Liu Xiaoyu MD, Presenter: Nothing to Disclose

To assess the image quality of low-dose CT of the liver obtained with 80kVp and low contrast dose (200mgI/kg) between low (270mgI/mL) and high (370 mgI/mL) concentration agent when BMI is lower than 23.

40 patients (average age 52ys, BMI<23) underwent unenhanced and enhanced liver CT were divided into 2 groups randomly：group 1 (n=20) with 80kVp and contrast dose of 200mgI/kg (270mgI/ml)；group 2 (n=20) 80kVp and 200mgI/kg (370mgI/ml). Another group of 20 (group 3) with no BMI restriction used 120kVp and 1ml/kg (370mgI/ml) as the conventional group. The injection time is fixed at 20 seconds, leading to an adjustable injection speed. The CT values were measured on liver, aorta, portal vein and muscle as background to calculate the CNR and SNR. Two senior radiologists evaluated the axial image quality with scores 1-5.

The CT value of the aorta during arteral phase (AP) were 296.44±37.68, 305.32±76.11, 262.99±41.62; and of the portal vein in portal phase (PP) were 156.04±26.02, 160.19±22.76, 147.76±24.61, respectively. The CT value of aorta in group 2 was significantly (p<0.05) higher than that in group 1 and 3. There was no diference in the CT value of portal vein in 3 groups (p>0.05). The CNR and SNR in the 3 groups in AP were (0.79±0.66, 5.83±0.94); (0.75±0.96, 5.75±1.33) and (0.96±1.14, 6.95±0.73), and in PP (2.21±1.02, 7.34±1.02), (2.29±1.37, 7.41±1.72) and (3.32±1.07, 9.20±1.07), respectively. There were no significant differences among the 3 groups in AP and VP (p>0.05). The image quality scores were 4.78±0.42, 4.55±0.51 and 4.73±0.46 for greoup 1, 2 and 3, respectively. There was no different between them (P>0.05). Volume CT dose index (CTDIvl) were 36.62±0.24mGy, 33.58±4.47mGy and 98.89±7.04 mGy for groups 1, 2 and 3, respetively.

Use low contrast medium (200mgI/kg) can provide similar image quality as the conventional protocal (370mgI/ml, 1ml/kg). And higher aorta enhancement achieved with 370 mgI/ml at the same amount of iodine dose(200mgI/kg) in this experment while CNR and SNR show no significantly differences.

 Low contrast medium (200mgI/kg) protocal can provide similar image quality as the conventional protocal (370mgI/ml, 1ml/kg) in patients with BMI< 23 no matter which concentration of contrast medium (270mgI/ml or 370mgI/ml) is used.

Xiaoyu, L, Image Quality in the Low Dose CT of the Liver: Contrast Study between 270mgI/ml and 370mgI/ml.  Radiological Society of North America 2014 Scientific Assembly and Annual Meeting, - ,Chicago IL. http://archive.rsna.org/2014/14018397.html