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RG • Volume 34 Number 7
Ameli-Renani et al 1791
Invited Commentary on “Dual-Energy CT for Imaging of Pulmonary Hypertension” From: Myrna Cobos Barco Godoy, MD, PhD Department of Diagnostic Radiology, University of Texas MD Anderson Cancer Center Houston, Texas In the past few years, radiologists have been fortunate to witness significant developments in imaging technology. These developments have allowed advanced imaging techniques such as DECT to be used in clinical practice. By using two different energies, DECT allows material-specific imaging through a mathematical process called material decomposition (1). Although DECT is not a novel concept and actually was proposed more than 30 years ago, only recently has image misregistration, a major limitation caused by the initial sequential acquisition technique, been overcome by use of single-acquisition DECT. The radiology group from St George’s Hospital in London, England, led by Dr Ioannis Vlahos, presents a thorough review of DECT for imaging of PH (2). Ameli-Renani et al (2) provide innovative insights into CT functional imaging of PH by combining the usual vascular analysis with qualitative and quantitative functional information regarding parenchymal enhancement. This information is obtained by using PBV postprocessing analysis as a surrogate indicator of lung perfusion, which allows the evaluation of perfusion inhomogeneities that may be useful in severity assessment and prognostication. Importantly, this is achieved without an increase in radiation dose. In addition, the authors illustrate the benefits of the low-kilovoltage imaging provided by DECT with increased iodine conspicuity, which overall improves vascular visualization and is particularly useful for characterizing prominent bronchial arteries. The authors also demonstrate the use of three-dimensional color-coded vascular maps as an interesting new method to display vascular perfusion for diagnosis and treatment monitoring of pulmonary embolism. Because DECT provides functional perfusion information similar to that of V/Q imaging and also provides high anatomic resolution for vessels, the authors raise the possibility of using the technique as a single diagnostic and preoperative planning study for patients with CTEPH (2). DECT adds a functional component to the anatomic information provided by multi detector CT and is a step forward in eliminating the need for multiple different imaging modalities to optimally evaluate PH. DECT has a wide range of potential applications and currently is being used clinically across
the United States. The advantages of DECT in the setting of acute pulmonary embolism, for example, have been well established. As pointed out by Ameli-Renani et al (2), the use of PBV associated to assessment of endoluminal vascular enhancement has been shown to improve detection, severity assessment, and treatment follow-up of pulmonary embolism (3–5). In addition, DECT may be beneficial in the evaluation of other vascular conditions such as aortic disease (6,7). Of particular interest is the use of reconstructed virtual nonenhanced (noncontrast) images and lowkilovoltage imaging in the evaluation of aortic endovascular repair. The combination of delayed phase low-kilovoltage images and postprocessed virtual nonenhanced images as a replacement for the traditional triple-phase protocol (with nonenhanced, arterial phase, and delayed phase image acquisition) enables detection of endoleaks after endovascular aortic aneurysm repair with high accuracy and a considerably lower radiation dose (a reduction of up to 60%) (8,9). Other clinical applications of DECT are as broad as characterization of lung nodule enhancement in a single-phase acquisition study (10), characterization of the chemical composition of kidney stones (11), and noninvasive detection of monosodium urate deposits in patients with gout (12). Recently, the use of DECT is being explored in oncology, including the complementary assessment of vascular enhancement in tumor monitoring, which is a promising method for evaluation of antiangiogenic therapy (13). In addition, DECT could be used as a “one-stop” comprehensive evaluation in baseline tumor staging, with simultaneous characterization of pulmonary perfusion enhancement for prediction of postoperative pulmonary function in patients being considered for lung resection (14). Although DECT has been commercially available for years, its widespread dissemination in clinical practice is yet to occur. The reasons for this are multifactorial and include equipment-related costs, lack of awareness, the need for further validation of several potential clinical applications, and the increasing demand for high clinical productivity that can preclude radiologists from spending the time required for image postprocessing. As with other available technologies
1792 November-December 2014
such as computer-aided detection and diagnosis, refinements that allow automated image postprocessing with specific CT protocols for different clinical indications and automated image transferal to a picture archiving and communication system (PACS) would facilitate the use of PBV maps, iodine maps, virtual nonenhanced images, and other DECT applications in daily imaging evaluation. Ameli-Renani et al (2) have provided an excellent comprehensive review of advanced CT techniques for imaging evaluation of PH, with new insights for potential improvements in patient care. With increased awareness of DECT, further studies for validation, and advances in the automation of postprocessing applications, the use of DECT is expected to become a more common clinical practice in the near future. Disclosures of Conflicts of Interest.—M.C.B.G: Ac-
tivities related to the present article: research grant from Siemens Medical Solutions. Activities not related to the present article: disclosed no relevant relationships. Other activities: disclosed no relevant relationships.
