Spectral imaging is now available on many computed tomography (CT) systems and is increasingly used in routine clinical practice, especially for abdomen CT examinations [1], [2], [3]. Spectral imaging is based on the acquisition or detection of two X-ray spectra (one at a low- and one at high-energy level) to separately assess the contribution of the photoelectric effect and the Compton effect [1], [2], [3], [4]. Spectral imaging can be used to generate several types of images, such as virtual monoenergetic images (VMIs) and iodine maps [1], [2], [3]. For contrast-enhanced abdominal CT acquisitions, VMIs at low energy levels enhance the tissue contrast [5], [6], [7], [8], [9]. However, the lower the energy level, the noisier the VMIs [1,10,11]. The impact of noise on VMIs is directly linked to the spectral performance of the dual-energy CT (DECT) platforms used [11,12]. The more limited the spectral separation, the more limited the use of the lowest energy levels [1,2].

In recent years, several technological developments have been made on DECT platforms to improve the quality of VMIs and reduce image noise. The two main developments are the use of reconstruction algorithms based on deep-learning [12,13] and the advent of new photon-counting CT (PCCT) systems [1,10,[14], [15], [16], [17], [18]]. PCCTs are equipped with photon-counting detectors (PCDs), which improve spatial resolution, remove the electronic noise, and lead to higher dose efficiency than the energy-integrating detectors (EIDs) usually used. These detectors also allow the energy of each photon to be counted, thus improving the sampling of the X-ray spectrum in several energy bins, making it possible to distinguish more accurately between photoelectric and Compton attenuation coefficients, thus producing better-quality VMIs [1,10,14].

Several PCCTs have been developed but, to our knowledge, only one PCCT is currently available for routine clinical use [1,14]. This PCCT is a dual-source CT system equipped with two PCD detector arrays of 57.6 mm coverage in z-direction [1,14]. Unlike a dual-source CT (DSCT) equipped with EIDs , spectral acquisitions can be performed in single-tube mode (120 or 140 kV) and the dual-source setup is used for acquisitions with high requirements on temporal resolution [1,14]. Various studies have assessed the impact of this new PCCT on conventional images and iodine maps of the abdomen [19], [20], [21]. However, to our knowledge, no studies have evaluated the impact of this new CT on noise magnitude, noise texture, spatial resolution and detectability of low-keV VMIs by comparison with the latest generation of DSCT equipped with EIDs.

The purpose of this study was to assess image quality and dose level using a PCCT scanner by comparison with a DSCT scanner on VMIs at low energy levels.