Philipp Riffel MD, Presenter: Nothing to Disclose

Stefan Haneder MD, Abstract Co-Author: Nothing to Disclose

Holger Haubenreisser, Abstract Co-Author: Nothing to Disclose

Bernhard Schmidt PhD, Abstract Co-Author: Employee, Siemens AG

Stefan Oswald Schoenberg MD, PhD, Abstract Co-Author: Institutional research agreement, Siemens AG

Thomas Henzler MD, Abstract Co-Author: Nothing to Disclose

Previous studies have demonstrated that calculated low keV monoenergetic datasets from Dual energy (DE)CT angiography of the lower extremity can significantly improve contrast-to-noise ratio (CNR) when compared to polyenergetic images (PEI). However, monoenergetic ultra-low keV datasets below 60 keV did not lead to improved CNR due to the dramatic increase in image noise at lower keV levels. The recently introduced frequency-split technique combines the lower spatial frequency stack at low keV for high contrast with the high spatial frequency stack for image noise at high keV levels to calculate noise-reduced images at ultra-low keV levels below 60 keV. The aim of this study was to evaluate the objective image quality of ultra-low keV virtual monoenergetic images (MEIs) calculated from lower extremity DECT angiography data.

20 patients (15 male; mean age 73±13 years) who underwent DECT angiography of the lower extremity were retrospectively included in this study. MEIs from 40 to 120 keV were reconstructed using the frequency-split technique. Signal intensity, noise, signal-to-noise ratio (SNR) and contrast-to-noise ratio (CNR) were assessed in external iliac, femoral, popliteal, and lower leg arteries. Comparisons between MEIs and PEIs were performed using a Mann-Whitney U test.

120 arteries were evaluated. 60, 50 and 40 keV images resulted in the greatest improvements in vessel attenuation (+26%, +85%, +180% all p < 0.05) and SNR (+53%, +48%, +48%, all p < 0.05) compared to PEIs. The highest CNR values were found in 50 keV MEIs (18.6 ± 10.4 averaged over all arteries), which were significantly higher compared to PEI (11.7 ± 6.9 averaged over all arteries, all p < 0.05).

Combining the lower spatial frequency stack for contrast at low keV levels with the high spatial frequency stack for noise at high keV levels leads to improved image quality of ultra-low keV monoenergetic lower extremity DECT datasets when compared to previous monoenergetic reconstruction techniques without the frequency-split technique.

With a frequency split approach, 40, 50 and 60 keV MEIs provide improved objective image quality in DECT lower extremity angiography compared to standard PEI and should therefore be considered for clinical use when DECT angiography of the lower extremity vessels is performed.

Riffel, P, Haneder, S, Haubenreisser, H, Schmidt, B, Schoenberg, S, Henzler, T, Lower Extremity Dual-energy CT Angiography: Evaluation of Ultra-low keV Calculated Monoenergetic Datasets by Means of a Frequency-split Approach for Noise Reduction at Ultra-low keV Levels.  Radiological Society of North America 2014 Scientific Assembly and Annual Meeting, - ,Chicago IL. http://archive.rsna.org/2014/14013123.html