A new and fundamentally different X-ray method is described. The cranium is scanned in successive layers by a narrow beam of X rays, in such a way that the transmission of the X-ray photons across a particular layer can be measured, and by means of a computer, used to construct a picture of the internal structure.Employing a suitably designed scanning gantry, a continuously operating X-ray tube, and a narrow collimated X-ray beam, the transmissions of X-ray photons across a slice of tissue may be measured by a system of crystal detectors in such a way that 28,800 readings are obtained. These form the basis of 28,000 simultaneous equations which are solved by a computer. The solutions are transformed into absorption coefficients and by means of a *This preliminary communication is a slightly expanded

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✓ Computerized scanning of the brain is a new diagnostic x-ray method that utilizes modern electronic and computer technology for the measurement of the transmission of x-ray photons through tissue. The cranium is scanned in successive layers by a narrow beam of x-rays in such a way that the transmission of x-ray photons across a particular slice can be measured, and by means of a computer and a suitable algorithm used to construct a detailed differential picture of the internal structure and tissues of the brain.

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Eighty patients with subarachnoid hemorrhage underwent computerized tomography (CT) scanning before and after administration of Conray contrast medium. Abnormal enhancement was seen in visual evaluation of the CT scans in 26 cases, in the regions bordering the subarachnoid spaces. Abnormal enhancement was associated with a poor clinical condition, angiographic spasm, and a poor outcome. Measurements of absorption values in the thalamus revealed significant increases in density after contrast enhancement in those patients whose scans showed abnormal enhancement in the regions bordering the subarachnoid spaces on visual evaluation. The authors suggest that the abnormal enhancement is parenchymal, in the gyri, and is not "subarachnoid." They suggest that it is due to gyral hyperemia or extravasation of contrast material into the cortex resulting from breakdown of the blood-brain barrier, or a combination of both factors.