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Image Processing Project Tomographic Image Reconstruction

Image Processing Project Tomographic Image Reconstruction. Introduction. This presentation will cover a brief description of tomographic imaging, image reconstruction methods, and design challenges. 1. Tomography. 2. Image Reconstruction. 3. Design Challenges. 4. Your Project.

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Image Processing Project Tomographic Image Reconstruction

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  1. Image Processing Project Tomographic Image Reconstruction Introduction

  2. This presentation will cover a brief description of tomographic imaging, image reconstruction methods, and design challenges. 1. Tomography 2. Image Reconstruction 3. Design Challenges 4. Your Project

  3. Background: Importance of Medical Imaging • There are an estimated 630,000 imaging procedures every week in the US. • The average radiologist has a case load around 35% higher than just 5 years ago. “Molecular imaging holds great promise for early detection and treatment of numerous diseases, for providing researchers with detailed information about cellular physiology and function, and for facilitating the goal of personalized medicine.” – NIH roadmap

  4. Modern imaging modalities cover the EM spectrum and all scales of resolution. Organism Organs Tissue Cells Proteins Genes

  5. Tomography X-ray CT Images of the Human Abdomen X-ray CT Scanner

  6. Tomography means to image using sections or slices, tomo is Greek for cut, graph means form (plot) an image. • Tomograms can be created using a variety of physical mechanisms • X-ray Attenuation • Nuclear Magnetic Resonance • Position-Electron Annihilation • Ultrasound Interactions • Modalities • X-ray Computed Tomography • Magnetic Resonance Imaging • Positron Emission Tomography • Ultrasound Interactions

  7. To do Tomography, we need to have many projections from different angles. • Transforms the object we are imaging to a Sinogram

  8. Forming the Sinogram

  9. = density of 25 = density of 0 = density of 50

  10. = density of 25 = density of 0 = density of 50

  11. = density of 25 = density of 50 = density of 0

  12. = density of 25 = density of 50

  13. = density of 25 = density of 50

  14. = density of 25 = density of 50 Our First Projection

  15. = density of 25 = density of 50 Our First Projection

  16. = density of 25 = density of 50 Our First Projection

  17. = density of 25 = density of 50 Our First Projection

  18. = density of 25 = density of 50 Our First Projection

  19. Our Second Projection

  20. Our Third Projection

  21. Sinogram

  22. Sinogram

  23. Sinogram

  24. Sinogram

  25. Sinogram

  26. Sinogram

  27. Sinogram

  28. Sinogram

  29. Sinogram

  30. Sinogram

  31. Sinogram

  32. Sinogram

  33. Sinogram

  34. Sinogram

  35. Sinogram

  36. Sinogram

  37. Sinogram

  38. Sinogram

  39. Given all these projections, how do we reconstruct the tomogram? • Filtered Backprojection

  40. Image Reconstruction Using Filtered Backprojection Filter Backprojection

  41. Backprojection • Backprojection “smears” the data back.

  42. Backprojection • Backprojection “smears” the data back.

  43. Backprojection • Backprojection “smears” the data back. infinite number of projections

  44. Filtered-Backprojection • If we filter the projections before backprojection we can recover the original object.

  45. Filtering the projection • Filtering is a basic operation in signal processing. • Spatial or Temporal domain filtering (convolution) • Frequency domain filtering • Lets consider spatial domain filtering: input signal (projection) filtered signal filter kernel convolution operator

  46. TPS: Think-Pair-Share • Match up the following Sinograms with their objects O1 S1 O? = S? O2 S2 O3 S3

  47. Design Challenges • In cases where the projection is taken using x-rays, there is a risk associated. • x-rays absorbed by the body can cause damage to DNA directly or through the formation of free radicals. • The larger the number of projections and the longer the x-rays are on, the higher the dose delivered to the patient. • There is a fundamental tradeoff between dose, the number of projections, and the noise in the projections.

  48. Basics of Radiation Biology • We are constantly exposed to naturally occurring radiation (radon, cosmic rays) • about 3 milli-Sieverts per year • there is some evidence that anti-oxidants, found in fruits and vegetables, can protect cells from free radical formation • A single chest x-ray is equivalent to about 10 days of natural exposure • A whole-body x-ray CT exam is equivalent to about 3 years of equivalent natural exposure

  49. Radiation Monitoring • OSHA requires all those who work with radiation to be badged and monitored for dose.

  50. Noise in X-rays • X-ray images are formed by counting the number of photons leaving the subject compared to those entering. • The count is a random variable that is Poisson distributed.

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