Design and Evaluation of a Variable-Angle Slant-Hole Collimator for 3D Molecular Imaging of the Breast

Date(s) - 06/30/2014
10:00 am

Olga Gopan, PhD Candidate

Purpose: The purpose of this work is to develop an improved method for 3D molecular imaging of the breast using limited angle SPECT.

Methods: The proposed method uses a variable-angle slant-hole (VASH) collimator.  Rather than rotate the camera around the breast, the VASH collimator allows limited angle, tomographic acquisition while the detector remains stationary and flush against the compression paddle. 

This design minimizes object-to-detector distance for high spatial resolution.  Theoretical analysis is presented of VASH spatial resolution and sensitivity, including depth-of-interaction (DOI) effects and magnification.  The theory is compared with Monte Carlo simulation results for a point source, a breast phantom including a compression paddle and a realistically segmented breast phantom with an inhomogeneous background uptake. A channelized Hotelling observer is applied to the evaluation of VASH using a lesion detection task, and the standard area-under-the-curve (AUC) metric is obtained.  Experimental results are presented using a proof-of-concept VASH collimator constructed of brass and used to image a low energy, Am-241 source.

Results: The theoretical model of the VASH system showed good agreement with Monte Carlo simulations based on spatial resolution, including DOI effects, and sensitivity.  The DOI effect resulted in roughly a 2 mm loss in spatial resolution only in depth dimension; in the other two dimensions the spatial resolution was not affected by DOI. In terms of contrast-to-noise ratio (CNR) and AUC, VASH outperformed a parallel hole SPECT approach. In terms of CNR, VASH outperformed a planar approach when the background inhomogeneity level was greater than 20% and in discerning two overlapping lesions. The difference in VASH and planar AUCs was not statistically significant. The reconstructed images from the proof-of-concept VASH collimator demonstrated the expected image blur in the depth dimension due to limited projection angle effects.

Conclusions: The proposed method for breast imaging using limited angle SPECT and VASH collimator demonstrated the potential for superior spatial resolution/sensitivity.  In addition, the system design has advantages of simple detector motion, ability to image close to the chest wall and conducive to on-board biopsy and multi-modal imaging with mammography.