Published January 19, 2012 as 10.3174/ajnr.A2909 Differentiation of Hemorrhage from Iodinated Contrast in Different Intracranial Compartments ORIGINAL RESEARCH Using Dual-Energy Head CT C.M. Phan BACKGROUND AND PURPOSE: Identification of ICH, particularly after ischemic stroke therapy, is A.J. Yoo important for guiding subsequent antithrombotic management and is often confounded by contrast staining or extravasations within intracerebral or extra-axial compartments. This study evaluates the J.A. Hirsch accuracy of DECT in distinguishing ICH from iodinated contrast in patients who received contrast via R.G. Nogueira IA or IV delivery. R. Gupta MATERIALS AND METHODS: Forty patients who had received IA or IV contrast were evaluated using a DECT scanner at 80kV and 140kV to distinguish hyperdensities secondary to contrast staining or extravasation from those representing ICH. A 3-material decomposition algorithm was used to obtain virtual noncontrast images and iodine overlay images. Sensitivity, specificity, and accuracy of DECT in prospectively distinguishing intracranial contrast from hemorrhage within parenchymal, subarachnoid, extra-axial, intraventricular, and intra-arterial compartments were computed using routine clinical follow-up imaging as the standard of reference. RESULTS: A total of 148 foci of intracranial hyperattenuation were identified. Of these, 142 were correctly classified for the presence of hemorrhage by DECT. The sensitivity, specificity, and accuracy for identifying hemorrhage, depending on the compartment being considered, were 100%, 84.4%– 100%, and 87.2%–100%, respectively. The only instances where DECT failed to correctly identify the source of hyperattenuation was in the presence of diffuse parenchymal calcification (n ϭ 5) and a metallic streak artifact (n ϭ 1). CONCLUSION: After IA and/or IV contrast administration, DECT can accurately differentiate all types of ICH from iodinated contrast without employing any additional radiation. ABBREVIATIONS: BP ϭ brain parenchyma; CNR ϭ contrast-to-noise ratio; DECT ϭ dual-energy CT; HEAD & NECK HU ϭ Hounsfield unit; IA ϭ intra-arterial; IAT ϭ intra-arterial therapy; ICH ϭ intracranial hemorrhage; SE ϭ single energy; VNCϭ virtual noncontrast taining of brain parenchyma and blood vessels is a well- or IV contrast administration, it can be difficult to differenti- 1 Srecognized phenomenon of IA contrast administration. ate a hyperattenuation resulting from iodinated contrast ver- ORIGINAL RESEARCH Furthermore, extravasation of contrast into the subarachnoid sus that arising from intracranial hemorrhage.2 This differen- space is fairly commonly seen following intra-arterial stroke tiation is especially critical in the setting of acute stroke or therapy with mechanical devices. These phenomena can also trauma, when antithrombotic therapy is being considered. be seen with IV contrast administration. For example, both The current standard of care for such discrimination is repeat intratumoral hemorrhage and contrast enhancement are follow-up imaging1: Contrast staining generally washes out common. Hemorrhagic transformation and gyriform en- within 24–48 hours, while hemorrhage persists for days to hancement of subacute stroke are well described, and distin- weeks. guishing them is clinically important. When contrast is ad- Early results have shown that DECT can distinguish hem- ministered in the setting of intracranial hemorrhage, petechial orrhage from iodinated contrast.3-5 This discrimination is extravasation of contrast in this hemorrhagic bed is a well- based on the differences between the photoelectric and Comp- recognized phenomenon and has been dubbed the “spot ton scattering components underlying the x-ray attenuation sign.” of hemorrhage and iodine. Because both phenomena are de- On a routine noncontrast head CT scan performed after IA pendent on the x-ray photon energy, one can discriminate the pixel attenuation arising from these 2 effects by scanning at 2 Received July 10, 2011; accepted after revision August 29. different energy levels, such as 80kV and 140kV. Assuming From the Department of Radiology (C.M.P., A.J.Y., J.A.H., R.G.), Massachusetts General Hospital, Boston, Massachusetts; Departments of Neurology, Neurosurgery, and Radiology that there can only be hemorrhage and/or iodine (in addition (R.G.N.), Emory University School of Medicine, Marcus Stroke & Neuroscience Center, to water and tissue), this information can be used to determine Grady Memorial Hospital, Atlanta, Georgia; Department of Neurology (R.G.N.), Massachu- the amount of each material present in each voxel. setts General Hospital, Harvard Medical School, Wang Ambulatory Care Center, Boston, Massachusetts. In this research, we considered a mixed cohort after both