Performance of magnetic resonance elastography and diffusion-weighted imaging for the staging of hepatic fibrosis: A meta-analysis

Noninvasive assessment of liver fibrosis in patients with chronic hepatitis B

Infection with hepatitis B virus is an important health problem worldwide: it affects more than 350 million people and is a leading cause of liver-related morbidity, accounting for 1 million deaths annually. Hepatic fibrosis is a consequence of the accumulation of extracellular matrix components in the liver. An accurate diagnosis of liver fibrosis is essential for the management of chronic liver disease. Liver biopsy has been considered the gold standard for diagnosing disease, grading necroinflammatory activity, and staging fibrosis. However, liver biopsy is unsuitable for repeated evaluations because it is invasive and can cause major complications, including death. Several noninvasive evaluations have been introduced for the assessment of liver fibrosis: serum biomarkers, combined indices or scores, and imaging techniques including transient elastography, acoustic radiation force impulse, real-time tissue elastography, and magnetic resonance elastography. Here, we review the recent progress of noninvasive assessment of liver fibrosis in patients with chronic hepatitis B. Most noninvasive evaluations for liver fibrosis have been validated first in patients with chronic hepatitis C, and later in those with chronic hepatitis B. The establishment of a noninvasive assessment of liver fibrosis is urgently needed to aid in the management of this leading cause of chronic liver disease.

Latest developments in the imaging of fibrotic liver disease

According to the World Health Organization, liver cirrhosis accounted for 1.8% of all deaths in Europe, causing about 170,000 deaths per year. Approximately 29 million persons in the EU suffer from chronic liver disease and this trend is on the rise. Liver disease is the EU's fifth most common cause of death accounting for at least one in six deaths. Early detection and monitoring of fibrosis has the potential to direct management of these chronic liver diseases and avert morbidity and mortality. Although the available techniques are in their infancy and the very early stages of fibrosis are difficult to detect, there have been significant advances in imaging over the last decade that has resulted in the use of these new imaging techniques being introduced into the patient pathway. This review explores the accuracies of these imaging techniques, their role in the management of patients, and the potential for the future.

Noninvasive assessment of liver fibrosis using ultrasound-based shear wave measurement and comparison to magnetic resonance elastography

OBJECTIVES

Magnetic resonance elastography (MRE) has excellent performance in detecting liver fibrosis and is becoming an alternative to liver biopsy in clinical practice. Ultrasound techniques based on measuring the propagation speed of the shear waves induced by acoustic radiation force also have shown promising results for liver fibrosis staging. The objective of this study was to compare ultrasound-based shear wave measurement to MRE.

METHODS

In this study, 50 patients (28 female and 22 male; age range, 19-81 years) undergoing liver MRE examinations were studied with an ultrasound scanner modified with shear wave measurement functionality. For each patient, 27 shear wave speed measurements were obtained at various locations in the liver parenchyma away from major vessels. The median shear wave speed from all measurements was used to calculate a representative shear modulus (μ) for each patient. Magnetic resonance elastographic data processing was done by a single analyst blinded to the ultrasound measurement results.

RESULTS

Ultrasound and MRE measurements were correlated (r = 0.86; P < .001). Receiver operating characteristic (ROC) analysis was applied to the ultrasound measurement results with the MRE diagnosis as the "ground truth." The area under the ROC curve for separating patients with minimum fibrosis (defined as μ(MRE) ≤2.9 kPa) was 0.89 (95% confidence interval, 0.77-0.95), and the area under the ROC curve for separating patients with advanced fibrosis (defined as μ(MRE) ≥5.0 kPa) was 0.96 (95% confidence interval, 0.87-0.99).

CONCLUSIONS

Results indicate that the ultrasound-based shear wave measurement correlates with MRE and is a promising method for liver fibrosis staging.

Functional MR imaging of the abdomen

In this article, functional magnetic resonance (MR) imaging techniques in the abdomen are discussed. Diffusion-weighted imaging (DWI) increases the confidence in detecting and characterizing focal hepatic lesions. The potential uses of DWI in kidneys, adrenal glands, bowel, and pancreas are outlined. Studies have shown potential use of quantitative dynamic contrast-enhanced MR imaging parameters, such as K(trans), in predicting outcomes in cancer therapy. MR elastography is considered to be a useful tool in staging liver fibrosis. A major issue with all functional MR imaging techniques is the lack of standardization of the protocol.

Noninvasive diagnosis of cirrhosis: A review of different imaging modalities

Progressive hepatic fibrosis can lead to cirrhosis, so its early detection is fundamental. Staging fibrosis is also critical for prognosis and management. The gold standard for these aims is liver biopsy, but it has several drawbacks, as it is invasive, expensive, has poor acceptance, is prone to inter observer variability and sampling errors, has poor repeatability, and has a risk of complications and mortality. Therefore, non-invasive imaging tests have been developed. This review mainly focuses on the role of transient elastography, acoustic radiation force impulse imaging, and magnetic resonance-based methods for the noninvasive diagnosis of cirrhosis.

