Effect of scan-time shortening on the 11 C-PHNO binding potential to dopamine D 3 receptor in humans and test–retest reliability

Objective 11 C-PHNO is a PET radioligand most specific to dopamine D 3 receptor (D 3 R). The long scan duration of 120 min used in quantification of 11 C-PHNO binding to D 3 R in previous studies is challenging to subjects. The main objective of this study was to investigate the effects of shorter scan times on the binding of 11 C-PHNO to D 3 R and test–retest reliability using the latest digital whole-body PET system. Methods Two 120-min 11 C-PHNO brain scans were performed in 7 healthy subjects using a digital whole-body PET/CT. The binding potential relative to non-displaceable tracer in the tissue (BP ND ) of D 3 R-rich regions: the pallidum, ventral striatum (VST), substantia nigra (SN) and hypothalamus, were quantified using the simplified reference tissue model. The bias, correlation, and test–retest reliability of BP ND , which includes the test–retest variability (TRV) and intraclass correlation coefficient (ICC), were evaluated and compared between scans of shorter durations (40–110 min post-injection) and the original 120-min scan acquisitions. Results Progressively, shorter scan durations were associated with underestimation of BP ND , slightly decreased correlation with 120-min derived BP ND , and decrease in test–retest reliability. The BP ND values of the pallidum, VST and SN from the shortened 90-min scans showed excellent correlation with those derived from the 120-min scans (determination coefficients > 0.98), and the bias within 5%. The test–retest reliability of BP ND in these regions derived from 90-min scan (TRV of 3% in the VST and pallidum, 7% in the SN and the ICC exceeded 0.88) was comparable to those obtained in previous 120-min studies using brain-dedicated PET scanners. In the hypothalamus, the BP ND values obtained from scan-time less than 110 min showed bias larger than 5% and the TRV more than 9%. Conclusion The scan-time shortening causes bias and decreasing test–retest reliability of 11 C-PHNO BP ND . However, in the whole-body PET system, 90-min scan duration was sufficient for estimating the 11 C-PHNO BP ND in the D 3 R-rich striatum and SN with small bias and at the test–retest reliability comparable to those derived from 120-min scans using the brain-dedicated PET systems.