basic fundamentals of mri a cquisition of mri images - physics b asic sequences & advanced...

Basic Fundamentals of MRIBasic Fundamentals of MRI

AAcquisition of MRI images - PHYSICScquisition of MRI images - PHYSICS

BBasic Sequences & Advanced asic Sequences & Advanced applicationsapplications

CCharacterisation of Lesions.haracterisation of Lesions.

MRI PhysicsMRI Physics

MRI Physics MRI Physics

MMagneticagnetic

RResonanceesonance

IImagingmaging

MRI Physics MRI Physics MAGNETICMAGNETIC

Tissues are made of Protons (H+)Tissues are made of Protons (H+) Positive electrical charge spinning Positive electrical charge spinning around its own axis.around its own axis. Moving Electrical charge produces Moving Electrical charge produces its own magnetic field.its own magnetic field.

Protons are analogous to small Protons are analogous to small BAR MAGNETS.BAR MAGNETS.

MRI Physics MRI Physics MAGNETICMAGNETIC

Presence of a strong Presence of a strong magnetic fieldmagnetic field

This leads to alignment This leads to alignment of protons in the tissue of protons in the tissue acc to the magnetic acc to the magnetic field- field- LEVEL 1LEVEL 1

MRI Physics MRI Physics RESONANCERESONANCE

A A specific radiofrequencyspecific radiofrequency wave passed in a wave passed in a specific mannerspecific manner & & specific specific plane.plane.

Radiofrequency waves are Radiofrequency waves are NOT RadiationNOT Radiation..

Apart from spinning motion Apart from spinning motion these protons are also these protons are also vibrating at a frequency.vibrating at a frequency.

MRI PhysicsMRI Physics RESONANCERESONANCE

MRI Physics MRI Physics RESONANCERESONANCE

Raises further raise Raises further raise the energy level of the energy level of protons – protons – Level 2Level 2

Level of excitation Level of excitation is different for is different for different different tissues tissues hence signal is hence signal is different – different – CONTRASTCONTRAST

IMAGINGIMAGING

Radiofrequncy Radiofrequncy switched offswitched off & & excited protons excited protons come back to come back to Level1Level1

Energy / Signal Energy / Signal is is released..released..

Signal picked up by Signal picked up by the Coil & the Coil & processed by a processed by a computer.computer.

MRI Physics MRI Physics IN NUTSHELLIN NUTSHELL

Patient is placed in a strong magnetic Patient is placed in a strong magnetic field.field.

Radiowave is sent in for a short time & Radiowave is sent in for a short time & switched off.switched off.

Patient emits signal.Patient emits signal. Recived & used for reconstruction of Recived & used for reconstruction of

image.image.

TESLA FACTOR !!TESLA FACTOR !!

Tesla is the unit of magnetic field strength.Tesla is the unit of magnetic field strength.

TYPES OF MAGNETS :

• Resistive Magnets – Low & Ultralow field strenghts.

• Permanent Magnets – Low & Med field strength (upto 0.3 T).

• Superconducting Magnets 0.5 - 14T


IMAGEQUALITY

S/N Ratio Contrast

FIELD SRENGTH

TYPE OF MAGNETIC FIELDVERTICAL/ HORIZONTAL

GRADIENTS

TYPE OF COILS

TYPE OF COMPUTERIMAGE PROCESSING & SEQUENCES

CAMERA


As Magnetic field strength As Magnetic field strength increases SNR increases – increases SNR increases – true for analyitical NMR But true for analyitical NMR But NOT for whole-body MRI.NOT for whole-body MRI.

In higher field strengths In higher field strengths body produces an inherent body produces an inherent noise.noise.

Most important factor in Most important factor in Medical imaging is tissue Medical imaging is tissue contrast – best in medium & contrast – best in medium & low field strngths.low field strngths.

SEQUENCESSEQUENCES

BASIC SEQUENCES :BASIC SEQUENCES :

T1W.T1W. T2W.T2W. FAT SUPP T2W/ STIR.FAT SUPP T2W/ STIR. FLUID SUPP T2W/ FLAIR.FLUID SUPP T2W/ FLAIR.

