Basic Concepts of Other Imaging Modalities

1. Basic Concepts of Other Imaging Modalities Dent 5101

2. Body-section Radiography • A special radiographic technique that blurs out the shadows of superimposed structures • Object of interest less blurred • Does not improve the sharpness

3. Tube and Film Move in Opposite Direction

5. Tube and film move in opposite direction, and rotate about a fulcrum • The level of the fulcrum is the focal plain

6. Blurring • Determined by: • Distance of the tube travel • Distance from the focal plain • Distance from the film • Orientation of tube travel

7. Types of Tomographic Motions Linear Circular Elliptical Trispiral Hypocycloidal Figure 8

8. Panoramic Radiography

9. Panoramic Radiography • Obtained by rotating a narrow beam of radiation in the horizontal plane • The film is rotated in the opposite direction while the object (jaws) is stationary

11. Focal Trough • A 3-dimensional curved zone or image layer in which structures are reasonably well defined.

12. Types of Panoramic Machines • Panorex – Two centers of rotation. Interruption of exposure in the midline • Orthopantomogram – Three centers of rotation. Continuous image

13. Panorex Image

14. Orthopantpmograph

16. Image Intensification

17. Early Fluoroscopy • Early fluoroscopy done by direct observation • Screen was poorly illuminated - image perception inadequate

18. Image Intensification • Image intensifier improved viewing of fluoroscopy

19. Intensifier Tube • Four parts: • Input phosphor and photocathode • Electrostatic focusing lens • Accelerating anode • Output phosphor

20. Intensifier Tube (Cont.) • Input phosphor: cesium iodide (CsI) or zinc-cadmium-sulfide. • Photocathode: A photo-emissive metal. • Electrostatic focusing lens: series of negatively charged electrodes—focuses the electron beam. • Output phosphor: Provides thousand-fold more light photons.

21. Intensifier Tube • Used in: • Sialography • Arthrography

22. Digital Imaging

23. Digital Imaging • Conventional film-intensifying screen radiograph - analog image. • Digital radiograph—film-less. • Conventional films can be digitized, with a likelihood of loss of information.

24. Photostimulable Phosphor (PSP) • Storage phosphor • Indirect Digital Radiography • Similar to the intensifying screen phosphors • Difference - PSP traps a significant number of electrons in its phosphor, which is later read by a laser beam

25. Photostimulable Phosphor (PSP)

29. Charge-coupled Devices • An amorphous silicon wafer containing an array of pixels (picture elements) • Each pixel acts as a capacitor storing charge • On radiation exposure, electric charge is deposited in the pixels proportional to the intensity of the beam • The variation in charge deposition can be digitally converted to an image

30. Pixels • Each square (pixel) has its own color (numerical value)

32. Pixel Array

33. CMOS • Complimentary Metal Oxide Semiconductor • Principle similar to CCD • Simpler circuit design

34. CCD, CMOS

35. Resolution • Ability to identify two different objects that are close to each other • D-speed films: >10 line pair/mm • Digital images:7-10 line pair/mm • Eyes: 4-6 line pair/mm

36. Digital Subtraction • Shows changes in an area over time • Requires two films exposed with similar geometry

37. Digital Subtraction • Two radiographs are obtained • Identical position • One superimposed over another • Differences in two images identified digitally • Allows identifying changes in hard tissue that occurred between the two examinations

38. Radiation Dose

39. Image Processing/Reconstruction • To improve diagnostic accuracy • May improve the diagnosis of one disease, while obscure another • Fraud

40. Digital Radiography: Advantages • Instant images • Consistent quality • High signal/noise ratio • Image Manipulation • Lower radiation dose

41. Disadvantages • Lower resolution • Quality depends on monitor and printer • Print quality often not optimal • Higher initial cost • Unwanted manipulation of images