Clinical value of MRI liver-specific contrast agents: a tailored examination for a confident non-invasive diagnosis of focal liver lesions

Can bile excretion on Gd-EOB-MRI be used as a visual criterion for the hepatobiliary phase?

To determine whether visually observed biliary excretion of gadolinium-ethoxybenzyl-diethylenetriamine pentaacetic acid (Gd-EOB-DTPA) can be used to assess contrast adequacy of hepatobiliary phase (HBP) images. Images of 121 patients undergoing Gd-EOB-DTPA-enhanced magnetic resonance imaging were used. Adequate HBP images were defined as a quantitative liver-spleen contrast ratio (Q-LSC) ≥ 1.5. Visual evaluation was performed to determine if an adequate HBP image could be obtained based on the presence or absence of bile excretion. Common bile duct-paravertebral contrast (CPC) was used to assess the degree of bile excretion, the albumin-bilirubin (ALBI) grade was used to assess liver reserve, and the Q-LSC was used to assess HBP image contrast. The results were used to quantitatively evaluate the relationships of the degree of bile excretion with HBP image contrast and liver reserve. The cases correctly determined by visual evaluation via bile excretion were 80 (66.1%) at HBP 10 min after injection and 89 (73.6%) at HBP 20 min after injection. Among cases with Q-LSC ≥ 1.5 indicating bile excretion, there were 33 cases at HBP 10 min after injection and 86 cases at HBP 20 min after injection. Furthermore, among cases with Q-LSC < 1.5, indicating no bile excretion, there were 47 cases at HBP 10 min after injection and 3 cases at HBP 20 min after injection. Visually observed biliary excretion of Gd-EOB-DTPA is not a criterion for adequate HBP image contrast.

Pulsation artifact reduction using compressed sensitivity encoding in Gd-EOB-DTPA contrast-enhanced magnetic resonance imaging

In Gd-EOB-DTPA-enhanced MRI, cardiac pulsation artifacts in the left lobe often hinder diagnosis, the image quality need to improve. This study aimed to reduce cardiac pulsation artifacts in Gd-EOB-DTPA-enhanced three-dimensional (3D) T1-weighted turbo-field echo (3D-T1TFE) using compressed sensitivity encoding (CS).For phantom evaluation, the cardiac phantom was manually operated using a metronome-synchronized apparatus, comprising a bag-valve mask, a breathing circuit, and a Jackson-Rees system. Transverse images of a liver phantom were acquired using enhanced T1 high-resolution isotropic volumetric excitation with CS (CS-eTHRIVE) and sensitivity encoding (S-eTHRIVE). For evaluation, images obtained during cardiac phantom operation were subtracted from those obtained when the phantom was stationary. Standard deviation (SD) of the difference images was used as the evaluation metric, and assessments were conducted based on changes in heart rate and TFE factor. For clinical image evaluation, artifacts in hepatobiliary phase images acquired 15 min after Gd-EOB-DTPA injection in the order of S-eTHRIVE and CS-eTHRIVE were visually evaluated at four levels. In heart-rate evaluation (40, 60, and 80 beats/min), CS-eTHRIVE revealed significantly lower SD values compared to S-eTHRIVE across all heart rates (P < 0.01), with no significant differences between heart rates. For TFE factor evaluation, CS-eTHRIVE with a factor of 35 exhibited the lowest SD, which was significantly different from all other groups (P < 0.01). In clinical image evaluation, CS-eTHRIVE achieved higher visual scores (mean ± SD: 3.72 ± 0.46) compared with S-eTHRIVE (2.72 ± 0.98, P < 0.01).CS reduced pulsation artifacts in Gd-EOB-DTPA-enhanced 3D-T1TFE.

Bimagnetic Core/Shell Nanoprobes with Tunable Exchange Coupling for High Resolution and Sensitive Magnetic Particle Imaging

Magnetic particle imaging (MPI) has demonstrated versatile applications in biomedicine, including tumor imaging, cell tracking, and image-guided hyperthermia. Despite these advancements, the prevalent use of clinically approved tracers has posed limitations on MPI's resolution and sensitivity. In this study, we engineered a bimagnetic core/shell nanocrystals (BMCS) tailored for MPI by optimizing the heterostructure and modulating the exchange coupling effect between the two magnetic components. The resulting BMCS exhibited remarkably heightened susceptibility and magnetization while maintaining low coercivity, thereby substantially improved both MPI resolution and sensitivity compared to conventional tracers such as VivoTrax. At an equivalent mass concentration, BMCS demonstrated a notable 5.08-fold increase in signal intensity and achieved an unprecedentedly high resolution down to 1 mm. The excellent MPI performance contributes to high resolution MPI and the sensitive detection of orthotopic colorectal cancer in mice. The design strategy employed in BMCS, centered on the exchange coupling effect, introduces an efficacious approach for the development of high performance MPI tracers.

Enhancing gadoxetic acid-enhanced liver MRI: a synergistic approach with deep learning CAIPIRINHA-VIBE and optimized fat suppression techniques

OBJECTIVE

To investigate whether a deep learning (DL) controlled aliasing in parallel imaging results in higher acceleration (CAIPIRINHA)-volumetric interpolated breath-hold examination (VIBE) technique can improve image quality, lesion conspicuity, and lesion detection compared to a standard CAIPIRINHA-VIBE technique in gadoxetic acid-enhanced liver MRI.

METHODS

This retrospective single-center study included 168 patients who underwent gadoxetic acid-enhanced liver MRI at 3 T using both standard CAIPIRINHA-VIBE and DL CAIPIRINHA-VIBE techniques on pre-contrast and hepatobiliary phase (HBP) images. Additionally, high-resolution (HR) DL CAIPIRINHA-VIBE was obtained with 1-mm slice thickness on the HBP. Three abdominal radiologists independently assessed the image quality and lesion conspicuity of pre-contrast and HBP images. Statistical analyses involved the Wilcoxon signed-rank test for image quality assessment and the generalized estimation equation for lesion conspicuity and detection evaluation.

RESULTS

DL and HR-DL CAIPIRINHA-VIBE demonstrated significantly improved overall image quality and reduced artifacts on pre-contrast and HBP images compared to standard CAIPIRINHA-VIBE (p < 0.001), with a shorter acquisition time (DL vs standard, 11 s vs 17 s). However, the former presented a more synthetic appearance (both p < 0.05). HR-DL CAIPIRINHA-VIBE showed superior lesion conspicuity to standard and DL CAIPIRINHA-VIBE on HBP images (p < 0.001). Moreover, HR-DL CAIPIRINHA-VIBE exhibited a significantly higher detection rate of small (< 2 cm) solid focal liver lesions (FLLs) on HBP images compared to standard CAIPIRINHA-VIBE (92.5% vs 87.4%; odds ratio = 1.83; p = 0.036).

CONCLUSION

DL and HR-DL CAIPIRINHA-VIBE achieved superior image quality compared to standard CAIPIRINHA-VIBE. Additionally, HR-DL CAIPIRINHA-VIBE improved the lesion conspicuity and detection of small solid FLLs. DL and HR-DL CAIPIRINHA-VIBE hold the potential clinical utility for gadoxetic acid-enhanced liver MRI.

CLINICAL RELEVANCE STATEMENT

DL and HR-DL CAIPIRINHA-VIBE hold promise as potential alternatives to standard CAIPIRINHA-VIBE in routine clinical liver MRI, improving the image quality and lesion conspicuity, enhancing the detection of small (< 2 cm) solid focal liver lesions, and reducing the acquisition time.

KEY POINTS

• DL and HR-DL CAIPIRINHA-VIBE demonstrated improved overall image quality and reduced artifacts on pre-contrast and HBP images compared to standard CAIPIRINHA-VIBE, in addition to a shorter acquisition time. • DL and HR-DL CAIPIRINHA-VIBE yielded a more synthetic appearance than standard CAIPIRINHA-VIBE. • HR-DL CAIPIRINHA-VIBE showed improved lesion conspicuity than standard CAIPIRINHA-VIBE on HBP images, with a higher detection of small (< 2 cm) solid focal liver lesions.

MRI for hepatocellular carcinoma and the role of abbreviated MRI for surveillance of hepatocellular carcinoma

INTRODUCTION

Hepatocellular carcinoma (HCC) constitutes the majority of liver cancers and significantly impacts global cancer mortality. While ultrasound (US) with or without alpha-fetoprotein is the mainstay for HCC surveillance, its limitations highlight the necessity for more effective surveillance tools. Therefore, this review explores evolving imaging modalities and abbreviated magnetic resonance imaging (MRI) (AMRI) protocols as promising alternatives, addressing challenges in HCC surveillance.

