Improved detectability of malignant lesions in SPECT scintimammography using effective multi-dimensional smoothing

Scintimammography, a nuclear-medicine imaging technique that relies on the preferential uptake of Tc-99m-sestamibi and other radionuclides in breast malignancies, has the potential to provide differentiation of mammographically suspicious lesions as well as outright detection of malignancies in women with radiographically dense breasts. In this work the authors use the ideal-observer framework to quantify the detectability of a 1-cm lesion using 3 different imaging geometries: the planar technique that is the current clinical standard, conventional single-photon emission computed tomography (SPECT), in which the scintillation cameras rotate around the entire torso, and dedicated breast SPECT, in which the cameras rotate around the breast alone. The authors also introduce an adaptive smoothing technique for the processing of planar images and of sinograms prior to reconstruction that exploits Fourier transforms to achieve effective multidimensional smoothing at a reasonable computational cost. For the detection of a 1-cm lesion with a clinically typical 6:1 tumor-background ratio, the authors find ideal-observer signal-to-noise ratios (SNR) of 6.5 for planar imaging without processing and 6.7 after applying this adaptive smoothing, 3.5 for conventional SPECT rising to 6.1 with adaptive smoothing, and finally 9.6 for the dedicated geometry rising to 11.4 with adaptive smoothing. The results suggest that the dedicated breast SPECT geometry is the most effective of the three, and that the adaptive, two-dimensional (2D) smoothing enhances idealized lesion detectability.