An evaluation of the performance characteristics of different types of collimators used with the EMI brain scanner (MKI) and their significance in specific clinical applications.

The characteristics of various types of collimators have been studied systematically for the EMI Mark I brain scanner. The degree of collimation ranged from the 13-mm adjacent A and B slices to 3-mm separated slices. Multiple phantom studies (including variable density immiscible liquid interfaces) have been performed to evaluate the effect of collimation on (a) the line-spread function, (b) the change in effective absorption number, and (c) volume averaging. Effects associated with the technique settings involving the kVp, the mA, and the scan time were also investigated. The results of TLD dose measurements as a function of collimation are presented. The significance of collimation in specific clinical studies involving small, fairly well-circumscribed lesions is discussed.