Proceedings of The Physiological Society

Europhysiology 2018 (London, UK) (2018) Proc Physiol Soc 41, PCA070

Poster Communications

Unbiased assessment of input function for positron emission tomography molecular imaging

J. Han1, H. Espedal2, A. Eikeland3, H. Wiig1, O. Tenstad1

1. Department of Biomedicine, University of Bergen, Bergen, Hordaland, Norway. 2. Molecular Imaging Center, University of Bergen, Bergen, Hordalad, Norway. 3. Department of Radiologi (Nuclear medicine/PET-centre), Haukeland University Hospital, Bergen, Hordaland, Norway.

Positron emission tomography (PET) is commonly used for diagnosis and evaluation of treatment efficiency. Two elements are required for dynamic quantitative PET data analysis; The activity of the region of interest (ROI) as a function of time after tracer injection, and the plasma activity as a function of time (PAF). For accurate assessment of PAF, the activity measured in the blood sample collected during the PET scanning is required. However, this is an invasive and time-consuming procedure. In this study, we aimed to develop an unbiased method to determine the PAF using the PET-signal from the abdominal vasculature. We verified our PAF by calculating PET labelled Cytochrome C clearance from kidney (CCyt) both from PET signal and ex vivo samples. Wistar male rats (350-450g, n=8) were anaesthetized with sevoflurane (3% volume and 1l/min oxygen flow). The femoral artery was cannulated for blood sampling and the tail vein for tracer injection. After i.v. injection of a bolus of PET labelled Cytochrome C (5-10 MBq), the rats were scanned dynamically for 10 minutes. During the PET-CT scanning, seven arterial blood samples (20ml) were collected at time 30 seconds, 1, 2, 4, 5, 7, 9 minutes for ex vivo verification. Immediately following the PET scanning, the rats were killed and their kidneys removed. Both blood samples and kidneys were gamma counted. CCyt was calculated as the total tracer activity in one kidney per ml volume or gram divided by the time integrated PAF. In another series, Wistar male rats (n=6) underwent contrast CT before the PET-CT dynamic scanning to measure kidney volume and abdominal vessel diameter. We found a good correlation (r2=0.99) between the mean intensity of the kidney and the ROI-volume calculated by the PET-software auto-segmentation tool using a range of standardized uptake values (SUV). Similarly, there was a good correlation (r2=0.99) between the mean intensity from abdominal blood vessels and their ROI-volumes. We used CT to obtain anatomical dimensions for kidney and abdominal blood vessels to decide an unbiased value for the time integrated plasma activity as well as the kidney activity per unit volume from the correlations described above. Contrast CT gave a kidney volume (mean ± SEM) of 1227± 23.7mm3, and an abdominal vessel diameter of 2.51± 0.06mm that were used in the PET-based clearance calculations. PET-CT assessed CCyt correlated well with CCyt calculated from ex vivo blood and kidney samples (r2=0.90). We here present a new method showing that an unbiased input signal can be used in the analysis of dynamic PET images.

Where applicable, experiments conform with Society ethical requirements