Hepatitis activity should be considered a confounder of liver stiffness measured with MR elastography

PURPOSE

To evaluate the effect of hepatitis activity on liver stiffness measurements and the role of serum alanine aminotransferase (ALT) in liver fibrosis staging by MR elastography (MRE).

MATERIALS AND METHODS

We measured liver stiffness (kPa) in 135 patients by MRE and histologically assessed fibrosis and hepatitis activity within 2 months. Stepwise multiple linear regression was performed to determine the maximum adjusted R(2) against liver stiffness, after adjusting for nothing (model 1), ALT/upper limit of normal categories (model 2), and hepatitis activity (A grade) by METAVIR (model 3). Logistic regression was used to identify independent factors associated with pathologically proven cirrhosis.

RESULTS

Platelet count and METAVIR F score were strongly associated with liver stiffness. The adjusted R(2) value of model 3 (0.7026) was higher than those of models 1 (0.6472) and 2 (0.6564), showing that hepatitis activity affected liver stiffness measurement. High ALT levels (odds ratio, 0.0066; P = 0.0003) as well as MRE (odds ratio, 9.91; P < 0.0001) were independently associated with cirrhosis.

CONCLUSION

Hepatitis activity may be a confounder of liver stiffness measurement during liver fibrosis staging using MRE. MRE can potentially make an overdiagnosis of liver cirrhosis if the patient has high ALT levels.

MR elastography for the assessment of hepatic fibrosis in patients with chronic hepatitis B infection: does histologic necroinflammation influence the measurement of hepatic stiffness?

PURPOSE

To determine the diagnostic performance of magnetic resonance (MR) elastography for the staging of hepatic fibrosis and to evaluate the influence of necroinflammation on hepatic stiffness in patients with chronic hepatitis B virus (HBV) infection by using histopathologic findings as the reference standard.

MATERIALS AND METHODS

One hundred thirteen consecutive patients with chronic HBV infection were recruited prospectively in this institutional review board-approved study after providing written informed consent between March 2012 and October 2013. The stiffness measurements were obtained by using two-dimensional gradient-echo MR elastography with a 3.0-T MR system. The METAVIR scoring system was used for the assessment of fibrosis ("F" stage) and necroinflammation ("A" grade). The predictive ability of MR elastography was evaluated by using the receiver operating characteristic (ROC) curve and the area under the ROC curve (AUC). Multiple linear regression analyses were conducted to determine the relationship between hepatic stiffness and the variables that showed a significant association in the univariate analysis or those that were of interest for comparison with earlier work (histologic scores, sex, age, aspartate aminotransferase level, and aspartate aminotransferase/alanine aminotransferase ratio).

RESULTS

MR elastography showed excellent performance for characterization of ≥ F1, ≥ F2, ≥ F3, and F4 findings, with AUC values of 0.961, 0.986, 1.000, and 0.998, respectively. It showed a moderate capability for evaluation of necroinflammatory activity of ≥ A1, ≥ A2, and A3 (AUC = 0.806, 0.834, and 0.906, respectively). Multiple linear regression analysis showed that fibrosis, necroinflammation, and sex were independently associated with hepatic stiffness (β = 0.799, 0.277, and 0.070, respectively; P < .05). For pairwise comparisons, log-transformed hepatic stiffness showed no difference between (a) groups F0/A2-3 and F1/A0-1 and (b) groups F1/A2-3 and F2/A0-1 (P > .99 and P = .486, respectively).

CONCLUSION

MR elastography demonstrated excellent performance for distinguishing the stages of hepatic fibrosis in patients with chronic HBV infection. For hepatic tissue with ≤ F2 fibrosis, necroinflammation can account for a substantial fraction of the increase in hepatic stiffness.

MR elastography for the assessment of hepatic fibrosis in patients with chronic hepatitis B infection: does histologic necroinflammation influence the measurement of hepatic stiffness?

PURPOSE

To determine the diagnostic performance of magnetic resonance (MR) elastography for the staging of hepatic fibrosis and to evaluate the influence of necroinflammation on hepatic stiffness in patients with chronic hepatitis B virus (HBV) infection by using histopathologic findings as the reference standard.

MATERIALS AND METHODS

One hundred thirteen consecutive patients with chronic HBV infection were recruited prospectively in this institutional review board-approved study after providing written informed consent between March 2012 and October 2013. The stiffness measurements were obtained by using two-dimensional gradient-echo MR elastography with a 3.0-T MR system. The METAVIR scoring system was used for the assessment of fibrosis ("F" stage) and necroinflammation ("A" grade). The predictive ability of MR elastography was evaluated by using the receiver operating characteristic (ROC) curve and the area under the ROC curve (AUC). Multiple linear regression analyses were conducted to determine the relationship between hepatic stiffness and the variables that showed a significant association in the univariate analysis or those that were of interest for comparison with earlier work (histologic scores, sex, age, aspartate aminotransferase level, and aspartate aminotransferase/alanine aminotransferase ratio).

