Basics Of MRI

Basics of MRI for junior doctors to understand the basic principles and its clinical pplications.

1. Kipling’s honest serving menKipling’s honest serving men
I keep six honest serving-menI keep six honest serving-men
(They taught me all I knew);(They taught me all I knew);
Their names are What and Why and Their names are What and Why and
WhenWhen
And How and Where and Who.And How and Where and Who.
Rudyard KiplingRudyard Kipling

2. MRI: What, Why and MRI: What, Why and
When?When?
Dr Keshav KulkarniDr Keshav Kulkarni
Consultant RadiologistConsultant Radiologist

3. ““Without history human is Without history human is
demoted to lower animals”demoted to lower animals”
►Dr Isidor Rabi (Nobel in 1944), discovered NMR Dr Isidor Rabi (Nobel in 1944), discovered NMR
(Nuclear Magnetic Resonance) in the late 1930s, (Nuclear Magnetic Resonance) in the late 1930s,
but considered it to be an artefact of his but considered it to be an artefact of his
apparatus! apparatus!
►Bloch and Purcell were awarded the Nobel Prize Bloch and Purcell were awarded the Nobel Prize
for Physics in 1952 for the discovery of NMR, for Physics in 1952 for the discovery of NMR,
and is widely used in assessing complex and is widely used in assessing complex
chemical compunds.chemical compunds.

4. We are so close to the man behind We are so close to the man behind
MRIMRI
►Prof Peter Mansfield was awarded Nobel in Prof Peter Mansfield was awarded Nobel in
2003 for his discoveries in MRI (with Prof 2003 for his discoveries in MRI (with Prof
Paul C Lauterbur of USA)Paul C Lauterbur of USA)
►Peter Mansfield is from Nottingham Peter Mansfield is from Nottingham
University, UKUniversity, UK

5. MRI: What is it?MRI: What is it?
Magnetic Resonance ImagingMagnetic Resonance Imaging
MagnetMagnet
Radio FrequencyRadio Frequency
ImagingImaging

6. WE ARE MAGNETS!WE ARE MAGNETS!
Really?Really?

7. We all are made up of elementsWe all are made up of elements
►92 elements occur naturally on earth. 92 elements occur naturally on earth.
►Human body is built of only 26 elements. Human body is built of only 26 elements.
►Oxygen, hydrogen, carbon, nitrogen Oxygen, hydrogen, carbon, nitrogen
elements constitute 96 % of human body elements constitute 96 % of human body
mass. mass.
►Oxygen is 65 % of body mass; carbon is Oxygen is 65 % of body mass; carbon is
18.5 %, 18.5 %, hydrogen 9.5 %hydrogen 9.5 %, nitrogen 3.2 %., nitrogen 3.2 %.
►Let us ignore all elements but Hydrogen.Let us ignore all elements but Hydrogen.

8. Why hydrogen?Why hydrogen?
►Simplest element with atomic number of 1 Simplest element with atomic number of 1
and atomic weight of 1and atomic weight of 1
►When in ionic state (H+), it is nothing but When in ionic state (H+), it is nothing but
a proton.a proton.
►Proton is not only positively charged, but Proton is not only positively charged, but
also has magnetic spin (wobble)!also has magnetic spin (wobble)!
►MRI utilizes this magnetic spin property of MRI utilizes this magnetic spin property of
protons of hydrogen to elicit images!!protons of hydrogen to elicit images!!
►We are magnets!We are magnets!

9. But why we can’t act like But why we can’t act like
magnets?magnets?
►The protons (i.e. The protons (i.e.
Hydrogen ions) in body Hydrogen ions) in body
are spinning in a hap are spinning in a hap
hazard fashion, and hazard fashion, and
cancel all the cancel all the
magnetism. That is our magnetism. That is our
natural state!natural state!
►We need to discipline We need to discipline
them first, how?them first, how?

