A SIMPLE METHOD FOR VERIFICATION OF CENTER OF ROTATION (COR) AND PATIENT POSITION IN SPECT OF THE HEAD

Abstract

Reconstruction of SPECT images requires accurate input parameters. We encountered artefacts in brain image reconstructions because the center of rotation (COR) of the clinical study was different than that determined during camera setup.·He devised a simple method to verify the COR on each study and also to provide an anatomic marker to indicate patient position on reconstruction images. A point source (5 uci Tc-99m) is suspended in space to the right, behind and above the patient's head so that it does not superimpose on the head and is visible on all rotational images. The level of the source is reconstructed using the COR previously determined by the manufacturer's method. The correct COR reconstructs the source as a round, uniform point. An incorrect COR reconstructs with a flattened side, a cresent or a ring depending on the size of the error. If the COR is verified reconstruction of the rest of the image can proceed. If the COR is wrong the appearance of the artefact indicates the degree and direction of error with reference to the computer matrix. Reconstruction with trial CORs can be assessed by this means to salvage studies which would otherwise be lost. The location of the reconstructed point source allows verification of patient position which is necessary when imaging symmetrical body parts such as the head. We have found this technique useful in the performance of more than 20 exams of the brain and skull. This technique has potential application for SPECT imaging of other organs.