RESULTS

MR elastography showed excellent performance for characterization of ≥ F1, ≥ F2, ≥ F3, and F4 findings, with AUC values of 0.961, 0.986, 1.000, and 0.998, respectively. It showed a moderate capability for evaluation of necroinflammatory activity of ≥ A1, ≥ A2, and A3 (AUC = 0.806, 0.834, and 0.906, respectively). Multiple linear regression analysis showed that fibrosis, necroinflammation, and sex were independently associated with hepatic stiffness (β = 0.799, 0.277, and 0.070, respectively; P < .05). For pairwise comparisons, log-transformed hepatic stiffness showed no difference between (a) groups F0/A2-3 and F1/A0-1 and (b) groups F1/A2-3 and F2/A0-1 (P > .99 and P = .486, respectively).

CONCLUSION

MR elastography demonstrated excellent performance for distinguishing the stages of hepatic fibrosis in patients with chronic HBV infection. For hepatic tissue with ≤ F2 fibrosis, necroinflammation can account for a substantial fraction of the increase in hepatic stiffness.

Investigation of publication bias in meta-analyses of diagnostic test accuracy: a meta-epidemiological study

Background

The validity of a meta-analysis can be understood better in light of the possible impact of publication bias. The majority of the methods to investigate publication bias in terms of small study-effects are developed for meta-analyses of intervention studies, leaving authors of diagnostic test accuracy (DTA) systematic reviews with limited guidance. The aim of this study was to evaluate if and how publication bias was assessed in meta-analyses of DTA, and to compare the results of various statistical methods used to assess publication bias.

Methods

A systematic search was initiated to identify DTA reviews with a meta-analysis published between September 2011 and January 2012. We extracted all information about publication bias from the reviews and the two-by-two tables. Existing statistical methods for the detection of publication bias were applied on data from the included studies.

Results

Out of 1,335 references, 114 reviews could be included. Publication bias was explicitly mentioned in 75 reviews (65.8%) and 47 of these had performed statistical methods to investigate publication bias in terms of small study-effects: 6 by drawing funnel plots, 16 by statistical testing and 25 by applying both methods. The applied tests were Egger’s test (n = 18), Deeks’ test (n = 12), Begg’s test (n = 5), both the Egger and Begg tests (n = 4), and other tests (n = 2). Our own comparison of the results of Begg’s, Egger’s and Deeks’ test for 92 meta-analyses indicated that up to 34% of the results did not correspond with one another.

Conclusions

The majority of DTA review authors mention or investigate publication bias. They mainly use suboptimal methods like the Begg and Egger tests that are not developed for DTA meta-analyses. Our comparison of the Begg, Egger and Deeks tests indicated that these tests do give different results and thus are not interchangeable. Deeks’ test is recommended for DTA meta-analyses and should be preferred.

Invasive and non-invasive diagnosis of cirrhosis and portal hypertension

With advances in the management and treatment of advanced liver disease, including the use of antiviral therapy, a simple, one stage description for advanced fibrotic liver disease has become inadequate. Although refining the diagnosis of cirrhosis to reflect disease heterogeneity is essential, current diagnostic tests have not kept pace with the progression of this new paradigm. Liver biopsy and hepatic venous pressure gradient measurement are the gold standards for the estimation of hepatic fibrosis and portal hypertension (PHT), respectively, and they have diagnostic and prognostic value. However, they are invasive and, as such, cannot be used repeatedly in clinical practice. The ideal noninvasive test should be safe, easy to perform, inexpensive, reproducible as well as to give numerical and accurate results in real time. It should be predictive of long term outcomes related with fibrosis and PHT to allow prognostic stratification. Recently, many types of noninvasive alternative tests have been developed and are under investigation. In particular, imaging and ultrasound based tests, such as transient elastography, have shown promising results. Although most of these noninvasive tests effectively identify severe fibrosis and PHT, the methods available for diagnosing moderate disease status are still insufficient, and further investigation is essential to predict outcomes and individualize therapy in this field.

Evaluation of hepatic fibrosis using intravoxel incoherent motion in diffusion-weighted liver MRI

OBJECTIVES

To determine whether intravoxel incoherent motion (IVIM)-diffusion-weighted image (DWI)-derived parameters showed better diagnostic performance than the apparent diffusion coefficient (ADC(total)) for the evaluation of hepatic fibrosis (HF).

METHODS

This retrospective study was approved by institutional review board, and informed consent was waived. Fifty-five patients with chronic liver disease who had undergone IVIM-DWI using 8 b-values at 3 T were included. True diffusion coefficient (Dt), pseudo-diffusion coefficient (Dp), perfusion fraction (f), and ADC(total) were calculated. Receiver operating characteristic analysis was performed for all parameters for the HF staging.

RESULTS

All parameters showed a significant correlation with the HF stages (-0.31 to -0.72, P < 0.05). All parameters were significantly higher in F0 to F1 than in F4 (P < 0.05). The Dp showed better performance than the ADC(total) in differentiating significant HF (≥F2) from F0 to F1.

