Characterization of accurate 3D collimator-detector response function for single- and multi-lofthole collimated SPECT...

Area of Science:

• Nuclear Medicine
• Medical Imaging Physics
• Computational Imaging

Background:

• The collimator-detector response function (CDRF) is crucial for Single-Photon Emission Computed Tomography (SPECT) imaging.
• Characterizing CDRF is essential for optimizing image quality and quantitative accuracy in SPECT systems.
• Breast-dedicated SPECT imagers require specialized collimation for improved lesion detection.

Purpose of the Study:

• To characterize the CDRF of a breast-dedicated SPECT imager with a lofthole collimator.
• To evaluate the impact of source-to-collimator distance and photon incidence angle on CDRF.
• To compare the performance of lofthole collimators with pinhole collimators and analytical models.

Main Methods:

• Modeled a cylindrical multi-lofthole collimation system using GATE Monte Carlo simulation.
• Assessed the CDRF dependency on source-to-collimator distance for single- and multi-lofthole configurations.
• Derived the 3D-sensitivity map and compared results with 8-pinhole collimators and analytical derivations.
• Simulated data acquisition with a ^99mTc point source over 5.0 minutes.

Main Results:

• Increasing magnification in a single-lofthole collimator improved sensitivity and spatial resolution.
• CDRF for the 8-lofthole collimator showed strong dependence on source-to-aperture distance and photon incidence angle.
• A 30 mm offset increased sensitivity by 25%, while a 34° angle reduced it by 50%.
• Spatial resolution followed a quadratic function of offset distance from the field center.

Conclusions:

• Lofthole collimation in SPECT imagers exhibits significant angle- and offset-dependency within the field of view.
• These findings are critical for accurate image reconstruction and quantitative analysis in breast SPECT imaging.
• Optimizing lofthole collimator design and acquisition protocols can enhance SPECT performance for breast imaging.