頭部外傷例におけるプロトン緩和時間値T<SUB>1</SUB>の経時変化とその意義

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  • Significance of Focal Relaxation Times in Head Injury

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Serial examinations by nuclear magnetic resonance-computed tomography were carried out in 35 head-injured patients aged 7 to 77 years. The injuries were classified as cerebral contusion (nine cases), acute epidural hematoma (eight cases), acute cerebral swelling (two cases), and chronic subdural hematoma (16 cases). The results of 92 measurements were divided into two groups: acute stage (within 3 days of injury) and chronic stage (2 weeks or longer after injury). The spinlattice relaxation times (T1) of brain tissue adjacent to chronic subdural hematoma were evaluated pre and postoperatively. A Fonar QED 80-alpha system was used for magnetic resonance imaging and measurement of focal T1. The T1 values at the region of interest were measured 3 to 5 times by the field focusing technique (468 gauss in the focused spot), and the mean value was used for evaluation. The standard T1 values obtained from healthy subjects were 290±41 msec in the cerebral cortex and 230±34 msec in the white matter.<BR> Prolongation of T1 in perifocal brain gradually shortened over time and normalized in the chronic stage. The degree of contusional edema may have been reflected in alterations in T1. In contrast, parenchymal injury resulted in a progressive T1 elevation, which far exceeded 500 msec in the chronic stage. Such time courses of T1 may indicate irreversible tissue damage. There were no noticeable changes in tissue T1 over time in patients with acute diffuse cerebral swelling or those who underwent evacuation of acute epidural or chronic subdural hematomas. The underlying pathophysiology in such situations seems to be not brain edema but cerebral hyperemia. In the presence of ischemia, the T1 value was prolonged in the early stage, reflecting progression of ischemic edema. Remarkable prolongation of T1—up to 1, 000 msec in the chronic stage—appears to be attributable to post-traumatic degeneration of brain tissue.

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