The Research Of The Normal And Pathologic Structures Of Temporal Bone Using Isotropic Multi-detector Helical CT

OBJECTIVE:1) to compare isotropic helical CT with 0.5mm slice width and conventional direct axial and coronal CT with 1.0mm slice width, so as to evaluate their advantage on the visualization of normal temporal bone.2) to compare 0.5 mm slice width /increment with the 1.0mm slice width/increment on axial and coranal MPR of isotropic helical CT, so as to evaluate the values of different slice width/increment of MPR on visualization of pathological temporal bone.METHODS:1 )for the first objective of the study, 15 subjects underwent both conventional 1.0 mm direct axial and coronal CT and helical 0.5mm axial CT. The helical data was reformation in a plane similar to that of the conventional CT ,with a slice width of 0.5 mm and 0.5mm increments.35 important structures of each temporal bone(the total of temporal bone is 27) were evaluated independently by two observers using a modified Likert scale, with unknown of the methods of imaging. The scale differences between the two techniques were evaluated using Wilcoxo signed rank test. Correlation between the two observers'gradings was evaluated using analysis of Spearman. and P<0.05 was thought significance statistically.2) for the second objective of the study, 25 patients underwent helical 0.5mm axial CT, then the helical data was reconstructed with 0.5 mm slice width /increment and with 1.0 mm slice width /increment respectively, 15 abnormal structures of temporal bone were evaluated by a observer using a modified Likert scale, with unknown of the methods of imaging. The interval between two evaluations was two weeks to avoid the bias of the memory. The scale differences between the two techniques were evaluated using rank sum test, and P<0.05 was thought significance statistically。RESULTS: 1) for the first objective of the study, of 30 temporal bones of fifteen adults, 27 normal temporal bones was included in this series, and 3 pathologic temporal bones were excluded. Results of evaluations by two observers revealed that 0.5 mm helical CT scored significantly higher than the 1.0mm conventional axial and coronal CT. The correlation coefficient between observers was 0.10928 for the whole temporal bone, and P<0.05. 2) for the second objective of the study, 31 abnormal temporal bone of 25 cases with auditory disorders were found in this series. The comparison of MPR between 0.5 mm and 1.0 mm slice width based on isotropic multi-slice helical CT revealed that MPR of 0.5 mm was superior to that of 1.0 mm on the visualization of abnormal temporal bone, and P<0.005.CONCLUSION:1) Multi-slice helical CT with collimation of 0.5 mm and coronal reformation of 0.5 mm slice width/increment is better than the conventional direct axial and coronal CT with 1.0mm slice width in displaying the small structures of the temporal bones. Volumetric data with submillimeter collimation acquired from the multi-slice helical CT offers the opportunity to perform nearly isotropic helical CT scanning, and the MPR (multi-planar reformation) on the base of the isotropic helical CT scan data may visualize tiny structures of the temporal bones satisfactorily. 2) Isotropic multi-slice helical CT has the advantage on displaying anatomic variation and the early lesions of temporal bones, especially, the MPR with 0.5 mm slice width /increment is superior to that with 1.0 mm slice width /increment. Therefore, it provides the better choice for the imaging examination of diseases of the temporal bones, for example, the congenital variation and abnormalities, trauma, infections, and so on. 3) As to the level of noise, multi-slice helical CT with 0.5mm collimation is slightly higher than conventional direct axial and coronal CT with 1.0mm slice width. However, because of better spatial resolution and excellent isotropic MPR, on the general effects of displaying structures of temporal bones, the isotropic multi-slice helical CT is superior to conventional direct axial and coronal CT with 1.0mm slice width.4) It can reduce the radiation dose using the MPR of the isotropic multi-slice helical CT. The acceleration of the helical CT's scanning speed can also reduce the motional artifacts resulted from the longer scanning time of the conventional direct CT .At the same time, it saves the patients' examing time,improves the efficiency,reduces the risk of the accident when the patient were scanned. 5)The MPR of the isotropic data and the faster scanning of the helical CT can avoid the bad displaying of the temporal bones caused by nonstandard scanning position when conventional direct coronal scanning and the forced scanning position were taken for the incooperative patients due to all kinds of diseases, so isotropic multi-slice helical CT is very useful for the clinic otology.6) The limitations of the 0.5-mm helical scanning include the slightly increased image noise,the additional time for post-processing of the images,the larger amount of image data and the bad displaying of some tiny structures such as some ligaments in the middle ear.