Thermography in the Diagnosis of Cerebrovascular Disease: Preliminary Report

Abstract

The integumentary and anterior ocular branches of the ophthalmic artery provide the only surface anatomic display of the internal carotid artery. By assessing the blood flow in the exteriorly disposed supraorbital and ocular segments in a physiologic state, deductions can be made concerning internal carotid artery circulation. A simple, atraumatic, harmless, and painless method of measuring the cutaneous blood supply to these external areas that are readily accessible to examination is to measure the skin temperature. Graphic recordings of radiant heat emitted from the orbital and supraorbital regions have been found useful in detecting asymmetrical blood flow in the internal carotid arterial systems. The technic employed utilizes a high-resolution scanning device which optically transfers collected infrared radiation to a thermal resistor bolometer, following which the electrical reaction produced is electronically amplified, converted to light, and photographed. The resultant “thermogram” is a black (cool) and white (warm) two-dimensional image formed by parallel lines, each of which contains approximately 350 point recordings of thermal data (Fig. 1). Semi-quantitative linear tracings of the multitude of heat readings can be made of each excursion during scanning, and calibrated temperature references are incorporated in the thermogram for visual analysis. The accuracy of the thermal scanning device is rated at plus or minus 0.1° F when examinations are carried out under standard conditions of ambient temperature. The method can be used for bedridden patients. In preliminary clinical investigations, particular attention has been given to the portions of the forehead supplied by the frontal and supraorbital arteries. The medial orbital region, where the inner canthus is supplied by branches of the medial palpebral and dorsal nasal arteries, has been scrutinized; the anterior ciliary arteries and a branch of the supraorbital artery also contribute warmth to the medial palpebral commissure. While the medial supraorbital integument is supplied almost exclusively by the internal carotid artery, the medial canthus has a dual supply because the terminal angular branch of the external carotid artery extends into this area. In normal persons, the infrared heat emitted by different portions of the face varies according to a fixed pattern. The nose and cheeks and the hair-insulated eyebrow, eyelash, and scalp areas are cool zones; the avascular cornea of the eye is cool. The anterior portion of the forehead is warm, and heat normally is trapped in the canthi and skin folds. In the average normal subject, a variation of not more than 0.5° F is found between the two sides when the flat lower half of the forehead is examined. In a large group of healthy students and hospital employees of all ages, the median supraorbital reading was 94.0° F.