ABSTRACT
Direct conversion radiation detectors offer new capabilities for medical CT imaging over indirect conversion detectors currently in use. The capabilities include energy resolution, variable energy weighting, noise reduction to the quantum statistical limit, as well as increased spatial resolution. These advantages in turn enable new applications such as material decomposition as well as improved image quality in low-dose screening applications and high-spatial-resolution imaging. The advantages stem from basic physics limits on the fidelity and entropy of cascaded energy
7.1 Photon-Counting Detectors for Medical Imaging ........................................ 169 7.1.1 Direct Conversion ............................................................................. 169 7.1.2 Material Properties ........................................................................... 170 7.1.3 Candidate Materials .......................................................................... 172 7.1.4 Detector Fabrication and Signal Formation ...................................... 172 7.1.5 Prospects for CT Application ........................................................... 176
7.2 Requirements for Photon-Counting Detectors in Medical CT Imaging ...... 177 7.2.1 Introduction ...................................................................................... 177 7.2.2 Image Quality (Spatial and Contrast Resolution) ............................. 179 7.2.3 Dose Efficiency ................................................................................. 180 7.2.4 Examination Time ............................................................................ 181 7.2.5 Rings (Bands) ................................................................................... 184 7.2.6 Multienergy Imaging ........................................................................ 185
7.3 Clinical Applications with Photon-Counting Detectors ............................... 185 7.3.1 K-Edge Imaging ................................................................................ 185 7.3.2 Improved Spatial Resolution ............................................................. 188 7.3.3 Dose Reduction ................................................................................. 190
References .............................................................................................................. 191
conversion processes [CUN99]. In direct conversion detectors, absorbed X-ray imaging photons generate individually detectable and measurable electric current pulses without the production and detection of light photons as an intermediary step. Since the signals are immediately available on the back of the detectors, they are sensed with close fitting miniature electronics that significantly reduces sources of noise and expensive infrastructure overhead. The technique, as it occurs in medical imaging, is called photon counting (PC).
