Effect of reference mAs in CARE kV technique on image quality and radiation dose in unenhanced chest CT

Abstract

Objective To evaluate the effect of reference mAs on radiation dose and image quality characteristics of chest CT scanned with CARE kV technique compared with CARE Dose4D. Methods According to the date of examination,158 consecutive patients were selected in our department and randomly divided into 5 groups: CARE Dose4D group (30 cases, group 1); using CARE kV technology, reference mAs were 110 (32 cases), 90 (31 cases), 70 (33 cases), 50 (32 cases), which were recorded asthe group from 2 to 5, respectively. Volume CT dose index (CTDIvol), dose length product (DLP) and the effective dose (ED) were analyzed. CT value and objective image noise were measured in the lungparenchyma and descending aorta.Two radiologists assessed the images for subjective noise, artefacts and diagnostic acceptability.The radiation dose, CT value and objective noise were compared with the analysis of variance, and the difference between two groups was compared with SNK test; the rank sum tests (Kruskal-Wallis) were used in subjective image quality score, and difference between two groups was compared with K-W test. Results The CTDIvol, DLP, ED values in five groups were(7.7±1.7),(7.7±2.0), (5.5±1.4), (4.2±1.5), (2.8±1.2)mGy, (290.7±67.4) , (290.1±85.2) , (194.2±52.1) , (150.7±63.8) , (96.5±38.9) mGy·cm, (4.1±0.9) , (4.1±1.2) , (2.7±0.7) , (2.1±0.9) , (1.3±0.5) mSv, respectively.There were significant difference among the 5 groups(F=59.305, 57.76, 57.76, P 0.05). The objective noise of 5 groups in pulmonary parenchyma and the descending aorta were (48.7±9.1) , (49.2±10.0) , (55.5±11.2) , (56.5±8.3) , (63.7±13.2) HU; (9.2±1.6) , (9.5 ± 2.1) , (10.7 ± 2.6) , (11.6 ± 2.7) , (13.6 ± 2.6) HU respectively, and the difference was significant(F= 10.774, 17.157, P 0.05). Conclusion Comparedwith CARE Dose4D, the use of CARE kV technique of suitable reference mAs for unenhanced chest CT can reduce radiation dose significantly with diagnostically acceptable image quality. Key words: Tomography, X-ray computed; Radiation dosage