Kipling’s honest serving Kipling’s honest serving menmen

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 Their names are What and

Why and WhenWhy and WhenAnd How and Where and Who.And How and Where and Who.

Rudyard Kipling

MRI: What, Why and MRI: What, Why and When?When?

Dr Keshav KulkarniDr Keshav Kulkarni

Consultant RadiologistConsultant Radiologist

““Without history human Without history human is demoted to lower is demoted to lower

animals”animals”► Dr Isidor Rabi (Nobel in 1944), discovered Dr Isidor Rabi (Nobel in 1944), discovered

NMR (Nuclear Magnetic Resonance) in the NMR (Nuclear Magnetic Resonance) in the late 1930s, but considered it to be an late 1930s, but considered it to be an artefact of his apparatus! artefact of his apparatus!

► Bloch and Purcell were awarded the Nobel Bloch and Purcell were awarded the Nobel Prize for Physics in 1952 for the discovery Prize for Physics in 1952 for the discovery of NMR, and is widely used in assessing of NMR, and is widely used in assessing complex chemical compunds.complex chemical compunds.

We are so close to the man We are so close to the man behind MRIbehind MRI

►Prof Peter Mansfield was awarded Prof Peter Mansfield was awarded Nobel in 2003 for his discoveries in Nobel in 2003 for his discoveries in MRI (with Prof Paul C Lauterbur of USA)MRI (with Prof Paul C Lauterbur of USA)

►Peter Mansfield is from Nottingham Peter Mansfield is from Nottingham University, UKUniversity, UK

MRI: What is it?MRI: What is it?

Magnetic Resonance ImagingMagnetic Resonance ImagingMagnetMagnet

Radio FrequencyRadio Frequency

ImagingImaging

WE ARE MAGNETS!WE ARE MAGNETS!

Really?Really?

We all are made up of We all are made up of elementselements

►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.

Why hydrogen?Why hydrogen?

►Simplest element with atomic number Simplest element with atomic number of 1 and atomic weight of 1of 1 and atomic weight of 1

►When in ionic state (H+), it is nothing When in ionic state (H+), it is nothing but a proton.but a proton.

►Proton is not only positively charged, Proton is not only positively charged, but also has magnetic spin (wobble)!but also has magnetic spin (wobble)!

►MRI utilizes this magnetic spin property MRI utilizes this magnetic spin property of protons of hydrogen to elicit of protons of hydrogen to elicit images!!images!!

►We are magnets!We are magnets!

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 Hydrogen ions) in body are spinning in body are spinning in a hap hazard a hap hazard fashion, and cancel fashion, and cancel all the magnetism. all the magnetism. That is our natural That is our natural state!state!

► We need to discipline We need to discipline them first, how?them first, how?

We need a big magnet from We need a big magnet from outside!outside!

►Magnetic field strength: 0.3 – 7 T Magnetic field strength: 0.3 – 7 T (2500 times more than earth’s (2500 times more than earth’s magnetic field). Average field strength magnetic field). Average field strength – 1.5 T– 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

Proton alignmentProton alignment► Compass aligns Compass aligns

with the earthwith the earth► In a similar fashion,In a similar fashion,► Our body protons Our body protons

(hydrogen) align (hydrogen) align with this external with this external magnetic field.magnetic field.

► Now, we are Now, we are disciplined disciplined (spinning in line (spinning in line with each other!), with each other!), what next?what next?

Now, its time to listen to Now, its time to listen to radio in RESONANCE.radio in RESONANCE.

►Pushing a swing in time with natural Pushing a swing in time with natural interval of the swing will make the interval of the swing will make the swing higher and higher.swing higher and higher.

►Similarly, radio frequency pulses in Similarly, radio frequency pulses in resonance push the aligned protons resonance push the aligned protons (H+) to a higher energy level.(H+) to a higher energy level.

What is Radio Frequency What is Radio Frequency pulse?pulse?

►Same as Radio waves – high Same as Radio waves – high wavelength, low energy wavelength, low energy electromagnetic waveselectromagnetic waves

►Radiofrequency coilsRadiofrequency coils Act as transmitter and receiverAct as transmitter and receiver Different types of coilsDifferent types of coils

Turn off the radioTurn off the radio

►The higher energy gained by the The higher energy gained by the protons is retransmitted (NMR signal)protons is retransmitted (NMR signal)

►The original magnetization begins to The original magnetization begins to recover (T1)recover (T1)

►The excessive spin begins to dephase The excessive spin begins to dephase (T2)(T2)

Now, we re-transmit the Now, we re-transmit the energy for image processingenergy for 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 Hence, repeated “ON-OFF” of RF pulses are required.are 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?

