Professor, Department of Diagnostic Sciences, School of Dentistry, University of North Carolina, Chapel Hill, NC.
Am J Orthod Dentofacial Orthop. 2013 Dec;144(6):802-17. doi: 10.1016/j.ajodo.2013.07.013.
The increasing use of cone-beam computed tomography in orthodontics has been coupled with heightened concern about the long-term risks of x-ray exposure in orthodontic populations. An industry response to this has been to offer low-exposure alternative scanning options in newer cone-beam computed tomography models.
Effective doses resulting from various combinations of field of view size and field location comparing child and adult anthropomorphic phantoms with the recently introduced i-CAT FLX cone-beam computed tomography unit (Imaging Sciences, Hatfield, Pa) were measured with optical stimulated dosimetry using previously validated protocols. Scan protocols included high resolution (360° rotation, 600 image frames, 120 kV[p], 5 mA, 7.4 seconds), standard (360°, 300 frames, 120 kV[p], 5 mA, 3.7 seconds), QuickScan (180°, 160 frames, 120 kV[p], 5 mA, 2 seconds), and QuickScan+ (180°, 160 frames, 90 kV[p], 3 mA, 2 seconds). Contrast-to-noise ratio was calculated as a quantitative measure of image quality for the various exposure options using the QUART DVT phantom.
Child phantom doses were on average 36% greater than adult phantom doses. QuickScan+ protocols resulted in significantly lower doses than standard protocols for the child (P = 0.0167) and adult (P = 0.0055) phantoms. The 13 × 16-cm cephalometric fields of view ranged from 11 to 85 μSv in the adult phantom and 18 to 120 μSv in the child phantom for the QuickScan+ and standard protocols, respectively. The contrast-to-noise ratio was reduced by approximately two thirds when comparing QuickScan+ with standard exposure parameters.
QuickScan+ effective doses are comparable with conventional panoramic examinations. Significant dose reductions are accompanied by significant reductions in image quality. However, this trade-off might be acceptable for certain diagnostic tasks such as interim assessment of treatment results.
随着锥形束 CT 在正畸中的应用日益增多，人们对正畸人群 X 射线照射的长期风险的担忧也日益增加。对此，业内的回应是在新型锥形束 CT 模型中提供低曝光替代扫描选项。
采用光学剂量计，利用先前验证的方案，对不同视野大小和视野位置组合在儿童和成人人体模型中产生的有效剂量进行了测量，比较了最近推出的 i-CAT FLX 锥形束 CT 仪（Imaging Sciences，Hatfield，Pa）。扫描方案包括高分辨率（360°旋转，600 个图像帧，120 kV[p]，5 mA，7.4 秒）、标准（360°，300 个帧，120 kV[p]，5 mA，3.7 秒）、QuickScan（180°，160 个帧，120 kV[p]，5 mA，2 秒）和 QuickScan+（180°，160 个帧，90 kV[p]，3 mA，2 秒）。利用 QUART DVT 体模，计算了各种曝光方案的对比度噪声比，作为图像质量的定量衡量指标。
儿童体模的剂量平均比成人体模的剂量高 36%。与标准方案相比，QuickScan+方案在儿童（P=0.0167）和成人（P=0.0055）体模中均显著降低了剂量。在成人体模中，13×16 cm 头影测量视野的剂量范围为 QuickScan+和标准方案分别为 11 至 85 μSv 和 18 至 120 μSv；在儿童体模中，QuickScan+和标准方案分别为 11 至 85 μSv 和 18 至 120 μSv。与标准曝光参数相比，QuickScan+的对比度噪声比降低了约三分之二。
QuickScan+的有效剂量与常规全景检查相当。显著的剂量降低伴随着图像质量的显著降低。然而，对于某些诊断任务，如治疗结果的中期评估，这种权衡可能是可以接受的。
