Revolutionary medical imaging with single-photon detection
Digital radiography has advanced medical X-ray imaging, providing very high contrast and spatial resolution. However, detailed information about the absorbed photons is largely lacking. Knowing the energy of the photons absorbed enables construction of a colour-coded energy map that facilitates the analysis of tissue based on chemical composition. In fact, coloured X-ray imaging (CXI) has enhanced the visibility of tumours and helped to determine their stages more accurately. The ability to count every photon absorbed not only takes the signal-to-noise ratio to its quantum limit but would also facilitate decreased doses of radiation. Scientists initiated the EU-funded project 'Large X-ray detectors for coloured X-ray imaging' (LACX) to develop the semiconductor detectors and associated photon-counting electronics required to make it possible. Conventional semiconductors such as silicon and germanium do not meet the technical requirements associated with high-energy photons used in medical imaging. Material properties of the new semiconductors: cadmium telluride (CdTe) and cadmium zinc telluride (CZT) enable effective conversion of radiation to electric charges (photons to electrons). However, until the project commenced they had never before been employed in radiation imaging. To realise large-area semiconductor X-ray detectors, investigators had to address issues with the cost and the availability of the detector material in a suitable form. A major problem is that the average size of single-crystal CdTe/CZT is too small. To overcome this barrier, the team developed a process to produce CdTe/CZT thick films with requisite properties that meet performance standards for large-area X-ray detector. Following the characterisation and optimisation of materials and methods, investigators fabricated detector-grade polycrystalline thick films and integrated them on detector chips. With software for image analysis exploiting algorithms to tile images, the detector system was implemented in computed tomography. Scientists demonstrated for the first time very high quality images from subjects using large-area semiconductor detectors. LACX technology for novel high-resolution, low-dose, colour-coded imaging of human tissues should improve the quality of diagnoses and reduce patient exposure to radiation. Additional applications in fields such as security are also likely.
