Kromek (United Kingdom)

A novel Molecular Breast Imaging system (MBI) is being developed by Kromek and University College London. MBI systems have been shown to provide excellent results in patients with dense breasts, but higher than mammography patient dose and long imaging time of 40 min impede their wide adoption. The design is based on a pair of opposing CZT detector arrays and high-density multi-pinhole (MPH) collimators. The new system combines superior energy and position resolution and depth of interaction (DOI) sensing of CZT detectors, wide range angular sampling of MPH collimators and novel de-multiplexing image reconstruction techniques to deliver tomographic images with stationary detectors. The new system is expected to mitigate the MBI drawbacks without compromising diagnostic content.Following the initial evaluation, a new feasibility prototype using upgraded ASIC and new front-end electronics was designed, built, and characterised. New image reconstruction and de-noising algorithms were developed on simulated data to improve the Contrast-to-Noise (CNR) ratio and reduce the fluctuations in the correlated background noise associated with MPH image reconstruction. The collimator geometry was further optimised by including non-local means noise filtering which increased the CNR by almost a factor of 3. The current results indicate that we can achieve the dose reduction to the mammography level, reduce the minimum size of detected lesions to about 6 mm and have an additional potential for reduction of the measurement time.

A pixelated cadmium zinc telluride (CZT) detector has been characterised for the purpose of developing a quantitative single photon emission computed tomography (SPECT) system for dosimetry of molecular radiotherapy (MRT). This is the aim of the Dosimetric Imaging with CZT (DEPICT) project, which is a collaboration between the University of Liverpool, The Royal Marsden Hospital, The Royal Liverpool and Broadgreen University Hospital, and the commercial partner Kromek. CZT is a direct band gap semiconductor with superior energy resolution and stopping power compared to scintillator detectors used in current SPECT systems. The inherent detector properties have been investigated and operational parameters such as bias voltage and peaking time have been selected to optimise the performance of the system. Good energy resolution is required to discriminate γ-rays that are scattered as they are emitted from the body and within the collimator, and high photon throughput is essential due to the high activities of isotopes administered in MRT. The system has an average measured electronic noise of 3.31 keV full width at half maximum (FWHM), determined through the use of an internal pulser. The energy response of the system was measured across the energy region of interest 59.5 keV to 364.5 keV and found to be linear. The reverse bias voltage and peaking time producing the optimum FWHM and maximum photon throughput were 600 V and 0.5 μs respectively. The average dead time of the system was measured as 4.84 μs and charge sharing was quantified to be 0.71 % at 59.5 keV . A pixel sensitivity calibration map was created and planar images of the medical imaging isotopes 99mTc and 123I were acquired by coupling the device to a prototype collimator, thereby demonstrating the suitability of the detector for the DEPICT project.