School of Medicine and Health Sciences Poster Presentations

Title

Pre- and Post-Contrast Dual Energy CT: Is Post-Contrast Attenuation Different for Single and Dual Energy Modes?

Document Type

Poster

Abstract Category

Clinical Specialties

Keywords

Computed Tomography, Dual Energy, Abdominal Imaging, Contrast

Publication Date

Spring 5-1-2019

Abstract

Background: Dual energy CT (DECT) is increasingly being used in clinical practice due to its assortment of applications beyond those of conventional single energy CT (SECT). While SECT and DECT attenuations are relatively comparable, small differences in the soft tissue attenuation range are not well established. Thresholds for lesion enhancement were created with SECT and small deviations between SECT and DECT attenuations could affect interpretation for enhancement. As a result, differences in post-contrast attenuation values between SECT and DECT may result in the overcalling or undercalling of these lesions. The purpose of this study is to compare attenuations between SECT images and 70 keV dual energy monochromatic image reconstructions (70MI). Methods: Four rows of four tubes containing saline and three dilutions of iodinated contrast (with approximate SECT attenuations of 5, 15, 25, and 35 HU) were suspended in a plastic water filled abdominal phantom. The phantom was scanned five times in SECT (120 kVp) and DECT (100/140 kVp and 80/140 kVp) modes with a CTDIvol of 8 and 16 mGy and constant remaining settings. 70MI reconstructions, considered the 120 kVp SECT equivalent-image, were then created. SECT and 70MI attenuations and noise were measured for each tube using 2.0 cm2 regions of interest and were compared using the Wilcoxon signed rank test. Results: All tubes had greater attenuation on 70MI than SECT (p < 0.01), with larger deviations at high attenuation tubes. The 70MI mode overestimated SECT attenuations by a mean of 6.5 ± 1.8 HU (range 2.1-10.6 HU) and 9.4 ± 2.3 HU (range 5.6 - 15.5 HU) for the 25 and 35 HU tubes respectively. There was no difference between deviations at CTDIvol of 8 and 16 mGy (p = 0.20). 70MI had slightly more noise than SECT with CTDIvol of 16 mGy (p < 0.02), although there was no difference in noise levels at CTDIvol of 8 mGy. Conclusion: At high iodine concentrations, 70MI DECT post-contrast imaging can overestimate enhancement attenuation as compared to SECT. Radiologists should be aware of these deviations when measuring attenuations with 70MI DECT.

Open Access

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Presented at Research Days 2019.

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Pre- and Post-Contrast Dual Energy CT: Is Post-Contrast Attenuation Different for Single and Dual Energy Modes?

Background: Dual energy CT (DECT) is increasingly being used in clinical practice due to its assortment of applications beyond those of conventional single energy CT (SECT). While SECT and DECT attenuations are relatively comparable, small differences in the soft tissue attenuation range are not well established. Thresholds for lesion enhancement were created with SECT and small deviations between SECT and DECT attenuations could affect interpretation for enhancement. As a result, differences in post-contrast attenuation values between SECT and DECT may result in the overcalling or undercalling of these lesions. The purpose of this study is to compare attenuations between SECT images and 70 keV dual energy monochromatic image reconstructions (70MI). Methods: Four rows of four tubes containing saline and three dilutions of iodinated contrast (with approximate SECT attenuations of 5, 15, 25, and 35 HU) were suspended in a plastic water filled abdominal phantom. The phantom was scanned five times in SECT (120 kVp) and DECT (100/140 kVp and 80/140 kVp) modes with a CTDIvol of 8 and 16 mGy and constant remaining settings. 70MI reconstructions, considered the 120 kVp SECT equivalent-image, were then created. SECT and 70MI attenuations and noise were measured for each tube using 2.0 cm2 regions of interest and were compared using the Wilcoxon signed rank test. Results: All tubes had greater attenuation on 70MI than SECT (p < 0.01), with larger deviations at high attenuation tubes. The 70MI mode overestimated SECT attenuations by a mean of 6.5 ± 1.8 HU (range 2.1-10.6 HU) and 9.4 ± 2.3 HU (range 5.6 - 15.5 HU) for the 25 and 35 HU tubes respectively. There was no difference between deviations at CTDIvol of 8 and 16 mGy (p = 0.20). 70MI had slightly more noise than SECT with CTDIvol of 16 mGy (p < 0.02), although there was no difference in noise levels at CTDIvol of 8 mGy. Conclusion: At high iodine concentrations, 70MI DECT post-contrast imaging can overestimate enhancement attenuation as compared to SECT. Radiologists should be aware of these deviations when measuring attenuations with 70MI DECT.