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

Comparative evaluation of non-contrast MRI versus gadoxetic acid-enhanced abbreviated protocols in detecting colorectal liver metastases

PURPOSE

This study compares the diagnostic efficacy of non-contrast abbreviated MRI protocols with Gadoxetic acid-enhanced abbreviated MRI for detecting colorectal liver metastasis (CRLM), focusing on lesion characterization and surveillance.

METHODS

Ninety-four patients, including 55 with pathologically verified CRLM, were enrolled, totaling 422 lesions (287 metastatic, 135 benign). Two independent readers assessed three MRI protocols per patient: Protocol 1 included non-contrast sequences (T2-weighted turbo spin-echo, T1-weighted Dixon, diffusion-weighted imaging (DWI), and ADC mapping). Protocol 2 included gadoxetic acid enhancement with hepatobiliary phase imaging, T2 TSE, DWI, and ADC maps. Protocol 3 utilized the standard Gadoxetic Acid-enhanced MRI sequence, which included pre-contrast T1-weighted imaging, T1-weighted Dixon sequences, post-contrast T1-weighted imaging (including arterial, portal venous, transitional and hepatobiliary phases), and additional T2-weighted and DWI sequences. Diagnoses were scored on a 5-point scale (benign = 1; malignant = 5), with scores ≥ 3 indicating CRLM. ROC curves analyzed diagnostic accuracy, comparing area under the curve (AUC) values across protocols.

RESULTS

No significant difference in AUCs was observed between Protocol 1 (0.899-0.909) and Protocol 2 (0.906-0.931) versus Protocol 3 (0.935-0.939) (p = 0.091-0.195). For lesions ≤ 10 mm, Protocol 1 was slightly inferior to Protocol 3 (p = 0.002-0.032), while Protocol 2 remained comparably effective (p = 0.096-0.179). These findings held when using a threshold of ≥ 4 to define CRLM.

CONCLUSION

The non-enhanced abbreviated MRI protocol is as effective as the gadoxetic acid-enhanced protocol in identifying CRLM. The proposed Ab-MRI approach may be a viable alternative for CRLM surveillance.

CRITICAL RELEVANCE STATEMENT

The non-enhanced abbreviated MRI (Ab-MRI) protocol is as effective as the gadoxetic acid-enhanced protocol in identifying colorectal liver metastasis (CRLM). The proposed Ab-MRI approach may be a viable alternative for CRLM surveillance.

KEY POINTS

Two abbreviated protocols are proposed for colorectal liver metastasis (CRLM) surveillance. The non-enhanced protocol showed equivalent efficacy and was more cost-effective. The non-enhanced protocol may be a viable alternative for CRLM surveillance.

Imaging cholangiocarcinoma: CT and MRI techniques

Cross-sectional imaging plays a crucial role in the detection, diagnosis, staging, and resectability assessment of intra- and extrahepatic cholangiocarcinoma. Despite this vital function, there is a lack of standardized CT and MRI protocol recommendations for imaging cholangiocarcinoma, with substantial differences in image acquisition across institutions and vendor platforms. In this review, we present standardized strategies for the optimal imaging assessment of cholangiocarcinoma including contrast media considerations, patient preparation recommendations, optimal contrast timing, and representative CT and MRI protocols with individual sequence optimization recommendations. Our recommendations are supported by expert opinion from members of the Society of Abdominal Radiology's Disease-Focused Panel (DFP) on Cholangiocarcinoma, encompassing a broad array of institutions and practice patterns.

Quantitative and qualitative evaluation of high-quality hepatobiliary phase imaging with shortened timing and utility in patients with compromised liver function

PURPOSE

To compare high flip angle (FA) hepatobiliary-phase (hHBP) imaging with variable time intervals to conventional HBP (cHBP) to assess the impact of increased FA on image quality in shortened HBP imaging.

METHODS

Data from 218 patients, divided into normal liver group (n = 184) and decompensated liver group (n = 34), who underwent liver magnetic resonance imaging (MRI) including 10-min, 15-min, 20-min hHBP, and cHBP were analyzed. Signal-to-noise ratio (SNR), contrast-ratio (CR), contrast-to-noise ratio (CNR), signal intensity ratios (SIRs), and relative enhancement (RE) of the liver were calculated for quantitative analysis. Sharpness, noise, and artifacts of the image, contrast media visibility, overall image quality, and lesion conspicuity were evaluated by two abdominal radiologists.

