Simultaneous (99m)Tc/(201)Tl dual-isotope SPET with Monte Carlo-based down-scatter correction

Area of Science:

• Nuclear Medicine
• Medical Imaging Physics
• Radiopharmaceutical Dosimetry

Background:

• Simultaneous dual-isotope (DI) single-photon emission tomography (SPET) using technetium-99m (99mTc) and thallium-201 (201Tl) is challenged by down-scatter contamination.
• This down-scatter degrades lesion contrast and reduces quantitative accuracy in 201Tl images.

Purpose of the Study:

• To develop and evaluate a Monte Carlo-based method for correcting down-scatter in simultaneous 99mTc/201Tl DI-SPET.
• To assess the impact of lead X-rays from collimators on down-scatter correction accuracy.
• To determine optimal adjustments to the data acquisition protocol for mitigating noise introduced by down-scatter.

Main Methods:

• Reconstruction of 99mTc activity distribution to simulate down-scatter into the 201Tl window.
• Utilizing a dedicated Monte Carlo simulator to model down-scatter projections, including lead X-ray detection.
• Iterative reconstruction of the 201Tl image with incorporated down-scatter correction.
• Evaluation using an anthropomorphic torso phantom with cardiac inserts, both with and without cold lesions.

Main Results:

• The Monte Carlo-based down-scatter correction achieved excellent agreement in lesion contrast and quantitative accuracy compared to virgin 201Tl images.
• Inclusion of lead X-ray effects in the simulation further improved the accuracy of the correction.
• Adjustments including a 15% lower 99mTc dose, 15% increased scan time, and 12% increased 201Tl dose effectively compensated for noise.

Conclusions:

• Monte Carlo-based down-scatter correction effectively recovers lesion contrast and quantitative accuracy in DI-SPET 201Tl images.
• The method demonstrates near-perfect performance in correcting for down-scatter.
• Minor adaptations in the data acquisition protocol can prevent noise degradation in simultaneous DI-SPET.