Dual energy CT via fast kVp switching spectrum estimation

Abstract

Recently there has been significant interest in dual energy CT imaging with several acquisition methods being actively pursued. Here we investigate fast kVp switching where the kVp alternates between low and high kVp every view. Fast kVp switching enables fine temporal registration, helical and axial acquisitions, and full field of view. It also presents several processing challenges. The rise and fall of the kVp, which occurs during the view integration period, is not instantaneous and complicates the measurement of the effective spectrum for low and high kVp views. Further, if the detector digital acquisition system (DAS) and generator clocks are not fully synchronous, jitter is introduced in the kVp waveform relative to the view period.In this paper we develop a method for estimation of the resulting spectrum for low and high kVp views. The method utilizes static kVp acquisitions of air with a small bowtie filter as a basis set. A fast kVp acquisition of air with a small bowtie filter is performed and the effective kVp is estimated as a linear combination of the basis vectors. The effectiveness of this method is demonstrated through the reconstruction of a water phantom acquired with a fast kVp acquisition. The impact of jitter due to the generator and detector DAS clocks is explored via simulation. The error is measured relative to spectrum variation and material decomposition accuracy.

Nonconvex prior image constrained compressed sensing (NCPICCS): Theory and simulations on perfusion CT

“…A final limitation, common to all methods investigated here, is that the collection of only a small number of projections would require a very fast pulsed x-ray system, allowing exposure at only selected projection angles. Although this might be technically feasible, 41 it is not currently implemented in any commercial CT clinical scanner. CT scanners based on multiple x-ray sources, pioneered with the dynamic spatial reconstructor, 42 and more recently stationary and multisource micro-CT systems using carbon nanotubes, 43 could benefit from CS-based reconstruction methods ͑including NCPICCS͒, as illustrated recently in small animal imaging.…”

Dual-Energy CT with Fast-kVp Switching and Its Applications in Orthopedics

“…In a recent dose and low contrast detectability (LCD) comparison [13,14], the effectiveness of this sampling scheme with respect to dose was demonstrated by matching the LCD at a slice thickness equal to 5 mm and object size of 3 mm.…”

“…Based on this principle, the low-and high-kVp Figure 6: Comparison of the measured CTDIvol (in mGy) between a FKS dual-energy and routine (i.e., single-energy) abdominal CT exams as a function of monochromatic energy (in keV, dual-energy only) and tube current (in mA, single-energy only) (All other acquisition protocols were the same between the two systems compared: kVp=120 kVp, gantry rotate speed=1.0 s, bowtie=large body, slice thickness=5 mm, display field of view=22.5 cm). The single-energy (SE) measurements are denoted as "SE xxx mA", where "xxx" describes the tube current, while the dual-energy measurements are denoted as "Mono xx keV", where "xx" represents the monochromatic energy (monochromatic energy will be discussed later in Through a mathematical change of basis one can express the energy dependent attenuation observed in two kVp measurements in terms of two basis materials [14]:…”

“…To address the motion issue, a fast-kVp switching (FKS) dualenergy CT imaging method, where kVp is rapidly switched between low-and high-kVp in adjacent views, has recently been proposed [12][13][14]. Compared to conventional dual-energy CT imaging, FKS dualenergy CT imaging has several benefits including fine temporal view registration, helical and axial acquisitions, and full field of view.…”

“…However, due to various technical challenges, only recently has dual-energy CT imaging become a reality. Recent advances in CT scanner technologies have generated a renewed interest in dual-energy CT [9][10][11][12][13][14], which has led to the commercialization of dual-energy CT systems available for routine clinical use [10,[12][13][14]. Dual-energy CT is a special CT imaging procedure in which two CT scans of a patient are acquired in different X-ray tube potentials (and spectra) and used to perform energy-and material-selective reconstruction of the patient.…”