RESULTS

Quantitative analysis showed that SNR, RE, SIR for liver/muscle, liver/spleen, and CR of all hHBP images demonstrated a significantly higher value compared to cHBP images in the normal liver group (p < 0.001). These values were also superior in the normal liver group compared to the decompensated liver group (p < 0.01). In qualitative analysis, both normal and decompensated liver groups exhibited significantly superior image sharpness in all hHBP images compared to cHBP images and the overall image quality of the 15-min and 20-min hHBP did not show significant difference compared to cHBP. All values tended to be better in the normal liver group than the decompensated liver group with statistical significance except for lesion conspicuity (p < 0.01).

CONCLUSION

High-FA HBP has proven to be a valuable image acquisition method, potentially shortening liver MR imaging time while maintaining acceptable image quality.

A convenient and reproducible protocol for acquisition of the hepatocyte phase for liver function-impaired patients in gadoxetic acid disodium-enhanced magnetic resonance imaging

Background

The hepatocyte phase (HCP) in gadoxetic acid disodium (Gd-EOB-DTPA)-enhanced magnetic resonance imaging (MRI) plays an important role in the detection and characterization of liver lesions, treatment planning, and liver function evaluation. However, the imaging protocol is complicated and time-consuming. This cross-sectional study aimed to develop a convenient and reproducible protocol for the HCP acquisition in Gd-EOB-DTPA-enhanced MRI.

Methods

A total of 107 patients were prospectively included and assigned to three groups based on Child-Pugh (CP) classification, with 37, 40, and 30 in the non-cirrhosis, CP A, and CP B groups, respectively. Dynamic HCPs were acquired every 5 min after the Gd-EOB-DTPA administration and ended in 25 min in non-cirrhosis patients and 40 min in cirrhotic patients. The HCP acquired 5 min after the initial visualization of the intrahepatic bile duct (IBD) was selected from the dynamic HCPs as the adequate HCP (HCPproposed) and the corresponding acquisition time was recorded as Timeproposed. In addition, according to the 2016 Expert Consensus (EC) on the definition of the adequate HCP from the European Society of Gastrointestinal and Abdominal Radiology (ESGAR), the adequate HCPEC and the corresponding TimeEC were also determined from the dynamic HCPs. The hepatic relative enhancement ratio (RER), the contrast-to-noise ratio (CNR), and signal-to-noise ratio (SNR) of hepatic focal lesions in the HCPEC and HCPproposed images, as well as the TimeEC and Timeproposed were compared by the paired t-test for the three groups, respectively. Inter-observer agreement of the determination of the HCPEC and HCPproposed was compared by the χ2 test.

Results

The RER, CNR, and SNR showed no significant difference between the HCPEC and HCPproposed in all three groups (all P>0.05). The paired differences between TimeEC and Timeproposed were 1.08±3.56 min (P=0.07), 2.88±4.22 min (P<0.001), and 5.83±5.27 min (P<0.001) in the three groups, respectively. Inter-observer agreement of the determination of the HCPEC and HCPproposed were 0.804 (86/107) and 0.962 (103/107), respectively (χ²=13.09, P=0.001).

Conclusions

The adequate HCP could be acquired 5 min after the initial visualization of the IBD, which could serve as a convenient and reproducible protocol for the HCP imaging.

Optimization of hepatobiliary phase imaging in gadoxetic acid-enhanced magnetic resonance imaging: a narrative review

Background and Objective

Gadolinium ethoxybenzyl-diethylenetriamine pentaacetic acid (Gd-EOB-DTPA)-enhanced magnetic resonance imaging (MRI) is widely used in clinical practice. Its unique hepatobiliary phase (HBP) has been used to improve the detection and identification of hepatic lesions and has also been used to evaluate hepatic function and fibrosis. At the early stage of its clinical practice, the HBP was typically collected empirically with a delay of 20 minutes after intravenous administration to image the liver with sufficient enhancement for diagnosis. However, numerous methods and consensus statements for optimizing HBP acquisition have been proposed. This review details the methods and consensus statements on optimizing HBP collection.

Methods

The electronic literature search was performed using the databases PubMed, MEDLINE, Cochrane, and Embase without limit on publication period to identify published reports on optimizing HBP imaging in Gd-EOB-DTPA-enhanced MRI. Articles with low relevance to the topics were excluded.

