摘要
目的研究使用Bowtie滤线器(F1)后,保证加速器CBCT患者扫描图像质量前提下,如何合理设置扫描条件,尽量降低辐射剂量。方法使用Piranha辐射测量仪测量CBCT在使用F1与未使用F1时射线的半价层。设定不同的扫描模式,使用直径30cm的有机玻璃模体测量扫描剂量,并使用XVI附带的Catphan503模体测量客观图像质量。在此基础上,研究扫描剂量以及图像质量与扫描条件的关系,提出了适合临床患者的胸部与腹部不同的扫描条件。结果使用F1后射束的半价层增加了0.77～0.92mmAl,扫描剂量明显减少,中心点减少了22%～29%,边缘点减少了41%～45%,皮肤剂量减少显著。图像质量随着扫描剂量的增大而提高。空间分辨力受FOV影响较大,但一般能识别1～2mm的物体,完全能够满足分辨细小骨结构与标记点的临床要求。图像伪影在使用L20时的大mAs下明显。胸部低剂量的CBCT图像如100kV,M20,0.5mAs的扫描条件亦可满足临床要求。腹部则需要使用较大剂量的扫描模式,CBCT图像才达到进行配准的要求。结论 F1的使用在改善图像质量的前提下降低了扫描剂量,使用新的扫描序列能平衡二者的关系。
Objective To explore the influence of bowtie filtration on absorb dose and half-value layer inaluminum （Al） of cone-beam CT, estimate the image dose under different scan protocol, and establish the relationship between the image quality and the scan protocol after using F1. Methods Piranha was used to measure the HVL. Dose measurements were performed with an 0.6 cc Farmer type ionization chamber with a 30 cm-diam cylindrical shaped water phantoms in 100 and 120 kV with a series of mAs and FOV. CNR, noise and uniformity were measured on the Catphan503 images. Results HVL increased 0.77-0.92 mmAl where XVI generally had more penetrating beams at the similar kV settings. Scanning dose significantly reduced, the center point decreased 22%-29%, the edge with a decrease of 41%-45% which meant a very significant reduction in skin dose. Image quality improved with mAs increase. The spatial resolution mainly changed with FOV. But generally can identify 1-2 mm-diam objects, fully meet the clinical requirements of identify small bone structure and marker. Through this clinical investigation, low-dose CBCT images in chest, such as 100 kV, M20, and 0.5 mAs scanning protocol appeared to be an optimal settings. Abdomen image needed a higher dose to reach the requirements of registration. Conclusions Using F1 under the premise of improving the image quality then reducing the scanning dose and using a new scanning sequence can balance the image quality and scanning dose.
出处
《华西医学》
CAS
2010年第12期2151-2155,共5页
West China Medical Journal
