Efficacy Of Test Bolus Technique For Low Voltage, High Pitch CT Angiography Of The Infra-renal Aorta And Lower Extremity Vessels

Objectives:Our aim was to assess image quality and radiation dose of low voltage high-pitch CT angiography （CTA） of the infra-renal aorta and lower extremities, evaluate the efficacy of test injection technique using a monitoring scan at knee level and investigate the diagnostic accuracy of low voltage high-pitch CT angiography （CTA） of the infra-renal aorta and lower extremities.Methods:A total of 60 patients with suspected peripheral arterial disease were divided into two groups:Group A [30 patients,80 kVp,high pitch （3.2）, and sinogram-affirmed iterative reconstruction （SAFIRE）] and Group 2 [30 patients,120 kVp,low pitch （1.0）, and filtered back projection reconstruction]. Patients of group A received an injection of 80 mL of iodinated contrast medium Ultravist₃70 at a flow rate of 3.0 milliliters per second, followed by a saline volume of 50 mL （flow,3.0 mL/second）. Patients of group B received an injection of 100 mL of iodinated contrast medium Ultravist₃70 at a flow rate of 3.0 milliliters per second, followed by a saline volume of 50 mL （flow,3.0 mL/second）. Test injection technique at knee level was used to determine the scan delay time in group 1. Bolus tracking technique at the level of distal infrarenal abdominal aorta was used to determine the scan delay time in group 2. The image quality, radiation exposure and diagnostic accuracy were compared.Results:The arterial attenuation of group A at sites of aortic bifurcation （AA）, bilateral common femoral arteries （CFA）, bilateral mid-superficial femoral arteries （SFA）, bilateral midcalf （CA） and mean arterial attenuation were 554.03±83.08HU, 569.23±74.95 HU,512.83±97.08 HU,395.95±54.63 HU and 507.78±103.01HU, respectively. The arterial attenuation of group B at sites of A A. CFA. SFA. CA and mean arterial attenuation were 345.33±86.91 HU,320.55±66.52 HU,328.72±61.78 HU,289.52±65.05 HU,317.54±62.03HU, respectively. All the arterial attenuation of group A were significantly higher than group B （all P<0.001）.The image noise in the 120 kVp group was lower than that in the 80 kVp group （9.33±3.79 vs 11.24±3.79 HU. respectively:P< 0.001）.There were significant differences between two groups in mean signal-to-noise ratio （51.04±20.29 vs.34.66±9.94, P<0.001） and contrast-to-noise ratio （44.83±17.93 vs.28.26±9.60. P<0.001）. No difference in subjective image quality was found between two groups （all P>0.05）.For the test injection, time-density curves for popliteal or collateral arteries could be obtained in all patients. Time-density curves for 1 （3.3%） of the 30 patients were obtained from the collateral artery and the opposite popliteal artery.In the assessment of degree of stenoses compared with DSA, there was no significant difference on sensitivity, specificity, positive predictive value, negative predictive value and accuracy of CTA using high-pitch （99%.92%,92%.99%,95%） and standard-pitch （98%,93%.93%,99%,96%）（p> 0.05）. The mean effective dose was significantly lower in 80 kVp group （0.76±0.06 vs.4.29±0.63 mSv, P< 0.001）.Conclusions:The 80-kVp high-pitch CTA of the lower limbs provides good diagnostic accuracy on peripheral arterial occlusive disease compared with DSA whereas with lower radiation dose if acquisition protocols are used in conjunction with test injection technique using monitoring scan at knee level to determine the delay time.