Molecular breast imaging using limited angle SPECT

Objectives Our objective is to develop a gamma camera for molecular breast imaging to perform high resolution, limited angle SPECT. The goal is a camera that can be readily integrated within a digital breast tomosynthesis system to facilitate correlative imaging.

Methods The novel feature of the proposed gamma camera is a variable-angle, slant-hole (VASH) collimator, which was originally proposed in the early 1980’s for limited angle cardiac SPECT. This collimator is well suited for limited angle SPECT of the breast with mild compression. The collimator holes change slant angle as the compact camera translates laterally along the surface of the compression paddle. This keeps the camera close to the object for superior spatial resolution. Theoretical analysis and Monte Carlo simulations were performed for a point source and an isolated breast phantom to evaluate spatial resolution, sensitivity and reconstructed image quality. Results were compared to an orbiting camera with parallel hole (PAR) collimator. The VASH collimator had 16 mm hole length, 1 mm hole diameter and +/- 30 deg. limited angle SPECT data were acquired. The SPECT data were reconstructed using an iterative MLEM algorithm.

Results The VASH camera demonstrated a substantial advantage in theoretical spatial resolution/sensitivity trade-off; for example, at a 20 deg. projection angle, VASH had approximately two times greater sensitivity than PAR with equal spatial resolution. The measured SPECT spatial resolution from simulated data was approx. 4 mm in-plane but degraded to approx. 6 mm in the Z direction due to the limited angle data. Sensitivity was 61 cps/μCi at 0 deg. slant and decreased to 37 cps/μCi at 30 deg. The SPECT images of the breast phantom confirmed the high spatial resolution with this approach.

Conclusions We conclude that the proposed limited angle SPECT approach using a VASH collimator has the potential to improve spatial resolution/sensitivity and 3D reconstructed image quality for molecular breast imaging