Magnetic Resonance ImagingMagnetic Resonance Imaging

Dr Mohamed El Safwany, MD.

Intended learning outcomeIntended learning outcome

►The student should learn at the end of The student should learn at the end of this lecture MRI basics .this lecture MRI basics .

►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 Let us ignore all elements but Hydrogen.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!

► 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 We need to discipline them firstdiscipline them first

►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!)

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

Radio Frequency pulseRadio Frequency 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

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

ImagesImages

► 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

T1-weighted contrast

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

sequence exercisesequence 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

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 Cochlear implantsCochlear implants Stents anywhere in the bodyStents anywhere in the body

Clinical Aspects of MRIClinical Aspects of MRI

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)

►MRI has limitations:MRI has limitations: BoneBone AirAir Time consumingTime consuming

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

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

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

Text BookText Book

►David Sutton’s RadiologyDavid Sutton’s Radiology►Clark’s Radiographic positioning and Clark’s Radiographic positioning and

techniquestechniques

AssignmentAssignment

►Two students will be selected for Two students will be selected for assignment.assignment.

QuestionQuestion

►Define differences between CT and Define differences between CT and MRI?MRI?

Thank YouThank You

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