Sebastian Tobias Schindera MD, Presenter: Nothing to Disclose

Rendon C. Nelson MD, Abstract Co-Author: Consultant, General Electric Company Research support, Bracco Group Research support, Covidien AG Speakers Bureau, Siemens AG

Terry T. Yoshizumi PhD, Abstract Co-Author: Research support, General Electric Company

Greta Toncheva BS, Abstract Co-Author: Nothing to Disclose

Peter Vock MD, Abstract Co-Author: Nothing to Disclose

Zsolt Szucs-Farkas MD, PhD, Abstract Co-Author: Nothing to Disclose

To assess optimal tube voltage for MDCT angiography in reference to the signal-to-noise ratio (SNR) and the effective dose (ED).

The abdomen and pelvis of an adult female anthropomorphic phantom (Model 702; CIRS Inc., Norfolk, VA, USA) was scanned on a 64-slice MDCT scanner (LightSpeed VCT, GE Healthcare) (64x0.625 mm, pitch 1.35) using four different tube voltages: (A) 140 kVp, (B) 120 kVp (C) 100 kVp, and (D) 80 kVp. To achieve similar noise, automatic tube current modulation was applied with a noise index of 20 HU. To determine the ED for the four tube voltages, 20 high-sensitivity metal oxide semiconductor field effect transistors were imbedded in the phantom. Image noise was measured in the center of the phantom. Three plastic vials filled with 14 mL of different concentrations of iodinated solution (5, 7.5, and 10 mgI/mL) were placed on the phantom’s abdomen. Attenuation measurements were obtained from each iodinated solution and the SNR was calculated. A figure of merit (FOM) for each iodinated solution was computed as SNR2/ED. Analysis of variance was used for verification of statistically significant differences (P < 0.05).

Image noise was maintained as the tube voltage decreased from 140 to 80 kVp: (A) 18.5 HU ± 0.3, (B) 19.2 HU ± 1.2 (C) 19.1 HU ± 1.1, and (D) 21.4 HU ± 2.4 (P > 0.05). The attenuation of the iodinated solutions increased significantly with decreasing tube voltage (P < 0.001). The ED was kept similar for the four different tube voltages: (A) 2.7 mSv ± 0.5, (B) 2.2 mSv ± 0.2, (C) 2.1 mSv ± 0.2 , and (D) 2.2 mSv ± 0.4 (P > 0.05). The FOM results indicated that at constant ED, a reduction of kVp from 140 to 120, 100, and 80, increases the SNR by at least a factor of 1.3, 1.7, and 2.1, respectively (P < 0.001). At constant SNR, corresponding reductions in ED are by a factor of 1.6, 2.9, and 4.2, respectively (P < 0.001).

Using a tube voltage of 80 kVp for MDCT angiography, the SNR can be substantially increased at a constant radiation dose or the radiation dose can be substantially decreased at a constant SNR.

With recent advent of high output MDCT scanners, delivering up to 800 mA, the tube voltage has to be lowered for MDCT angiography to increase efficiency in radiation dose and contrast media volume.

Schindera, S, Nelson, R, Yoshizumi, T, Toncheva, G, Vock, P, Szucs-Farkas, Z, Optimal Selection of Tube Voltage for MDCT Angiography: Effect on Image Quality and Radiation Dose in an Anthropomorphic Phantom Study.  Radiological Society of North America 2008 Scientific Assembly and Annual Meeting, February 18 - February 20, 2008 ,Chicago IL. http://archive.rsna.org/2008/6007477.html