断層局所脳血流測定—連続CT-Xe吸入法

COMPUTED TOMOGRAPHIC MEASUREMENT OF REGIONAL CEREBRAL BLOOD FLOW BY XENON ENHANCEMENT

　抄録　従来のアイソトープによる血流測定法は頭蓋外モニターであり局所性に乏しく，しかも乏血部位の血流は反映されず，理上論的にも病的組織の血流は求まらない等の欠点がある。この点我々の行なっている断層脳血流測定法はこれらの欠点のいくつかを克服し，血流値がCT画像との関係でみられ，局所性にすぐれ，しかも血流値表示画像の分解能が3mmと高いという利点がある。50％のゼノンガスを25分間吸入させその間3〜5分の間隔で連続的にスキャンを施行し，サブドラによるHU値の変化と呼気中ゼノン濃度の推移からFickの原理に基づいて，K （立ち上がり率），λ（分配係数），f （血流値）を求めCRT上に画像表示した。正常人灰白質のf血流吊は82±11，白質は24±5ml／100g／min （mean±SD）であった。一方異常例では病巣部以外の灰白質での血流低下は著明で27〜57ml／100g／minであるのに対して白質は16〜21と比較的保存されていた。一方浮腫部や梗塞部では従来の方法で求まらない分配係数が0〜0.9と低く，従って最終的な血流値が著明に低下していた。

The present study was conducted to overcome some of disadvantages of cerebral blood flow study by radionuclide, such as poor regionality of flow values and errors involved in pathological brains.

Serial CT scanning was carried out during and after inhalation of 50 to 70% non-radioactive xenon in humans. Diffusible gas with high atomic number enhanced gray matter first 19±4 HU (mean±SD) on an average in Hounsfield unit (HU) and later white matter 24±4 HU. In seven normal subjects, blood flow in gray matter was 82±11 and that in white matter 24±5 ml/100 gm/min. Partition coef-ficient which is not readily obtainable by radio-nuclide study was 0.9±0. 1 in normal gray matter and 1.4±0.2 in normal white matter.

Two cases were presented to show k-map (clear-ance rate), 2-map (partition coefficient) and CBF map, which displayed images of values calculated automatically, in black and white or color on CRT. The first case was a patient with metastatic brain tumor from lung in the left parietal region. The blood flow of the tumor was close to that of gray matter, whereas blood flow of edematous white matter surrounding the tumor was decreased to below 10ml/100g/min with partition coefficient ranged from 0 to 0.9. The second case was pres-ented to demonstrate the resolution of the blood flow map obtained by this method. Multiple lacunar infarcts of the basal ganglia and white matter in the size of 1 to 3 mm, which were hardly identified on regular CT picture, were well visualized on CBF map.

This method appeared to have several advantages over conventional isotope method and to provide useful clinical and research informations.