IBEX TECHNOLOGY APPLIED TO DIGITAL RADIOGRAPHY

Transcription

1 WHITE PAPER: IBEX TECHNOLOGY APPLIED TO DIGITAL RADIOGRAPHY

2 IBEX Innovations Ltd. Registered in England and Wales: Address: Discovery 2, NETPark, William Armstrong Way, Sedgefield, UK Patents: GB ; GB ; GB ; GB ; US Quality Management System accredited to ISO9001:2008 and ISO13485:2012

3 Abstract Medical X ray imaging is a vital diagnostic tool that brings enormous benefits to patients every year. IBEX technology delivers additional beam-energy-dependent information for material composition measurements and other image enhancements on every Digital Radiography (DR) scan. The core of the IBEX technology is a passive structured layer added to the detector which does not compromise the standard high resolution, high quality conventional radiograph. The additional information gathered by an IBEX equipped detector can distinguish between dense or thick soft tissue and thinner bone, or generate familiar diagnostic measurements such as areal Bone Mineral Density (BMD). In addition, improvements are gained in gridless scatter correction, helping to produce high quality diagnostic images at a reduced patient dose. Introduction Digital Radiography (DR) systems use a fixed kv source to provide absorption contrast images (radiographs). Energydependent information, which relates to sample/patient composition, is lost. Dual Energy X Ray Absorptiometry (DEXA) or other multi-spectral X ray techniques use multiple energy measurements gathered by multiple exposures or by complex energy-discriminating detectors. This enables access to energydependent attenuation information produced by samples with different compositions. These techniques can provide specialist measurements of, for example, areal bone mineral density (BMD) which may be interpreted to give fracture risk estimates for a particular patient. The IBEX MAP technology recovers energy-dependent information from DR systems with minimal modification to existing equipment. In typical DR detectors, such as TFT detectors, all deposited X-ray photon energy is integrated into a single pixel intensity value, so information about how different X-ray energies are attenuated is lost. The IBEX technology restores this Figure 1: Standard DR configuration, with the addition of the IBEX MAP. information by spatially modulating the X ray beam energy periodically across a detector with a multi-absorption plate (MAP), allowing a group of pixels to be analysed for differences in response to an object placed in the beam. Since the information is captured in a single exposure, the potential for motion artefacts is eliminated and the overall dose to the patient can be reduced. The low form-factor of the MAP means that it can be easily added to existing X-ray equipment in the form of a cover plate replacement. This approach removes Page 1 of 5

4 the need for specialised DEXA systems or multiple scans to acquire energy dependent information. Alongside the passive MAP component, the IBEX technology incorporates a software development kit (SDK) compatible with most modern programming languages. The SDK interprets the information generated by a detector fitted with an IBEX MAP to give both high quality diagnostic radiographs and other imaging outputs. With appropriate calibration and training, the SDK can generate material classifications and areal BMD, or be used to generate a gridless scatter corrected image. An IBEX-equipped system Figure 1 shows a schematic of a conventional X ray imaging system, with the IBEX MAP included. The MAP replaces the cover plate of the detector. Once added the IBEX equipped detector is indistinguishable from a standard detector both in terms of overall thickness and weight. IBEX technology The absorption of X rays by a material depends on the material type, its thickness, and the energy of the incident X rays. The energy dependant attenuation is described by the Beer-Lambert Law (Eq. 1): I(E)=I 0 (E)exp(-μ(E)t) Eq. 1 where I is the intensity incident on the detector after the sample; I 0 is the incident intensity in the absence of a sample; μ is the linear attenuation coefficient of the material and t is the material thickness. E indicates that each of the variables are functions of photon energy. Figure 2: Impact of an IBEX MAP structure on an incident monochromatic X ray beam. I m1 =I 0.exp( μ s t s μ m1 t m1 ) I mn =I 0.exp( μ s t s μ mn t mn ) Eq. 2 Figure 2 shows the local effect (a few pixels) of an IBEX MAP structure, which is repeated across the whole detector. Eq. 2, which is derived from Eq. 1, describes how incident X-rays (intensity I 0 ) are attenuated by both a MAP and a uniform sample. In a system with a polychromatic X ray beam, the detector forms an image proportional to the integral of I m over an X ray spectrum which is modified locally by the IBEX MAP (known) and the sample (to be analysed). For a given sample, the measured intensity signature ( I m1...n (E)dE ) behind the MAP can be uniquely identified. Therefore, with suitable training, material properties can be labelled and therefore identified by comparing these unique signatures. In addition to the material information described above, a high resolution conventional absorption contrast image is also delivered. This is achieved by a tuned filter which removes the MAP from the image without compromising the Page 2 of 5

