Comparison of a standard resolution PET-CT scanner with an HRRT brain scanner for imaging small tumours within the head

We compared a conventional PET-CT scanner (Siemens Biograph TruePoint TrueV) with and without resolution modeling (RM) image reconstruction with a high resolution research tomograph (HRRT) in order to assess the utility of conventional scanners for brain scanning. A modified Esser phantom and 6 neurofibromatosis 2 (NF2) patients with vestibular schwannomas (VS) were scanned using both scanners. The phantom was filled with fluorine-18 (40 MBq, 4:1 contrast ratio) and scanned for 60 min on separate occasions. Patients were injected with ~200 MBq of [18F]fluorodeoxyglucose (FDG) and [18F]fluorothymidine (FLT) on separate occasions and scanned for three consecutive 30 min periods moving between scanners. The HRRT images, although noisier, resulted in higher contrast recovery for the smallest cylindrical inserts in comparison to TrueV with and without RM. With the TrueV, higher uptake values were observed in VS lesions with both FDG and FLT which is consistent with greater spill-in from the brain for FDG and bone marrow for FLT. RM decreased measured FDG uptake. For large homogenous lesions the conventional TrueV gives similar or better results compared to the HRRT. For smaller lesions, the HRRT has benefit, with RM on the TrueV unable to restore parity, and with the potential for image artifacts.