BASICS OF MRI
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Transcript of BASICS OF MRI
Contents of this talk
Introduction.MRI of brain.MRI of spine.Others.
My aim is to focus on common and significant findings.
Tiny motion of protons
in a magnetic field is
responsible for MR
images.
Difficult to believe but
true !
How does MRI (Magnetic Resonance Imaging) work..?
Design of MRI Magnet
Peter Mansfield
Paul Lautebur
Raymond Damadian
Inventors of MRI
Nobel prize for physiology or medicine 2003
What`s so special about MRI..
Its unique multiecho technique gives tremendous insight to living body in health and disease.
What is T1 sequence..
T1 refers to time taken for return of net magnetization.
A T1 weighted image is produced by this property.
Practically , we need to identify T1 weighted image.
Remember FLUID IS BLACK on T1.
T1 image of brain
What is T2 sequence..T2 image of brain
T2 refers to loss of transverse magnetization.
A T2 weighted image is produced by using this property.
Practically we need to know FLUID IS BRIGHT on T2
More than 100 different sequences are there FLAIR ,STIR,CISS,SPACE,GRE,SSSFE , FSE,TSE………..
Brain MRI is the gold standard in detecting intracranial lesions.
It approaches histopathology , can predict functional outcome of treatment, assess brain vessels.
It does have few limitations
What we will do..Anatomy/ Identifying lobes.Few case examples.
Case 1.39 year old male
with headache and left frontal seizures.
CT brain shows edema right frontal lobe.
T2 hypointensity with edema in right frontal lobe.
T1 mild hypointensity in right frontal lobe.
Conglomerate ring enhancing lesions. Consistent with tuberculoma.
Is MRI pathognomonic in diagnosis of tuberculoma..?No.Ring enhancing lesion with T2 hypointensity
in appropriate clinical situation suggests tuberculoma.
Lesion needs follow up.Presence of caseation is responsible for T2
hypointensity.
Case 2Headache in 28 year
old femalePapilloedema
presentCT -? Filling defect
in venous sinuses.
Lack of visualization of superior sagittal sinus and left lateral sinus. Suggestive of thrombus.
Brain images show mild edema in right frontal lobe.
MRI with venogram is the modality of choice in assessing venous sinus thrombus and its complications.
Normal MR venogram.
Case 3.21 year old lady with
previous history of vision loss. Now complains of numbness of lower limbs.
Sagittal T2 shows periventricular hyperintensities.
Coronal FLAIR
Axial T2Axial T1 POST CONTRAST
Diagnosis- multiple sclerosis.
Though lesions are characteristic of multiple sclerosis , temporal clinical course is necessary to confirm clinical diagnosis.
Enhancement detects acute plaques.
Case 45 month old infant with growth retardation
and recurrent seizures.Sibling had similar history and died due to
unknown illness.
T2 hyperintensity seen in basal ganglia.
No abnormality in FLAIR or T1 sequence
Diffusion imaging shows areas of diffusion restriction.
Diffusion imaging shows areas of recent ischemia / infarct well.It also has other applications.
Diagnosis– Mitochondrial cytopathy / Leigh`s diseaseBilateral symmetrical areas of abnormal
signal in an infant with diffusion restriction in an infant is suggestive of mitochondrial disease.
Findings need to be confirmed with serum lactate estimation.
Spine imaging…
MRI is widely used to image spine.
It has become first line investigation in spine imaging.
Key in spine MRI is to pick up the significant and discard insignificant.
Lateral section
Paramedian section
Midsagittal section
Nerve root
conus
Axial section at L4-L5 disc level , shows L4 root exiting out of neural foramen , L5 root at lateral recess
Axial section at vertebral body level , shows pedicles , nerve roots in cauda equina
• Lateral recess is the space bordered anteriorly by posterior vertebral body , posteriorly by superior articular facet , laterally by pedicle. In lumbar spine , nerve root is usually trapped by herniated disc here.
Disc bulge
Disc protrusion , note broad base
Migrated , extruded disc.
Right paracentral disc extrusion with lateral recess stenosis and S1 root compression
Why is this classification important..?52% of adult population have disc bulges.27% have disc protrusions.1% have extrusions and are invaribly
symptomatic.
N Eng J Med 1994: 331
Degenerative fatty endplate change.Look for fat , paravertebral swelling to differentiate from infection.
Tuberculosis of DL spine causing low back ache
Check list for infection1.Disc involvement.2.Contiguous vertebrae.3.Pre and para vertebral fluid collection/abscess
Intradural extramedullary tumor , possibly neurofibroma.
Old fracture at D12 vertebral level.
Presence of fat signal is helpful in differentiating fat from edema signal.
Case 563 year old lady with sudden onset of renal
function deterioration. Pulses not felt in lower limbs.
Color doppler -- ? Renal artery embolus.
Aortic occlusion , left renal artery also occluded.
Patient was thrombolysed.Follow up MRI after 1 week shows good improvement
Case 6Middle aged male with history of right side
sensory symptoms. CT showing right thalamic lesion, ?infarct/SOL
MR Spectroscopy showing normal metabolites
This graph is called spectroscopy , a sort of chemical assessment of brain lesions.
Normal Glioma spectrum.
spectroscopyAs different lesions have different chemical
composition , spectroscopy gives different graphs to different lesions.
Though not 100% accuracy , is a good tool in assessing brain lesions.
This case was a high grade glioma.
Tuberculoma spectrum
Normal spectrum
Cardiac MRI , valuable tool in assessing viability , cardiomyopathy , pediatric cardiology. This is a case of cardiomyopathy.
Infrarenal aortic occlusion
MR angiography lower limbs nearly equals conventional angiogram.
MR based cholangiogram is an ideal technique for biliary tract assessment.
CBD Calculi
Which MRI is betteropen or 1.5 Tesla ..?
Which MRI is betteropen or 1.5 Tesla ..?
Open 0.2 T1.5 Tesla
I have a patient with metallic implant , can I ask for MRI..?
A titanium implant can be done immediately after surgery.
Rest of metallic implant , better wait for 6 weeks and then proceed for MRI.
J MRI 2002
Is MRI safe in pregnancy…?No harmful effects demonstrated so far to
mother and fetus.However concerns remain , FDA has not
declared MRI is completely safe in pregnancy.
Present consensus is that MRI to be done under Definite indications for mother and fetus.
Why musculoskeletal system not discussed.. Sorry , as other systems were thought more
relevant to today`s audience..
Are MRI contrast gadolinium based compounds harmful in renal failure..Use is safe in mild- moderate renal failure.It should be used with caution in patients
with severe renal failure.Large amounts of MR contrast when used in
severe CRF (GFR less than 30 ml/minute) is suspected to cause a disease called NSF (nephrogenic systemic fibrosis).
Hence caution is indicated in these circumstances.
Summary ….MRI has made tremendous clinical impact.Findings need interpretation with caution
and after proper discussion.
Thank
youCan you
guess the probable diagnosis