted. Ultrasound allows for assessment of vascular access site maturation by evaluating the time-averaged blood flow and helping characterize the outflow vein in the case of an AVF. CT and MRI can play a complementary role to ultrasound. Vascular access site complications include non-maturation, aneurysm, pseudoaneurysm, thrombosis, stenosis, steal phenomena or occlusion typically of the outflow vein, infection, bleeding and rarely angiosarcoma. In this article, we review the role of multimodality imaging in the pre- and post-procedural evaluation of patients with AVF and AVG. Additionally, novel technologies of vascular access site creation using endovascular techniques and upcoming non-invasive imaging techniques for evaluation of AVFs and AVGs are discussed.

Magnetic Resonance Safety: Pregnancy and Lactation.

MRI is a powerful diagnostic tool with excellent soft tissue contrast that uses nonionizing radiation. These advantages make MRI an appealing modality for imaging the pregnant patient; however, specific risks inherent to the magnetic resonance environment must be considered. MRI may be performed without and/or with intravenous contrast, which adds further fetal considerations. The risks of MRI with and without intravenous contrast are reviewed as they pertain to the pregnant or lactating patient and to the fetus and nursing infant. Relevant issues for gadolinium-based contrast agents and ultrasmall paramagnetic iron oxide particles are reviewed.

Müllerian duct anomalies coincident with endometriosis: a review.

The association between obstructed müllerian duct anomalies and endometriosis has been well established and the pathogenesis is attributed to the theory of retrograde menstruation. However, this relationship with endometriosis is less clear in women with unobstructed müllerian duct anomalies and in those with rudimentary uterine structures that lack functioning endometrial tissue. This article reviews the embryology, genetics, pathophysiology, and American Society for Reproductive Medicine (ASRM) classification for müllerian duct anomalies together with the genetics and pathophysiology of endometriosis to provide a framework for understanding the complex relationship between these two entities. Available published data examining the coexistence of endometriosis in relationship to müllerian duct anomalies, including studies that stratify this relationship according to specific classes of anomalies, are reviewed and organized. Awareness of the increased prevalence of endometriosis among patients with uterine anomalies, particularly those with outflow obstruction, may facilitate early diagnosis of endometriosis and subsequent intervention, with the potential to reverse disease symptoms and arrest disease progression.

Imaging Appearance and Nonsurgical Management of Pelvic Venous Congestion Syndrome.

Pelvic venous congestion syndrome (PVCS) is a challenging and complex cause of chronic pelvic pain in female patients. PVCS due to incompetent vein valves is the combination of gonadal vein reflux and pelvic venous engorgement in patients with chronic pelvic pain without other causes. However, pelvic venous engorgement and gonadal vein reflux can be seen in patients without pelvic pain, which makes obtaining a detailed history and physical examination important for workup and diagnosis. The underlying cause of PVCS may be incompetent gonadal vein valves or structural causes such as left renal vein compression with an incompetent gonadal vein valve (nutcracker syndrome) or iliac vein compression (May-Thurner configuration) with reflux into the ipsilateral internal iliac vein. Venography is considered the criterion standard for imaging diagnosis; however, more recently, US and MRI have been shown to provide adequate accuracy for diagnosis. Noninvasive imaging studies aid in the diagnosis of PVCS and also aid in pretreatment planning. When PVCS is caused by incompetent gonadal vein valves, treatment typically is performed by means of embolization via a minimally invasive catheter with excellent technical and clinical success rates. When PVCS is caused by venous obstruction, the obstruction must be treated first before gonadal vein embolization and sclerotherapy are considered. ©RSNA, 2019 Online supplemental material is available for this article.

Non-alcoholic fatty liver disease-associated hepatocellular carcinoma: effect of hepatic steatosis on major hepatocellular carcinoma features at MRI.

