Magnetic resonance imagin

Doherty MJ, Kumar K, Nicholson AA, et al. Cardiac sarcoidosis the value of magnetic resonance imagine in diagnosis and assessment of response to treatment. Respir Med 1998 92 697-699. 

We sometimes say that the CHCI3 proton resonates downfield (at a smaller external magnetic field) with respect to TMS, which in turn resonates upheld (at a larger external magnetic field) if we imagine to keep the frequency fixed and to vary the magnetic field. 

If we imagine an on-resonance or hard pulse we have already determined from Fig. 3.13 that the y-component of magnetization after a pulse of flip angle P is proportional to sin (J>. If we therefore do a pulse-acquire experiment (section 3.6) and vary the flip angle of the pulse, we should see that the intensity of the signal varies as sin ft. A typical outcome of such an experiment is shown in Fig. 3.18. 

Let us firsl consider the effect of the methylene protons in ethanol on the resonance of the molhyl protons. Recall that the ratio of protons in the two possible spin stales is very nearly unity, even in a strong magnetic lield. We then imagine that the two methylene protons in the molecule can have four possible combinations of spin slates and that in an entire sample the number of each of these combinations will be approximately etjual. If wc represent the spin orientation of each nucleus with a small arrow, the bmr states arc as follows ... 

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