Evaluation of contrast enhancement and image quality:a comparison between different tube voltages and iodine concentrations in abdominal dynamic CT scans in minipigs

Abstract

Objective To investigate the effect of tube voltage and iodine concentration of contrast medium (CM) on abdominal dynamic enhanced CT image quality. Methods Six miniature pigs underwent repeated upper abdomen dynamic contrast-enhanced CT scans in 4 scanning protocols with different concentration of CM and tube voltage, namely, protocol 1, CM with iodine concentration of 270 milligrams iodine per milliliter (mg/ml) and 80 kV tube voltage; protocol 2, 270 mg/ml and 120 kV; protocol 3, 370 mg/ml and 80 kV and protocol 4, 370 mg/ml and 120 kV. The same iodine dose (600 mg/ml) and iodine delivery rate (IDR) (920 mg/s) were used in all protocols. The CM with iodine concentration of 270 mg/ml were injected at a flow rate of 3.4 ml/s, and 370 mg/ml CM injected at 2.5 ml/s. Image reconstruction was performed with iterative reconstruction (iDose4) in protocol 1 and 3,filtered back projection (FBP) was used in protocol 2 and 4. A subjective scoring system for image quality, image noise and sharpness was conducted by 2 radiologists independently. The measured values (peak of enhanced CT values, image noise of aorta, inferior vena cava, portal vein, hepatic vein and liver parenchyma) as well as the calculated values [their time-to-peak, signal-to-noise (SNR) and contrast-to-noise (CNR) ratios] were compared between among 4 protocols. The CT volume dose index (CDTIvol) and dose length product (DLP) were recorded from the CT console after each scanning. Factorial designed ANOVA was used for comparison of enhanced CT values of vessels and liver parenchyma, noise, SNR and CNR. The Kruskal-Wallis test was used for comparison of values among the 4 protocols, including the time-to-peak enhancement of vessels and liver parenchyma, the subjective scores of image quality indices. Result There was no significant differences in subjective scores of the image quality, image noise and image sharpness (P>0.05). The scored were more than 3, and the images with 4 scanning protocols were all acceptable for diagnosis. There was no significant differences between protocol 1 and 3, protocol 2 and 4 in the peak enhancement CT values of aorta [(729±46) HU vs.(707±59)HU,(515±84)HU vs. (513±53)HU], inferior vena cava [(366±95)HU vs. (368±92)HU, (282±39)HU vs. (262 ± 67)HU], portal vein [(213 ± 18)HU vs.(201 ± 29)HU, (180 ± 21)HU vs. (176 ± 27)HU], hepatic vein[(207±18)HU vs. (193±10)HU, (179±24)HU vs. (170±14)HU] and liver parenchyma [(128±7) HU vs. (127±4) HU,(135±5)HU vs.(135±6)HU] (P>0.05). But the CT values of vessels (aorta, inferior vena cava, portal vein and hepatic vein) in protocol 1 and 3 were significantly higher than those in protocol 2 and 4 (P 0.05). No significant differences were observed on the peak times, SNR and CNR in aorta, inferior vena cava, portal vein, hepatic vein and liver parenchyma among 4 protocols (P>0.05). The CDTIvol and DLP! were 199.67 mGy, 1 597.4 mGy·cm respectively in protocol 1 and 3,585.12 mGy and 4 680.9 mGy·cm in protocol 2 and 4 (scanning with 120 kV). Conclusions CM with different iodinated concentration could achieve the same enhancement in the abdominal vessels and liver parenchyma by using the proper scan protocols, which have the same IDR and iodine dose per kilogram body weight.Higher vessel enhanced peak values were achieved when using the protocols with 80 kV tube voltage than 120 kV. By using a low dose protocol of 80 kV tube voltage with the iterative reconstruction algorithm, the quality of image can be warranted. Key words: Tomography, X-ray computed; Contrast media; Radiation dosage