ADVANCED APPLICATIONS :ADVANCED APPLICATIONS :

MR ANGIOGRAPHY.MR ANGIOGRAPHY. MR CHOLANGIOPANCREATOGRAPHY & MR CHOLANGIOPANCREATOGRAPHY & MR UROGRAPHY.MR UROGRAPHY. DIFFUSION.DIFFUSION. JOINT MOTION STUDY – KINEMATIC MRI.JOINT MOTION STUDY – KINEMATIC MRI.

BASIC SEQUENCESBASIC SEQUENCES

T1 Weighted – T1 Weighted – ANATOMY.ANATOMY.

FAT- FAT- WHITEWHITE FLUID- FLUID- BLACKBLACK


T2 Weighted – T2 Weighted – PATHOLOGY.PATHOLOGY.

FLUID- FLUID- WHITEWHITE FAT- FAT- NOT SO NOT SO

WHITEWHITE


T2 Weighted T2 Weighted

FAT SUPP/ STIR.FAT SUPP/ STIR.

- PATHOLOGY FOR - PATHOLOGY FOR MOST EXTRACRANIAL MOST EXTRACRANIAL REGIONS.REGIONS.

FLUID- FLUID- WHITEWHITE FAT- FAT- BLACKBLACK

T2 W FAT SUPPT2 W FAT SUPPT2 WT2 W



T2 Weighted T2 Weighted WATER SUPP/ FLAIR.WATER SUPP/ FLAIR. - BRAIN PATHOLOGY - BRAIN PATHOLOGY

CSF/ CLEAR FLUID - CSF/ CLEAR FLUID - BLACKBLACK

PATHOLOGY/ PATHOLOGY/ PATHOLOGICAL FLUIDPATHOLOGICAL FLUID- - WHITEWHITE


FLAIR- WATER SUPPFLAIR- WATER SUPP T2 WT2 W

ADVANCED APPLICATION ADVANCED APPLICATION DIFFUSIONDIFFUSION

Very sensitive to motionVery sensitive to motion - picks up - picks up microscopic motion of protons in edema.microscopic motion of protons in edema.

Can differentiate between Can differentiate between CytotoxicCytotoxic Edema (infarct) & Edema (infarct) & VasogenicVasogenic Edema Edema (tumor/infection etc).(tumor/infection etc).

Special sequence, picks up infarct Special sequence, picks up infarct within within hourshours (2-3 hrs). (2-3 hrs).

To diffrentiate between Old & Fresh To diffrentiate between Old & Fresh infarct.infarct.

ADVANCED APPLICATION ADVANCED APPLICATION DIFFUSIONDIFFUSION

FLAIR DIFFUSION

H/O dense Left Hemiplegia – 3 hrs back.H/O dense Left Hemiplegia – 3 hrs back.

FLAIR DIFFUSION

ADVANCED APPLICATION ADVANCED APPLICATION MRCPMRCP

Heavily T2W sequence – Only Fluid appears Heavily T2W sequence – Only Fluid appears bright.bright.

2 types – (1) Single shot breath hold (3 secs)2 types – (1) Single shot breath hold (3 secs)

(2) 3D MRCP.(2) 3D MRCP. No contrast / injection.No contrast / injection. Non-invasive modality for deliniation of biliary Non-invasive modality for deliniation of biliary

anotomy.anotomy. All non-theraputic indications of ERCP.All non-theraputic indications of ERCP.


T2 W FSE

3D MRCP


T2 W AxialT2 W Axial Single Shot MRCP - 3 secSingle Shot MRCP - 3 sec

ADVANCED APPLICATION ADVANCED APPLICATION MRAngioMRAngio

Flow sensitive sequences – picks up flow.Flow sensitive sequences – picks up flow. No contrast / injection.No contrast / injection.

Arterial study – Head & Neck vessels(2D/3D TOF)Arterial study – Head & Neck vessels(2D/3D TOF) Venous study – Intracranial venous sinusesVenous study – Intracranial venous sinuses

(2D TOF & Phase Contrast)(2D TOF & Phase Contrast)


INDICATIONS :INDICATIONS :

1.1. Stroke – infarct (Single vessel / Multiple vessel).Stroke – infarct (Single vessel / Multiple vessel).2.2. TIA.TIA.3.3. Secondary Hemorrhage – AVM, Aneurysm.Secondary Hemorrhage – AVM, Aneurysm.4.4. VBI.VBI.5.5. Trigeminal Neuralgia & Hemifacial spasm – aberrent Trigeminal Neuralgia & Hemifacial spasm – aberrent

loops.loops.6.6. Venography - Venous sinus thrombosis .Venography - Venous sinus thrombosis .

