Photon counting computed tomography: Concept and initial results

Abstract

A concept of a photon counting cone beam CT is proposed. The system uses a new Multi Slit Multi Slice (MSMS) cone beam acquisition geometry utilizing a linear array photon counting detectors. The MSMS cone beam acquisition is a direct analogy of the scanning multislit acquisition used in projection x-ray imaging. This geometry provides a CT imaging with dose efficient scatter rejection and allows for using available photon counting detectors. The microchannel plate (MCP) detector is proposed as a linear array photon counting detector for MSMS cone beam CT system. Initial testing of the MCP detector for CT application was performed. The field of view of the prototype MCP detector is 60 mm. A delay line position encoding electronics was used. The electronics has a single channel input for evaluation of events from the entire detector field of view. This limits the system count rate at 2 x 10(5) count/s. The spatial resolution of this detector is 80 microm FWHM at 40 kVp and 200 microm FWHM at 90 kVp tube voltages. The detector noise in CT projections is less than 1 count/pixel for the 80 microm pixel size. The CT projections contain quantum-limited and scatter free signal. Images of a contrast phantom and a small animal were acquired at 50 kVp and 80 kVp tube voltages. The CT numbers for different contrast elements were calculated for a given x-ray spectrum and compared with experimental values. The quantum efficiency of the current detector is 56% at 90 kVp, which is suboptimal because of the large channel diameter (25 microm) of these MCPs. The MCPs with smaller channels and higher efficiencies are being tested. The quantum efficiency was measured to be 70% for a new MCP with 5 microm channel diameter. Design parameters of a clinically applicable photon counting MSMS cone beam CT for breast imaging was evaluated. System uses 20 cm field of view MCP detectors based on 5 microm channel MCPs and high count rate ASIC electronics. It was concluded that the MSMS cone beam CT with a photon counting MCP detector is feasible for volume breast imaging.

Vision 20/20: Single photon counting x‐ray detectors in medical imaging

“…There are also some table-top CT systems with clinical and animal CT geometries. 105 A LightSpeed VCT scanner (GE Healthcare; Waukesha, WI) equipped with DxRay's first generation PCDs (DXMCT-1) was operated with x-ray tube voltage and current of 140 kVp and 40 mA. Details of the imaging technologies discussed in Sec.…”

“…17,28 Other research groups have also developed CT systems and reported promising performance such as improved contrastto-noise ratio 7 and high spatial resolution. 105 An animal PCD-CT (Philips Research; Hamburg, Germany) was developed and equipped with Gamma MedicaIdea's PCDs. 6,9 Phantom and animal images obtained by the scanner showed that multiple contrast agents (iodine and gadolinium, 6 or iodine and gold 106 ) were simultaneously imaged, that metal artifacts from stents were reduced, 9 that the characteristic effect of K-edges was imaged, 9 and that targeted molecules (fibrin 107,108 or macrophage 106 ) were successfully enhanced by nanoparticle contrast agents.…”

Musculoskeletal imaging with a prototype photon-counting detector

“…In order to improve contrast at reduced doses, photoncounting detectors have been considered in the search for alternatives to the conventional X-ray detectors used in radiography and CT [3][4][5].…”

Investigating the effect of characteristic x-rays in cadmium zinc telluride detectors under breast computerized tomography operating conditions

“…Two promising semiconductor materials that are being studied for breast CT are cadmium telluride (CdTe) and CZT. 6,17,[31][32][33][34] An interacting x-ray can produce secondary characteristic x-rays (x-ray fluorescence) with energy equivalent to the binding energies characteristic of the Cd and Te atoms. As discussed below, these characteristic x-rays can exit the semiconductor material or be reabsorbed at a misplaced location resulting in loss of spatial and energy resolution, as well as double counting of the incident x-ray.…”