A modified orthogonal-distance ray-tracer method applied to dual rotation PET systems

Area of Science:

• Medical Imaging
• Nuclear Medicine
• Biophysics

Background:

• Preclinical Positron Emission Tomography (PET) systems require advanced modeling for high-quality imaging.
• Shift-variant point-spread function (PSF) modeling is crucial for accurate image reconstruction in dual-rotation PET.
• Existing methods like orthogonal-distance ray-tracer (OD-RT) and tube-of-response (ToR) have limitations in capturing complex PSF variations.

Purpose of the Study:

• To develop and evaluate a novel projector, the orthogonal-distance ray-tracer varying-full width at half maximum (OD-RT-VF), for preclinical dual-rotation PET.
• To improve image quality (IQ) by accurately modeling shift-variant elliptical PSF responses.
• To assess the performance of OD-RT-VF against existing OD-RT and constant response ToR models.

Main Methods:

• Implementation of the OD-RT-VF projector to model varying PSF full width at half maximum (FWHM) values in multiple directions.
• Utilizing half-height and half-width tube-of-response (ToR) values within the OD-RT-VF model.
• Performance evaluation using NEMA NU 4-2008 IQ and Derenzo phantoms, alongside in-vivo imaging of a mouse with [18F]-NaF on an easyPET.3D system.

Main Results:

• OD-RT-VF demonstrated superior image resolution and uniformity (11.9% vs 15.9%) compared to the OD-RT model.
• Micro-Derenzo phantom simulations showed OD-RT-VF resolving rods down to 1.0 mm.
• IQ phantom simulations yielded hot rod recovery coefficients from 22.4% to 93.3% and reduced spillover ratios (0.22 for air, 0.33 for water).
• In vivo bone radiotracer imaging showed clearer skeletal structures with less noise and better resolution using OD-RT-VF.

Conclusions:

• The OD-RT-VF projector method significantly enhances PET imaging resolution, uniformity, and overall image quality.
• This advanced modeling approach, combined with list-mode and GPU-based reconstruction, unlocks the full imaging potential of dual-rotation PET systems for small animal studies.
• OD-RT-VF provides a more accurate and effective tool for preclinical PET imaging research.