《MRI of the brain》.pdfVIP

Amit Malhotra September 2000 Gillian Lieberman, MD MRI of the Brain: A Primer on What, How, Why, and When Hornak, J.P. The Basics of MRI. 1996-2000 Amit Malhotra, Harvard Medical School, Year- IV Gillian Lieberman, MD Amit Malhotra Gillian Lieberman, MD Magnetic Resonance Imaging A Brief History Magnetic Resonance phenomenon first described by Felix Bloch and Edward Purcell in 1946. In 1952 they were awarded the Nobel Prize. 1971 - Raymond Damadian showed that the nuclear magnetic relaxation times of tissues and tumors differed, sparking interest in medical uses (Science 03/19/71). In 1975 Richard Ernst proposed magnetic resonance imaging using phase and frequency encoding, and the Fourier Transform, which forms the basis of current MRI techniques. 1987 – MR angiography developed by Charles Dumoulin. 1993 functional MRI (fMRI) was developed. 2 Amit Malhotra Gillian Lieberman, MD Physical Principles Based on the absorption and emission of radiofrequency energy – so there is NO ionizing radiation. Uses magnets ranging in strength from 0.3 to 1.5 Tesla to create a magnetic field around the patient. Magnetic field causes protons in the body to align and then pulsed radiowaves are directed at the patient causing a disturbance of the proton alignment. Atoms then realign and in doing so, emit the absorbed radiofrequency. 3 Physical Principles cont. The time it takes the protons to regain their equilibrium state = RELAXATION TIME. 2 types of relaxation time: T1 –