Pros and Cons of Dual-Energy CT Systems: “One Does Not Fit All”

Abstract

Dual-energy computed tomography (DECT) uses different energy spectrum X-ray beams for differentiating materials with similar attenuation at a certain energy. Compared with single-energy CT, it provides images with better diagnostic performance and a potential reduction of contrast agent and radiation doses. There are different commercially available DECT technologies, with machines that may display two X-ray sources and two detectors, a single source capable of fast switching between two energy levels, a specialized detector capable of acquiring high- and low-energy data sets, and a filter splitting the beam into high- and low-energy beams at the output. Sequential acquisition at different tube voltages is an alternative approach. This narrative review describes the DECT technique using a Q&A format and visual representations. Physical concepts, parameters influencing image quality, postprocessing methods, applicability in daily routine workflow, and radiation considerations are discussed. Differences between scanners are described, regarding design, image quality variabilities, and their advantages and limitations. Additionally, current clinical applications are listed, and future perspectives for spectral CT imaging are addressed. Acknowledging the strengths and weaknesses of different DECT scanners is important, as these could be adapted to each patient, clinical scenario, and financial capability. This technology is undoubtedly valuable and will certainly keep improving.

Transparent Organic and Metal Halide Tandem Scintillators for High-Resolution Dual-Energy X-ray Imaging

“…However, this scheme provides limited information on substance composition. For instance, a typical example is the discrimination between calcified plaques and iodine-containing blood in the human body, which is one of the challenges of conventional single-energy clinical computed tomography (CT). − Although the atomic numbers of these materials differing widely (Z Ca = 20, Z I = 53), the grayscale of calcified plaques and iodinated blood in CT image may be identical at a certain energy, depending on the respective mass density or iodine concentration . This is because the CT number used to quantify the image grayscale of a substance is based on the linear attenuation coefficient of the objects being imaged, which is not unique for any given material, even in the case of different elemental compositions .…”

“…The emergence of dual-energy X-ray imaging provides a feasible strategy to evaluate the material-specific information at different X-ray energy bins . This technique is based on the modification of the X-ray source to generate two different polychromatic X-ray energy spectra, or spectral separation at the detector level. , The current commercial solutions for dual-energy X-ray imaging can be broadly categorized into three types, each with its own advantages and limitations . The first type is the DSDE system, which involves two X-ray tubes operating at high- and low-kilovoltage (kVp), respectively, and corresponding detectors positioned orthogonally (Scheme a) .…”

“…Rather than modulating the X-ray source energy spectra, the SSDLD system as a third type, enables the separation of energy bins at the detector level, allowing simultaneous and sequential acquisition of low- and high-energy projections within a single X-ray exposure (Scheme c). ,− The system includes a single X-ray source and a dual-layer detector composed of two scintillator layers with different energy sensitivity (low-energy X-ray photons tend to be absorbed by the top layer, while the remaining high-energy X-ray photons were absorbed by the bottom layer). This structure makes the SSDLD system always operate in “dual-energy mode”, which allows it to exhibit unparalleled spatial-temporal resolution and is promising for lower dose imaging through optimization of the detector. , However, this dual-layer detector is extremely demanding on each scintillator layer. Each scintillator layer requires careful design and trade-offs between various parameters, such as X-ray attenuation coefficient, thickness, optical absorption, emission spectral wavelength, brightness, spatial resolution, and fabrication cost.…”

“…7,10 The current commercial solutions for dual-energy X-ray imaging can be broadly categorized into three types, each with its own advantages and limitations. 8 The first type is the DSDE system, which involves two X-ray tubes operating at high-and low-kilovoltage (kVp), respectively, and corresponding detectors positioned orthogonally (Scheme 1a). 14 Two sequential scans were performed to acquire the low-and high-energy projections at each of the two tube voltages.…”

“…This structure makes the SSDLD system always operate in "dual-energy mode", which allows it to exhibit unparalleled spatial-temporal resolution and is promising for lower dose imaging through optimization of the detector. 8,11 However, this dual-layer detector is extremely demanding on each scintillator layer. Each scintillator layer requires careful design and trade-offs between various parameters, such as Xray attenuation coefficient, thickness, optical absorption, emission spectral wavelength, brightness, spatial resolution, and fabrication cost.…”