Identifying Clinical applications of Spectroscopic x-ray imaging

Spectroscopic x-ray detectors, such as Medipix, are opening the door to the widespread use of energy selective biomedical x-ray imaging. With dual energy computed tomography quickly becoming the clinical standard, spectroscopic imaging is a likely next step. However to confirm the utility of spectroscopic x-ray detectors there needs to be a clearer indication of the clinical benefits of the technology

Pixel sensitivity variation in a CdTe-Medipix2 detector using poly-energetic x-rays

We have a 1-mm-thick cadmium telluride (CdTe) sensor bump-bonded to a Medipix2 readout chip. This detector has been characterized using a poly-energetic x-ray beam. Open beam images (i.e. without an attenuating specimen between the x-ray source and the detector) have been acquired at room temperature using the MARS-CT system. Profiles of various rows and columns were analyzed for one hundred, 35-ms exposures taken with a bias voltage of -300 V (operating in electron collection mode). A region of increased sensitivity is observed around the edges of the detector. A reasonably periodic, repeatable variation in pixel sensitivity is observed. Some small regions with very low sensitivity and others with zero signals are also observed. Surrounding these regions are circular rings of pixels with higher counts. At higher flux (higher tube current in the x-ray source) there is evidence of saturation of the detector assembly. In this paper we present our understanding of the origin of these features and demonstrate the improved image quality obtained after correcting for these variations

Spectroscopic biomedical imaging with the Medipix2 detector

This study confirms that the Medipix2 x-ray detector enables spectroscopic bio-medical plain radiography. We show that the detector has the potential to provide new, useful information beyond the limited spectroscopic information of modern dual-energy computed tomography (CT) scanners. Full spectroscopic 3D-imaging is likely to be the next major technological advance in computed tomography, moving the modality towards molecular imaging applications. This paper focuses on the enabling technology which allows spectroscopic data collection and why this information is useful. In this preliminary study we acquired the first spectroscopic images of human tissue and other biological samples obtained using the Medipix2 detector. The images presented here include the clear resolution of the 1.4mm long distal phalanx of a 20 week old miscarried foetus, showing clear energy-dependent variations. The opportunities for further research using the forthcoming Medipix3 detector are discussed and a prototype spectroscopic CT scanner (MARS, Medipix All Resolution System) is briefly described

The increasing role of bioengineering and medical physics in the practice of medicine

Technology is playing an increasing role in the diagnosis and care of our patients. This trend will continue. Practitioners need to have a broad appreciation of the technology they use. In particular they need to understand the benefits as well as the potential risks that that increased technology brings both at the patient level and at a systems level. Having a broad understanding of technology allows practitioners to work closely with groups developing and implementing care systems. This can only be good for the patient

Energy-resolved Compton scatter estimation for micro-CT

X-ray scatter can cause significant distortion in CT imaging especially with the move to cone-beam geometries. Incoherent scatter (Compton scatter) is known to reduce the energy of scattered photons according to the angle of the scattering. The emergence of energy-resolved x-ray detectors offers an opportunity to produce and apply more accurate scatter estimates leading to improved image quality. We have developed a scatter estimation algorithm that accounts for the variation in scatter with incident radiation energy. Where existing methods generate estimates of scatter for the complete detected energy band, our new method produces separate estimates for each of the energy bands that are measured allowing a more focused correction of scatter. Our method is intended to be used in an iterative compensation framework like that of Ruhrnschopf and Klingenbeck (2011); it calculates the scatter contribution to each energy bin used in a scan based on the current volume estimate. Comparisons with Monte Carlo simulations indicate that this algorithm is effective at estimating the scatter level in separate energy bins. We found that the amount of scatter that loses enough energy to hop between energy bands is small enough to neglect but that scatter intensity is dependent on the incident energy so application of a spectrally-aware compensation technique is valuable

Multiple contrast agent imaging using MARS-CT, a spectroscopic (multi-energy) photon counting microCT scanner

Purpose: To establish that a spectroscopic (multi-energy) CT scanner can differentiate multiple contrast agents and background tissues. This is clinically significant because it enables multi-phase contrast studies to be performed in a single scan. eg. A "triple phase liver" is possible in a one acquisition. This is a significant improvement from dual energy CT which is limited to non-contrast and post-contrast images from a single acquisition

The Christchurch MARS-CT Project

The MARS-CT project aims to develop novel x-ray imaging systems based on state of the art spectral x-ray detectors from CERN (European Centre for Nuclear Research). The MARS-CT system being developed provides energy-specific attenuation of tissue, in addition to conventional information

MARS: Colour x-rays of people

Goal: To produce a poster for New Zealand high schools explaining a new form of medical imaging. Background: The MARS team has developed an novel x-ray scanner which produces three dimensional spectroscopic x-ray images of small animals and pathology specimens. The scanner, dubbed MARS (Medipix All Resolution System), has been built by University of Canterbury physicists and engineers. The scanner uses the Medipix photon processsing x-ray detector. It is now being used by the radiology department of the University of Otago, Christchurch to establish clinical applications. Method: To convey the difference between traditional medical x-ray systems and spectroscopic systems we used the analogy of observing patterns in a stained glass windows using visible light. To present our initial results, MARS images are shown next to conventional non-spectroscopic CT images. Colour was chosen to display the spectroscopic nature of the MARS images. Results: The poster will be used for the “Medical Imaging Outreach Kit”. The kit also contains a short video on the MARS project and equipment for demonstrating a range of radiation physics. Conclusion: The analogy of colour is felt to be useful for for explaining spectroscopy. It is accurate as the spectroscopic information in x-rays is equivalent to colour for visible light, except in a different part of the electromagnetic spectrum. In future we will solicit feedback from high school teachers and from the outreach program's speakers to further refine our explanation of the MARS technology

Charge sharing between pixels in the spectral Medipix2 x-ray detector

This paper gives an overview of the Medipix2 x-ray detector and its use in medical imaging, with the MARS-CT scanner (MARS, Medipix All Resolution System) as an example. The Medipix2 chip is a photon counting pixel detector with the ability of energy discrimination. It was developed at CERN and is composed of a sensor layer bump bonded to electronics layer. It has 256x256 pixels, each one covering an area of 55x55µm². Furthermore, every pixel can be read out separately. The MARS-CT scanner uses these properties to scan biological objects obtaining multi-energy (spectral) x-ray images with high contrast between materials and high spatial resolution. Charge sharing is the phenomenon by which the electron-hole charge cloud, induced in the sensor layer by an absorbed photon, is detected by a cluster of neighbouring pixels. Each pixel in the cluster generates a signal corresponding to its fraction of the cloud, so the detector will record several photons each of lower energies. This effect has to be considered with the use of Medipix2, because of its small pixels and the hybrid architecture. The effect was measured and a simulation modelled with the aim to reconstruct the spectrum removing the distortion of the detection process