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Dual energy exposure control (DEEC) for computed tomography: Algorithm and simulation study
Author(s) -
Stenner Philip,
Kachelrieß Marc
Publication year - 2008
Publication title -
medical physics
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.473
H-Index - 180
eISSN - 2473-4209
pISSN - 0094-2405
DOI - 10.1118/1.2982150
Subject(s) - digital enhanced cordless telecommunications , imaging phantom , image quality , image noise , iterative reconstruction , noise (video) , radon transform , noise reduction , attenuation , image resolution , computer science , nuclear medicine , image processing , artificial intelligence , algorithm , image (mathematics) , optics , physics , medicine , telecommunications , wireless
DECT means acquiring the same object at two different energies, respectively two different tube voltages U 1 and U 2 . The raw data q 1 and q 2 undergo a decomposition process of type p = p ( q 1 , q 2 ) . The raw data p are reconstructed to obtain monochromatic images of the attenuation μ , of the object density ρ , or of a specific material distribution. Recent advances in DECT focus on noise reduction techniques [S. Richard and J. H. Siewerdsen, Med. Phys. (2), 586–600 (2008)] and enable high performance DECT such as lung nodule detection [Shkumat et al. , Med. Phys. (2), 629–632 (2008)]. Given p and a raw data‐based projection‐wise patient dose estimation D ( α )the authors determine the optimal tube current curvesI 1 ( α )andI 2 ( α ) , with α being the view angle, which minimizes image noise for a given patient dose level. DEEC can perform online;I 1 ( α )andI 2 ( α )can be determined during the scan. Simulation studies using semianthropomorphic phantom data were carried out. In particular, functions p that generate μ ‐images and density images were evaluated. Image quality was compared to standard scans atU 0 = 120 kV (clinical CT) andU 0 = 45 kV (micro‐CT) that were taken at the same dose level ( D 0 = D 1 + D 2 ) and identical spatial resolution. Appropriate choice of p ( q 1 , q 2 )allows to obtain μ ‐images that show fewer artifacts and yield image noise levels comparable to the noise of the standard scan. The authors compared the standard scan to μ ‐images at 70 keV , which is the effective energy used in clinical CT, and found optimal results with μ ‐images at 25 keV for micro‐CT. Nonoptimal choice of the decomposition function will, however, significantly increase image noise. In particular μ ‐images at 511 keV , as needed for PET/CT attenuation correction, exhibit more than twice as much image noise as the standard scan. With DEEC, which guarantees best dose usage possible, monochromatic images are generated with only slightly increased noise levels at the same dose compared to a standard scan. The benefit of significantly decreased artifacts appears to allow using DEEC‐generated monochromatic images in daily routine. Furthermore, DEEC is not restricted to DECT and the inherent tube current modulation algorithm may also be applied to single energy CT.