CONCLUSIONS

The IVIM-derived parameters and ADC(total) showed significant correlation with HF. The D p showed better diagnostic performance for differentiating significant HF than did ADC(total).

Short- and midterm repeatability of magnetic resonance elastography in healthy volunteers at 3.0 T

The purpose of this study was to evaluate the short- and midterm repeatability of liver stiffness measurements with magnetic resonance elastography (MRE) in healthy subjects at 3.0T. Twenty-two healthy volunteers were enrolled in this prospective study. The stiffness measurements were obtained from three slices with three repeated acquisitions for each slice (session 1) by two independent raters. After a mean period of 7±2days (session 2) and 195±15days (session 3), each subject was scanned again using the same protocol and MR system. The liver stiffness differences were calculated between sessions or raters. The intraclass correlation coefficient (ICC) was calculated to assess interrater agreement and intersession agreement. The stiffness differences over the short- and midterm intervals was (-0.004±0.086) kPa for sessions 1-2, lower than (-0.055±0.150) kPa for sessions 1-3 and (-0.051±0.173) kPa for sessions 2-3. The liver stiffness was more repeatable for the short-term interval with the mean overall ICC of 0.96 (sessions 1-2) (95% confidence interval [CI]: 0.90-0.98) compared with 0.91 (sessions 1-3) (95% CI: 0.78-0.96) and 0.87 (sessions 2-3) (95% CI: 0.69-0.95) for the midterm intervals. The overall ICC of interrater agreement was excellent at 0.987 (95% CI: 0.983 to 0.990). These results confirm that MRE is a reproducible technique for liver stiffness quantification over short- and midterm intervals up to 6months in a healthy population at 3.0T.

P4 radiology of hepatobiliary diseases with gadoxetic acid-enhanced MRI as a biomarker

A recent paradigm shift in radiology has focused on the globalization of so-called P4 radiology. P4 radiology represents delivery of imaging results that are predictive, personalized, pre-emptive and participatory. The combination of the P4 approach and biomarkers is particularly pertinent to MRI, especially with technological advances such as diffusion-weighted imaging. The development of new liver-specific MRI contrast media, particularly gadoxetic acid, demonstrate specific pharmacokinetic properties, which provide combined morphologic and functional information in the same setting. The evaluation of hepatobiliary pathology beyond morphology gives rise to the possibilty of using gadoxetic acid-enhanced MRI as an imaging biomarker of hepatobiliary diseases. The integration of functional imaging with an understanding of complex disease mechanisms forms the basis for P4 radiology, which may ultimately lead to individualized, cost-effective, targeted therapy for patients. This will enable radiologists to determine the prognosis of the disease and estimate early response to treatment, with the participation of all the required medical disciplines.

The effect of low b-values on the intravoxel incoherent motion derived pseudodiffusion parameter in liver

PURPOSE

To examine the effect of low b-values (0 < b < 50 s/mm(2)) on the calculation of the intravoxel incoherent motion (IVIM) derived pseudodiffusion parameter in the normal liver.

METHODS

Simulations were performed to examine the effects of adding low b-values on the pseudodiffusion parameter. Low b-values were cumulatively added to the distribution and the IVIM signal was generated with varying pseudodiffusion values. The signal was fit with the IVIM model after the addition of Gaussian noise, and the simulated values were compared with the true values. In addition, the livers of eight control subjects were imaged using respiratory-triggered DWI. Pseudodiffusion was calculated with and without low b-values and compared.

RESULTS

Pseudodiffusion tended to be underestimated when low b-values were not included in the b-value distribution as predicted by simulations and confirmed with in vivo imaging. The number of outlier values was also reduced as more low b-values were added.

CONCLUSION

In conclusion, this study showed pseudodiffusion in the liver tended to be underestimated when too few low b-values (0 < b < 50 s/mm(2)) were included in the distribution. Therefore, it is recommended to include at least two low b-values when performing liver IVIM studies.

Non-invasive diagnosis of hepatitis B virus-related cirrhosis

Chronic hepatitis B (CHB) infection is a major public health problem associated with significant morbidity and mortality worldwide. Twenty-three percent of patients with CHB progress naturally to liver cirrhosis, which was earlier thought to be irreversible. However, it is now known that cirrhosis can in fact be reversed by treatment with oral anti-nucleotide drugs. Thus, early and accurate diagnosis of cirrhosis is important to allow an appropriate treatment strategy to be chosen and to predict the prognosis of patients with CHB. Liver biopsy is the reference standard for assessment of liver fibrosis. However, the method is invasive, and is associated with pain and complications that can be fatal. In addition, intra- and inter-observer variability compromises the accuracy of liver biopsy data. Only small tissue samples are obtained and fibrosis is heterogeneous in such samples. This confounds the two types of observer variability mentioned above. Such limitations have encouraged development of non-invasive methods for assessment of fibrosis. These include measurements of serum biomarkers of fibrosis; and assessment of liver stiffness via transient elastography, acoustic radiation force impulse imaging, real-time elastography, or magnetic resonance elastography. Although significant advances have been made, most work to date has addressed the diagnostic utility of these techniques in the context of cirrhosis caused by chronic hepatitis C infection. In the present review, we examine the advantages afforded by use of non-invasive methods to diagnose cirrhosis in patients with CHB infections and the utility of such methods in clinical practice.