AREAS COVERED

This comprehensive review delves into the evaluation and challenges of HCC surveillance tools, focusing on non-contrast abbreviated MRI (NC-AMRI) and contrast-enhanced abbreviated MRI protocols. It covers the implementation of AMRI for HCC surveillance, patient preferences, adherence, and strategies for optimizing cost-effectiveness. Additionally, the article provides insights into prospects for HCC surveillance by summarizing meta-analyses, prospective studies, and ongoing clinical trials evaluating AMRI protocols.

EXPERT OPINION

The opinions underscore the transformative impact of AMRI on HCC surveillance, especially in overcoming US limitations. Promising results from NC-AMRI protocols indicate its potential for high-risk patient surveillance, though prospective studies in true surveillance settings are essential for validation. Future research should prioritize risk-stratified AMRI protocols and address cost-effectiveness for broader clinical implementation, alongside comparative analyses with US for optimal surveillance strategies.

Assessment of liver function by gadoxetic acid avidity in MRI in a model of rapid liver regeneration in rats

BACKGROUND

This animal study investigates the hypothesis of an immature liver growth following ALPPS (associating liver partition and portal vein ligation for staged hepatectomy) by measuring liver volume and function using gadoxetic acid avidity in magnetic resonance imaging (MRI) in models of ALPPS, major liver resection (LR) and portal vein ligation (PVL).

METHODS

Wistar rats were randomly allocated to ALPPS, LR or PVL. In contrast-enhanced MRI scans with gadoxetic acid (Primovist®), liver volume and function of the right median lobe (=future liver remnant, FLR) and the deportalized lobes (DPL) were assessed until post-operative day (POD) 5. Liver functionFLR/DPL was defined as the inverse value of time from injection of gadoxetic acid to the blood pool-corrected maximum signal intensityFLR/DPL multiplied by the volumeFLR/DPL.

RESULTS

In ALPPS (n = 6), LR (n = 6) and PVL (n = 6), volumeFLR and functionFLR increased proportionally, except on POD 1. Thereafter, functionFLR exceeded volumeFLR increase in LR and ALPPS, but not in PVL. Total liver function was significantly reduced after LR until POD 3, but never undercuts 60% of its pre-operative value following ALPPS and PVL.

DISCUSSION

This study shows for the first time that functional increase is proportional to volume increase in ALPPS using gadoxetic acid avidity in MRI.

Image Quality and Diagnostic Performance of Low-Dose Liver CT with Deep Learning Reconstruction versus Standard-Dose CT

Purpose To compare the image quality and diagnostic capability in detecting malignant liver tumors of low-dose CT (LDCT, 33% dose) with deep learning-based denoising (DLD) and standard-dose CT (SDCT, 100% dose) with model-based iterative reconstruction (MBIR). Materials and Methods In this prospective, multicenter, noninferiority study, individuals referred for liver CT scans were enrolled from three tertiary referral hospitals between February 2021 and August 2022. All liver CT scans were conducted using a dual-source scanner with the dose split into tubes A (67% dose) and B (33% dose). Blended images from tubes A and B were created using MBIR to produce SDCT images, whereas LDCT images used data from tube B and were reconstructed with DLD. The noise in liver images was measured and compared between imaging techniques. The diagnostic performance of each technique in detecting malignant liver tumors was evaluated by three independent radiologists using jackknife alternative free-response receiver operating characteristic analysis. Noninferiority of LDCT compared with SDCT was declared when the lower limit of the 95% CI for the difference in figure of merit (FOM) was greater than -0.10. Results A total of 296 participants (196 men, 100 women; mean age, 60.5 years ± 13.3 [SD]) were included. The mean noise level in the liver was significantly lower for LDCT (10.1) compared with SDCT (10.7) (P < .001). Diagnostic performance was assessed in 246 participants (108 malignant tumors in 90 participants). The reader-averaged FOM was 0.880 for SDCT and 0.875 for LDCT (P = .35). The difference fell within the noninferiority margin (difference, -0.005 [95% CI: -0.024, 0.012]). Conclusion Compared with SDCT with MBIR, LDCT using 33% of the standard radiation dose had reduced image noise and comparable diagnostic performance in detecting malignant liver tumors. Keywords: CT, Abdomen/GI, Liver, Comparative Studies, Diagnosis, Reconstruction Algorithms Clinical trial registration no. NCT05804799 © RSNA, 2024 Supplemental material is available for this article.

Monitoring and Surveillance of Patients with Gastroenteropancreatic Neuroendocrine Tumors Undergoing Radioligand Therapy

Radioligand therapy (RLT) with [177Lu]Lu-DOTA-TATE is a standard of care for adult patients with somatostatin-receptor (SSTR)-positive gastroenteropancreatic neuroendocrine tumors (GEP-NETs). Taking advantage of this precision nuclear medicine approach requires diligent monitoring and surveillance, from the use of diagnostic SSTR-targeted radioligand imaging for the selection of patients through treatment and assessments of response. Published evidence-based guidelines assist the multidisciplinary healthcare team by providing acceptable approaches to care; however, the sheer heterogeneity of GEP-NETs can make these frameworks difficult to apply in individual clinical circumstances. There are also contradictions in the literature regarding the utility of novel approaches in monitoring and surveilling patients with GEP-NETs receiving RLT. This article discusses the emerging evidence on imaging, clinical biochemistry, and tumor assessment criteria in the management of patients receiving RLT for GEP-NETs; additionally, it documents our own best practices. This allows us to offer practical guidance on how to effectively implement monitoring and surveillance measures to aid patient-tailored clinical decision-making.

Effect of type 2 diabetes on liver images of GD-EOB-DTPA-enhanced MRI during the hepatobiliary phase

To analyze alterations of the liver appearance during the hepatobiliary phase of individuals with type 2 diabetes who are receiving gadolinium ethoxybenzyl diethylenetriamine pentaacetic acid (Gd-EOB-DTPA) enhanced magnetic resonance imaging (MRI). Fifty-seven individuals who received Gd-EOB-DTPA-enhanced MRI and had normal liver and renal function but did not have (control group) or have type 2 diabetes (observation group) were retrospectively included in this study. The liver enhancement ratio (LER) and contrast between liver parenchyma and portal vein (LPC) were calculated from hepatobiliary phase images. Utilizing liver to kidney signal intensity, signs of the biliary system, and signs of the portal vein, a functional liver imaging score (FLIS) was calculated. Wilcoxon rank-sum test was used to assess the between-group differences in LER, LPC, and FLIS. FLIS constituent ratios between the two groups were tested using the χ² test. The effectiveness of LER, LPC, and FLIS for identifying type 2 diabetes was assessed by receiver operating characteristic curves (ROCs). The interobserver consistency of FLIS was evaluated using the intraclass correlation coefficients. The observation group's LER and LPC were lower than the control group. The constituent ratio of the FLIS score (liver to kidney signal intensity, p = 0.011) showed a significant between-group difference. According to ROCs, LER and LPC were associated with the identification of type 2 diabetes. LER = 0.54 and LPC = 1.46 were the optimal cutoff for identifying type 2 diabetes, respectively. FLIS demonstrated excellent inter-reader agreement. The relative signal intensity of the liver during the hepatobiliary phase is decreased in patients with type 2 diabetes. This should be considered when individuals with type 2 diabetes undergo Gd-EOB-DTPA-enhanced MRI to avoid misdiagnoses, such as small hepatocellular carcinoma or abnormal liver function.

