Performance evaluation of a sub-millimetre spectrally resolved CT system on high- and low-frequency imaging tasks: A simulation

Department of Physics, Royal Institute of Technology, SE-106 91 Stockholm, Sweden.
Physics in Medicine and Biology (Impact Factor: 2.76). 04/2012; 57(8):2373-91. DOI: 10.1088/0031-9155/57/8/2373
Source: PubMed


We are developing a photon-counting silicon strip detector with 0.4 × 0.5 mm² detector elements for clinical CT applications. Except for the limited detection efficiency of approximately 0.8 for a spectrum of 80 kVp, the largest discrepancies from ideal spectral behaviour have been shown to be Compton interactions in the detector and electronic noise. Using the framework of cascaded system analysis, we reconstruct the 3D MTF and NPS of a silicon strip detector including the influence of scatter and charge sharing inside the detector. We compare the reconstructed noise and signal characteristics with a reconstructed 3D MTF and NPS of an ideal energy-integrating detector system with unity detection efficiency, no scatter or charge sharing inside the detector, unity presampling MTF and 1 × 1 mm² detector elements. The comparison is done by calculating the dose-normalized detectability index for some clinically relevant imaging tasks and spectra. This work demonstrates that although the detection efficiency of the silicon detector rapidly drops for the acceleration voltages encountered in clinical computed tomography practice, and despite the high fraction of Compton interactions due to the low atomic number, silicon detectors can perform on a par with ideal energy-integrating detectors for routine imaging tasks containing low-frequency components. For imaging tasks containing high-frequency components, the proposed silicon detector system can perform approximately 1.1-1.3 times better than a fully ideal energy-integrating system.

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Available from: Hans Bornefalk, Jan 27, 2014
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    • "IV for a silicon detector system with sub-millimeter resolution by using a simplified system model first developed in [11]. Apart from our current efforts in spectral CT [20], [21], [22], the main reason for modeling a silicon detector is the 120 combination of relatively low linear attenuation coefficient of silicon, high degree of long-range Compton scatter and charge sharing, giving rise to mainly low-but as well some amount of high-frequency spatial correlation structures between different bin images and distinct point spread functions of separate bins. "
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    • "This note illustrates the extent to which this phenomenon occurs in energy integrating systems, and also shows that for photon counting multibin systems, i.e. systems with energy resolving capabilities where events are allocated to bins according to the deposited energy of individual photons, this problem of total contrast cancellation does not occur. The absence of this effect in multibin systems is a result of the capability to utilize any local difference in the attenuation coefficients to generate contrast in the final image by means of energy weighting (Tapiovaara and Wagner 1985, Schmidt 2009, Bornefalk 2011, Yveborg et al 2012). Such energy weighting can be performed post-acquisition and therefore optimized for any iodine contrast thus eliminating the risk of contrast cancellation. "
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