Contrast Enhanced MRA :Contrast Enhanced MRA :

1.1. Renal Vessels – RAS.Renal Vessels – RAS.2.2. Limb vessels – Femoral, Popliteal , Subclavian & Limb vessels – Femoral, Popliteal , Subclavian &

Brachial.Brachial.


MRA – CIRCLE OF WILLIS

MRA – NECK VESSELS


CONTRAST MRA – RENAL VESSELS.


PCA ANEURYSM AVM

ADVANCED APPLICATION ADVANCED APPLICATION KINEMATIC STUDYKINEMATIC STUDY

EXTENSION NEUTRAL FLEXION

PathologyPathologyinflammation, infection, infarct, tumor etc. have high water content inflammation, infection, infarct, tumor etc. have high water content

Hypintense on T1 & Hyperintense in T2Hypintense on T1 & Hyperintense in T2

SOLID FLUID

HIGH PROTEIN FLUID

BLOOD- METH Hb

T1W - ++T2W - ++

T1W - ++T2W - ++

T1W - +T2W - +

FATFAT – T1W – T1W +++ +++

T2W T2W ++++CALCIFICATIONCALCIFICATION – T1W– T1W+++

T2WT2W+++ FLOWFLOW – T1W – T1W +++ T2W +++

T1W - +++T2W - +++FLAIR - SUPP

LESION CHARACTERISATIONLESION CHARACTERISATION

CYTOTOXICCYTOTOXIC

BRAIN EDEMABRAIN EDEMA

VASOGENIC

Due to tumor, infection, Due to tumor, infection, venous infarctvenous infarct

Involves only white matter.Involves only white matter.

NOT along specific arterial NOT along specific arterial distributiondistribution

Not bright on diffusion.Not bright on diffusion.

CONTRAST MRI INDICATEDCONTRAST MRI INDICATED

Due to arterial infarct.Due to arterial infarct.

Extends thru grey-white Extends thru grey-white matter junction (involves matter junction (involves grey matter).grey matter).

Along specific arterial Along specific arterial distribution.distribution.

Bright on diffusion.Bright on diffusion.

LESION CHARACTERISATION LESION CHARACTERISATION BRAIN EDEMABRAIN EDEMA

CYTOTOXIC EDEMACYTOTOXIC EDEMA VASOGENIC EDEMA

T2W AXIAL

T2W SAG

T1W AXIAL

FLAIR COR

T1W +++

T2W +++

FLAIR NOT SUPP

POST CONT ENHANCEMENT


T1 W AXIAL++

T2 W AXIAL+++

FLAIR AXIAL+++

H/O headache following vehicular accident.


TT1W T2W POST CONT T1

T1W

T2W

POST CONT T1


T2W AXIAL.

T1W AXIAL

T1W SAGT2W SAG


T2W SAG T1W SAG

T2W AXIAL.

T1W AXIAL.


T1W T2W POST CONT T1


T2W AXIAL.

T1W AXIAL.

T2W CORONAL T1W CORONAL T2 FAT SUPP


T2W SAG FAT SUPP COR

T2W AXIAL.

T1W AXIAL.


T2 SAG T1 SAG

T2W AXIAL

T1W AXIAL

MRI Basics MRI Basics SEQUENCESSEQUENCES

SEQUENCESEQUENCE FATFAT FLUIDFLUID

T1WT1W WHITEWHITE BLACKBLACK

T2WT2W NOT SO NOT SO WHITEWHITE

WHITEWHITE

T2 FAT T2 FAT SUPPSUPP

STIRSTIR

BLACKBLACK WHITEWHITE

T2 FLU T2 FLU SUPPSUPP

FLAIRFLAIR

CSF/CLEAR FLUID - CSF/CLEAR FLUID - BLACKBLACK

PATH FLUIDPATH FLUID- WHITE- WHITE

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basic fundamentals of mri a cquisition of mri images - physics b asic sequences & advanced...

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