Parametric mapping of the hepatic perfusion index with gadolinium-enhanced volumetric MRI

Perfusion MR Imaging of Liver: Principles and Clinical Applications

Perfusion imaging techniques provide quantitative characterization of tissue microvasculature. Perfusion MR of liver is particularly challenging because of dual afferent flow, need for large organ high-resolution coverage, and significant movement with respiration. The most common MR technique used for quantifying liver perfusion is dynamic contrast-enhanced MR imaging. Here, the authors describe the various perfusion MR models of the liver, the basic concepts behind implementing a perfusion acquisition, and clinical results that have been obtained using these models.

Tumor attenuation and quantitative analysis of perfusion parameters derived from tri-phasic CT scans in hepatocellular carcinoma: Relationship with histological grade

The aim of the current study was to explore the value of tumor attenuation and quantitative analysis of perfusion parameters obtained from traditional tri-phasic CT scans in grading hepatocellular carcinoma (HCC).Totally 39 patients (42 lesion samples) with pathologically confirmed HCC who underwent tri-phasic CT scans were enrolled. HCC lesions were divided into non-poorly differentiated HCC (NP-HCC; n = 31) and poorly differentiated HCC (pHCC; n = 11). All lesions were divided into 5 groups according to the attenuation on different CT enhancement phase. The values of tumor attenuation on different scanning phases were measured. The following parameters were calculated: arterial enhancement fraction (AEF), portal venous supply coefficient (PVC), and hepatic arterial supply coefficient (HAC). The relationship of perfusion parameters with the histological grade of HCC was analyzed. Receiver operating characteristic curves were generated.No significant correlation was observed between the perfusion parameters and tumor grading. Only HAC showed a non-significant trend in different grades of HCC (pHCC < NP-HCC; P = .07). The pHCC cases had significantly decreased values of tumor attenuation on the unenhanced phase (TAu), tumor attenuation on the portal phase portal phase (TAp), and equilibrium phase (TAe) (P < .01). The difference of tumor attenuation between the portal phase and the unenhanced phase (TAp-TAu) of the pHCC cases was decreased than that of the NP-HCC cases (P < .01), whereas the difference of attenuation between the equilibrium phase and portal phase (TAe-TAp) was significantly higher in the pHCC cases than that in the NP-HCC cases (P < .01). TAe-TAp had the highest area under the curve. The number of tumor enhancement pattern in Group 5 of HCCs with a diameter of 3 cm or more was significantly more than that of HCCs with a diameter of less than 3 cm or with other different enhancement patterns (P < .01).Histological HCC grading cannot be predicted by the perfusion parameters derived from traditional tri-phasic CT scans, whereas the tumor attenuation on different phases and the tumor attenuation differences among different phases, especially the mean value of TAe-TAp, might be useful for non-invasive prediction on the degree of HCC differentiation.

Assessment of Hepatic Perfusion Using GRASP MRI: Bringing Liver MRI on a New Level

PURPOSE

The aim of this study was to demonstrate the feasibility of hepatic perfusion imaging using dynamic contrast-enhanced (DCE) golden-angle radial sparse parallel (GRASP) magnetic resonance imaging (MRI) for characterizing liver parenchyma and hepatocellular carcinoma (HCC) before and after transarterial chemoembolization (TACE) as a potential alternative to volume perfusion computed tomography (VPCT).

METHODS AND MATERIALS

Between November 2017 and September 2018, 10 patients (male = 8; mean age, 66.5 ± 8.6 years) with HCC were included in this prospective, institutional review board-approved study. All patients underwent DCE GRASP MRI with high spatiotemporal resolution after injection of liver-specific MR contrast agent before and after TACE. In addition, VPCT was acquired before TACE serving as standard of reference. From the dynamic imaging data of DCE MRI and VPCT, perfusion maps (arterial liver perfusion [mL/100 mL/min], portal liver perfusion [mL/100 mL/min], hepatic perfusion index [%]) were calculated using a dual-input maximum slope model and compared with assess perfusion measures, lesion characteristics, and treatment response using Wilcoxon signed-rank test. To evaluate interreader agreement for measurement repeatability, the interclass correlation coefficient (ICC) was calculated.