5 diagnostic quality. The equations above describe an approximation to the underlying physical processes which give rise to information from the IBEX MAP. In addition to this, the IBEX algorithms incorporate the effect of scattering by the sample. This helps to refine material information and improves image quality. Supporting data Measurements below have been taken on cadaver donor parts using typical clinical doses on a GE VMX Plus conventional mobile radiography system fitted with a standard TFT detector (Rayence 1417). The IBEX MAP was fitted to the flat-panel detector (FPD). The source-to-detector distance was fixed at 115 cm and the donor body part was placed as close to the detector as possible. Figure 3: Radiograph output of an IBEX equipped detector, measuring a fractured wrist DR images were acquired of the wrist, ankle, and neck of femur of two cadaveric donors with X ray tube kv and mas values appropriate for clinical assessment (Table 1). Donor body part Source kv Source mas Wrist 60 2 Ankle Neck of femur 80 1 Table 1: Exposure conditions for the diagnostic radiography measurements. Diagnostic quality Figure 3, shows an image of a cadaver donor wrist and demonstrates the ability of the IBEX technology to return a diagnostic image with no significant compromise to image quality. Figure 4 shows a subsection of the fracture in the wrist with a high zoom to demonstrate the retention of detail and the rejection of any modulation Figure 4: Close up of fracture in figure 4, demonstrating the retention of high resolution information. introduced by the IBEX technology. It is important to note here that the procedure used to remove the MAP imprint from the image results in an image which retains the full pixel resolution of the detector. The capability of the IBEX technology to deliver high quality outputs can be demonstrated quantitatively by an analysis of imaging system parameters. Modulation transfer function (MTF) has been assessed with the IBEX technology with an RQA5 beam quality, giving the graph in Figure 5. Page 3 of 5

6 Figure 5: MTF for an IBEX equipped Rayence 1417 FPD The effect of the IBEX technology on the MTF is a notch in the frequency response of the detector. This can be tuned to have minimal effect on image quality by positioning the notch outside of the sensitive frequency range. This is demonstrated by the retention of important detail in Figure 4. Composition measurement Figure 6 shows a radiograph of an ankle captured with an IBEX equipped detector. Using the material information gathered, this image can be transformed into an image displaying BMD, as presented in Figure 7. Furthermore, as in standard DEXA measurements, a region of interest can be used to generate an average BMD. Figure 7: BMD heat map generated from material information provided by an IBEX equipped detector. Scatter removal The unique information gathered when using an IBEX-equipped detector can be used for more than composition measurement. IBEX technology can remove scatter without the need for an anti-scatter-grid (ASG), as demonstrated in Figures 8 and 9. Our use of measured material information gives image improvements with potential benefits over existing naïve algorithms. In this case both images of the same neck of femur have been contrast stretched to saturate the same number of image pixels, the IBEX scatter corrected version returns a flatter, higher contrast image which is representative of the scatter free case. Figure 6: Radiographic image of an ankle using an IBEX equipped detector. Page 4 of 5

7 Summary The application of IBEX technology to medical radiography creates a series of outputs from a single acquisition. These are: Material and composition information, including BMD measurement. A high quality, full resolution radiograph. Improved image quality at lower dose by gridless scatter correction. Figure 8: Raw image of hip with no anti-scatter grid. Acknowledgments This technology has been developed in collaboration Durham University with testing carried out in partnership with clinicians and medical physicists at the Freeman Hospital and Newcastle Surgical Training Centre. The project has been funded with support from Innovate UK. Patents IBEX technology is covered by UK patents GB , GB , GB , GB and US patent US Patents in other territories pending. Figure 9: Gridless scatter-corrected image of the same body part as Figure 8 using an IBEX equipped detector. Since an ASG is no longer required, images can be captured at significantly lower patient dose and the resulting images have none of the artefacts associated with the ASG. Page 5 of 5

8 About IBEX IBEX Innovations Limited was created in 2010 to develop and commercialise an innovative X-ray detector technology. IBEX is based in modern facilities on the NETPark Science Park in the North-East of England, where it employs a team of highly skilled scientists, engineers and business professionals. IBEX is supported by private venture capital investment and grant funding from both the UK Government and the European Commission. Contact IBEX Innovations Ltd. Discovery 2 NETPark William Armstrong Way Sedgefield UK T: +44 (0) W: