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MRI in dentistry

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This is a presentation describing in brief regarding the physics behind MRI and it's application from dental point of view. It contains few videos as well.

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MRI in dentistry

  1. 1. MRI (MAGNETIC RESONANCE IMAGING) Prepared by- DIVYA PANDAY Under the guidance of – • Dr. Sunita • Dr. Sujoy Ghosh • Dr. Meera chaudhary • Dr. khushboo
  2. 2. CONTENTS  Introduction  Protons  Precession  Resonance  Magnetic resonance signal  T1 and T2 relaxation  Radiofrequency pulse sequence  Tissue contrast  Scanner gradient  Advantages  Disadvantages  Applications  references
  3. 3. PROTONS  Proton – spin – angular momentum  Spin – associated with charge – B generated in nuclei – act as magnet– magnet dipole has magnetic moment.
  4. 4.  Magnetic dipoles randomly oriented –Bext - SPIN UP SPIN DOWN
  5. 5. PRECESSION  Magnetic moment of H+ in a Bext – do not align exactly with the direction of Bext – TILT from a position exactly parallel to Bext
  6. 6.  Bext – axis of spinning of H+ to wobble(precess) around the lines of B ext.  This frequency of precession • PRECESSION FREQUENCY/ • RESONANCE FREQUENCY/ • LARMOR FREQUENCY  Depends on • Atom • Strength of Bext- 0.1-4 Tesla
  7. 7. RESONANCE  Energy to energy – provided by radiofrequency(RF) spectrum of EM spectrum.  When RF = larmor frequency  resonance.
  8. 8. COIL PATIENT RESONANCE Spin up to spin down BH+ longitudinal ses RF Causes the H+ to precess in phase BH+ transverse
  9. 9.  Longer RF pulse –BH+ longitudinal BH+ transverse  90 degree RF pulse/flip angle of 90 degree Significant intensity and duration – BH+ longitudinal sed to 0
  10. 10. MAGENTIC RESONANCE SIGNAL Current in a receiver coil Precession of H+ in phase MR signal
  11. 11.  Frequency of this AC current = RF pulse = larmor frequency.  Magnitude of MR signal 1. Density of H+ 2. Loosely bound H+
  12. 12. BH+ longitudinal returned to original Dephase RELAXATION RF turned off  BH+ Transverse- DECAY MR signal  FREE INDUCTION DECAY SIGNAL
  13. 13. BH+ longitudinal returned to original Dephase RELAXATION RF turned off  BH+ Transverse- DECAY T2 - magnetic moment of H+ interact with each other SPIN SPIN RELAXATION TIME T1 – energy absorbed by lattice SPIN – LATTICE REALAXATIO N TIME T1 and T2 RELAXATION
  14. 14. T1 RELAXATION TIME  It is an exponential process and the time required for 63% of the magnetization to return to equilibrium (the time constant) by this transfer of energy.
  15. 15.  Varies with tissue  Ability to transfer their excess energy to lattice fluid content TI TI fat content  Inherent energy of water- Inhibit transfer of energy  Inherent energy- quickly transfer energy
  16. 16. T2 RELAXATION TIME  Time constant that describes the exponential rate of loss of transverse magnetization.
  17. 17.  Varies with tissue  Depend on packing of tissues. fluid content T2 T2 fat content Closely packed - interaction Loosely packed - interaction
  18. 18.  T2 occurs more rapidly then T1
  19. 19. RF PULSE SEQUENCE Components of RF pulse sequence are set by the operator. Can be used to emphasize various features of tissue being examined
  20. 20. TR and TE  TR(REPETITION TIME) : duration between repeat RF pulses.  TE (ECHO TIME) : time after application of the RF pulse when the MR signal is read.
  21. 21. BH+ longitudinal returned to original Dephase RELAXATION  BH+ Transverse- DECAY Controlled by TE Controlled by TR
  22. 22. IMAGE CONTRAST INTRINSIC- Features of tissues. EXTRINSIC- Parameters of a given pulse • H+ density • T1 • T2 • TR • TE
  23. 23. T1 –Weighted Image Emphasizes differences in T1 values of tissues Accomplished by 1. short TR(300-700ms) 2. short TE(20ms)
  24. 24. Tissue with short T1 Tissue with long T1 BRIGHT DARK • anatomy USE
  25. 25. T2 –Weighted Image Emphasizes differences in T2 values of tissues Accomplished by 1. Long TR(2000ms) 2. Long TE(≥60ms)
