Towards pediatric molecular imaging: development of a low-dose and high-performance Total Body PET scanner

Introduction

Positron Emission Tomography (PET) constitutes the imaging modality of excellence in nuclear medicine. Conventional whole body (WB) PET are used for both adult and pediatric studies. However, these scanners are not large enough to image the entire infant body, are not optimized in terms of sensitivity imposing the injection of high radiotracer doses, and their spatial resolution is at best 3-5 mm at the center of the scanner, which is not enough for visualizing small lesions.

Moreover, since PET imaging requires the injection of a radiotracer compound, its use is compromised in pediatrics due to radiation regulations and patient safety.

Project Objective

To overcome these limitations, I aim to develop an affordable high-performance, high-sensitivity total body (TB)-PET for pediatric imaging. The system, named PHOENIX, targets a high effective sensitivity of x25-30 that of clinical WB-PET.

Design Specifications

To achieve this goal, we propose a large axial scanner of 54.5 cm with a bore diameter of 32 cm to cover all organs of children—without becoming claustrophobic—and, thus, permitting dynamic multi-organ studies.

Detector Technology

For the best cost-performance tradeoff, the PHOENIX detectors would be based on semi-monolithic BGO crystals coupled to SiPMs. This design allows characterizing the light distribution profiles to retrieve photon depth of interaction information, resulting in a uniform image spatial resolution of <3 mm while simultaneously providing time-of-flight (TOF) capabilities.

To offer significant TOF information, I aim to exploit the low Cherenkov light yield produced in BGO. We will implement a scalable custom readout circuit composed of three stages:

1. Signal multiplexing
2. Event classification - Cherenkov and Scintillation
3. Commercial ASIC adaptation for digitization

Conclusion

Developing the PHOENIX scanner constitutes a major research and technological challenge. If successful, it will promote PET imaging of children and improve its diagnostic capabilities, staging, and response assessment.