Key Content and Findings

Recently, an increasing number of investigations suggest that collecting HBP after 20 min is too drawn-out for patients with normal liver function but is too short for patients with cirrhosis. Previous studies demonstrated that liver enhancement is closely related to liver function in Gd-EOB-DTPA-enhanced MRI. Therefore several reports have proposed various HBP delay times at different liver function levels. These delay times could be evaluated by laboratory indicators, such as prothrombin (PT) activity, total bilirubin, direct bilirubin, and the model for end-stage liver disease. Other investigations have found that the initial visualization time of the intrahepatic bile duct (IHD) in Gd-EOB-DTPA-enhanced MRI to also be related to liver enhancement and function. Therefore, initial visualization of the IHD is considered necessary for adequate HBP and has been employed in HBP acquisition in recent reports.

Conclusions

Optimizing HBP acquisition according to individual hepatic function is a good strategy and was followed in most of the investigations included in our review. Obtaining adequate HBP in the shortest possible time is the target condition in Gd-EOB-DTPA-enhanced MRI. However, a more concise and efficient HBP acquisition strategy is still expected to be developed in the future.

Role of gadoxetic acid-enhanced liver magnetic resonance imaging in the evaluation of hepatocellular carcinoma after locoregional treatment

Locoregional treatments, as alternatives to surgery, play a key role in the management of hepatocellular carcinoma (HCC). Liver magnetic resonance imaging (MRI) enables a multiparametric assessment, going beyond the traditional dynamic computed tomography approach. Moreover, the use of hepatobiliary agents can improve diagnostic accuracy and are becoming important in the diagnosis and follow-up of HCC. However, the main challenge is to quickly identify classical responses to loco-regional treatments in order to determine the most suitable management strategy for each patient. The aim of this review is to provide a summary of the most common and uncommon liver MRI findings in patients who underwent loco-regional treatments for HCC, with a special focus on ablative therapies (radiofrequency, microwaves and cryoablation), trans-arterial chemoembolization, trans-arterial radio-embolization and stereotactic ablative radiotherapy techniques, considering the usefulness of gadoxetate disodium (Gd-EOB-DTPA) contrast agent.

Dual contrast liver MRI: a pictorial illustration

Liver magnetic resonance imaging (MRI) is a commonly performed imaging technique with multiple indications and applications. There are two general groups of contrast agents used when imaging the liver, extracellular contrast agents (ECA) and hepatobiliary agents (HBA), each of which has its own advantages and limitations. Liver MRI with ECA provides excellent information on abdominal vasculature and better quality multi-phasic studies for characterization of focal liver lesions. HBA improves lesion detection, provides information regarding liver function and can be helpful for evaluating biliary tree anatomy, excretion, anastomotic stenoses, or leaks. Most liver MRI studies are usually performed with one agent, however in some cases, a second study is performed with another agent to obtain additional information or confirm the findings in the first study. Administering both agents in a single exam can potentially eliminate the need for additional imaging in certain situations. In this pictorial review, the techniques and indications for dual contrast MRI will be detailed with multiple demonstrative examples.

Assessing locoregional treatment response to Hepatocellular Carcinoma: comparison of hepatobiliary contrast agents to extracellular contrast agents

Cross-sectional imaging with contrast-enhanced magnetic resonance imaging (MRI) is routinely performed in patients with hepatocellular carcinoma (HCC) to assess tumor response to locoregional therapy (LRT). Current response assessment algorithms, such as the Liver Imaging Reporting and Data System (LI-RADS) treatment response algorithm (TRA), allow assessment using conventional gadolinium-based extracellular contrast agents (ECA) for accurate tumor response assessment following LRT. MRI with hepatobiliary agents (HBA) allows an acquisition of hepatobiliary phase (HBP), which is proven to increase sensitivity for detection of observations in at-risk patients, particularly for findings < 2 cm. The use of HBA is not yet incorporated into the TRA; however, it is increasingly used in clinical practice. Few published studies have evaluated the performance of LI-RADS TRA by applying ancillary features related to HBP that has resulted in category adjustment, enabling more sensitive and unequivocal diagnosis. This may help timely management of viable cases, without a significant loss of specificity in comparison with the ECA-based LI-RADS TRA assessment. In this review, we will describe and compare the imaging appearance of treated HCC on MRI using extracellular and hepatobiliary contrast agents and discuss emerging evidence and pitfalls in the assessment of tumor response following LRT with HBA.

