Potential of contrast agents based on high‐Z elements for contrast‐enhanced photon‐counting computed tomography

Abstract

Purpose In clinics, only iodine‐ and barium‐based contrast agents are currently used for contrast‐enhanced x‐ray computed tomography (CT). Recently, the introduction of new photon‐counting (PC) detectors increased the interest in developing new contrast agents based on heavier elements. These elements may provide more contrast and spectral information compared to iodine and barium thanks to their k‐edges at higher energies. In this paper, the potential of high‐Z elements in contrast‐enhanced CT was evaluated for different patient sizes and x‐ray spectra using a PC detector. Methods An adult liver phantom with five high‐Z element solutions (iodine, gadolinium, ytterbium, tungsten, and bismuth) was scanned with a whole‐body photon‐counting computed tomography (PCCT) prototype. For each element, the contrast‐to‐noise ratio at unit concentration and at unit dose (CNRCD) was evaluated in low threshold images (T0=20keV) as function of the tube voltage (80, 100, 120, and 140 kV) and in bin images (tube voltage = 120 kV) as function of the higher threshold (T0=20keV and T1∈false[50,90false]keV). Simulations were performed for validation with measurements and to investigate more elements (cerium and gold), different patient sizes (infant, adult, and obese), and spectrum filtration (with and without 0.4‐mm tin filter). The dose reductions associated with the CNRCD improvements over iodine were quantified as well. Results CNRCD improvements and dose reductions depend on the investigated scenario. For the infant phantom, dose reductions around 30% were reached using cerium or gadolinium in combination with the tin filter. For the adult and obese phantom, reductions around 50% were provided by gadolinium or ytterbium in combination with the tin filter. Independently of the high‐Z element, the CNRCD of two optimally combined bin images was higher than the CNRCD of the low threshold image. Good agreement was found between measurements and simulations. Conclusions Between the investigated elements, gadolinium resulted to have the highest potential as novel contrast agent in PCCT, providing significant dose reductions for all patient sizes. Compared to the other elements, the implementation of gadolinium as CT contrast agent may be facilitated since it is already deployed as contrast agents for magnetic resonance imaging.

New Composite Contrast Agents Based on Ln and Graphene Matrix for Multi-Energy Computed Tomography

“…These include elements with Z = 64–83 [ 8 , 9 , 10 ]. Recently, CAs including Hf [ 4 ], Ta, Gd, Yb [ 8 ], W, Bi [ 11 ], Au [ 12 ], La, Lu, Ho [ 13 ], Eu, Er [ 14 ], and Dy [ 15 ] were studied. Among the lanthanides, the most frequently applied element is Gd [ 16 ].…”

Dose reduction potential in diagnostic single energy CT through patient‐specific prefilters and a wider range of tube voltages

“…One way to prevent the need for such low tube voltages would be the use of contrast agents with higher k-edge energies such as, for example, hafnium or tungsten, which have their k-edges at 65.35 keV and 69.53 keV, 15 respectively. Such high-Z contrast agents are currently under consideration, 27,28 also driven by the upcoming introduction of photon-counting CT technology. 29 Note that if tube voltage and filter thickness are optimized for the contrast agent one has to accept nonoptimal soft tissue contrast.High-Z contrast agents would be advantageous here as well.…”

“…Such high‐Z contrast agents are currently under consideration, 27,28 also driven by the upcoming introduction of photon‐counting CT technology 29 . Note that if tube voltage and filter thickness are optimized for the contrast agent one has to accept nonoptimal soft tissue contrast.…”

Threshold-dependent iodine imaging and spectral separation in a whole-body photon-counting CT system

“…Hence, our focus is on contrast-enhanced imaging. The optimal threshold positions for other applications, e.g., virtual non-calcium images or imaging of potential other contrast agents [12,13], might differ given the spectral properties of the materials of interest. In particular, an experimental CT system equipped with a prototype photon-counting detector is used in all studies presented here.…”