Liver fat has a greater negative effect on health than fat stored under the skin. Increased liver fat is an indicator of metabolic disorders associated with being overweight or diabetes. This thesis seeks to compare whole liver estimation of liver fat by magnetic resonance imaging (MRI) techniques with methods that sample small areas of the liver, namely the current clinical gold standard, liver biopsy, single voxel MRS in 2 positions and two small regions-of-interest for imaging techniques.
Currently, the clinically accepted method to measure liver fat is through biopsy. A liver biopsy requires inserting a needle into the liver and removing a small sample. This procedure has significant risks to the patient. Use of liver biopsy to measure liver fat is not suitable for research because it cannot be repeated on the same patient within a short period of time. Validation of non-invasive techniques has enormous benefits for patient management and research. Magnetic resonance imaging and spectroscopy allows several different methods for determination of liver fat non-invasively.
This study used information from a database of patients that had liver biopsy for clinical assessment along with assessment by magnetic resonance imaging and magnetic resonance spectroscopy. The first step was optimizing a liver segmentation method on a sub-set of 15 patients. The optimized whole liver manual segmentation protocol was developed to select liver tissue from the whole organ and exclude non-liver tissue including vessels, image artefacts and image calculation errors when generating the liver fat images. The optimised method was then applied to the whole data set of 63 patients.
Direct comparison of region-of-interest versus whole liver methods for calculating liver fat from two different imaging techniques was included. Whole liver segmentation was performed using manual segmentation methods. These are very time consuming and operator dependent methods, particularly compared to ROI methods. However, manual segmentation remains the “gold standard”. ROI methods could be completed in less than one minute and easily incorporated into the imaging time with the patient in the MRI scanner.
Investigations to evaluate correlations were done between the following: ROI and whole liver analysis of in-phase/out-of-phase and with/without fat saturation, magnetic resonance spectroscopy, biopsy results using the percentage of hepatocytes with visible fat. All methods tested for the determination of liver fat were highly correlated. There was no consistent improvement in the correlation of either imaging method, ROI or whole liver, compared to MRS or biopsy. However, the calculated value for steatosis was different for almost all methods. This resulted in different numerical ranges being required to match the steatosis grading determined from liver biopsy.
This work demonstrates high correlation, yet numerically different values for liver steatosis, determined from the ROI or whole liver from IP/OP and ±FS MRI techniques, compared to MRS or liver biopsy. No benefit was evident for ROI versus whole liver calculation of liver, however quick visual inspection of images with fat dependent image intensity should be included. This work supports the growing body of evidence that MRI can provide safe, non-invasive and reliable methods for determining liver steatosis. However, standardisation of acquisition and analysis methods is required to enable definition of numerical ranges for clinical steatosis grading.