10. We need a big magnet from We need a big magnet from
outside!outside!
►Magnetic field strength: 0.3 – 7 T (2500 Magnetic field strength: 0.3 – 7 T (2500
times more than earth’s magnetic field). times more than earth’s magnetic field).
Average field strength – 1.5 TAverage field strength – 1.5 T
►Open magnet – less field strength, less Open magnet – less field strength, less
claustrophobicclaustrophobic
►Closed magnet – more field strength, Closed magnet – more field strength,
claustrophobicclaustrophobic

11. Proton alignmentProton alignment
►Compass aligns with Compass aligns with
the earththe earth
►In a similar fashion,In a similar fashion,
►Our body protons Our body protons
(hydrogen) align with (hydrogen) align with
this external magnetic this external magnetic
field.field.
►Now, we are Now, we are
disciplined (spinning disciplined (spinning
in line with each in line with each
other!), what next?other!), what next?

12. Now, its time to listen to radio in Now, its time to listen to radio in
RESONANCE.RESONANCE.
►Pushing a swing in time with natural interval Pushing a swing in time with natural interval
of the swing will make the swing higher and of the swing will make the swing higher and
higher.higher.
►Similarly, radio frequency pulses in Similarly, radio frequency pulses in
resonance push the aligned protons (H+) to resonance push the aligned protons (H+) to
a higher energy level.a higher energy level.

13. What is Radio Frequency pulse?What is Radio Frequency pulse?
►Same as Radio waves – high wavelength, Same as Radio waves – high wavelength,
low energy electromagnetic waveslow energy electromagnetic waves
►Radiofrequency coilsRadiofrequency coils
Act as transmitter and receiverAct as transmitter and receiver
Different types of coilsDifferent types of coils

14. Turn off the radioTurn off the radio
►The higher energy gained by the protons is The higher energy gained by the protons is
retransmitted (NMR signal)retransmitted (NMR signal)
►The original magnetization begins to recover The original magnetization begins to recover
(T1)(T1)
►The excessive spin begins to dephase (T2)The excessive spin begins to dephase (T2)

15. Now, we re-transmit the energy Now, we re-transmit the energy
for image processingfor image processing
►The emitted energy is too small (despite The emitted energy is too small (despite
2500 times the magnetic field with 2500 times the magnetic field with
resonance RF pulse) to convert them into resonance RF pulse) to convert them into
images.images.
►Hence, repeated “ON-OFF” of RF pulses are Hence, repeated “ON-OFF” of RF pulses are
required.required.
►The emitted energy is stored (K-space), The emitted energy is stored (K-space),
analysed and converted into images. analysed and converted into images.
►What kind of images?What kind of images?

16. What kind of images?What kind of images?
►T1WIT1WI
►T2WIT2WI
►PDWIPDWI
►DWIDWI
►ADCADC
►GEGE
►Perfusion imagesPerfusion images
►fMRIfMRI
►BOLD imagesBOLD images
►MRAMRA
►MRVMRV
►Post-Gd imagesPost-Gd images
►Volumetric imagesVolumetric images
►MR arthrogramsMR arthrograms
►FLAIRFLAIR
►STIRSTIR
►Etc etc etcEtc etc etc

17. Copyright ©Radiological Society of North America, 2005
Pooley, R. A. Radiographics 2005;25:1087-1099
T1-weighted contrast

18. Copyright ©Radiological Society of North America, 2005
Pooley, R. A. Radiographics 2005;25:1087-1099
T2-weighted contrast