OBJECTIVE:: To evaluate the effect of hepatic steatosis on LI-RADS® major features at MRI in patients with non-alcoholic fatty liver disease (NAFLD)-associated hepatocellular carcinoma (HCC). METHODS:: HCC and liver parenchyma features at MRI from 48 consecutive patients with NAFLD and histology proven HCC (mean ± SD; 4.5 ± 3.4 cm) were independently reviewed by three radiologists. Inter-rater agreement was determined by prevalence/bias-adjusted kappa. Hepatic fat signal fraction (FS%) was independently calculated. HCC features were compared by FS% at MRI using logistic regression analysis and histologic steatosis grade using Cochran-Armitage test for trend, stratified by cirrhotic liver morphology or histologic fibrosis stage. Receiver operating characteristic curves were generated to determine the sensitivity and specificity for major HCC features by FS%. RESULTS:: Major HCC features included arterial phase hyperenhancement (APHE) in 45 (93%), portal venous phase washout (PVWO) in 30 (63%), delayed phase washout (DPWO) in 38 (79%) and enhancing "capsule" in 34 (71%). Cirrhotic morphology was present in 22 (46%). Inter-rater agreement was 0.75 for APHE, 0.42-0.58 for PVWO, 0.58-0.71 for DPWO and 0.38-0.67 for enhancing "capsule". There was an 18%, 14% and 22% increase in the odds of absent PVWO, DPWO and capsule appearance for every 1% increase in hepatic FS% in patients with non-cirrhotic liver morphology (p = 0.011, 0.040 and 0.029, respectively). Hepatic FS% ≥ 14.8% had a sensitivity and specificity of 64 and 100% for absent PVWO and 71 and 90% for absent DPWO in patients with non-cirrhotic liver morphology. CONCLUSION:: Absent washout and capsule appearance are associated with increasing hepatic steatosis in patients with non-cirrhotic, NAFLD-associated HCC. ADVANCES IN KNOWLEDGE:: In patients with non-cirrhotic, non-alcoholic fatty liver disease (NAFLD)-associated hepatocellular carcinoma (HCC), absent HCC washout and capsule appearance are associated with increasing hepatic steatosis, thereby potentially impacting the noninvasive imaging diagnosis of HCC in these patients. Lack of washout or capsule appearance in steatotic livers at MRI may require alternative criteria for the diagnosis of HCC in patients with non-cirrhotic NAFLD.

MR elastography in primary sclerosing cholangitis: correlating liver stiffness with bile duct strictures and parenchymal changes.

AIM: To determine correlation of liver stiffness measured by MR Elastography (MRE) with biliary abnormalities on MR Cholangiopancreatography (MRCP) and MRI parenchymal features in patients with primary sclerosing cholangitis (PSC). METHODS: Fifty-five patients with PSC who underwent MRI of the liver with MRCP and MRE were retrospectively evaluated. Two board-certified abdominal radiologists in agreement reviewed the MRI, MRCP, and MRE images. The biliary tree was evaluated for stricture, dilatation, wall enhancement, and thickening at segmental duct, right main duct, left main duct, and common bile duct levels. Liver parenchyma features including signal intensity on T2W and DWI, and hyperenhancement in arterial, portal venous, and delayed phase were evaluated in nine Couinaud liver segments. Atrophy or hypertrophy of segments, cirrhotic morphology, varices, and splenomegaly were scored as present or absent. Regions of interest were placed in each of the nine segments on stiffness maps wherever available and liver stiffness (LS) was recorded. Mean segmental LS, right lobar (V-VIII), left lobar (I-III, and IVA, IVB), and global LS (average of all segments) were calculated. Spearman rank correlation analysis was performed for significant correlation. Features with significant correlation were then analyzed for significant differences in mean LS. Multiple regression analysis of MRI and MRCP features was performed for significant correlation with elevated LS. RESULTS: A total of 439/495 segments were evaluated and 56 segments not included in MRE slices were excluded for correlation analysis. Mean segmental LS correlated with the presence of strictures (r = 0.18, p < 0.001), T2W hyperintensity (r = 0.38, p < 0.001), DWI hyperintensity (r = 0.30, p < 0.001), and hyperenhancement of segment in all three phases. Mean LS of atrophic and hypertrophic segments were significantly higher than normal segments (7.07 ± 3.6 and 6.67 ± 3.26 vs. 5.1 ± 3.6 kPa, p < 0.001). In multiple regression analysis, only the presence of segmental strictures (p < 0.001), T2W hyperintensity (p = 0.01), and segmental hypertrophy (p < 0.001) were significantly associated with elevated segmental LS. Only left ductal stricture correlated with left lobe LS (r = 0.41, p = 0.018). Global LS correlated significantly with CBD stricture (r = 0.31, p = 0.02), number of segmental strictures (r = 0.28, p = 0.04), splenomegaly (r = 0.56, p < 0.001), and varices (r = 0.58, p < 0.001). CONCLUSION: In PSC, there is low but positive correlation between segmental LS and segmental duct strictures. Segments with increased LS show T2 hyperintensity, DWI hyperintensity, and post-contrast hyperenhancement. Global liver stiffness shows a moderate correlation with number of segmental strictures and significantly correlates with spleen stiffness, splenomegaly, and varices.

