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Resident Physics Lectures

Resident Physics Lectures. Plain Film Tomography. George David Associate Professor Department of Radiology Medical College of Georgia. Body Section Tomography. Not CT Body Section Imaging Goal keep plane of interest in focus blur all other plans enhances contrast

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Resident Physics Lectures

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  1. Resident Physics Lectures Plain Film Tomography George David Associate Professor Department of Radiology Medical College of Georgia

  2. Body Section Tomography • Not CT • Body Section Imaging • Goal • keep plane of interest in focus • blur all other plans • enhances contrast • Popularity decreasing because of • CT • MRI

  3. Tomography History • Predates CT by decades • Used to be popular for inner ear studies • Still used at MCG for IVP’s

  4. Tomography Blurring • Blurring accomplished by synchronous movement of tube & film • tube & bucky physically connected by rod • rod pivots around fulcrum • tube moves one direction • film moves in other direction

  5. Conventional Tomography Blurring • Image produced on film • Objects above or below fulcrum plane change position on film & thus blur

  6. Tomography Blurring • the further from the fulcrum an object is, the more it blurs!

  7. Tomography Blurring • objects shaped & oriented in direction of motion • elongate • do not blur

  8. Tomographic Blurring • Blurring improved by use of complex motions circular tri-spiral elliptical Hypocycloidal

  9. Complex Blurring • The more complex the blurring motion • the sharper the tomographic image • better blurring • the more expensive the machine $

  10. Tomo Patient Doses • Tomo can be high dose procedure • several rads not unusual • one image per cut with film • cuts at many levels routinely employed to find cut of interest • each cut exposes entire field • Can do multiple images per cut with digital receptor

  11. Thickness of Cut • Same as thickness of region in focus • Determined by angle tube moves • Larger angles yield thinner cuts • more motion = more blurring • Smaller angles yield thicker cuts • 0o (stationary) yields conventional film

  12. Thickness of Cut Smaller Angle; Thicker Cut Larger Angle; Thinner Cut

  13. Cut Thickness • Approximate cut thickness for linear tomo Tomo Angle Thickness of Cut (mm) (degrees) ------------------------------------------------------- 0 Infinite (non-tomo) 2 31 4 16 6 11 10 6 20 3 35 2 50 1

  14. Grids & Tomo • Linear grid used • Grid lines parallel with table for linear tomo • Grid must change orientation (rotate) in complex motion tomo • eliminates grid cutoff

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