Iterative model reconstruction and hybrid iterative reconstruction techniques iDose4 in low-dose abdominal CT: comparison of image quality in evaluation of hypovascular metastases of liver

Abstract

Objective To assess the image quality of iterative model reconstruction algorithm(IMR) compared with hybrid iterative reconstruction algorithm (iDose4) for hypovascular hepatic metastases. Methods Medical history and pathological results of 33 cases with primary malignant tumor were retrospective analyzed. Follow-up with enhanced CT or enhanced MRI at more than 3 months confirmed hypovascular metastases in these patients. All patients underwent abdominal CT scanning and dynamic enhanced CT scanning. Portal vein phase of low dose scanning data were taken as the research object. According to the different tube currents and reconstruction algorithm, the images were divided into 4 groups. Group A included images with tube current of 175 mAs and IMR post-processing (17 cases). Group B included images with tube current of 175 mAs and iDose4 post-processing (17 cases). Group C included images with tube current of 125 mAs and IMR post-processing (16 cases). Group D included images with tube current of 125 mAs and iDose4 post-processing (16 cases). In the cases with multiple lesions, the largest lesion was selected to evaluate. For each image of the objective evaluation [including noise, the signal-to-noise ratio (SNR), contrast to noise ratio (CNR)] and subjective evaluation (including lesion sharpness, necrosis interface and diagnostic confidence). The CT dose index of each scanning was recorded. The objective evaluation, subjective evaluation indexes were compared by paired samples t test and Wilcoxon signed rank test. Results The tube current of Group A and Group B were (7.7±1.8) and (12.8±3.7)HU, while CNR were 10.3 ± 2.6 and 5.6 ± 1.4, SNR were 13.2 ± 3.2 and 8.1 ± 2.2, and the differences were statistically significant (t values were 9.966, 12.670, 9.203; P<0.01). The tube current of Group C and Group D were (7.2±1.3) and (9.9±1.8)HU, while CNR were 7.4±2.0 and 3.7±0.9, SNR were 13.9±2.9 and 9.8±1.9, and the differences were statistically significant (t values were 9.209, 12.320, 9.628; P<0.01).The lesion sharpness score of Group A and Group B were 4.95±0.24 and 4.29±0.59, while the necrosis interface score were 4.76 ± 0.36 and 3.68 ± 0.30, diagnostic confidence score were 4.94 ± 0.24 and 4.44 ± 0.56, and the differences were statistically significant (P<0.05). The lesion sharpness score of Group C and Group D were 3.94 ± 0.68 and 3.56 ± 0.63, while the necrosis interface score were 3.91 ± 0.64 and 3.03 ± 0.50, diagnostic confidence score were 4.19±0.40 and 3.94±0.44, and the differences were statistically significant (P<0.05). CTDIvol of 175 mAs group and 125 m As group were(11.83 ± 0.28)and(8.44 ± 0.24)mGy respectively. Conclusion Compared with iDose4, iterative reconstruction technology IMR significantly reduces the image noise and enhances image quality of hypovascular hepatic metastases. Key words: Liver neoplasms; Tomography, X-ray computed; Comparative study