Magnetic Resonance Imaging Dr Mohamed El Safwany, MD.

Intended learning outcome ► The student should learn at the end of this lecture MRI basics.

► Oxygen, hydrogen, carbon, nitrogen elements constitute 96 % of human body mass. ► Oxygen is 65 % of body mass; carbon is 18.5 %, hydrogen 9.5 %, nitrogen 3.2 %. ► Let us ignore all elements but Hydrogen.

► Simplest element with atomic number of 1 and atomic weight of 1 ► When in ionic state (H+), it is nothing but a proton. ► Proton is not only positively charged, but also has magnetic spin (wobble)! ► MRI utilizes this magnetic spin property of protons of hydrogen to elicit images!! ► We are magnets!

► The protons (i.e. Hydrogen ions) in body are spinning in a hap hazard fashion, and cancel all the magnetism. That is our natural state! ► We need to discipline them first

► Magnetic field strength: 0.3 – 7 T (2500 times more than earth’s magnetic field). Average field strength – 1.5 T ► Open magnet – less field strength, less claustrophobic ► Closed magnet – more field strength, claustrophobic

Proton alignment ► Compass aligns with the earth ► In a similar fashion, ► Our body protons (hydrogen) align with this external magnetic field. ► Now, we are disciplined (spinning in line with each other!)

► Radio frequency pulses in resonance push the aligned protons (H+) to a higher energy level.

Radio Frequency pulse ► Same as Radio waves – high wavelength, low energy electromagnetic waves ► Radiofrequency coils  Act as transmitter and receiver  Different types of coils

► The higher energy gained by the protons is retransmitted (NMR signal)

Images ► T1WI ► T2WI ► PDWI ► DWI ► ADC ► GE ► Perfusion images ► fMRI ► BOLD images ► MRA ► MRV ► Post-Gd images ► Volumetric images ► MR arthrograms ► FLAIR ► STIR ► Etc etc etc

T1-weighted contrast

T2-weighted contrast

Tissue Appearance WTFATH2OMUSCLIGBONE T1BDIDD Proton Density IIIDD T2IBIDD

sequence exercise

Which sequence is it? T2

Which sequence is it? T1

Which sequence is it? FLAIR

Which sequence is it? DWI

Which sequence is it? ADC

Which sequence is it? GE

Which sequence is it? PostGd

Which sequence is it? MRV

Which sequence is it?, 3D MRV

Which sequence is it? MRA

Which sequence is it? T2

Which sequence is it? T1

Which sequence is it? STIR

Which sequence is it? MR arthrogram

Before entering tunnel, there is a checklist! ► No mobiles, no credit cards, please! ► Known potential safety concerns due to large static magnetic field:  Internal cardiac pacemakers  Steel cerebral aneurysm clips (ferromagnetic)  Small steel slivers embedded in eye  Cochlear implants  Stents anywhere in the body

Clinical Aspects of MRI

Advantages of MRI 1. No ionizing radiation & no short/long-term effects demonstrated 2. Variable thickness, any plane 3. Better contrast resolution & tissue discrimination 4. Various sequences to play with to characterise the abnormal tissue 5. Many details without I.V contrast

Disadvantages of MRI ► Time consuming ► Not easily available (long waiting list)

► MRI has limitations:  Bone  Air  Time consuming

MR ► Faster ► Less expensive ► Less sensitive to patient movements ► Easier in claustrophobics ► Acute haemorrhage ► Calcification ► Bone details ► Foreign body ► No ionising radiation ► Greater details, hence more sensitive and more specific ► Any plane scanning ► Contrast less allergic ► No beam hardening artefact CT

Indications (almost everything) ► Anatomy ► Congenital anomalies ► Hereditary and metabolic diseases ► Infections ► Demyelination ► Vascular event ► Tumours ► Trauma ► Dementia ► Hydrocephalus ► Cranial nerves ► Arteriograms ► Venograms ► Skull base ► Pituitary gland

Vascular MRI ► Peripheral vascular arteriogram with or without I.V contrast ► Aortogram  Dissection ► Pulmonary arteriogram  When CT is contraindicated

Cardiac MRI ► Coming in a big way ► Very useful in congenital heart diseases, cardiomyopathies ► Evidence is emerging in the evaluation of myocardial infarction

Breast MRI ► Problem solving  Breast implants  Recurrence  Multifocal disease

Foetal MRI ► Assessment of congenital anomalies ► Placental abnormalities ► Twin assessment

Text Book ► David Sutton’s Radiology ► Clark’s Radiographic positioning and techniques

Assignment ► Two students will be selected for assignment.

Question ► Define differences between CT and MRI?

Thank You 44