State of the Art and Future Trends in Radiation Detection for Computed Tomography

2013 AAPM Annual Meeting
Amiaz (Ami) Altman, PhD, Philips Medical Systems, Haifa, Israel, 31004 ISRAEL
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Over the last two decades CT detection evolved to support three major CT imaging trends: increasing number of slices and axial coverage, increasing rotation and acquisition speed, and patient dose reduction. Advanced solid state detectors, segmented to isolated detection pixels, read simultaneously in parallel by miniaturized electronics, have been the main technology enablers for these trends. In recent years, some niche CT types, categorized as Cone-Beam CT, especially in association with online verification of radiation therapy, have been using Flat-Panel detectors practiced in digital & interventional X-Ray radiography and fluoroscopy. Finally, very new trends related to spectral CT lead to the pursuit of spectral-detector solutions, with some published results. For this purpose, Direct-Conversion photon-counting detectors have been investigated intensively, in recent years. The goal of this talk is to review current and state of the art CT detectors, along with their performance figure of merit, and the clinical applications enabled by them. In addition, the new trends of spectral radiation detectors, especially those based on photon-counting direct-converting material are reported.
The major components current CT detector arrays are described along with their unique features enabling them to meet the requirements of a fast-rotating Multi-Slice CT, and its applications. This include the scintillator arrays converting X-Ray to visible light, the photodiode arrays that converts visible light to electric current, the electronic readout for signal digitization, and the anti-scatter grid. The various approaches to implement a large area detector array for CT scanners are described, along with the main required calibrations and corrections needed for these detectors. Few specific types of spectral detectors for CT are discussed, with emphasis on photon-counting. The main issues associated with these detectors are reviewed, especially the capability to tolerate CT high flux. Various solutions proposed by different groups are discussed along with their advantages and drawbacks.
Clinical applications and procedures, enabled by the various CT detectors types are reviewed and discussed with specific examples. Major differences between the imaging features: MTF, DQE, and CNR, of the various CT detectors types are presented.
CT scanners continue to be the leading imaging modality in use, for its evolving and new capabilities, scanning speed, and availability. The enabling of its continuously emerging new clinical applications is, to a large extent, due to the evolutions and revolutions in its detection system over the last two decades.

Learning Objectives:
1. Identify and understand the differentiating features of different digital projection x-ray detector technologies
2. Understand the impact of detector design on system imaging performance
3. Appreciate the detector capabilities that enable advanced applications
4. Develop an awareness of future detector/system capabilities
5. Understanding the clinical advantages and opportunities associated with current and future CT detection systems
6. Understanding some of the limitations of the various CT detectors types and how to take them in account in decision making in applying CT scanners for different clinical procedures and needs.

Conflict of Interest:
John Yorkston is an employee of Carestream Health
Ami Altman is an employee of Philips Healthcare

Funding Support, Disclosures, and Conflict of Interest: Carestream Health Inc, Philips Healthcare

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