1 Nuclear Magnetic Resonance ANIMATED ILLUSTRATIONS MS Powerpoint Presentation Files Uses Animation Schemes as available in MS XP or MS 2003 versions A class room educational material Relaxation and In-homogeneities Longitudinal and transverse Relaxation Slide # 2 Description, depiction and definitions in Field In-homogeneities Slide # 3 In-homogeneities and NMR line widths Slide # 4 Elements of NMR Imaging Slide # 5 Isochromats and spin evolutions in inhomogeneous fields Slide # 6 Field-Gradient description for In-homogeneities Slide # 7 Set to Video conversion on 17 th Dec. 2009

2 Randomization in XY plane I h NET Magnetization Transverse T 2 Relaxation Relaxation Longitudinal and transverse Longitudinal T 1 Relaxation π/2 pulse

3 N S N S N Set of equally spaced parallel lines indicates homogeneous field No. of lines within a unit area of cross section [in plane perpendicular] Is the field strength/ Intensity of magnetic field Area of cross section Inhomogeneous Fields Presence of a Magnetic field is pictorially depicted by a vector-line pointing along the direction in which an isolated North pole would move It is important to realize the difference between two poles forming magnet pole faces and two poles making up the dipole with a dipole moment Increasingly More intense homogeneous Fields

4 H0H0 H 0 - ΔH 180°pulse 90°Pulse Thermal equilibrium Boltzmann population distribution H0H0 Net Magnetization only along H 0 and no magnetization in plane perpendicular (zero component) Magnetization has non-zero component in XY-plane… Tilted to XY plane Homogeneous Field Inhomogeneous Field

5 If the spatial location within the sample where a particular filed is present can be encoded along the frequency axis, then it is spatial resolution which results. Elements of NMR imaging Precession frequency would be proportional to the strength of the filed at the point where the spin is located

6 6 spins/all precess with same frequency Single isochromat of 6 spins All the 6 Superposed spins result in 5 Isochromats Each with a bunch of spins Multitude of isochromats and resultant vector evolution Degree of field homogeneity is represented by set of parallel lines of force in homogeneous fieldThese 6 spins placed closer Weakest fieldStrongest field Lowest precession frequency Highest precession frequency Vector Resultant

7 Equal number of lines pass through fixed area of cross section along the length 3 lines inside 6 lines inside Linear Field Gradient along z-axis. Along the length same nmr frequency for the sample NMR frequency will vary linearly along the length. In the Pulsed Field Gradient PFG and Magnetic Resonance Imaging MRI techniques calculated field gradient are externally superposed. The inherent unwanted and incidental inhomogeneities are reduced by Shimming and sample spinning The End