Evaluation of liver function in patients with liver cirrhosis and chronic liver disease using functional liver imaging scores at different acquisition time points

Purpose: This paper aims to explore whether functional liver imaging score (FLIS) based on Gd-EOB-DTPA-enhanced magnetic resonance imaging (MRI) images at 5, 10, and 15 min can predict liver function in patients with liver cirrhosis or chronic liver disease and its association with indocyanine green 15-min retention rate (ICG-R₁₅), Child-Pugh (CP) score, albumin-bilirubin (ALBI) score, and model for end-stage liver disease (MELD) score. In addition, it also examines the inter- and intra-observer consistency of FLIS and three FLIS parameters at three different time points. Methods: This study included 110 patients with chronic liver disease (CLD) or liver cirrhosis (LC) (93 men, 17 women; mean ± standard deviation = 56.96 ± 10.16) between July 2019 and May 2022. FLIS was assigned in accordance with the sum of the three hepatobiliary phase characteristics, all of which were scored on the 0-2 ordinal scale, including the biliary excretion, hepatic enhancement and portal vein signal intensity. FLIS was calculated independently by two radiologists using transitional and hepatobiliary phase images at 5, 10, and 15 min after enhancement. The relationship between FLIS and three FLIS quality scores and the degree of liver function were evaluated using Spearman's rank correlation coefficient. The ability of FLIS to predict hepatic function was investigated using receiver operating characteristic (ROC) curves. Results: Intra- and inter-observer intraclass correlation coefficients (ICCs) (ICC = 0.937-0.978, 95% CI = 0.909-0.985) for FLIS at each time point indicated excellent agreement. At each time point, FLIS had a moderate negative association with liver function classification (r = [-0.641]-[-0.428], p < 0.001), and weak to moderate correlation with some other clinical parameters except for creatinine (p > 0.05). FLIS showed moderate discriminatory ability between different liver function levels. The area under the ROC curves (AUCs) of FLIS at 5, 10, and 15 min after enhancement to predict ICG-R₁₅ of 10% or less were 0.838, 0.802, and 0.723, respectively; those for predicting ICG-R₁₅ greater than 20% were 0.793, 0.824, and 0.756, respectively; those for predicting ICG-R₁₅ greater than 40% were 0.728, 0.755, and 0.741, respectively; those for predicting ALBI grade 1 were 0.734, 0.761, and 0.691, respectively; those for predicting CP class A cirrhosis were 0.806, 0.821, and 0.829, respectively; those for predicting MELD score of 10 or less were 0.837, 0.877, and 0.837, respectively. No significant difference was found in the AUC of FLIS at 5, 10 and 15 min (p > 0.05). Conclusion: FLIS presented a moderate negative correlation with the classification system of hepatic function at a delay of 5, 10, and 15 min, and patients with LC or CLD were appropriately stratified based on ICG-R₁₅, ALBI grade, MELD score, and CP classification. In addition, the use of FLIS to evaluate liver function can reduce the observation time of the hepatobiliary period.

Influence of dilution on arterial-phase artifacts and signal intensity on gadoxetic acid-enhanced liver MRI

OBJECTIVES

To investigate the effect of saline-diluted gadoxetic acid, done for arterial-phase (AP) artifact reduction, on signal intensity (SI), and hence focal lesion conspicuity on MR imaging.

METHODS

We retrospectively examined 112 patients who each had at least two serial gadoxetic acid-enhanced liver MRIs performed at 1 ml/s, first with non-diluted (ND), then with 1:1 saline-diluted (D) contrast. Two blinded readers independently analyzed the artifacts and graded dynamic images using a 5-point scale. The absolute SI of liver parenchyma, focal liver lesions (if present), aorta, and portal vein at the level of the celiac trunk and the SI of the paraspinal muscle were measured in all phases. The signal-to-norm (SI_Norm) of the vascular structures, hepatic parenchyma and focal lesions, and the contrast-to-norm (C_Norm) of focal liver lesions were calculated.

RESULTS

AP artifacts were significantly reduced with dilution. Mean absolute contrast-enhanced liver SI was significantly higher on the D exams compared to the ND exams. Likewise, SI_Norm of liver parenchyma was significantly higher in all contrast-enhanced phases except transitional phase on the D exams. SI_Norm values in the AP for the aorta and in the PVP for portal vein were significantly higher on the diluted exams. The C_Norm was not significantly different between ND and D exams for lesions in any imaging phase. The interclass correlation coefficient was excellent (0.89).

CONCLUSION

Gadoxetic acid dilution injected at 1ml/s produces images with significantly fewer AP artifacts but no significant loss in SI_Norm or C_Norm compared to standard non-diluted images.

KEY POINTS

• Diluted gadoxetic acid at slow injection (1 ml/s) yielded images with higher SI_Norm of the liver parenchyma and preserved C_Norm for focal liver lesions. • Gadoxetic acid-enhanced MRI injected at 1 ml/s is associated with arterial-phase (AP) artifacts in 31% of exams, which may degrade image quality and limits focal liver lesion detection. • Saline dilution of gadoxetic acid 1:1 combined with a slow injection rate of 1 ml/s significantly reduced AP artifacts from 31 to 9% and non-diagnostic AP artifacts from 16 to 1%.

Influence of age on gadoxetic acid disodium-induced transient respiratory motion artifacts in pediatric liver MRI

PURPOSE

Gd-EOB-DTPA-enhanced liver MRI is frequently compromised by transient severe motion artifacts (TSM) in the arterial phase, which limits image interpretation for the detection and differentiation of focal liver lesions and for the recognition of the arterial vasculature before and after liver transplantation. The purpose of this study was to investigate which patient factors affect TSM in children who undergo Gd-EOB-DTPA-enhanced liver MRI and whether younger children are affected as much as adolescents.

METHODS

One hundred and forty-eight patients (65 female, 83 male, 0.1-18.9 years old), who underwent 226 Gd-EOB-DTPA-enhanced MRIs were included retrospectively in this single-center study. The occurrence of TSM was assessed by three readers using a four-point Likert scale. The relation to age, gender, body mass index, indication for MRI, requirement for sedation, and MR repetition was investigated using uni- and multivariate logistic regression analysis.

RESULTS

In Gd-EOB-DTPA-enhanced MRIs, TSM occurred in 24 examinations (10.6%). Patients with TSM were significantly older than patients without TSM (median 14.3 years; range 10.1-18.1 vs. 12.4 years; range 0.1-18.9, p<0.001). TSM never appeared under sedation. Thirty of 50 scans in patients younger than 10 years were without sedation. TSM were not observed in non-sedated patients younger than 10 years of age (p = 0.028). In a logistic regression analysis, age remained the only cofactor independently associated with the occurrence of TSM (hazard ratio 9.152, p = 0.049).

CONCLUSION

TSM in Gd-EOB-DTPA-enhanced liver MRI do not appear in children under the age of 10 years.

High Frame Rate Contrast-enhanced Ultrasound Helps Differentiate Malignant and Benign Focal Liver Lesions

BACKGROUND AND AIMS

This study aimed to evaluate the diagnostic performance of high frame rate contrast-enhanced ultrasound (H-CEUS) of focal liver lesions (FLLs).

METHODS

From July 2017 to June 2019, conventional contrast-enhanced ultrasound (C-CEUS) and H-CEUS were performed in 78 patients with 78 nodules. The characteristics of C-CEUS and H-CEUS in malignant and benign groups and the differences between different lesion sizes (1-3 cm, 3-5 cm, or >5 cm) of C-CEUS and H-CEUS were examined. The diagnostic performance of C-CEUS and H-CEUS was analyzed. The chi-square test or Fisher's exact test was used to assess inter-group differences. The receiver operating characteristic curve was plotted to determine the diagnostic performance of C-CEUS and H-CEUS.

RESULTS

There were significant differences in the enhancement area, fill-in direction and vascular architecture between C-CEUS and H-CEUS for both benign and malignant lesions (all p=0.000-0.008), but there were no significant differences in washout results (p=0.566 and p=0.684, respectively). For lesions 1-3 cm in size, the enhancement area, fill-in direction, and vascular architecture on C-CEUS and H-CEUS were significantly different (all p=0.000), unlike for lesions 3-5 cm or >5 cm in size. For differentiation of malignant from benign FLLs in the 1-3 cm group, H-CEUS showed sensitivity, specificity, accuracy, and positive and negative predictive values of 92.86%, 95.0%, 96.3%, 90.48% and 93.75%, respectively, which were higher than those for C-CEUS (75.0%, 70.0%, 77.78%, 66.67% and 72.91%, respectively).

CONCLUSIONS

H-CEUS provided more vascular information which could help differentiate malignant from benign FLLs, especially for lesions 1-3 cm in size.

Characteristics of false-positive lesions in evaluating colorectal liver metastases on gadoxetic acid-enhanced magnetic resonance imaging

PURPOSE

Gadoxetic acid-enhanced MRI (Gd-EOB-MRI) shows higher sensitivity for colorectal liver metastases (CRLM) than contrast-enhanced computed tomography (CECT). However, the details of false-positive lesions for each imaging modality are unknown.

