Gadoxetic acid disodium-enhanced hepatocyte phase MRI: can increasing the flip angle improve focal liver lesion detection?

Gadoxetic acid-enhanced MR imaging for hepatocellular carcinoma: molecular and genetic background

Gadoxetic acid-enhanced magnetic resonance imaging (MRI) plays important roles in diagnosis of hepatic lesions because of its superiority in the detectability of small lesions, its differentiation ability, and its utility for the early diagnosis of hepatocellular carcinoma (HCC). In HCC, expression of organic anion transporting polypeptide (OATP) 1B3 correlates with the enhancement ratio in the hepatobiliary phase. Gadoxetic acid-enhanced MRI, an indirect molecular imaging method, reflects OATP1B3 expression in HCC. OATP1B3 expression gradually decreases from the dysplastic nodule stage to advanced HCC. Decreased expression is a sensitive marker of multistep hepatocarcinogenesis, especially in the early stages. Hypervascular HCCs commonly show hypointensity in the hepatobiliary phase corresponding to a decrease in OATP1B3; however, approximately 10% of HCCs show hyperintensity due to OATP1B3 overexpression. This hyperintense HCC shows less aggressive biological features and has a better prognosis than hypointense HCC. Hyperintense HCC can be classified into a genetic subtype of HCC with a mature hepatocyte-like molecular expression. OATP1B3 expression and the less aggressive nature of hyperintense HCC are regulated by the molecular interaction of β-catenin signaling and hepatocyte nuclear factor 4α, a tumor suppressor factor. Gadoxetic acid-enhanced MR imaging has the potential to be an imaging biomarker for HCC. KEY POINTS: • The hepatobiliary phase is a sensitive indirect indicator of organic anion transporting polypeptide1B3 (OATP1B3) expression in hepatocellular carcinoma (HCC). • The OATP1B3 expression, namely, enhancement in the hepatobiliary phase, decreases from the very early stage of hepatocarcinogenesis, contributing to early diagnosis of HCC. • HCC showing hyperintensity on the hepatobiliary phase is a peculiar genetic subtype of HCC with OATP1B3 overexpression, a less aggressive nature, and mature hepatocyte-like molecular/genetic features.

Sirlin C, Song B, Taouli B, Yoshimitsu K, Koh DM. Consensus report from the 8th International Forum for Liver Magnetic Resonance Imaging

OBJECTIVES

The 8th International Forum for Liver Magnetic Resonance Imaging (MRI), held in Basel, Switzerland, in October 2017, brought together clinical and academic radiologists from around the world to discuss developments in and reach consensus on key issues in the field of gadoxetic acid-enhanced liver MRI since the previous Forum held in 2013.

METHODS

Two main themes in liver MRI were considered in detail at the Forum: the use of gadoxetic acid for contrast-enhanced MRI in patients with liver cirrhosis and the technical performance of gadoxetic acid-enhanced liver MRI, both opportunities and challenges. This article summarises the expert presentations and the delegate voting on consensus statements discussed at the Forum.

RESULTS AND CONCLUSIONS

It was concluded that gadoxetic acid-enhanced MRI has higher sensitivity for the diagnosis of hepatocellular carcinoma (HCC), when compared with multidetector CT, by utilising features of hyperenhancement in the arterial phase and hypointensity in the hepatobiliary phase (HBP). Recent HCC management guidelines recognise an increasing role for gadoxetic acid-enhanced MRI in early diagnosis and monitoring post-resection. Additional research is needed to define the role of HBP in predicting microvascular invasion, to better define washout during the transitional phase in gadoxetic acid-enhanced MRI for HCC diagnosis, and to reduce the artefacts encountered in the arterial phase. Technical developments are being directed to shortening the MRI protocol for reducing time and patient discomfort and toward utilising faster imaging and non-Cartesian free-breathing approaches that have the potential to improve multiphasic dynamic imaging.

KEY POINTS

• Gadoxetic acid-enhanced MRI provides higher diagnostic sensitivity than CT for diagnosing HCC. • Gadoxetic acid-enhanced MRI has roles in early-HCC diagnosis and monitoring post-resection response. • Faster imaging and free-breathing approaches have potential to improve multiphasic dynamic imaging.

Combined gadoxetic acid and gadobenate dimeglumine enhanced liver MRI: a parameter optimization study

PURPOSE

To demonstrate the feasibility of combined delayed-phase gadoxetic acid (GA) and gadobenate dimeglumine (GD) enhanced liver MRI for improved detection of liver metastases, and to optimize contrast agent dose, timing, and flip angle (FA).

METHODS

Fourteen healthy volunteers underwent liver MRI at 3.0T at two visits during which they received two consecutive injections: 1. GA (Visit 1 = 0.025 mmol/kg; Visit 2 = 0.05 mmol/kg) and 2. GD (both visits = 0.1 mmol/kg) 20 min after GA administration. Two sub-studies were performed: Experiment-1 Eight subjects underwent multi-phase breath-held 3D-fat-saturated T1-weighted spoiled gradient echo (SGRE) imaging to determine the optimal imaging window for the combined GA + GD protocol to create a homogeneously hyperintense liver and vasculature ("plain-white-liver") with maximum contrast to muscle which served as a surrogate for metastatic lesions in both experiments. Experiment-2 Six subjects underwent breath-held 3D-fat-saturated T1-weighted SGRE imaging at three different FA to determine the optimal FA for best image contrast. Signal-to-noise ratio (SNR) and contrast-to-noise ratio (CNR) were evaluated.

