Comparing of image quality of axial and coronal CT scan of temporal bone

Abstract

CT image quality has been affected by many factors such as KVP, ma, exposure time, alogorithm and section thickness. Gantry tilt has the main role in visualization of the temporal bone anatomic structures. In this study, we tried to optimize these factors to determine the best gantry tilt. This study was performed on the human skull phantom and then extended to 15 patients. The phantom was made by inserting a normal human dry skull into a water- filled radiolucent cylindrical container. A lateral scout view was obtained and the OMBL (orbitomeatal baseline) was used as the anatomical landmark.The phantom was scanned in 9, 15 , 30 , 45, 60 , 75, 90,105, 120 degree in relation to OMBL and 24 important anatomical structures were evaluated in each. Kilovoltage of 80, 120, 140 millimeters of 40, 70, 100, 120, 140, 170, 200, 240, exposue time of 2, 2, 4 second , algorithm of smooth, soft, standard, detail, bone adge and section thickness of 1.5, 3,5 millimeter were studied separately. In general, most of the anatomical structures are well demonstrated in 0 or 30 degrees of axial scans and 90 or 105 degrees in coronal scans. The best imaging techniques in Kv=140, Ma=100, S=2 seconds, algorithm of edge or bone, section thickness of 1.5 millimeter for small structures and 3 millineters for greater ones.The best 3-D image is provided by 3 millimeter slice thickness without overlapping but they couldn’t assist in diagnosis of our patient’s diseases. In indirect sagital reformatted images, the greater anatomical structures such as vestibule and cochlea are also shown, but they are recommended due to the slight degradation of the images and some loss of resolution.