Katharine Tansavatdi MD, Presenter: Nothing to Disclose

Ramit Lamba MBBS, MD, Abstract Co-Author: Nothing to Disclose

John Michael Boone PhD, Abstract Co-Author: Research Consultant, Varian Medical Systems, Inc Speaker, General Electric Company Speaker, Imaging Diagnostic Systems, Inc Researcher, Hologic, Inc

To determine the effect of a sequential decrease in kVp from 120 to 80 on the contrast attenuation of lower extremity arteries during lower extremity run-off MDCT angiography.

Seventy-seven consecutive patients underwent aorto-iliac with lower extremity run-off CTA on a GE 16-detector scanner. In all patients, 150 mL of Omnipaque-350 was injected at 4 ml/sec and real time bolus tracking of the injected contrast was used to time the CTA acquisition. The protocol involved scanning three different anatomic regions at sequentially decreasing kVp: the abdomen and pelvis was scanned at 120 kVp, the thigh at 100 kVp, and the calf at 80 kVp. There was at least a 1 cm overlap between the different regions. In the overlap regions, ROI’s were placed in bilateral common femoral and popliteal arteries to measure contrast attenuation in Hounsfield units (HU) at the same anatomic location at the different tube voltages. For the 77 patients, this resulted in 154 possible data points per kVp change. The absolute and percentage change in attenuation were calculated for each kVp change  

  In 77 patients (age range 6 to 85, mean age 60), out of 154 possible data points, 133 were obtained for the kVp change from 120 (abdomen & pelvis) to 100 (thigh). Twenty-one data points could not be obtained because the vessel was either occluded or too small to obtain a reliable measurement. In all 133, the contrast attenuation increased (mean 112.5 HU, range 2 to 303). The mean percent increase was 33.5% (range 0.6 to 119.8), which was statistically significant (P <0.0001).   In the same patients, 132 data points were obtained for the kVp change from 100 (thigh) to 80 (calf). Twenty-two data points could not be obtained for the same reasons as above. In 115 of 132 (87.1%), the contrast attenuation increased and in 17 (12.9%) it decreased. The overall mean absolute and percent increases were 128.4 HU (range -167 to 443) and 26.2% (range -28.5 to 79.6), respectively. This increase was statistically significant (P <0.0001).    

Sequential decrease in the tube voltage from 120 to 80 significantly improves the arterial contrast attenuation during lower extremity run-off CTA.

Low kVp improves the arterial contrast attenuation in lower extremity CTA and decreases radiation dose. This can allow the use of a lower concentration or rate of injected contrast.

Tansavatdi, K, Lamba, R, Boone, J, Aorto-Iliac with Lower Extremity Run-Off MDCT Angiography: Increased Contrast Attenuation with Sequentially Decreasing kVp.  Radiological Society of North America 2008 Scientific Assembly and Annual Meeting, February 18 - February 20, 2008 ,Chicago IL. http://archive.rsna.org/2008/6007677.html