Physiological determinants of quantification in longitudinal molecular imaging of small animals

Datum: 14 april 2016

Locatie: UAntwerp, Campus Drie Eiken, Building Q, Promotiezaal - Universiteitsplein 1 - 2610 WILRIJK

Tijdstip: 18 uur

Promovendus: Steven Deleye

Promotor: Prof S. Staelens & Prof J. Verhaeghe

Korte beschrijving: PhD defence Steven Deleye - Faculty of Medicine and Health Sciences



Abstract

Molecular imaging of small animals allows us to visualize biological processes over time without the need to sacrifice the animals. In this thesis the performance of µSPECT (Single Photon Emission Computed Tomography) scanners was evaluated and the influence of physiological variables was studied on the 18F-FDG (=radioactive labeled glucose) uptake/quantification in µPET (Positron Emission Tomography) imaging of small animals.

Three commercial available scanners were compared: the U-SPECT-II, the NanoSPECT and the X-SPECT. The different performance measures were spatial resolution, image uniformity, sensitivity and contrast recovery, the latter measured with a new mouse phantom.

The different physiological factors that have an influence on 18F-FDG brain uptake were glycemic variables, the body weight and the peripheral tracer distribution. The glycemic variables include the influence of the fasting duration, the inter-scan duration and repetitive scanning. We found a higher uptake after 12 hours fasting. A short inter-scan duration (<br>To investigate the significant increased brain uptake at a later timepoint when body weight was significantly increased, the metabolic glucose rate MRglc and the 18F-FDG uptake were measured in two groups of rats with a low and high body mass respectively. We could confirm that for large weight differences the 18F-FDG uptake did not reflect the FDG-influx rate Ki (or MRglc). A correction method was proposed to correlate the uptake correctly with the Ki and the MRglc.

In a mouse model of Alzheimer's disease the expected hypometabolism could only be obtained when the uptake was corrected for glucose. Moreover, we observed that the cerebellum could not be used as a reference region as the 18F-FDG uptake in the cerebellum was also reduced.

Finally, we investigated the influence of the peripheral tracer distribution of 18F-FDG in the bladder on the 18F-FDG quantification of the colon. Flushing the bladder before scanning improved correlation between the PET measure and the colonoscopy and histology readings.