RESULTS

Perfusion maps could be successfully generated from all DCE MRI and VPCT data. The ICC was excellent for all perfusion maps (ICC ≥ 0.88; P ≤ 0.001). Image analyses revealed perfusion parameters for DCE MRI and VPCT within the same absolute range for tumor and liver tissue. Dynamic contrast-enhanced MRI further enabled quantitative assessment of treatment response showing a significant decrease (P ≤ 0.01) of arterial liver perfusion and hepatic perfusion index in the target lesion after TACE.

CONCLUSIONS

Dynamic contrast-enhanced GRASP MRI allows for a reliable and robust assessment of hepatic perfusion parameters providing quantitative results comparable to VPCT and enables characterization of HCC before and after TACE, thus posing the potential to serve as an alternative to VPCT.

Whole-volume vs. segmental CT texture analysis of the liver to assess metachronous colorectal liver metastases

PURPOSE

It is unclear whether changes in liver texture in patients with colorectal cancer are caused by diffuse (e.g., perfusional) changes throughout the liver or rather based on focal changes (e.g., presence of occult metastases). The aim of this study is to compare a whole-liver approach to a segmental (Couinaud) approach for measuring the CT texture at the time of primary staging in patients who later develop metachronous metastases and evaluate whether assessing CT texture on a segmental level is of added benefit.

METHODS

46 Patients were included: 27 patients without metastases (follow-up >2 years) and 19 patients who developed metachronous metastases within 24 months after diagnosis. Volumes of interest covering the whole liver were drawn on primary staging portal-phase CT. In addition, each liver segment was delineated separately. Mean gray-level intensity, entropy (E), and uniformity (U) were derived with different filters (σ0.5-2.5). Patients/segments without metastases and patients/segments that later developed metachronous metastases were compared using independent samples t tests.

RESULTS

Absolute differences in entropy and uniformity between the group without metastases and the group with metachronous metastases group were consistently smaller for the segmental approach compared to the whole-liver approach. No statistically significant differences were found in the texture measurements between both groups.

CONCLUSIONS

In this small patient cohort, we could not demonstrate a clear predictive value to identify patients at risk of developing metachronous metastases within 2 years. Segmental CT texture analysis of the liver probably has no additional benefit over whole-liver texture analysis.

Changes in hepatic perfusion assessed by dynamic contrast enhanced MRI, associated with morphologic evaluation, in patients with liver metastases from colorectal cancer treated with first-line chemotherapy

INTRODUCTION

Blood perfusion of liver metastases can be non-invasively assessed by dynamic contrast enhanced magnetic resonance imaging (DCE-MRI). The aim of this study was to explore whether the ratio of hepatic arterial to total liver blood flow (Hepatic Perfusion Index-HPI) and the area under the enhancement curve (AUC) of selected liver areas in patients with hepatic metastases from colorectal cancer treated with first-line chemotherapy could predict response and/or be a prognostic variable.

PATIENTS AND METHODS

Sequential liver DCE-MRI studies with morphological imaging reconstruction were performed in 43 consecutive patients at baseline and every 3 months during oxaliplatin-based first-line chemotherapy. Data about HPI of the whole liver, and AUC of metastatic and healthy areas were calculated at each time-point and compared both at baseline and sequentially during the treatment.

RESULTS

Baseline HPI and AUC values did not discriminate patients responsive to chemotherapy, nor those with better survival outcomes. HPI and AUC values at 3 months decreased significantly more in responders than non-responders. AUCs calculated from areas of the liver with or without neoplastic lesions varied consistently, being increased in progressing patients and decreased in responding patients.

DISCUSSION

Our results did not support the hypothesis of a predictive or prognostic role of HPI and AUCs calculated by DCE-MRI in liver metastatic CRC patients, thus the primary endpoint of the study was not reached. However, reduced arterial blood flow in metastatic liver can be obtained by chemotherapy alone, without any anti-angiogenic agent; interestingly, HPI and AUC data suggest a possible relationship between tumor metabolism and entire liver perfusion.

