University of Twente Student Theses


Diagnosis of mesenteric ischemia using magnetic resonance spectroscopy Refocused double-quantum editing for lactate detection in the portal vein

Cnossen, S. (2019) Diagnosis of mesenteric ischemia using magnetic resonance spectroscopy Refocused double-quantum editing for lactate detection in the portal vein.

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Abstract:Objective: In acute mesenteric ischemia (AMI) the blood flow to the intestine is decreased below the level necessary for the continuous maintenance of aerobic metabolism. Chronic mesenteric ischemia (CMI) occurs when the blood flow to the gastrointestinal (GI) tract gradually decreases to below the level required for all motor, secretory and absorptive activities to function. Nowadays the diagnosis of AMI and CMI is a combination of recognition of the early aspecific clinical symptoms and appropriate assessment of the mesenteric vascular anatomy. To improve the timely diagnosis of AMI and CMI there clearly is a need for a non-invasive, fast and easy applicable test assessing the adequacy of the bowel wall perfusion. The portal vein is the drain of the bowel. Increased lactate concentration indicates anaerobic metabolism. The aim of the present study is to develop a proton magnetic resonance spectroscopy (1H-MRS) technique which can be used for the measurement of physiological and pathological lactate concentrations in the portal vein for early diagnosis of acute and chronic mesenteric ischemia. Methods: A 7 Tesla MR system was used to explore the enhanced spectral resolution and increased signal to noise ratio of this field strength for the acquisition of lactate in the portal vein. Spin system simulations were performed to find the best sequence parameters for the best lactate signal detection. Experiments were performed at 7T, where three different 1H-MRS techniques (STEAM, PRESS and DQF) were tested on lactate phantoms (static and with flow up to 924 ml/min) of different concentrations (2.5, 20 and 50 mM lactate). The flow phantom was embedded in either water or oil to test the lipid suppression of each technique. In vivo experiments on the portal vein of two volunteers and the brain of another volunteer were also performed. Additionally, a portal vein simulating MATLAB script was created to calculate the theoretical signal loss caused by the blood flow during the refocused DQF sequence. Results:Lactate was detected in phantoms containing 2.5, 20 and 50 mM lactate solutions with STEAM, PRESS and the refocused DQF sequence. However, when surrounded by lipids, STEAM and PRESS showed overlapping signals of lactate and lipids on the spectrum. Only the DQF sequence was able to measure lactate in the presence of lipids. However, part of the signal was lost for all sequences when flow was present. Lactate was detected in the presence of flow (up to 924 ml/min). The in vivo scans did not show a distinguishable lactate peak in the spectrum as it clearly overlapped with the lipids coming from elsewhere and the DQF sequence showed extreme sensitivity to motion due to the strong gradients used. According to the simulations, the signal loss in the lowest portal vein flow was found to be approximately 33% and in the fastest portal vein flow approximately 55%. Conclusion: The refocused DQF sequence can be used to detect lactate in stagnant phantoms with physiological lactate concentrations in the presence of lipids. However, this sequence is extremely sensitive to motion (i.e. flow, cardiac and breathing motion). The incorporation of velocity sensitive gradients to the refocused DQF sequence is recommended, in addition to flow triggering for an accurate detection of the lactate signal.
Item Type:Essay (Master)
Faculty:TNW: Science and Technology
Subject:44 medicine
Programme:Technical Medicine MSc (60033)
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