DEPARTMENT OF BIOMEDICAL ENGINEERING An Open Source Imaging Platform for Small Animal Imaging and Therapy Jay Sekhon—Leader Jon Seaton—Communicator Whitney Johnson—BSAC Sarah Springborn—BWIG Client: Dr. Thomas Rockwell Mackie Dr. Robert Jeraj Surendra Prajapati Advisor: Prof. Willis Tompkins March 10, 2010Mid-Semester Report Mar.10.2010 ______________________________________________________________________________________ 2 Table of Contents: Abstract............................................................................................................................... 3 Open Source........................................................................................................................ 3 Computed Tomography Background.................................................................................. 3 CT Specifications................................................................................................................ 7 Positron Emission Tomography.......................................................................................... 8 PET Specifications............................................................................................................ 10 Radiation Therapy............................................................................................................. 11 RT Specifications.............................................................................................................. 12 Combination Systems ....................................................................................................... 13 Combination System Specifications ................................................................................. 14 Conclusion and Future Work............................................................................................ 14 References......................................................................................................................... 16 Appendix A-Product Design Specifications ..................................................................... 18Mid-Semester Report Mar.10.2010 ______________________________________________________________________________________ 3 Abstract An open source medical device has the benefits of a cheaper cost and more collaboration amongst researchers. A combined computer tomography (CT), positron emission tomography (PET) and radiation therapy (RT) system is being developed in the spirit of open source technology. The combination of these systems has the added benefit of correlating data among the imaging systems and using this data for precise radiation therapy treatment. The CT system uses X-ray radiation and detectors to produce 2-D and 3-D cross-sectional images of anatomical structures at high resolution. The PET system uses radioactive tracers to highlight metabolic activity of different biological structures. The RT system uses high intensity X-ray radiation to non-invasively obliterate cancerous cells in the body. A table of specifications for various components of the different systems has been developed with the intention of designing a combined system with the minimal number of components. Open Source In collaboration with the Morgridge Institute for Research, the client is developing an Open Source Medical Device (OSMD) program, which would provide researchers around the world free access to a device’s design and development. The OSMD program brings researchers together, encouraging cooperation during the design process. Another advantage to open sourcing is that it makes expensive instruments and technology available to research groups with limited funding. As all software and hardware specifications are accessible, researchers can build and design the system for their own use, avoiding buying an expensive unit directly from one manufacturer [11]. Computed Tomography Background Computed Tomography (CT) is a common technique used to obtain 2-D or 3-D images that display internal structure. CT by itself is not a specific imaging system; instead the term is used to describe the method in which an image is reconstructed. Positron Emission Tomography (PET), Single Photon Emission Tomography (SPECT), and x-ray imaging all use CT to create 2-D or 3-D representations from projections. For the purposes of this project, x-ray CT will be the primary technique implemented in the imaging device. In x-ray CT systems, electromagnetic radiation is applied to an object and attenuated as seen in Figure 1. Detectors located opposite the x-ray source measure the remaining radiation, creating a projection of how the objected scattered the energy. The x-ray source is then rotated about the object to create an array of projection data, which can be used to reconstruct a 2-D image. By moving the object in the y-direction as seen in Figure 1, multiple slices can be obtained and used to create a 3-D image.Mid-Semester Report Mar.10.2010 ______________________________________________________________________________________ 4 Figure 1. Method of X-Ray CT data collection. [8] In order to create x-rays, one must first understand the nature of electromagnetic (EM) radiation. X-rays are a subclass of electromagnetic radiation occurring with energies between 20keV to 120keV [6]. Electromagnetic radiation is primarily the result of both an oscillation electric and magnetic field. However, while it can be modeled as a wave, such radiation also has particle properties, the particle being known as a photon. This type of radiation is known as non-ionized radiation since it does not contain a charge. Thus, the energy of EM radiation comes from kinetic energy of photon’s motion. The relationship between the energy of the photon and the frequency of its oscillations as a wave is given by: E = hf Where E is the energy, h is Plank’s constant, and f is frequency. Thus, in order to create x-rays, one must create an event in which energy is released from the system. A common method is to collide electrons with a target and by conservation of energy. As the electrons slow down, they release energy by conservation, also called Bremsstrahlung radiation [6]. Thus by adjusting the speed in which the electrons hit a target, we can adjust the energy of radiation produced. Since x-rays can be thought of as a particle, it is clear to understand their interaction with other
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