Successfully reported this slideshow.
We use your LinkedIn profile and activity data to personalize ads and to show you more relevant ads. You can change your ad preferences anytime.
Upcoming SlideShare
NANOPARTICLES IN CANCER DIAGNOSIS AND TREATMENT
Next
Download to read offline and view in fullscreen.

147

Share

Download to read offline

MRI

Download to read offline

MRI - Strange physics ahead . Step by step approach of basics of MRI physics with applications in dentistry.

Related Books

Free with a 30 day trial from Scribd

See all

MRI

  1. 1. MAGNETIC RESONANCE IMAGING By: Ujjwala Rastogi MDS
  2. 2. CONTENTS 1. Introduction 2. Basic principle of MRI 3. T1 and T2 relaxation and image weighting 4. K-space and scanning parameter 5. MRI instrumentation 6. MRI Artifacts 7. MRI contrast media 8. Principles of interpretation 9. Conclusion 10. References
  3. 3. Introduction Definition History Indications and Contraindications Advantages and Disadvantages
  4. 4. Definition Magnetic Resonance Imaging Magnet Radio Frequency = Resonance Imaging It is a non-invasive method for mapping internal structure within the body which uses non-ionizing electromagnetic radiation and employes radio frequency radiation in the presence of carefully controlled magentic fields to produce high quality cross-sectional images of the body in any plane
  5. 5. French mathematician & engineer. Developed Mathematical transformation: analysis of heat transfer b/w solid bodies. Rapidly process the frequency signals of NMR data & utilize this for image Reconstruction. Invented tesla coil in 1891 Started studying the magnetic Properties in1930 He succeeded in detecting and Measuring single states of rotation of atoms and molecules, and in determining the magnetic moments of the nuclei. Had the idea of applying magnetic gradient in 3 spatial dimension & used computer to create 2D NMR Images c/d “ZEUGMATOGRAPHY” Raymond Damadian 1977 Produced the MR image of The body.
  6. 6. Indications • Diagnosing: strokes; infections of the brain/spine/CNS; tendonitis • Visualising: Injuries; torn ligaments – especially in areas difficult to see like the wrist, ankle or knee • Evaluating: Masses in soft tissue; cysts; bone tumours or disc problems.
  7. 7. Contraindications • The strength of the magnet is 5000 times stronger than the earth so all metals must be removed. • People with pacemakers or metal fragments in the eye cannot have a scan • There has not been enough research done on babies and magnetism, so pregnant women shouldn’t have one done before the 4th month of pregnancy – unless it is highly necessary.
  8. 8. Advantages The MRI does not use ionizing radiation, which is a comfort to patients • Also the contrast dye has a very low chance of side effects • ‘Slice’ images can be taken on many planes
  9. 9. Disadvantages 1. Claustrophobia-Patients are in a very enclosed space. 2. Weight and size - There are limitations to how big a patient can be. 3. Noise - The scanner is very noisy. 4. Keeping still - Patients have to keep very still for extended periods of time. 5. Cost - A scanner is very, very expensive, therefore scanning is also costly. 6. Medical Contraindications - Pacemakers, metal objects in body etc.
  10. 10. Basic principle of MRI 4 steps Longitudinal and transverse magnetization MR signal and localization of signal
  11. 11. • Placing the patient in the magnet • Sending radiofrequency (RF) pulse by coil • Receiving signals from the patient by coil • Transformation of signals into image by complex processing in the computer. Four basics steps are involved in getting an MR image :
  12. 12. • Body has many such atoms that can act as good MR nuclei (1H, 13C, 19F, 23Na) • Hydrogen nuclei is not only positively charged, but also has magnetic spin • MRI utilizes this magnetic spin property of protons of hydrogen to elicit images
  13. 13. A Single Proton There is electric charge on the surface of the proton, thus creating a small current loop and generating magnetic moment m. The proton also has mass which generates an angular momentum J when it is spinning. Thus proton “magnet” differs from a magnetic bar in that it also possesses angular momentum caused by spinning. + + + J m
  14. 14. Why Hydrogen ions are used in MRI? an unpaired proton which is positively charged Every hydrogen nucleus is a tiny magnet which produces small but noticeable magnetic field. Hydrogen atom is the only major species in the body that is MR sensitive Abundant in the body in the form of water and fat MRI is hydrogen (proton) imaging The protons - being little magnets - align themselves in the external magnetic field like a compass needle in the magnetic field of the earth. May align parallel or anti-parallel
  15. 15. • Larmor equation 𝜔0is the precession frequency (in Hz or MHz), B0 is the strength of the external magnetic field, which is given in Tesla (T) and 𝛾is the so-called gyromagnetic ratio. the value for protons is 42.5 MHz/T The equation states that the precession frequency becomes higher when the magnetic field strength increases.
