Biomedical subjects

D J Pusiol

Publications and source records attributed to D J Pusiol.

8 recordsLinked to original sources

PubMed2006

Three-dimensional high-inductance birdcage coil for NQR applications.

A birdcage coil capable of operating simultaneously and independently in three orthogonal dimensions has been developed. A co-rotational end-ring mode producing an RF field in the longitudinal direction was utilized in addition to the two common transverse orthogonal modes. Two conductor turns were used for each of the coil's windows, increasing its inductance by a factor of four, thereby, making the coil suitable for low-frequency applications. Two or three-frequency detection can be easily carried out with this device. Orthogonality of the coil's channels allows arbitrarily close frequency positioning of each resonant mode, potentially useful in wide-line NQR studies, in which simultaneous excitation/detection of signals from three adjacent regions of a single wide line can be performed. The coil's performance was evaluated using a three-dimensional scheme, in which a circularly polarized experiment was combined with a linearly polarized measurement at another frequency, resulting in SNR improvement by 55%.

Equipment Design↗

PubMed2005

RF probe recovery time reduction with a novel active ringing suppression circuit.

A simple Q-damper device for active probe recovery time reduction is introduced along with a straightforward technique for the circuit's component value optimization. The device is inductively coupled to a probe through a coupling transformer positioned away from the main coil, which makes the design independent of the coil type being used. The Q-damper is a tuned circuit, which is resonant at the same frequency as the probe and can be actively interrupted. When the circuit is interrupted, it is detuned and, thereby, is uncoupled from the probe, which operates normally. Turning the device on leads to re-coupling of the circuits and causes splitting of the probe's resonance line, which can be observed through its drive port. A resistance of an appropriate value is introduced into the Q-damper circuit, resulting in smoothing of the resonance splitting into one broad line, representing the coupled system's low-Q state, in which the energy stored in the main coil is efficiently dissipated. The circuit's component values are optimized by monitoring the shape of this low-Q state. Probe recovery time reduction by, approximately, an order of magnitude has been obtained with this device. Application of the device during an NQR experiment led to an increase in the signal-to-noise ratio by a factor of 4.9.

Calibration↗

PubMed2004

Micellar anisometry in lyotropic uniaxial nematic phases studied by transversal NMR relaxation dispersion.

A new method, based on the measurement of the (23 )( )Na nuclei spin-spin NMR relaxation times ( T2 ), is proposed to investigate the shape of micelles in lyotropic nematic phases. We investigate the ternary lyotropic mixture of sodium dodecyl sulfate, 1-decanol, and water by using the NMR technique, measuring T2 in the two lyotropic uniaxial nematic phases. The characteristic relaxation time curves of each particular phase are analyzed by considering that they are constituted by a superposition of exponential decays with typical characteristic times: in a sense, a T2 spectroscopy. The analysis of the T2 dispersion profiles in both the uniaxial nematic calamitic and discotic phases indicates that our results can be interpreted in terms of the model of intrinsically biaxial micelles in all the nematic phases.

Journal Article↗

PubMed2002

Raman spectroscopy on surfacted ferrofluids in a magnetic field.

We investigated the effect of an external magnetic field up to 0.25 T on the Raman spectra of surfacted ferrofluids with various magnetic-particle concentrations. With increasing magnetic field the Raman spectra, which display the characteristic broad bands associated with vibrations of surfactant and water molecules, show a pronounced decrease in intensity in the range up to 50 mT. We interpret this behavior as due to an increase of the local particle concentration in the magnetic fluid. At larger fields a magnetic excitation with an intensity growing in proportion to the magnetization of the ferrofluid becomes apparent at around 4400 cm(-1). We consider both effects as evidence for the formation of a solid structure by the magnetic nanoparticles in the presence of a magnetic field.

Journal Article↗

PubMed2002

Slow molecular dynamics of water in a lyotropic complex fluid studied by deuterium conventional and spin-lattice relaxometry NMR.

A nuclear magnetic resonance study of protons and deuterons in the mesomorphic phases of the micellar lyotropic mixture potassium laurate/1-decanol/heavy water is reported. The slow dynamical behavior of water molecules has been investigated with deuterons spin-lattice relaxation dispersion in the Larmor frequency range 10(3)<nu(L)<4.2x10(7) Hz. In order to compare relative behaviors additional T1 dispersion of micellar protons has been measured in the same compound, temperature, and Larmor frequency range. From the experimental behaviors, we conclude that in the nematic phases the water slow reorientational dynamics is closely related to the slow reorientation of the micellar aggregates. In addition, conventional deuterium nuclear magnetic resonance at nu(L)=4.2x10(7) Hz spectra has been measured at different places in the phase diagram. The line shapes show a quadrupolar splitting in nematic phases, meanwhile in the isotropic phase the spectral structure collapses in a single line. This indicates that in the nematic phases the water reorientations are not enough to average the deuterons quadrupolar Hamiltonian. On the other hand, fast isotropic water reorientations reduce the quadrupolar interactions in the isotropic phase.

Journal Article↗

PubMed2001

Solid state proton imaging detected by quadrupole resonance.

A double resonance method for imaging of solid materials containing quadrupole nuclei via the coupled protons is reported. The technique uses a static field gradient to encode the position on the protons and the method of double resonance spin-echo to detect the occurrence of proton resonances by affecting the zero-field echo signal from the quadrupole system. The double resonance imaging method offers the advantages of higher spatial resolution and straightforward image reconstruction for powder samples compared with rotating-frame and Zeeman-perturbated nuclear quadrupole resonance encoding techniques.

Journal Article↗

PubMed2000

Experimental NMR spin-lattice relaxometry study in the liquid crystalline nematic phase of propylcyano-phenylcyclohexane.

The NMR spin-lattice proton relaxation dispersion T1(nu(L)) of the liquid crystal propylcyano-phenylcyclohexane is studied over several decades of Larmor frequencies and at different temperatures in the nematic mesophase. The results show that the order fluctuation of the local nematic director contribution to T1(nu(L)) undergoes a transition between two power regimes: from T1(nu(L)) protional to nu(1/2)L to nu(alpha)L (alpha approximately 1/3) on going from low to high Larmor frequencies.

Journal Article↗

PubMed1999

Pseudonematic order fluctuations of the director in the smectic phase of thermotropic liquid crystals.

The NMR spin-lattice proton relaxation dispersion in the smectic mesophase of two liquid crystals, 4cyano-4'-8-alkylbiphenyl and 4,4'-bis-heptyloxyazoxybenzene, are studied over several decades of Larmor frequencies. The results show that the order fluctuation of the local smectic director contribution to T1(nu(L)) undergoes a transition between two power regimes: from T1(nu(L)) proportional, variantnu(1)(L) to nu(1/2)(L) on going from low to high Larmor frequencies. We explain this behavior by assuming, in the smectic mesophases, short coherence length nematiclike cooperative molecular reorientations.

Journal Article↗