Double-tuned Probe Research Articles

Design and testing of a 1.5 Tesla double-tuned ( 1H/ 31P) RF surface coil with intrinsic geometric isolation

We analyse the isolation characteristics of axial and transverse field surface radio frequency coils, used to design a double-tuned surface coil composed by two coils, that combine proton ( 1H) detection and localized spectra of phosphorous ( 31P). Several geometrical configurations were analysed, including circular loop and figure-of-eight coils, with the aim to optimize the isolation between the two channels. Our analysis shows that by using at least one transverse coil for the design of the double-tuned probe, it is possible to achieve a good intrinsic geometrical decoupling, without the need of additional decoupling circuits. On the basis of the experimental results, we have designed and built a 1.5 T double-tuned probe composed by a circular loop coil and a transverse field coil, with the external coil tuned at the 1H frequency and the internal coil tuned at the 31P frequency, that shows a good intrinsic decoupling and signal-to-noise ratio.

Single-input double-tuned circuit for double resonance nuclear magnetic resonance experiments

A single-input double-tuned probe was designed for double resonance nuclear magnetic resonance (NMR) experiments, in which high radio frequency power irradiations were achieved at two closely spaced frequencies (such as 26.1 MHz for Al27 and 28.4 MHz for Cu65). The efficiency of the probe for both nuclei was determined to be about 80%, compared to that obtained with a single-tuned probe. The probe was used successfully for Al–6527Cu SEDOR experiments to derive the internuclear distance between Al and Cu in Cu-ZSM-5 zeolite. The circuit is ideal for SEDOR-type double resonance NMR experiments, when high power irradiation is required for nuclei with closely spaced resonance frequencies.

A new goniometer design for single-crystal nuclear magnetic resonance spectroscopy

A new goniometer for single-crystal nuclear magnetic resonance (NMR) spectroscopy has been constructed and built into a multinuclear X–1H double-tuned probe for cross-polarization and/or 1H decoupling. Improvements in the ease of mounting/remounting the crystal on the three rotational axes and in the accuracy of the stepwise rotation about these axes have been achieved compared to the usual cube goniometer. A similar improvement is achieved for the determination of the orientation of the crystal relative to the goniometer frame. The NMR goniometer has three dovetail mortises that enable rotation of the crystal about three orthogonal axes, all perpendicular to the magnetic field. The crystal is glued onto a tenon that fits precisely into the dovetails of the NMR goniometer and also into a slightly modified x-ray diffraction goniometer, thereby allowing a high-accuracy determination of the orientation for the tensorial NMR interactions with respect to the crystal frame. The performance of the goniometer is illustrated by single-crystal 23Na NMR spectra of NaNO3.

Single-input double-tuned mutually coupled surface coil circuits: An analysis

The input reactance of a pair of coupled coils is a function of the latter’s primary, secondary, and mutual inductances as well as the secondary tuned frequency. It is thus possible to synthesize two appropriate equivalent inductances for use in a double-tuned probe by a judicious choice of these parameters. From a given coil configuration and hence the associated self and mutual inductances, the present note analyzes and derives the essential equations showing the possible values of the tuned secondary frequency to be used to design this type of probe circuit first proposed by Fitzsimmons, Brooker, and Beck [Magn. Resoh. Med. 10, 302 (1989)]. In cases where an intercoil coupling capacitor is needed, its value also can be calculated from a biquadratic equation. A numerical example is given to check the validity of the theoretical results.

Efficiency estimation for single-coil, separate-input, double-tuned NMR probes

The signal-to-noise ratio for the NMR observation of a nucleus using a double-tuned probe depends on the power efficiency of the observe channel. In a similar manner, the minimum decoupling power is a function of the efficiency of the proton channel. Efficiencies are often determined in several steps, which involve measuring electrical characteristics of disassembled probe elements. In this work, we show how efficiencies can be simply computed from measurements of the quality factors of each port, at its resonant frequency. Thus, an index of the probe performance, especially its signal-to-noise ratio, is readily available for the complete, loaded device.

Toxicity of dysprosium shift reagents in the isolated perfused rat kidney.