  16. 16. Main Magnet Field Bo • Purpose is to align H protons in H2O (little magnets) [Main magnet and some of its lines of force] [Little magnets lining up with external lines of force]
  17. 17. Net magnetization • Half of the protons align along the magnetic field and rest are aligned opposite • At room temperature, the population ratio of anti- parallel versus parallel protons is roughly 100,000 to 100,006 per Tesla of B0 • These extra protons produce net magnetization vector (M) • Net magnetization depends on B0 and temperature
  18. 18. Longitudinal magnetization External magnetic field is directed along the z axis. Z axis is the long axis of the patient as well as bore of the magnet.
  19. 19. Transverse magnetization When radiofrequency pulse is send, the precessing protons pick up some energy from RF pulse. Some of these protons go to higher energy level and start precessing antiparallel (along negative side of z axis). The imbalance results in magnetization into the transverse (X-Y) plane  transverse magnetization
  20. 20. MR signal MR Signal • NMV rotates around transverse plane. It passes across Receiver Coil inducing voltage in it. • RF Removed  Signal decreased  Amplitude of MR Signal decreased • Free Induction Decay "FID": – Free (No RF Pulse) – ID (because of Decay of Induced signal in Receiver Coil)
  21. 21. • Measuring the MR Signal: – the moving proton vector induces a signal in the RF antenna – The signal is picked up by a coil and sent to the computer system. – The computer receives mathematical data, which is converted through the use of a Fourier transform into an image.
  22. 22. T1 and T2 relaxation and image weighting Longitudina l and transverse relaxation T1 and T2 relaxation TR and TE Proton density image
  23. 23. T1 and T2 relaxation • When RF pulse is stopped higher energy gained by proton is retransmitted and hydrogen nuclei relax by two mechanisms • T1 or spin lattice relaxation- by which original magnetization begins to recover. • T2 relaxation or spin spin relaxation - by which magnetization in X-Y plane decays towards zero in an exponential fashion. It is due to incoherence of H nuclei.
  24. 24. T1 relaxation After protons are Excited with RF pulse They move out of Alignment with B0 But once the RF Pulse is stopped they Realign after some Time And this is called T1 relaxation T1 is defined as the time it takes for the hydrogen nucleus to recover 63% of its longitudinal magnetization
  25. 25. T2 relaxation time is the time for 63% of the protons to become dephased owing to interactions among nearby protons.
  26. 26. Repetition Time "TR" Time from application of one RF pulse To the application of the next Or the time between two excitations is called repetition time (it affects the length of relaxation period after application of one RF excitation pulse to the beginning of the next).
  27. 27. Time to Echo "TE" Time between RF excitation pulse and collection of signal Or time interval in which signals are measured after RF excitation (it affects the length of relaxation period after removal of RF excitation pulse and the peak of signal received in receiver coil)
  28. 28. TE/2 TE/2 TR (repetition time) = time between RF excitation pulses FID TE = time from 90o pulse to center of spin echo 90 o 90o 180o Spin Echo Spin Echo (SE) sequence
  29. 29. T1 in WaterT1 in Fat inefficient at receiving energy T1 is longer i.e. nuclei take a lot longer to dispose energy to surrounding water tissue absorb energy quickly T1 is very short i.e. nuclei dispose their energy to surrounding fat tissue and return to B0 in very short time FAT WATER
  30. 30. T2 Decay Fat much better at energy exchange than Water Because T2 depends on: 1-How closely molecular motion of atoms matches Larmor Frequency 2-Proximity of other spins So; Fat's T2 time is very short compared to water FAT WATER
  31. 31. T1 time & T2 Decay are an intrinsic contrast parameter that are inherent to tissue being imaged.
  32. 32. • By varying the TR and TE one can obtain T1WI and T2WI • In general a short TR (<1000ms) and short TE (<45 ms) scan is T1WI • Long TR (>2000ms) and long TE (>45ms) scan is T2WI • Long TR (>2000ms) and short TE (<45ms) scan is proton density image
  33. 33. Types of MRI imagings T1WI T2WI FLAIR STIR DWI ADC GRE MRA MRV MRS MT Post-Gd images
  34. 34. Short TI inversion-recovery (STIR) sequence • In STIR sequences, an inversion-recovery pulse is used to null the signal from fat (180° RF Pulse). • When NMVof fat passes its null point , 90° RF pulse is applied. As little or no longitudinal magnetization is present and the transverse magnetization is insignificant. • It is transverse magnetization that induces an electric current in the receiver coil so no signal is generated from fat. • STIR sequences provide excellent depiction of bone marrow edema which may be the only indication of an occult fracture. • Unlike conventional fat-saturation sequences STIR sequences are not affected by magnetic field inhomogeneities, so they are more efficient for nulling the signal from fat.
