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

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 μm 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 μm resulting in pixel pitch of 60 and 51.96 μm 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 μGy/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 minimizingmore » 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 μm. After resampling to 54 μm 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.« less

Authors:
; ; ; ;  [1]; ; ; ;  [2]
  1. Department of Radiology, University of Massachusetts Medical School, Worcester, Massachusetts 01655 (United States)
  2. Istituto Nazionale di Fisica Nucleare (INFN), Pisa 56127, Italy and Pixirad Imaging Counters s.r.l., L. Pontecorvo 3, Pisa 56127 (Italy)
Publication Date:
OSTI Identifier:
22620873
Resource Type:
Journal Article
Resource Relation:
Journal Name: Medical Physics; Journal Volume: 43; Journal Issue: 5; Other Information: (c) 2016 American Association of Physicists in Medicine; Country of input: International Atomic Energy Agency (IAEA)
Country of Publication:
United States
Language:
English
Subject:
46 INSTRUMENTATION RELATED TO NUCLEAR SCIENCE AND TECHNOLOGY; APERTURES; BIOMEDICAL RADIOGRAPHY; BLOOD VESSELS; CDTE SEMICONDUCTOR DETECTORS; IMAGES; MODULATION; NICKEL ALLOYS; PEDIATRICS; SPATIAL RESOLUTION; TITANIUM ALLOYS; TRANSFER FUNCTIONS; TUNGSTEN; PHOTON COUNTING

Citation Formats

Vedantham, Srinivasan, Shrestha, Suman, Karellas, Andrew, E-mail: andrew.karellas@umassmed.edu, Shi, Linxi, Gounis, Matthew J., Bellazzini, Ronaldo, Spandre, Gloria, Brez, Alessandro, and Minuti, Massimo. Photon-counting hexagonal pixel array CdTe detector: Spatial resolution characteristics for image-guided interventional applications. United States: N. p., 2016. Web. doi:10.1118/1.4944868.
Vedantham, Srinivasan, Shrestha, Suman, Karellas, Andrew, E-mail: andrew.karellas@umassmed.edu, Shi, Linxi, Gounis, Matthew J., Bellazzini, Ronaldo, Spandre, Gloria, Brez, Alessandro, & Minuti, Massimo. Photon-counting hexagonal pixel array CdTe detector: Spatial resolution characteristics for image-guided interventional applications. United States. doi:10.1118/1.4944868.
Vedantham, Srinivasan, Shrestha, Suman, Karellas, Andrew, E-mail: andrew.karellas@umassmed.edu, Shi, Linxi, Gounis, Matthew J., Bellazzini, Ronaldo, Spandre, Gloria, Brez, Alessandro, and Minuti, Massimo. Sun . "Photon-counting hexagonal pixel array CdTe detector: Spatial resolution characteristics for image-guided interventional applications". United States. doi:10.1118/1.4944868.
@article{osti_22620873,
title = {Photon-counting hexagonal pixel array CdTe detector: Spatial resolution characteristics for image-guided interventional applications},
author = {Vedantham, Srinivasan and Shrestha, Suman and Karellas, Andrew, E-mail: andrew.karellas@umassmed.edu and Shi, Linxi and Gounis, Matthew J. and Bellazzini, Ronaldo and Spandre, Gloria and Brez, Alessandro and Minuti, Massimo},
abstractNote = {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 μm 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 μm resulting in pixel pitch of 60 and 51.96 μm 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 μGy/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 μm. After resampling to 54 μm 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.},
doi = {10.1118/1.4944868},
journal = {Medical Physics},
number = 5,
volume = 43,
place = {United States},
year = {Sun May 15 00:00:00 EDT 2016},
month = {Sun May 15 00:00:00 EDT 2016}
}