Abstract
Objective: The aim of this study was to investigate lesion detection with very low doses of radiotracer concentration using a PEM Flex Solo II breast PETscanner. Methods: We imaged a phantom with hot radioactive spheres in a warm background of known radiotracer concentration and lesion‐to‐background ratios (LBR) on a PEM Flex Solo IIpositron emission mammographyscanner (Naviscan Inc.). Two detectors with variable separation each 5.6cm X 16cm scan in unison to cover a 24cm × 16cm field. We tested two breast compression thicknesses of 55mm and 85mm. Sphere diameters were 3.9 7.8 16 and 20 mm and LBRs were 4‐to‐1 and 10‐to‐1. We imaged the phantom with between 0.1kBq/mL and 5.0kBq/mL background concentration of 18‐FDG solution. Image acquisition was 10min. Lesion uptake was characterized by lesion‐to‐background metrics used clinically; LBR equals the maximum of a lesion region of interest (ROI) divided by the mean of a background ROI. Overall image uniformity was measured as the coefficient of variation (COV) calculated from 72 ROIs placed throughout the image volume. Contrast‐to‐noise ratio (CNR) was calculated as LBR/COV and was compared for different activity concentrations and true LBRs. Results: Our phantom results show little change in measured LBR over the range of background activity of 0.5 to 5.0 kBq/mL. Image COV increased slowly from 5 kBq/mL to 1 kBq/mL and then increased rapidly below 1 kBq/mL. Resulting CNR decreased little between l‐5kBq/mL then fell to ∼50% of nominal value at ∼0.1–0.3kBq/mL. When true LBR = 4 the 3.9mm sphere was not visible for any tested concentration; the limits for visualizing the 7.8mm sphere were ∼0.2 and 0.4 kBq/mL for compression = 5.8cm and 8.5cm respectively. These tests require receiver operator analyses but suggest that PEMimaging may use significantly lower injected doses than routine clinical whole‐body PET.
Published Version
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