18FDG-SPECT Imaging of Brain Tumours

Abstract

The purpose of this prospective study was to examine, if it is possible in principal to obtain suitable information to grade brain tumours and detect recurrences in follow up with 18Fluoro-Deoxyglucose (18FDG) and Single Photon Emission Computed Tomography (SPECT) using ultra high energy collimators. Fifty two brain SPECT investigations were carried out in 41 patients. Forty patients had primary brain tumours and one an anaplastic meningioma. SPECT acquisition was started 30 min after application of 400 MBq 18FDG using special high energy 511 KeV collimators. After attenuation correction (coef.= 0.07 cm−1/) brain tumour FDG uptake was quantified as ratio to contralateral brain cortex (RUV: relative uptake value). SPECT data were compared with histopathological findings and CT/MR images. In grade 4 gliomas (glioblastomas), 18FDG uptake depended on the ratio viable tumour tissue, taking up contrast media in CT/MRI, to cystic tumour areas. Two cases showed increased uptake (RUV = 1.33 and 1.05) compared to the contralateral cortex and four with central necrosis a decreased uptake (RUV = 0.79 ± 0.14). Grade 2 gliomas (five cases) showed a decreased 18FDG uptake (RUV = 0.68 ± 0.02) compared with contralateral brain cortex. In grade 3 astrocytomas (two cases), 18FDG uptake was significantly lower than cortex uptake, but slightly increased when compared with white matter uptake (RUV = 0.79 and 0.82). In follow-up, eight patients with a grade 4 glioma recurrence and one patient with a medulloblastoma recurrence showed an increased 18FDG uptake (RUV = 1.2 ±0.09 and 1.2). In one grade 4 glioma recurrence, SPECT results were false negative showing decreased FDG-uptake due to the presence of necrotic areas induced by radiotherapy. Grade 2 glioma recurrences (eight cases) showed low 18FDG uptake values (RUV = 0.73 ± 0.11). Radionecrosis also showed a decreased 18FDG uptake (RUV = 0.64 ± 0.09) compared with unaffected cortex. These results demonstrate that grading and follow-up tests of brain tumours are possible with 18FDG-SPECT, although SPECT with high energy collimators provides a relatively poor spatial resolution which requires further technical improvements.