Yang Shin Park

Usefulness of controlled aliasing in parallel imaging results in higher acceleration in gadoxetic acid-enhanced liver magnetic resonance imaging to clarify the hepatic arterial phase.

PurposeWe aimed to determine whether the controlled aliasing in parallel imaging results in higher acceleration (CAIPIRINHA) technique could improve the image quality of the hepatic arterial phase of gadoxetic acid–enhanced liver magnetic resonance (MR) imaging. Materials and MethodsA total of 320 patients underwent gadoxetic acid–enhanced liver MR imaging: a conventional protocol (a fixed scan delay and 2-mL/s injection) using a standard 3-T MR system (Trio-Tim; Siemens, commercialized since 2005) (group A), an optimized protocol (bolus tracking and 1-mL/s injection) using a standard 3-T MR (group B), an optimized protocol using a new 3-T MR (Skyra; Siemens, commercialized since 2012) (group C), and an optimized protocol with CAIPIRINHA using a new 3-T MR (group D). The image quality of the hepatic arterial phase was graded using a 4-point rating scale from 1 (no artifacts) to 4 points (non–diagnostic images with severe artifacts). The differences in image quality scores among the 4 groups were evaluated. In addition, the detection rates of hypervascular hepatocellular carcinomas among the 4 groups were evaluated. ResultsScores of 4 points were observed in groups A (n = 7), B (n = 5), and C (n = 3) but not in group D. The median image quality score was 2 in groups A and B and 1 in groups C and D. From group A to group D, the median image quality score decreased significantly (P = 0.0001). The median image quality score was significantly lower in group D than in groups A and B (P = 0.0001 and 0.001, respectively), whereas there was no significant difference observed between groups C and D (P = 0.656). The detection rates of hypervascular hepatocellular carcinomas on the hepatic arterial phase were not significantly different among the groups (all P > 0.03), except between groups A and D (P = 0.007). ConclusionsThe CAIPIRINHA technique improved the image quality of hepatic arterial phase imaging with gadoxetic acid, reducing the number of non–diagnostic arterial phase studies.

Solitary fibrous tumor of the genitourinary tract

OBJECTIVE The purpose of this article is to describe the imaging features of solitary fibrous tumors involving the kidney, bladder, adrenal gland, retroperitoneum, or pelvis and other rare locations. CONCLUSION Although clear radiologic differentiation of solitary fibrous tumors from malignancy is not possible, we suggest that familiarity with the manifestations of solitary fibrous tumors can help to avoid unnecessary radical surgery before histopathologic proof of malignancy is obtained.

Using intravoxel incoherent motion (IVIM) MR imaging to predict lipiodol uptake in patients with hepatocellular carcinoma following transcatheter arterial chemoembolization: A preliminary result☆

PURPOSE To assess the usefulness of intravoxel incoherent motion diffusion weighted imaging (IVIM-DWI) for predicting lipiodol uptake in patients with hepatocellular carcinoma (HCC) after transcatheter arterial chemoembolization (TACE). MATERIALS AND METHODS The institutional review board approved this study. 44 HCC patients underwent IVIM-DWI and Gd-EOB-DTPA-enhanced MRI prior to TACE. Using post-TACE CT as a reference standard, each HCC was classified into either lipiodol good uptake (LGU) or poor uptake (LPU) group. Apparent diffusion coefficient (ADC), true diffusion coefficient (D), perfusion coefficient (D*), and perfusion fraction (f) in HCC were calculated. Arterial enhancement ratio (AER) and IVIM parameters were compared between those two groups using the Mann-Whitney U test. RESULTS Of the 51 HCCs, 37 (72.5%) were LGU group and 14 (27.5%) were LPU group. AER of HCC was significantly higher in LGU than LPU (0.99±0.54 and 0.67±0.45; P=.034). ADC, D, and f values were not significantly different (P=.073, .059, and .196, respectively) between these two groups. D* was significantly elevated in LGU than LPU (48.10±15.33 and 26.75±9.55; P=.001). CONCLUSION Both AER derived from contrast enhanced MRI and D* values derived from IVIM-DWI for HCC were significantly higher in LGU than in LPU. These parameters would be helpful for predicting the lipiodol uptake.

