High-Flux Multi-Spectral X-Ray Imaging for Accurate and Early Cancer Diagnosis

Conventional medical x-ray imaging systems are equipped with: i) a powerful x-ray tube, mounted on a fast rotating gantry, which generates polychromatic radiation characterised by a broad spectrum of energies, and ii) an x-ray detector, which records the total energy of all the x-rays that transmitted through the body of the patient.

The attenuation of the x-ray beam, as it passes through the patient's body, depends on the photon energy and this energy dependence is different for different materials, tissues and elements. Therefore, the energy of each detected photon contains additional valuable information about the elemental composition of the scanned object. The current x-ray detectors are mostly insensitive to this spectral information, because their signal output is proportional to the total energy deposited within the active area of the detector, while a detector with energy-discrimination capabilities can provide the solution for enhanced exploitation of this additional spectral information by recording all these different energy photons and arranging them into respective spectral bins.

Direct conversion CdZnTe (CZT) semiconductor detectors with high sensitivity, high stopping power, high spatial resolution and excellent energy resolution have emerged as the dominant solid-state room temperature detectors in a wide range of spectroscopic and imaging applications. Most recently, there has been a growing interest in using the CZT detectors for the next generation of high-flux multi-energy x-ray imaging systems, with a particular emphasis on Computed Tomography (CT) and 3D x-ray breast imaging. Both these imaging modalities have common goals, the ability to make quantitative measurements, and therefore, the enhancement of diagnostic capability at low patient doses. However, these applications require very fast data acquisition, and hence, there is a need for detectors that can efficiently operate at a high photon flux, almost 100 million photons per second per square millimetre. The design and fabrication of energy-sensitive CZT detector based scanner for high-flux photon-counting multi-spectral x-ray imaging is the focus of this proposal.

The main motivation of this work is to investigate to which extent photon-counting, energy discriminating CZT detectors are capable of overcoming fundamental performance limits and carrying out quantitative imaging revealing the additional spectral information, and therefore, improving conventional x-ray medical imaging. If energy information is recorded alongside the intensity, x-ray medical imaging modalities could increase diagnostic accuracy through soft-tissue differentiation, material decomposition, tumour characterisation, target quantification and development of disease-specific targeted contrast agents and drugs. The latter could improve low-contrast resolution and overall image quality at significantly reduced radiation doses and lead to superior diagnostic performance with lower cost. Spectral x-ray imaging can become an important imaging technique providing material-specific quantitative information in combination with high spatial resolution imaging, and therefore, leading to a paradigm shift in x-ray medical diagnostics.

Multispectral x-ray imaging will introduce a paradigm shift in medical x-ray diagnostic imaging, drastically improving the accuracy of the technique, resulting in more effective patient diagnosis and enhanced functional imaging capabilities. The enhanced soft tissue contrast will enable more effective tumour detection and differentiation, increasing the rate of early detection of cancer and allowing for more personalised medical treatment. Although the main focus of this project is the early detection and more effective treatment of cancer, this technique will improve the diagnostic accuracy of all x-ray transmission modalities, such as conventional, dual-energy and paediatric CT, 3D breast imaging, general radiography, vascular imaging, k-edge imaging, hybrid/multimodality imaging and pre-clinical (small animal) imaging.

The direct beneficiaries of this technology will clearly be cancer patients, their carers and relatives by enhancing quality of life, health and well-being with the UK NHS potentially benefiting from the use of new improved cutting-edge technologies and more accurate detection, advanced disease characterisation, early and reliable diagnosis and efficient treatment of cancer. The end result of this project will be a fully characterised and optimised x-ray imaging system that will be ready to scale up for clinical trials and small pilot groups. Looking beyond the scope of just cancer care, all patients requiring x-ray transmission imaging will benefit from the enhanced soft tissue contrast and reduction in radiation dose, especially in paediatric CT where the absorbed dose is of a higher concern than with adult patients. Once this technology has been scaled up to a full size system, clinical trials will be carried out in house at the Royal Marsden & ICR NIHR Biomedical Research Centre of Excellence for Cancer, making use of the wealth of experience and expertise available and promoting our 'bench to bedside' approach.

Enhanced contrast and improved diagnostic ability will result in a less frequent need for multiple scans, reducing dose rates further and reducing waiting times for scans, improving the overall service to the patient. This enhanced service and the reduction in waiting times for scans will have a direct positive impact on the UK National Health Service (NHS) as a whole.

Our industrial partner, Kromek, is the only UK company that has the complete capability to fabricate CdTe and CdZnTe crystals in conjunction with the advanced readout electronics required for the multispectral detector. It is therefore of significant importance for the economic benefit of the UK that its commercial activities maximise the return on the deployment of the outcomes of this research.

Larger healthcare manufacturers also stand to gain significantly from this work as this technology moves into clinical use, giving the UK a competitive edge in medical imaging. The development of disease specific contrast agents to be used specifically with this technology to further enhance the advantages will promote further growth in the pharmaceutical industry.

Postdoctoral researchers, PhD and MSc students will be trained and involved in cutting-edge research, at the forefront in the field of medical imaging at an international level. This training will provide a necessary, unique and in-depth knowledge of this technology, making them invaluable to the progression of this work to the clinical arena.