Magnetic resonance imaging and spectroscopy for monitoring liver steatosis

Non-invasive assessment and quantification of liver steatosis by ultrasound, computed tomography and magnetic resonance

Hepatic steatosis is the most prevalent liver disorder in the developed world. It is closely associated with features of metabolic syndrome, especially insulin resistance and obesity. The two most common conditions associated with fatty liver are alcoholic liver disease (ALD) and non-alcoholic fatty liver disease (NAFLD). Liver biopsy is considered the gold standard for the assessment of liver fat, but there is a need for less invasive diagnostic techniques. New imaging modalities are emerging, which could provide more detailed information about hepatic tissue or even replace biopsy. In the present review, available imaging modalities (ultrasound, computed tomography, magnetic resonance imaging and proton magnetic resonance spectroscopy) are presented which are employed to detect or even quantify the fat content of the liver. The advantages and disadvantages of the above-mentioned imaging modalities are discussed. Although none of these techniques is able to differentiate between microvesicular and macrovesicular steatosis and to reveal all features visible using histology, the proposed diagnostic modalities offer a wide range of additional information such as anatomical and morphological information non-invasively. In particular, magnetic resonance imaging and proton magnetic resonance spectroscopy are able to quantify the hepatic fat content hence avoiding exposure to radiation. Except for proton magnetic resonance spectroscopy, all modalities offer additional information about regional fat distribution within the liver. MR elastography, which can estimate the amount of fibrosis, also appears promising in the differentiation between simple steatosis and steatohepatitis.

Magnetic resonance imaging and spectroscopy accurately estimate the severity of steatosis provided the stage of fibrosis is considered

BACKGROUND/AIMS

Currently the diagnosis and severity of hepatic steatosis can be established accurately only by liver biopsy. Previous small studies found that steatosis measured by magnetic resonance spectroscopy (MRS) and imaging (MRI) correlated with histological assessment of liver triglyceride content. However, the accuracy of MRS/MRI for grading the severity of steatosis has not been addressed. The aims of this study were (1) to determine whether MRS and MRI can discriminate grades of steatosis in a large cohort of consecutive patients with a wide spectrum of liver disease aetiology and severity (2) to evaluate the effect of hepatic fibrosis, inflammation and iron on quantitation of intrahepatocellular lipid (IHCL) by these techniques.

METHODS

Ninety-four sequential patients who underwent percutaneous liver biopsy or liver resection had MRS and MRI (Dixon in phase/out of phase (Dixon IP/OP) and with/without fat saturation (+/-FS) images) to determine IHCL. Histology was used as the reference standard.

RESULTS

Close relationships were observed between the percentage of steatosis estimated by histology and MRS/MRI (r(s)=0.88 p<0.001 for all techniques). However, separate equations were required for the percentage of steatosis to avoid underestimation by imaging for patients with moderate or advanced fibrosis. All techniques had good diagnostic accuracy for mild steatosis (AUROC > or =0.87) as well as moderate/severe steatosis (AUROC > or =0.89). Hepatic inflammation and mild iron deposition (Perls' grade 1 and 2) did not interfere with estimation of steatosis by imaging.

CONCLUSIONS

MRS and MRI had good accuracy for grading the severity of steatosis in subjects with liver disease, provided that stage of fibrosis was considered.

Management of chemotherapy-associated hepatotoxicity in colorectal liver metastases

Effective systemic drugs are increasingly used to treat patients with colorectal liver metastases. Recent trials have shown that chemotherapy can reduce the size of metastases that are unresectable rendering them resectable, and decrease postoperative recurrence rates in patients with initially resectable tumours. The increasing use of chemotherapy for colorectal liver metastases has raised awareness of the potential hepatotoxicities induced by systemic drugs and the effects of these drugs on outcome after hepatic resection. In this Review, we outline the rationale for the use of perioperative chemotherapy for colorectal liver metastases, associations between specific agents and patterns of liver injury, and strategies to treat patients with suspected or known chemotherapy-associated hepatotoxicity.

Mapping of liver fat with triple-echo gradient echo imaging: validation against 3.0-T proton MR spectroscopy

The purpose of this study was to validate a magnetic resonance imaging (MRI) technique for mapping liver fat, using (1)H magnetic resonance spectroscopy ((1)H-MRS) as the reference standard. In 91 patients with type 2 diabetes, 3.0-T single-voxel point-resolved (1)H-MRS was used to calculate the liver fat fraction (LFF) from the water (4.76 ppm) and methylene (1.33 ppm) peaks, corrected for T1 and T2 decays. LFF (corrected for T1 and T2* decays) was also obtained from the mean signal intensity on a map built from a triple-echo (consecutive in-phase, opposed-phase, and in-phase echo times) breath-hold gradient echo sequence, using basic image calculation functions (arithmetic mean, subtraction, division, multiplication by a numerical factor). Mean LFF was 8.9% (range, 0.9-33.5) by MRI and 8.8% (range, 0-34.1) by (1)H-MRS. Pearson's coefficient was 0.976 (P < 0.0001) and Lin's coefficient was 0.975 (P < 0.0001). Liver segment had no significant influence. With Bland-Altman analysis, 95.6% (87/91) of data points were within the limits of agreement. Given its excellent agreement with (1)H-MRS, our mapping technique can be used for visual and quantitative evaluation of liver fat in everyday practice.