Standardized Approach for ROI-Based Measurements of Proton Density Fat Fraction and R2* in the Liver.

OBJECTIVE: The purpose of this study was to evaluate the reproducibility (interreviewer agreement) and repeatability (intrareviewer agreement) of ROI sampling strategies to measure chemical shift-encoded (CSE) MRI-based liver proton density fat fraction (PDFF) and R2* (1 / T2*). A secondary purpose was to standardize ROI-based liver PDFF and R2* measurements by providing a compromise between measurement reproducibility and repeatability and time burden for image analysts. MATERIALS AND METHODS: CSE data from two cohorts were retrospectively analyzed. Cohort A included 53 patients referred for abdominal MRI and healthy subjects recruited for a comparison study of CT and MRI. Cohort B included 37 patients with suspected liver iron overload. Three reviewers measured liver PDFF and R2* using previously reported ROI sampling strategies. Inter- and intrareviewer agreement of liver PDFF and R2* were evaluated using Bland-Altman analysis. RESULTS: Averaging largest-fit ROIs over the nine Couinaud segments resulted in the narrowest limits of agreement (LOA) for liver PDFF and R2* measurements in both cohorts. For PDFF, interreviewer agreement had mean LOA of ± 0.8% for cohort A and ± 1.7% for cohort B. Intrareviewer agreement was ± 0.5% for cohort A and ± 0.9% for cohort B. For R2* interre-viewer agreement had mean LOA of ± 3.0 s-1 for cohort A and ± 17.9 s-1 for cohort B. Intrare-viewer agreement was ± 2.6 s-1 for cohort A and ± 14.6 s-1 for cohort B. This approach was the most time-burdensome, requiring a mean ± SD of 149.7 ± 8.6 s per dataset. CONCLUSION: For improved reproducibility and repeatability of liver PDFF and R2* measurements, clinicians and researchers should sample as much area of the liver as possible using multiple large ROIs.

Combined gadoxetic acid and gadofosveset enhanced liver MRI for detection and characterization of liver metastases.

PURPOSE: To compare gadoxetic acid alone and combined gadoxetic acid/gadofosveset trisodium-enhanced liver MRI for detection of metastases and differentiation of metastases from haemangiomas. METHODS: Ninety-one patients underwent gadoxetic acid-enhanced liver MRI before and after additional injection of gadofosveset. First, two readers retrospectively identified metastases on gadoxetic acid alone enhanced delayed hepatobiliary phase T1-weighted images together with all other MR images (dynamic images, T2-weighted images, diffusion-weighted images). Second, readers assessed additional T1-weighted images obtained after administration of gadofosveset trisodium. For both interpretations, readers rated lesion conspicuity and confidence in differentiating metastases from haemangiomas. Results were compared using alternative free-response receiver-operating characteristic (AFROC) and conventional ROC methods. Histology and follow-up served as reference standard. RESULTS: There were 145 metastases and 16 haemangiomas. Both readers detected more metastases using combined gadoxetic acid/gadofosveset (reader 1 = 130; reader 2 = 124) compared to gadoxetic acid alone (reader 1 = 104; reader 2 = 103). Sensitivity of combined gadoxetic acid/gadofosveset (reader 1 = 90 %; reader 2 = 86 %) was higher than that of gadoxetic acid alone (reader 1 = 72 %; reader 2 = 71 %, both P < 0.01). AFROC-AUC was higher for the combined technique (0.92 vs. 0.86, P < 0.001). Sensitivity for correct differentiation of metastases from haemangiomas was higher for the combined technique (reader 1 = 98 %; reader 2 = 99 % vs. reader 1 = 86 %; reader 2 = 91 %, both P < 0.01). ROC-AUC was significantly higher for the combined technique (reader 1 = 1.00; reader 2 = 1.00 vs. reader 1 = 0.87; reader 2 = 0.92, both P < 0.01). CONCLUSION: Combined gadoxetic acid/gadofosveset-enhanced MRI improves detection and characterization of liver metastases compared to gadoxetic acid alone. KEY POINTS: • Combined gadoxetic acid and gadofosveset-enhanced liver MRI significantly improves detection of metastases. • The combined enhancement technique improves the accuracy to differentiate metastases from haemangiomas. • Prospective studies need to determine the clinical impact of the combined technique.