Physicians' practices for diagnosing liver fibrosis in chronic liver diseases: a nationwide, Canadian survey

OBJECTIVE

To determine practices among physicians in Canada for the assessment of liver fibrosis in patients with chronic liver diseases.

METHODS

Hepatologists, gastroenterologists, infectious diseases specialists, members of the Canadian Gastroenterology Association and⁄or the Canadian HIV Trials Network who manage patients with liver diseases were invited to participate in a web-based, national survey.

RESULTS

Of the 237 physicians invited, 104 (43.9%) completed the survey. Routine assessment of liver fibrosis was requested by the surveyed physicians mostly for chronic hepatitis C (76.5%), followed by autoimmune⁄cholestatic liver disease (59.6%) and chronic hepatitis B (52.9%). Liver biopsy was the main diagnostic tool for 46.2% of the respondents, Fibroscan (Echosens, France) for 39.4% and Fibrotest (LabCorp, USA) for 7.7%. Etiology-specific differences were observed: noninvasive methods were mostly used for hepatitis C (63% versus 37% liver biopsy) and hepatitis B (62.9% versus 37.1% liver biopsy). For 42.7% of respondents, the use of noninvasive methods reduced the need for liver biopsy by >50%. Physicians' characteristics associated with higher use of noninvasive methods were older age and being based at a university hospital or in private practice versus community hospital. Physicians' main concerns regarding noninvasive fibrosis assessment methods were access⁄availability (42.3%), lack of guidelines for clinical use (26.9%) and cost⁄lack of reimbursement (14.4%).

CONCLUSIONS

Physicians who manage patients with chronic liver diseases in Canada require routine assessment of liver fibrosis stage. Although biopsy remains the primary diagnostic tool for almost one-half of respondents, noninvasive methods, particularly Fibroscan, have significantly reduced the need for liver biopsy in Canada. Limitations in access to and availability of the noninvasive methods represent a significant barrier. Finally, there is a need for clinical guidelines and a better reimbursement policy to implement noninvasive tools to assess liver fibrosis.

Texture-based classification of liver fibrosis using MRI

PURPOSE

To investigate the ability of texture analysis of MRI images to stage liver fibrosis. Current noninvasive approaches for detecting liver fibrosis have limitations and cannot yet routinely replace biopsy for diagnosing significant fibrosis.

MATERIALS AND METHODS

Forty-nine patients with a range of liver diseases and biopsy-confirmed fibrosis were enrolled in the study. For texture analysis all patients were scanned with a T2 -weighted, high-resolution, spin echo sequence and Haralick texture features applied. The area under the receiver operating characteristics curve (AUROC) was used to assess the diagnostic performance of the texture analysis.

RESULTS

The best mean AUROC achieved for separating mild from severe fibrosis was 0.81. The inclusion of age, liver fat and liver R2 variables into the generalized linear model improved AUROC values for all comparisons, with the F0 versus F1-4 comparison the highest (0.91).

CONCLUSION

Our results suggest that a combination of MRI measures, that include selected texture features from T2 -weighted images, may be a useful tool for excluding fibrosis in patients with liver disease. However, texture analysis of MRI performs only modestly when applied to the classification of patients in the mild and intermediate fibrosis stages.

Shear wave elastography for differentiation of benign and malignant thyroid nodules: a meta-analysis

OBJECTIVES

The purpose of this study was to assess the performance of shear wave elastography for identification of benign and malignant thyroid nodules using meta-analysis.

METHODS

PubMed, MEDLINE, Embase, the Cochrane Library, and the China National Knowledge Infrastructure were searched. Patients' clinical characteristics, sensitivity, specificity, positive predictive value, and negative predictive value were extracted. The diagnostic odds ratio and summary receiver operating characteristic curve were used to examine the accuracy of shear wave elastography. A meta-analysis was performed to evaluate the clinical utility of shear wave elastography for identification of benign and malignant thyroid nodules.

RESULTS

The summary sensitivity and specificity for the diagnosis of malignant thyroid nodules by shear wave elastography were 0.84 (95% confidence interval [CI], 0.76-0.90) and 0.90 (95% CI, 0.87-0.92), respectively. The pooled positive likelihood ratio was 7.39 (95% CI, 4.09-13.35), and the negative likelihood ratio was 0.20 (95% CI, 0.13-0.29). The summary diagnostic odds ratio was 41.35 (95% CI, 17.38-98.41), and the summary area under the receiver operating characteristic curve was 0.92 (Q* = 0.8538).

CONCLUSIONS

Shear wave elastography has high sensitivity and specificity in the evaluation of thyroid nodules and can potentially reduce unnecessary fine-needle aspiration biopsies.

