QUANTITATIVE MAGNETIC-RESONANCE METHODS FOR IN-VIVO INVESTIGATION OF THE HUMAN LIVER AND SPLEEN - TECHNICAL ASPECTS AND PRELIMINARY CLINICAL-RESULTS

This project was initiated with the introduction of magnetic resonance (MR) in Denmark in order to evaluate the possibilities of this techni que as a diagnostic aid in non-focal liver and splenic diseases. The s ignal intensities in the MR image are sensitive to the longitudinal re laxation (T-1), the transverse relaxation (T-2), flow and chemical shi ft. All these parameters may be quantified by developing specific puls e sequences sensitive to the parameter in question. Previous studies h ad indicated that relaxation time measurements might be of value in th e diagnosis of liver cirrhosis and haemochromatosis. Measuring relaxat ion times in these 2 groups patients posed different challenges. In pa tients with liver cirrhosis a method had to be developed for simultane ous T-1 and T-2 relaxation time measurements, which was robust to the respiratory motion of the liver. A combination of multi-echo pulse seq uences with different repetition times was chosen, because motion effe cts were partly refocused. Multi acquisition was used to improve the s ignal-to-noise ratio in the heavily saturated experiments with short r epetition times, to further reduce the sensitivity to motion. To test the quality of this pulse sequence, phantom experiments were performed , and sensitivity to motion was tested by measuring with and without r espiratory synchronization. Respiratory synchronization gave a marked improvement in focal liver diseases, whereas no difference was found i n non-focal diseases. Standard imaging sequences with a minimum echo t ime of 30 ms could not be used to measure the short T-2 relaxation tim es found in patients with increased liver iron. A volume-selective mul tiecho spectroscopic pulse sequence was developed with a minimum echo time of 4 ms. Biexponential signal decay could be shown in patients wi th increased liver iron by using this sequence. Patients with liver ci rrhosis, as a group, had increased T-1 relaxation times compared to no rmal volunteers, but an overlap in T-1 values was found. No correlatio n between the degree of fibrosis and the T-1 relaxation time was found . Liver iron concentration could be quantified either by using the fas t component of the T-2 signal decay or by using the decreased signal i n spin-echo and gradient echo images. Patients with leukemias and myel oproliferative disorders had prolonged T-1 relaxation times in the spl een, but a considerable overlap was found between this group and a gro up of patients with benign hyperplasia and patients with splenomegaly secondary to portal hypertension. Volume-selective proton spectroscopy was developed and used to quantify the liver fat concentration. The a ccuracy of the method was about 3 g/100 g. With the implementation of a second generation scanner system it became possible to develop a pul se sequence, using the phase information in the MR signal, to measure portal vein flow during breath-holding. This method made it possible t o estimate the portal vein flow during fasting, and the flow increase after eating. Quantitative MR methods may contribute to the diagnosis of non-focal liver diseases by estimation of liver fat and liver iron and by assessment of portal vein blood how. Increased T-1 relaxation t ime is a sign of a disease process in the liver rather than specific f or any liver disease.