Virtual monoenergetic reconstructions of dynamic DECT acquisitions for calculation of perfusion maps of blood flow: Quantitative comparison to conventional, dynamic 80 kVp CT perfusion

Purpose: Investigation of potential improvements in dynamic CT perfusion measurements by exploitation of improved visualization of contrast agent in virtual monoenergetic reconstructions of images acquired with dual-energy computed tomography (DECT). Method: For 17 patients with pancreatic carcinoma, dynamic dual-source DECT acquisitions were performed at 80kV(p)/Sn140kV(p) every 1.5 s over 51 s. Virtual monoenergetic images (VMI) were reconstructed for photon energies between 40 keV and 150 keV (5 keV steps). Using the maximum-slope model, perfusion maps of blood flow were calculated from VMIs and 80kV(p) images and compared quantitatively with regard to blood flow measured in regions of interest in healthy tissue and carcinoma, standard deviation (SD), and absolute-difference-to-standard-deviation ratio (ADSDR) of measurements. Results: On average, blood flow calculated from VMIs increased with increasing energy levels from 114.3 +/- 37.2 mL/100 mL/min (healthy tissue) and 45.6 +/- 25.3 mL/100 mL/min (carcinoma) for 40 keV to 128.6 +/- 58.9 mL/100 mL/min (healthy tissue) and 75.5 +/- 49.8 mL/100 mL/min (carcinoma) for 150 keV, compared to 114.2 +/- 37.4 mL/100 mL/min (healthy tissue) and 46.5 +/- 26.6 mL/100 mL/min (carcinoma) for polyenergetic 80kV(p). Differences in blood flow between tissue types were significant for all energies. Differences between perfusion maps calculated from VMIs and 80kV(p) images were not significant below 110 keV. SD and ADSDR were significantly better for perfusion maps calculated from VMIs at energies between 40 keV and 55 keV than for those calculated from 80kV(p) images. Compared to effective dose of dynamic 80kVp acquisitions (4.6 +/- 2.2mSv), dose of dynamic DECT/VMI acquisitions (8.0 +/- 3.7mSv) was higher. Conclusions: Perfusion maps of blood flow based on low-energy VMIs between 40 keV and 55 keV offer improved robustness and quality of quantitative measurements over those calculated from 80kV(p) image data (reference standard), albeit at increased patient radiation exposure.