A quantitative study of the EMI values obtained for normal brain cerebral infarction and certain tumours

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Abstract
A quantitative study was made of the EMI [electrical and musical industries] numbers of normal brain, cerebral infarction and certain tumors. The scans were recorded on magnetic tape and analyzed using a minicomputer linked to a graphic display unit. This system not only yielded 16 grey scales compared with the 10 currently available, but was programmed to allow selected regions of the scans to be outlined. From these regions the computer calculated the area, the mean EMI number and its SD. In 15 normal brain scans, the EMI values obtained for normal frontal and temporal lobes were similar, but the values for the basal ganglia and occipital lobes were significantly different from the first regions and from each other. Ten cases of cerebral infarction and 30 cases of cerebral tumor were analyzed and it was shown that analyzing representative areas was more informative than surveying the whole lesion. While only half of the brain tumor scans had a significantly altered EMI number compared with that of normal brain, enhancement of tumor density with sodium iothalamate revealed a consistent and significant elevation of the EMI number for all tumors. The value for enhanced meningiomas was almost double and malignant tumors more than a third larger than normal brain. It was not possible to differentiate quantitatively between astrocytomas and metastases.