Optimization of timing of hepatocellular phase imaging after gadoxetate disodium injection for evaluation of patients with neuroendocrine tumor

PURPOSE

Metastatic gastroenteropancreatic neuroendocrine neoplasms (mGEP-NEN) are indolent malignancies which undergo frequent imaging follow-up. Hepatocellular phase (HCP) MR with hepatocellular-specific contrast agent is widely used to evaluate mGEP-NEN liver metastases but is commonly performed after a 20-min delay which prolongs scan time. The purpose of this study was to evaluate if HCP MR at 15 min offers comparable performance to 20-min delay for patients with mGEP-NEN undergoing routine imaging surveillance.

MATERIALS AND METHODS

In this IRB-approved retrospective study, we evaluated 52 patients with mGEP-NEN who were imaged for routine surveillance with gadoxetate disodium (Eovist^®)-enhanced MR including 15- and 20-min delayed HCP. Two readers (R1, R2), blinded to HCP timing, independently reviewed each set of images in random order at least 1 month apart. Readers assessed presence and conspicuity of metastases, and subjective image quality using 5-point scales. Readers quantified the number of metastases and diameter of the largest lesion. Statistical analysis was performed to determine individual-reader and inter-reader differences for qualitative and quantitative data.

RESULTS

No differences were observed for subjective image quality (R1 p = 0.86, R2 p = 0.17) or lesion conspicuity (R1 p = 0.56, R2 p = 0.74) at 15 min and 20 min for either reader. Individual-reader concordance correlation coefficient between 15 and 20 min was high for number of metastases detected (R1 = 0.9842, R2 = 0.9579) and diameter of largest metastasis (R1 = 0.9629, R2 = 0.8859).

CONCLUSION

HCP imaging at 15 min provides similar diagnostic yield to standard 20-min delay, which may help reduce the scan time and costs, and improve throughput and patient satisfaction.

Convolutional neural network-automated hepatobiliary phase adequacy evaluation may optimize examination time

PURPOSE

To develop and evaluate the performance of a fully-automated convolutional neural network (CNN)-based algorithm to evaluate hepatobiliary phase (HBP) adequacy of gadoxetate disodium (EOB)-enhanced MRI. Secondarily, we explored the potential of the proposed CNN algorithm to reduce examination length by applying it to EOB-MRI examinations.

METHODS

We retrospectively identified EOB-enhanced MRI-HBP series from examinations performed 2011-2018 (internal and external datasets). Our algorithm, comprising a liver segmentation and classification CNN, produces an adequacy score. Two abdominal radiologists independently classified series as adequate or suboptimal. The consensus determination of HBP adequacy was used as ground truth for CNN model training and validation. Reader agreement was evaluated with Cohen's kappa. Performance of the algorithm was assessed by receiver operating characteristics (ROC) analysis and computation of the area under the ROC curve (AUC). Potential examination duration reduction was evaluated descriptively.

RESULTS

1408 HBP series from 484 patients were included. Reader kappa agreement was 0.67 (internal dataset) and 0.80 (external dataset). AUCs were 0.97 (0.96-0.99) for internal and 0.95 (0.92-96) for external and were not significantly different from each other (p = 0.24). 48 % (50/105) examinations could have been shorter by applying the algorithm.

CONCLUSION

A proposed CNN-based algorithm achieves higher than 95 % AUC for classifying HBP images as adequate versus suboptimal. The application of this algorithm could potentially shorten examination time and aid radiologists in recognizing technically suboptimal images, avoiding diagnostic pitfalls.

Intravenous gadolinium-based hepatocyte-specific contrast agents (HSCAs) for contrast-enhanced liver magnetic resonance imaging in pediatric patients: what the radiologist should know

Hepatocyte-specific contrast agents (HSCAs) are a group of intravenous gadolinium-based MRI contrast agents that can be used to characterize hepatobiliary pathology. The mechanism by which these agents are taken up by hepatocytes and partially excreted into the biliary tree improves characterization of hepatic lesions and biliary abnormalities relative to conventional extracellular gadolinium-based contrast agents (GBCAs). This manuscript presents an overview of HSCA use in pediatric patients with the intent to provide radiologists a guide for clinical use. We review available HSCAs and discuss dosing and age specifications for use in children. We also review various hepatic and biliary indications for HSCA use in children, with emphasis on the imaging characteristics distinct to HSCAs, as well as discussion of pitfalls one can encounter when imaging with HSCAs. Given the growing concern regarding gadolinium deposition in soft tissues and brain, we also discuss safety of HSCA use in children.