Using Gd-EOB-DTPA-enhanced 3-T MRI for the differentiation of infiltrative hepatocellular carcinoma and focal confluent fibrosis in liver cirrhosis.

PURPOSE The purpose of the study was to determine significant imaging features to differentiate between infiltrative hepatocellular carcinoma (HCC) and confluent fibrosis (CF) in liver cirrhosis using Gd-EOB-DTPA-enhanced 3-T magnetic resonance imaging. MATERIAL AND METHODS Nineteen infiltrative HCCs and eight CFs were included. We evaluated the difference in imaging findings and apparent diffusion coefficient (ADC) between the two entities. We compared T2-weighted image (WI) and hepatobiliary phase (HBP) in terms of the clarity of the lesion outer margin. RESULTS Seventeen infiltrative HCCs showed lobulated margin, while focal CFs showed either straight (n=3) or irregular margins (n=5) (P=.001). All infiltrative HCCs had intact or bulging contours, and all focal CFs showed capsular retraction (P=.001). Fourteen infiltrative HCCs and two focal CFs showed arterial enhancement (P=.035). The ADC of infiltrative HCCs was significantly lower than that of CFs (P=.001). Satellite nodules were noted in 10 infiltrative HCCs. In terms of outer margin clarity, infiltrative HCCs showed a more distinct margin on HBP than on T2-WI (P=.005), while these two sequences were not significantly different in focal CFs (P=1.000). CONCLUSION HBP improved the imaging characteristics of infiltrative HCC, allowing it to be distinguished from focal CF. Infiltrative HCC showed lower ADC values than focal CF. Lobular configuration, contour bulging, enhancement pattern, associated satellite nodules and portal vein thrombosis were still found to be highly suggestive MR findings for infiltrative HCC.

Using Low Tube Voltage (80 kVp) Quadruple Phase Liver CT for the Detection of Hepatocellular Carcinoma: Two-Year Experience and Comparison with Gd-EOB-DTPA Enhanced Liver MRI

PURPOSE To validate the diagnostic performance of quadruple phase low tube voltage liver CT through the comparison with Gd-EOB-DTPA enhanced liver MRI for the detection of HCC. MATERIALS AND METHODS Non-obese patients (38 men, eight women) with 68 HCCs underwent quadruple-phase CT at 16 MDCT (using low tube voltage, 80kVp; moderately high tube current, 280mAs) and Gd-EOB-DTPA-enhanced 3T MRI. Three observers independently and randomly reviewed the CT and MR images on a tumor-by-tumor basis. The diagnostic accuracy of these techniques for detecting HCC was assessed using alternative free-response receiver operating characteristic analysis. Sensitivity and positive predictive values were evaluated. The mean effective doses for the low dose CT were also evaluated. RESULTS The areas under the ROC curves were 0.963, 0.959, and 0.941 for low dose CT and 0.981, 0.982, and 0.976 for MRI. Differences in Az of the two techniques for each observer were not statistically significant (P>.05). Differences in sensitivity and positive predictive values between the two techniques for each observer were not also statistically significant: sensitivity (86.8%, 82.4%, 85.3% for CT and 95.6%, 94.1%, 91.2% for MRI) and positive predictive values (92.2%, 90.3%, 89.2% for CT and 92.9%, 92.8%, 92.5% for MRI). Six HCCs (8.8%) in five patients were observed only on hepatobiliary phase of MRI, and all were smaller than 1.5cm. The mean effective dose for CT was approximately 10.2mSv. CONCLUSIONS Quadruple-phase low-dose liver CT (80kVp, 280mAs) had relatively good diagnostic performance for detecting HCC in non-obese patients. Because no significant difference was observed between low-dose CT and MRI, the use of low-dose liver CT can be justified based on its reduced radiation effects.

