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In this study, the quantification of fluid volumes was implemented in a clinical 1.0 Tesla MRI scanner in phantoms, animals, volunteers and patients.
Quantification of fluid volumes is a well known application in NMR. However, these applications were limited to in vitro studies. Theoretically, spectroscopic applications in MRI allow a similar quantification. But they are not applicable in clinical routine due to their long investigation times and limited spatial resolution.
This study was conducted in collaboration with the Department of Diagnostic Radiology and the Department of Internal Medicine of the University Hospital of the Philipps University Marburg.
Phantom studies showed a linear relationship between signal intensity of fast (single-shot), heavily T2-weighted MRI sequences and the fluid volume in the volume of interest. Therefore, it is possible to quantify these fluid volumes. Moreover, the phantom studies demonstrated reproducibility of the measurements and that their results are independent from the chosen slice thickness and pixel size. The influence of presaturation due to preceding measurements can be eliminated by a delay of at least 11 seconds between both measurements.
Both the animal and volunteer studies confirmed the linear relationship between signal intensity and fluid volume. The volunteer studies allowed calibrating the measurements in order to calculate changes in the fluid volume from changes in the signal intensity.
The patient studies divided into three parts:
1. Diagnosis of chronic pancreatitis using MRI in comparison to endoscopic retrograde cholangiopancreaticography.
2. Comparison of the results of MRI and the Secritin-Caerulein tube-test.
3. Diagnosis of functional impairment of pancreas grafts.
Patients results showed that MRI results correlated significantly with the results of the Secritin-Caerulein tube-test. The remaining results could be explained by the different test conditions. The results of the tube test were always higher in comparison to the MRI results. The reason for this was mainly the longer investigation time for tube tests. Moreover, the duodenum was not blocked by a balloon during the MRI investigation. Therefore, fluid could have been transported out of the imaging volume.
Altogether, the patient studies showed that MRI is able to diagnose chronic pancreatitis. Especially the introduction of the MRH score, a combination of secreted fluid volume and duration of secretion, improved accuracy. In the future, MR spectroscopy should be able to improve the accuracy even more.
After Transplantation, MRI is able to demonstrate differences between patients with and without impairment of the exocrine graft function. MRI could also demonstrate differences between various forms of impairment. A patient with chronic graft rejection still produced a small amount of fluid, while both patients with necrotizing pancreatitis did not produce any secretion.