Use of Eovist in Pediatric Patients: Pearls and Pitfalls

Magnetic resonance imaging is excellent at characterizing pediatric hepatobiliary pathology. Noncontrast MRI is helpful due to T2 hyperintensity associated with bile, but contrast enhancement offers additional means of lesional characterization. In particular, hepatocyte-specific contrast agents such as gadoxetate disodium (Eovist) exhibit partial hepatobiliary excretion which may be leveraged in these contexts. In this review, we will discuss gadoxetate disodium usage, including a sample-imaging protocol, and demonstrate applications and limitations in the pediatric population.

Hepatocellular Carcinoma: Current Imaging Modalities for Diagnosis and Prognosis

As opposed to most solid cancers, hepatocellular carcinoma (HCC) does not necessarily require histological confirmation. Noninvasive diagnosis is possible and relies on imaging. In cirrhotic patients, the diagnosis can be obtained in tumors displaying typical features that include non-rim arterial phase hyperenhancement followed by washout during the portal venous and/or delayed phases on CT or MR imaging. This pattern is very specific and, as such, has been endorsed by both Western and Asian diagnostic guidelines and systems. However, its sensitivity is not very high, especially for small lesions. Numerous ancillary features favoring the diagnosis of HCC may be depicted, including appearance after injection of hepatobiliary MR imaging contrast agents. These features increase confidence in diagnosis, but cannot be used as substitutes to liver biopsy. Aside from its diagnostic purpose, imaging also helps to assess tumor biology and patient outcome, by identifying features of local invasiveness. The purpose of this review article is to offer an overview of the role of imaging for the diagnosis and prognostication of HCC.

Hepatobiliary phase in cirrhotic patients with different Model for End-stage Liver Disease score: comparison of the performance of gadoxetic acid to gadobenate dimeglumine

OBJECTIVES

The purpose of this study was to compare the performance of gadobenate dimeglumine-enhanced MRI and gadoxetic acid-enhanced MRI in the hepatobiliary phase (HBP) in cirrhotic patients with different degrees of liver dysfunction.

METHODS

In this retrospective cross-sectional study, we analyzed the unenhanced phase and the HBP of 131 gadobenate dimeglumine-enhanced MRI examinations (gadobenate dimeglumine group) and 127 gadoxetic acid-enhanced MRI examinations (gadoxetic acid group) performed in 249 cirrhotic patients (181 men and 68 women; mean age, 64.8 years) from August 2011 to April 2017. For each MRI, the contrast enhancement index of the liver parenchyma was calculated and correlated to the Model For End-Stage Liver Disease (MELD) score (multiple linear regression analysis). A qualitative analysis of the adequacy of the HBP, adjusted for the MELD score (logistic regression analysis), was performed.

RESULTS

The contrast enhancement index was inversely related (r = - 0.013) with MELD score in both gadoxetic acid and gadobenate dimeglumine group. At the same MELD score, the contrast enhancement index in the gadoxetic acid group was increased by a factor of 0.23 compared to the gadobenate dimeglumine group (p < 0.001), and the mean odds ratio to have an adequate HBP with gadoxetic acid compared to gadobenate dimeglumine was 3.64 (p < 0.001). The adequacy of the HBP in the gadoxetic acid group compared to the gadobenate dimeglumine group increased with the increase of the MELD score (exp(b)interaction = 1.233; p = 0.011).

CONCLUSION

In cirrhotic patients, the hepatobiliary phase obtained with gadoxetic acid-enhanced MRI is of better quality in comparison to gadobenate dimeglumine-enhanced MRI, mainly in patients with high MELD score.

KEY POINTS

• In cirrhotic patients, the adequacy of the hepatobiliary phase with gadoxetic acid-enhanced MRI is better compared to gadobenate dimeglumine-enhanced MRI. • Gadoxetic acid-enhanced MRI should be preferred to gadobenate dimeglumine-enhanced MRI in cirrhotic patients with MELD score > 10, if the hepatobiliary phase is clinically indicated. • In patients with high MELD score (> 15), the administration of the hepatobiliary agent could be useless; even though, if it is clinically indicated, we recommend to use gadoxetic acid given the higher probability of obtaining clinically relevant information.