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

Copyright ©Radiological Society of North America, 2005

Pooley, R. A. Radiographics 2005;25:1087-1099

T1-weighted contrast

Copyright ©Radiological Society of North America, 2005

Pooley, R. A. Radiographics 2005;25:1087-1099

T2-weighted contrast

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

A bit of sequence exerciseA bit of sequence exercise

Which sequence is it? T2Which sequence is it? T2

Which sequence is it? T1Which sequence is it? T1

Which sequence is it? FLAIRWhich sequence is it? FLAIR

Which sequence is it? DWIWhich sequence is it? DWI

Which sequence is it? ADCWhich sequence is it? ADC

Which sequence is it? GEWhich sequence is it? GE

Which sequence is it? PostGdWhich sequence is it? PostGd

Which sequence is it? MRVWhich sequence is it? MRV

Which sequence is it?, 3D Which sequence is it?, 3D MRVMRV

Which sequence is it? MRAWhich sequence is it? MRA

Which sequence is it? T2Which sequence is it? T2

Which sequence is it? T1Which sequence is it? T1

Which sequence is it? STIRWhich sequence is it? STIR

Which sequence is it? MR Which sequence is it? MR arthrogramarthrogram

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

How MR is done?How MR is done?

In a Tunnel, of course!In a Tunnel, of course!

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 Known potential safety concerns due to

large static magnetic field:large 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

Further checklist!Further checklist!

► Malfunction: ICDs, neurostimulators, bone Malfunction: ICDs, neurostimulators, bone growth stimulators (prosthetic heart valves)growth stimulators (prosthetic heart valves)

► Superficial burns (uninsulated wire leads)Superficial burns (uninsulated wire leads)► NEED sedation: infants, younger peds, NEED sedation: infants, younger peds,

agitated adults (claustrophobia)agitated adults (claustrophobia)► Precautions: magnetic plastic cards, Precautions: magnetic plastic cards,

watches, hearing aids, ferromagnetic steel watches, hearing aids, ferromagnetic steel objects (LEAVE OUTSIDE)objects (LEAVE OUTSIDE)

► Loud noise (long-term hearing loss)Loud noise (long-term hearing loss)► Pregnancy!Pregnancy!

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, Pregnancy is a relative contraindication,

as we will never be able to tell with as we will never be able to tell with 100% certainty that MRI is 100% safe 100% certainty that MRI is 100% safe during pregnancy!during pregnancy!

►Babies and children need sedation or Babies and children need sedation or GAGA

►Some people fear tunnels Some people fear tunnels (claustrophobia)(claustrophobia)

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 Alien (radiographers) like voices in

between, “another 5 minutes to between, “another 5 minutes to go”,or, “please stay still”.go”,or, “please stay still”.

►Somebody can come and inject.Somebody can come and inject.

Clinical Aspects of MRIClinical Aspects of MRI

When to MRI?When to MRI?

►When everything else fails, there is When everything else fails, there is MRIMRI

►When you want to borrow time from 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 the waiting time will take care of the patientpatient

Advantages of MRIAdvantages of MRI

1.1. No ionizing radiation & no short/long-No ionizing radiation & no short/long-term effects demonstrated term 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

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 Need to tweak sequences as per the

clinical questions; hence cannot be clinical questions; hence cannot be generalisedgeneralised Pain abdomen - ? causePain abdomen - ? cause

Nothing is perfect in this Nothing is perfect in this worldworld

►MRI has limitations:MRI has limitations: BoneBone AirAir Time consumingTime consuming Poor spatial resolutionPoor spatial resolution Expertise!Expertise!

We presumed MR contrast is We presumed MR contrast is safe 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 Can be used as CT contrast when a

patient has impaired renal functions!patient has impaired renal functions!

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 and/or renal transplant as triggering cause (someone even suggested cause (someone even suggested Anthrax ourbreak!)Anthrax ourbreak!)

►Two reports in 2006 changed it all!Two reports in 2006 changed it all!►Disfiguring and potentially disabling or Disfiguring and potentially disabling or

fatal disorder involving skin, muscles, fatal disorder involving skin, muscles, lungs, pleura, pericardium, and bones.lungs, pleura, pericardium, and bones.

We need to get used to We need to get used to artefacts,artefacts,

and sometimes are major and sometimes are major limitationslimitations

How to get the best from How to get the best from MRI?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.

