[Radiation dose to the head, and particularly to the lens of the eye, during tomography with EMI scanner].

Radiation dose to the lens of the eye was estimated using thermoluminescence and film dosimetry on patients undergoing computerised axial skull tomography with the EMI scanner, and also on various phantoms. The dose decreases from the lateral margin of the right eye to the lateral margin of the left eye. During conventional three layer tomography, maximal exposure to the eye is about 0.6 R (1.55 X 10 10-4 C.kg-1), produced entirely by scatter. Direct irradiation of the plane of orbits produces maximal exposure rate of 3 R (7.7X 10-4 C.kg-1). Maximal dose to the head depends on skull size and is about 4 R (approximately 10-3 C.kg-1). The local dose dependence of the eyes was confirmed theoretically by drawing up a computer programme, and was related to the method used by the EMI scanner.