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I.はじめに
201Thallium chloride(201TIC1)は,single photon emission computed tomography(SPECT)上,脳腫瘍への選択的な集積を示し,放射線治療後には,その集積がcomputed tomography(CT),magnetic resonance im—aging(MRI)上の腫瘍形態の変化よりも以前に低下を示すことから,早期の照射効果判定に有用である3).また,脳血流イメージ剤であるN-isopropyl-p—[123Ⅰ]—iodo—amphetamine(123Ⅰ—IMP)を用いたSPECTでは20),腫瘍周囲浮腫に関連した血流低下領域をとらえることができ16),脳血管障害例のみでなく,脳腫瘍例においてもその病態把握に有用な検査であると考えられる.しかし,CT,MRIに比較すると,SPECTの空間分解能は依然低く,画像評価に難があることは否めない.そこで,われわれは,SPECTの三次元画像を作成し,視覚的な面から低い空間分解能を補うとともに,核種の集積容積や,欠損容積を算出する新たな評価方法を考案した.今回,転移性脳腫瘍例におけるradiosurgery後の極早期での治療効果判定に関して,この方法を用いて検討を行ったので報告する.
Concurrent use of two different isotopes, 201T1C1 and 123Ⅰ-IMP, in SPECT is useful in separative evalua-tion of tumor metabolism and peritumoral circulation. Three dimensional SPECT employed in our study has an obvious advantage over two dimensional SPECT for its accurate imaging of tumors and peritumoural areas. Changes of tumor metabolism and regional circulation in peritumoral edematous tissues were investigated by fused 3-D SPECT images using 201T1C1 and 123Ⅰ-IMP. In this study, the volume of isotope accumulative and isotope defective regions were measured. Fusion of SPECT images was performed by the use of panning visualization software; Application Visualization Sys-tern Medical View (K. G. T.). The threshold of 3-D rendering was determined by conforming the volume of the hemisphere and of the tumor estimated on CT to the volume of 123Ⅰ-IMP and 201T1C1 accumulating area respectively.
Accumulative volume of 201T1C1 in the tumor de-creased remarkably at 7 days after radiosurgery (p < 0.01). Defective volume of peritumoral hypoperfusion was measured on 3-D SPECT. The average volume was 80.5±32.5cm3 before radiosurgery. It decreased by approximately 60% at 7 days after radiosurgery (p<0.05).
Analysis of 3-D SPECT images using two different isotope tracers is reliable and useful to evaluate early the changes of metabolism and peritumoral circulation in or around intracerebral tumors.
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