  35. 35. Fluid-attenuated inversion recovery (FLAIR) • First described in 1992 and has become one of the corner stones of brain MR imaging protocols • An IR sequence with a long TR and TE and an inversion time (TI) that is tailored to null the signal from CSF • In contrast to real image reconstruction, negative signals are recorded as positive signals of the same strength so that the nulled tissue remains dark and all other tissues have higher signal intensities.
  36. 36. • Most pathologic processes show increased SI on T2-WI, and the conspicuity of lesions that are located close to interfaces b/w brain parenchyma and CSF may be poor in conventional SE or FSE T2-WI sequences. • FLAIR images are heavily T2-weighted with CSF signal suppression, highlights hyperintense lesions and improves their conspicuity and detection, especially when located adjacent to CSF containing spaces
  37. 37. • In addition to T2- weightening, FLAIR possesses considerable T1-weighting, because it largely depends on longitudinal magnetization • As small differences in T1 characteristics are accentuated, mild T1-shortening becomes conspicuous. • This effect is prominent in the CSF-containing spaces, where increased protein content results in high SI (eg, associated with sub-arachnoid space disease) • High SI of hyperacute SAH is caused by T2 prolongation in addition to T1 shortening
  38. 38. K-space and scanning parameter K-space Parameters for scanning
  39. 39. K- space • Simply put, k-space is a matrix usually 512x512 OR 256 x 256 that is used to store data acquired from magnetic resonance of protons. • The math is complex but there is an analogy to this.
  40. 40. • The k-space is filled up in iterations by using the resonance data obtained from magnetic field gradients. • First, we select a slice (in millimeters) by applying a field gradient in the horizontal plane. • Within this slice we try to map out objects in both x and y planes by collecting raw data in these planes. • The y-plane is called phase encoding direction. To obtain this one has to apply field gradient in the vertical (or y-plane) direction. • The x-plane is called frequency encoding direction. To obtain this one has to apply field gradient in the horizontal (or x-plane) direction.
  41. 41. This is an example of how the matrix is filled with data during each slice.
  42. 42. THE SECRET IS IN THE K-SPACE One can see below that the center of k-space is where the contrast information is stored. The periphery is where the fine details of the images are stored. This is nicely depicted in the images below.
  43. 43. MRI instrumentation Magnetism and magnetic field strength Magnets used in MRI Gradients Radiofrequency coil
  44. 44. Magnetism and magnetic field strength
  45. 45. Magnets used in MRI • It produce magnetic field. • By it body protons get align. • It will be around 0.5 to 3.5 Tesla. • Types: » Permanent magnet. » Superconducting magnet. » Resistive magnet. » Gradient magnet.
  46. 46. Coils • A coil consists of one or more loops of conductive wire, looped around the core of the coil. • Used to create a magnetic field or to detect a changing magnetic field by voltage induced in the wire. • A coil is usually a physically small antenna. • The perfect coil produces a uniform magnetic field without significant radiation.
  47. 47. Different Types of MRI Coils in MR Systems • Gradient coils • RF coil 1. Transmit Receive Coil 2. Receive Only Coil 3. Transmit Only Coil 4. Multiply Tuned Coil
  48. 48. Gradient Coils • Coils that produce magnetic field gradients along x- ,y-,and z-directions to encode spatial information • Selective excitation: (during RF) excite those spins within a thin “slice” of the subject • Frequency encoding: (during readout) make the signal’s frequency depend on position • Phase encoding: (between excitation and readout) make the signal’s phase depend on position
  49. 49. Radio Frequency Coil • RF coils are components of every scanner . • Used for two essential purposes – transmitting and receiving signals at the resonant frequency of the protons within the patient. • A typical coil is a tuned LC circuit and may be considered a near-field antenna
  50. 50. Comprehensive Receiving coils  standard configuration: QD head coil QD Neck Coil QD Body Coil QD Extremity Coil Flat Spine Coil Breast Coil
  51. 51. Making Images of the NMR Signal • Uniform magnetic field to set the stage (Main Magnet) • Gradient coils for positional information • RF transceiver (excite and receive) • Digitizer (convert received analog to digital) • Pulse sequencer (controls timing of gradients, RF, and digitizer) • Computer (FFT to form images, store pulse sequences, display results, archive, etc.)
  52. 52. MRI Artifacts Motion related artifacts Para- magnetic artifacts Phase Wrap artifacts Frequency artifacts Susceptibility artifacts Clipping artifact Chemical Shift Artifact Spike artifact “Zebra” artifact
