Construction and characterization of an arterial input function measurement system for dynamic PET

Dynamic positron emission tomography is an under utilized clinical technique. It requires knowledge of the time-course activity concentration in the patient's arterial blood, called arterial input function (AIF), normally acquired via arterial blood sampling. Alternative methods to acquire the AIF do exist, but each has its own limitations. This study presents a non-invasive radiation detector, called Radian-PET, designed to measure the AIF non-invasively.

10 cm long scintillating fibers arranged in two bands of 32 fibers were read out by a 64-channel silicon photomultiplier array. Calibration measurements were performed using ⁶⁸Ge rod sources placed over the sensitive volume of the detector. Inter-channel variability was measured using the scans with the source perpendicular to the fibers. Two decay measurements were performed using ¹⁸F samples with varying activity. Cross-validation measurements were performed by placing a microfluidic blood sampling detector before Radian-PET in a microfluidic circuit. ¹⁸F, ¹¹C and ⁶⁸Ga injections were used to simulate the AIF.

Calibration measurements show that the electronic discriminator threshold, with minimal detectable activity below 100 kBq per mL for a 1-second integration window. The measured ¹⁸F half-lives were 109.75 ± 0.04 min and 110.82 ± 0.73 min and agreed within uncertainties with the literature. Linear regressions from the cross-validation measurements showed good agreement (R²> 0.96) for all scans.

Radian-PET can accurately measure clinically relevant activity concentrations and detect quickly changing activity levels like those used to perform kinetic analysis. Further work is required to increase detector efficiency and reduce sources of noise.