RESULTS

Experiment-1 The combined GA + GD protocol created a homogeneously hyperintense liver and vasculature with maximum CNR liver/muscle at approximately 60-120 s after automatic GD-bolus detection. Experiment-2 Flip angles between 25° and 35° at a dose of 0.025 mmol/kg GA provided the best combination that minimized liver/vasculature CNR, while maximizing liver/muscle CNR. CNR performance to achieve a "plain-white-liver" was superior with 0.025 mmol/kg GA compared to 0.05 mmol/kg.

CONCLUSION

Combined GA + GD enhanced T1-weighted MRI is feasible to achieve a homogeneously "plain-white-liver". Future studies need to confirm that this protocol can improve sensitivity of liver lesion detection in patients with metastatic liver disease.

Quantitative Evaluation of Display Contrast of Gd-EOB-DTPA-Enhanced Magnetic Resonance Images: Effects of the Flip Angle and Grayscale Gamma Value

INTRODUCTION

Display contrast can be changed nonlinearly by manipulating the gamma value of the grayscale. We investigated the contrast of the hepatobiliary-phase images acquired with different flip angles (FAs) and displayed with different gamma values in Gd-EOB-DTPA-enhanced magnetic resonance imaging.

MATERIAL AND METHODS

Twenty patients with liver tumors were studied. Hepatobiliary-phase images were acquired at low (12°) and high (30°) FAs. Low-FA images were converted to simulate images displayed with different gamma values, using ImageJ software. To assess image contrast, the liver-to-muscle signal ratio (LMR), liver-to-spleen signal ratio (LSR), contrast ratio (CR), liver signal-to-noise ratio (SNR), and contrast-to-noise ratio (CNR) were calculated.

RESULTS

The LMR, LSR, and CR were higher in the high-FA images than in the low-FA original images. Although the SNR was lower in the high-FA images, indicating an increase in noise, the CNR was higher. Raising the gamma value increased the LMR, LSR, and CR, notably decreased the SNR, and slightly decreased the CNR.

CONCLUSION

Increasing the FA enhanced image contrast, supporting its usefulness for improving the delineation of focal liver lesions. Although the associated increase in noise may be problematic, raising the grayscale gamma value enhances the display contrast of low-FA images.

Gadoxetic Acid-Enhanced Hepatobiliary-Phase Magnetic Resonance Imaging for Delineation of Focal Nodular Hyperplasia: Superiority of High-Flip-Angle Imaging

OBJECTIVE

The aim of this study was to investigate whether hepatobiliary-phase (HBP) flip-angle (FA) increase to 25° improves conspicuity of focal nodular hyperplasia (FNH) and enables HBP delay reduction.

METHODS

This was a retrospective study of 23 patients with 46 FNHs. In each patient, HBP was performed with reduced-delay high FA (early/high), standard-delay high FA (late/high), and standard-delay standard FA (standard). Relative enhancement of liver and FNH periphery, FNH periphery-to-liver contrast ratio, and FNH periphery-to-central scar contrast ratio were compared between each HBP.

RESULTS

Early/high, late/high, and standard HBPs were performed after 13.00 ± 2.12, 19.12 ± 3.10, and 19.68 ± 3.22 minutes, respectively. Liver and FNH periphery relative enhancement, FNH periphery-to-liver contrast ratio, and FNH periphery-to-central scar contrast ratio were higher for early/high and late/high than for standard HBP (P < 0.001 to P = 0.0048).

CONCLUSIONS

Increasing FA to 25° improves delineation of FNHs in HBP. Combining FA increase with delay reduction is superior to standard HBP and is sufficient for FNH characterization.

Contributions of Magnetic Resonance Imaging to Gastroenterological Practice: MRIs for GIs

MRI has transformed from the theoretical, investigative realm to mainstream clinical medicine over the past four decades and has become a core component of the diagnostic toolbox in the practice of gastroenterology (GI). Its success is attributable to exquisite contrast and the ability to isolate specific proton species through the use of different pulse sequences (i.e., T1-weighted, T2-weighted, diffusion-weighted) and exploiting extracellular and hepatobiliary contrast agents. Consequently, MRI has gained preeminence in various GI clinical applications: liver and pancreatic lesion evaluation and detection, liver transplantation evaluation, pancreatitis evaluation, Crohn's disease evaluation (using MR enterography) rectal cancer staging and perianal fistula evaluation. MR elastography, in concert with technical innovations allowing for fat and iron quantification, provides a noninvasive approach, or "MRI virtual liver biopsy" for diagnosis and management of chronic liver diseases. In the future, the arrival of ultra-high-field MR systems (7 T) and the ability to perform magnetic resonance spectroscopy in the abdomen promise even greater diagnostic insight into chronic liver disease.

