Metal artifact reduction and contrast agent performance as a function of source spectral shape

Objective.Empirically map the x-ray source of a Medipix All Resolution Scanner (MARS) photon counting CT (PCCT) with Cu and Sn pre-filters, assess metal artifact reduction (MAR) capabilities of these pre-filters, and measure pre-filtration impact on contrast performance (CP) of FDA approved iopromide and experimental tantalum oxide nanoparticles (TaO_xNPs).Approach.The x-ray source of a MARS-PCCT system was empirically mapped with no pre-filtration, seven Cu filters (0.3-2.1 mm), and seven Sn filters (0.15-1.05 mm). A phantom with inserts containing water, lipid, iopromide, TaO_xNPs, and metal was scanned with no pre-filtration and Cu and Sn pre-filters. Insert noise, signal, contrast-to-pooled-noise ratio (CPNR), and a fast Fourier transform artifact metric (FFTAM) were calculated for each filter to quantify MAR and CP.Main results.Thick filters for Cu and Sn shifted mean energy of the unfiltered x-ray source (47.9 keV) by 19.2 and 23.4 keV, respectively. Thick filtration, 2.1 mm Cu and 0.6 mm Sn, greatly reduced noise (up to 74%) and FFTAM (up to 71%) for all inserts and energy bins. Thin filtration, 0.3 mm Cu and 0.15 mm Sn, also reduced noise (up to 47%) and FFTAM (up to 41%). In most cases, iopromide lost significant contrast (up to 50%). TaO_xNPs also lost contrast, though to a lesser extent (up to 38%). Pre-filtration improved image efficacy (i.e. CPNR), especially for TaO_x(up to 61%).Significance.By empirically mapping the source spectrum of a MARS-PCCT system with pre-filters, valuable information was gathered about photon flux distribution and detector artifacts; these findings will prove insightful for applications such as energy binning for effective material decomposition. Furthermore, this information will potentially guide clinical MAR development, most notably for the MARS Extremity 5 × 120 recently deployed for first-in-human trials. Lastly, TaO_xNPs were shown to be more compatible than iopromide with spectral shaping.