Rf probe

Some applications are shown in the following sections, where the standard hardware, software and methods have been partially modified or connected to special experimental constructions. In the past, other applications have been performed by specific groups, who built their own dedicated rf probes and/or gradient systems. These originally specialized products have now found their way into the commercially available NMR microscopy products of today [18, 19]. 

Most of the commercially available NMR imaging probes have an accessible clear bore above and below the coil, which can be used for remote signal encoding. A detection-only probe can be inserted from the top into the bore of the magnet in such a way that the detection coil sits immediately above the imaging coil [Figure 2.6.5 (c)]. Similarly, an rf probe with a narrow body can be built that can be inserted into the... 

MHz (55Mn). For 1H MRI experiments, a 25-mm birdcage rf insert was used. For other nuclei, the broadband rf probe supplied with the instrument for high resolution NMR spectroscopy with a saddle-shaped rf coil (6-mm inside diameter) was used with the external aluminum shield removed. 

Fry RF Probing the world of cytochrome P450 enzymes. Mol Interv 2004 4 157-162. 

Roudaut et al. (1999a) used low-frequency pulsed-proton NMR and dielectric dynamic mechanical spectroscopies to study molecular mobility in glassy bread (<9%) as a function of temperature. Based on NMR results, they reported that some (if not all) of the water molecules were much more mobile than the polymer matrix whose relaxation time could not be measured within the 20-p,s dead time of the RF probe. 

Since investigators continuously strive to extract increasing amounts of data from shrinking sample sizes, much commercial and academic research on NMR hardware focuses on optimizing RF probe sensitivity to allow the analysis of trace materials. Significant advances have been achieved through several distinct modifications of instrumentation. This present chapter provides a review of the characterization of nanoliter volumes via static NMR spectroscopy and emphasizes some of the more relevant developments in probe technology that have enabled such measurements. 

In order to carry out complete structural elucidation of unknown compounds (especially for complex molecules), the RF probe should enable a variety of heteronuclear NMR techniques to be performed. In particular, inverse detection H-15N and 1H-13C experiments such as heteronuclear multiple quantum coherence (HMQC) [29,30] and heteronuclear single quantum coherence (HSQC) [31] find almost ubiquitous application in myriad research environments. Although the microliter-scale probes described above feature both heteronuclear and homonuclear capabilities, no commerical product is... 

As techniques for chemical analysis are used in continually smaller domains, experimental challenges for inherently insensitive methods such as NMR spectroscopy become increasingly severe. Among the various schemes to boost the intrinsic sensitivity of an NMR experiment, the development of small-volume RF probes has experienced a renaissance during the past decade. Commercial NMR probes now allow analyses of nanomole quantities in microliter volumes from natural product extracts and combinatorial chemical syntheses. Figure 7.3.1.9 illustrates the range of volumes that can be examined by NMR probes and accessories such as microsample tubes and inserts. With recently reported advances in sample preconcentration for microcoil NMR analysis [51], dilute microliter-volume samples can now be concentrated into nanoliter-volume... 

RF probes operate by applying a constant voltage to a metallic rod and monitoring the current, which is proportional to the admittance or capacitance (if conductivity is absent). The current then flows to a second electrode, such as the tank wall. The difference between conductance and RF probes is that the conductance types use DC or low-frequency AC, whereas the latter... 

The reaction mechanism of the photoinduced interaction between Et3SnCH2CH=CH2 (11) and CChBr was also studied by means of another physical method — the so-called radio frequency (RF) probing technique49. To facilitate the interpretation of CIDNP data and to identify the primary reaction stage which does not involve radical pairs, it is convenient to start from the RF probing technique. 

The radio frequency (RF) probing technique — general background... 

The groundwork for the RF probing technique was laid back in the 1960s when Fors6n and Hoffman50 proposed using the method of RF saturation to study the kinetics of fast... 

C. The recording time also should not exceed the relaxation time of the diamagnetic molecule, otherwise one will observe only equilibrium NMR signals t T C. All the above possibilities and restrictions of the RF probing technique allow us to use this method to investigate the photoreactions of allylic derivatives of tin and germanium. 

A big advantage of laser ablation over radiofrequency (RF) ablation is that it can be combined with MR because (laser) light is used instead of RF. To generate an MR image an RF pulse is used. If there is any RF source in the MR room there is always interference between the radiofrequencies from the RF generator and the radiofrequencies from the MR scanner. The result is that the MR image is completely destroyed. Even with an MR-compatible RF probe it is necessary to disconnect the probes for every MR scan and this is quite uncomfortable. 

Another advantage of the laser is that multiple laser applicators can be used in completely different parts of the liver simultaneously, because the different laser applicators do not interact. Multiple RF probes would interact. Therefore, two or three... 

Fig. 4.1a-e. A 46-year-old male patient with multiple tumors of the right kidney after left-sided nephrectomy 2 years before. Multiplanar reformat (MPR) depicts two small tumors in the right kidney (a). For RF ablation the RF probe was inserted via a dorsal approach. Repositioning was needed to reach the different tumors and to ensure complete ablation (b,c). Post-interventional MPR (d) as well as axial multislice spiral CT (MSCT) image (e) show the typical wedge-shaped areas of necrosis... 

Fig. 4.2a-e. A 73-year-old male patient with renal cell carcinoma, diabetes mellitus and cardiovascular comorbidity. Multiplanar reformat (MPR) in the coronal plane from a pre-interventional multislice spiral CT depicts an eccentric 3.6-cm tumor of the right kidney (arrows) (a). The patient was considered to be at high risk for surgery. Because of the size of the hypervascularized tumor, a tumor embolization was performed prior to RF ablation (b,c). An umbrellashaped RF probe was introduced percutaneously via a lateral approach (d). Four months after RFA the axial CT image shows no contrast enhancement in the tumor area (arrows), corresponding to complete tumor necrosis (e). A sufficient safety margin without contrast enhancement is visible... 

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