Transient severe motion during arterial phase in patients with Gadoxetic acid administration: Can a five hepatic arterial subphases technique mitigate the artifact?

Gadoxetic acid (Gd-EOB-DTPA) is a hepatocyte-specific magnetic resonance (MR) contrast agent, which has been increasingly used in recent years. However, it has been reported that Gd-EOB-DTPA related transient severe motion (TSM) is sometimes observed during the hepatic arterial phase of MR imaging, which may influence image quality. Since the hepatic arterial phase of contrast enhancement is used for the diagnosis of hepatocellular carcinoma, it is crucial to obtain a decent arterial phase imaging. The present study analyzed motion in patients receiving Gd-EOB-DTPA, comparing a single arterial phase acquisition to a five arterial phase acquisition to determine whether the multiphase acquisition was able to alleviate the TSM-related hepatic arterial MR imaging artifact. It was demonstrated that the single-phase acquisition failed to provide adequate diagnostic image quality in patients with TSM, whereas the multiphase arterial acquisition provided acceptable image quality in 20/22 (90.9%) patients with TSM. In conclusion, the results of the present study demonstrated that multiphase arterial acquisition is superior to single-phase arterial acquisition, mitigating arterial MR imaging artifacts caused by TSM after the administration of Gd-EOB-DTPA.

Simultaneous acquisition of high-contrast and quantitative liver T1 images using 3D phase-sensitive inversion recovery: a feasibility study

Background Tumor-to-liver contrast is low in images of chronically diseased livers because gadolinium-based hepatocyte-specific contrast agents (Gd-EOB-DTPA) accumulate less to hepatocytes. Purpose To determine whether phase-sensitive inversion recovery (PSIR) could improve the T₁ contrasts of Gd-based contrast agents and liver parenchyma and simultaneously provide accurate T₁ values for abdominal organs. Material and Methods The image contrasts of phantoms with different Gd concentrations that were obtained using PSIR were compared to conventional turbo field echo (TFE) results. T₁ value was estimated using PSIR by performing iterations to investigate the two IR magnetization evolutions. The estimated T₁ values were validated using IR-spin echo (IR-SE) and Look-Locker (L-L) sequences. In an in vivo study, the liver-to-spleen and liver-to-muscle contrasts of the PSIR and TFE images of seven volunteers were compared, as were the T₁ values of liver parenchyma, spleen, and muscle obtained using PSIR and L-L sequences. Results The PSIR images showed T₁ contrasts higher than those in the TFE results. The PSIR and IR-SE T₁ values were linearly correlated. Additionally, the R₁ estimated using PSIR were correlated with those measured using IR-SE and L-L. In the in vivo study, the liver-to-spleen and liver-to-muscle contrasts of PSIR were significantly higher than those obtained using TFE. T₁ values of abdominal organs obtained using PSIR and L-L were clearly correlated. Conclusion PSIR may be capable of improving liver image T₁ contrasts when Gd-based contrast agents are employed and simultaneously yielding accurate T₁ values of abdominal organs.

Feasibility of 10-Minute Delayed Hepatocyte Phase Imaging Using a 30° Flip Angle in Gd-EOB-DTPA-Enhanced Liver MRI for the Detection of Hepatocellular Carcinoma in Patients with Chronic Hepatitis or Cirrhosis

Objectives

To compare 10-minute (min) delayed hepatocyte phase imaging (HPI) using a 30° flip angle (FA) (10m-FA30) and 20-min delayed HPI using a 10° FA (20m-FA10) or 30° FA (20m-FA30) in Gd-EOB-DTPA-enhanced MRI in patients with chronic hepatitis or cirrhosis, in terms of lesion-to-liver contrast-to-noise ratio (CNR) for hepatocellular carcinoma (HCC) and detection sensitivity for focal hepatic lesions (FHLs).

Materials and Methods

One hundred and four patients with 168 HCCs and 55 benign FHLs who underwent Gd-EOB-DTPA-enhanced MRI with 10m-FA30, 20m-FA10, and 20m-FA30 were enrolled. Patients were divided into two groups according to the Child-Pugh classification: group A with chronic hepatitis or Child-Pugh A cirrhosis and group B with Child-Pugh B or C cirrhosis. Lesion-to-liver CNR for HCCs was compared between 10m-FA30 and 20m-FA10 or 20m-FA30 for each group. The presence of FHLs was evaluated using a four-point scale by two independent reviewers, and the detection sensitivity was analyzed.

Results

In group A, the CNR for HCCs (n = 86) on 10m-FA30 (165.8 ± 99.7) was significantly higher than that on 20m-FA10 (113.4 ± 71.4) and lower than that of 20m-FA30 (210.2 ± 129.3). However, there was no significant difference in the sensitivity of FHL detection between 10m-FA30 (mean 95.0% for two reviewers) and 20m-FA10 (94.7%) or 20m-FA30 (94.7%). In group B, the CNR (54.0 ± 36.4) for HCCs (n = 57) and the sensitivity (94.2%) of FHL detection for 10m-FA30 were significantly higher than those for 20m-FA10 (41.8 ± 36.4 and 80.8%, respectively) and were not different from those for 20m-FA30 (62.7 ± 44.4 and 93.3%, respectively).

