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Session: Poster session II
Session starts: Thursday 24 January, 16:00

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Marinette van der Graaf (Depts of Radiology and Paediatrics, Radboud University Nijmegen Medical Centre)
Geert Wanten (Dept of Gastroenterology and Hepatology, Radboud University Nijmegen Medical Centre)

Abstract:
INTRODUCTION: Patients with severe chronic intestinal failure depend on parenteral nutrition, often administered at home as home parenteral nutrition (HPN) [1]. These patients are at risk for developing steatosis, and their hepatic iron and manganese content may increase. The aim of this study was to non-invasively determine hepatic lipid content by MRS in patients receiving HPN, taking into account the possibility of altered relaxation behavior as result of increased hepatic manganese or iron content. SUBJECTS AND METHODS: 13 patients (5M/8F) with a mean age of 46 yrs (range 20-64 yrs), who have been on HPN for 8.2 yrs (range 2-36 yrs). MRS was performed on a clinical 3T MR system (Siemens Magnetom Tim Trio). Proton MR spectra were acquired from a volume of 30x30x30mm3 positioned in the center of a liver lobe avoiding large vessel structures using STEAM without water suppression (TR=3s). Six averages were obtained during 15-sec breath holding for different echo times (TE=20,30,40,50msec; each TE was measured twice). Post-processing consisted of time-domain fitting of the water signal at 4.7 ppm and the methylene lipid signal at 1.3 ppm using AMARES [2]. To correct for T2 relaxation the ratio (lipid intensity (L)/water intensity (W)) was plotted as function of echo time and an exponential function {L/W=(L/W)0•exp(TE*K) with K=(1/T2W-1/T2L)}was fitted to the data to obtain the value for TE=0 msec. From this ratio the hepatic lipid content was calculated by the formula (100x(L/W)0)/(1+(L/W)0). RESULTS: Five patients showed an increased hepatic lipid content (>5%) with an average value of 12.8±3.5% (mean±SD), while the other eight had normal liver fat concentration (1.1±0.6%). K-values were obtained in the range between 0.0148 and 0.0330 msec-1 (0.0216±0.0056 msec-1). The lowest value agrees very well with a reference K-value of 0.0147 msec-1 calculated from literature values for T2W and T2L of 34 and 68 msec, respectively [3]. The other patients showed higher K-values, caused by increased T2 relaxation behavior probably due to elevated hepatic iron or manganese content. CONCLUSION: Our results show that hepatic lipid content of HPN patients can be non-invasively determined by MRS. However, for these patients possible increased T2-relaxation behavior has to be taken into account to obtain reliable values. REFERENCES: [1] Wanten GJ and Calder PC, 2007, Am J Clin Nutr. 85:1171-1184; [2] http://sermn02.uab.es/mrui/; [3] de Bazelaire CM, et al., 2004, Radiology 230:652–659.