Combining hyperpolarized 13 C MRI with a liver-specific gadolinium contrast agent for selective assessment of hepatocyte metabolism

PURPOSE

Hyperpolarized 13 C MRI is a powerful tool for studying metabolism, but can lack tissue specificity. Gadoxetate is a gadolinium-based MRI contrast agent that is selectively taken into hepatocytes. The goal of this project was to investigate whether gadoxetate can be used to selectively suppress the hyperpolarized signal arising from hepatocytes, which could in future studies be applied to generate specificity for signal from abnormal cell types.

METHODS

Baseline gadoxetate uptake kinetics were measured using T1 -weighted contrast enhanced imaging. Relaxivity of gadoxetate was measured for [1-13 C]pyruvate, [1-13 C]lactate, and [1-13 C]alanine. Four healthy rats were imaged with hyperpolarized [1-13 C]pyruvate using a three-dimensional (3D) MRSI sequence prior to and 15 min following administration of gadoxetate. The lactate:pyruvate ratio and alanine:pyruvate ratios were measured in liver and kidney.

RESULTS

Overall, the hyperpolarized signal decreased approximately 60% as a result of pre-injection of gadoxetate. In liver, the lactate:pyruvate and alanine:pyruvate ratios decreased 42% and 78%, respectively (P < 0.05) following gadoxetate administration. In kidneys, these ratios did not change significantly. Relaxivity of gadoxetate for [1-13 C]alanine was 12.6 times higher than relaxivity of gadoxetate for [1-13 C]pyruvate, explaining the greater selective relaxation effect on alanine.

CONCLUSIONS

The liver-specific gadolinium contrast-agent gadoxetate can selectively suppress normal hepatocyte contributions to hyperpolarized 13 C MRI signals. Magn Reson Med 77:2356-2363, 2017. © 2016 International Society for Magnetic Resonance in Medicine.

Rapid Cartesian versus radial acquisition: comparison of two sequences for hepatobiliary phase MRI at 3 tesla in patients with impaired breath-hold capabilities

Background

Hepatocyte-specific gadolinium based contrast agents (HSCA) provide substantial information for the classification of liver lesions in magnetic resonance imaging (MRI). However, breathing artifacts which reduce image quality and diagnostic confidence of hepatobiliary phase acquisitions are regularly observed in clinical routine. The aim of this study was to evaluate two approaches to reduce breathing artifacts for hepatobiliary phase imaging.

Methods

Twenty minutes after administration of a HSCA (gadoxetic acid), a T1-weighted VIBE sequence with radial k-space sampling (radialVIBE, 180 s acquisition time in free breathing) and a highly accelerated Cartesian VIBE with Dixon fat separation (CD-VIBE, CAIPIRINHA acceleration with r = 2 × 2, breath-hold 8–10 s) were acquired in 35 patients (12 female, 57 ± 13 years), who showed breath-holding difficulties in early phases of the examinations. Image quality (image sharpness, noise, artifacts, homogeneity of fat saturation, bile duct delineation and overall image quality) as well as conspicuity and liver-to-lesion signal intensity (SI) ratios of focal liver lesions were assessed for both radial- and CD-VIBE.

Results

Overall image quality was rated good to excellent for both sequences, while CD-VIBE was preferred in most cases. Though radialVIBE received better results regarding image noise and artifacts, both sequences were rated equally regarding bile duct delineation and sharpness. Focal liver lesion (n = 42) conspicuity was rated significantly better and SI-ratios were significantly higher on CD-VIBE (2.45 ± 1.44 vs. 1.61 ± 0.70 in radialVIBE, p = 0.0001). In three patients, CD-VIBE was rated non-diagnostic due to severe breathing artifacts, while radialVIBE was diagnostic in those patients.

Conclusion

Both highly accelerated Cartesian as well as radial acquisition techniques provide good to excellent image quality in hepatobiliary phase MRI. In comparison, CD-VIBE offered better overall image quality and liver lesion conspicuity. However, radialVIBE was a valuable alternative in patients unable to sustain even short breath-hold intervals. Further studies including lager patient cohorts are desirable to allow a transfer of these results to a general patient population.

Effect of steatosis on liver signal and enhancement on multiphasic contrast-enhanced magnetic resonance imaging

PURPOSE

To investigate the effect of steatosis on liver signal and enhancement in multiphasic contrast-enhanced (MCE) MRI.