Perfusion imaging in liver MRI

Liver perfusion magnetic resonance (MR) imaging is currently being actively investigated as a functional imaging technique that provides physiologic information on the microcirculation and microenvironment of liver tumors and the underlying liver. It has gained importance in light of antiangiogenic therapy for hepatocellular carcinoma and colorectal liver metastases. This article explains the various model-free and model-based approaches for liver perfusion MR imaging and their relative clinical utility. Relevant published works are summarized for each approach so that the reader can understand their relative strengths and weaknesses, to make an informed choice when performing liver perfusion MR imaging studies.

Biliary collateral veins and associated biliary abnormalities of portal hypertensive biliopathy in patients with cavernous transformation of portal vein

PURPOSE

The purpose was to investigate magnetic resonance imaging (MRI) features of biliary collateral veins and associated biliary abnormalities of portal hypertensive biliopathy (PHB).

MATERIALS AND METHODS

Thirty-six patients including 18 patients with abnormal biliary changes and 18 patients as control group were involved in this study. MRI features of biliary collateral veins were analyzed.

RESULTS

Stenosis with dilated proximal bile ducts occurred in 33.3% of patients, 27.8% of patients had irregular ductal walls, 22.2% of patients had thickened ductal walls, 16.7% of patients had angulated ductal walls, and 44.4% of patients had thickened gallbladder walls.

CONCLUSIONS

Biliary collateral veins and associated biliary abnormalities of PHB can be detected by MRI.

Whole-liver CT texture analysis in colorectal cancer: Does the presence of liver metastases affect the texture of the remaining liver?

BACKGROUND

Liver metastases limit survival in colorectal cancer. Earlier detection of (occult) metastatic disease may benefit treatment and survival.

OBJECTIVE

The objective of this article is to evaluate the potential of whole-liver CT texture analysis of apparently disease-free liver parenchyma for discriminating between colorectal cancer (CRC) patients with and without hepatic metastases.

METHODS

The primary staging CT examinations of 29 CRC patients were retrospectively analysed. Patients were divided into three groups: patients without liver metastases (n = 15), with synchronous liver metastases (n = 10) and metachronous liver metastases within 18 months following primary staging (n = 4). Whole-liver texture analysis was performed by delineation of the apparently non-diseased liver parenchyma (excluding metastases or other focal liver lesions) on portal phase images. Mean grey-level intensity (M), entropy (E) and uniformity (U) were derived with no filtration and different filter widths (0.5 = fine, 1.5 = medium, 2.5 = coarse).

RESULTS

Mean E1.5 and E2.5 for the whole liver in patients with synchronous metastases were significantly higher compared with the non-metastatic patients (p = 0.02 and p = 0.01). Mean U1.5 and U2.5 were significantly lower in the synchronous metastases group compared with the non-metastatic group (p = 0.04 and p = 0.02). Texture parameters for the metachronous metastases group were not significantly different from the non-metastatic group or synchronous metastases group (p > 0.05), although - similar to the synchronous metastases group - there was a subtle trend towards increased E1.5, E2.5 and decreased U1.5, U2.5 values. Areas under the ROC curve for the diagnosis of synchronous metastatic disease based on the texture parameters E1.5,2.5 and U1.5,2.5 ranged between 0.73 and 0.78.

CONCLUSION

Texture analysis of the apparently non-diseased liver holds promise to differentiate between CRC patients with and without metastatic liver disease. Further research is required to determine whether these findings may be used to benefit the prediction of metachronous liver disease.

The evaluation of haemodynamics in cirrhotic patients with spectral CT

OBJECTIVE

To evaluate haemodynamics in cirrhotic patients with portal hypertension using spectral CT imaging.

METHODS

118 cirrhotic patients with portal hypertension were included in the study group (further divided into Child-Pugh A, B and C subgroups). The control group consisted of 21 subjects with normal liver functionality. All subjects underwent three-phase spectral CT scans. Material decomposition images with water and iodine as basis material pairs were reconstructed. The iodine concentrations for the hepatic parenchyma in both arterial and portal venous phases were measured. The arterial iodine fraction (AIF) was obtained by dividing the iodine concentration in the hepatic arterial phase by that in the portal venous phase. AIF values from the study and control groups were compared using analysis of variance and between subgroups using a post-hoc test with Bonferroni correction, with a statistical significance of p<0.05.