Percutaneous liver biopsy practice patterns among Canadian hepatologists

BACKGROUND

Percutaneous liver biopsy (PLB) is the standard procedure to obtain histological samples essential for the management of various liver diseases. While safe, many hepatologists no longer perform their own PLBs; the reasons for this practice shift are unknown.

OBJECTIVE

To describe the attitudes, practice patterns and barriers to PLB among hepatologists in Canada.

METHODS

A survey was distributed to all hepatologists in Canada.

RESULTS

Thirty-two of 40 (80%) hepatologists completed the survey; the majority of respondents were male (72%) and had been in practice for >5 years in an academic setting. Fifty-six per cent of hepatologists referred all PLBs to radiology, and only 19% of hepatologists reported performing their own PLBs most or all of the time. There were no sex differences nor were there differences based on years in practice. Fifty per cent of respondents who performed PLB routinely used ultrasound, and PLBs are performed in equal frequency in an ambulatory procedure area (50%) versus the endoscopy suite (36%). For almost one-half of hepatologists (47%), their performance of PLBs decreased in the past five years. The majority of respondents at an academic centre (75%) reported access to FibroScan (Echosens, France), and most estimated a resultant 25% to 50% reduction in the need for PLBs. Lack of resources, patient preference and suboptimal reimbursement were the most common reasons cited for not performing PLBs.

CONCLUSION

Most hepatologists in Canada do not perform PLBs to the extent that they did in the past, but refer to radiology. The reasons for this shift in practice include lack of resources, improved perception of safety and patient preference. Where available, FibroScan resulted in a perceived 25% to 50% reduction in required liver biopsies.

MR elastography of the liver: defining thresholds for detecting viscoelastic changes

PURPOSE

To define thresholds for detecting significant change in liver viscoelasticity with magnetic resonance (MR) elastography, both for whole-liver measurements and for voxel-wise measurements in relation to spatial resolution.

MATERIALS AND METHODS

This prospective study was approved by the institutional review board, and all participants provided written informed consent. Thirty participants (16 volunteers and 14 patients with hepatitis B or C; 18 men; median age, 30.4 years; age range, 18.9-58.6 years) underwent imaging twice while in the same position (intraimage reproducibility), after repositioning (within-day reproducibility), and 1-4 weeks later (between-weeks reproducibility). MR elastography parameters comprised elasticity, viscosity, attenuation parameter α, and propagation parameter β. Bland-Altman analysis was used to calculate repeatability indexes for each parameter. Analyses were performed in a region-of-interest and a voxel-by-voxel level. Voxel-wise results were calculated in relation to spatial resolution by applying Gaussian filtering to establish the optimal trade-off point between resolution and reproducibility.

RESULTS

For elasticity, α, and β, within-day and between-weeks results were significantly lower than intraimage results (P ≤ .018 for all). Within-day and between-weeks results did not differ significantly. Over-time changes of more than 22.2% for elasticity, 26.3% for viscosity, 26.8% for α, and 10.1% for β represented thresholds for significant change. The optimal trade-off between spatial resolution and reproducibility was found at a filter size of 8-mm full width at half maximum (FWHM) for elasticity and propagation parameter β and at 16-mm FWHM for viscosity and attenuation parameter α.

CONCLUSION

Repositioning causes a significant decrease in the reproducibility of MR elastography. The propagation parameter β is the most reliable parameter, with an over-time threshold for significant change of 10.1% and the ability to reproduce viscoelasticity up to a resolution of 8-mm FWHM. Online supplemental material is available for this article.

Liver elastography, comments on EFSUMB elastography guidelines 2013

Recently the European Federation of Societies for Ultrasound in Medicine and Biology Guidelines and Recommendations have been published assessing the clinical use of ultrasound elastography. The document is intended to form a reference and to guide clinical users in a practical way. They give practical advice for the use and interpretation. Liver disease forms the largest section, reflecting published experience to date including evidence from meta-analyses with shear wave and strain elastography. In this review comments and illustrations on the guidelines are given.

Rapid acquisition of multifrequency, multislice and multidirectional MR elastography data with a fractionally encoded gradient echo sequence