Conclusion

The diagnostic performance of 10m-FA30 was similar to or higher than 20m-FA10 or 20m-FA30 in both groups A and B. This finding indicates that 10m-FA30 could replace 20-min delayed HPI regardless of patient liver function and reduce the delay time by 10 minutes.

Usefulness of breath-hold inversion recovery-prepared T1-weighted two-dimensional gradient echo sequence for detection of hepatocellular carcinoma in Gd-EOB-DTPA-enhanced MR imaging

The aim is to evaluate the diagnostic performance and the added value of breath-hold inversion recovery-prepared T1-weighted two-dimensional gradient echo (IR-2D-GRE) sequence for detection of hepatocellular carcinoma (HCC) in patients with insufficient liver parenchymal enhancement during the hepatobiliary phase (HBP) of Gd-EOB-DTPA-enhanced magnetic resonance imaging (MRI). Seventeen patients with a quantitative liver-to-spleen contrast ratio of ≤1.5 on HBP images and 36 HCCs were included. Liver-to-lesion contrast ratios on HBP images obtained with IR-2D-GRE sequence were significantly higher than those with three-dimensional gradient echo sequence. The addition of IR-2D-GRE sequence during HBP of Gd-EOB-DTPA-enhanced MRI yielded higher diagnostic accuracy and improved sensitivity.

Influence of the Magnetic Field Strength on Image Contrast in Gd-EOB-DTPA-enhanced MR Imaging: Comparison between 1.5T and 3.0T

Purpose:

We quantitatively investigated hepatic enhancement in gadolinium-ethoxybenzyl-diethylenetriamine pentaacetic acid (Gd-EOB-DTPA)-enhanced magnetic resonance (MR) imaging at 1.5T and 3.0T.

Methods:

A total of 40 patients who underwent Gd-EOB-DTPA-enhanced MR imaging were included in the study. Precontrast and hepatobiliary-phase images acquired at a low flip angle (FA, 12°) and hepatobiliary-phase images acquired at a high FA (30°) were analyzed. From these images, the liver-to-muscle signal intensity ratio (LMR) and liver-to-spleen signal intensity ratio (LSR) were estimated, and the contrast enhancement ratio (CER) was calculated from the liver signal, LMR, and LSR as the ratio of the low-FA hepatobiliary-phase value to the precontrast value. The coefficient of variance in the liver signal was determined to represent image noise.

Results:

LMR and LSR indicated similar image contrast between 1.5T and 3.0T. A higher FA provided larger LMRs and LSRs, and the degree of the FA-dependent increase was similar between 1.5T and 3.0T. CER did not differ significantly between 1.5T and 3.0T, regardless of the calculation method. A better correlation to CER calculated from the liver signal was found for the LMR-based CER values than for the LSR-based CER. The coefficient of variance in the liver signal was significantly smaller at 3.0T for precontrast and low-FA hepatobiliary-phase images, but not for high-FA hepatobiliary-phase images.

Conclusion:

The indices of hepatic enhancement were similar between 1.5T and 3.0T, indicating that the magnetic field strength does not substantially influence image contrast after administration of Gd-EOB-DTPA.

A meta-analysis of diffusion-weighted and gadoxetic acid-enhanced MR imaging for the detection of liver metastases

OBJECTIVES

To obtain the diagnostic performance of diffusion-weighted (DW) and gadoxetic-enhanced magnetic resonance (MR) imaging in the detection of liver metastases.

METHODS

A comprehensive search (EMBASE, PubMed, Cochrane) was performed to identify relevant articles up to June 2015. Inclusion criteria were: liver metastases, DW-MR imaging and/or gadoxetic acid-enhanced MR imaging, and per-lesion statistics. The reference standard was histopathology, intraoperative observation and/or follow-up. Sources of bias were assessed using the QUADAS-2 tool. A linear mixed-effect regression model was used to obtain sensitivity estimates.

RESULTS

Thirty-nine articles were included (1,989 patients, 3,854 metastases). Sensitivity estimates for DW-MR imaging, gadoxetic acid-enhanced MR imaging and the combined sequence for detecting liver metastases on a per-lesion basis was 87.1 %, 90.6 % and 95.5 %, respectively. Sensitivity estimates by gadoxetic acid-enhanced MR imaging and the combined sequence were significantly better than DW-MR imaging (p = 0.0001 and p < 0.0001, respectively), and the combined MR sequence was significantly more sensitive than gadoxetic acid-enhanced MR imaging (p < 0.0001). Similar results were observed in articles that compared the three techniques simultaneously, with only colorectal liver metastases and in liver metastases smaller than 1 cm.

CONCLUSIONS

In patients with liver metastases, combined DW-MR and gadoxetic acid-enhanced MR imaging has the highest sensitivity for detecting liver metastases on a per-lesion basis.

KEY POINTS

• DW-MRI is less sensitive than gadoxetic acid-enhanced MRI for detecting liver metastases • DW-MRI and gadoxetic acid-enhanced MRI is the best combination • Same results are observed in colorectal liver metastases • Same results are observed in liver metastases smaller than 1 cm • Same results are observed when histopathology alone is the reference standard.

