A line-source method for aligning on-board and other pinhole SPECT systems

Area of Science:

• Medical Imaging
• Nuclear Medicine
• Radiation Oncology

Background:

• Developing robotic multipinhole SPECT systems for functional and molecular imaging during radiation therapy.
• Essential need for precise alignment of SPECT systems with linear accelerators (LINAC) and cone-beam CT (CBCT) for accurate target localization and image reconstruction.

Purpose of the Study:

• To propose and investigate a novel alignment method for robotic multipinhole SPECT systems.
• To achieve accurate alignment with LINAC and CBCT coordinate frames for enhanced image-guided radiation therapy.
• To explore the applicability of this method for calibrating other pinhole SPECT systems.

Main Methods:

• Developed an alignment model mapping 3D line sources to 2D SPECT detector projections.
• Utilized computer simulations with varying parameters (noise, resolution, geometry) and experimental evaluations with a physical phantom.
• Employed the Radon transform to determine projection angles and offsets, followed by nonlinear least squares estimation of alignment parameters.

Main Results:

• Simulation studies demonstrated accurate estimation of six alignment parameters with three line sources under ideal conditions.
• Accuracy decreased with Radon transform limitations, but improved significantly with four or more line sources and thinner projections.
• Experimental results showed median errors of ~1.8 mm for translations and ~0.5° for rotations, validating the method's precision.

Conclusions:

• Alignment parameters for robotic multipinhole SPECT can be effectively estimated using single pinhole projections of line sources.
• Alignment accuracy is influenced by Radon transform precision and system parameters; using more line sources enhances accuracy.
• This method is crucial for multipinhole SPECT on radiation therapy machines, enabling precise SPECT-CBCT-LINAC coordinate alignment for improved treatment delivery.