TITLE:

QUANTITATIVE ROTATING MULTI-SEGMENT SLANT-HOLE SPECT MAMMOGRAPHY WITH ATTENUATION AND COLLIMATOR-DETECTOR RESPONSE COMPENSATION

 

AUTHORS:

Jingyan Xu, Ph.D. 1, Benjamin M.W. Tsui, Ph.D 1, Chi Liu, B.S. 1 and Eric C. Frey, Ph.D. 1 ; 1 Radiology, Johns Hopkins University, Baltimore, MD, United States.

 

PURPOSE:

The objective of this work was to improve the quality and quantitative accuracy of rotating multi-segment slant-hole (RMSSH) SPECT reconstruction by compensating for both attenuation and collimator-detector response (CDR).

 

METHODS AND MATERIALS:

Attenuation is modeled using an attenuation map obtained from a transmission CT scan. The CDR of a slant-hole collimator is asymmetric and has a different orientation relative to the patient for each segment and at each collimator rotation stop. All required CDRs were pre-calculated using an analytical formulation.

The implementation of the projector and back-projector is based on a rotation-transformation of the image reconstruction matrix that makes subsequent incorporation of attenuation correction (AC) similar to a parallel-hole SPECT system. Attenuated photon activities from the same distance to the collimator are convolved with the asymmetric CDR corresponding to that distance. The attenuated and convolved voxel values were then summed along the projection rays to obtain the estimated projections. Due to the asymmetry of the CDR, this process was performed independently for each collimator segment. The back-projector was implemented similarly, but the steps were performed in the opposite order. This projector/back-projector pair was incorporated in a 3D iterative RMSSH SPECT image reconstruction algorithm for attenuation and CDR compensation.

We performed simulations using both cold spheres and a realistic 3D female NCAT phantom to validate and demonstrate the improvement obtained with the new reconstruction method. A modified SIMIND Monte Carlo code was used to generate the RMSSH SPECT projection data. The CDR of the slant-hole collimator had a FWHM of 0.95 cm at the center of the field-of-view (FOV). The projection data were reconstructed using the new method with and without attenuation and CDR compensation.

 

RESULTS:

Our results show that in RMSSH SPECT, (1) while AC by itself improves quantitative accuracy, it may reduce lesion contrast in breast imaging, and (2) simultaneous AC and CDR compensation provides better quantitative accuracy and improved image quality in terms of resolution enhancement with minimum noise increase. Observer studies are on-going to further evaluate the clinical applicability of RMSSH SPECT reconstruction with compensation.

 

CONCLUSIONS:

 

We conclude that improved image quality and quantitative accuracy can be obtained with attenuation and CDR compensation in RMSSH SPECT.

 

FUNDING SOURCES:

R01---EB0001983