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 D3 receptor (D3 R). The long scan duration of 120 min used in quantification of 11 C-PHNO binding to D3 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 D3 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 (BPND ) of D3 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 BPND , 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 BPND , slightly decreased correlation with 120-min derived BPND , and decrease in test-retest reliability. The BPND 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 BPND 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 BPND 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 BPND . However, in the whole-body PET system, 90-min scan duration was sufficient for estimating the 11 C-PHNO BPND in the D3 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.