Data analysis of low dose multislice helical CT scan in orbital trauma

To explore the optimal low dose of MSCT in orbital trauma examination.

Sixty transverse images of the fracture layer were selected. Low-dose images acquired at 30, 70, 100, 140, 170, and 200 milliampere (mA) were simulated by adding noise to the image space using software. After assessing the images according to the conditions of image quality and fracture, we found the optimal tube current that met diagnostic requirements and then applied it to clinical use. The CT Dose Index volume (CTDIvol), dose length product (DLP) and effective dose (ED) were recorded. The image quality was classified as good, fairly good, ordinary, poor, or very poor according to image level, noise, anatomic structure and whether the diagnostic requirements were met or not. The rank-sum test was used to perform statistical analysis on the ranked data. The Chi-square test was used for the numerical data.

Under the scan conditions of a conventional dose of 300 mA, 60 cases of orbital fracture, 38 cases of orbital emphysema, 25 cases of ocular damage, and 3 cases of intraorbital foreign body were demonstrated in the images of the 60 orbital trauma patients. Among the low dose simulated images, the image quality difference of the different doses was of statistical significance (χ(2)=15.678, P=0.016). When the dose was lowered to 70 mA, the above mentioned clinical signs were still clear and diagnostic, however the image quality assessment results indicated that 2 cases were good, 16 cases were fairly good, and 42 cases were ordinary, poor or very poor. When the simulated dose tube current was 100mA, the image quality assessment results were 18 cases good, 34 cases fairly good, and 8 cases ordinary, poor and very poor; compared with the conventional dose, there was no statistical significance (P>0.05). When using a 100 mA tube current to examine 40 cases of orbital trauma patients in the clinic, the acquired image quality was 10 cases good, 26 cases fairly good and 4 cases ordinary, without any cases of poor or very poor. The CTDIvol, DLP and ED were 20.72mGy, 124.97 mGy·cm and 0.26mSv, respectively, while the CTDIvol, DLP and ED were 62.53mGy, 375.18 mGy•GTtl and 0.86mSv, respectively, when using a conventional dose of 300 mA. Compared with the tube current of 100 mA for scanning, the ED declined 70%.

When conducting an MSCT scan for orbital trauma, the acquired images using the 100 mA tube current can meet the clinical diagnostic requirements, and the radiation dose to the patients can be decreased.