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    Photon-counting hexagonal pixel array CdTe detector: Spatial resolution characteristics for image-guided interventional applications

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    Authors
    Vedantham, Srinivasan
    Shrestha, Suman
    Karellas, Andrew
    Shi, Linxi
    Gounis, Matthew J.
    Bellazzini, Ronaldo
    Spandre, Gloria
    Brez, Alessandro
    Minuti, Massimo
    UMass Chan Affiliations
    Department of Radiology
    Document Type
    Journal Article
    Publication Date
    2016-05-01
    Keywords
    Medical Biophysics
    Physics
    Radiology
    
    Metadata
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    Link to Full Text
    http://dx.doi.org/10.1118/1.4944868
    Abstract
    PURPOSE: High-resolution, photon-counting, energy-resolved detector with fast-framing capability can facilitate simultaneous acquisition of precontrast and postcontrast images for subtraction angiography without pixel registration artifacts and can facilitate high-resolution real-time imaging during image-guided interventions. Hence, this study was conducted to determine the spatial resolution characteristics of a hexagonal pixel array photon-counting cadmium telluride (CdTe) detector. METHODS: A 650 mum thick CdTe Schottky photon-counting detector capable of concurrently acquiring up to two energy-windowed images was operated in a single energy-window mode to include photons of 10 keV or higher. The detector had hexagonal pixels with apothem of 30 mum resulting in pixel pitch of 60 and 51.96 mum along the two orthogonal directions. The detector was characterized at IEC-RQA5 spectral conditions. Linear response of the detector was determined over the air kerma rate relevant to image-guided interventional procedures ranging from 1.3 nGy/frame to 91.4 muGy/frame. Presampled modulation transfer was determined using a tungsten edge test device. The edge-spread function and the finely sampled line spread function accounted for hexagonal sampling, from which the presampled modulation transfer function (MTF) was determined. Since detectors with hexagonal pixels require resampling to square pixels for distortion-free display, the optimal square pixel size was determined by minimizing the root-mean-squared-error of the aperture functions for the square and hexagonal pixels up to the Nyquist limit. RESULTS: At Nyquist frequencies of 8.33 and 9.62 cycles/mm along the apothem and orthogonal to the apothem directions, the modulation factors were 0.397 and 0.228, respectively. For the corresponding axis, the limiting resolution defined as 10% MTF occurred at 13.3 and 12 cycles/mm, respectively. Evaluation of the aperture functions yielded an optimal square pixel size of 54 mum. After resampling to 54 mum square pixels using trilinear interpolation, the presampled MTF at Nyquist frequency of 9.26 cycles/mm was 0.29 and 0.24 along the orthogonal directions and the limiting resolution (10% MTF) occurred at approximately 12 cycles/mm. Visual analysis of a bar pattern image showed the ability to resolve close to 12 line-pairs/mm and qualitative evaluation of a neurovascular nitinol-stent showed the ability to visualize its struts at clinically relevant conditions. CONCLUSIONS: Hexagonal pixel array photon-counting CdTe detector provides high spatial resolution in single-photon counting mode. After resampling to optimal square pixel size for distortion-free display, the spatial resolution is preserved. The dual-energy capabilities of the detector could allow for artifact-free subtraction angiography and basis material decomposition. The proposed high-resolution photon-counting detector with energy-resolving capability can be of importance for several image-guided interventional procedures as well as for pediatric applications.
    Source
    Med Phys. 2016 May;43(5):2118. doi: 10.1118/1.4944868. Link to article on publisher's site
    DOI
    10.1118/1.4944868
    Permanent Link to this Item
    http://hdl.handle.net/20.500.14038/48065
    PubMed ID
    27147324
    Related Resources
    Link to Article in PubMed
    ae974a485f413a2113503eed53cd6c53
    10.1118/1.4944868
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