References 1. Johnson TR, Krauss B, Sedlmair M, et al. Material differentiation by dual energy CT: initial experience. Eur Radiol 2007;17(6):1510–1517. 2. Ameli-Renani S, Rahman F, Nair A, et al. Dualenergy CT for imaging of pulmonary hypertension: challenges and opportunities. RadioGraphics 2014;34(7):1769–1790. 3. Thieme SF, Ashoori N, Bamberg F, et al. Severity assessment of pulmonary embolism using dual energy CT: correlation of a pulmonary perfusion defect score with clinical and morphological parameters of blood oxygenation and right ventricular failure. Eur Radiol 2012;22(2):269–278. 4. Lee CW, Seo JB, Song JW, et al. Evaluation of computer-aided detection and dual energy software in detection of peripheral pulmonary embolism on
radiographics.rsna.org dual-energy pulmonary CT angiography. Eur Radiol 2011;21(1):54–62. 5. Thieme SF, Graute V, Nikolaou K, et al. Dual energy CT lung perfusion imaging: correlation with SPECT/CT. Eur J Radiol 2012;81(2):360–365. 6. Vlahos I, Godoy MC, Naidich DP. Dual-energy computed tomography imaging of the aorta. J Thorac Imaging 2010;25(4):289–300. 7. Godoy MC, Naidich DP, Marchiori E, et al. Singleacquisition dual-energy multidetector computed tomography: analysis of vascular enhancement and postprocessing techniques for evaluating the thoracic aorta. J Comput Assist Tomogr 2010;34(5): 670–677. 8. Chandarana H, Godoy MC, Vlahos I, et al. Abdominal aorta: evaluation with dual-source dual-energy multidetector CT after endovascular repair of aneurysms—initial observations. Radiology 2008;249(2): 692–700. 9. Stolzmann P, Frauenfelder T, Pfammatter T, et al. Endoleaks after endovascular abdominal aortic aneurysm repair: detection with dual-energy dualsource CT. Radiology 2008;249(2):682–691. 10. Chae EJ, Song JW, Seo JB, Krauss B, Jang YM, Song KS. Clinical utility of dual-energy CT in the evaluation of solitary pulmonary nodules: initial experience. Radiology 2008;249(2):671–681. 11. Manglaviti G, Tresoldi S, Guerrer CS, et al. In vivo evaluation of the chemical composition of urinary stones using dual-energy CT. AJR Am J Roentgenol 2011;197(1):W76–W83. 12. Bongartz T, Glazebrook KN, Kavros SJ, et al. Dualenergy CT for the diagnosis of gout: an accuracy and diagnostic yield study. Ann Rheum Dis doi:10.1136/annrheumdis-2013-205095. Published online March 25, 2014. Accessed June 5, 2014. 13. Kim YN, Lee HY, Lee KS, et al. Dual-energy CT in patients treated with anti-angiogenic agents for non-small cell lung cancer: new method of monitoring tumor response? Korean J Radiol 2012;13(6): 702–710. 14. Chae EJ, Kim N, Seo JB, et al. Prediction of postoperative lung function in patients undergoing lung resection: dual-energy perfusion computed tomography versus perfusion scintigraphy. Invest Radiol 2013;48(8):622–627.