Magnetic resonance imaging of the cirrhotic liver in the era of gadoxetic acid

Gadoxetic acid improves detection and characterization of focal liver lesions in cirrhotic patients and can estimate liver function in patients undergoing liver resection. The purpose of this article is to describe the optimal gadoxetic acid study protocol for the liver, the unique characteristics of gadoxetic acid, the differences between gadoxetic acid and extra-cellular gadolium chelates, and the differences in phases of enhancement between cirrhotic and normal liver using gadoxetic acid. We also discuss how to obtain and recognize an adequate hepatobiliary phase.

Evaluation of hypointense liver lesions during hepatobiliary phase MR imaging in normal and cirrhotic livers: is increasing flip angle reliable?

Gd-EOB-DTPA is a newly developed liver specific magnetic resonance contrast agent, which is widely used for focal liver lesion (FLL) detection and liver function evaluation. However, it has been demonstrated that hepatocytes uptake of Gd-EOB-DTPA obviously decreased in cirrhotic liver, and cirrhotic liver parenchyma may show reduced enhancement in hepatobiliary phase, which would result in decreased liver-to-lesion contrast (LLC) and liver to lesion signal intensity ratio (LLSIR). Therefore, it is important to improve the image quality in cirrhotic liver, as it may alter therapeutic strategy. In this paper, we have shown adjustments of the flip angle (FA) provides a simple step to achieve better image quality for evaluation of FLLs, especially to those patients with severe liver cirrhosis. On the basis of our quantitative analysis, both of the LLC and the LLSIR with high FA protocol were always higher than those of low FA protocol. Additionally, on high FA images, more FLLs were detected, peritumoral invasion was found, boundary of the tumor was more remarkably, and better visualization of bile duct was observed. In conclusion, for the patient with severe liver cirrhosis, increasing FA can obviously improve the image quality, which is helpful for FLLs depiction.

Hypovascular hepatic nodules at gadoxetic acid-enhanced MRI: whole-lesion hepatobiliary phase histogram metrics for prediction of progression to arterial-enhancing hepatocellular carcinoma

PURPOSE

To explore whole-lesion histogram analysis of the hepatobiliary phase (HBP) defect in indeterminate hypovascular liver lesions for predicting progression to arterial-enhancing hepatocellular carcinoma (HCC).

METHODS

Twenty patients undergoing gadoxetic acid-enhanced MRI for HCC screening with 12° and 25° flip angle (FA) HBP acquisitions demonstrating an indeterminate lesion showing HBP hypointensity but no arterial enhancement were included. Volumes-of-interest were placed on HBP defects, from which histogram metrics were obtained. Associations between these metrics and progression to arterial-enhancing HCC on follow-up imaging were investigated. Lesions were also assessed for the presence of a signal abnormality on conventional sequences.

RESULTS

40% of lesions progressed to arterial-enhancing HCC; 60% were stable at ≥6 months follow-up. Neither T2-hyperintensity increased diffusion signal nor portal/equilibrium phase washout was different between progressing and nonprogressing lesions (p = 1.0). Among direct signal intensity-based measures (overall mean; mean of bottom 10th, 10-25th, and 25-50th percentiles), area-under-the-curve (AUC) for prediction of progression to arterial-enhancing HCC was consistently higher at 25° (range 0.619-0.657) than at 12° (range 0.512-0.548). However, at both FAs, the four measures with highest AUC were measures related to lesion texture and heterogeneity [standard deviation (SD), coefficient of variation (CV), skewness, and entropy], having AUC of 0.655-0.750 at 12° and 0.686-0.800 at 25. The metric with highest AUC at 12° was SD (AUC = 0.750) and at 25° was CV (AUC = 0.800).

CONCLUSION

Whole-lesion histogram HBP measures of indeterminate hypovascular liver lesions may help predict progression to arterial-enhancing HCC by reflecting greater lesion heterogeneity, particularly at higher FA. Larger studies are therefore warranted.

Gd-EOB enhanced MRI T1-weighted 3D-GRE with and without elevated flip angle modulation for threshold-based liver volume segmentation

BACKGROUND

Despite novel software solutions, liver volume segmentation is still a time-consuming procedure and often requires further manual optimization. With the high signal intensity of the liver parenchyma in Gd-EOB enhanced magnetic resonance imaging (MRI), liver volume segmentation may be improved.

PURPOSE

To evaluate the practicability of threshold-based segmentation of the liver volume using Gd-EOB-enhanced MRI including a customized three-dimensional (3D) sequence.

MATERIAL AND METHODS

A total of 20 patients examined with Gd-EOB MRI (hepatobiliary phase T1-weighted (T1W) 3D sequence [VIBE]; flip angle [FA], 10° and 30°) were enrolled in this retrospective study. The datasets were independently processed by two blinded observers (O1 and O2) in two ways: manual (man) and threshold-based (thresh; study method) segmentation of the liver each followed by an optimization step (man+opt and thresh+opt; man+opt [FA10°] served as reference method). Resulting liver volumes and segmentation times were compared. A liver conversion factor was calculated in percent, describing the non-hepatocellular fraction of the total liver volume, i.e. bile ducts and vessels.

