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