Caroline Reid

Pixellated Cd(Zn)Te high-energy X-ray instrument

We have developed a pixellated high energy X-ray detector instrument to be used in a variety of imaging applications. The instrument consists of either a Cadmium Zinc Telluride or Cadmium Telluride (Cd(Zn)Te) detector bump-bonded to a large area ASIC and packaged with a high performance data acquisition system. The 80 by 80 pixels each of 250 μm by 250 μm give better than 1 keV FWHM energy resolution at 59.5 keV and 1.5 keV FWHM at 141 keV, at the same time providing a high speed imaging performance. This system uses a relatively simple wire-bonded interconnection scheme but this is being upgraded to allow multiple modules to be used with very small dead space. The readout system and the novel interconnect technology is described and how the system is performing in several target applications.

Terahertz pulsed imaging of freshly excised human colonic tissues

We present the results from a feasibility study which measures properties in the terahertz frequency range of excised cancerous, dysplastic and healthy colonic tissues from 30 patients. We compare their absorption and refractive index spectra to identify trends which may enable different tissue types to be distinguished. In addition, we present statistical models based on variations between up to 17 parameters calculated from the reflected time and frequency domain signals of all the measured tissues. These models produce a sensitivity of 82% and a specificity of 77% in distinguishing between healthy and all diseased tissues and a sensitivity of 89% and a specificity of 71% in distinguishing between dysplastic and healthy tissues. The contrast between the tissue types was supported by histological staining studies which showed an increased vascularity in regions of increased terahertz absorption.

Accuracy and resolution of THz reflection spectroscopy for medical imaging

The use of THz radiation as a potential tool for medical imaging is of increasing interest. In this paper three methods of analysis of THz spectroscopic information for diagnosis of tissue pathologies at THz frequencies are presented. The frequency-dependent absorption coefficients, refractive indices and Debye relaxation times of pure water and pure lipids were measured and used as prior knowledge in the different theoretical methods for the determination of concentration. Three concentration analysis methods were investigated: (a) linear spectral decomposition, (b) spectrally averaged dielectric coefficient method and (c) the Debye relaxation coefficient method. These methods were validated on water and lipid emulsions by determining the concentrations of phantom chromophores and comparing to the known composition. The accuracy and resolution of each method were determined to assess the potential of each method as a tool for medical diagnosis at THz frequencies.

Terahertz Time-Domain Spectroscopy of Human Blood

In the continuing development of terahertz technology to enable the determination of tissue pathologies in real-time during surgical procedures, it is important to distinguish the measured terahertz signal from biomaterials and fluids, such as blood, which may mask the signal from tissues of interest. In this paper, we present the frequency-dependent absorption coefficients, refractive indices, and Debye relaxation times of whole blood, red blood cells, plasma, and a thrombus.

Optimizing multi-dimensional terahertz imaging analysis for colon cancer diagnosis

Highlights? THz imaging has potential in medical diagnosis but needs consensus about analysis. ? Intelligent analysis methods can help find relevant THz wave parameters. ? The intelligent analysis methods used produce better results than previous analyses. ? A non-patient-specific, generalized analysis method may be possible. ? Results suggest THz imaging analysis can be optimized for accuracy and efficiency. Terahertz reflection imaging (at frequencies ~0.1-10THz/1012Hz) is non-ionizing and has potential as a medical imaging technique; however, there is currently no consensus on the optimum imaging parameters to use and the procedure for data analysis. This may be holding back the progress of the technique. This article describes the use of various intelligent analysis methods to choose relevant imaging parameters and optimize the processing of terahertz data in the diagnosis of ex vivo colon cancer samples. Decision trees were used to find important parameters, and neural networks and support vector machines were used to classify the terahertz data as indicating normal or abnormal samples. This work reanalyzes the data described in Reid et al. (2011) (Physics in Medicine and Biology, 56, 4333-4353), and improves on their reported diagnostic accuracy, finding sensitivities of 90-100% and specificities of 86-90%. This optimization of the analysis of terahertz data allows certain recommendations to be suggested concerning terahertz reflection imaging of colon cancer samples.

Identification of simulants for explosives using pixellated X-ray diffraction

A new method of material identification has been developed utilising pixellated X-ray diffraction (PixD) to probe the molecular structure of hidden items. Since each material has a unique structure, this technique can be used to “fingerprint” items and has significant potential for use in security applications such as airport baggage scanning. The pixellated diffraction technique allows two distinct forms of diffraction, angular-dispersive and energy-dispersive X-ray diffraction, to be combined, exploiting the benefits of both. Thus, fast acquisition times are possible with a small system which contains no moving parts and can be easily implemented. In this work, the capability of the system to identify specific materials within a sample is highlighted. Such an approach would be highly beneficial for detecting explosive materials which are concealed amongst or inside other masking items. The technology could easily be added to existing baggage scanning equipment and would mean that if a suspicious item is seen in a regular X-ray image, the operator of the equipment could analyse the object in detail without opening the bag. The net result would be more accurate analysis of baggage content and faster throughput, as manual searching of suspicious objects would not be required.

The use of tissue mimicking phantoms in analysing contrast in THz pulsed imaging of biological tissue

In this study, tissue mimicking phantoms for the THz regime were developed to aid the current understanding of contrast mechanisms of tissue with THz pulsed imaging (TPI). The phantoms, compromising mixtures of water and protein, mimic biological tissue in both spatial and spectroscopic regimes. THz spectroscopy of the individual phantom constituents was compared with reflection measurements of phantoms of varying compositions. Phantom composition was varied enabling the emulation of specific tissue properties, thus allowing the analysis of parameters such as the error with which discreet components can be identified; 7.5% for low gelatin concentration gels and 17% for higher concentration gels. Identifying this uncertainty is important when imaging tissues that have surface features not obvious to other techniques such as visible imaging of dysplasia.

Using terahertz pulsed imaging (TPI) to identify colonic pathology.

Terahertz pulsed imaging (TPI) is a non-ionizing and non-destructive technique. Image contrast has been seen between normal and diseased tissues in ex vivo measurements. In this study, terahertz images of excised colon tissue show contrast between regions of tumor and normal tissue. Averaged waveforms from within tumor and normal regions are different. A number of parameters from the data have been identified that show statistically significant differences (p<0.01) between data from tumor and normal regions.

An oil and water emulsion phantom for biomedical terahertz spectroscopy

In order to determine the ability of THz spectroscopy to analyse the composition of biological tissue, a phantom containing combinations of water and lipids was developed. Initially, the absorption coefficient and refractive index of five pure commercially available lipids was measured between 0 and 3 THz. A suitable lipid for phantom manufacture was then chosen and a series of oil-water emulsions were made using surfactants. The lipid content ranged from 0% to 100%. THz spectra of the absorption coefficient and refractive index of these emulsions were measured. Using spectral decomposition techniques based on the Beer Lambert law, the percentage of oil and water in the emulsion was determined. The results show good qualitative agreement with the known compositions. The absolute oil and water content showed a systematic error of 10%. These initial results demonstrate that THz spectroscopy has the potential to determine the composition of biological tissues

The future of medical imaging

Medical physics is advancing rapidly, making use of many imaging and spectroscopic techniques across the electromagnetic spectrum. There are many cases where the demand for a medical imaging technique that is safe and non-invasive has not been met. Can terahertz meet that need?