RESULTS

Thresh+opt (FA10°) was significantly faster compared to the reference method leading to a median volume overestimation of 4%/8% (P < 0.001). Using thresh+opt (FA30°), segmentation was even faster (P < 0.001) and even reduced median volume deviation of 0%/2% (O1/O2; both P > 0.2). The liver conversion factor was found to be 10%.

CONCLUSION

Threshold-based liver segmentation employing Gd-EOB-enhanced hepatobiliary phase standard T1W 3D sequence is accurate and time-saving. The performance of this approach can be further improved by increasing the FA.

Validation of 10-Minute Delayed Hepatocyte Phase Imaging with 30° Flip Angle in Gadoxetic Acid-Enhanced MRI for the Detection of Liver Metastasis

Objectives

To compare 10-minute delayed hepatocyte phase imaging using a 30° flip angle (10min-FA30) and 20-minute hepatocyte phase imaging using a 10° FA (20min-FA10) in gadoxetic acid-enhanced MRI of patients with possible liver metastases, regarding lesion-to-liver contrast-to-noise ratio (CNR) and focal hepatic lesion (FHL) detection to evaluate whether 10min-FA30 would be superior to 20min-FA10.

Materials and Methods

Eighty-three patients with 248 liver metastases and 78 benign FHLs who underwent gadoxetic acid-enhanced MRI with 10min-FA30 and 20min-FA10 were enrolled. Lesion-to-liver CNRs were compared between the two image groups. Two radiologists independently assessed the presence of FHLs using a four-point scale and detection sensitivity was calculated.

Results

The mean CNR for liver metastases on the 10min-FA30 (248.5 ± 101.6) were significantly higher than that of the 20min-FA10 (187.4 ± 77.4) (p < 0.001). The mean CNR difference between the two image groups was 61.2 ± 56.8. There was no significant difference in detection sensitivity of FHLs for two readers between 10min-FA30 (mean 97.7%) and 20min-FA10 (mean 97.9%), irrespective of the lesion size or malignancy.

Conclusion

10min-FA30 yielded higher CNR with similar sensitivity compared to 20min-FA10. This finding indicates that 10min-FA30 can potentially replace 20min-FA10 with higher diagnostic performance and save 10 minutes of time.

Effect of increasing the flip angle during the hepatocyte phase of gadobenate dimeglumine-enhanced 1.5T MRI in cirrhotic patients with hepatocellular carcinoma

PURPOSE

To evaluate the effects of increasing the flip angle during the hepatocyte phase of gadobenate dimeglumine-enhanced magnetic resonance imaging (MRI) in cirrhotic patients with hepatocellular carcinoma (HCC).

MATERIALS AND METHODS

Sixty-three patients with liver cirrhosis underwent gadobenate dimeglumine-enhanced 1.5T MRI with 90-minute delayed hepatocyte phase with flip angles of 10°, 20°, 30°, consecutively. Relative enhancement and signal-to-noise ratio (SNR) of liver parenchyma at hepatocyte phase according to flip angle were calculated. The liver-to-lesion (low signal intensity HCCs, n = 63; ≥1 cm) and contrast-to-noise ratio (CNR) at the hepatocyte phase according to flip angle were calculated. Two radiologists independently assessed the presence of HCCs using a 5-point scale, and detection sensitivity of HCCs was calculated according to flip angle.

RESULTS

The relative enhancement of hepatic parenchyma differed significantly according to flip angle (10°, mean relative enhancement = 0.69 ± 0.46; 20°, mean relative enhancement = 0.63 ± 0.47; 30°, mean relative enhancement = 0.49 ± 0.45; P = 0.043). The SNR of hepatic parenchyma was significantly different according to flip angle (10°, mean SNR = 26.2 ± 5.6; 20°, mean SNR = 25.3 ± 5.7; 30°, mean SNR = 22.8 ± 6.1; P = 0.004). The CNR of lesion was not significantly different according to flip angle (10°, mean CNR = 7.5 ± 6.6; 20°, mean CNR = 10.2 ± 6.9; 30°, mean CNR = 10.1 ± 7.1; P = 0.051). The sensitivities with 10° and 20° for HCCs were significantly higher than those with 30° for one reader (P < 0.05).

CONCLUSION

In patients with cirrhosis, hepatocyte phase gadobenate dimeglumine-enhanced 1.5T MRI with 20° flip angle should be recommended rather than 10° and 30° flip angle.

Feasibility of 5-minute delayed transition phase imaging with 30° flip angle in gadoxetic acid-enhanced 3D gradient-echo MRI of liver, compared with 20-minute delayed hepatocyte phase MRI with standard 10° flip angle

OBJECTIVE

The purpose of this study was to compare 5-minute delayed transitional phase imaging using a 30° flip angle (hereafter, 5 min-FA30) and 20-minute hepatocyte phase imaging using a 10° flip angle (hereafter, 20 min-FA10) in gadoxetic acid-enhanced MRI for focal hepatic lesion detection and lesion-to-liver contrast-to-noise ratio (CNR), and to determine whether 5 min-FA30 could replace 20 min-FA10 with a 15-minute time saving.