  53. 53. Motion Artifacts  Motion artifacts are caused by phase mis-mapping of the protons. Para-Magnetic Artifacts  Para-magnetic artifacts are caused by metal (~ iron Phase Wrap Artifacts  Phase wrap artifacts are caused by mis-mapping of phase.
  54. 54. Frequency Artifacts  Frequency artifacts are caused by „dirty‟ frequencies. Faulty electronics, external transmitters, RF-cage leak, non-shielded equipment in the scanner room, metal in the patient, Susceptibility Artifacts  Susceptibility is the ability of substances to be magnetized, for example iron in blood. Clipping Artifact  Signal clipping or „over flow‟ occurs when the receiver gain is set to high during the pre-scan.
  55. 55. Chemical Shift Artifact  Chemical shift artifacts are caused by different resonance frequencies of hydrogen in lipids and hydrogen in water Spike Artifact  A spike artifact is caused by one „bad‟ data point in k-space “Zebra” Artifact  The “Zebra” artifact may occur when the patient touches the coil, or as a result of phase wrap.
  56. 56. MRI contrast media Definition Classification of MR contrast media Mechanism of MR contrast enhancement Gadolinium Other MR contrast Agents
  57. 57. Contrast  In MRI: relative difference of the signal intensity between two adjoining tissues. Contrast agent  Substance administered during MRI to: • Enhance natural contrast • Obtain dynamic information Definition
  58. 58. Classification of MR contrast media Contrast agent PARENTERAL Relaxivity Positive relaxation agent (T1 agent) Negative relaxation agent (T2 agent) Susceptibility Paramagnetic agent. Eg gadolinium Superamagnetic agent. Eg iron oxide ORAL Positive contrast. Eg Manganese chloride, Gd- DTPA, oil emulsions Negative contrast. T1 agent : Affects T1 relaxation of the tissue. T1 of the tissue in which contrast media is accumulated is reduced. Reduction in T1 results into increase in the signal intensity on T1-W images , hence called positive relaxation agent. Eg. Gadolinium, Mn-DPDPT2 agent : Affects T2 relaxation and reduce T2 of the tissue where they accumulate. This results in reduction in the signal intensity of the tissue on T2-W images. Eg. Iron oxide particles, gadolinium (high doses) Gadolinium : Positive agent, but at higher doses cause T2 shortening resulting into decreased signal on T2-W images. When initially pass through vascular bed of brain local T2 shortening and decreased in the signal of T2-W images  effect used in perfusion studies. Superparamagnetic agent : Negative contrast, causes proton dephasing  T2 shortening and signal loss. Positive contrast : image degradation can occur with peristaltic movements of bowel. For MR Enterography, sorbitol (3%) with or without barium or polyethylene glycol solutions can be used as oral contrast. Negative contrast : they decrease signal from bowel lumen reducing the motion related image degradation. Eg. Superparamagnetic iron oxide particle reduce signal by suseptibility effects. Barium , blue- berry or pinapple juice (contain manganese) and perfluorochemicals are also used to reduce signal from bowel.
  59. 59. • spin density • Relaxivity (T1, T2) • Magnetic suseptibility • Diffusion • Perfusion of contrast agent. In MR imaging, contrast mechanism is multifactorial and includes Mechanism of MR contrast enhancement
  60. 60. Relaxivity  determines the strength of an MR contrast medium. Paramagnetic ions increase relaxation of water protons by a dipole- dipole relaxation. This phenomenon in which excited protons are affected by nearby excited protons or electrons is called dipole-dipole interaction. The dipole-dipole interaction affects the rotational and translational diffusion of water molecules leading to their relaxation. The more and closer the water molecules approach the paramagnetic ions, greater will be the relaxation.
  61. 61. Rare earth metal of lanthanide group Atomic no 64 Free Gd ions tend to accumulate in the body and do not get excreated. Free Gd ions are toxic. Therefore, Gd ions are combined with chelates such as DTPA, DOTA, BOPTA that causes their rapid and total renal secretion. Gd causes both T1 and T2 relaxation of the tissues in which it is accumulated. Increased T1 relaxation  bright signal on T1-W images. Usual dose – 0.1 mmol/Kg Median lethal dose(LD 50) : 6-30 mmol/kg Overall adverse reaction rate : 3-5 % Gadolinium
  62. 62. • Iron oxide • Mn-DPDP (mangafodipir trisodium) • Dysprosium Chelates Other MR contrast Agents
