Feasibility study of automatic spectral imaging protocol selection combined with double low technique in CT portal vein imaging

Objective: To explore the application value of virtual monochromatic imaging combined with adaptive statistical iterative reconstruction (ASIR) and automatic spectral imageing mode selection (ASIS) in reducing the radiation dose and contrast dose of CT portal venography. Methods: We retrospectively collected 120 cases (80 males and 40 females) who underwent upper abdominal enhancement CT from January 2017 to April 2017. Patients were divided into 3 groups (40 cases in each group) according to the scanning program. Group A used conventional 120 kVp scan, NI = 10, contrast agent dosage was 450 mgI/kg of body weight, image was reconstructed with 50% ASIR technique; Groups B and C used spectral CT mode, NI = 10 (Group B), NI = 13 (Group C), the amount of contrast agent was 300 mgI/kg of body weight, and the image was reconstructed with 60 keV + 50% ASIR. One-way analysis of variance was used to compare the mean CT values and their differences, image noise, SNR and CNR of portal vein and liver parenchyma in three groups of images. Subjective image quality scores were performed on three groups of images by two senior radiologists. The patient's CTDI_vol, DLP were recorded and the E was calculated. Results: The amount of contrast agent in group B and C was reduced by about 30% compared with group A. The portal vein CT values of groups A, B, and C were 168.22 ± 17.82, 209.06 ± 20.07, and 211.03 ± 25.60. The portal vein CT values of group B and C were significantly higher than those of group A, respectively (t = -9.625, -8.680, P < 0.05). The CT value difference between portal vein and liver parenchyma was 60.01 ± 17.01, 106.63 ± 25.83, 107.72 ± 25.39, respectively. SNRs were 8.48 ± 1.41, 12.64 ± 2.94, 10.77 ± 1.94, and CNR were 5.16 ± 1.80, 8.13 ± 2.54, 7.32 ± 1.84, respectively. The image quality scores were 3.53 ± 0.68, 4.75 ± 0.54 and 4.53 ± 0.64, respectively. The CT value difference, SNR, CNR and image quality scores of group B and group C were significantly higher than those in group A (t= -9.536, -9.857, -8.082, -6.064, -6.050, -5.308, -8.912, 6.779, P < 0.05). The CTDI_vol of groups A, B and C were (12.15 ± 5.02) mGy, (12.34 ± 4.18) mGy, (10.03 ± 3.13) mGy, DLP were (348.62 ± 155.99) mGy · cm, (355.56 ± 131.07) mGy · cm, (287.10 ± 92.25) mGy · cm, respectively, E were (5.23 ± 2.34) mSv, (5.33 ± 1.97) mSv, (4.31 ± 1.38) mSv, compared with the A and B groups, the CTDI, ol, DLP and E of the C group were significantly lower (t = 2.274, 2.147, 2.147, 2.812, 2.702, 2.702, P < 0.05), and CTDI_vol, DLP and E were decreased by 19%. Conclusions: In CT portal venography, NI = 13, 60 keV combined with 50% ASIR reconstruction and ASIS can be used to personalize the contrast dose and radiation dose of the patient and provide images that meet the diagnostic requirements. (authors)