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Letters to the Editor Dual-Energy CT for Diagnostic CT Colonography From: Musturay Karcaaltincaba, MD, Ilknur Ozdeniz, MD, Department of Radiology, Hacettepe University School of Medicine, Ankara 06100, Turkey e-mail: [email protected]
Editor: We read the article by Cai et al (1) entitled “DualEnergy Electronic Cleansing for Fecal-Tagging CT Colonography” in the May-June 2013 issue of RadioGraphics with great interest. Dual-energy CT is a promising method with abdominal applications (2,3). CT colonography can be used with either diagnostic or screening methods (4). The technique described by Cai et al (1) is promising for use with screening CT colonography with fecal tagging. For diagnostic CT colonography, contrast material–enhanced imaging is used. The main problem with CT colonography with use of either method is differentiation of stool from polyps. We think that dual-energy CT can be useful for this purpose and suggest an alternative approach to that described by Cai et al (1). Fecal tagging is used to differentiate stool from polyps, and Cai et al used dual-energy CT to perform electronic cleansing after fecal tagging. Dual-energy CT can also potentially be used to differentiate stool from polyps by using findings on iodine maps and virtual noncontrast (water) images. This technique can be used for cases of incomplete optical colonoscopy and for patients who cannot use laxatives. The use of a dual-energy CT technique for diagnostic CT colonography and colonoscopy has been described by our group (4). We reported our initial experience with dual-energy dual-source CT colonoscopy in 2009 and also showed the feasibility of using iodine maps and virtual noncontrast images for colon evaluation with dual-source CT and fast kilovoltage-peak switching (2,4). Recently, Boellaard et al (5) reported dualenergy CT characterization of colon tumors without the use of bowel preparation or bowel
distention. In their study, the authors were able to visualize all colorectal tumors on dual-energy CT images. Our unpublished data are promising for differentiation of colon tumors, polyps, and stool by using dual-energy CT without the use of laxatives or fecal tagging. Colonoscopic screening currently is recommended for people older than 50 years. If we want to use CT colonography to screen more people, we must use more practical and widely used methods. The use of laxatives for CT colonography in elderly patients is difficult, and patients may be noncompliant. In clinical practice, most contrast-enhanced CT examinations are obtained in patients with cancer and in elderly patients. In these patients, dual-energy CT may allow noninvasive screening for colon cancer, in addition to evaluation of the primary indication for CT. However, prospective studies are needed to validate this technique. Although a slight dose penalty has been observed for dual-energy CT with the use of early dual-source CT scanners, it is possible to obtain dose-neutral dual-energy CT images by using a newer generation of dual-source CT scanners (2). I would like to congratulate Cai et al for their study of dual-energy CT for electronic cleansing. Dual-energy CT may open new horizons for screening and diagnostic CT colonography.
References 1. Cai W, Kim SH, Lee JG, Yoshida H. Dual-energy electronic cleansing for fecal-tagging CT colonography. RadioGraphics 2013;33(3):891–912. 2. Karcaaltıncaba M, Aktas A. Dual-energy CT revisited with multidetector CT: review of principles and clinical applications. Diagn Interv Radiol 2011; 17(3):181–194. 3. Yeh BM, Shepherd JA, Wang ZJ, Teh HS, Hartman RP, Prevrhal S. Dual-energy and low-kVp CT in the abdomen. AJR Am J Roentgenol 2009;193(1):47–54. 4. Karcaaltincaba M, Karaosmanoglu D, Akata D, Sentürk S, Ozmen M, Alibek S. Dual energy virtual CT colonoscopy with dual source computed tomography: initial experience. Röfo 2009;181(9): 859–862. 5. Boellaard TN, Henneman OD, Streekstra GJ, et al. The feasibility of colorectal cancer detection using dual-energy computed tomography with iodine mapping. Clin Radiol 2013;68(8):799–806.
Letters to the Editor should be submitted at http://ms.manuscriptcentral.com/rg.
