Evaluation of rotating slant hole SPECT mammography with respect to planar scintimammography using Monte Carlo simulation methods

The purpose of this study is to evaluate mammoSPECT using a rotating 4-segment slant-hole (R4SSH) collimator compared to planar scintimammography (SM). Four pairs of R4SSH and parallel-hole collimators with the same spatial resolutions of 0.7 cm, 0.9 cm, 1.1 cm and 1.3 cm at 16.5 cm, 16.8 cm, 17.0 cm and 17.1 cm respectively, which are the distances to the centers of the common volume-of-view (CVOV) of the R4SSH collimators, were used. Monte Carlo simulated noise-free and noisy planar SM and R4SSH projection images of the left breast were obtained from the 4-D NCAT phantom. The breast was placed within the CVOV of the R4SSH collimator and 14 cm from the LEHR collimator. A 0.78 cm diameter lesion with a lesion/background activity ratio of 9:1 was placed in the lateral, central and medial region of the breast. The R4SSH projection data were reconstructed using a 3D iterative OSEM method. Image quality was evaluated in terms of lesion contrast and FWHM, background noise level and contrast-to-noisy ratio (CNR). The results indicated that, for each collimator pair, the lesion contrast increases and FWHM of lesion decreases in the R4SSH SPECT images while the noise level increases with iteration number. When compared to the planar SM images obtained with equal acquisition time, the R4SSH SPECT images have higher noise level and poorer spatial resolution but significantly higher lesion contrast especially for the medial lesions. Using appropriate iteration number, R4SSH SPECT images can provide higher CNR for medial and even central lesions, but lower CNR for lateral lesions. We conclude that RMSSH SPECT can potentially provide improved image quality as compared to planar SM