19. Tissue AppearanceTissue Appearance
WTWT FATFAT H2OH2O MUSCMUSC LIGLIG BONEBONE
T1T1 BB DD II DD DD
Proton Proton

DensityDensity
II II II DD DD
T2T2 II BB II DD DD

21. A bit of sequence exerciseA bit of sequence exercise

22. Which sequence is it? T2Which sequence is it? T2

23. Which sequence is it? T1Which sequence is it? T1

24. Which sequence is it? FLAIRWhich sequence is it? FLAIR

25. Which sequence is it? DWIWhich sequence is it? DWI

26. Which sequence is it? ADCWhich sequence is it? ADC

27. Which sequence is it? GEWhich sequence is it? GE

28. Which sequence is it? PostGdWhich sequence is it? PostGd

29. Which sequence is it? MRVWhich sequence is it? MRV

30. Which sequence is it?, 3D MRVWhich sequence is it?, 3D MRV

31. Which sequence is it? MRAWhich sequence is it? MRA

32. Which sequence is it? T2Which sequence is it? T2

33. Which sequence is it? T1Which sequence is it? T1

34. Which sequence is it? STIRWhich sequence is it? STIR

35. Which sequence is it? MR Which sequence is it? MR
arthrogramarthrogram

36. I hope I was able to confuse you!I hope I was able to confuse you!

37. How MR is done?How MR is done?

38. In a Tunnel, of course!In a Tunnel, of course!

39. Before entering tunnel, there isBefore entering tunnel, there is
a checklist! a checklist!
►No mobiles, no credit cards, please!No mobiles, no credit cards, please!
►Known potential safety concerns due to large Known potential safety concerns due to large
static magnetic field:static magnetic field:
Internal cardiac pacemakersInternal cardiac pacemakers
Steel cerebral aneurysm clips (ferromagnetic)Steel cerebral aneurysm clips (ferromagnetic)
Small steel slivers embedded in eyeSmall steel slivers embedded in eye
Life-support equipment with magnetic steelLife-support equipment with magnetic steel
Cochlear implantsCochlear implants
Stents anywhere in the bodyStents anywhere in the body

40. Further checklist!Further checklist!
►Malfunction: ICDs, neurostimulators, bone growth Malfunction: ICDs, neurostimulators, bone growth
stimulators (prosthetic heart valves)stimulators (prosthetic heart valves)
►Superficial burns (uninsulated wire leads)Superficial burns (uninsulated wire leads)
►NEED sedation: infants, younger peds, agitated NEED sedation: infants, younger peds, agitated
adults (claustrophobia)adults (claustrophobia)
►Precautions: magnetic plastic cards, watches, Precautions: magnetic plastic cards, watches,
hearing aids, ferromagnetic steel objects (LEAVE hearing aids, ferromagnetic steel objects (LEAVE
OUTSIDE)OUTSIDE)
►Loud noise (long-term hearing loss)Loud noise (long-term hearing loss)
►Pregnancy!Pregnancy!

41. Is entering the tunnel safe? Is entering the tunnel safe?
►No definite long-term harmful effectsNo definite long-term harmful effects
►Pregnancy is a relative contraindication, as Pregnancy is a relative contraindication, as
we will never be able to tell with 100% we will never be able to tell with 100%
certainty that MRI is 100% safe during certainty that MRI is 100% safe during
pregnancy!pregnancy!
►Babies and children need sedation or GABabies and children need sedation or GA
►Some people fear tunnels (claustrophobia)Some people fear tunnels (claustrophobia)

42. What happens in MRI?What happens in MRI?
►Stay still for 15 minutes to 45 minutes!Stay still for 15 minutes to 45 minutes!
►Noise, Noise and Noise!Noise, Noise and Noise!
►Listen to music in darknessListen to music in darkness
►Alien (radiographers) like voices in between, Alien (radiographers) like voices in between,
“another 5 minutes to go”,or, “please stay “another 5 minutes to go”,or, “please stay
still”.still”.
►Somebody can come and inject.Somebody can come and inject.

