Beam-Hardening Correction for Virtual Monochromatic Imaging of Myocardial Perfusion via Fast-Switching Dual-kVp 64-Slice Computed Tomography

Abstract

here has been a growing interest in using computed tomography (CT) for combined assessment of myocardial perfusion and morphology of the coronary artery. 1 First-pass coronary artery imaging using CT has the potential to assess the physiologic relevance of a coronary artery lesion. 2, 3 In conventional single-kVp CT images, however, a considerable decrease in the myocardial CT value is often seen at the posterobasal wall, mimicking perfusion defects, and such decreases have been attributed to beam-hardening (BH) artifacts caused by high iodine concentrations in the left ventricular (LV) chamber and descending aorta. 4 Therefore, a rigorous BH correction algorithm for coronary CT imaging is essential for more accurate myocardial perfusion assessments. 5, 6 Virtual monochromatic images (VMI) generated using dualkVp projection-based material decomposition technology are a known solution to reducing BH artifacts in imaging of the head. 7 Newly developed high-definition CT (HDCT) allows the simultaneous acquisition of 80-and 140-kVp data in a single rotation. 8 The present study used an ex-vivo human heart specimen to investigate the effectiveness of HDCT for BH correction in the myocardium. MethodsAn ex-vivo human heart specimen from a patient with no history of coronary artery disease and that had right coronary artery dominance was obtained from the university's clinical anatomy laboratory after institutional review board approval. The LV cavity of the specimen and an artificial descending aorta (25-mm diameter syringe) were filled with iodinated contrast material (Iohexol; Daiichi-sankyo, Tokyo, Japan) diluted with purified water to achieve 400 Hounsfield units (HU) at 120 kVp. The specimen and the descending aorta were placed 15-mm apart in a chest phantom (WAC type; Kyoto-kagaku, Kyoto, Japan). A mixture of iodinated contrast material and polyethylene glycol (400 HU at 120 kVp) was injected into the left coronary artery, which generated a perfused myocardium in the left coronary artery area. Contrast material was not injected into the right coronary artery, so the area of the right coronary artery was not enhanced, similar to the non-perfused area. This phantom was scanned using HDCT (Discovery CT750 HD; GE Healthcare, WI, USA) in both the single 120-kVp and dualkVp scanning modes.The scanning parameters for the single 120-kVp scanning mode were prospectively artificial electrocardiogram (ECG)-

Fast kVp‐switching dual energy contrast‐enhanced thorax and cardiac CT: A phantom study on the accuracy of iodine concentration and effective atomic number measurement

“…On the contrary, fast kVp‐switching spectral CT enables near‐simultaneous acquisition of high and low energy datasets allowing the implementation of projection‐based material decomposition algorithms. These algorithms have been shown to greatly reduce BH artifacts and allow for better image quality compared to DSCT scanning . To our knowledge, this is the first study employed to assess iodine concentration accuracy using a modern fast kVp‐switching dual energy CT scanner.…”

“…These algorithms have been shown to greatly reduce BH artifacts and allow for better image quality compared to DSCT scanning. 5,6,9 To our knowledge, this is the first study employed to assess iodine concentration accuracy using a modern fast kVp-switching dual energy CT scanner.…”

“…Therefore, in single‐kVp CT no quantitative information can be derived separately for each of the spatially overlapping tissue constituents. Besides, in highly attenuating tissue compositions, such as iodinated or calcified tissue, the use of HU as a measure of attenuation is subject to errors originating from beam hardening (BH) artifacts . These artifacts are attributed to the variable absorption between low and high energy photons contained in the polychromatic spectrum emitted by the x‐ray tube.…”

New Applications of Cardiac Computed Tomography

“…With stress myocardial perfusion CT, beam-hardening arising from high-density iodinated contrast hampers accurate assessment of myocardial perfusion. Studies using ex vivo hearts and phantom models demonstrated improved detection of myocardial perfusion defects by reduction of beam-hardening artifacts mimicking perfusion deficits using fast-switching kVp DECT technology (37,38). A clinical study by So et al showed rapid kV-switching projection-based DECT to improve ischemia detection by elimination of beam-hardening artifacts (4).…”

Noninvasive Physiologic Assessment of Coronary Stenoses Using Cardiac CT

“…Recent study shows that image-based beam-hardening correction algorithm is feasible for the correction of beam-hardening artifacts that mimic perfusion defects. The beam-hardening correction used in the study was an image-based correction algorithm that enables individual estimation of the beam hardening from high-enhancing material and water-enhancing material for accurate calculation of the amount of beam hardening and to reconstruct a corrected image [ 74 , 75 ]. The study also demonstrates that virtual monochromatic images generated using fast-switching dual-kVp technology are feasible for the correction of beam-hardening artifacts in myocardial CT imaging [ 71 ].…”