MRMR

► FasterFaster► Less expensiveLess expensive► Less sensitive to Less sensitive to

patient movementspatient movements► Easier in Easier in

claustrophobicsclaustrophobics► 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 sensitive and more specificmore specific

► Any plane scanningAny plane scanning► Contrast less allergicContrast less allergic► No beam hardening No beam hardening

artefactartefact

CTCT

Neuroimaging = MRINeuroimaging = MRI

►No neurology or neurosurgery without No neurology or neurosurgery without MRIMRI

►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!

Indications (almost Indications (almost everything)everything)

► AnatomyAnatomy► Congenital Congenital

anomaliesanomalies► 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

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

Stroke imagingStroke imaging

►MR superior to CT in diagnosing MR superior to CT in diagnosing hyperacute infarcthyperacute infarct

►MR is as sensitive as CT in diagnosing MR is as sensitive as CT in diagnosing acute intracranial haemorrhageacute intracranial 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

Acute infarct best shown on Acute infarct best shown on DWIDWI

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, Suspected demyelination, dysmyelination, vasculitis, SOLs, dysmyelination, vasculitis, SOLs, hydrocephalus, pituitary lesionshydrocephalus, pituitary lesions

►Non-invasive, non-contrast MRA and MRVNon-invasive, non-contrast MRA and MRV►Cranial nerve evaluationCranial nerve evaluation

Herpes encephalitisHerpes encephalitis

GliomaGlioma

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 First line of investigation in suspected

spinal infection, cord compression, cauda spinal infection, cord compression, cauda equina, sciaticaequina, sciatica

Disc lesion and MRIDisc lesion and MRI

►Virtually everyone after the age of 40 Virtually everyone after the age of 40 years will have at least one years will have at least one degenerative disc/ end platedegenerative disc/ end plate

►Not all patients with sciatica will have Not all patients with sciatica will have a positive MRIa positive MRI

►Ask MRI to answer a specific question; Ask MRI to answer a specific question; otherwise MRI might completely otherwise MRI might completely mislead the clinician.mislead the clinician.

MetastasisMetastasis

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 Characterise the head and neck lesions better than CTbetter than CT

► Complementary to CT in petrous temporal Complementary to CT in petrous temporal and paranasal sinus evaluationand paranasal sinus evaluation

► First line of investigation in orbital lesionsFirst line of investigation in orbital lesions

Second branchial cleft cystSecond branchial cleft cyst

Tongue base carcinomaTongue base carcinoma

Musculoskeletal imagingMusculoskeletal imaging

► Initial evaluation of bones – Plain films; Initial evaluation of bones – Plain films; then MRIthen MRI

►MRI sensitive than CT in diagnosing MRI sensitive than CT in diagnosing occult fracturesoccult fractures

► Initial evaluation of soft tissues – USG; Initial evaluation of soft tissues – USG; then MRIthen MRI

► Joint imaging = MRIJoint imaging = MRI

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

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

FractureFracture

Avascular necrosisAvascular necrosis

Rotator cuff tearRotator cuff tear

Bankart and Hillsachs lesionsBankart and Hillsachs lesions

Abdominal MRIAbdominal MRI

►Problem solving tool in liver, Problem solving tool in liver, pancreatic, renal and adrenal lesionspancreatic, renal and adrenal lesions

►Primary modality in local staging of Primary modality in local staging of rectal ca, endometrial ca, cervical ca, rectal ca, endometrial ca, cervical ca, prostate ca, vaginal caprostate ca, vaginal 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

MRCPMRCP

Rectal caRectal ca

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

Cardiac MRICardiac MRI

►Coming in a big wayComing in a big way►Very useful in congenital heart Very useful in congenital heart

diseases, cardiomyopathiesdiseases, cardiomyopathies►Evidence is emerging in the evaluation Evidence is emerging in the evaluation

of myocardial infarctionof myocardial infarction

Breast MRIBreast MRI

►Problem solvingProblem solving Breast implantsBreast implants RecurrenceRecurrence Multifocal diseaseMultifocal disease

Foetal MRIFoetal MRI

►Assessment of congenital anomaliesAssessment of congenital anomalies►Placental abnormalitiesPlacental abnormalities►Twin assessmentTwin assessment

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 Ask specific question to get the right

answeranswer

SummarySummary

►MRI invaluable imaging tool in the MRI invaluable imaging tool in the diagnosis of various diseases from diagnosis of various diseases from head to toehead 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 Invaluable tool in local staging of most of the malignanciesof the malignancies

meningiomameningioma

gliomaglioma