RESULTS

The AIF was 0.25±0.05 in the control group, and 0.29±0.10, 0.37±0.12 and 0.43±0.14 in the study group with Child-Pugh Grades A, B and C, respectively. The difference in AIF between the control and study groups was statistically significant. The differences were statistically significant between the subgroups with multiple comparisons except between the control group and the Child-Pugh A group (p=0.685).

CONCLUSION

AIF measured in spectral CT could be used to evaluate the liver haemodynamics of cirrhotic patients.

ADVANCES IN KNOWLEDGE

The AIF, provided by spectral CT, could be used as a new parameter to observe liver haemodynamics.

Functional imaging of the liver

Anatomical-based imaging is used widely for the evaluation of diffuse and focal liver, including detection, characterization, and therapy response assessment. However, a limitation of anatomical-based imaging is that structural changes may occur relatively late in a disease process. By applying conventional anatomical-imaging methods in a more functional manner, specific pathophysiologic alterations of the liver may be assessed and quantified. There has been an increasing interest in both the clinical and research settings, with the expectation that functional-imaging techniques may help solve common diagnostic dilemmas that conventional imaging alone cannot. This review considers the most common functional magnetic resonance imaging, computed tomography, and ultrasound imaging techniques that may be applied to the liver.

Detection of recurrent hepatocellular carcinoma in cirrhotic liver after transcatheter arterial chemoembolization: value of quantitative color mapping of the arterial enhancement fraction of the liver

Objective

To investigate the additional diagnostic value of color mapping of the hepatic arterial enhancement fraction (AEF) for detecting recurrent or residual hepatocellular carcinoma (HCC) in patients treated with transcatheter arterial chemoembolization (TACE).

Materials and Methods

Seventy-six patients with 126 HCCs, all of whom had undergone previous TACE, and subsequently, underwent follow-up multiphasic liver CT scans, were included in this study. Quantitative color maps of the AEF of the whole liver were created, by using prototype software with non-rigid registration. The AEF was defined as the ratio of the attenuation increment during the arterial phase to the attenuation increment during the portal phase. Two radiologists independently analyzed the two image sets at a two-week interval, i.e., the multiphasic CT image set and the second image set of the AEF color maps and the CT images. The additional diagnostic value of the AEF color mapping was determined, by the use of the jackknife-alternative free-response receiver-operating-characteristic analysis. The sensitivity and positive predictive values for detecting HCCs of each image set were also evaluated and compared.

Results

The reader-averaged figures of merit were 0.699 on the initial interpretation of the MDCT image set, and 0.831 on the second interpretation of the combined image set; the difference between the two interpretations was significant (p value < 0.001). The mean sensitivity for residual or recurrent HCC detection increased from 62.7% on the initial analysis to 82.1% on the second analysis using the AEF color maps (p value < 0.001). The mean positive predictive value for HCC detection was 74.5% on the initial analysis using MDCT, and 71.6% on the second analysis using AEF color mapping.

Conclusion

Quantitative color mapping of the hepatic AEF may have the possibility to increase the diagnostic performance of MDCT for the detection of recurrent or residual HCC without the potential risk of radiation-related hazards.

New acquisition techniques: fields of application

Conventional MR imaging of the liver has a central role in the assessment of liver diseases. Diffusion-weighted MR imaging, MR elastography, and time-resolved dynamic contrast-enhanced MR imaging improve the anatomical information provided by conventional MR imaging and add quantitative functional information in diffuse and focal liver diseases. Particularly, accurate detection and characterization of liver fibrosis are feasible with quantitative MR elastography, detection of liver tumors is increased with diffusion-weighted MR imaging and time-resolved dynamic contrast-enhanced MR imaging, characterization of tumors can be improved with quantitative diffusion-weighted MR imaging and MR elastography. These methods also have the potential to provide adequate biomarkers for assessing the response to treatment. Currently, the main limitations of quantitative MR imaging are related to reproducibility, standardization, and/or limited clinical data. It is important to improve and standardize the quantitative MR methods and validate their role in large multicenter trials.

