IRIS算法对儿童头颅CT图像质量的影响

The influence of Iterative reconstruction in image space(IRIS) on image quality of cranial CT in children

目的:探讨在儿童头颅扫描时迭代图像空间重建算法(IRIS)对图像客观噪声和主观图像质量的影响,评价其在儿童头颅CT低剂量扫描中的价值。方法:回顾性分析头颅螺旋CT诊断报告显示无异常的80例儿童病例的原始影像数据,分别采用滤过反投影(FBP)算法和IRIS算法进行重建,选择后颅窝颞骨岩部小脑层面和基底节层面为兴趣区来研究两种算法对图像质量的影响。图像客观评价以兴趣区内测量的CT值的标准差表示客观图像噪声值,图像主观质量评价由两位放射医师采用5分制进行评分。对两组算法的图像客观噪声值与图像主观质量评分进行相关性分析。结果:在IRIS组和FBP组图像客观噪声值中,后颅窝层面分别为(3.65±0.35)和(3.83±0.41)HU,基底节层面分别为(3.58±0.42)和(3.73±0.26)HU,两组算法间差异有统计学意义(P<0.05),IRIS组较FBP组客观噪声值减低。在IRIS组和FBP组图像主观质量评分中,后颅窝层面分别为(3.99±0.42)和(3.31±0.57)分,基底节层面分别为(4.15±0.54)和(3.59±0.57)分,两组间差异有统计学意义(P<0.05),IRIS组在两个层面的图像质量评分均高于FBP组。两组算法的图像客观噪声值与图像主观质量评分之间呈负相关性(r=-0.730,P=0.001),说明图像客观噪声降低,图像主观质量评分增加。结论:在儿童头颅CT扫描中运用IRIS算法可减低图像客观噪声,提高图像主观评价质量,为儿童头颅低剂量CT扫描提供依据。

Objective：To evaluate the feasibility of using Iterative reconstruction in image space（IRIS） to reduce image noise and improve subjective image quality in cranial CT in children.Methods：Eighty children undergoing cranial CT without abnormal finding were retrospective analyzed.Raw data were reconstructed using standard（Filtered back projection,FBP） and IRIS.Two anatomic levels（posterior fossa,basal ganglia） were collected respectively,and the objective noise of all 320 images as well as subjective classification of image quality（using a scale with five categories） were recorded and analysed statistically.Results：The objective noise in the posterior fossa level was（3.65±0.35 in IRIS） and（3.83±0.41 in FBP）,while the noise in basal ganglia level was（3.58±0.42） and（3.73±0.26） respectively.The difference between the two groups was statistically significant（P〈0.05）,IRIS images subjective score was better than FBP images in two levels,including the level of the posterior fossa（3.99±0.42） and（3.31±0.57）,basal ganglia level showed（4.15±0.54） and（3.59±0.57）.The relationship between subjective image quality score and objective noise showed a negative correlation（r=-0.730,P=0.001）,as the objective noise reducing and subjective image quality score increasing.Conclusion：Using IRIS reconstruction can reduce image noise and improve subjective image quality in cranial CT,comparing with standard FBP reconstruction.IRIS reduces image noise in cranial CT thus provids potential for reducing radiation exposure.