Brain SPECT with short focal-length cone-beam collimation

Area of Science:

• Medical Imaging
• Nuclear Medicine
• Biomedical Engineering

Background:

• Single-photon emission-computed tomography (SPECT) imaging of deep brain structures faces challenges due to photon attenuation.
• Existing parallel-hole collimators on dual-head SPECT systems struggle to balance sensitivity and spatial resolution for central brain imaging.

Purpose of the Study:

• To design and evaluate novel collimator pairs for dual-head SPECT systems to enhance sensitivity, particularly in the brain's center.
• To compare the performance of new collimation strategies against conventional methods for activity concentration estimation in small brain structures.

Main Methods:

• Designed and evaluated cone-beam and fan-beam collimator pairs for dual-head SPECT systems.
• Calculated ideal signal-to-noise ratios (SNRCRB) using Cramer-Rao lower bound on variance for spherical lesions in a brain phantom.
• Reconstructed images using ordered-subset expectation-maximization (OS-EM) for visual assessment and artifact detection.

Main Results:

• A combination of a 20 cm focal length cone-beam collimator and a 40 cm focal length fan-beam collimator demonstrated superior performance.
• This optimized pair increased SNRCRB by 1.1 to 3.5 times compared to parallel-parallel collimators across the imaging volume.
• Artifact-free image reconstructions were achieved, showing robustness to positioning mismatches.

Conclusions:

• Combining fan-beam and short-focusing cone-beam collimation offers a significant improvement for dual-head brain SPECT imaging.
• This approach substantially enhances sensitivity and image quality, particularly for deep and centrally located brain structures.