LETTERS TO THE EDITOR
847
848 May-June 2014
Dr Cai and colleagues respond: We are grateful for the opportunity to respond to Dr Karcaaltincaba’s comments about our article regarding dual-energy CT colonography. Dr Karcaaltincaba points out two methods to apply dual-energy CT technology to CT colonography: iodine mapping and electronic cleansing. Each method has pros and cons. In the studies by Karcaaltincaba et al (1) and Boellaard et al (2), dual-energy CT colonography was performed with administration of intravenous contrast material. Iodine maps calculated from dual-energy CT colonographic images were used for cancer diagnosis; thus, the method used was diagnostic. The advantage of the iodine mapping method is that it may assist in differentiation of cancer from fecal residuals without the need for bowel preparation and bowel distention. However, its limitation is that its use may be feasible only for detection of large lesions (27–60 mm). In the recently published study by Boellaard et al (2), smaller polyps (7–15 mm) were not detected on iodine maps. In addition, without bowel distention, the capability for three-dimensional (3D) virtual flythrough of the colon is not available for reading of CT colonographic images. All readings in the study by Boellaard et al (2) were performed using two-dimensional CT images. The electronic cleansing method was developed for use with screening CT colonography and makes 3D virtual fly-through of the colon possible by cleansing of tagged fecal residuals. Many clinical studies have demonstrated the feasibility of this method for detection of polyps larger than 6
radiographics.rsna.org
mm. The shortcoming is the inconvenience of the required bowel preparation and colon distention, which may lower patients’ compliance, particularly when a cathartic agent is used for bowel preparation. The use of dual-energy CT may significantly improve the quality of electronic cleansing, as demonstrated in our article. We greatly appreciate Dr Karcaaltincaba’s valuable comments regarding the use of iodine mapping with dual-energy CT colonography and its application to diagnosis of colorectal cancer, which was not covered in our article. His comments provide readers with a complete overview of the use of state-of-the-art dual-energy CT colonography for diagnosis and screening.
References 1. Karcaaltincaba M, Karaosmanoglu D, Akata D, Sentürk S, Ozmen M, Alibek S. Dual energy virtual CT colonoscopy with dual source computed tomography: initial experience. Röfo 2009;181(9): 859–862. 2. Boellaard TN, Henneman OD, Streekstra GJ, et al. The feasibility of colorectal cancer detection using dual-energy computed tomography with iodine mapping. Clin Radiol 2013;68(8):799–806.
Wenli Cai, PhD, June-Goo Lee, PhD, Hiroyuki Yoshida, PhD, Department of Radiology, Massachusetts General Hospital and Harvard Medical School, 25 New Chardon St, 400C, Boston, MA 02114 Se Hyung Kim, MD, Department of Radiology, Seoul National University Hospital College of Medicine, Seoul, Korea e-mail: [email protected]
Letters to the Editor Dual-Energy CT for Diagnostic CT Colonography From: Musturay Karcaaltincaba, MD, Ilknur Ozdeniz, MD, Department of Radiology, Hacettepe University School of Medicine, Ankara 06100, Turkey e-mail: [email protected]
Editor: We read the article by Cai et al (1) entitled “DualEnergy Electronic Cleansing for Fecal-Tagging CT Colonography” in the May-June 2013 issue of RadioGraphics with great interest. Dual-energy CT is a promising method with abdominal applications (2,3). CT colonography can be used with either diagnostic or screening methods (4). The technique described by Cai et al (1) is promising for use with screening CT colonography with fecal tagging. For diagnostic CT colonography, contrast material–enhanced imaging is used. The main problem with CT colonography with use of either method is differentiation of stool from polyps. We think that dual-energy CT can be useful for this purpose and suggest an alternative approach to that described by Cai et al (1). Fecal tagging is used to differentiate stool from polyps, and Cai et al used dual-energy CT to perform electronic cleansing after fecal tagging. Dual-energy CT can also potentially be used to differentiate stool from polyps by using findings on iodine maps and virtual noncontrast (water) images. This technique can be used for cases of incomplete optical colonoscopy and for patients who cannot use laxatives. The use of a dual-energy CT technique for diagnostic CT colonography and colonoscopy has been described by our group (4). We reported our initial experience with dual-energy dual-source CT colonoscopy in 2009 and also showed the feasibility of using iodine maps and virtual noncontrast images for colon evaluation with dual-source CT and fast kilovoltage-peak switching (2,4). Recently, Boellaard et al (5) reported dualenergy CT characterization of colon tumors without the use of bowel preparation or bowel
distention. In their study, the authors were able to visualize all colorectal tumors on dual-energy CT images. Our unpublished data are promising for differentiation of colon tumors, polyps, and stool by using dual-energy CT without the use of laxatives or fecal tagging. Colonoscopic screening currently is recommended for people older than 50 years. If we want to use CT colonography to screen more people, we must use more practical and widely used methods. The use of laxatives for CT colonography in elderly patients is difficult, and patients may be noncompliant. In clinical practice, most contrast-enhanced CT examinations are obtained in patients with cancer and in elderly patients. In these patients, dual-energy CT may allow noninvasive screening for colon cancer, in addition to evaluation of the primary indication for CT. However, prospective studies are needed to validate this technique. Although a slight dose penalty has been observed for dual-energy CT with the use of early dual-source CT scanners, it is possible to obtain dose-neutral dual-energy CT images by using a newer generation of dual-source CT scanners (2). I would like to congratulate Cai et al for their study of dual-energy CT for electronic cleansing. Dual-energy CT may open new horizons for screening and diagnostic CT colonography.