  63. 63. • Purpose: Our goal was to evaluate the efficacy of dynamic contrast- enhanced fat-suppressed MRI of the temporomandibular joint (TMJ) in detecting early joint involvement in patients with rheumatoid arthritis (RA). • Method: Conventional T1-and T2-weighted, gadolinium-enhanced T1-weighted, and dynamic gadolinium-enhanced fat-suppressed SE imaging sequences were performed in 22 patients with RA. • Results: The dynamic gadolinium-enhanced fat-suppressed T1- weighted SE sequence was more sensitive than the other techniques in detecting early changes in inflamed synovium of periarticular tissue and in detecting condylar bone marrow involvement. In patients with RA, 17 joints with joint pain showed synovial proliferation in 10 (59%) cases and joint effusion in 4 (24%). Of 14 joints with joint sound, 4 (29%) showed synovial proliferation and 7 (50%) showed joint effusion. A lower positional change of the disk was observed in joints with RA than in those with TMJ disorders (82 patients). • Conclusion: Gadolinium-enhanced fat-suppressed MRI was extremely effective in diagnosing early changes of the inflamed TMJ. Severity of Synovium and Bone Marrow Abnormalities of the Temporomandibular Joint in Early Rheumatoid Arthritis: Role of Gadolinium-Enhanced Fat-Suppressed T1- Weighted Spin Echo MRI, Suenaga, Shigeaki; Ogura, Tadashi; Matsuda, Takemasa; Noikura, Takenori. Journal of Computer Assisted Tomography: May/June 2000 - Volume 24 - Issue 3 - pp 461-465 Neuroimaging
  64. 64. MRI in Dentistry Applications with interpretation Signal intensity Indications in oral and maxillofacial region Normal anatomy Maxillofacial disorders
  65. 65. Applications with interpretation • MR images are commonly acquired using Spin echo pulse sequence. • T1 and T2 Weighted images are obtained for examinations of oral and maxillofacial regions. • T1-Weighted images  anatomical evaluation • T2- weighted images  detection of pathological processes. • Both T1 and T2 - Weighted images are studied for disease detection, extent and character.
  66. 66. • Images in the Coronal and Axial planes are routinely obtained for three-dimensional evaluation of disease in MR examinations. • Images in the Sagittal plane are sometimes added. • To understand normal MRI Anatomy of Oral and Maxillofacial regions, it is necessary to be familiar with some terms that express MR signal intensities.
  67. 67. • The intensity of signal from each tissue on MR images is termed the “Signal Intensity”. 1) Low signal intensity: If the signal intensity from a tissue is lower than that of muscle on T1 or T2 –Weighted images. 2) High signal intensity: If the signal intensity from a tissue is same or higher than that from fat tissue on T1 or T2 – Weighted images. 3) Intermediate signal intensity: If the signal intensity from a tissue is somewhere between muscle and fat tissue signals on T1 or T2 –Weighted images. Signal intensity
  68. 68. Signal intensity for each tissue Fat tissues: appears high signal intensity on T1-Weighted images and low signal intensity on T2-Weighted images with fat suppression.
  69. 69. Signal intensity for each tissue Muscle tissue: appears as low signal intensity on both T1 and T2- weighted images with fat suppression except Lingual muscles  intermediate signal intensity on T1-weighted images due to their relatively high fat component compared to other muscles.
  70. 70. Muscle tissue: appears as low signal intensity on both T1 and T2- weighted images with fat suppression except Lingual muscles  intermediate signal intensity on T1-weighted images due to their relatively high fat component compared to other muscles.
  71. 71. Cortical bone tissue: signal intensity void on T1 and T2-weighted images. Cancellous bone tissue : high intensity on T1-weight images and low intensity on T2-weighted images with fat suppression.
  72. 72. Lymph nodes and tonsils: low intensity on T1- Weighted images and intermediate –high signal intensity on T2-Weighted images with fat suppression. Teeth : signal void on T1 and T2-weighted images; except pulp tissue which has intermediate signal intensity on T1 –Weighted images and high signal intensity on T2 weighted images with fat suppression.
  73. 73. Signal intensities differ among the tissues of the salivary glands. Parotid gland: high signal intensity on T1-weighted images and low signal intensity on T2-weighted images with fat suppression
  74. 74. Submandibular gland: intermediate signal intensity on T1 – weighted images and low signal intensity on T2-weighted images with fat suppression.
  75. 75. Sublingual gland: intermediate signal intensity on T1–weighted images and high signal intensity on T2-weighted images with fat suppression Temporo-Mandibular Joint (TMJ): • The discs of the TMJ have low signal intensity on T1 and T2- weighted images. • TMJ effusion appears as low signal intensity on T1-weighted images and high signal intensity on T2-weighted images.
  76. 76. Blood vessels: • usually have void signal intensity due to blood flow termed “signal void”, on both T1 and T2 –weighted images, • some vessels with lower flow rate appear with high signal intensity on T2-weighted images with fat suppression and low intensity on T1-weighted images, like the signal from water
  77. 77. T1 W Images: T2 W Images: FLAIR Images: • Subacute Hemorrhage • Fat-containing structures • Anatomical Details • Edema • Demyelination • Infarction • Chronic Hemorrhage • Edema, • Demyelination • Infarction esp. in Periventricular location Which scan best defines the abnormality
