Contrast, in NMR imaging

1 f) Sasrital imajic thmujih a human head. Thu contrast is determined by the local values olThe spin density and the / i relaxation time. Adapted from IBliidj with permission from 

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Wehrli F W, MacFall J R, Shutts D, Breyer R and Flerfkens R J 1984 Mechanisms of contrast in NMR imaging J. Comput. Assist. Tomogr. 8 369-80... 

Figure 7.1 Most modern NMR techniques are based on the fact, that the phase (p of the precessing transverse magnetisation M t) kann be measured. By use of the Fourier transformation the phase provides access to NMR spectra, images, and parameters of translational motion like velocity v and acceleration a. Spectroscopic parameters as well as components of translational velocity and acceleration can be used for generating contrast in NMR imaging. In the drawing the magnetisation M(t) has been generated from Mz by use of a 90° pulse of the B1 radio-frequency (rf) field in y direction...

In contrast to the saturation recovery technique, negative z magnetization can be generated, but care must be taken to start from thermodynamic equilibrium. If these techniques are used for generation of T contrast in NMR images, different contrast is obtained because signal is suppressed by the saturation recovery technique while it is preserved but inverted by the inversion recovery technique. 

The contrast parameters relevant to material characterization through NMR imaging are the intrinsic NMR parameters of the sample. They are referred to as the contrast parameters per se. They can be divided into chemical and physical parameters, and into molecular, mesoscopic, microscopic, and macroscopic parameters. A list of NMR parameters for contrast in NMR imaging is compiled in Table 7.1.1. 

The principles of spatial resolution and contrast in NMR imaging have been presented in this chapter. An overview of selected applications of NMR to investigations of fluid systems, technical elastomers and rigid polymers has been given. The examples chosen demonstrate the potential of NMR for measurement of macroscopic properties of polymer materials. The importance of developments of NMR methods and equipment for materials science applications was underlined by example of the NMR MOUSE. 

In network characterization, there are three origins for the contrast in NMR images ... 

Young IR (1984) Signal and contrast in NMR imaging. British Medical Bulletin 40(2) 139-147. 

The term Moo defines NMR spectroscopy including relaxometry [Kiml]. This is the type of NMR applied most often in chemistry and physics. It forms a subject in itself [Abrl, Eml, Slil] but is not the focus of this book. Here NMR spectroscopy and relaxometry are considered to be a highly important asset to imaging, because they provide most of the contrast features exploited in NMR imaging of materials. Although NMR spectroscopy and relaxometry are introduced in Chapters 2 and 3 of this book, because they constitute the most important term in the perturbation expansion (1.2.4), they are treated in more variety from the point of view of contrast in Chapter 7. 

Proper choice of tR and tE for suitable Ti and T2 weights is an important factor for determining image contrast in medical imaging. Due to less restrictions in measurement time and the use of rf power, a much wider variety of contrast parameters can be accessed in material applications of NMR imaging (cf. Chapter 7). 

In addition, Feindel et al. used hydrogen—deuterium (H—D) exchange method to introduce contrast in NMR microscopy images and to inves-... 

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