Dual-Energy CT: New Horizon in Medical Imaging

Abstract

Dual-energy CT has remained underutilized over the past decade probably due to a cumbersome workflow issue and current technical limitations. Clinical radiologists should be made aware of the potential clinical benefits of dual-energy CT over single-energy CT. To accomplish this aim, the basic principle, current acquisition methods with advantages and disadvantages, and various material-specific imaging methods as clinical applications of dual-energy CT should be addressed in detail. Current dual-energy CT acquisition methods include dual tubes with or without beam filtration, rapid voltage switching, dual-layer detector, split filter technique, and sequential scanning. Dual-energy material-specific imaging methods include virtual monoenergetic or monochromatic imaging, effective atomic number map, virtual non-contrast or unenhanced imaging, virtual non-calcium imaging, iodine map, inhaled xenon map, uric acid imaging, automatic bone removal, and lung vessels analysis. In this review, we focus on dual-energy CT imaging including related issues of radiation exposure to patients, scanning and post-processing options, and potential clinical benefits mainly to improve the understanding of clinical radiologists and thus, expand the clinical use of dual-energy CT; in addition, we briefly describe the current technical limitations of dual-energy CT and the current developments of photon-counting detector.

Dual‐energy CT iodine quantification for characterizing focal thyroid lesions

“…In this study, we used a recently implemented DECT scanner, which only a few studies used . This scanner achieves spectral separation using a different method from the previous fast‐kVp switching scanner in which the X‐ray tube rapidly modulates tube voltage . In contrast, our DECT scanner built with 2 scintillating layers has a single X‐ray source that operates at a fixed tube potential, typically 120 or 140 kVp .…”

“…[30][31][32][33][34][35] This scanner achieves spectral separation using a different method from the previous fast-kVp switching scanner in which the X-ray tube rapidly modulates tube voltage. 7,8,10 In contrast, our DECT scanner built with 2 scintillating layers has a single X-ray source that operates at a fixed tube potential, typically 120 or 140 kVp. 7,8,10 Its upper yttrium-based layer mostly absorbs low-energy photons, whereas the lower gadoliniumbased layer mostly absorbs high-energy photons.…”

“…7,8,10 In contrast, our DECT scanner built with 2 scintillating layers has a single X-ray source that operates at a fixed tube potential, typically 120 or 140 kVp. 7,8,10 Its upper yttrium-based layer mostly absorbs low-energy photons, whereas the lower gadoliniumbased layer mostly absorbs high-energy photons. These simultaneously obtained different energy data sets are decomposed in projection space to generate a materialspecific or energy-specific display based on the differences in X-ray attenuation and changes in attenuation at different energy levels, in addition to routine diagnostic images by directly combing data from the top and bottom layers.…”

“…1,6 The recent technical advance of dual-energy CT (DECT) has provided the material-specific imaging, also known as material decomposition, which can separate several numbers of substances, such as water, iodine, calcium, uric acid, and fat. [7][8][9][10] Especially, quantitative information for iodine distribution, among the DECT-based material decomposition techniques, has been considered a promising tool for lesion characterization to distinguish not only malignancy from benignity but also hyperdense cystic lesions or hematomas from enhancing lesions. 7,8,[10][11][12][13][14][15][16][17][18] In the head and neck region, several studies showed iodine concentration (IC) could be useful in CT imaging of cervical lymph nodes or patients with underlying neck malignancy.…”

“…[7][8][9][10] Especially, quantitative information for iodine distribution, among the DECT-based material decomposition techniques, has been considered a promising tool for lesion characterization to distinguish not only malignancy from benignity but also hyperdense cystic lesions or hematomas from enhancing lesions. 7,8,[10][11][12][13][14][15][16][17][18] In the head and neck region, several studies showed iodine concentration (IC) could be useful in CT imaging of cervical lymph nodes or patients with underlying neck malignancy. [19][20][21][22] Until now, a few studies have evaluated IC of thyroid nodules using the DECT data sets to find the malignancy or intranodular hemorrhage; however, they decided the individual CT images for quantification without the detailed topographic knowledge based on ultrasound, which is widely considered as reference imaging modality to assess thyroid nodule.…”