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- Karlsson, Markus, 1990-
(författare)
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Non-Invasive Characterization of Liver Disease : By Multimodal Quantitative Magnetic Resonance
- 2019
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- There is a large and unmet need for diagnostic tool that can be used to characterize chronic liver diseases (CLD). In the earlier stages of CLD, much of the diagnostics involves performing biopsies, which are evaluated by a histopathologist for the presence of e.g. fat, iron, inflammation, and fibrosis. Performing biopsies, however, have two downsides: i) biopsies are invasive and carries a small but non-negligible risk for serious complications, ii) biopsies only represents a tiny portion of the liver and are thus prone to sampling error. Moreover, in the later stages of CLD, when the disease has progressed far enough, the ability of the liver to perform its basic function will be compromised. In this stage, there is a need for better methods for accurately measuring liver function. Additionally, measures of liver function can also be used when developing new drugs, as biomarkers for drug-induced liver injury (DILI), which is a serious drug-safety issue.Magnetic resonance imaging (MRI) is a non-invasive medical imaging modality, which have shown much promise with regards to characterizing liver disease in all of the abovementioned aspects. The aim of this PhD project was to develop and validate MR-based methods that can be used to non-invasively characterize liver disease.Paper I investigated if R2* mapping, a MR-method for measuring liver iron content, can be confounded by liver fat. The results show fat does affect R2*. The conclusion was therefore that fat must be taken into account when measuring small amounts of liver iron, as a small increase in R2* could be due to either small amounts of iron or large amounts of fat.Paper II examined whether T1 mapping, which is another MR-method, can be used for staging liver fibrosis. The results of previous research have been mixed; some studies have been very promising, whereas other studies have been less promising. Unfortunately, the results in Paper II belongs to the less promising studies.Paper III focused on measuring liver function by dynamic contrast-enhanced MRI (DCEMRI) using a liver specific contrast agent, which is taken up the hepatocytes and excreted to the bile. The purpose of the paper was to extend and validate a method for estimating uptake and efflux rates of the contrast agent. The method had previously only been applied in health volunteers. Paper II showed that the method can be applied to CLD patients and that the uptake of the contrast agent is lower in patients with advanced fibrosis.Paper IV also used studied liver function with DCE-MRI in patients with primary sclerosing cholangitis (PSC). PSC is a CLD where the bile ducts are attacked by the immune system. When diagnosing PSC patients, it is common to use magnetic resonance cholangiopancreatography (MRCP), which is a method for imaging the bile ducts. Paper IV examined if there was any correlation between number and severity of the morphological changes, seen on MRCP, and measures of liver function derived using DCE-MRI. However, the results showed no such correlation. The conclusion was that the results indicates that MRCP should not be used to predict parenchymal function.Paper V developed a method for translating DCE-MRI liver function parameters from rats to humans. This translation could be of value when developing new drugs, as a tool for predicting which drugs might cause drug-induced liver injury.In summary, this thesis has shown that multimodal quantitative MR has a bright future for characterizing liver disease from a range of different aspects.
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| 2. |
- Nasr, Patrik, 1987-
(författare)
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Non-Alcoholic Fatty Liver Disease : Aspects on Diagnosis and Long-term Prognosis
- 2019
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Non-alcoholic fatty liver disease (NAFLD) is the most common cause of chronic liver disease affecting approximately 25% of the global population and is commonly recognized as the hepatic manifestation of the metabolic syndrome. The histological spectrum of NAFLD ranges from isolated steatosis to non-alcoholic steatohepatitis (NASH), with risk of developing fibrosis and subsequent cirrhosis and hepatocellular carcinoma. The gold standard for diagnosing NAFLD is liver biopsy. However, because of its invasive nature, several non-invasive methods have been developed and validated in evaluating fat and fibrosis in patients with NAFLD.Liver fat content can be assessed using various methods. The conventional histopathological method consists of a visual semiquantitative approach in which the pathologist uses a four-point scale: grade 0 corresponds to fat deposition in <5% of hepatocytes and grade 1−3 (which is needed for the diagnosis of NAFLD) corresponds to ≥5%. An alternate approach is to quantitatively assess steatosis using stereological point counting (SPC) – which rely on liver biopsy. However, in vivo proton magnetic resonance spectroscopy (1H-MRS) is a reliable noninvasive method that can be used to quantitatively assess total hepatic lipid content, or proton density fat fraction (PDFF).In Paper I we compared the conventional semiquantitative histological method (grade 0-3) with SPC and 1H-MRS. We found a strong positive correlation between 1H-MRS and SPC, whereas the correlations between 1H-MRS or SPC and histopathological grading were substantially weaker. Using the widely used cut-off value of PDFF ≥5%, all participants were found to have steatosis (specificity 100%, sensitivity 53%). Reducing the cut-off value to 3% maintained 100% specificity while increasing sensitivity to 79%.In Paper IV we evaluated quantitative steatosis, by SPC, in 106 biopsy-proven NAFLD patients during a 20-year follow-up. SPC was independently associated with an increased risk of all-cause mortality and development of T2DM. Moreover, in the 59 patients with sequential biopsies (approximately 10 years apart), a reduction of quantitative hepatic steatosis decreased the all-time risk of developing T2DM.NASH is commonly seen as a histological feature portending a worse prognosis in NAFLD. Interestingly, no dual biopsy study has ever shown that NASH predicts fibrosis progression. Yet, NASH is seen as a surrogate marker in pharmaceutical trials – were resolution in NASH is equivalent to future resolution of fibrosis.In Paper II we conducted a long-term follow-up study (20 years) in a large cohort of biopsy-proven NAFLD patients (n=646), in a collaboration with Karolinska Institute. We could not ascertain that NASH had any effect on all-cause, or disease-specific mortality. However, higher stages of fibrosis predicted all-cause and disease specific mortality. In Paper III, we present 129 biopsy-proven NAFLD patients, in which we had prospective, longitudinal data. They were included between 1988 and 1993. All patients alive, were re-invited 2003-2005 and 2013-2015. Dual biopsies were present in 68 patients, and three consecutive biopsies were available in 33 patients. Results showed that NAFLD is a highly heterogeneous disease, with 9.3% developing end-stage liver disease and 16% progressing to advanced stages of fibrosis without any clinically significant baseline data predicting disease progression. In summary, when using 1H-MRS as a diagnostic method for NAFLD, the diagnostic cut-off should be reduced from 5% to 3%. Furthermore, quantitative amount of hepatic steatosis could be used to stratify patients with NAFLD related to future risk of developing T2DM. Moreover, we have shown that NASH does not predict future all-cause or disease-specific mortality nor end-stage liver disease, therefore a different surrogate marker should be used in clinical trials when assessing NAFLD improvement, so to not imbue false reliance in new therapies. Lastly, we have shown that NAFLD has a more dismal prognosis than previously reported, and that it is unexpectedly difficult to predict fibrosis progression in individual NAFLD patients, emphasizing the need for robust non-invasive biomarkers suitable to monitor large number of patients.
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