References 1. Cai W, Kim SH, Lee JG, Yoshida H. Dual-energy electronic cleansing for fecal-tagging CT colonography. RadioGraphics 2013;33(3):891–912. 2. Karcaaltıncaba M, Aktas A. Dual-energy CT revisited with multidetector CT: review of principles and clinical applications. Diagn Interv Radiol 2011; 17(3):181–194. 3. Yeh BM, Shepherd JA, Wang ZJ, Teh HS, Hartman RP, Prevrhal S. Dual-energy and low-kVp CT in the abdomen. AJR Am J Roentgenol 2009;193(1):47–54. 4. Karcaaltincaba M, Karaosmanoglu D, Akata D, Sentürk S, Ozmen M, Alibek S. Dual energy virtual CT colonoscopy with dual source computed tomography: initial experience. Röfo 2009;181(9): 859–862. 5. Boellaard TN, Henneman OD, Streekstra GJ, et al. The feasibility of colorectal cancer detection using dual-energy computed tomography with iodine mapping. Clin Radiol 2013;68(8):799–806.
Letters to the Editor should be submitted at http://ms.manuscriptcentral.com/rg.
LETTERS TO THE EDITOR
847
848 May-June 2014
Dr Cai and colleagues respond: We are grateful for the opportunity to respond to Dr Karcaaltincaba’s comments about our article regarding dual-energy CT colonography. Dr Karcaaltincaba points out two methods to apply dual-energy CT technology to CT colonography: iodine mapping and electronic cleansing. Each method has pros and cons. In the studies by Karcaaltincaba et al (1) and Boellaard et al (2), dual-energy CT colonography was performed with administration of intravenous contrast material. Iodine maps calculated from dual-energy CT colonographic images were used for cancer diagnosis; thus, the method used was diagnostic. The advantage of the iodine mapping method is that it may assist in differentiation of cancer from fecal residuals without the need for bowel preparation and bowel distention. However, its limitation is that its use may be feasible only for detection of large lesions (27–60 mm). In the recently published study by Boellaard et al (2), smaller polyps (7–15 mm) were not detected on iodine maps. In addition, without bowel distention, the capability for three-dimensional (3D) virtual flythrough of the colon is not available for reading of CT colonographic images. All readings in the study by Boellaard et al (2) were performed using two-dimensional CT images. The electronic cleansing method was developed for use with screening CT colonography and makes 3D virtual fly-through of the colon possible by cleansing of tagged fecal residuals. Many clinical studies have demonstrated the feasibility of this method for detection of polyps larger than 6
radiographics.rsna.org
mm. The shortcoming is the inconvenience of the required bowel preparation and colon distention, which may lower patients’ compliance, particularly when a cathartic agent is used for bowel preparation. The use of dual-energy CT may significantly improve the quality of electronic cleansing, as demonstrated in our article. We greatly appreciate Dr Karcaaltincaba’s valuable comments regarding the use of iodine mapping with dual-energy CT colonography and its application to diagnosis of colorectal cancer, which was not covered in our article. His comments provide readers with a complete overview of the use of state-of-the-art dual-energy CT colonography for diagnosis and screening.
References 1. Karcaaltincaba M, Karaosmanoglu D, Akata D, Sentürk S, Ozmen M, Alibek S. Dual energy virtual CT colonoscopy with dual source computed tomography: initial experience. Röfo 2009;181(9): 859–862. 2. Boellaard TN, Henneman OD, Streekstra GJ, et al. The feasibility of colorectal cancer detection using dual-energy computed tomography with iodine mapping. Clin Radiol 2013;68(8):799–806.
Wenli Cai, PhD, June-Goo Lee, PhD, Hiroyuki Yoshida, PhD, Department of Radiology, Massachusetts General Hospital and Harvard Medical School, 25 New Chardon St, 400C, Boston, MA 02114 Se Hyung Kim, MD, Department of Radiology, Seoul National University Hospital College of Medicine, Seoul, Korea e-mail: [email protected]
