External delay and dispersion correction of automatically sampled arterial blood with dual flow rates.

Objective: Arterial sampling for PET imaging often involves continuously measuring the radiotracer activity concentration in blood using an automatic blood sampling system (ABSS). We proposed and validated an external delay and dispersion correction procedure needed when a change in flow rate occurs during data acquisition. We also measured the external dispersion constant of [11C]CURB, [18F]FDG, [18F]FEPPA, and [18F]SynVesT-1.

Approach: External delay and dispersion constants were measured for the flow rates of 350, 300, 180, and 150 mL/h, using 1-minute-long rectangular inputs (n = 10; 18F-fluoride in saline). Resulting constants were used to validate the external delay and dispersion corrections (n = 6; 18F-fluoride in saline; flow rate change: 350 to 150 mL/h and 300 to 180 mL/h); constants were modelled to transition linearly between flow rates. Corrected curves were assessed using the percent area-under-the-curve (AUC) ratio and a modified model selection criterion (MSC). External delay and dispersion constants were measured for various radiotracers using a blood analog (i.e., similar viscoelastic properties).

Main Results: ABSS outputs were successfully corrected for external delay and dispersion using our proposed method accounting for a change in flow rate. AUC ratio reduced from ~10% for the uncorrected 350-150 mL/h output (~6% for the 300-180 mL/h) to < 1% after correction when compared to true input (511 keV energy window); approx. 5-fold increase in MSC. Assuming an internal dispersion constant of 5 seconds, the dispersion constant (internal + external) for [11C]CURB, [18F]FDG, [18F]FEPPA, and [18F]SynVesT-1 was 13, 9, 16, and 10 s, respectively.

Significance: This study presented an external delay and dispersion correction procedure needed when a change in flow rate occurs during ABSS data acquisition. Additionally, this is the first study to measure the external delay and dispersion constants using a blood analog solution, a suitable alternative to blood when estimating external dispersion.