43. Clinical Aspects of MRIClinical Aspects of MRI

44. When to MRI?When to MRI?
►When everything else fails, there is MRIWhen everything else fails, there is MRI
►When you want to borrow time from the When you want to borrow time from the
patient, request MRI and hope that the patient, request MRI and hope that the
waiting time will take care of the patientwaiting time will take care of the patient

45. Advantages of MRIAdvantages of MRI
1.1.No ionizing radiation & no short/long-term No ionizing radiation & no short/long-term
effects demonstrated effects demonstrated
2.2.Variable thickness, any planeVariable thickness, any plane
3.3.Better contrast resolution & tissue Better contrast resolution & tissue
discriminationdiscrimination
4.4.Various sequences to play with to Various sequences to play with to
characterise the abnormal tissuecharacterise the abnormal tissue
5.5.Many details without I.V contrastMany details without I.V contrast

46. Disadvantages of MRIDisadvantages of MRI
►Time consumingTime consuming
►Not easily available (long waiting list)Not easily available (long waiting list)
►No on-call serviceNo on-call service
►Need to tweak sequences as per the clinical Need to tweak sequences as per the clinical
questions; hence cannot be generalisedquestions; hence cannot be generalised
Pain abdomen - ? causePain abdomen - ? cause

47. Nothing is perfect in this worldNothing is perfect in this world
►MRI has limitations:MRI has limitations:
BoneBone
AirAir
Time consumingTime consuming
Poor spatial resolutionPoor spatial resolution
Expertise!Expertise!

48. We presumed MR contrast is safe We presumed MR contrast is safe
►No side effectsNo side effects
►No allergy ( as with Iodine)No allergy ( as with Iodine)
►Can be used in renal impairmentCan be used in renal impairment
►Can be used as CT contrast when a patient Can be used as CT contrast when a patient
has impaired renal functions!has impaired renal functions!

49. Necrotising Systemic FibrosisNecrotising Systemic Fibrosis
►No cases identified prior to 1997No cases identified prior to 1997
►Initial research were targeting dialysis Initial research were targeting dialysis
and/or renal transplant as triggering cause and/or renal transplant as triggering cause
(someone even suggested Anthrax (someone even suggested Anthrax
ourbreak!)ourbreak!)
►Two reports in 2006 changed it all!Two reports in 2006 changed it all!
►Disfiguring and potentially disabling or fatal Disfiguring and potentially disabling or fatal
disorder involving skin, muscles, lungs, disorder involving skin, muscles, lungs,
pleura, pericardium, and bones.pleura, pericardium, and bones.

50. We need to get used to artefacts,We need to get used to artefacts,
and sometimes are major and sometimes are major
limitationslimitations

51. How to get the best from MRI?How to get the best from MRI?
►Ask a specific questionAsk a specific question
►Get a specific answerGet a specific answer
►Because the sequences can be tailored Because the sequences can be tailored
accordingly.accordingly.

52. MRMR
►FasterFaster
►Less expensiveLess expensive
►Less sensitive to patient Less sensitive to patient
movementsmovements
►Easier in claustrophobicsEasier in claustrophobics
►Acute haemorrhageAcute haemorrhage
►CalcificationCalcification
►Bone detailsBone details
►Foreign bodyForeign body
►No ionising radiationNo ionising radiation
►Greater details, hence Greater details, hence
more sensitive and more more sensitive and more
specificspecific
►Any plane scanningAny plane scanning
►Contrast less allergicContrast less allergic
►No beam hardening No beam hardening
artefactartefact
CTCT

53. Neuroimaging = MRINeuroimaging = MRI
►No neurology or neurosurgery without MRINo neurology or neurosurgery without MRI
►MR brain has largely replaced CT brain in MR brain has largely replaced CT brain in
USA (but for head injury, suspected acute USA (but for head injury, suspected acute
intracranial haemorrhage)intracranial haemorrhage)
►Superior to CT in most occasions Superior to CT in most occasions
►CT is poor man’s MRI in all other CT is poor man’s MRI in all other
indications!indications!
►Show me a person with migraine who has Show me a person with migraine who has
not undergone MRI in USA!not undergone MRI in USA!

