Basic Fundamentals of MRI A cquisition of MRI images - PHYSICS B asic Sequences & Advanced...
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Transcript of 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
TESLA FACTOR !!TESLA FACTOR !!
IMAGEQUALITY
S/N Ratio Contrast
FIELD SRENGTH
TYPE OF MAGNETIC FIELDVERTICAL/ HORIZONTAL
GRADIENTS
TYPE OF COILS
TYPE OF COMPUTERIMAGE PROCESSING & SEQUENCES
CAMERA
TESLA FACTOR !!TESLA FACTOR !!
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.
TESLA FACTOR !!TESLA FACTOR !!
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
BASIC SEQUENCESBASIC SEQUENCES
T2 Weighted – T2 Weighted – PATHOLOGY.PATHOLOGY.
FLUID- FLUID- WHITEWHITE FAT- FAT- NOT SO NOT SO
WHITEWHITE
BASIC SEQUENCESBASIC SEQUENCES
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
BASIC SEQUENCESBASIC SEQUENCES
BASIC SEQUENCESBASIC SEQUENCES
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
BASIC SEQUENCESBASIC SEQUENCES
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
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.
ADVANCED APPLICATION ADVANCED APPLICATION MRCPMRCP
T2 W FSE
3D MRCP
ADVANCED APPLICATION ADVANCED APPLICATION MRCPMRCP
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)
ADVANCED APPLICATION ADVANCED APPLICATION MRAngioMRAngio
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.
ADVANCED APPLICATION ADVANCED APPLICATION MRAngioMRAngio
MRA – CIRCLE OF WILLIS
MRA – NECK VESSELS
ADVANCED APPLICATION ADVANCED APPLICATION MRAngioMRAngio
CONTRAST MRA – RENAL VESSELS.
ADVANCED APPLICATION ADVANCED APPLICATION MRAngioMRAngio
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
LESION CHARACTERISATIONLESION CHARACTERISATION
T1 W AXIAL++
T2 W AXIAL+++
FLAIR AXIAL+++
H/O headache following vehicular accident.
LESION CHARACTERISATIONLESION CHARACTERISATION
TT1W T2W POST CONT T1
T1W
T2W
POST CONT T1
LESION CHARACTERISATIONLESION CHARACTERISATION
T2W AXIAL.
T1W AXIAL
T1W SAGT2W SAG
LESION CHARACTERISATIONLESION CHARACTERISATION
T2W SAG T1W SAG
T2W AXIAL.
T1W AXIAL.
LESION CHARACTERISATIONLESION CHARACTERISATION
T1W T2W POST CONT T1
LESION CHARACTERISATIONLESION CHARACTERISATION
T2W AXIAL.
T1W AXIAL.
T2W CORONAL T1W CORONAL T2 FAT SUPP
LESION CHARACTERISATIONLESION CHARACTERISATION
T2W SAG FAT SUPP COR
T2W AXIAL.
T1W AXIAL.
LESION CHARACTERISATIONLESION CHARACTERISATION
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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