  78. 78. Indications of MRI in the oral and maxillofacial region 1. Diagnosis and evaluation of benign and malignant tumors of jaws. 2. Tumor staging evaluation of the site, size and extent of all soft tissue tumors and tumor like lesions, involving all areas including. The salivary glands The pharynx The Sinuses The orbits.
  79. 79. 3. To evaluate structural integrity of trigeminal nerve in trigeminal neuralgia. 4. In surgery of parotid gland MRI can detect the cause of facial nerve within the glandular tissue and help lessen the post-operative facial nerve palsy. 5. For the assessment of intracranial lesions involving particular posterior cranial fossa, the pituitary and the spinal cord.
  80. 80. 6. For non-invasive evaluation of the integrity and position of articular disk within the TMJ. 7. Investigation of the TMJ to show both the bony and soft tissue components of joint including disc position: a). When diagnosis of internal derangement is in doubt, b). As a preoperative assessment before disc surgery, c). Implant assessment.
  81. 81. Normal anatomy 11. CORONOID PROCESS 6. BUCCAL SPACE FAT 77. MASSETER Ms 145. TEMPORALIS MUSCLE 146. TONGUE 55. LINGUAL SEPTUM 142. SUBMANDIBULAR SPACE 35. HYOGLOSSUS Ms 151. ZYGOMATIC ARCH 103. MYLOHYOID Ms 27. GENIOGLOSSUS Ms
  82. 82. 19. FACIAL VEIN 64. MANDIBULAR RAMUS 77. MASSETER Ms 112. ORBICULARIS ORIS Ms 118. PAROTID GLAND 119. PG , ACCESSORY 120. PG, DEEP LOBE 121. PG, SUPERFICIAL LOBE 136. STENSEN’S DUCT 148. UVULA
  83. 83. 3. Ant. BELLY OF DIGASTRIC Ms 28. GENIOHYOID Ms 35. HYOGLOSSUS Ms 45 INTERNAL CAROTID ARTERY 46. INTERNAL JUGULAR VEIN 56.LONGUS COLLI Ms 141. SUBMANDIBULAR GLAND 142. SUBMANDIBULAR SPACE 58. MANDIBLE
  84. 84. 1.ANTERIOR BAND OF ARTICULAR DISC 2. ARTICULAR DISC 4. GLENOID FOSSA 6.INTERMEDIATE (CENTRAL) THIN ZONE 9.MANDIBULAR CONDYLE(HEAD 12. POST. BAND OFARTICULAR DISC 13. POST. DISC ATTACHMENT 9.MANDIBULAR CONDYLE(HEAD) 5. INFERIOR JOINT SPACE 7. LATERAL PTERIGOID MUSCLE RAPHE 15. UPPER HEAD OF LATERAL PTERIGOID Ms. 14. SUPERIOR JOINT SPACE
  85. 85. Maxillofacial Disorders • Foci of bright signal intensity are intermixed with the more typical hypointense signal of fibroosseous tissue on both T1 and T2 – weighted images. Fibrous Dysplasia
  86. 86. • The soft tissue mass exhibits low to intermediate signal intensity on T1 –weighted images and high signal intensity on T2 –weighted image. Osteosarcoma
  87. 87. • cystic fluid exhibits low to intermediate signal intensity on T1-wt images and high signal intensity on T2- wt images , whereas the partially completed crown appears as an area devoid of signal or of low signal because of its low mobile proton density. • The cyst wall is of intermediate intensity on T2-wt images (not as bright as sinus mucosa) Dentigerous Cyst
  88. 88. Ameloblastoma • Purely cystic areas have been noted to exhibit low signal intensity on T1-wt images and high signal intensity on T2-wt images.
  89. 89. Sjogren’s Syndrome • Enlarged parotid gland with an inhomogeneous speckled or nodular pattern(salt and pepper appearance) on T2-wt images
  90. 90. Temporomandibular Joint • Axial plane - to define the location of the joints and provide a global view of the surrounding anatomy. • Coronal images - are routinely obtained because they provide information about mediolateral relationships at the TMJ. • Sagittal images - are assigned from the axial in an oblique plane corresponding to the axis of the condyle and body of the mandible Proton Density-Weighted Imaging ( PDWI ) Slice At Closed Mouth PDWI Slice at Open Mouth
  91. 91. MRI is a complex but effective imaging system that has a variety of clinical indications directly related to the diagnosis and treatment of oral and maxillofacial abnormalities. While not routinely applicable in dentistry, appropriate use of MRI can enhance the quality of patient care in selected cases. Conclusion
  92. 92. MRI research is ever changing. Smaller, lighter machines are always been developed. Work is on going to develop area specific machines to scan small areas like feet, arms, hands. Ventilation dynamic research is being tested with Helium to examine lung function. Brain mapping is having and will continue to grow and give us a better image of how the brain works than ever before. Further advances in 3D imaging and dynamic scanning will enhance the use of this imaging technique even further. MRI in future
  93. 93. References 1. Textbook of Dental and Maxillofacial Radiology Freny R Karjodkar 2nd edition 2. MRI made easy Govind B Chavan 2nd edition 2013 3. Magnetic Resonance Imaging (MRI) – A Review Girish Katti, 2013 4. D. W. McRobbie, E. A. Moore, M. J. Graves, M. R. Prince. MRI – From Picture to Proton (2003). Cambridge University Press. 5. Gandy. S. MRI Physics Lecture Series (2004). Soft Tissue Contrast in MRI. NinewellsHospital, NHS Tayside 6. Evert J Blink Application Specialist MRI
  • UjjvalSen