METHODS

Cases undergoing hepatectomy for CRLM following a preoperative evaluation with both CECT and Gd-EOB-MRI between July 2008 and December 2016 were reviewed. The false-positive and false-negative rates were assessed for each modality, and the characteristics of false-positive lesions were evaluated.

RESULTS

We evaluated 275 partial hepatectomies in 242 patients without preoperative chemotherapy. Among the 275 hepatectomies, 546 lesions were recognized by CECT and/or Gd-EOB-MRI. The false-positive rates for CECT and Gd-EOB-MRI were 4% (18/422) and 7% (37/536), respectively. The size of false-positive lesions was significantly smaller than that of correctly diagnosed lesions (median: 28 mm [3-120 mm] vs 7.6 mm [320 mm], P  < 0.001). Compared with the 233 correctly diagnosed lesions ≤ 20 mm in diameter, false-positive lesions were more frequently located near the liver surface or vasculobiliary structures than true lesions (33/37 [89%] vs 149/233 [64%], respectively; P  = 0.0021).

CONCLUSION

Gd-EOB-MRI had a 7% false-positive rate. A small size and tumor location near the surface or near vasculobiliary structures were associated with false positivity.

Somatostatin Receptor Imaging and Theranostics: Current Practice and Future Prospects

A new era of precision diagnostics and therapy for patients with neuroendocrine neoplasms began with the approval of somatostatin receptor (SSTR) radiopharmaceuticals for PET imaging followed by peptide receptor radionuclide therapy (PRRT). With the transition from SSTR-based γ-scintigraphy to PET, the higher sensitivity of the latter raised questions regarding the direct application of the planar scintigraphy-based Krenning score for PRRT eligibility. Also, to date, the role of SSTR PET in response assessment and predicting outcome remains under evaluation. In this comprehensive review article, we discuss the current role of SSTR PET in all aspects of neuroendocrine neoplasms, including its relation to conventional imaging, selection of patients for PRRT, and the current understanding of SSTR PET-based response assessment. We also provide a standardized reporting template for SSTR PET with a brief discussion.

Evaluation of liver function in patients with chronic hepatitis B using Gd-EOB-DTPA-enhanced T1 mapping at different acquisition time points: a feasibility study

PURPOSE

This study aimed to explore the impact of different acquisition times on the evaluation of liver function levels in chronic hepatitis B using Gd-EOB-DTPA-enhanced T1 positioning technology under 3.0 Tesla magnetic resonance imaging (MRI).

METHODS

A total of 146 patients with chronic hepatitis B (CHB) were classified into four groups as follows: chronic hepatitis B without liver cirrhosis (CH, 22 cases), liver cirrhosis with Child-Pugh classification A (LCA 63 cases), Child-Pugh B (LCB 47 cases) and Child-Pugh C (LCC 14 cases). Normal liver function (NLF) group was composed of 23 persons who had healthy liver and no medical histories of hepatitis. T1 mapping images were performed before and after administration of Gd-EOB-DPTA using Look-Locker sequence. Changes in T1 relaxation time (T1rt), the reduction rate of T1 relaxation time (ΔT1) and the increase in T1 relaxation rate (ΔR1) of liver over time (at 5, 10, 15 and 20 min) were investigated and compared among all five groups using a one-way analysis of variance (ANOVA). The Spearman's rank correlation coefficient (r) was used to show the correlations of these parameters in different liver function groups.

RESULTS

In the NLF, CH, LCA and LCB groups, postT1 gradually decreased, while the ΔT1 and ΔR1 gradually increased with time. The parameters were compared between different liver function levels at the same time point, and the differences were statistically significant except for NLF-CH, NLF-LCA and CH-LCA. There was no significant difference in the area under the ROC curve of other parameters at 10, 15 and 20 min. At each time point, no correlation was found between preT1rt and the degrees of liver function. PostT1rt was positively correlated with liver function classification, while ΔT1 and ΔR1 were negatively correlated with liver function classification.

CONCLUSION

Gd-EOB-DTPA-enhanced T1 mapping magnetic resonance imaging is beneficial to assess liver function. Using the Gd-EOB-DTPA to enhance T1 mapping imaging to assess liver function can shorten the observation time of the hepatobiliary period and 10 min after enhancement may be the best time point.

Glutathione-Responsive Magnetic Nanoparticles for Highly Sensitive Diagnosis of Liver Metastases

Liver metastasis (LM) occurs in various cancers, and its early and accurate diagnosis is of great importance. However, the detection of small LMs is still a great challenge because of the subtle differences between normal liver tissue and small metastases. Herein, we prepare glutathione (GSH)-responsive hyaluronic acid-coated iron oxide nanoparticles (HIONPs) for highly sensitive diagnosis of LMs through a facile one-pot method. HIONPs greatly enhance the signal of MRI in tumor metastases as T₁ contrast agent (CA), whereas they substantially decrease the signal of liver as T₂ CA as they aggregate into clusters upon the high GSH in liver. Consequently, MRI contrasted by HIONPs clearly distinguishes metastatic tumors (bright) from surrounding liver tissues (dark). HIONPs with superior LM contrasting capability and facile synthesis are very promising for clinical translation and indicate a new strategy to develop an ultrasensitive MRI CA for LM diagnosis that exploits high GSH level in the liver.

Shear-wave velocity for colorectal cancer liver metastases as a potential prognostic factor after chemotherapy: a preliminary study

AIM

To evaluate whether shear-wave velocity (SWV) can be used for predicting the prognoses of patients with colorectal cancer liver metastases (CRLMs) after chemotherapy.

MATERIALS AND METHODS

Our institutional review board approved this prospective study, and written informed consent was obtained. SWV of CRLMs were obtained using point shear-wave elastography using acoustic radiation force impulse from 25 patients prior to and 2, 7, and 14 days after chemotherapy. Progression-free survival (PFS) after chemotherapy was estimated using the Kaplan-Meier method. The Cox proportional hazard regression model was used to determine significant predictive factors for PFS. For measurement reproducibility, an additional 37 patients with CRLMs were enrolled and assessed using intraclass correlation coefficients (ICCs).

RESULTS

After chemotherapy, 10 and 15 patients were classified into responder and non-responder groups, respectively. The estimated 1- and 3-year PFS values in the whole cohort were 36% and 8%, respectively. A decrease in the SWV value on day 2 relative to the initial value was a significant predictive factor for better PFS outcome (hazard ratio = 0.20, 95% confidence interval = 0.07-0.57, p=0.003). The estimated 1 and 3-year PFS rates were 66.7% and 22.2%, respectively, in nine patients with decreased SWV values on day 2 and significantly higher than 18.8% and 0% of 16 patients with increased SWV values on day 2. The ICC value of SWV of CRLMs in the additional 37 patients was 0.823 (95% CI = 0.685-0.905), indicating good agreement.

CONCLUSION

SWV values of CRLMs could provide prognostic information in patients with CRLMs treated with chemotherapy, as decreased SWV values on day 2 after chemotherapy was a significant predictive factor for better PFS.

Ultrasmall Fe@Fe3O4 nanoparticles as T1-T2 dual-mode MRI contrast agents for targeted tumor imaging

Targeted T₁-T₂ MRI contrast agents, which can eliminate the difficulty of image matching across multiple imaging instruments and permit specific localization of lesions, are promising candidates for more accurate diagnosis of tumors. In this study, ultrasmall Fe@Fe₃O₄ nanoparticles were designed and synthesized as T₁-T₂ dual-mode MRI contrast agents for accurate tumor imaging. First, to investigate the influence of nanoparticle size, Fe@Fe₃O₄ nanoparticles with diameters of 4, 8, and 12 nm were prepared, among which the 8 nm 3-(3,4-dihydroxyphenyl)propionic acid (DHCA)-modified nanoparticles exhibited the optimal T₁-T₂ dual-mode MRI performance. Next, to develop a tumor-targeted contrast agent, the DHCA-Fe@Fe₃O₄ nanoparticles were conjugated with the F56 peptide, which targets the vascular endothelial growth factor receptor, and the resulting F56-DHCA-Fe@Fe₃O₄ nanoparticles were found to exhibit good T₁-T₂ dual-mode imaging and tumor-targeting performance both in vitro and in vivo, indicating the nanoparticles represent a new research tool for accurate tumor diagnosis.