An Investigation of Transient Severe Motion Related to Gadoxetic Acid-enhanced MR Imaging.

PURPOSE: To investigate the cause of imaging artifacts observed during gadoxetic acid-enhanced arterial phase imaging of the liver. MATERIALS AND METHODS: This HIPAA-compliant study was approved by the institutional review board. Data were collected prospectively at two sites (site A, United States; site B, Japan) from patients undergoing contrast material-enhanced MR imaging with gadoxetic acid (site A, n = 154, dose = 0.05 mmol/kg; site B, n = 130, 0.025 mmol/kg) or gadobenate dimeglumine (only site A, n = 1666) from January 2014 to September 2014 at site A and from November 2014 to January 2015 at site B. Detailed comparisons between the two agents were made in the patients with dynamic liver acquisitions (n = 372) and age-, sex-, and baseline oxygen saturation (Spo2)-matched pairs (n = 130) at site A. Acquired data included self-reported dyspnea after contrast agent injection, Spo2, and breath-hold fidelity monitored with respiratory bellows. RESULTS: Self-reported dyspnea was more frequent with gadoxetic acid than with gadobenate dimeglumine (site A, 6.5% [10 of 154] vs 0.1% [two of 1666], P < .001; site B, 1.5% [two of 130]). In the matched-pair comparison, gadoxetic acid, as compared with gadobenate dimeglumine, had higher breath-hold failure rates (site A, 34.6% [45 of 130] vs 11.7% [15 of 130], P < .0001; site B, 16.2% [21 of 130]) and more severe artifacts during arterial phase imaging (site A, 7.7% [10 of 130] vs 0% [none of 130], P < .001; site B, 2.3% [three of 130]). Severe imaging artifacts in patients who received gadoxetic acid were significantly associated with male sex (P = .023), body mass index (P = .021), and breath-hold failure (P < .001) but not with dyspnea or Spo2 decrease. CONCLUSION: Severe motion-related artifacts in the arterial phase of gadoxetic acid-enhanced liver MR imaging are associated with breath-hold failure but not with subjective feelings of dyspnea or a substantial decrease in blood Spo2. Subjective feelings of dyspnea are not necessarily associated with imaging artifacts. The phenomenon, albeit at a lower rate, was confirmed at a second site in Japan.

Multiple overlapping k-space junctions for investigating translating objects (MOJITO).

It is a well-known property in Fourier transform magnetic resonance imaging (MRI) that rigid body translational motion in image space results in linear phase accumulation in k -space. This work describes Multiple Overlapping k-space Junctions for Investigating Translating Objects (MOJITO), a correction scheme based on phase differences at trajectory intersections caused by 2-D alterations in the position of an object during MR imaging. The algorithm allows both detection and correction of motion artifacts caused by 2-D rigid body translational motion. Although similar in concept to navigator echoes, MOJITO does not require a repeating path through k-space, uses k-space data from a broader region of k -space, and uses the repeated data in image reconstruction; this provides the potential for a highly efficient self-navigating motion correction method. Here, the concept and theoretical basis of MOJITO is demonstrated using the continuous sampling BOWTIE trajectory in simulation and MR experiments. This particular trajectory is selected since it is well suited for such an algorithm due to numerous trajectory intersections. Specifically, the validity of the technique in the presence of noise and off-resonance effects is demonstrated through simulation.

Analysis of signal-to-noise behavior in Cartesian continuous sampling sequences: predictions and experimental validation of opportunities for improved image SNR.

Image signal-to-noise ratio (SNR) limits many MRI applications. Here we propose a method to improve SNR based on continuous sampling (CS) during each TR without significant increases in acquisition time. The general concept of CS is defined here as sampling the NMR signal immediately after slice excitation including ramp times, both the dephase and rephase lobes, the phase-encoding (PE) gradient application, and the slice refocusing gradient. This study analyzes several cases of CS and demonstrates a specific case where sampling occurs during an isolated and balanced readout gradient in order to increase SNR in a rectilinear Cartesian sequence without significantly increasing overall acquisition time. The noise correlation consequences of rectilinear CS are mathematically derived and proven through simulation. The SNR improvement of up to approximately 40% measured in both phantom and asymptomatic human volunteer images is comparable to theoretical prediction of increased SNR proportional to the increase in the square root of the sampling time.