Surface-coil techniques

While in vivo 19F MR has provided unique insight into fluoropyrimidine metabolism, most spectroscopic studies have limited numbers of patients and thus are subject to potential bias due to the variability in individual biometabolism. The small number of subjects can further limit generalization of the results to a larger population. In addition, studies of deep tissues or small lesions are challenging using 19F MR spectroscopy because they cannot be adequately evaluated using surface coil techniques and the low signal levels preclude use of a volume coil. 

The sensitive volume, which can be investigated by a circular surface coil in a homogeneous polarizing field, is approximately given by a half sphere with the coil radius. As the coil radius is typically small compared to the largest dimension of the object, the use of surface-coil techniques is restricted to volume elements near the sample surface. 

Fluorine-19 NMR spectroscopy has been used to study biological systems in a number of ways. Structural information can be obtained if the fluorine is used as a probe, for example as part of an amino acid in a protein. Biochemical pathways can be elucidated by observing the fluorine-19 chemical shifts of products and intermediates which are usually well separated owing to the wide chemical shift range. Finally, the distribution of fluoro-organic molecules within an organism can be detected using such techniques as surface coils. 

Fluorine-19 NMR has also been used to examine the fate of anesthetics in vivo. Figure 9 shows the spectra of two anesthetics in rabbit brain using a surface coil. The 70-Hz geminal fluorine-proton coupling is well resolved, however, the smaller fluorine-proton vicinal couplings are not resolved owing to the large line widths obtained by this technique. 

Transmit-receive surface coils are generally used for MR spectroscopic studies in organs other than the brain. If dual-frequency techniques such as NOE, polarization transfer, or decoupling are to be utilized with surface coil excitation, or if relaxation time measurements are to be performed, RF pulses that are insensitive to spatial and amplitude... 

A new system for the metabolic investigation of the isolated perfused rat heart has been developed. The novel two surface-coil probe was combined with a dual perfusion system which allows spectra to be collected independently from the two coronary beds of the heart. The technique has been demonstrated in an experiment where P NMR spectra were collected from a perfused rat heart in which the septum and right ventricle were made ischaemic whilst the left ventricle wall was fully perfused.Spatially localised in vivo P NMR and MRI have been used to measure mean murine myocardial PCr/ ATP ratios of 2.0 0.2 and left ventricular ejection fractions of 65 7% at a physiological heart rate of approximately 600 beats min . ... 

See also Air Analysis Sampling Outdoor Air Workplace Air. Fourier Transform Techniques. Nuciear Magnetic Resonance Spectroscopy Techniques Solid-State Surface Coil In Vivo Spectroscopy Using Localization Techniques. Nuclear Magnetic Resonance Spectroscopy Instrumentation. 

Nuclear magnetic resonance (NMR) spectroscopy can be used as a powerful noninvasive tool for clinical and other investigations of tissue biochemistry in vivo. There are many techniques for obtaining spectra from only a localized region of tissue, the simplest being to use a surface coil probe as both radio-frequency (RF) transmitter and receiver. This article reviews briefly surface coil spectroscopy, covering design, spectroscopic techniques, and clinical applications. 

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