The short breath-hold technique, controlled aliasing in parallel imaging results in higher acceleration, can be the first step to overcoming a degraded hepatic arterial phase in liver magnetic resonance imaging: A prospective randomized control study

ObjectiveThe aim of this study was to assess whether a short breath-hold technique can improve hepatic arterial phase (HAP) image quality in gadoxetic acid–enhanced magnetic resonance (MR) imaging compared with a conventional long breath-hold technique. Materials and MethodsInstitutional review board approval and patient consent were obtained for this prospective randomized control study. One hundred nineteen patients undergoing gadoxetic acid–enhanced MR imaging were randomly assigned to groups A or B. Group A patients underwent an 18-second long breath-hold MR technique (conventional VIBE [volumetric interpolated breath-hold examination] technique with GRAPPA [generalized autocalibrating partially parallel acquisition]), and group B patients underwent a 13-second short breath-hold MR technique (VIBE technique with CAIPIRINHA [controlled aliasing in parallel imaging results in higher acceleration]). Respiratory-related graphs of the precontrast and HAP were acquired. The breath-hold degree was graded based on the standard deviation (SD) value of respiratory waveforms. Gadoxetic acid–related dyspnea was defined as when the SD value of the HAP was 200 greater than that of the precontrast phase without degraded image quality in the portal and transitional phases (SD value of the HAP − SD value of the precontrast phase). The overall image quality and motion artifacts of the precontrast and HAP images were evaluated. The groups were compared using the Student t or Fisher exact test, as appropriate. ResultsThe incidence of breath-holding difficulty (breath-hold grades 3 and 4) during the HAP was 43.6% (27/62) and 36.8% (21/57) for group A and B, respectively. The SD value during the precontrast phase and the SD value difference between the precontrast and HAP were both significantly higher in group A than in group B (P = 0.047 and P = 0.023, respectively). Gadoxetic acid–related dyspnea was seen in 19.4% (12/62) of group A and 7.0% (4/57) of group B. Group B showed better precontrast and HAP image quality than group A (P < 0.001). Degraded HAP (overall image quality ≥4) was observed in 9.7% (6/62) and 3.5% (2/57) of group A and B, respectively. ConclusionsThe short breath-hold MR technique, CAIPIRINHA, showed better HAP image quality with less degraded HAP and a lower incidence of breath-hold difficulty and gadoxetic acid–related dyspnea than the conventional long breath-hold technique.

Hepatic Arterial Phase in Gadoxetic Acid-Enhanced Liver Magnetic Resonance Imaging: Analysis of Respiratory Patterns and Their Effect on Image Quality.

ObjectiveThe aims of this study were to objectively evaluate patient respiration and breathing change after contrast injection and to assess its potential impact on image quality for the hepatic arterial phase in gadoxetic acid–enhanced magnetic resonance imaging. Materials and MethodsThis retrospective study was approved by the institutional review board, and the requirement for informed consent was waived. One hundred fifty-four patients underwent gadoxetic acid–enhanced liver magnetic resonance imaging with a 13-second breath-hold hepatic arterial phase. During the acquisition of precontrast and hepatic arterial phases, the respiratory motion signal was acquired and graded on a 4-point scale based on the SD of the respiratory waveform, with the highest grade indicating the worst breath-hold. Breath-holding grades 3 and 4 for the hepatic arterial phases were considered as breath-holding difficulty during the hepatic arterial phase. Gadoxetic acid–related dyspnea was defined as when the SD value of respiratory waveform during the hepatic arterial phase was 200 greater than that of the precontrast image. Then, the precontrast and hepatic arterial phase images were evaluated with respect to overall image quality and motion artifact using a 5-point scale, with the highest score indicating the worst image quality. In the hepatic arterial phase, the correlation between breath-holding degree and image quality parameters was evaluated using Pearson correlation. The differences in mean image quality scores between patients with and without gadoxetic acid–related dyspnea were evaluated using Student t test. ResultsBased on the analysis of the respiratory waveforms, the incidence of breath-holding difficulty during the hepatic arterial phase was 23.4% (33/154), and the incidence of gadoxetic acid–related dyspnea was 6.5% (10/154). By image analysis, the incidence of a degraded hepatic arterial phase (overall image quality score ≥4) was 5.2% (8/154). During the hepatic arterial phase, the breath-holding degree correlated with overall image quality and motion artifacts (r = 0.564 and 0.578, respectively). Patients with gadoxetic acid–related dyspnea showed significantly worse image qualities of the hepatic arterial phase than patients without gadoxetic acid–related dyspnea (all, P < 0.001), although image qualities for the precontrast image were not statistically significant between the 2 groups (all, P > 0.05). ConclusionsThe objective analysis of respiratory patterns during a breath-hold is feasible and useful for evaluating gadoxetic acid–related dyspnea and its effect on image quality analysis.

