2. Basic Concepts of Other Imaging Modalities Dent 5101

3. 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

4. Tube and Film Move in Opposite Direction

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

7. Blurring Blurring Determined by: –Distance of the tube travel –Distance from the focal plain –Distance from the film –Orientation of tube travel

8. Panoramic Radiography

9. 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. Computed Tomography

23. Introduced in 70’s Principle: Internal structures of an object can be reconstructed from multiple projections of the object

24. Philips CTVision Secura

25. Mechanism of CT X-ray tube is rotated around the patient Radiation transmitted through the patient is absorbed by a ring of detectors Absorbed radiation is converted to an image Detectors

26. Detectors Scintillation crystals Xenon-gas ionization chamber

27. Scintillation Crystals Materials that produce light (scintillate) when x-rays interact Similar to intensifying screen Number of light photons produced energy ofincident x-ray beam Light photons need to be converted to electrical signal

28. Ionization Chamber X-ray ionizes xenon gas Electrons move towards anode Generates small current Converted to electrical signal

29. Attenuation Reduction in the intensity of an x- ray beam as it traverses matter, by either the absorption or deflection of photons from the beam

30. Pixel - Voxel Pixel - picture element Voxel - volume element

31. CT Number Typical CT values TissuesRange (Hounsfield unit) Air-1000 Lung-200 to –500 Fat-50 to –200 Water0 Muscle+25 to +45 Bone+200 to +1000

32. Image Display: Windowing Usual CRT can display ~256 gray levels 2000 CT numbers Select the CT number of the tissue of interest, then range of ±128 shades

33. Cone Beam CT Uses cone shaped x- ray beam. Beam scans the head in 360 degrees. Raw data are reformatted to make images

36. Benefits of Cone Beam Imaging Less radiation than multi-detector CT due to focused X-rays (less scatter) Fast and comfortable for the patient (9 to 60s) Procedure specific to head and neck applications One scan yields multiple 2D and 3D images

37. Anatomic Landmarks on CT

39. Axial CT Sections

43. 1.Zygomatic Arch 2.Lat. Pterygoid plate 3.Optic canal 4.Sphenoid sinus 5.Soft tissues of nasopharynx Coronal Sections

44. 1.Frontal bone (orbital plate) 2.Ethmoid air cells 3.Middle concha 4.Maxillary sinus 5.Inferior concha

45. 1.Vomer 2.Ramus 3.Follicle of molar 4.Gr. wing of Sphenoid 5.Tongue 6.Mylohyoid m

46. Magnetic Resonance Imaging

47. Three steps of MRI MRR –Magnetic Field –Radio-frequency Pulse –Relaxation

48. Magnetic Moment Direction

49. Application of RF Pulse Relaxation

50. Spin or Angular Moment 1 H, 14 N, 31 P, 13 C, and 23 Na has nuclear spin They spin around their axes similar to earth spinning around its axis Elements with nuclear spin has odd number of protons, neutrons

51. Magnetic Moment When a nucleus spins, it has angular momentum When the spinning nucleus has a charge, it has magnetic dipole moment Moving charges produce magnetic fields

52. Hydrogen Nucleus Most abundant Yields strongest MR signal

53. Radiofrequency Pulse RF pulse is an electromagnetic wave Caused by a brief application of an alternating electric current

54. Receiver Coils Send or “broadcast” the RF pulse Receive or “pick up” the MR signals Types: Body coils, head coils, and a variety of surface coils

55. Philips Gyroscan Intera

56. Relaxation This is the process that occurs after terminating the RF pulse The physical changes caused by the RF pulse revert back to original state

57. T1- Spin Lattice Relaxation At the end of RF pulse, transversely aligned nuclei tend to return back to equilibrium This return to equilibrium results in the transfer of energy

58. T2- Spin-spin Relaxation While the nuclei are in transverse phase, their magnetization interfere with each other. This interference leads to the loss of transverse magnetization.

59. Magnetic Field Strengths Measured in Tesla or Gauss Usual MRI field strength ranges from 0.5 to 2.0 Tesla Earth’s magnetic field is about 0.00005 Tesla (0.5 Gauss)

60. Advantages of MRI Higher resolution of tissues No ionizing radiation Multiplanar imaging

61. Disadvantages of MRI Long imaging time Hazards with ferromagnetic metals (pacemakers, vascular clips, etc) Claustrophobia Higher cost

62. Relative Brightness of Tissues FatWhite Marrow Brain MuscleGray Body Fluid TMJ Disk Cortical Bone AirBlack

65. Nuclear Medicine

66. Radioactive compounds Target tissues Radioactive agents pools in the target tissues Detected and imaged by external detectors (gamma camera).

67. Nuclear Medicine Shows structure and function of the target tissues Static and dynamic conditions Scintigraphy scans or RN (radionuclide) scans Bone scans or salivary gland scans

68. Technetium 99m TcO 4 - - thyroid and salivary gland scan 99 Tc phosphate - bone scan

69. Is this an active disease?

72. Phases of Salivary Gland Scan Flow phase: –Five to 10 mCi of 99m TcO 4 –first 30 to 120 seconds –shows flow of blood Concentration phase: –next 30 to 45 minutes –demonstrate the anatomy and function Washout Phase: –administer sialagogue –demonstrates secretory capabilities

73. Cephalometric Radiography Reproducible and standardized views For measurements and assess growth Fixed source to film distance – 60 inches Cephalostats and earplugs help in reproducible positions

74. Cephalometric Radiography

75. Contrast Agents

76. Radiopaque materials Water soluble Fat soluble 28 – 38% iodine

77. Phases of Sialography Ductal Acinar Evacuation

78. Indications of Sialography Acute swelling secondary to ductal obstruction Recurrent Inflammation Palpable salivary gland mass Autoimmune Sialadenitis

79. Contraindications of Sialography Sensitivity to contrast agents Acute Sialadenitis Limited use in tumor diagnosis

81. Scintigraphy Sialography Radioactive materialRadiopaque material Through blood stream Through duct All glands imaged at the same time One gland at a time Imaged by gamma camera Imaged by fluoroscopy

82. Contrast Studies: Arthrography

83. Arthrography Contrast media is introduced in joint spaces Upper vs. lower joint space Viewed by Image Intensifier Fluoroscopy Video recording allows study of joint movement

84. Contrast Material Injection

85. Open Position Translation of condyle Reduction of disk