The effects of object activity distribution on multiplexing multi-pinhole SPECT

Area of Science:

• Nuclear Medicine
• Medical Imaging Physics

Background:

• Multi-pinhole (MPH) Single Photon Emission Computed Tomography (SPECT) systems offer potential for increased detection efficiency.
• Optimizing MPH collimator design requires understanding the impact of multiplexing on image quality across various activity distributions.

Purpose of the Study:

• To investigate the effects of different degrees of multiplexing in MPH SPECT on image quality.
• To evaluate the trade-offs between noise, artifacts, and resolution for varying multiplexing strategies.

Main Methods:

• Utilized three digital phantoms (hot rod, cold rod, cold sphere) to simulate different activity distributions.
• Generated noise-free and noisy projections using a 3D analytical MPH projector.
• Reconstructed projections using Ordered Subset Expectation Maximization (OS-EM) without resolution recovery.
• Assessed image quality using Normalized Mean-Square-Error (NMSE), noise levels, image profiles, and signal-to-background ratios (SBR).

Main Results:

• Multiplexing slightly improved NMSE-noise trade-offs for sparse (hot rod) objects, particularly with increased pinhole numbers.
• Significant artifacts and worsened NMSE-noise trade-offs were observed for non-sparse (cold) phantoms.
• Resolution degraded by approximately 39-65% for the cold rod phantom with higher multiplexing.
• For the cold sphere phantom, non-multiplexing designs showed better image profiles, while ~20% multiplexing maintained comparable SBR.

Conclusions:

• Multiplexing in MPH SPECT benefits sparse object imaging but significantly degrades image quality in non-sparse distributions.
• The gains in detection efficiency from multiplexing are often offset by image degradations, especially with non-specific tracers.
• Minimizing multiplexing is crucial for designing optimal MPH collimators to achieve the best balance between sensitivity and image fidelity.