RG • Volume 34 Number 7
Ameli-Renani et al 1791
Invited Commentary on “Dual-Energy CT for Imaging of Pulmonary Hypertension” From: Myrna Cobos Barco Godoy, MD, PhD Department of Diagnostic Radiology, University of Texas MD Anderson Cancer Center Houston, Texas In the past few years, radiologists have been fortunate to witness significant developments in imaging technology. These developments have allowed advanced imaging techniques such as DECT to be used in clinical practice. By using two different energies, DECT allows material-specific imaging through a mathematical process called material decomposition (1). Although DECT is not a novel concept and actually was proposed more than 30 years ago, only recently has image misregistration, a major limitation caused by the initial sequential acquisition technique, been overcome by use of single-acquisition DECT. The radiology group from St George’s Hospital in London, England, led by Dr Ioannis Vlahos, presents a thorough review of DECT for imaging of PH (2). Ameli-Renani et al (2) provide innovative insights into CT functional imaging of PH by combining the usual vascular analysis with qualitative and quantitative functional information regarding parenchymal enhancement. This information is obtained by using PBV postprocessing analysis as a surrogate indicator of lung perfusion, which allows the evaluation of perfusion inhomogeneities that may be useful in severity assessment and prognostication. Importantly, this is achieved without an increase in radiation dose. In addition, the authors illustrate the benefits of the low-kilovoltage imaging provided by DECT with increased iodine conspicuity, which overall improves vascular visualization and is particularly useful for characterizing prominent bronchial arteries. The authors also demonstrate the use of three-dimensional color-coded vascular maps as an interesting new method to display vascular perfusion for diagnosis and treatment monitoring of pulmonary embolism. Because DECT provides functional perfusion information similar to that of V/Q imaging and also provides high anatomic resolution for vessels, the authors raise the possibility of using the technique as a single diagnostic and preoperative planning study for patients with CTEPH (2). DECT adds a functional component to the anatomic information provided by multi detector CT and is a step forward in eliminating the need for multiple different imaging modalities to optimally evaluate PH. DECT has a wide range of potential applications and currently is being used clinically across
the United States. The advantages of DECT in the setting of acute pulmonary embolism, for example, have been well established. As pointed out by Ameli-Renani et al (2), the use of PBV associated to assessment of endoluminal vascular enhancement has been shown to improve detection, severity assessment, and treatment follow-up of pulmonary embolism (3–5). In addition, DECT may be beneficial in the evaluation of other vascular conditions such as aortic disease (6,7). Of particular interest is the use of reconstructed virtual nonenhanced (noncontrast) images and lowkilovoltage imaging in the evaluation of aortic endovascular repair. The combination of delayed phase low-kilovoltage images and postprocessed virtual nonenhanced images as a replacement for the traditional triple-phase protocol (with nonenhanced, arterial phase, and delayed phase image acquisition) enables detection of endoleaks after endovascular aortic aneurysm repair with high accuracy and a considerably lower radiation dose (a reduction of up to 60%) (8,9). Other clinical applications of DECT are as broad as characterization of lung nodule enhancement in a single-phase acquisition study (10), characterization of the chemical composition of kidney stones (11), and noninvasive detection of monosodium urate deposits in patients with gout (12). Recently, the use of DECT is being explored in oncology, including the complementary assessment of vascular enhancement in tumor monitoring, which is a promising method for evaluation of antiangiogenic therapy (13). In addition, DECT could be used as a “one-stop” comprehensive evaluation in baseline tumor staging, with simultaneous characterization of pulmonary perfusion enhancement for prediction of postoperative pulmonary function in patients being considered for lung resection (14). Although DECT has been commercially available for years, its widespread dissemination in clinical practice is yet to occur. The reasons for this are multifactorial and include equipment-related costs, lack of awareness, the need for further validation of several potential clinical applications, and the increasing demand for high clinical productivity that can preclude radiologists from spending the time required for image postprocessing. As with other available technologies
1792 November-December 2014
such as computer-aided detection and diagnosis, refinements that allow automated image postprocessing with specific CT protocols for different clinical indications and automated image transferal to a picture archiving and communication system (PACS) would facilitate the use of PBV maps, iodine maps, virtual nonenhanced images, and other DECT applications in daily imaging evaluation. Ameli-Renani et al (2) have provided an excellent comprehensive review of advanced CT techniques for imaging evaluation of PH, with new insights for potential improvements in patient care. With increased awareness of DECT, further studies for validation, and advances in the automation of postprocessing applications, the use of DECT is expected to become a more common clinical practice in the near future. Disclosures of Conflicts of Interest.—M.C.B.G: Ac-
tivities related to the present article: research grant from Siemens Medical Solutions. Activities not related to the present article: disclosed no relevant relationships. Other activities: disclosed no relevant relationships.