Quantification of liver function using gadoxetic acid-enhanced MRI

The introduction of hepatobiliary contrast agents, most notably gadoxetic acid (GA), has expanded the role of MRI, allowing not only a morphologic but also a functional evaluation of the hepatobiliary system. The mechanism of uptake and excretion of gadoxetic acid via transporters, such as organic anion transporting polypeptides (OATP1,3), multidrug resistance-associated protein 2 (MRP2) and MRP3, has been elucidated in the literature. Furthermore, GA uptake can be estimated on either static images or on dynamic imaging, for example, the hepatic extraction fraction (HEF) and liver perfusion. GA-enhanced MRI has achieved an important role in evaluating morphology and function in chronic liver diseases (CLD), allowing to distinguish between the two subgroups of nonalcoholic fatty liver diseases (NAFLD), simple steatosis and nonalcoholic steatohepatitis (NASH), and help to stage fibrosis and cirrhosis, predict liver transplant graft survival, and preoperatively evaluate the risk of liver failure if major resection is planned. Finally, because of its noninvasive nature, GA-enhanced MRI can be used for long-term follow-up and post-treatment monitoring. This review article aims to describe the current role of GA-enhanced MRI in quantifying liver function in a variety of hepatobiliary disorders.

No Cases of Nephrogenic Systemic Fibrosis after Administration of Gadoxetic Acid

Background Gadoxetic acid (GA) has distinctive pharmacokinetic properties with important applications in hepatobiliary imaging. However, there are limited data evaluating the safety of GA administration in patients with impaired kidney function and the incidence of nephrogenic systemic fibrosis (NSF). Purpose To evaluate safety of GA regarding risk of NSF in patients with impaired kidney function. Materials and Methods This retrospective study identified all GA-enhanced MRI (hereafter, GA MRI) examinations performed between July 2008 and December 2019 through a search of the electronic medical record. Serum creatinine values within 180 days or less of each GA MRI examination were retrieved and estimated glomerular filtration rate (eGFR) was calculated. The eGFR value nearest to each MRI examination was used. A separate search in the electronic medical record was also performed to identify patients with NSF. Dermatologists, nephrologists, and nephrologists at our institution were surveyed for any cases of NSF. In patients with NSF, all MRI examinations performed and contrast agents administered to these patients were recorded. Results Overall, 7820 GA MRI examinations were identified, performed in 5351 patients (3022 women and 2329 men). These included 299 examinations (242 patients) with eGFR of 30-44 mL/min/1.73 m² and 183 examinations (157 patients) with eGFR less than 30 mL/min/1.73 m². There were 109 examinations (in 94 patients) with eGFR of 15-29 mL/min/1.73 m², 40 examinations (in 39 patients) with eGFR less than 15 mL/min/1.73 m², and 34 examinations in 27 patients undergoing hemodialysis. Seventeen patients with eGFR less than 30 mL/min/1.73 m² or undergoing dialysis underwent GA MRI two or more times. Eighteen patients with biopsy-confirmed NSF were identified, none of whom were exposed to GA. The mean follow-up period for GA MRI examinations performed in patients with severe kidney impairment was 4.2 years (range, 0.2-11.3 years). Conclusion Gadoxetic acid may be safe with respect to nephrogenic systemic fibrosis in this patient population, although further studies are needed to confirm this. © RSNA, 2020 Online supplemental material is available for this article. See also the editorial by Davenport and Shankar in this issue.

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.

Metal-Organic Frameworks as a Theranostic Nanoplatform for Combinatorial Chemophotothermal Therapy Adapted to Different Administration

With the rapid development of nanotechnology, nanomaterial drug delivery systems have provided an alternative for designing controllable drug delivery systems due to their spatiotemporally controllable properties. As a new type of porous material, metal-organic frameworks (MOFs) have been widely used in biomedical applications, especially drug delivery systems, owing to their tunable pore size, high surface area and pore volume, and easy surface modification. Here, we demonstrate an MOF as a theranostic nanoplatform to combine drug therapy and phototherapy after labeling targeting peptide iRGD. The micropore Fe-MOF was used as MRI agents for locating tumors and as nanocarriers to upload chemotherapeutic drugs. Moreover, MOF showed excellent targeting performance under different administration including intravenous injection for breast cancer and local instillation for bladder cancer. Notably, when irradiated with an 808 nm laser, the agent demonstrates the high efficacy of photothermal therapy and heat release efficiency of the drug around the tumor site. This combination therapy provides an alternative drug administration method and can be adapted to a series of cancer cell types and molecular targets associated with disease progression.

Automatic classification of focal liver lesions based on MRI and risk factors

OBJECTIVES

Accurate classification of focal liver lesions is an important part of liver disease diagnostics. In clinical practice, the lesion type is often determined from the abdominal MR examination, which includes T2-weighted and dynamic contrast enhanced (DCE) MR images. To date, only T2-weighted images are exploited for automatic classification of focal liver lesions. In this study additional MR sequences and risk factors are used for automatic classification to improve the results and to make a step forward to a clinically useful aid for radiologists.

MATERIALS AND METHODS

Clinical MRI data sets of 95 patients with in total 125 benign lesions (40 adenomas, 29 cysts and 56 hemangiomas) and 88 malignant lesions (30 hepatocellular carcinomas (HCC) and 58 metastases) were included in this study. Contrast curve, gray level histogram, and gray level co-occurrence matrix texture features were extracted from the DCE-MR and T2-weighted images. In addition, risk factors including the presence of steatosis, cirrhosis, and a known primary tumor were used as features. Fifty features with the highest ANOVA F-score were selected and fed to an extremely randomized trees classifier. The classifier evaluation was performed using the leave-one-out principle and receiver operating characteristic (ROC) curve analysis.

RESULTS

The overall accuracy for the classification of the five major focal liver lesion types is 0.77. The sensitivity/specificity is 0.80/0.78, 0.93/0.93, 0.84/0.82, 0.73/0.56, and 0.62/0.77 for adenoma, cyst, hemangioma, HCC, and metastasis, respectively.

CONCLUSION

The proposed classification system using features derived from clinical DCE-MR and T2-weighted images, with additional risk factors is able to differentiate five common types of lesions and is a step forward to a clinically useful aid for focal liver lesion diagnosis.

PET/MR Imaging of the Pancreas

PET/MR imaging has the potential to markedly alter pancreatic care in both the malignant, and premalignant states with the ability to perform robust, high-resolution, quantitative molecular imaging. The ability of PET/MR imaging to monitor disease processes, potentially correct for motion in the upper abdomen, and provide novel biomarkers that may be a combination of MR imaging and PET biomarkers, offers a unique, precise interrogation of the pancreatic milieu going forward.

Conspicuity of Malignant Liver Tumors on Diffusion-Weighted Imaging With Short tau Inversion Recovery After Gadolinium Ethoxybenzyl Diethylenetriaminepentaacetic Acid Administration

BACKGROUND

Diffusion-weighted imaging (DWI) has been used for the detection and characterization of liver tumors because it has excellent contrast resolution. DWI using short tau inversion recovery (STIR) can improve tumor-to-liver contrast after gadolinium ethoxybenzyl diethylenetriaminepentaacetic acid (Gd-EOB-DTPA) administration that shortens the T₁ relaxation of liver parenchyma.

PURPOSE

To quantitatively and qualitatively compare the conspicuity of malignant liver tumors on DWI after Gd-EOB-DTPA administration between STIR and chemical shift selective (CHESS) sequences.

STUDY TYPE

Single-institution retrospective study.

SUBJECTS

Fifty-seven patients with histologically confirmed malignant liver tumors were evaluated.

FIELD STRENGTH/SEQUENCE

Low b-value DWIs with STIR and CHESS sequences 18-20 minutes after Gd-EOB-DTPA administration were acquired at 1.5T.

ASSESSMENT

Tumor contrast-to-noise ratio (CNR) and visual grade of tumor conspicuity on DWI between STIR and CHESS sequences were compared.

STATISTICAL TESTS

Paired Student's t-test and the Wilcoxon signed rank-test were applied. P < 0.05 was considered statistically significant.

