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Test-Retest Studies of Cerebral Glucose Metabolism Using Fluorine-18 Deoxyglucose: Validation of Method

Neuroimaging Section, NINCDS, and Nuclear Medicine Department, Clinical Center, National Institutes of Health, Bethesda, Maryland

Correspondence: For reprints contact: Rodney A. Brooks, MD, Bldg. 10, Room 1C451, National Institutes of Health, Bethesda, MD 20892.

ABSTRACT

In studies using [¹⁸F]deoxyglucose (FDG), one often wants to compare metabolic rates following stimulation (drug or motor-sensory) with the baseline values. However, because of reproducibility problems with baseline variations of 25% in the same individual not uncommon, the global effect of the stimulation may be difficult to see. One approach to this problem is to perform the two studies sequentially. This means that, with the 110-min half-life of ¹⁸F, one must take into account the residual activity from the first study when calculating metabolic rates for the second. We performed TEST-RETEST baseline studies on four subjects, with a 1-hr interval between injections. These studies were done without stimulation, in order to validate the repeatability of the method. To reduce the amount of residual activity from the first study, the first injection was only 2 mCi in three cases, and only 1 mCi in one case, out of a total injected dose of 5 mCi. A correction for residual activity was included in the RETEST calculation of metabolic rate. The results showed a global metabolic shift between the two studies of 2% to 9%. An error analysis shows that the shift could be further reduced if anatomically comparable scans are done at comparable postinjection times.

FOOTNOTES

^* Presented at the 32nd Annual Meeting of the Society of Nuclear Medicine, Washington, DC.

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