Calibration of DOI-Capable PET Detector Panels Using Uncollimated Front-Face Irradiation

Objective.

Gold-standard depth-of-interaction (DOI) calibration using collimated gamma-ray irradiation is time-consuming and impractical for system-level calibration of detector arrays.

This work investigates an efficient DOI and energy calibration method for detector panels using uncollimated irradiation, with gamma rays incident nearly parallel to the crystal depth direction.

Approach.

The 511-keV photopeak location in a dual-ended readout PET detector block was evaluated as a function of crystal depth using collimated and uncollimated $^{22}$Na irradiation.

A $4\times4$ dual-ended readout PET detector panel was then assembled.

Three detector blocks were calibrated using the gold-standard method, and two uncollimated-irradiation DOI calibration approaches--a physics-informed model and a multilayer perceptron (MLP)--were compared against it.

Finally, the full panel was calibrated for DOI and energy using the MLP-based approach.

Main Results.

The median relative RMSE between second-order polynomial fits from collimated and uncollimated irradiation was 1%, showing that uncollimated irradiation can provide reliable estimates when accurate DOI calibration parameters are available.

Compared with gold-standard DOI calibration, the physics-informed and MLP-based approaches achieved RMSEs of 0.38-0.58 mm and 0.36-0.61 mm, respectively.

The MLP-based approach provided better DOI resolution estimates and was therefore used for full-panel calibration.

After saturation correction, the panel achieved a mean energy resolution of 15.6% and a DOI resolution of 2.0 mm.

Significance.

The proposed MLP-based calibration requires only a single uniform 511-keV irradiation, making it simple to implement and suitable for in situ calibration of DOI-capable PET detector arrays.