关键词: 计算机断层扫描; 能谱扫描; 后颅窝

Abstract:

Objective To discuss the value of improving the quality of the image and the removal of hardening artifact for the usage of GE Discovery computed tomography(CT)750 HD 70 keV monochromatic image in the posterior cranial fossa imaging. Methods ①From June 2011 to October 2012, 87 patients were taken spectrum scan mode head CT scan in our hospital, 400 patients were taken conventional mixed energy head CT scan using GE Discovery CT750 HD, their image informations were used to create database respectively. ②From each database, 20 cases were extracted using random number method at random respectively. CT value and its standard deviation(SD) of 20 mm2 region of interest(ROI) were measured for different position of brain tissue inside posterior cranial fossa in the cases selected, including:midpoint of the bilateral internal auditory meatus, pons center and cerebellar white matter in the level with maximum 4th ventricle. Image quality was measured by the noise level(CT value standard deviation SD), and statistical analysis between the 2 groups was taken. In addition, from each database, 30 cases were extracted using random number method at random respectively. Then for the cases selected, score for the posterior fossa artifact was taken and a statistical analysis was made. Results All cases of spectrum scan mode 70 keV monochromatic image in our study can meet the diagnosis need of posterior cranial fossa. Median noise level of bilateral internal auditory meatus midpoint, pons center and cerebellar white matter in the level with maximum 4th ventricle are(unit:HU):70 keV monochromatic image group3.96(3.60, 4.24)、3.66(3.40, 3.92)、3.37(3.06, 3.65), mixed energy head CT group 5.52(5.16, 5.80)、4.52(4.15, 5.36)、4.26(3.95, 4.74), respectively. Compared to mixed energy head CT, noise index of different brain tissue position inside the posterior fossa is decreased significantly, there are significant statistical differences, all P<0.001. As to posterior cranial fossa artifact, median score of 70 keV monochromatic image(4, 3-4) is higher than the mixed energy CT image(3, 2-3), and there are significant statistical differences, P<0.001. Conclusions Spectrum scan mode 70 keV monochromatic image can meet the diagnosis need of posterior cranial fossa after initial studies. Compared with conventional mixed energy CT image, 70 keV monochromatic image can significantly reduce image noise of the posterior fossa brain parenchyma, improve image quality, and inhibit the artifact of posterior cranial fossa.

Key words: Computed tomography; Spectral scan; Posterior fossa