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目的探讨迭代重组(IRIS)算法在低剂量肝脏增强CT扫描中的可行性及应用价值。方法选择100例(男65例,女35例,平均年龄48岁)拟行肝脏三期增强的患者,常规剂量(120 k V)A组58例,采用滤波反投影算法(FBP)重组生成图像A;低剂量(100 k V)B组42例,分别采用FBP生成图像(B1组)及采用IRIS生成图像(B2组),记录A与B两组的剂量长度乘积(DLP)、CT剂量容积指数(CTDI)并比较两组的有效剂量(ED)。计算正常肝脏门脉期的噪声及对比噪声比(CNR),由3名有经验的放射科医师对血管边缘锐利度、图像主观噪声、病灶显示按1~5分评分。采用SPSS 20.0软件包对A、B两组的辐射剂量、图像质量进行统计学分析,检验水准α=0.05。结果低剂量组ED[(1.23±0.32)m Sv]较常规剂量组ED[(2.30±0.73)m Sv]平均降低了46.24%。在3组图像客观噪声值中,B2组(8.85±1.11)较B1组(11.82±1.59)明显降低,不同算法的两组噪声值的差异有显著统计学差异(P<0.001),B2组与A组(8.09±1.52)算法无统计学意义(P>0.05);CNR分别为B2组(3.94±1.99)、B1组(3.46±2.38)、A组(3.87±2.19),三组均无统计学差异(P>0.05);B2组图像各项诊断信息评分与A组无差异(P>0.05)。结论 IRIS算法行肝脏增强扫描,可以降低图像噪声,提高CNR,在扫描剂量接近减半的情况下仍可获得满足诊断要求的肝脏增强CT图像。
Objective To investigate the feasibility and application value of iterative recombination (IRIS) algorithm in low-dose hepatic enhanced CT scanning. Methods A total of 100 patients (65 males and 35 females with a mean age of 48 years) were enrolled in this study. Fifty-eight patients in the conventional dose (120 kVA) group A were enrolled in this study. The images were reconstructed using FBP A, B (42) in low dose (100 kv) group B, FBP imaging (group B1) and IRIS (group B2) imaging were used to record the dose length product (DLP) Index (CTDI) and compare the effective dose (ED) of both groups. The normal liver portal venous phase noise and contrast-to-noise ratio (CNR) were calculated and scored 1 to 5 by three experienced radiologists for sharpness of the edge of the blood vessel, subjective noise of the image and lesions. The radiation dose and image quality of A and B groups were statistically analyzed by using SPSS 20.0 software package. The test level α = 0.05. Results ED [(1.23 ± 0.32) m Sv] decreased by 46.24% compared with ED [(2.30 ± 0.73) m Sv] in the low dose group. B2 (8.85 ± 1.11) was significantly lower than that of B1 (11.82 ± 1.59) in the three groups of objective noise. There was significant difference (P <0.001) between two groups of noise in B2 algorithm (8.09 ± 1.52) in group A were significantly higher than those in group A (P <0.05); CNR was significantly higher in group B2 (3.94 ± 1.99), group B1 (3.46 ± 2.38) and group A (3.87 ± 2.19) (P> 0.05). There was no significant difference between group A and group A (P> 0.05). Conclusions The IRIS algorithm can enhance the CNR by reducing the image noise and improving the liver function. In addition, the IRIS algorithm can still obtain the liver enhancement CT image which can meet the diagnostic requirements when the scanning dose is reduced by half.