The importance of MRI, a few The importance of MRI, a few numbersnumbers

10 000 MRI units worldwide in 200310 000 MRI units worldwide in 2003

75 millions scans per year performed75 millions scans per year performed

Constant need for over 1000 MRI technologists per yearConstant need for over 1000 MRI technologists per year

MRI magnet have 1.5-2.0 Tesla (same strength as MRI magnet have 1.5-2.0 Tesla (same strength as magnet used in car junk yard)magnet used in car junk yard)

1 Tesla=10 000 gauss, earth magnetic field=0.5 gauss 1 Tesla=10 000 gauss, earth magnetic field=0.5 gauss

Background Info on Magnetic Background Info on Magnetic ResonanceResonance

Proton imaging and the use of hydrogenProton imaging and the use of hydrogen

Magnetic field of HMagnetic field of H

Behaviour in an external magnetic fieldBehaviour in an external magnetic field

Nuclear magnetic resonanceNuclear magnetic resonance

How is an image obtained?How is an image obtained? Isolation of slice of tissueIsolation of slice of tissue

Creation of a magnetic fieldCreation of a magnetic field

The perpendicular magnetic fieldThe perpendicular magnetic field

Repetition at different anglesRepetition at different angles

Collection of data in computer and Fourier Collection of data in computer and Fourier transformtransform

Diagram taken from “Basics of Magnetic Resonance Imaging” p.21

Tissue T1 (s) T2 (ms)

CSF 0.8 - 20110 - 2000

White0.76 - 1.08 61-100

Gray1.09 - 2.15 61 - 109

Meninges 0.5 - 2.2 50 - 165

Muscle0.95 - 1.82 20 - 67

Adipose 0.2 - 0.75 53 - 94

What can we deduce from the H What can we deduce from the H values obtained?values obtained?

The behaviour of regional hydrogenThe behaviour of regional hydrogen

T1 of hydrogenT1 of hydrogenTime required for the hydrogen nuclei to emit 63% of absorbed energy Time required for the hydrogen nuclei to emit 63% of absorbed energy

from stimulating pulsefrom stimulating pulse

T2 of hydrogen (relaxation constant)T2 of hydrogen (relaxation constant)Time necessary for 63% of signal to be lost due to dephasingTime necessary for 63% of signal to be lost due to dephasing

Factors affecting T1 and T2Factors affecting T1 and T2

Main component of an MRIMain component of an MRI Main magnetic fieldMain magnetic field

The problem of electrical The problem of electrical resistance resistance

Aluminium as the Aluminium as the conductor of choiceconductor of choice

Gradient coilsGradient coils

Rf coils (radio frequency Rf coils (radio frequency source and pulse source and pulse programmer)programmer)

MRI LimitationsMRI Limitations

Shape and sizeShape and size

Scanning timeScanning time

Gradient coil and noiseGradient coil and noise

Patient discomfortPatient discomfort

Pacemaker and artificial body partPacemaker and artificial body part

Complexity and costComplexity and cost

Advantages of MRIAdvantages of MRI

Bones are invisiblesBones are invisibles

Any plane can be scannedAny plane can be scanned

Tissue characterizationTissue characterization

Less tissue heatingLess tissue heating

The Future of MRIThe Future of MRI

The trend toward lower field strengthThe trend toward lower field strength

Understanding Alzheimer’s diseaseUnderstanding Alzheimer’s disease

Non-invasive quantification of blood flowNon-invasive quantification of blood flow

Open doors in understanding brain Open doors in understanding brain processes processes