    Sep. 11, 2021
  • NidhiGamit

    Sep. 7, 2021
  • AfifAhmad13

    Aug. 27, 2021
  • prajjwalkarki

    Aug. 20, 2021
  • donalduronu

    Aug. 10, 2021
  • PinakinTandel1

    Aug. 5, 2021
  • ssuserf2da43

    Aug. 4, 2021
  • DipaliBhagat3

    Aug. 2, 2021
  • NareshKumar1938

    Jul. 26, 2021
  • JAYAPANDIJ

    Jul. 20, 2021
  • VinayGupta390

    Jul. 19, 2021
  • PinakinTandel

    Jul. 17, 2021
  • bheemraya

    Jul. 15, 2021
  • NivedyaRamachandran

    Jul. 12, 2021
  • JeegishaTrada

    Jul. 12, 2021
  • SameemSj

    Jul. 11, 2021
  • LakshmiAnandan

    Jul. 9, 2021
  • DrChaitra1

    Jul. 7, 2021
  • ChiduguManikanta

    Jun. 13, 2021
  • asfakhossain21

    Jun. 11, 2021

MRI - Strange physics ahead . Step by step approach of basics of MRI physics with applications in dentistry.

Views

Total views

32,721

On Slideshare

0

From embeds

0

Number of embeds

35

Actions

Downloads

1,042

Shares

0

Comments

0

Likes

147

×