54. Indications (almost everything)Indications (almost everything)
►AnatomyAnatomy
►Congenital anomaliesCongenital anomalies
►Hereditary and Hereditary and
metabolic diseasesmetabolic diseases
►InfectionsInfections
►DemyelinationDemyelination
►Vascular eventVascular event
►TumoursTumours
►TraumaTrauma
►DementiaDementia
►HydrocephalusHydrocephalus
►Cranial nervesCranial nerves
►ArteriogramsArteriograms
►VenogramsVenograms
►Skull baseSkull base
►Pituitary glandPituitary gland

55. Tools in neuroimagingTools in neuroimaging
►T2WIT2WI
►T1WIT1WI
►FLAIRFLAIR
►MRAMRA
►MRVMRV
►GEGE
►GadoliniumGadolinium
►DWIDWI
►ADCADC
►Diffusion tensor Diffusion tensor
imagingimaging
►fMRIfMRI
►Perfusion mappingPerfusion mapping
►CSF flow mappingCSF flow mapping
►MR spectroscopyMR spectroscopy

56. Stroke imagingStroke imaging
►MR superior to CT in diagnosing hyperacute MR superior to CT in diagnosing hyperacute
infarctinfarct
►MR is as sensitive as CT in diagnosing acute MR is as sensitive as CT in diagnosing acute
intracranial haemorrhageintracranial haemorrhage
►MR is more expensive and less easily MR is more expensive and less easily
available compared to CT in the UKavailable compared to CT in the UK
►CT is currently widely used to exlcude CT is currently widely used to exlcude
haemorhage before thrombolysishaemorhage before thrombolysis

57. Acute infarct best shown on DWIAcute infarct best shown on DWI

58. When to skip CT?When to skip CT?
►Babies and children (avoid ionising Babies and children (avoid ionising
radiation)radiation)
►Evaluation of headache (controversial in Evaluation of headache (controversial in
NHS setting)NHS setting)
►Suspected demyelination, dysmyelination, Suspected demyelination, dysmyelination,
vasculitis, SOLs, hydrocephalus, pituitary vasculitis, SOLs, hydrocephalus, pituitary
lesionslesions
►Non-invasive, non-contrast MRA and MRVNon-invasive, non-contrast MRA and MRV
►Cranial nerve evaluationCranial nerve evaluation

59. Herpes encephalitisHerpes encephalitis

60. GliomaGlioma

61. Spine imagingSpine imaging
►MR is the investigation of choiceMR is the investigation of choice
►Conventional CT, CT myelogram and Conventional CT, CT myelogram and
conventional myelogram are no longer conventional myelogram are no longer
performed, unless MR is contraindicated.performed, unless MR is contraindicated.
►Indications and contraindications – sameIndications and contraindications – same
►First line of investigation in suspected spinal First line of investigation in suspected spinal
infection, cord compression, cauda equina, infection, cord compression, cauda equina,
sciaticasciatica

62. Disc lesion and MRIDisc lesion and MRI
►Virtually everyone after the age of 40 years Virtually everyone after the age of 40 years
will have at least one degenerative disc/ end will have at least one degenerative disc/ end
plateplate
►Not all patients with sciatica will have a Not all patients with sciatica will have a
positive MRIpositive MRI
►Ask MRI to answer a specific question; Ask MRI to answer a specific question;
otherwise MRI might completely mislead the otherwise MRI might completely mislead the
clinician.clinician.

63. MetastasisMetastasis

64. Head and Neck imagingHead and Neck imaging
►MR is complementary or second line of MR is complementary or second line of
investigation in many of head and neck investigation in many of head and neck
pathologiespathologies
►Superior to CT in staging head and neck Superior to CT in staging head and neck
malignanciesmalignancies
►Characterise the head and neck lesions better than Characterise the head and neck lesions better than
CTCT
►Complementary to CT in petrous temporal and Complementary to CT in petrous temporal and
paranasal sinus evaluationparanasal sinus evaluation
►First line of investigation in orbital lesionsFirst line of investigation in orbital lesions