In MR elastography (MRE), periodic tissue motion is phase encoded using motion-encoding gradients synchronized to an externally applied periodic mechanical excitation. Conventional methods result in extended scan time for quality phase images, thus limiting the broad application of MRE in the clinic. For practical scan times, researchers have been relying on one-dimensional or two-dimensional motion-encoding, low-phase sampling and a limited number of slices, and artifact-prone, single-shot, echo planar imaging (EPI) readout. Here, we introduce a rapid multislice pulse sequence capable of three-dimensional motion encoding that is also suitable for simultaneously encoding motion with multiple frequency components. This sequence is based on a gradient-recalled echo (GRE) sequence and exploits the principles of fractional encoding. This GRE MRE pulse sequence was validated as capable of acquiring full three-dimensional motion encoding of isotropic voxels in a large volume within less than a minute. This sequence is suitable for monofrequency and multifrequency MRE experiments. In homogeneous paraffin phantoms, the eXpresso sequence yielded similar storage modulus values as those obtained with conventional methods, although with markedly reduced variances (7.11 ± 0.26 kPa for GRE MRE versus 7.16 ± 1.33 kPa for the conventional spin-echo EPI sequence). The GRE MRE sequence obtained better phase-to-noise ratios than the equivalent spin-echo EPI sequence (matched for identical acquisition time) in both paraffin phantoms and in vivo data in the liver (59.62 ± 11.89 versus 27.86 ± 3.81, 61.49 ± 14.16 versus 24.78 ± 2.48 and 58.23 ± 10.39 versus 23.48 ± 2.91 in the X, Y and Z components, respectively, in the case of liver experiments). Phase-to-noise ratios were similar between GRE MRE used in monofrequency or multifrequency experiments (75.39 ± 14.93 versus 86.13 ± 18.25 at 28 Hz, 71.52 ± 24.74 versus 86.96 ± 30.53 at 56 Hz and 95.60 ± 36.96 versus 61.35 ± 26.25 at 84Hz, respectively).

Magnetic resonance elastography for the detection and staging of liver fibrosis in chronic hepatitis B

OBJECTIVES

We measured the accuracy of magnetic resonance elastography (MRE) for the detection and staging of liver fibrosis in chronic hepatitis B (CHB) and compared it with serum fibrosis markers.

METHODS

Prospective comparison of MRE and routine serum fibrosis markers, namely serum alanine aminotransferase (ALT), serum aspartate aminotransferase (AST), ALT/AST ratio (AAR), AST to platelet ratio index (APRI) and prothrombin index (PI), was performed in 63 consecutive CHB patients who underwent MRE and histological confirmation of liver fibrosis within a 6-month interval. Diagnostic performance of MRE and serum markers for staging fibrosis (≥F1), significant fibrosis (≥F2), advanced fibrosis (≥F3) and cirrhosis (F4) was compared.

RESULTS

The study group comprised 63 patients (19 female; mean age ± SD, 50 ± 11.9 years). MRE (ρ = 0.94, P < 0.0001), APRI (ρ = 0.42, P = 0.0006), PI (ρ = 0.42, P = 0.0006) and AST (ρ = 0.28, P = 0.028) results correlated significantly with fibrosis stage. MRE was significantly more accurate than serum fibrosis markers for the detection of significant fibrosis (0.99 vs. 0.55-0.73) and cirrhosis (0.98 vs. 0.53-0.77). Sensitivity, specificity, positive predictive and negative predictive values for MRE for significant fibrosis and cirrhosis were 97.4 %, 100 %, 100 % and 96 %, and 100 %, 95.2 %, 91.3 % and 100 %, respectively.

CONCLUSION

MRE is an accurate non-invasive technique for the detection and staging of liver fibrosis in CHB.

KEY POINTS

• Magnetic resonance elastography is accurate for liver fibrosis detection and staging. • MR elastography is more accurate than serum tests for staging liver fibrosis. • MR elastography can potentially replace liver biopsy in chronic hepatitis B.

Magnetic resonance elastography in the diagnosis of hepatic fibrosis

Liver fibrosis is a common feature of many chronic liver diseases, and can ultimately progress to cirrhosis. Conventional imaging is insensitive to liver fibrosis, necessitating a liver biopsy for diagnosis and monitoring of progression. However, liver biopsy risks complications, and is an imperfect gold standard in view of sampling error and intraobserver or interobserver variation. Magnetic resonance elastography (MRE) is a noninvasive method for assessing the mechanical properties of tissues and is gaining credence as a method of assessment for hepatic fibrosis. The aim of this review is to describe how MRE is performed, to review the present literature on the subject, to compare MRE with other noninvasive techniques used to assess for liver fibrosis, and to highlight areas of future research.

Magnetic resonance elastography for staging liver fibrosis in chronic hepatitis C

PURPOSE

We evaluated the use of magnetic resonance (MR) elastography (MRE) for staging liver fibrosis in patients with chronic hepatitis C and compared the ability of MRE and serum fibrosis markers for discriminating each stage of fibrosis.

METHODS

We evaluated 114 patients with chronic hepatitis C in whom the pathological fibrosis stage was determined (fibrosis stage 0 [F0], 3; F1, 15; F2, 28; F3, 25; and F4, 43). All patients underwent MRE using a 1.5-tesla MR system and pneumatic driver system. We measured stiffness values (kPa) of the liver in a circular region of interest placed on elastograms. We determined the optimal cutoff value and diagnostic ability for discriminating each stage of fibrosis using receiver operating characteristic (ROC) curve analysis and compared the discriminative ability of MRE with that of serum fibrosis markers.

