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目的探讨颞骨高分辨率CT扫描时降低扫描mA值对其图像质量的影响及临床应用价值。方法将60例颞骨高分辨率冠状面CT扫描患者根据扫描mA值设置分为100mA和50mA组。全部图像行高分辨率骨密度算法重组,并利用多平面重建(MPR)技术重建轴面图像,得到2组不同mA值的直接扫描冠状面图像和与之对应的2组通过重建的轴面图像。分别评价不同扫描mA时直接冠状面及重建轴面图像质量。评价指标为:冠状面:鼓室盾板、Prussak’s腔、卵圆窗、鼓室盖、耳蜗底圈5个解剖结构。经MPR重建轴面:锤砧关节、水平半规管、鼓窦入口、锥隆起、面神经水平段5个解剖结构;评价标准为:清晰显示2分;显示、但不清晰1分;未显示0分。以左右两侧单独记分。结果当扫描mA值由100减至50时单次扫描加权CT剂量指数量(CTDIw)值由42.00mGy下降至21.00mGy,下降幅度达50.0%,而直接扫描冠状面图像质量无明显下降(P>0.05);并且颞骨低剂量高分辨率CT能基本达到图像向同性,经MPR重建的轴面图像能较好地显示颞骨细小解剖结构,保证病灶检出率。结论50mA的颞骨CT扫描能够提供较好诊断质量的影像信息。
Objective To investigate the effect of reducing the scanning mA value on the image quality of temporal bone high resolution CT scans and its clinical value. Methods Sixty patients with temporal bone high resolution coronal CT scan were divided into 100mA and 50mA groups according to the scanning mA value. All the images were reconstructed by high resolution bone density algorithm. The axial images were reconstructed by multiplanar reconstruction (MPR) to obtain two groups of direct scanning coronal images with different mA values and two corresponding reconstructed axial images . The images of direct coronal plane and reconstructed axial plane were evaluated respectively under different scanning mA. Evaluation indicators: coronal plane: tympanic shield, Prussak’s cavity, oval window, tympanic cap, cochlear five anatomical structures. Reconstructed by MPR Axial: hammer anvil, horizontal semicircular canal, drum sinus entrance, cone uplift, facial nerve horizontal section of the five anatomical structures; evaluation criteria: clearly show 2; display, but not clear 1; did not show 0. Scoring left and right individually. Results The CTDIw value decreased from 42.00 mGy to 21.00 mGy when the mA value was reduced from 100 to 50, with a decrease of 50.0%. However, there was no significant difference in CTDIW between the two groups (P> 0.05). And low-dose and high-resolution temporal bone CT can achieve the image isotropy basically. The MPR reconstructed axial images can show the fine anatomy of the temporal bone and ensure the detection rate of lesions. Conclusion 50mA temporal bone CT scan can provide better diagnostic quality of the image information.