RESUMEN
We investigated PET image quantification when using a uniform attenuation coefficient (µ) for attenuation correction (AC) of anthropomorphic density phantoms derived from high-resolution breast CT scans. A breast PET system was modeled with perfect data corrections except for AC. Using uniform µ for AC resulted in quantitative errors roughly proportional to the difference between µ used in AC (µ AC) and local µ, yielding approximately ± 5% bias, corresponding to the variation of µ for 511 keV photons in breast tissue. Global bias was lowest when uniform µ AC was equal to the phantom mean µ (µ mean). Local bias in 10-mm spheres increased as the sphere µ deviated from µ mean, but remained only 2-3% when the µ sphere was 6.5% higher than µ mean. Bias varied linearly with and was roughly proportional to local µ mismatch. Minimizing local bias, e.g., in a small sphere, required the use of a uniform µ value between the local µ and the µ mean. Thus, biases from using uniform-µ AC are low when local µ sphere is close to µ mean. As the µ sphere increasingly differs from the phantom µ mean, bias increases, and the optimal uniform µ is less predictable, having a value between µ sphere and the phantom µ mean.
RESUMEN
The goal for positron emission tomography (PET)/X is measuring changes in radiotracer uptake for early assessment of response to breast cancer therapy. Upper bounds for detecting such changes were investigated using simulation and two image reconstruction algorithms customized to the PET/X rectangular geometry. Analytical reconstruction was used to study spatial resolution, comparing results with the distance of the closest approach (DCA) resolution surrogate that is independent of the reconstruction method. An iterative reconstruction algorithm was used to characterize contrast recovery in small targets. Resolution averaged [Formula: see text] full width at half maximum when using depth-of-interaction (DOI) information. Without DOI, resolution ranged from [Formula: see text] to [Formula: see text] for scanner crystal thickness between 5 and 15 mm. The DCA resolution surrogate was highly correlated to image-based FWHM. Receiver-operating characteristic analysis showed specificity and sensitivity over 95% for detecting contrast change from 5:1 to 4:1 (area under curve [Formula: see text]). For PET/X parameters modeled here, the ability to measure contrast changes benefited from higher photon absorption efficiency of thicker crystals while being largely unaffected by degraded resolution obtained with thicker crystals; DOI provided marginal improvements. These results assumed perfect data corrections and other idealizations, and thus represent an upper bound for detecting changes in small lesion radiotracer uptake of clinical interest using the PET/X system.