RESULTS

The mean stiffness values of the liver increased with stage of fibrosis: F0, 2.10±0.10 kPa; F1, 2.42±0.29 kPa; F2, 3.16±0.32 kPa; F3, 4.21±0.78 kPa; and F4, 6.20±1.08 kPa. The mean area under the ROC curve (Az) values for discriminating liver fibrosis stages were: ≥F1, 0.984 (95% confidence interval, 0.933-0.996); ≥F2, 0.986 (0.956-0.996); ≥F3, 0.973 (0.935-0.989); and ≥F4, 0.976 (0.945-0.990). The Az values for discriminating fibrosis stages were significantly higher for MRE than serum fibrosis markers.

CONCLUSION

MRE is a reliable technique for staging liver fibrosis and discriminating liver fibrosis stages in patients with chronic hepatitis C.

Diffusion-weighted imaging of the liver: an update

Diffusion-weighted magnetic resonance imaging (DW-MRI) is now widely used as a standard imaging sequence for evaluation of the liver. The technique is easy to implement across different MRI platforms, and results in enhanced disease detection and characterization. With careful implementation, the quantitative apparent diffusion coefficient derived shows good measurement reproducibility, which can be applied for tissue characterization, the assessment of tumour response and disease prognostication. There is now a body of evidence that highlights the relative strengths and limitations of the technique for the assessment of liver diseases. The potential for more sophisticated analysis of DW-MRI data is currently being widely investigated.

MR imaging of primary sclerosing cholangitis: additional value of diffusion-weighted imaging and ADC measurement

BACKGROUND

Primary sclerosing cholangitis (PSC) is a cholestatic liver disease with chronic inflammation and progressive destruction of biliary tree. Magnetic resonance (MR) examination with diffusion-weighted imaging (DWI) allows analysis of morphological liver parenchymal changes and non-invasive assessment of liver fibrosis. Moreover, MR cholangiopancreatography (MRCP), as a part of standard MR protocol, provides insight into bile duct irregularities.

PURPOSE

To evaluate MR and MRCP findings in patients with primary sclerosing cholangitis and to determine the value of DWI in the assessment of liver fibrosis.

MATERIAL AND METHODS

The following MR findings were reviewed in 38 patients: abnormalities in liver parenchyma signal intensity, changes in liver morphology, lymphadenopathy, signs of portal hypertension, and irregularities of intra- and extrahepatic bile ducts. Apparent diffusion coefficient (ADC) was calculated for six locations in the liver for b = 800 s/mm(2).

RESULTS

T2-weighted hyperintensity was seen as peripheral wedge-shaped areas in 42.1% and as periportal edema in 28.9% of patients. Increased enhancement of liver parenchyma on arterial-phase imaging was observed in six (15.8%) patients. Caudate lobe hypertrophy was present in 10 (26.3%), while spherical liver shape was noted in 7.9% of patients. Liver cirrhosis was seen in 34.2% of patients; the most common pattern was micronodular cirrhosis (61.5%). Other findings included lymphadenopathy (28.9%), signs of portal hypertension (36.7%), and bile duct irregularities (78.9%). The mean ADCs (x10(-3)mm(2)/s) were significantly different at stage I vs. stages III and IV, and stage II vs. stage IV. No significant difference was found between stages II and III. For prediction of stage ≥II and stage ≥III, areas under receiver-operating characteristic curves were 0.891 and 0.887, respectively.

CONCLUSION

MR with MRCP is a necessary diagnostic procedure for diagnosis of PSC and evaluation of disease severity. Moreover, DWI could be used in continuation with standard MR sequences for the evaluation of liver fibrosis stage and distribution.

Liver fibrosis in type I Gaucher disease: magnetic resonance imaging, transient elastography and parameters of iron storage

Long term liver-related complications of type-1 Gaucher disease (GD), a lysosomal storage disorder, include fibrosis and an increased incidence of hepatocellular carcinoma. Splenectomy has been implicated as a risk factor for the development of liver pathology in GD. High ferritin concentrations are a feature of GD and iron storage in Gaucher cells has been described, but iron storage in the liver in relation to liver fibrosis has not been studied. Alternatively, iron storage in GD may be the result of iron supplementation therapy or regular blood transfusions in patients with severe cytopenia. In this pilot study, comprising 14 type-1 GD patients (7 splenectomized, 7 non-splenectomized) and 7 healthy controls, we demonstrate that liver stiffness values, measured by Transient Elastography and MR-Elastography, are significantly higher in splenectomized GD patients when compared with non-splenectomized GD patients (p = 0.03 and p = 0.01, respectively). Liver iron concentration was elevated (>60±30 µmol/g) in 4 GD patients of whom 3 were splenectomized. No relationship was found between liver stiffness and liver iron concentration. HFE gene mutations were more frequent in splenectomized (6/7) than in non-splenectomized (2/7) participants (p = 0.10). Liver disease appeared more advanced in splenectomized than in non-splenectomized patients. We hypothesize a relationship with excessive hepatic iron accumulation in splenectomized patients. We recommend that all splenectomized patients, especially those with evidence of substantial liver fibrosis undergo regular screening for HCC, according to current guidelines.