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

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

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

Pilot Study to Confirm that Fat and Liver can be Distinguished by Spectroscopic Tissue Response on a Medipix-All-Resolution System-CT (MARS-CT)

NAFLD, liver component of the “metabolic” syndrome, has become the most common liver disease in western nations. Non-invasive imaging techniques exist, but have limitations, especially in detection and quantification of mild to moderate fatty liver. In this pilot study, we produced attenuation curves from biomedical-quality projection images of liver and fat using the MARS spectroscopic-CT scanner. Difficulties obtaining attenuation spectra after reconstruction demonstrated that standard reconstruction programs do not preserve spectral information

A Novel Solid State Detector for Mammography

The Medipix2 chip is a photon counting X-ray pixel detector, which was developed by the Medipix Collaboration [1] at the European Centre for Nuclear Research (CERN). It consists of a 700?m silicon detector layer with 256?256 square pixels of 55?m size (Fig.1) which is bump bonded to an equally dimensioned pixel read-out chip [2]. The chip is suitable for mammographic applications due to increased relative efficiency at the low kV values involved. This initial study investigates the dose reductions achieved over conventional mammographic screen-film techniques and evaluates image quality. METHODS: The chip is used in the first clinical study of mammographic applications, comparing Medipix images of lumpectomies to conventional film images. The detector sits in a magnification table (Fig. 2) above the film housing with simple translation used to build up tiled images. RESULTS: Fig.3 shows film (a,c) and initial chip (b,d) lumpectomy images, there is a hook wire for localisation and several faulty pixel lines. Calcifications and a lesion are clearly seen; the locations are slightly altered due to repositioning of the excised sample

The Medipix Detector in Mammography

INTRODUCTION: The Medipix2 chip is a photon counting X-ray detector, which was developed by the Medipix Collaboration [1] at the European Centre for Nuclear Research (CERN). It consists of a 700?m silicon detector layer with 256?256 square pixels of 55?m size (Fig.1) which is bump bonded to an equally dimensioned pixel read-out chip [2]. The chip is suitable for mammographic applications due to the high absorption efficiency of silicon at the low kV values involved. This initial study compares Medipix lumpectomy images with those acquired using conventional mammographic screen-film techniques. METHODS: The detector sits in a mammography magnification table above the film housing (Fig. 2), with lumpectomy translation used to build up tiled images. Images are acquired using the same exposures as for the clinical film/screen images. RESULTS: Figure 3 shows a film/screen image (left) and a Medipix image (right) of the same breast lesion. The Medipix image was tiled from several sub-images and tiling artifacts are apparent. Similar images of lumpectomies with calcifications have also been acquired. DISCUSSION & CONCLUSIONS: We have shown that breast lumpectomies containing lesions and calcifications can be successfully imaged using Medipix. Other collaboration members have performed rigorous image quality measurements to show that Medipix is suitable for mammography. The prototype Medipix3 detector achieves improved quality and efficiency, which will allow us to develop a low dose mammography system

Development of a CT scanner based on the Medipix family of detectors

Photon counting detectors are of growing importance in medical imaging because they enable routine measurement of photon energy. Detectors such as Medipix2 and Medipix3 record the energy of incident photons with minimal loss of spatial resolution. Their use is being investigated for both pre-clinical and clinical applications of X-ray CT. The Medipix3 detector has 256 x 256 55 µm pixels and a silicon or cadmium telluride detector layer, giving a spatial resolution comparable to mammographic film. Each Medipix pixel can be seen as an individual spectral detector. The logic circuits for each pixel (some 1300 transistors) can analyze incoming events at megahertz rates, comparing the charge of the electron-hole cloud with preset levels, giving a resolution of about 2 keV across the range of 8 - 140 keV. A prototype CT scanner has been developed for laboratory animals and excised specimens. Applications under investigation include: K-edge imaging: Using spectral information to measure heavy elements (e.g., preparations of iodine, barium, and gadolinium) and Soft tissue contrast: Dual energy systems have shown that image contrast for soft tissue can be improved, e.g., distinguishing between iron and calcium within vascular plaques

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

Energy calibration of the Medipix-2 Quad MXR detector

The Medipix-2 Quad MXR detector is a recent version of the Medipix hybrid silicon pixel detector, which was developed at CERN. It combines four Medipix-2 chips with one common sensor chip. The photon processing x-ray detector will be incorporated into the Medipix All Resolution System (MARS) scanner, a 3D spectroscopic imaging system being developed by a collaboration of researchers from the University of Canterbury and the Canterbury District Health Board. This paper reports on a method developed to carry out an energy calibration for the Quad MXR detector

Contrast agent recognition in small animal CT using the Medipix2 detector

Energy resolving capabilities of X-ray detectors like the Medipix2 and the upcoming Medipix3 offer access to spectral information which is a new domain of information in medical imaging. In conventional CT of a composite object only the cumulative contribution of all involved materials to the attenuation is measurable, but not how much each material component contributes to this attenuation is measured. Therefore, contrast agent cannot be distinguished from bone or calcifications. The method of material reconstruction exploits the energy information to determine the partial densities of the involved materials using a maximum likelihood approach, i.e. it allows the separation of contrast agent from tissue, bones and calcifications. We have employed the Medipix All Resolution System (MARS) scanner equipped with a Medipix2 MXR and performed a CT scan of a mouse with iodine contrast agent in stomach and bowel. The method allows to separate the iodine contrast agent from all the other absorbing structures. In the iodine image, only the iodine concentration is visible, while the non-iodine (water) image shows all the other tissue structures and bones. The method of material reconstruction was applied to real CT data of a biological sample for the first time