Single-Scan Dual-Energy CT Using Primary Modulation

Abstract

Compared with conventional computed tomography (CT), dual-energy CT (DECT) provides better material differentiation but requires projection data acquired with two different effective x-ray spectra, limiting DECT applications to specialized scanners. We propose a hardware-based method, known as PM-DECT, which utilizes primary beam modulation to enable single-scan DECT on a conventional CT scanner. PM-DECT inserts an attenuation sheet with a spatially varying pattern-primary beam modulator-between the x-ray source and imaged object. During a CT scan, the modulator selectively hardens the x-ray beam, thereby increasing the average photon energy at specific detector pixel locations. Thus, PM-DECT simultaneously acquires high and low energy data at each projection angle. From the sparse projection data, high and low energy CT images are jointly reconstructed and simultaneously decomposed into basis materials via an iterative CT reconstruction algorithm with gradient weighting and an improved version of similarity based regularization. Studies on Catphan 600 and anthropomorphic head phantoms demonstrate that PM-DECT retains a high level of spatial resolution compared with conventional CT scans. Electron density values calculated from decomposed images indicate a limited error of 1.12% for PM-DECT. Comparison against a two-scan DECT technique shows that PM-DECT's image reconstruction from sparse data sets contributes only 0.66% error. By granting the opportunity for high-quality single-scan DECT on conventional CT scanners via limited hardware modification, PM-DECT has the potential to liberate DECT from specialized scanners, extending clinical availability, and implementation.

Densely sampled spectral modulation for x‐ray CT using a stationary modulator with flying focal spot: a conceptual and feasibility study of scatter and spectral correction

“…However, it is not obvious that any of them will meet COND-I as the detected scatter distributions likely will change when the low-and high-energy data are acquired or separated. Fortunately, recent developments of the modulator-based approach for scatter correction 1,2 and dual-energy CT 3 have suggested that COND-I can be met innovatively in DSSM as described in the following section.…”

“…In recent years, to achieve a desired intensity or spectral distribution of x-ray photon flux across the scan field of view, modulation of the x-ray source in computed tomography (CT) by a designated filter, has been continuously developed. Examples include the primary modulator for scatter correction and dual-energy CT, [1][2][3] the split filter for twin-beam helical dual-energy CT, 4 the dynamic bowtie filter for patient dose or photon flux optimization, [5][6][7][8] as well as the spatial-spectral filter for dual-energy CT, 9 and K-edge imaging. 10 Among them, the primary modulator and the split filter are kept stationary with respect to the x-ray source, leading to advantages of simplicity in mechanical design and practical implementations.…”

“…12 It can partially filter the spectrum of the x-ray in an alternating way over the detector field of view. 3 Such a stationary modulator alone has the potential of enabling multienergy imaging, but with sparse data sampling. On the other hand, flying focal spot technology has been successfully applied to diagnostic CT scanners to improve spatial sampling and reduce image artifacts.…”

“…17,18 However, more cost-effective alternatives through hardware or algorithm innovations nowadays are also being extensively investigated in both academia and industry, in particular for low-cost systems. 3,4 Taking flatpanel detector based cone-beam CT as an example, its spectral imaging capability is an active research area in the field, [19][20][21] but so far there is a lack of mature solutions for clinical applications. A major challenge for cone-beam CT spectral imaging is that CT projections can be badly contaminated by x-ray scatter if not handled well.…”

A Novel Low-Dose Dual-Energy Imaging Method for a Fast-Rotating Gantry-Type CT Scanner

“…High-end CT systems are usually equipped with the dual-energy scanning option. They employ various methods for dual-energy scan such as fast kV-switching [29], [30], dualsource technology [31], [32], dual-layer detector [33], energydiscriminating detector [34]- [37], primary modulation method [38], and use of spectral CT filters [39], [40]. Our proposed method, as will be detailed later, not only offers an alternative way of dual-energy scan but also enables it at an inherently lowdose manner.…”