Study finds gain from delayed cerebral imaging

Monday 28th January 2008

Acquisition of PET images as long as six hours after fluorodeoxyglucose (FDG) injection can be a useful and easy-to-perform technique in delineating gliomas from grey matter and detecting cerebral lymphomas, a study has found.

Researchers based at the department of nuclear medicine and radiology at Jean Minjoz University Hospital in Besançon, France, presented their findings at the 2007 RSNA meeting in Chicago.

Detailing results, Dr Oleg Blagosklonov noted that very delayed cerebral FDG-PET scans â€" performed after six hours â€" can reveal both hypermetabolic and hypometabolic lesions in oncological and nononcological patients.

The research team's analysis extends the value of delayed or dual-time-point (two to three hours after injection) FDG-PET imaging for detecting abnormal lesions.

All PET scans reviewed in the study were conducted at the Jean Minjoz nuclear medicine and radiology department.

Between January 2005 and March 2007, 58 cerebral FDG-PET scans were performed in 44 patients with the following diagnoses:

• Cerebral metastasis suspected on MRI (15).
• Glioma (12).
• Pituitary adenoma or Cushing's syndrome (six).
• Epilepsy (four).
• Cerebral lymphoma (two).
• Unknown (five).

After six hours’ fasting 4â€"5MBq/kg of FDG were administered to patients intravenously.

Then PET images were acquired twice, with the first scan one hour after injection and the second six hours after injection, using a Siemens Biograph Duo PET/CT system.

The CT portion of the procedure was performed in a spiral mode with 2mm slice thickness. FDG images were acquired with an axial field of view of 12cm.

Images show high-grade transformation of an oligodendroglioma visualised at the delayed PET scan.

A standard one-hour PET scan showed no lesion in one case, one or more high-uptake lesions in 18 cases, and one or more low-uptake lesions in 39 cases, Dr Blagosklonov noted.

The delayed acquisition revealed an additional 11 high-uptake lesions, allowing the detection of six recurrent cerebral metastases, three high-grade gliomas, one pituitary microadenoma and one focus of epilepsy.

The researchers observed enhanced contrast between grey matter and all hypermetabolic lesions, even visible at the first PET scan.

Contrast between grey matter and hypometabolic lesion was also enhanced by the very late acquisition technique.

Dr Blagosklonov said the research showed that the easy-to-perform and well-accepted technique was comparable with FDG-PET scanning without attenuation correction in lung cancer diagnosis.

Jean Minjoz University Hospital