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  • Title: Virtual monochromatic reconstruction of dual-energy unenhanced head CT at 65-75 keV maximizes image quality compared with conventional polychromatic CT.
    Author: Pomerantz SR, Kamalian S, Zhang D, Gupta R, Rapalino O, Sahani DV, Lev MH.
    Journal: Radiology; 2013 Jan; 266(1):318-25. PubMed ID: 23074259.
    Abstract:
    PURPOSE: To determine the virtual monochromatic imaging (VMI) energy levels that maximize brain parenchymal image quality in dual-energy unenhanced head computed tomography (CT) and to assess the improvement with this technique compared with conventional polychromatic scanning. MATERIALS AND METHODS: Institutional review board approval was obtained with no informed consent required for this HIPAA-compliant retrospective analysis. Twenty-five consecutive unenhanced head CT scans were acquired with a 64-section dual-energy scanner with fast tube voltage switching (80-140 kVp). Scans were retrospectively reconstructed at VMI energy levels from 40 to 140 keV in 5-keV increments and were analyzed by using four quality indexes: gray matter (GM) signal-to-noise ratio (SNR), white matter (WM) SNR, GM-WM contrast-to-noise ratio (CNR), and posterior fossa artifact index (PFAI). Optimal mean values for each parameter were compared with those from 50 consecutive scans obtained with the same scanner in 120-kVp single-energy mode. Repeated-measures analysis of variance and Dunnett post hoc t test were then used to determine significance. RESULTS: Maximal GM SNR, WM SNR, and GM-WM CNR values were observed at 65 keV, and minimal PFAI was observed at 75 keV. These values were significantly better than those of conventional polychromatic CT (P < .01); quality index improvement ratios (corrected for radiation dose) ranged from 17% to 50%. CONCLUSION: Virtual monochromatic reconstruction of dual-energy unenhanced head CT scans at 65-75 keV (optimal energy levels) maximizes image quality compared with scans obtained with conventional polychromatic CT.
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