Survey
* Your assessment is very important for improving the workof artificial intelligence, which forms the content of this project
* Your assessment is very important for improving the workof artificial intelligence, which forms the content of this project
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 ► BOLD ► T1WI ► MRA ► T2WI ► MRV ► PDWI ► Post-Gd ► DWI ► ADC ► GE ► Perfusion ► fMRI images images images ► Volumetric images ► MR arthrograms ► FLAIR ► STIR ► Etc etc etc T1-weighted contrast T2-weighted contrast Tissue Appearance WT FAT H2O MUSC LIG BONE T1 B D I D D Proton I I I D D T2 B I D D Density I 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. 2. 3. 4. 5. No ionizing radiation & no short/long-term effects demonstrated Variable thickness, any plane Better contrast resolution & tissue discrimination Various sequences to play with to characterise the abnormal tissue 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 CT 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 Indications (almost everything) ► Anatomy ► Trauma ► Congenital ► Dementia anomalies ► Hereditary and metabolic diseases ► Infections ► Demyelination ► Vascular event ► Tumours ► 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