MRI的基本知识PPT.ppt

Magnetic resonance imaging（MRI）;In 1946, Felix Bloch and Edward Purcell independently discovered the magnetic resonance (MR) phenomena (Nobel Prize in 1952) In 1971, Raymond Damadian showed that nuclear magnetic relaxation times of tissues and tumors differed In 1973, By utilizing gradients in the magnetic field, Paul Lauterbur demonstrated MR imaging on small test tube samples (Nobel Prize in 2003) In 1975 Richard Ernst proposed MR imaging using phase and frequency encoding, and the Fourier Transform, which are the basis of current MRI techniques. (Nobel Prize in 1991) In 1977, Peter Mansfield developed the echo-planar imaging technique (Nobel Prize in 2003) In 1977, Raymond Damadian completed the first MR scanner (Indomitable). ;3.1 Basic Principles of MRI ;;;MRI reveals chemical compositions of objects as well as their molecular structure arrangement , but not density. Electromagnetic wave is used in MRI , not ionizing radiation wave (X-ray ,γ-ray) or mechanical wave(ultrasound) ;MR describes the phenomenon whereby the nuclei of certain atoms, when placed in a magnetic field, absorb and emit energy of a specific frequency. ;Nuclei suitable for MRI are those which have an odd number of protons or neutrons and therefore possess a net charge and have angular magnetic momentum (tiny magnetic field generated by the spinning motion of atomic nuclei);Hydrogen nucleus (one proton, no neutron) is the best element for general clinical utility of MRI due to its strongest magnetic moment and greatest abundance in human tissues.;N;x;The flip angles typically range from 1 to 180 degrees, depending on the amplitude and duration of applied RF.;x;T2 relaxation;T1 relaxation;Pulse sequences refer to the manner in which the radiofrequencies and gradients are applied with appropriate time intervals between them in order to highlight a certain inherent tissue property.;Spin echo pulse sequence is the most important sequence in clinical imaging and forms the basis of MR ti