Update on Cardiovascular Applications of Multienergy CT

Abstract

Advances in scanner technology enabling shorter scan times, improvements in spatial and temporal resolution, and more dose-efficient data reconstruction coupled with rapidly growing evidence from clinical trials have established computed tomography (CT) as an important imaging modality in the evaluation of cardiovascular disorders. Multienergy (or spectral or dual-energy) CT is a relatively recent advance in which attenuation data from different energies are used to characterize materials beyond what is possible at conventional CT. Current technologies for multienergy CT are either source based (ie, dual source, rapid kilovoltage switching, dual spin, and split beam) or detector based (ie, dual layer and photon counting), and material-based decomposition occurs in either image or projection space. In addition to conventional diagnostic images, multienergy CT provides image sets such as iodine maps, virtual nonenhanced, effective atomic number, and virtual monoenergy (VM) images as well as data at the elemental level (CT fingerprinting), which can complement and in some areas overcome the limitations posed by conventional CT methods. In myocardial perfusion imaging, iodine maps improve the sensitivity of perfusion defects, and VM images improve the specificity by decreasing artifacts. Iodine maps are also useful in improving the performance of CT in delayed-enhancement imaging. In pulmonary perfusion imaging, iodine maps enhance the sensitivity of detection of both acute and chronic pulmonary emboli. Low-energy (as measured in kiloelectron volts) VM images allow enhancement of vascular contrast, which can either be used to lower contrast dose or salvage a suboptimal contrast-enhanced study. High-energy VM images can be used to decrease or eliminate artifacts such as beam-hardening and metallic artifacts. Virtual nonenhanced images have similar attenuation as true nonenhanced images and help in reducing radiation dose by eliminating the need for the latter in multiphasic vascular studies. Other potential applications of multienergy CT include calcium scoring from virtual nonenhanced images created from coronary CT angiograms and myocardial iron quantification. Online supplemental material is available for this article. RSNA, 2017.

Computed tomographic evaluation of myocardial ischemia

“…DECT allows for characterization of materials with similar attenuation coefficients but different atomic numbers because the tissues show different attenuation properties at different energy levels [42]. Commonly used DECT techniques include dual-source, rapid kVp switching, and dual-layer detector technologies [43]. DECT allows generation of multiple additional images, including iodine maps (Fig.…”

“…4). Iodine maps have better diagnostic performance than conventional images [43] and also provide quantitative information [45]. VMIs mimic images obtained at a single energy level and can be generated from 40 to 200 keV.…”

Acute pulmonary embolism multimodality imaging prior to endovascular therapy

“…Dual-energy CTPA involves using two distinct energy levels to capture the image [71]. This technique enables differentiation between tissues with similar attenuation values using various processing techniques such as iodine maps, virtual non-contrast (VNC) and virtual monochromatic images (VMI).…”

“…VMI imitate an X-ray beam with one energy level and are created by a linear combination of basis pair images in different proportions. VMI can decrease artifacts and thereby improve specificity [71,72]. Lung perfusion maps can be derived from iodine maps (Figs.…”

Acute Pulmonary Embolism: Imaging Techniques, Findings, Endovascular Treatment and Differential Diagnoses

“…Dual-energy CT, which can be performed using dual-source, dual-layer, dual-spin, dual-filter and rapid kVp switching technologies, collects data at two different energy levels [12]. This makes it possible to distinguish tissues with similar attenuation values using additional image sets such as iodine or Z-effective maps, virtual non-contrast and virtual monoenergetic images (VMI).…”