Magnetization longitudinal

For large molecules, such as proteins, the main method in use is a 2D technique, called NOESY (nuclear Overhauser effect spectroscopy). The basic experiment [33, 34] consists of tluee 90° pulses. The first pulse converts die longitudinal magnetizations for all protons, present at equilibrium, into transverse magnetizations which evolve diirhig the subsequent evolution time In this way, the transverse magnetization components for different protons become labelled by their resonance frequencies. The second 90° pulse rotates the magnetizations to the -z-direction. 

The interval between the second and third pulse is called the mixing time, during which the spins evolve according to the multiple-spin version of equation B 1.13.2 and equation B 1.13.3 and the NOE builds up. The final pulse converts the longitudinal magnetizations, present at the end of the mixing time, into detectable transverse components. The detection of the FID is followed by a recycle delay, during which the equilibrium... 

Longitudinal magnetization This is the magnetization directed along the z-axis parallel to the Bq field. 

Beaulieu C, de Crespigny A, Tong DC, Moseley ME, Alhers GW, Marks MP. Longitudinal magnetic resonance imaging study of perfusion and diffusion in stroke evolution of lesion volume and correlation with clinical outcome. Arm Neurol 1999 46 568-578. 

Fig. 7.45 Outer two components of the magnetic hyperfine spectrum of a W/W source versus a Ta absorber, measured at zero velocity as a function of a longitudinal magnetic field ( Zeeman drive experiment) (from [185])...

Here m(r, t) is the relative difference of the longitudinal magnetization M and its equilibrium value Mo m = (M — Mo)/Mo, D is the bulk diffusion coefficient and p is the bulk relaxation rate. The general solution to the Torrey-Bloch equation can be written as... 

Assume a 180° PIP is applied at the centre of the 13CO in the middle of the 13C evolution time for homonuclear decoupling and at the same time a compensating PIP is applied on the other side of the l3C (Fig. 11) to minimize the disturbance to the 13C that may have a transverse or longitudinal magnetization. The two simultaneous PIPs become an amplitude modulated pulse described by 2/i cos (27iAft)Ix, where f is the pulse strength of each 180°... 

Here 2tt Aft = trm is imposed to eliminate the effect by the zero-order interaction of the RF field, otherwise a term containing Ix will remain and it will distort the longitudinal magnetization, transverse magnetization, as well as the BSPS of the 13C . For the on-resonance condition, 5 = 0, all the higher-order average Hamiltonians vanish since [7f(/ ), = 0 for arbitrary l and... 

Unlike the compensation of the BSPS for a long pulse,44 the pulsewidth r for short PIPs is crucial. Away from the condition of lit Aft = mix, a significant zero-order term will arise and the longitudinal magnetization, the transverse magnetization, and the BSPS can be distorted so severely that the BSPS compensation scheme does not work at all.42... 

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