65. Second branchial cleft cystSecond branchial cleft cyst

66. Tongue base carcinomaTongue base carcinoma

67. Musculoskeletal imagingMusculoskeletal imaging
►Initial evaluation of bones – Plain films; then Initial evaluation of bones – Plain films; then
MRIMRI
►MRI sensitive than CT in diagnosing occult MRI sensitive than CT in diagnosing occult
fracturesfractures
►Initial evaluation of soft tissues – USG; then Initial evaluation of soft tissues – USG; then
MRIMRI
►Joint imaging = MRIJoint imaging = MRI

68. Tools in MSK imagingTools in MSK imaging
►T1WIT1WI
►T2WIT2WI
►Fat sat T1Fat sat T1
►STIRSTIR
►Fat sat T2Fat sat T2
►Gadolinium studiesGadolinium studies
►MR arthrographyMR arthrography

69. IndicationsIndications
►Occult fracturesOccult fractures
►Marrow abnormalityMarrow abnormality
►Ligament pathologiesLigament pathologies
►Tendon pathologiesTendon pathologies
►Muscular injuriesMuscular injuries
►InfectionInfection
►Bone and soft tissue tumourBone and soft tissue tumour
►Labral pathologiesLabral pathologies

70. FractureFracture

71. Avascular necrosisAvascular necrosis

72. Rotator cuff tearRotator cuff tear

73. Bankart and Hillsachs lesionsBankart and Hillsachs lesions

74. Abdominal MRIAbdominal MRI
►Problem solving tool in liver, pancreatic, Problem solving tool in liver, pancreatic,
renal and adrenal lesionsrenal and adrenal lesions
►Primary modality in local staging of rectal Primary modality in local staging of rectal
ca, endometrial ca, cervical ca, prostate ca, ca, endometrial ca, cervical ca, prostate ca,
vaginal cavaginal ca
►Non-invasive modality in evaluating Non-invasive modality in evaluating
pancreaticobiliary tract – MRCPpancreaticobiliary tract – MRCP
►Scrotal and penile imagingScrotal and penile imaging
►Uterus and ovary imagingUterus and ovary imaging

75. MRCPMRCP

76. Rectal caRectal ca

77. Vascular MRIVascular MRI
►Peripheral vascular arteriogram with or Peripheral vascular arteriogram with or
without I.V contrastwithout I.V contrast
►Aortogram Aortogram
DissectionDissection
►Pulmonary arteriogramPulmonary arteriogram
When CT is contraindicatedWhen CT is contraindicated

78. Cardiac MRICardiac MRI
►Coming in a big wayComing in a big way
►Very useful in congenital heart diseases, Very useful in congenital heart diseases,
cardiomyopathiescardiomyopathies
►Evidence is emerging in the evaluation of Evidence is emerging in the evaluation of
myocardial infarctionmyocardial infarction

79. Breast MRIBreast MRI
►Problem solvingProblem solving
Breast implantsBreast implants
RecurrenceRecurrence
Multifocal diseaseMultifocal disease

80. Foetal MRIFoetal MRI
►Assessment of congenital anomaliesAssessment of congenital anomalies
►Placental abnormalitiesPlacental abnormalities
►Twin assessmentTwin assessment

81. SummarySummary
►Expensive time-consuming investigationExpensive time-consuming investigation
►Complex physics, too many sequences, Complex physics, too many sequences,
difficult to interpret to untrained eyesdifficult to interpret to untrained eyes
►Relatively safe, but there are definite Relatively safe, but there are definite
contraindicationscontraindications
►Ask specific question to get the right answerAsk specific question to get the right answer

82. SummarySummary
►MRI invaluable imaging tool in the diagnosis MRI invaluable imaging tool in the diagnosis
of various diseases from head to toeof various diseases from head to toe
►Chief modality in neuroimaging, and Chief modality in neuroimaging, and
musculoskeletal imagingmusculoskeletal imaging
►Problem solving tool in abdominal Problem solving tool in abdominal
pathologiespathologies
►Invaluable tool in local staging of most of Invaluable tool in local staging of most of
the malignanciesthe malignancies

83. meningiomameningioma

84. gliomaglioma