Improvements of a prototype 3D PET scanner using semiconductor detectors for pharyngeal cancers

Objectives A prototype brain PET scanner using CdTe detectors was developed to achieve high spatial resolution. Through the clinical experiences, it was found that the scanner has a potential for better identification of pharyngeal cancer. However, the axial field of view was limited in nasopharynx, because of interference between a patient and the end shield of the scanner. To expand the field of view (FOV) for mesopharynx, we replaced the shield made of thick lead with thin tungsten. Because of a reduction in shielding, the contamination gamma ray from patient may cause degradation of image quality. In this work, we evaluated the influence of these improvements on imaging capabilities.

Methods The original end shield of the scanner was made of lead with 3 cm thickness. To prevent the interference between the scanner and the patient, a part of the shield was replaced with 0.5mm thickness tungsten and also the make-up cover was improved. Influences to physical performance of the scanner were evaluated using NEMA 2001 phantom. Also imaging capabilities were evaluated by volunteer studies.

Results Random fraction to prompt count rate after the improvements increases 10% in the body side of the FOV. However, after random correction, true plus scatter count rates of before and after the reconstruction agree within 3%. So, image quality is expected to be almost the same as before the improvements. The volunteer studies showed mesopharynx of the patient can be set in the FOV by the cancellation of the interference and the feasibility was confirmed.

Conclusions A prototype brain PET scanner using CdTe semiconductor detectors was improved to apply mesopharynx region and its feasibility was confirmed.