MATERIALS AND METHODS

One hundred sixteen patients with 282 focal hepatic lesions (size range, 0.2-12.5 cm; malignant, n = 146; benign, n = 136) underwent gadoxetic acid-enhanced MRI with 5 min-FA30 and 20 min-FA10 with a 3D T1-weighted gradient-echo sequence. Three radiologists independently assessed the presence of focal hepatic lesions using a 4-point scale, and detection sensitivity of focal hepatic lesions was calculated. Lesion-to-liver CNRs were calculated and compared in two image groups.

RESULTS

There was no significant difference in detection sensitivity of focal hepatic lesions for all three readers between 5 min-FA30 (mean, 95.4%) and 20 min-FA10 (mean, 95.6%), irrespective of lesion size or malignancy. The mean CNR on 5 min-FA30 (167.9 ± 84.1) was significantly higher than that on 20 min-FA10 (160.2 ± 79.5). However, the mean CNR difference between the two image groups was relatively small (7.8 ± 41.9).

CONCLUSION

Compared with 20 min-FA10, 5 min-FA30 provided higher CNR and similar sensitivity. These findings indicate that 5 min-FA30 could replace 20-min delayed hepatocyte phase imaging using a 10° flip angle with similar diagnostic performance and 15 minutes of time saving.

Hepatobiliary MR contrast agents in hypovascular hepatocellular carcinoma

Hepatocellular carcinoma (HCC) develops via multistep hepatocarcinogenesis, during which hypovascular/early HCC precedes the typical hypervascular HCC. The hypovascular HCC lacks the typical hallmark imaging features of HCC, such as late arterial phase enhancement and portal venous washout, limiting early detection using conventional extracellular contrast agents for dynamic magnetic resonance imaging (MRI) or computed tomography (CT) imaging. In recent years, gadolinium-based contrast agents with hepatobiliary uptake have garnered interest from radiologists and hepatologists due to their potential for improved detection of HCC during hepatobiliary phase MRI. Lesions with reduced or absent hepatocyte function appear hypointense in the hepatobiliary phase of gadoxetic acid-enhanced MRI. This behavior can be exploited for earlier detection of hypovascular HCC. This review describes the general characteristics and advantages of gadoxetic acid for the diagnosis of HCC with a particular focus on hypovascular/early HCC.

Diffusion weighted MR and apparent diffusion coefficient measurement in classification and characterization of noncystic focal liver lesions: does a clinical role exist?

The objective of this study was to assess the clinical role of apparent diffusion coefficient (ADC) analysis in noncystic focal liver lesion (FLL) classification/characterization.Six hundred liver magnetic resonances with multi-b (b = 50, 400, 800 s/mm) diffusion-weighted imaging (DwI) were retrospectively reviewed. Mean ADC was measured in 388 lesions (195 benign and 193 malignant) excluding internal necrotic areas. Cystic benign lesions were excluded from analysis. Sensitivity and specificity in distinguishing benign from malignant lesions were calculated. Analysis of variance was performed to detect differences among subgroups of solid lesions.Mean ADC of malignant lesions was 0.980 × 10 mm/s, significantly (P < 0.05) lower than mean ADC of benign lesions (1.433 × 10 mm/s). Applying an ADC cutoff of 1.066 × 10 mm/s, specificity and sensitivity for malignancy were respectively 86.6% and 73.6%. Of all lesions, >1/3 (39.5%) presented values lower than 1 × 10 mm/s, with 90.0% chance of malignancy. Above 1.5 × 10 mm/s (about 20% of all lesions) chance of malignancy was 9.5%.DwI cannot assist in noncystic FLL characterization, but can help in FLL classification in about half the cases.

Optimal timing and diagnostic adequacy of hepatocyte phase imaging with gadoxetate-enhanced liver MRI

RATIONALE AND OBJECTIVES

To evaluate clinical and imaging features associated with adequacy of the hepatocyte phase (HP) in gadoxetate disodium-enhanced liver magnetic resonance imaging (MRI) in patients without chronic liver disease (CLD).

MATERIALS AND METHODS

This was a retrospective institutional review board-approved study of 97 patients who underwent liver MRI examinations with gadoxetate disodium and had no history of CLD. Available late dynamic and HP sequences (3-20 minutes postinjection) were independently analyzed by four radiologists for perceived image adequacy and level of biliary enhancement. Signal intensity ratios (SIRs) of liver/inferior vena cava (IVC), liver/spleen, and liver/muscle were measured. The Spearman ρ and receiver operating characteristic analyses were performed correlating various factors with HP adequacy. A rule for predicting HP adequacy was also derived and tested to determine whether overall examination time could be shortened.

RESULTS

A visually adequate HP was observed in 12% of subjects by 10 minutes, 80% by 15 minutes, and 93% by 20 minutes. An SIRliver/IVC > 1.8 was the imaging feature that had the strongest correlation with an adequate HP (ρ = 0.813, P < .001), and was more predictive of adequacy of the HP than the time postinjection (ρ = 0.5, P < .001). The time at which an adequate HP was first observed did not correlate with any tested demographic or laboratory values. Stopping imaging when an SIRliver/IVC > 1.8 would have successfully reduced mean postcontrast time to 15:39 ± 4:02 from 20:00 (P < .001), although maintaining HP adequacy.

