Precession magnetic

The quantitative formulation of chemical exchange involves modification of the Bloch equations making use of Eq. (4-67). We will merely develop a qualitative view of the result." We adopt a coordinate system that is rotating about the applied field Hq in the same direction as the precessing magnetization vector. Let and Vb be the Larmor precessional frequencies of the nucleus in sites A and B. Eor simplicity we set ta = tb- As the frequency Vq of the rotating frame of reference we choose the average of Va and Vb, thus. 

Figure 1. Precessing magnetic moment in (a) the laboratory reference frame and in (b-d) the rotating reference frame.

LARMOR PRECESSION MAGNETICALLY ANISOTROPIC GROUP MAGNETOTACTIC Magnetic field strength,... 

Remember from Section 2.3 that to tip M off the z axis, so it has a component in the x,y plane, we need an irradiating magnetic field (B[) that oscillates at exactly the precessional frequency of the nuclei of interest and is oriented perpendicular to B0. How are we going to generate such a precessing magnetic field ... 

The rationale for INEPT can best be understood by looking first at a somewhat simpler continuous wave experiment for transferring polarization, selective population transfer (SPT). SPT can be understood simply in terms of the populations of energy levels, whereas INEPT requires consideration of coherent precessing magnetization. Figure 9.9 shows the energy levels and populations of an AX spin system, which we take to be H and 13C, respectively, in this example. At equilibrium the populations conform to a Boltzmann distribution. Because the H... 

The decay of the pulse response is described by the transverse relaxation time Tz, which accounts for loss of the phase coherence of the precessing magnetization components as a result of time-dependent differences in local NMR frequencies. These components accumulate different precession phases as time goes on, so that the vector sum of all magnetization components eventually vanishes (Fig. 2.2.3(c)). 

Fig. 3.3 The precessing magnetization will cut a coil wound round the x axis, thereby inducing a current in the coil. This current can be amplified and detected it is this that forms the free induction signal. For clarity, the coil has only been shown on one side of the x axis.

Suppose that a particular spectrometer is only capable of recording one, say the x-, component of the precessing magnetization. The time domain signal will then just have a real part (compare Eqn. [7.2] in section 7.6.1)... 

On exact resonance, pg and Bj can remain in phase so the precessing magnetic moment experiences a constant field Bj in the xy-plane (see figure Bl.15.1. It will respond to this by precessing about it with frequency coj = g P Bj//). 

After the rf field Hj is turned off, the magnetization will precess freely. In an actual experiment, the precessing magnetization decays owing to various mechanisms which usually are the objects of an NMR study. In a coil with its axis perpendicular to the laboratory field, this decaying magnetization will induce an rf current at the Larmor frequen-... 

Nguyen TD, Spincemaille P, Vaidya A, Prince MR, Lu ZR, Wang Y. Biodegradable intravascular (Gd-DTPA)-cystamine copolymer for contrast-enhanced steady-state free precession magnetic resonance angiography comparison with MS-325 in a swine model. MolPharm 2006 3 558-565. 

Thus, the expectation value of the magnetization evolves in the rotating frame with the frequencies 0 and 6tug. When viewed from the laboratory frame, these precessing magnetizations give rise to alternate electric signals detected with frequencies - 6a>g,... 

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