RESULTS

The mean tumor CNR and visual grade of tumor conspicuity on DWI were significantly higher for STIR than for CHESS (both P < 0.001). Regardless of the presence of chronic liver disease, the mean CNR (normal liver 33.5 ± 19.8 vs. 15.7 ± 12.2, P < 0.001; chronic liver disease 19.6 ± 11.0 vs. 9.2 ± 7.8, P < 0.001) and the visual conspicuity grade (normal liver 3.36 ± 0.64 vs. 2.56 ± 0.77, P < 0.001; chronic liver disease 2.94 ± 0.80 vs. 2.25 ± 0.84, P = 0.001) were significantly higher for STIR than for CHESS. Mean CNR and the visual conspicuity grade were also significantly higher for STIR than for CHESS in patients with hepatocellular carcinomas (CNR 18.1 ± 10.5 vs. 8.8 ± 7.2, P < 0.001; visual grade 2.88 ± 0.83 vs. 2.22 ± 0.87, P = 0.001) or metastases (CNR 35.0 ± 19.3 vs. 16.2 ± 13.1, P < 0.001; visual grade 3.45 ± 0.51 vs. 2.59 ± 0.73, P < 0.001).

DATA CONCLUSION

DWI using STIR may be more helpful for depicting malignant liver tumors after Gd-EOB-DTPA administration compared with DWI using CHESS.

LEVEL OF EVIDENCE

3 Technical Efficacy: Stage 2 J. Magn. Reson. Imaging 2019;49:565-573.

Theranostics and contrast agents for magnetic resonance imaging

BACKGROUND

Magnetic resonance imaging is one of the diagnostic tools that uses magnetic particles as contrast agents. It is noninvasive methodology which provides excellent spatial resolution. Although magnetic resonance imaging offers great temporal and spatial resolution and rapid in vivo images acquisition, it is less sensitive than other methodologies for small tissue lesions, molecular activity or cellular activities. Thus, there is a desire to develop contrast agents with higher efficiency. Contrast agents are known to shorten both T1 and T2. Gadolinium based contrast agents are examples of T1 agents and iron oxide contrast agents are examples of T2 agents. In order to develop high relaxivity agents, gadolinium or iron oxide-based contrast agents can be synthesized via conjugation with targeting ligands or functional moiety for specific interaction and achieve accumulation of contrast agents at disease sites.

MAIN BODY

This review discusses the principles of magnetic resonance imaging and recent efforts focused on specificity of contrast agents on specific organs such as liver, blood, lymph nodes, atherosclerotic plaque, and tumor. Furthermore, we will discuss the combination of theranostic such as contrast agent and drug, contrast agent and thermal therapy, contrast agent and photodynamic therapy, and neutron capture therapy, which can provide for cancer diagnosis and therapeutics.

CONCLUSION

These applications of magnetic resonance contrast agents demonstrate the usefulness of theranostic agents for diagnosis and treatment.

Diagnostic accuracy of Magnetic Resonance Imaging using liver tissue specific contrast agents and contrast enhanced Multi Detector Computed Tomography: A systematic review of diagnostic test in Hepatocellular Carcinoma (HCC)

OBJECTIVES

The aim of this systematic review is to investigate diagnostic accuracy of Magnetic Resonance Imaging (MRI) scans using liver specific tissue contrast media over contrast enhanced Multi Detector CT (MDCT) in diagnoses of Hepatocellular Carcinoma (HCC) in patients with chronic liver disease.

KEY FINDINGS

A total of 8 diagnostic studies were identified and generally considered of high quality. The studies reported sufficient evidence on sensitivity and specificity, which was synthesised and summarised providing an overview of the evidence. Findings indicate that MRI scans using liver specific tissue contrast have a better diagnostic performance compared to contrast enhanced MDCT in diagnostic work-up of HCC in patients with chronic liver disease.

CONCLUSION

The current review identified sufficient high quality studies reporting statistical difference (P < 0.05), to establish the superiority of gadoxetetic acid enhanced MRI for sensitivity and specificity in comparison to MDCT in the diagnosis of HCC in chronic liver disease.

The Roles of Morphology on the Relaxation Rates of Magnetic Nanoparticles

The shape of magnetic nanoparticles is of great importance in determining their contrast abilities for magnetic resonance imaging. Various magnetic nanoparticles have been developed to achieve high T₁ or T₂ relaxivities, but the mechanism on how morphology influences the water proton relaxation process is still unrevealed. Herein we synthesize manganese-doped iron oxide (MnIO) nanoparticles of the same volume with six different shapes and reveal the relationship between morphologies and T₁/ T₂ relaxation rates. The morphology of magnetic nanoparticles largely determines the effective radius and the gradient of stray field, which in turn affects the transverse relaxation rate. The longitudinal relaxivity has positive correlation with the surface-area-to-volume ratio and the occupancy rate of effective metal ions on exposed surfaces of magnetic nanoparticles. These findings together with the summary of r₂/ r₁ ratios could help to guide the screening for the optimal shapes of promising T₁ or T₂ contrast agents. Varying effective radii could be utilized to change negative contrast abilities. The surface-area-to-volume ratio and the amount of effective metal ions on exposed surface are instrumental for tuning positive contrast abilities. These principles could serve as guidelines for design and development of high-performance nanoparticle-based contrast agents.

Imaging features of fibrolamellar hepatocellular carcinoma in gadoxetic acid-enhanced MRI

Background

Fibrolamellar hepatocellular carcinoma (FLC) is a rare malignancy occurring in young patients without cirrhosis. Objectives of our study were to analyze contrast material uptake in hepatobiliary phase imaging (HBP) in gadoxetic acid-enhanced liver MRI in patients with FLC and to characterize imaging features in sequence techniques other than HBP.

Methods

In this retrospective study on histology-proven FLC, contrast material uptake in HBP was quantitatively assessed by calculating the corrected FLC enhancement index (CEI) using mean signal intensities of FLC and lumbar muscle on pre-contrast imaging and HBP, respectively. Moreover, enhancement patterns in dynamic contrast-enhanced MRI and relative signal intensities compared with background liver parenchyma were determined by two radiologists in consensus for HBP, diffusion-weighted imaging using high b-values (DWI), and T2 and T1 weighted pre-contrast imaging.

Results

In 6 of 13 patients with FLC gadoxetic acid-enhanced liver MRI was available. The CEI suggested presence of HBP contrast material uptake in all FLCs. A mean CEI of 1.35 indicated FLC signal increase of 35% in HBP compared with pre-contrast imaging. All FLCs were hypointense in HBP compared with background liver parenchyma. Three of 6 FLCs had arterial hyperenhancement and venous wash-out. In DWI and T2 weighted imaging, 5 of 6 FLCs were hyperintense. In T1 weighted imaging, 5 of 6 FLCs were hypointense.

Conclusion

Hepatobiliary uptake of gadoxetic acid was quantitatively measurable in all FLCs investigated in our study. The observation of hypointensity of FLCs in HBP compared with background liver parenchyma emphasizes the role of gadoxetic acid-enhanced liver MRI for non-invasive diagnosis of FLC and its importance in the diagnostic work-up of indeterminate liver lesions.

Recommendations on the use of magnetic resonance imaging in PSC-A position statement from the International PSC Study Group

Primary sclerosing cholangitis (PSC) is a chronic cholestatic liver disorder characterized by inflammation and fibrosis of the intra- and/or extrahepatic bile ducts. Magnetic resonance imaging (MRI) is a noninvasive imaging modality that can be used to diagnose PSC and detect disease related complications. Quantitative MRI technologies also have the potential to provide valuable prognostic information. Despite the potential of this imaging technology, the clinical application of MRI in the care of PSC patients and imaging standards vary across institutions. Moreover, a unified position statement about the role of MRI in the care of PSC patients, quality imaging standards, and its potential as a research tool is lacking.

CONCLUSION

Members of the International PSC Study Group and radiologists from North America and Europe have compiled the following position statement to provide guidance regarding the application of MRI in the care of PSC patients, minimum imaging standards, and future areas of research. (Hepatology 2017;66:1675-1688).

Utility of T1-weighted MRI as a predictor of liver lesion visibility on ultrasound: A clinical tool to determine feasibility of ultrasound-guided percutaneous interventions

PURPOSE

To determine the utility of fat-suppressed T1-weighted gradient recalled echo (FS-T1W-GRE) MRI to predict visibility of focal liver lesions (FLL) on abdominal ultrasound (US).

MATERIALS AND METHODS

With IRB approval, between 2010 and 2013, 109 patients (28.4% females, age 66.9±10.9years) with 177 FLL (hepatocellular carcinoma=132, metastases=44, other=1) underwent MRI and prospective, radiologist-performed treatment-planning US (to determine eligibility for US-guided ablation). MRI examinations were reviewed by a blinded radiologist who assessed: a) size and location of FLL, b) presence of hepatic steatosis on dual-echo T1W-GRE, and c) quantitative signal intensity of FLL relative to liver on FS-T1W-GRE. Associations between MR imaging findings and visibility on US were assessed using independent t-tests and the chi-squares test.

