133Xe吸入法による局所脳血流量測定の年齢対応正常値と判定イメージの作製—フーリエ解析法で算出したISIに関して

AGE-MATCHED NORMAL VALUES OF REGIONAL CEREBRAL BLOOD FLOW MEASUREMENTS BY 133Xe INHALATION AND PRODUCTION OF JUDGMENT IMAGE:AS TO INITIAL SLOPE INDEX COMPUTED BY FOURIER ANALYSIS FOURIER ANALYSIS

　抄録　健常者90人（年齢19〜80歳）に計125回の¹³³Xe吸入法による局所脳血流量測定を閉眼安静状態で行ない，加齢との関係をフーリエ解析法で算出したinitial slope index （ISI）を用いて検討し，年齢対応正常値を算出した。全脳平均値と年齢の間には有意な負の相関が得られ（r＝−0.67, P＜0.001），回帰直線はY＝−0.30X＋67.8，またその95％信頼区間は±11.8となつた。局所ごとの値も全脳領域で年齢と有意な（P＜0.001）負の相関を示したが，中大脳動脈領域は他の動脈領域よりも負の相関が強く有意差（P＜0.05）が認められた。全年齢にわたつて前頭葉の血流量は他の部位よりも多く優位性を示したが，加齢による減少が他の部位よりも著しく，部位の差が縮まる傾向を示した。このように脳血流量は加齢により減少し，部位により減少する程度が異なるため患者の測定値は同年齢の局所ごとの正常値と比較しなければならない。われわれは年齢対応正常値の95％信頼限界を局所ごとに算出し，この値で患者の測定値を割ることにより判定イメージを作製したところ，推計学上有意な減少あるいは増加部位を視覚的に容易に評価することができ，有用であつた。

In order to investigate an influence of advancing age on regional cerebral blood flow (rCBF), 125 measurements of rCBF were made by ¹³³Xe inha-lation method in 90 normal subjects without cere-bral symptoms and risk factors of atherothrombo-tic stroke including hypertension, diabetes melli-tus, and hyperlipidemia. There were 46 male and 44 female aged 19 to 80 years old (mean 42.5). The measurements were carried out in a quiet, semi-darkened room with the subjects at rest and eye closed. ¹³³Xe inhalation system (Meditronic-Novo Diagnostic Systems, Inhalation Cerebrograph, Den-mark) consists of 32 scintillation detectors, the lateral part of each hemisphere being covered by 16 detectors placed in parallel. One pair of the detectors is mounted in place over the brain stem and cerebellar region. Relationship of age and rCBF computed as the initial slope index (ISI) by Fourier analysis was investigated with both cor-relation and regression analyses, and age-matched normal values were calculated. End-tidal partial pressured for carbon dioxide (PECO₂) was recor-ded from the face mask during the measurements along with the mean arterial blood pressure (MABP). ISI values were not corrected for chan-ges in PECO₂.

PECO₂ and MABP did not differ significantly among the normal subjects. There were no signi-ficant differences in the hemispheric mean ISI va-lues between the right and left hemispheres. Mean brain ISI values showed significant negative correlation with advancing age (r=-0.67, p< 0.001), and regression line was Y=-0.30X+67. 8. Ninety five per-cent confidence interval of the regression line was±11.8. Regional ISI values also showed significant negative correlations with advancing age in the whole brain (p<0.001). There were no significant differences in the cor-relation coefficients obtained from parallel regions between the right and left hemispheres. The regional reduction of ISI values with advancingage was significantly greater in the regional dis-tribution of the middle cerebral arteries bilate-rally, compared with regions in the distribution of either the anterior cerebral, the posterior cere-bral, or vertebrobasilar arteries (p<0.05). Regio-nal hemispheric percent value of frontal lobe was greater than that of either parietal, tempo-ral, occipital lobe, or brain stem and cerebellar region in the whole age. But, this hyperfrontal distribution became gradually obscured with ad-vancing age, because reduction of ISI values with aging was significantly greater in the frontal than in other regions.

It is concluded that measured rCBF of a patient have to be compared with age-matched normal values of mean brain and each region. Judgment image was produced with dividing patient value by 95% confidence limit of age-matched normal value. According to this image, regions in which rCBF significantly decrease or increase can be easily evaluated.