MATERIALS AND METHODS

In this IRB-approved, HIPAA-compliant, retrospective, observational study, 1217 MCE abdominal MRIs performed during 2014 at a single institution were reviewed. Of these, 1085 were excluded, due to potential factors other than steatosis that may affect liver signal intensity and/or enhancement. In the remaining 132, liver fat fraction (FF) was calculated from the in- and opposed-phase 2D T1-weighted images. Liver signal intensity, absolute enhancement, and relative enhancement on fat-suppressed (Dixon method) 3D T1-weighted images before and after injection of gadobutrol (arterial, portal venous, and equilibrium phases) were plotted against co-localized FF values and the linear trend was evaluated by Pearson correlation coefficient (r). P values <0.05 were considered statistically significant.

RESULTS

Liver signal intensity negatively correlated with FF for all phases (r = -0.388 to -0.544, p < 0.001). Absolute enhancement negatively correlated with FF for the portal venous and equilibrium phases (r = -0.286 and -0.289, respectively, p < 0.001), but not for the arterial phase (r = -0.042, p = 0.632). Relative enhancement did not significantly correlate with FF for any phase (p ≥ 0.125).

CONCLUSION

Steatosis reduces liver signal intensity in MCE MRI. This effect of steatosis was reduced in calculated absolute enhancement and eliminated in calculated relative enhancement.

Stability of liver proton density fat fraction and changes in R 2* measurements induced by administering gadoxetic acid at 3T MRI

OBJECTIVE

To assess changes in liver proton density fat fraction (PDFF) and R 2* measurements in the presence of changes in tissue relaxation rates induced by administrating gadoxetic acid, using two different image reconstruction methods at 3T MRI.

METHODS

Forty-five patients were imaged at 3T with chemical-shift-based MRI sequences before and 20 min after administration of gadoxetic acid. Image reconstructions were performed using hybrid and complex methods to obtain PDFF and R 2* images. A single radiologist measured PDFF and R 2* values on precontrast and postcontrast images. Precontrast and postcontrast PDFF values were compared using intraclass correlation coefficient (ICC), linear regression, and Bland-Altman analysis. Changes in R 2* values from precontrast to postcontrast were correlated with relative liver enhancement (RLE) based on signal intensities on T 1-weighted images using Spearman's rank correlation.

RESULTS

PDFF values were similar between precontrast and postcontrast images (ICC = 0.99, linear regression slopes = 0.98, mean difference = -0.21 to -0.31%). PDFF measurements were stable between precontrast and postcontrast images. Changes in R 2* values were correlated with RLE (p < 0.001, r = 0.49-0.71).

CONCLUSIONS

PDFF measurements from both image reconstruction methods are stable in the presence of changes in tissue relaxation rates after administering gadoxetic acid at 3T MRI. Changes in R 2* values correlate with established measures of gadoxetic acid uptake based on T 1-weighted images.

Comparison of gadoxetic acid to gadobenate dimeglumine for assessment of biliary anatomy of potential liver donors

PURPOSE

To compare MRI using gadobenate dimeglumine (Gd-BOPTA) vs. gadoxetic acid disodium (Gd-EOB-DTPA) for the assessment of biliary anatomy of potential liver donors.

METHODS

76 potential liver donors (39 M/37 F, mean 38 years) who underwent 1.5T MRI using Gd-BOPTA (n = 37) or Gd-EOB-DTPA (n = 39) were retrospectively evaluated. T2 cholangiogram (T2 MRC) and delayed hepatobiliary phase (HBP) T1 cholangiogram (T1 MRC) (performed during HBP 20 min after injection of Gd-EOB-DTPA and 1-2 h after Gd-BOPTA injection) were obtained in addition to MR angiogram/venogram. Two independent observers evaluated image quality (IQ) and conspicuity scores (CS) of the biliary system. Biliary anatomy was assessed in 3 reading sessions (T2 MRC, T1 MRC, and combined T2/T1 MRC). Reference standard consisted of consensus reading of two separate observers of all image sets, clinical/surgical information and intraoperative cholangiogram when available. Datasets were compared using the Mann-Whitney U test or Chi-squared test.

RESULTS

There was no difference in IQ for T1 MRC using either contrast agent or T2 MRC vs. T1 MRC for both observers (all p values >0.07). There was superior CS for T2 MRC vs. Gd-BOPTA T1 MRC for both observers and T2 MRC vs. Gd-EOB for one observer (p < 0.001). No difference was found for biliary variant detection for T1 MRC (with either contrast agent) vs. T2 MRC. Combined T2/T1 MRC demonstrated improved sensitivity for biliary variant detection using Gd-BOPTA for both observers (p < 0.004) and Gd-EOB-DTPA for one observer (p < 0.001).