IA C.M.P. and A.J.Y. contributed equally to this article. and IV contrast administration. The overall goal was to estab- lish the general hypothesis that DECT is useful in all settings Please address correspondence to Catherine M. Phan, Department of Radiology, Massa- chusetts General Hospital, 55 Fruit St, Neuroradiology GRB-273A, Boston, MA 02114; where one has to distinguish between ICH and iodine from e-mail: [email protected] prior contrast administration, irrespective of how the contrast Indicates article with supplemental on-line tables. was administered. The sensitivity, specificity, and accuracy of http://dx.doi.org/10.3174/ajnr.A2909 DECT in differentiating hemorrhage from iodinated contrast AJNR Am J Neuroradiol ●:● ͉ ● 2012 ͉ www.ajnr.org 1 Copyright 2012 by American Society of Neuroradiology. were assessed for the intraparenchymal, subarachnoid, extra- settings split the overall dose nearly equally between the 2 imaging axial, intraventricular, and intra-arterial compartments. chains. The total effective dose was similar to that in a conventional head CT (approximately 3 mSv). The average CT dose index-volume Materials and Methods for a dual-energy head scan was 66 mGy, which is quite similar to that for a single-energy conventional head CT. It is also well within the Patient Selection American College of Radiology guidelines of 80 mGy. The patients were prospectively screened and retrospectively ana- The projection data acquired at 80 and 140 kV were reconstructed lyzed. The determination of which patients were routed to the DECT separately at 4.0-mm section thickness using an H30 kernel (medium scan was based on the following criteria: 1) all patients who received smooth), generating 3 sets of images: an 80-kV image, a 140-kV im- IAT after an acute stroke, and 2) patients who received IV contrast for age, and an SE image. The SE image set, which is a weighted sum of the any reason (eg, carotid stent placement, tumor evaluation, or 80-kV and 140-kV images, simulates an equivalent 120-kV image; it trauma), where a question of hemorrhage versus contrast was raised has a higher signal intensity–to-noise ratio than the constituent 80- by an SE energy scan. and 140-kV image sets. This study was approved by the local institutional review board Dual-energy postprocessing was performed using dedicated soft- (IRB Protocol #2008P002351). The requirement for informed con- ware (Syngo Dual Energy Brain Hemorrhage, Siemens): Images were sent for the retrospective analysis was waived by the IRB. From Octo- reconstructed at 1.5-mm section thickness, with 0.7-mm increments ber 2008 to May 2010, 40 patients (mean age 64.9 years; range 28–94) (D30s kernel). The analysis of low- and high-energy images7,8 was were referred for a DECT scan and were included in the analysis. performed using a 3-material decomposition algorithm based on There were 27 men (mean age 63.1 years; range 28–94) and 13 women brain parenchyma, hemorrhage, and iodine, producing a VNC and an (mean age 68.7 years; range 43–84). The study cohort included 20 iodine-only overlay image. DECT allows one to split every voxel in the acute stroke patients, of whom 18 underwent IAT; 15 patients evalu- acquired (80 kV, 140 kV) image pair along any 2 preselected base ated for carotid stenosis; 3 patients evaluated for trauma; and 2 pa- materials. In this application, the 2 base materials were BP and ICH. If tients evaluated for tumor assessment. At our institution, all stroke each voxel only consisted of these 2 materials, its measured attenua- patients who undergo conventional angiography for intra-arterial tion would be a linear combination of the attenuation values of BP embolectomy or thrombolysis are evaluated by using a postprocedure and ICH, both at 80 kVp and 140 kVp. To the extent the measured noncontrast CT for any complications. Therefore, this cohort consti- value of a voxel does not conform to a mixture of the 2 base materials, tuted the largest subpopulation of patients scanned by DECT. All IAT the difference can be attributed to a third preselected material. In the patients were scanned within 30 minutes of the end of the interven- current application, the third material chosen was iodine. The offset tional procedure. from the linear combination of ICH and BP represents the amount of It should be noted that our cohort of patients includes 15 cases iodinated contrast present in a voxel. The iodine-only images display with suspected carotid stenosis and old strokes. These patients under- this offset, and the VNC images display a combination of BP and ICH went a DECT angiogram that included a dual-energy head CT. These values. It should be noted that DECT is limited to 3-material decom- cases do not contribute to the hyperattenuated lesions that