RESULTS

69.5% (123/177) FLL were identified with US and 30.5% (54/177) were not visible. Size of FLL on MRI was associated with visibility on US (p<0.0001) with no association between FLL visibility on US and segmental or subcapsular location (p=0.29 and p=0.25, respectively). 20.2% (22/109) patients had hepatic steatosis on MRI, which was not associated with non-visibility of FLL on US (p=0.67). 38.4% (68/177) FLL were isointense to liver on FS-T1W-GRE which was associated with non-visibility on US (p=0.036) particularly in non-steatotic livers (p=0.014).

CONCLUSION

FLL size and isointensity of FLL to liver parenchyma on FS-T1W-GRE MRI are associated with non-visibility on US, particularly in non-steatotic livers. These results have implications when planning US-guided percutaneous interventions of FLL detected with MRI.

Albumin-based nanoparticles loaded with hydrophobic gadolinium chelates as T1-T2 dual-mode contrast agents for accurate liver tumor imaging

Magnetic resonance contrast agents with T₁-T₂ dual mode contrast capability have attracted considerable interest because they offer complementary and synergistic diagnostic information, leading to high imaging sensitivity and accurate diagnosis. Here, we reported a facile strategy to construct albumin based nanoparticles loaded with hydrophobic gadolinium chelates by hydrophobic interaction for magnetic resonance imaging (MRI). We synthesized a glycyrrhetinic acid-containing Gd-DOTA derivative (GGD) and loaded GGD molecules into BSA nanoparticles to form GGD-BSA nanoparticles (GGD-BSA NPs). The large size and porous structure endow GGD-BSA NPs with geometrical confinement, which restricts the tumbling of GGD and the diffusion of surrounding water molecules. As a result, GGD-BSA NPs exhibit ultrahigh T₁ and T₂ relaxivities, which are approximately 8-fold higher than those of gadolinium-based clinical contrast agents at 0.5 T. Besides, due to the intrinsic properties of their components, GGD-BSA NPs show good biocompatibility in vitro and in vivo, which warrants their great potential in clinical translation. Furthermore, GGD-BSA NPs show remarkable sensitivity in noninvasive detection of liver tumors by self-confirmed T₁-T₂ dual-mode contrast-enhanced MRI. All of these merits make GGD-BSA NPs a potential candidate for fruitful biomedical and preclinical applications.

Risk factor assessment to predict the likelihood of a diagnosis of metastasis for indeterminate hepatic lesions found at computed tomography in patients with rectal cancer

AIM

To assess the significant factors on rectal magnetic resonance imaging (MRI) to predict the likelihood of a diagnosis of metastasis for indeterminate hepatic lesions found at computed tomography (CT) in patients with rectal cancer.

MATERIALS AND METHODS

A total of 207 patients with rectal cancer who underwent preoperative contrast-enhanced abdominopelvic CT, and rectal and liver MRI were included. Univariate analysis and multivariate logistic regression were used to evaluate the determining factors for the significance of indeterminate hepatic lesions on CT in patients with rectal cancer.

RESULTS

Hepatic metastases were diagnosed in 29 (20.9%) of 139 patients who had indeterminate hepatic lesions on preoperative CT obtained for rectal cancer. On univariate analysis, carcinoembryonic antigen level, N stage, mesorectal fascia (MRF) invasion, diameter of superior haemorrhoidal vein, and mesorectal vascular lesion (MVL) grade on rectal MRI (p<0.05) were associated with the possibility of metastasis for indeterminate hepatic lesions on CT. On multivariate analysis, MVL grade and MRF invasion on rectal MRI were independent factors associated with the possibility of metastasis for indeterminate hepatic lesions on CT (p<0.0005 and p=0.0066, respectively).

CONCLUSION

MVL grade and MRF invasion on rectal MRI are independent factors for estimating hepatic metastasis among indeterminate hepatic lesions on CT in patients with rectal cancer.

Quantitative analysis of gadoxetic acid-enhanced magnetic resonance imaging predicts histological grade of hepatocellular carcinoma

OBJECTIVE

To confirm the histological grade of hepatocellular carcinoma (HCC) by gadoxetic acid-enhanced MRI.

METHODS

Ninety-five HCC patients underwent gadoxetic acid-enhanced MRI before surgical intervention. The correlations among the signal absolute enhancement, contrast enhancement ratio (CER) and tumor histological grade were analyzed.

RESULTS

The correlation between CER of tumor-to-liver and the grades of tumor differentiation is the most significant negative. The k-value for the CER of tumor-to-liver and histopathologic analysis is 0.62, which gives evidence of good agreement.

CONCLUSION

The quantitative analysis of gadoxetic acid-enhanced MRI can predict the histological grades of small HCCs.

Hepatic gadoxetic acid uptake as a measure of diffuse liver disease: Where are we?

MRI has emerged as the most comprehensive noninvasive diagnostic tool for focal liver lesions and diffuse hepatobiliary disorders. The introduction of hepatobiliary contrast agents, most notably gadoxetic acid (GA), has expanded the role of MRI, particularly in the functional imaging of chronic liver diseases, such as nonalcoholic fatty liver disease (NAFLD). GA-enhanced MRI (GA-MRI) may help to distinguish between the two subgroups of NAFLD, simple steatosis and nonalcoholic steatohepatitis. Furthermore, GA-MRI can be used to stage fibrosis and cirrhosis, predict liver transplant graft survival, and preoperatively estimate the risk of liver failure should major resection be undertaken. The amount of GA uptake can be estimated, using static images, by the relative liver enhancement, hepatic uptake index, and relaxometry of T1-mapping during the hepatobiliary phase. On the contrary, the hepatic extraction fraction and liver perfusion can be measured on dynamic imaging. Importantly, there is currently no clear consensus as to which of these MR-derived parameters is the most suitable for assessing liver dysfunction. This review article aims to describe the current role of GA-enhanced MRI in quantifying liver function, primarily in diffuse hepatobiliary disorders.

LEVEL OF EVIDENCE

3 J. Magn. Reson. Imaging 2017;45:646-659.

Associating liver partition and portal vein ligation for staged hepatectomy (ALPPS) in colorectal liver metastasis: the radiologist's perspective

PURPOSE

Hepatic resection is the only potentially curative treatment for patients with colorectal liver metastasis (CRLM). Many multidisciplinary approaches, including the associating liver partition and portal vein ligation for staged hepatectomy (ALPPS) procedure, have been proposed to increase the resectability rate in these patients. ALPPS is the most recently described staged liver resection technique, representing an advantageous strategy to induce a rapid and marked increase in the future liver remnant (FLR) volume. The aim of this article is to describe the radiological evaluation of this procedure and its variation.

METHODS

This retrospective study included 9 patients with CRLM who underwent the ALPPS procedure. Abdominal imaging studies were reviewed, with an emphasis on a rational radiological approach. The number of liver metastases, the FLR volume (pre- and postportal vein ligation), anatomical variations, potential pitfalls related to disease progression, and postoperative complications were evaluated.

RESULTS

The types of hepatic resection included 4 classical ALPPS cases, 3 right ALPPS variations, and 2 left ALPPS variations. The mean FLR volume calculated in the initial evaluation was 453 mL (213-790 mL). Following the first surgery, the mean FLR volume increased to 634 mL (410-957 mL), which indicated a mean volume increase of 181.1 mL (95% CI 149.7-212.5 mL; p < 0.001) and a mean absolute volume increase of 48% (19%-88%).

CONCLUSION

The ALPPS procedure is an emerging form of two-stage hepatectomy. In this context, radiologists should provide crucial preoperative and perioperative information that may change surgical planning and contribute to an improvement in the oncologic outcome.

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

PURPOSE

To compare gadoxetic acid alone and combined gadoxetic acid/gadofosveset trisodium-enhanced liver MRI for detection of metastases and differentiation of metastases from haemangiomas.

METHODS

Ninety-one patients underwent gadoxetic acid-enhanced liver MRI before and after additional injection of gadofosveset. First, two readers retrospectively identified metastases on gadoxetic acid alone enhanced delayed hepatobiliary phase T1-weighted images together with all other MR images (dynamic images, T2-weighted images, diffusion-weighted images). Second, readers assessed additional T1-weighted images obtained after administration of gadofosveset trisodium. For both interpretations, readers rated lesion conspicuity and confidence in differentiating metastases from haemangiomas. Results were compared using alternative free-response receiver-operating characteristic (AFROC) and conventional ROC methods. Histology and follow-up served as reference standard.