Sodium and water spectra were acquired from the isolated perfused rat kidney by using a double-tuned probe designed to have high X nucleus sensitivity and low 1H sensitivity. Both DyTTHA and DyPPP were used to distinguish intra and extracellular 23Na resonances before and after the onset of hypoxia. Only DyPPP was useful in separating the two compartments, with a maximal chemical shift difference produced at a concentration of 4.5 mM. Both shift reagents were nephrotoxic at concentrations under 5 mM and produced an immediate decrease in renal-concentrating capacity and increases in fractional sodium and potassium excretion and increased renal vascular resistance. These disturbances of renal physiological parameters were accompanied by progressive broadening of the renal H2O resonance. 1H NMR may be a subtle means of monitoring nephrotoxicity.

A balanced-matched double-tuned probe for in vivo1H and 3 31P NMR

A balanced-matched double-tuned probe for in vivo1H and 3 31P NMR

4443761 NMR spectroscopy

We analyse the isolation characteristics of axial and transverse field surface radio frequency coils, used to design a double-tuned surface coil composed by two coils, that combine proton (1H) detection and localized spectra of phosphorous (31P). Several geometrical configurations were analysed, including circular loop and figure-of-eight coils, with the aim to optimize the isolation between the two channels. Our analysis shows that by using at least one transverse coil for the design of the double-tuned probe, it is possible to achieve a good intrinsic geometrical decoupling, without the need of additional decoupling circuits. On the basis of the experimental results, we have designed and built a 1.5 T double-tuned probe composed by a circular loop coil and a transverse field coil, with the external coil tuned at the 1H frequency and the internal coil tuned at the 31P frequency, that shows a good intrinsic decoupling and signal-to-noise ratio.

39K, 23Na, and 31P NMR studies of ion transport in Saccharomyces cerevisiae.

The relationship between efflux and influx of K+, Na+, and intracellular pH (pHin) in yeast cells upon energizing by oxygenation was studied by using the noninvasive technique of 39K, 23Na, and 31P NMR spectroscopy. By introducing an anionic paramagnetic shift reagent, Dy3+(P3O5(-10))2, into the medium, NMR signals of intra- and extracellular K+ and Na+ could be resolved, enabling us to study ion transport processes by NMR. Measurements showed that 40% of the intracellular K+ and Na+ in yeast cells contributed to the NMR intensities. By applying this correction factor, the intracellular ion concentrations were determined to be 130-170 mM K+ and 2.5 mM Na+ for fresh yeast cells. With the aid of a home-built solenoidal coil probe for 39K and a double-tuned probe for 23Na and 31P, we could follow time courses of K+ and Na+ transport and of pHin with a time resolution of 1 min. It was shown that H+ extrusion is correlated with K+ uptake and not with Na+ uptake upon energizing yeast cells by oxygenation. When the cells were deenergized after the aerobic period, K+ efflux, H+ influx, and Na+ influx were calculated to be 1.6, 1.5, and 0.15 mumol/min per ml of cell water, respectively. Therefore, under the present conditions, K+ efflux is balanced by exchange for H+ with an approximate stoichiometry of 1:1.

A multinuclear double-tuned probe for applications with solids or liquids utilizing lumped tuning elements

A high-efficiency multinuclear double-tuned probe using lumped-element construction is compared and contrasted with a transmission line probe. A rationale for improved efficiency at the high frequency and a commensurate improvement in the signal-to-noise ratio is developed. Powder spectra obtained at 44.4 MHz with the lumped-element probe are shown and pertinent construction details are given.

Versatile heteronuclear-decoupler for use with a Varian HA-100 spectrometer

Specific details are given for double-tuning the Varian V-4333 probe for use in the following heteronuclear magnetic double resonance experiments: observe 1H at 100 MHz; irradiate 2H, 19F, or 31P; observe 19F at 94 MHz; irradiate 1H, 2H, or 31P. An inexpensive source of audiofrequency-noise is described which, in conjunction with the double-tuned probe and several commercially available components, constitutes the basis of a versatile heteronuclear-decoupler. Examples are given which illustrate the effectiveness of this decoupler. Double-tuning of the Varian V-4333 probe by introducing a second transmitter coil is also described.