Monte Carlo-based scatter correction for the SMARTZOOM collimator

Abstract

Background: Myocardial perfusion imaging is a commonly performed SPECT protocol and hence it would be beneficial if its scan duration could be shortened. For traditional gamma cameras, two developments have separately shown to allow for a shortened scan duration: (i) reconstructing with Monte Carlo-based scatter correction instead of dual-energy window scatter correction and (ii) acquiring projections with the SMARTZOOM collimator instead of a parallel-hole collimator. This study investigates which reduction in scan duration can be achieved when both methods are combined in a single system.

Results: The SMARTZOOM collimator was implemented in a Monte Carlo-based reconstruction package and the implementation was validated through image quality phantom experiments. The potential for scan duration reduction was evaluated with a phantom configuration that is realistic for myocardial perfusion imaging. The original reconstruction quality was achieved in 76 ± 8% of the original scan duration when switching from dual-energy window scatter correction to Monte Carlo-based scatter correction. The original reconstruction quality was achieved in 56 ± 13% of the original scan duration when switching from the parallel-hole to the SMARTZOOM collimator. After combining both methods in a single system, the original reconstruction quality was achieved in 34 ± 7% of the original scan duration.

Conclusions: Monte Carlo-based scatter correction combined with the SMARTZOOM collimator can further decrease the scan duration in myocardial perfusion imaging.

Keywords: Correction; Monte Carlo; Myocardial; Perfusion; Reconstruction; SPECT; Scatter.

Fig. 1

An illustration of the field of view of a conventional parallel-hole collimator and the SMARTZOOM collimator. The highest sensitivity is achieved in the regions with the highest line density

Fig. 2

The anthropomorphic phantom that comprises a cardiac insert with a defect

Fig. 3

Projections of the five ^99mTc point sources obtained with the parallel-hole and the SMARTZOOM collimator

Fig. 4

The reconstructions of the point sources obtained with the parallel-hole and the SMARTZOOM collimator when reconstructed with the clinical software and UMCS shown together with the profile at the location of the dashed line in the upper left reconstruction

Fig. 5

The reconstructions of the uniformly filled cylinder obtained with the parallel-hole and the SMARTZOOM collimator when reconstructed with the clinical software and UMCS shown together with the profile at the location of the dashed line in the upper left reconstruction. The dashed rectangle in the upper right reconstruction represents the volume in which the noise was calculated for the CNR analysis

Fig. 6

a The reconstructions of the myocardial perfusion phantom at iteration 100 obtained with the parallel-hole and the SMARTZOOM collimator when reconstructed with dual-energy window and Monte Carlo-based scatter correction. The dotted line in the upper left reconstruction represents the location of the profiles. The red lines in the upper right reconstruction represent the mask of the hot wall and the blue lines represent the mask of the defect. b The profiles over the cardiac insert. The left and the right (lower) peaks are the hot wall and the defect, respectively

Fig. 7

The a contrast, b noise, and c contrast-to-noise ratios, as a function of the iteration number. The shaded regions in b and c represent the standard deviation over the 20 noise realizations. The dotted lines in c indicate the maximum achieved CNR values

Fig. 8

The maximum CNR, as a function of the scan duration. The black dashed line is drawn at the maximum CNR achieved by the parallel-hole collimator with dual-energy window scatter correction. The dashed lines in color are drawn at the scan durations at which the same maximum CNR is achieved for the other collimator and scatter correction combinations. The shaded areas represent the standard deviation over the 20 noise realizations