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Assessing the Impact of Post-Injection Acquisition Time in [F-18]-NaF PET/CT

D Huff

D Huff1*, T Perk1 , C Lin1 , G Liu1 , R Jeraj1,2 , (1) University of Wisconsin-Madison, Madison, WI, (2) University of Ljubljana, Ljubljana, Slovenia


WE-F-201-5 (Wednesday, August 2, 2017) 1:45 PM - 3:45 PM Room: 201

Purpose: Current standards recommend imaging with [F-18]-NaF PET 45-60 minutes post-injection, although tracer kinetics suggest that scan postponement may lead to increased image quality. This study aims to determine whether delaying acquisition of NaF PET scans impacts the images’ quantitative power to diagnose disease and assess change during treatment.

Methods: 16 prostate cancer patients with bone metastases received NaF PET/CT scans for analysis. Lesions bigger than 1.5cc were segmented with a location-specific thresholding technique and tracked with articulated registration. Patients with adequate healthy background bone (9) were eligible for diagnostic ability analysis, performed on same-day scans acquired 60(early) and 120(delayed) minutes post-injection. Diagnostic ability was assessed with tumor-to-background ratio (TBR=SUVmax,lesion/ SUVmean,bkgd) and contrast-to-noise ratio (CNR=(SUVmax,lesion-SUVmean,bkgd)/σmean,bkgd). Patients with complete scan sets (11) were eligible for repeatability analysis on both early and delayed test-retest scans taken 2-5 days apart. Repeatability was assessed using repeatability coefficients (RC) of lesion SUV metrics.

Results: 7/9 patients demonstrated an increased median TBR on delayed scans (median +17%, range -5%: +62%). CNR decreased in 7/9 patients from early to delayed scans, with a median change of -21% (range -56%: +36%). Median TBR was significantly higher on delayed scans (Wilcoxon signed-rank test, p = 0.02), while median CNR was not significantly lower on delayed scans (p = 0.07). Early repeatability scans tracked 351 lesions between scans, while delayed scans tracked 353. SUVmax,lesion values derived from early and delayed scans had RC values of 27.7 and 27.8 respectively. SUVmean,lesion RCs for early and delayed scans were 19.3 and 17.7 respectively. SUVtotal,lesion RCs for early and delayed scans were 53.0 and 53.6 respectively.

Conclusion: Delaying post-injection acquisition of NaF PET images results in images with higher tumor-to-background uptake ratios without significantly lowering contrast-to-noise ratios. The repeatability of NaF PET is not impacted by a delay in post-injection acquisition time.

Funding Support, Disclosures, and Conflict of Interest: This project was funded by the PCF Challenge Grant.

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