Contrast agents as a biological marker in magnetic resonance imaging of the liver: conventional and new approaches

Liver imaging is an important clinical area in everyday practice. The clinical meaning of different lesion types in the liver can be quite different. Therefore, the result of imaging studies of the liver can change therapeutic concepts fundamentally. Contrast agents are used in the majority of MR examinations of the liver parenchyma-despite the already good soft-tissue contrast in plain MRI. This can be explained by the advantages in lesion detection and characterization of contrast-enhanced MRI of the liver. Beyond the qualitative evaluation of contrast-enhanced liver MR examinations, quantification of parameters will be the demand of the future. This can be achieved by perfusion MRI, also called dynamic contrast-enhanced MRI (DCE-MRI) of the liver. Its basic principles and different clinical applications will be discussed in this article. Definite cut-off values to determine disease or therapeutic response will help to increase the objectivity and reliability of liver MRI in future. This is especially important in the oncological setting, where modern therapies cannot be assessed based on changes in size only.

Visualization and segmentation of liver tumors using dynamic contrast MRI

Hepatocellular carcinoma (liver tumor) is one of the most common malignancies causing an estimated one million deaths annually, and the fastest growing form of cancer in the United States. Dynamic Contrast Enhanced MRI (DCE-MRI) is a useful way to characterize tumor response to contrast agent uptake, but the method still lacks maturity in terms of quantifying tumor burden and viability. We propose a semi-supervised technique for visualizing and measuring liver tumor burden and viability from DCE-MRI examinations. In order to solve the challenging segmentation problem, we exploit prior information about the spatio-temporal characteristics of DCE-MRI data, and perform k-means clustering in a hybrid intensity-spatial feature space.

Hepatic perfusion imaging using factor analysis of contrast enhanced ultrasound

Contrast enhanced ultrasound imaging provides a real-time tool for evaluating vasculature in the liver. Primary liver cancer is known to be perfused exclusively by blood from the hepatic artery, whereas normal liver is also supplied by the portal vein. Visual separation of two different phases of enhancement from the independent feeding vessels is important for diagnosis but remains a challenge. This paper presents a method of using factor analysis for extracting distinct time-intensity curves. A key component to this extraction is the clustering of measured bolus curves and their projection onto a positivity domain to obtain nonnegative curves. This technique provides complementary images representing spatial loadings on each curve. As little as 1% of the data is required to contain unmixed signals to extract time-intensity curves that correlate well with true curves. A method of combining this information to display a regional hepatic perfusion image is proposed, and results are tested on a set of 10 patients. Region of interest analysis suggests it is possible to detect changes in the hepatic perfusion index of liver lesions relative to normal liver parenchyma using contrast ultrasound.

Quantitative mapping of hepatic perfusion index using MR imaging: a potential reproducible tool for assessing tumour response to treatment with the antiangiogenic compound BIBF 1120, a potent triple angiokinase inhibitor

Hepatic metastases are arterially supplied, resulting in an elevated hepatic perfusion index (HPI). The purpose of this study was to use dynamic contrast-enhanced (DCE) MR imaging to quantify the HPI of metastases and the liver before and after treatment with a novel antiangiogenic drug. Ten patients with known metastatic liver disease underwent DCE-MR studies. HPIs of metastases and whole liver were derived using regions of interest (ROIs) and calculated on a pixel-by-pixel basis from quantified changes in gadopentetate dimeglumine (Gd-DTPA) concentration. The HPI measurement error prior to treatment was derived by the Bland-Altman analysis. The median HPI before and after treatment with antiangiogenic drug BIBF 1120 were compared using the Wilcoxon signed rank test. Prior to treatment, the median HPI of metastases, 0.75 +/- 0.14, was significantly higher than that of the whole liver, 0.66 +/- 0.16 (p < 0.01). Bland-Altman reproducibility coefficients of the median HPI from metastases and whole liver were 13.0 and 5.1% respectively. The median HPI of metastases decreased significantly at 28 days after treatment with BIBF 1120 (p < 0.05). This pilot study demonstrates that HPI determined using quantified Gd-DTPA concentration is reproducible and may be useful for monitoring antiangiogenic treatment response of hepatic metastases.