CONCLUSION

Equivalent image quality was found for T1 MRC obtained with Gd-BOPTA or Gd-EOB-DTPA and T2 MRC. T1 MRC is equivalent to T2 MRC for detection of variant biliary anatomy, and the combination of sequences may have added value.

Consensus report from the 7th International Forum for Liver Magnetic Resonance Imaging

Objectives

Liver-specific MRI is a fast-growing field, with technological and protocol advancements providing more robust imaging and allowing a greater depth of information per examination. This article reports the evidence for, and expert thinking on, current challenges in liver-specific MRI, as discussed at the 7th International Forum for Liver MRI, which was held in Shanghai, China, in October 2013.

Methods

Topics discussed included the role of gadoxetic acid-enhanced MRI in the differentiation of focal nodular hyperplasia from hepatocellular adenoma and small hepatocellular carcinoma (HCC) from small intrahepatic cholangiocarcinoma (in patients with chronic liver disease), the differentiation of low-grade dysplastic nodule (DN) from pre-malignant high-grade DN and early HCC, and treatment planning and assessment of treatment response for patients with HCC and colorectal liver metastasis. Optimization of the gadoxetic acid-enhanced MRI protocol to gain robust arterial and hepatobiliary phase images was also discussed.

Results and conclusions

Gadoxetic acid-enhanced MRI demonstrates added value for the detection and characterization of focal liver lesions and shows promise in a number of new indications, including regional liver functional assessment and patient monitoring after therapy; however, more data are needed in some areas, and further developments are needed to translate cutting-edge techniques into clinical practice.

Key Points

• Liver-specific MRI is a fast-growing field, with many technological and protocol advancements.

• Gadoxetic acid-enhanced MRI demonstrates value for detecting and characterizing focal liver lesions.

• Gadoxetic acid-enhanced MRI shows promise in regional functional assessment and patient monitoring.

• Further developments are needed to translate cutting-edge techniques into clinical practice.

Combined gadoxetic acid and gadofosveset enhanced liver MRI: A feasibility and parameter optimization study

PURPOSE

Demonstration of feasibility and protocol optimization for the combined use of gadofosveset trisodium with gadoxetic acid for delayed T1-weighted liver MRI.

METHODS

Eleven healthy volunteers underwent hepatobiliary phase imaging at 3 Tesla (T) using gadoxetic acid. Multiple breathheld T1-weighted three-dimensional spoiled gradient echo sequences were performed at varying flip angles before and after injection of gadofosveset. Signal-to-noise ratio (SNR) and contrast-to-noise ratio (CNR) were measured to determine optimal T1-weighting. Examples of three patients with focal liver lesions were acquired.

RESULTS

The addition of gadofosveset to the hepatobiliary phase of gadoxetic acid renders vessels isointense to liver tissue at low flip angles due to increased vessel SNR (P < 0.001). The lowest CNR of liver relative to portal vein (CNR = 15; 95% confidence interval [CI]: -14-44) was observed at a 10º flip angle. The highest CNR of liver relative to muscle (CNR = 214; 95% CI: 191-237) was observed at a 20º flip angle. The combined enhancement leads to homogenously enhanced liver tissue and liver vasculature. Cysts were detected in three volunteers and metastases were detected in two patients. In these anecdotal cases the cysts and metastases stood out as conspicuous focal hypointensities on combined gadoxetic acid and gadofosveset enhanced images.

CONCLUSION

Combined gadoxetic acid and gadofosveset enhanced liver MRI is feasible, with low flip angles minimizing contrast between vessels and liver. Further clinical studies are needed to confirm that low flip angles provide an optimal combination of sensitivity and specificity for lesion detection in patients.

Hepatocellular carcinoma: diagnostic criteria by imaging techniques

Imaging plays a very important role in the diagnosis of HCC. Indeed, in high-risk patients a noninvasive diagnosis can only be obtained by imaging in presence of typical features. These features include arterial enhancement followed by washout during the portal venous and/or delayed phases on CT scan or MRI. This pattern is quite specific and has been endorsed by both Western and Asian diagnostic guidelines. However, its sensitivity is not very high, especially for small lesions. Therefore ancillary signs may be needed to increase the reliability of the diagnosis. Recent hepatobiliary MRI contrast agents seem to be interesting to improve characterization of small nodules in the cirrhotic liver.