Abstract
BackgroundWe assessed and compared image quality obtained with clinical 18F-FDG whole-body oncologic PET protocols used in three different, state-of-the-art digital PET/CT and two conventional PMT-based PET/CT devices.Our goal was to evaluate an improved trade-off between administered activity (patient dose exposure/signal-to-noise ratio) and acquisition time (patient comfort) while preserving diagnostic information achievable with the recently introduced digital detector technology compared to previous analogue PET technology.MethodsWe performed list-mode (LM) PET acquisitions using a NEMA/IEC NU2 phantom, with activity concentrations of 5 kBq/mL and 25 kBq/mL for the background (9.5 L) and sphere inserts, respectively. For each device, reconstructions were obtained varying the image statistics (10, 30, 60, 90, 120, 180, and 300 s from LM data) and the number of iterations (range 1 to 10) in addition to the employed local clinical protocol setup. We measured for each reconstructed dataset: the quantitative cross-calibration, the image noise on the uniform background assessed by the coefficient of variation (COV), and the recovery coefficients (RCs) evaluated in the hot spheres. Additionally, we compared the characteristic time-activity-product (TAP) that is the product of scan time per bed position × mass-activity administered (in min·MBq/kg) across datasets.ResultsGood system cross-calibration was obtained for all tested datasets with < 6% deviation from the expected value was observed. For all clinical protocol settings, image noise was compatible with clinical interpretation (COV < 15%). Digital PET showed an improved background signal-to-noise ratio as compared to conventional PMT-based PET. RCs were comparable between digital and PMT-based PET datasets. Compared to PMT-based PET, digital systems provided comparable image quality with lower TAP (from ~ 40% less and up to 70% less).ConclusionsThis study compared the achievable clinical image quality in three state-of-the-art digital PET/CT devices (from different vendors) as well as in two conventional PMT-based PET. Reported results show that a comparable image quality is achievable with a TAP reduction of ~ 40% in digital PET. This could lead to a significant reduction of the administered mass-activity and/or scan time with direct benefits in terms of dose exposure and patient comfort.
Highlights
We assessed and compared image quality obtained with clinical 18F-FDG whole-body oncologic Positron emission tomography (PET) protocols used in three different, state-of-the-art digital PET/ computed tomography (CT) and two conventional Photo multiplier tube (PMT)-based PET/CT devices
The coefficient of variation (COV) used for image noise assessment was defined by the ratio between the standard deviation (SDbg) over all the voxels contained in the four cubic background volume of interest (VOI) and Ac;bg : C
We considered a COV ≤ 15% as an acceptable noise level for clinical image interpretation as suggested in the Research Life (EARL) procedure [24]; even if this value is somehow arbitrary, it has already been used as a reference value in previously published works [14, 25, 26], which enables a term of comparison for 18F-FDG PET image quality assessments
Summary
We assessed and compared image quality obtained with clinical 18F-FDG whole-body oncologic PET protocols used in three different, state-of-the-art digital PET/ CT and two conventional PMT-based PET/CT devices. The PET-to-local dose calibrator cross-calibration (BGcal) was tested by calculating the ratio between the measured ðAc;bgÞand expected average activity concentration (Ac,bg) evaluated in the homogeneous phantom background: BGcal 1⁄4 A c;bg Ac;bg. We considered a COV ≤ 15% (background SNR ≥ 6.7) as an acceptable noise level for clinical image interpretation as suggested in the EARL procedure [24]; even if this value is somehow arbitrary, it has already been used as a reference value in previously published works [14, 25, 26], which enables a term of comparison for 18F-FDG PET image quality assessments. We reported and compared TAP obtained with clinical setup (TAPclinic) and TAP obtained for a matched image noise level by considering a COV = 15% (TAPCOV-15).
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