Differentiation of hepatocellular carcinoma from its various mimickers in liver magnetic resonance imaging: What are the tips when using hepatocyte-specific agents?

Hepatocellular carcinoma is the most common primary hepatic malignant tumor. With widespread use of liver imaging, various cirrhosis-related nodules are frequently detected in patients with chronic liver disease, while diverse hypervascular hepatic lesions are incidentally detected but undiagnosed on dynamic computed tomography and magnetic resonance imaging (MRI). However, use of hepatocyte-specific MR contrast agents with combined perfusion and hepatocyte-selective properties have improved diagnostic performance in detection and characterization of focal liver lesions. Meanwhile, the enhancement patterns observed during dynamic phases using hepatocyte-specific agents may be different from those observed during MRI using conventional extracellular fluid agents, leading to confusion in diagnosis. Therefore, we discuss useful tips for the differentiation of hepatocellular carcinoma from similar lesions in patients with and without chronic liver disease using liver MRI with hepatocyte-specific agents.

Using intravoxel incoherent motion MR imaging to evaluate cortical defects in the first episode of upper urinary tract infections: Preliminary results

To compare intravoxel incoherent motion diffusion weight imaging IVIM‐DWI MRI with DMSA for the evaluation of cortical defect in pediatric upper urinary tract infection (UTI) patients.

Effect of Gd-EOB-DTPA on hepatic fat quantification using high-speed T2-corrected multi-echo acquisition in 1H MR spectroscopy

PURPOSE To determine whether gadolinium ethoxybenzyldiethylenetriaminepentaacetic acid (Gd-EOB-DTPA) administration affects hepatic fat quantification by magnetic resonance spectroscopy (MRS) using the fast breath-hold high-speed T2-corrected multiecho (HISTO) technique. MATERIALS AND METHODS Seventy-six patients underwent Gd-EOB-DTPA-enhanced liver MR and 15sec breath-hold HISTO MRS (4 times), twice before and twice after Gd-EOB-DTPA administration. Two consecutive MRSs were performed immediately before the dynamic study. Post-contrast MRS was performed twice continuously, approximately 15min after contrast injection, prior to obtaining 20-min hepatobiliary phase images. We used paired t-test and intraclass correlation coefficient (ICC) to evaluate the variability of the mean fat fraction (FF) on pre-contrast MRS and post-contrast MRS and the effect of the contrast agent on the mean FF. RESULTS The mean FFs were not significantly different between pre-contrast MRS and post-contrast MRS (6.50%±6.54 versus 6.70%±6.61, P=0.15). The ICC of FF calculation between pre- and post-contrast MRS was 0.984. The ICCs for the FF magnitude between pre- and post-contrast MRS were 0.452, 0.771, and 0.995 for FF <5%, FF 5-10%, and FF ≥10%, respectively. CONCLUSION Gd-EOB-DTPA does not appear to influence hepatic fat quantification, especially for patients with hepatic steatosis.