Abstract
PurposeWhile acquisition of images in [68 Ga]Ga-PSMA-11 following longer uptake times can improve lesion uptake and contrast, resultant imaging quality and count statistics are limited by the isotope’s half-life (68 min). Here, we present a series of cases demonstrating that when performed using a long axial field-of-view (LAFOV) PET/CT system, late imaging is feasible and can even provide improved image quality compared to regular acquisitions.MethodsIn this retrospective case series, we report our initial experiences with 10 patients who underwent standard imaging at 1 h p.i. following administration of 192 ± 36 MBq [68 Ga]Ga-PSMA-11 with additional late imaging performed at 4 h p.i. Images were acquired in a single bed position for 6 min at 1 h p.i. and 16 min p.i. at 4 h p.i. using a LAFOV scanner (106 cm axial FOV). Two experienced nuclear medicine physicians reviewed all scans in consensus and evaluated overall image quality (5-point Likert scale), lesion uptake in terms of standardised uptake values (SUV), tumour to background ratio (TBR) and target-lesion signal to background noise (SNR).ResultsSubjective image quality as rated on a 5-point Likert scale was only modestly lower for late acquisitions (4.2/5 at 4 h p.i.; 5/5 1 h p.i.), TBR was significantly improved (4 h: 3.41 vs 1 h: 1.93, p < 0.001) and SNR was improved with borderline significance (4 h: 33.02 vs 1 h: 24.80, p = 0.062) at later imaging. Images were obtained with total acquisition times comparable to routine examinations on standard axial FOV scanners.ConclusionLate acquisition in tandem with a LAFOV PET/CT resulted in improvements in TBR and SNR and was associated with only modest impairment in subjective visual imaging quality. These data show that later acquisition times for [68 Ga]Ga-PSMA-11 may be preferable when performed on LAFOV systems.
Highlights
Introduced long axial field-of-view (LAFOV) PET/CT scanners offer significant improvements over previous standard axial FOV (SAFOV) systems [1, 2], with substantially improved sensitivity and count densities [3]
Pioneering publications with LAFOV scanners report increased dynamic range for LAFOV systems, meaning that radiopharmaceuticals can be followed usefully over more half-lives as a result of the scanner’s higher sensitivity [1]. The aim of this short communication is to report our initial experiences with a LAFOV scanner in late imaging with [68 Ga]Ga-PSMA-11, to demonstrate that later acquisition of imaging is feasible and that even improved image quality can be obtained at late imaging when compared to regular acquisitions
signal to background noise (SNR) was improved at late acquisition (4 h p.i. 33.02 vs. 1 h p.i. 24.80, p = 0.062; median 15.1 vs 14.2), with borderline significance owing to the limited data in this case series
Summary
Introduced long axial field-of-view (LAFOV) PET/CT scanners offer significant improvements over previous standard axial FOV (SAFOV) systems [1, 2], with substantially improved sensitivity and count densities [3]. Acquisition of images at later time points is associated with improved tumour to background (TBR) and lesion detectability [11–15] and is mentioned in current guidelines [9] Despite these benefits to later acquisition, limiting factors are encountered: e.g. the short half-life of the radiopharmaceutical (68 min) results in decay at later imaging, and additional scanning can be difficult to integrate into a busy clinical service. Pioneering publications with LAFOV scanners report increased dynamic range for LAFOV systems, meaning that radiopharmaceuticals can be followed usefully over more half-lives as a result of the scanner’s higher sensitivity [1] The aim of this short communication is to report our initial experiences with a LAFOV scanner in late imaging with [68 Ga]Ga-PSMA-11, to demonstrate that later acquisition of imaging is feasible and that even improved image quality can be obtained at late imaging when compared to regular acquisitions
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