Detection of Lumbar Disk Herniation with Virtual Noncalcium Dual-Energy CT: Is This a Real Virtual Noncalcium Image?

Abstract

HomeRadiologyVol. 292, No. 2 PreviousNext CommunicationsFree AccessLetters to the EditorDetection of Lumbar Disk Herniation with Virtual Noncalcium Dual-Energy CT: Is This a Real Virtual Noncalcium Image?Chankue Park* , JaeWon Choi†, Hee Seok Jeong*Chankue Park* , JaeWon Choi†, Hee Seok Jeong*Author AffiliationsDepartment of Radiology, Pusan National University Yangsan Hospital, 20 Geumo-ro, Mulgeum-eup, Yangsan-si, Gyeongsananam-do 50612, Korea*Healthcare Sector, Siemens Healthineers Korea, Seoul, Korea†e-mail: [email protected]Chankue Park* JaeWon Choi†Hee Seok Jeong*Published Online:Jul 2 2019https://doi.org/10.1148/radiol.2019190883MoreSectionsPDF ToolsImage ViewerAdd to favoritesCiteTrack CitationsPermissionsReprints ShareShare onFacebookTwitterLinked In Editor:We read with interest the article by Dr Booz and colleagues in the February 2019 issue of Radiology, “Virtual Noncalcium Dual-Energy CT: Detection of Lumbar Disk Herniation in Comparison with Standard Gray-Scale CT” (1). Dr Booz and colleagues used a virtual noncalcium (VNCa) reconstruction algorithm optimized for the analysis of intervertebral disks applied by using dedicated software settings (color lookup tables low-energy value, spectrum; color lookup tables high-energy value, gray scale; CT preset 1, liver; and CT preset 2, bone). However, we noted several issues with regard to the reconstruction methods in the study.First, the images obtained with the reconstruction method may not be VNCa images. VNCa images are obtained by subtracting calcium from unenhanced CT images with a mathematical subtraction of the substances with a relevant photoelectric effect and Compton scattering based on the fact that attenuation at different energy levels is different (2). However, the images obtained by Dr Booz and colleagues are not images created by material decomposition with mathematic subtraction; they are images with color coding after overlapping a low-kilovolt-peak CT image with the liver setting and a high-kilovolt-peak image with the bone setting. We believe that if Dr Booz and colleagues used the VNCa result, they should be shown as VNCa and calcium map images and not as an overlap of two series of high- and low-energy data sets.Moreover, we can make a similar color-coded image using a single-energy CT image rather than a dual-energy CT image by setting the CT preset to liver and the color lookup table to spectrum. We can also create a very similar color-coded image by reconstructing the single-energy CT series twice and overlapping these series after applying the same color lookup table and window according to the values specified in this study because the image is reconstructed by overlapping without material decomposition.In conclusion, we think that depicting lumbar disk herniation well with color-coded overlapping images from different energy-level images with different color lookup tables and window settings is a novel approach. However, the images in this study may not be VNCa images and might have been obtained without a dual-energy CT image.Disclosures of Conflicts of Interest: C.P. disclosed no relevant relationships. J.C. disclosed no relevant relationships. H.S.J. disclosed no relevant relationships.