てんかん患者のポジトロンCT

POSITRON CT OF EPILEPSY

　抄録　ポジトロン放出核種より製造した¹¹CO，¹³NH₃，¹⁸FDGを用い，放射線医学総合研究所にて開発されたポジトロン断層装置を使用し，種々の中枢神経疾患の三次元イメージングを行ってきた。各々のトレーサーは局所脳血液量局所脳灌流量，局所脳ブドウ糖消費量を表わしていると考えられる。2例のinter—ictalのてんかん患者に使用し，1例は¹¹CO，¹³NH₃のみを用いて検査を行い，他1例は¹¹CO，¹³NH₃と¹⁸FDGを用いたが，脳波にて徐波の認められる側に¹³NH₃，¹⁸FDGとも低集積を示した。¹³NH₃，¹⁸FDG両者を用いた症例では，¹⁸FDGがより狭い範囲の異常を表わした。X線CTはともに同側の萎縮を認めた。このポジトロンCT結果はKuhlらの報告と一致する。しかし¹³³Xeによる局所脳血流量測定ではinterictalでも血流の増加を認める報告もあり，てんかん焦点の機能的，代謝的にfluctuating stateである事が指摘されている。¹³NH₃，¹⁸FDGの三次元イメージングはてんかんの診断，治療，特に手術を意図する際には重要な情報を提供すると思われる。

Positron CT was performed in two epileptic patients. Positron emitting isotopes of ¹¹C, ¹³N and ¹⁸F were made at National Institute of Radiological Sciences using cyclotrone. Device of Positron CT is "POSITOLOGICA " which has a ring of unequally spaced 64 bithmus germanate detectors arranged in a circle, and the ring rotates contineouslly.

¹¹CO binds with hemoglobin in red cell tightly and circulates in vessels of brain, so ¹¹CO image shows local cerebral blood volume. ¹³NH₃ was injected intravenously, and diffused easily to the brain tissue and then was incorporated into a glutamate-glutamine pool of large size and slow turnover rate. Amount of ¹³NH₃ uptake to brain depends on local capillary perfusion. ¹⁸FDG was analogous substance of glucose, and incorporated into the brain competitively with same carrier ofglucose. It is phosphorylated to ¹³FDG-phosphate by hexokinase but it is not metabolized further-more. And only a little ¹³FDG-6-phosphate is dephosphorylated. Amount of ¹³F accumulated in the brain tissue depends on local glucose utiliza-tion.

Case 1. This is a 49 year-old man who had five years' history of convulsive seizures. CT scan reveals progressive right hemispheric atrophy, and high density area in right frontal lobe but was not enhanced with contrastmedia. Positron CT of ¹³NH₃ shows decreased accumulation of ¹³N in right frontal lobe and the area surrounding the sylvian fissure.

Case 2. Thirtythree year old man was found unconscious 3 years ago and convulsive seizure was noted 3 months before the Positron CT. Positron CT of ¹³NH₃ and ¹⁸FDG reveals decreased uptake in left temporo-occipital region. Area of decrease of ¹³FDG is smaller than that of ¹³NH₃. It seems that the area of decreased glucose me-talism is smaller than the area of decreased perfusion. This finding of decreased uptake of ¹³NH₃ and ¹⁸FDG in interictal state is same as report of Kuhl et al. But there are reports that cerebral blood flow is increased while interictal state measured by ¹³³Xe method. And it is men-tioned that epileptogenic focus is fluctuating state functionally and metabolically.

Positron CT of epileptic patient is valuable in diagnosis and therapy,especially surgical procedure was intended.