RESULTS

There were 145 metastases and 16 haemangiomas. Both readers detected more metastases using combined gadoxetic acid/gadofosveset (reader 1 = 130; reader 2 = 124) compared to gadoxetic acid alone (reader 1 = 104; reader 2 = 103). Sensitivity of combined gadoxetic acid/gadofosveset (reader 1 = 90 %; reader 2 = 86 %) was higher than that of gadoxetic acid alone (reader 1 = 72 %; reader 2 = 71 %, both P < 0.01). AFROC-AUC was higher for the combined technique (0.92 vs. 0.86, P < 0.001). Sensitivity for correct differentiation of metastases from haemangiomas was higher for the combined technique (reader 1 = 98 %; reader 2 = 99 % vs. reader 1 = 86 %; reader 2 = 91 %, both P < 0.01). ROC-AUC was significantly higher for the combined technique (reader 1 = 1.00; reader 2 = 1.00 vs. reader 1 = 0.87; reader 2 = 0.92, both P < 0.01).

CONCLUSION

Combined gadoxetic acid/gadofosveset-enhanced MRI improves detection and characterization of liver metastases compared to gadoxetic acid alone.

KEY POINTS

• Combined gadoxetic acid and gadofosveset-enhanced liver MRI significantly improves detection of metastases. • The combined enhancement technique improves the accuracy to differentiate metastases from haemangiomas. • Prospective studies need to determine the clinical impact of the combined technique.

Percutaneous biopsy in the abdomen and pelvis: a step-by-step approach

Percutaneous abdominal biopsies provide referring physicians with valuable diagnostic and prognostic information that guides patient care. All biopsy procedures follow a similar process that begins with the preprocedure evaluation of the patient and ends with the postprocedure management of the patient. In this review, a step-by-step approach to both routine and challenging abdominal biopsies is covered with an emphasis on the differences in biopsy devices and imaging guidance modalities. Adjunctive techniques that may facilitate accessing a lesion in a difficult location or reduce procedure risk are described. An understanding of these concepts will help maintain the favorable safety profile and high diagnostic yield associated with percutaneous biopsies.

Inter-observer agreement on the assessment of relative liver lesion signal intensity on hepatobiliary phase imaging with gadoxetate (Gd-EOB-DTPA)

PURPOSE

The purpose of the study was to assess the inter-observer agreement on the qualitative and quantitative evaluation of relative signal intensity of liver lesions on delayed hepatobiliary phase (HBP) MRI with gadoxetate (Gd-EOB-DTPA).

METHODS

105 patients with liver lesions, who had delayed HPB MRI using gadoxetate were reviewed retrospectively. For each patient, four readers (two fellows in training and two attending radiologists) qualitatively assessed the relative SI of the largest representative lesion on a five point scale, and quantitatively measured the relative SI of the lesion to adjacent liver parenchyma using region of interests (ROI). Intra-class correlation (ICC) and kappa statistics with quadratic weights (k) analysis, and maximally selected rank statistic were performed.

RESULTS

Substantial agreement between fellows (k = 0.719; ICC = 0.705) and almost perfect agreement between attending radiologists (k = 0.853; ICC = 0.849) were found for both qualitative and quantitative assessments of relative SI on delayed HPB imaging. A cut-off ratio to differentiate between hypointense and iso- to hyperintense lesions by ROI was calculated to be 0.90.

CONCLUSION

Inter-observer agreement of liver lesion relative SI on delayed HBP imaging is high and may improve with radiologist experience. A cut-off ratio of relative SI at 0.90 may be useful to quantitatively distinguish hypointense from iso- to hyperintense liver lesions.

Navigated three-dimensional T1-weighted gradient-echo sequence for gadoxetic acid liver magnetic resonance imaging in patients with limited breath-holding capacity

PURPOSE

To determine whether a navigator-gated three-dimensional T1-weighted gradient-echo sequence (T1W-GRE, navigated LAVA) can improve diagnostic performance for the detection of focal liver lesions (FLLs) compared to standard breath-hold (BH) T1W-GRE breath-hold LAVA (BH-LAVA) during the hepatobiliary phase (HBP) of gadoxetic acid liver magnetic resonance imaging (MRI) in patients with limited breath-holding capacity.

MATERIALS AND METHODS

This retrospective study was approved by our institutional review board and the requirement for informed consent was waived. We included 372 patients who underwent liver MRI including both navigated LAVA and BH-LAVA sequences. Overall image quality of the two HBP image sets was compared. In patients with limited breath-holding capacity, diagnostic performances in detecting FLLs on the two HBP images were compared using jackknife-alternative free-response receiver-operating characteristic (JAFROC) analysis by two reviewers.

RESULTS

There were 13 cases (13/372; 3.5%) of image acquisition failure using the navigated LAVA sequence due to severe irregular breathing, and 50 of 359 patients had limited breath-holding capacity. In these patients, overall image quality of navigated LAVA (2.78 ± 0.95) was significantly better than that of BH-LAVA (2.42 ± 0.81, P < 0.005), and both readers showed significantly higher JAFROC figure-of-merit values with navigated LAVA compared to BH-LAVA (0.94 and 0.86 in reviewer 1, respectively; 0.89 and 0.83 in reviewer 2, respectively, P < 0.005). Overall image quality of navigated LAVA was also better than that of BH-LAVA in patients with sufficient breath-holding capacity (n = 309, 3.96 ± 0.88, 3.81 ± 0.66, respectively, P < 0.001).

CONCLUSION

The navigated LAVA sequence could provide better image quality and diagnostic performance in detecting FLLs than BH-LAVA in patients with limited breath-holding capacity during HBP of gadoxetic acid MRI.

[Modern imaging of liver metastases]

CLINICAL/METHODICAL ISSUE

The liver is the second most common location of metastases following the lymph nodes. The accurate characterization of focal liver lesions in oncology patients is especially important because of the high prevalence of benign liver lesions and the possibility of co-existing benign and malignant lesions. The exact interpretation of these lesions is crucial for therapeutic decisions and thus for the prognosis of the patient.

STANDARD RADIOLOGICAL METHODS

It is essential to detect all focal liver lesions and to distinguish benign from malignant lesions, especially in the management of oncology patients. Numerous imaging modalities are available for these challenges in the daily routine. An extensive understanding of the advantages and limitations of the various imaging modalities and knowledge of the morphology and the typical and atypical appearances of the different metastases is important.

METHODICAL INNOVATIONS

This review explains the radiological criteria for various metastases in different modalities. To evaluate the individual prognosis and risk assessment preoperatively, functional imaging is necessary. These personalized pretherapeutic diagnostics are discussed.

[Focal nodular hyperplasia and hepatocellular adenoma]

CLINICAL ISSUE

Focal nodular hyperplasia (FNH) and hepatocellular adenoma (HCA) are liver lesions of hepatocellular origin. The FNH is a commonly occurring hepatic lesion whereas HCA is very rare. Non-invasive differentiation between HCA subtypes and atypical FNH may pose a diagnostic challenge as both entities predominantly occur in middle-aged female patients.

STANDARD RADIOLOGICAL METHODS

The conventional imaging modalities include ultrasound (US), computed tomography (CT) and magnetic resonance imaging (MRI). Distinguishing FNH from HCA is of great importance clinically as FNH is considered to be a benign lesion and needs no further management. In contrast HCA is considered to be a borderline tumor due to the risk of hemorrhage, growth and even malignant transformation and requires individualized management.

METHODOLOGICAL INNOVATIONS

The above mentioned radiological procedures usually enable an accurate and certain diagnosis of a typical FNH to be achieved. In cases of atypical FNH, particularly in patients with a clinical history of malignancy, these imaging modalities are insufficient to establish a clear diagnosis. In this scenario, the use of modern hepatobiliary contrast-enhanced MRI will enable a differentiation between FNH and metastasis with a high sensitivity and specificity. Furthermore, it allows a differentiation of FNH from 90 % of adenoma subtypes.

ACHIEVEMENTS

This article describes the histopathological and radiological features of these lesions and explains the advantages and limitations of various imaging modalities used for the diagnosis and differentiation of these entities.

PRACTICAL RECOMMENDATIONS

The new classification of HCAs according to phenotype and genotype and their imaging features, as well as different enhancement patterns, are described. The correlation between HCA subtypes and their individual management are also discussed.