  26. 26. Tissue with short T2 (eg-fat) Tissue with long T2 (eg-TMJ fluid CSF fluid) DARK BRIGHT USE • Pathology- since pathologic tissue has more water.
  27. 27. OTHER METHODS  STIR(short tau inversion recovery) – dec signal from fat(FAT SATURATION) – better visualization of adjacent structures.  FLAIR(fluid attenuation inversion recovery) - dec signal from fluid – better visualization of pathology.  CONTRAST AGENT – gadolinium. It dec T1 of enhancing tissue – they appear bright.
  28. 28. SCANNER GRADIENT  3 gradient coils 1. X-axis : left to right 2. Y-axis : anterior to posterior 3. Z-axis : head to toe  Intensity of Bext can be modified when gradient applied  Z gradient turned on  precessional frequency of H+ varies linearly along Bext  RF pulse applied – nuclei with RF = PF – resonate  Hence, desired slice selected.  Z gradient coil turned off – X(phase encoding) and Y(frequency encoding) gradients are turned on – location of signal within xand y is determined.
  29. 29. ADVANTAGES Time Presence of ferromagnetic material Claustrophobic patient Best contrast resolution of soft tissues No ionizing radiation Multiplanar image without reorienting the patient DISADVANTAGES
  30. 30. APPLICATIONS  Soft tissue condition – position and integrity of disk of TMJ  Soft tissue disease –  tongue, cheek, salivary gland, neck – neoplasia  lymph nodes - malignant involvement  Perineural invasion - by malignant neoplasia  Extent of penetration of carcinoma- in cortex of mandible – SWIFT  Neoplasia - Gadolinium enhanced
  31. 31.  Osteomyelitis – edematous change in marrow and surrounding tissue  Location of mandibular nerve  MR angiography
  32. 32. closed NORMAL TMJ
  33. 33. Anterior disk displacement with reduction closed Lateral displacement Open- Normal
  34. 34. T2 image - effusion Anterior disk displacement without reduction T2 image- effusion T1 image- anterior displacement T1 image- remains anterior to condyle
  35. 35. a. T1 image- bow tie appearance b. T2 image- inflammatory effusion c. Anterior disk displacement TMJ
  36. 36. DEGENERATIVE JOINT DISEASE
  37. 37. a. T1 image b. T1 post gadolinium c. T2 image RHABDOMYOSARCOMA- soft tissue of right face
  38. 38. MULTIPLE MYELOMA- right mandible and right carotid space T1 post- contrast(fat saturation) T1 image T2 post- saturation(fat saturation)
  39. 39. T1 image post- gadolinium, Fat saturation T2 image T1 image ADENOID CYSTIC CARCINOMA in submandibular gland
  40. 40. T2 image – hyperintense to muscle T1 image – isointense to muscle PLEOMORPHIC ADENOMA
  41. 41. CYST IN LEFT PAROTID GLAND
  42. 42. SIALECTASES of parotid gland T2 image
  43. 43. ANGIOGRAPHY
  44. 44. 1. RF pulse causes a. B transverse b. B longitudinal c. Both d. None 2. T1 weighted image is used for studying a. Anatomy b. pathology 3. T1 weighted image uses a. Short TR, short TE b. Long TR, long TE c. Short TR, long TE d. Long TR, short TE
  45. 45. 4. In T2 weighted image, tissue with long T2 (eg- TMJ fluid) appears a. Bright b. Dark c. Both d. None 5. Which diagnostic method would you prefer for diagnosing collection of effusion in TMJ a. T1 b. T2 c. Both d. None 6. Which diagnostic method would you prefer for diagnosing disk displacement in TMJ? a. T1 b. T2 c. Both d. none
  46. 46. 7. This is a case of lymphoepithelial cyst in right parotid space, which is T2? a. A b. B
  47. 47. 8. MRI uses a. Ionizing radiation b. Non-ionizing radiation c. Both d. None 9. MRI is used for- a. Neoplasia of soft tissue b. Mallignant involvement of lymph nodes c. Both d. none 10. Contrast agent used is ________?
  48. 48. REFERENCES  White and pharaoh – 1st South Asian edition
  49. 49. THANKYOU
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This is a presentation describing in brief regarding the physics behind MRI and it's application from dental point of view. It contains few videos as well.

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