References 1. Johnson TR, Krauss B, Sedlmair M, et al. Material differentiation by dual energy CT: initial experience. Eur Radiol 2007;17(6):1510–1517. 2. Ameli-Renani S, Rahman F, Nair A, et al. Dualenergy CT for imaging of pulmonary hypertension: challenges and opportunities. RadioGraphics 2014;34(7):1769–1790. 3. Thieme SF, Ashoori N, Bamberg F, et al. Severity assessment of pulmonary embolism using dual energy CT: correlation of a pulmonary perfusion defect score with clinical and morphological parameters of blood oxygenation and right ventricular failure. Eur Radiol 2012;22(2):269–278. 4. Lee CW, Seo JB, Song JW, et al. Evaluation of computer-aided detection and dual energy software in detection of peripheral pulmonary embolism on
radiographics.rsna.org dual-energy pulmonary CT angiography. Eur Radiol 2011;21(1):54–62. 5. Thieme SF, Graute V, Nikolaou K, et al. Dual energy CT lung perfusion imaging: correlation with SPECT/CT. Eur J Radiol 2012;81(2):360–365. 6. Vlahos I, Godoy MC, Naidich DP. Dual-energy computed tomography imaging of the aorta. J Thorac Imaging 2010;25(4):289–300. 7. Godoy MC, Naidich DP, Marchiori E, et al. Singleacquisition dual-energy multidetector computed tomography: analysis of vascular enhancement and postprocessing techniques for evaluating the thoracic aorta. J Comput Assist Tomogr 2010;34(5): 670–677. 8. Chandarana H, Godoy MC, Vlahos I, et al. Abdominal aorta: evaluation with dual-source dual-energy multidetector CT after endovascular repair of aneurysms—initial observations. Radiology 2008;249(2): 692–700. 9. Stolzmann P, Frauenfelder T, Pfammatter T, et al. Endoleaks after endovascular abdominal aortic aneurysm repair: detection with dual-energy dualsource CT. Radiology 2008;249(2):682–691. 10. Chae EJ, Song JW, Seo JB, Krauss B, Jang YM, Song KS. Clinical utility of dual-energy CT in the evaluation of solitary pulmonary nodules: initial experience. Radiology 2008;249(2):671–681. 11. Manglaviti G, Tresoldi S, Guerrer CS, et al. In vivo evaluation of the chemical composition of urinary stones using dual-energy CT. AJR Am J Roentgenol 2011;197(1):W76–W83. 12. Bongartz T, Glazebrook KN, Kavros SJ, et al. Dualenergy CT for the diagnosis of gout: an accuracy and diagnostic yield study. Ann Rheum Dis doi:10.1136/annrheumdis-2013-205095. Published online March 25, 2014. Accessed June 5, 2014. 13. Kim YN, Lee HY, Lee KS, et al. Dual-energy CT in patients treated with anti-angiogenic agents for non-small cell lung cancer: new method of monitoring tumor response? Korean J Radiol 2012;13(6): 702–710. 14. Chae EJ, Kim N, Seo JB, et al. Prediction of postoperative lung function in patients undergoing lung resection: dual-energy perfusion computed tomography versus perfusion scintigraphy. Invest Radiol 2013;48(8):622–627.