CONCLUSIONS

Most patients without CLD undergoing gadoxetate-enhanced liver MRI achieve adequate HP at 20 minutes. However, a shorter postcontrast stopping time can be used in most patients.

Combination of increased flip angle, radial k-space trajectory, and free breathing acquisition for improved detection of a biliary variant at living donor liver transplant evaluation using gadoxetic acid-enhanced MRCP

Gadoxetic acid-enhanced magnetic resonance cholangiopancreatography (MRCP) was performed for evaluation of living donor liver transplantation. T2-weighted MRCP and hepatobiliary-phase postcontrast MRCP showed an aberrant right posterior bile duct, although the precise variant was uncertain. Optimized hepatobiliary-phase MRCP was obtained using 3 sequence modifications: increased flip angle to improve contrast between the biliary tree and surrounding tissues; radial k-space sampling to minimize motion artifact; and free-breathing acquisition to improve signal-to-noise ratio and, in turn, spatial resolution (resolution of 1.28 × 1.28 × 1.5 mm). The optimized sequence demonstrated that the right posterior bile duct drained into the cystic duct, consistent with type 3C biliary variant, thus modifying surgical planning.

Evaluation of gadolinium-EOB-DTPA uptake after portal vein embolization: value of an increased flip angle

BACKGROUND

The optimal sequence for Gd-EOB-DTPA uptake measurement in the liver with the purpose of liver function measurement is still not defined.

PURPOSE

To prospectively evaluate the effect of an increased flip angle (FA) of a T1-weighted fat-saturated 3D sequence for the measurement of hepatocyte uptake of Gd-EOB-DTPA magnetic resonance imaging (MRI) after right portal vein embolization (PVE).

MATERIAL AND METHODS

Ten patients who received a PVE prior to an extended hemihepatectomy were examined 14 days after PVE using Gd-EOB-DTPA enhanced MRI of the liver using the standard FA of 10° and the increased FA of 30°.

RESULTS

Relative enhancement of the right liver lobe (RLL) was 0.52 ± 0.12 for 10° and 1.41 ± 0.39 for 30°. Relative enhancement of the left liver lobe (LLL) was 0.58 ± 0.11 for 10° and 2.05 ± 0.61 for 30°. Relative enhancement of the RLL was significantly higher for 30° than for 10° (P = 0.009) and significantly higher in the 30° than in the 10° sequences (P = 0.005) for the LLL.

CONCLUSION

A flip angle of 30° increases the contrast between liver partitions with and without portal venous embolization. Thereby, the sensitivity for differences in uptake intensity is increased. This could be of value for a more exact determination of differences in regional liver function and, consequently, the estimation of the future remnant liver function.

Liver-specific agents for contrast-enhanced MRI: role in oncological imaging

Liver-specific magnetic resonance (MR) contrast agents are increasingly used in evaluation of the liver. They are effective in detection and morphological characterization of lesions, and can be useful for evaluation of biliary tree anatomy and liver function. The typical appearances and imaging pitfalls of various tumours at MR imaging performed with these agents can be understood by the interplay of pharmacokinetics of these contrast agents and transporter expression of the tumour. This review focuses on the applications of these agents in oncological imaging.

Diagnosis of focal nodular hyperplasia with MRI: multicenter retrospective study comparing gadobenate dimeglumine to gadoxetate disodium

OBJECTIVE

The purpose of this article is to report the results from a multicenter retrospective MRI study comparing gadobenate dimeglumine and gadoxetate disodium for diagnosis of hepatic focal nodular hyperplasia (FNH).

MATERIALS AND METHODS

Thirty patients (28 women and two men; mean age, 37.1 years) with hepatic FNH who underwent both gadobenate dimeglumine- and gadoxetate disodium-enhanced MRI at 1.5 T were assessed. MRI was performed during the arterial, portal venous, late venous, and hepatobiliary contrast-enhanced phases (10 and 20 minutes or 1-3 hours after contrast administration, respectively, for gadoxetate disodium and gadobenate dimeglumine). Qualitative (lesion conspicuity score) and quantitative (lesion signal intensity [SI] ratio and lesion contrast ratio) assessments were performed.

RESULTS

In 30 patients, 51 FNHs were assessed (mean size 3.1 ± 1.5 cm). There was equivalent qualitative lesion conspicuity in the arterial phase between the two contrast agents and higher qualitative lesion conspicuity and SI ratio in the hepatobiliary phase with gadoxetate disodium (p < 0.002). Lesion contrast ratio was significantly higher in the arterial and late venous phases with gadobenate dimeglumine (p < 0.009), with no difference in the portal venous and hepatobiliary phases between the two contrast agents (p > 0.22).

CONCLUSION

These results indicate an advantage for gadobenate dimeglumine for detection of FNH at the dynamic phase and for gadoxetate disodium at the hepatobiliary phase. However, the equivalent or better qualitative lesion conspicuity coupled with the ability to obtain a comprehensive evaluation of the liver within a standard 30-minute imaging window suggests that gadoxetate disodium may be a better choice for diagnosis of FNH.