Biomedical subjects

V T Mikhaltsevitch

Publications and source records attributed to V T Mikhaltsevitch.

6 recordsLinked to original sources

PubMed2005

A study of the spin-echo spin-locking effect in multi-pulse sequences in 14N nuclear quadrupole resonance.

Experimental evidence of observing a rather unusual spin-locking spin echo (SLSE) effect in the fields of two multi-pulse sequences (varphi(0))(x)-(tau-varphi(x)-2tau-varphi(x)-2tau-varphi(-x)-2tau-varphi(-x)-tau)(n) and (varphi(0))(x)-(tau-varphi(x)-2tau-varphi(y)-tau)(n) in (14)N nuclear quadrupole resonance is presented. It was demonstrated that the SLSE effect is observed only in the even pulse intervals of both sequences. All experiments were carried out at room temperature on a powder sample of NaNO2. A theoretical description of the effect is given.

Journal Article↗

PubMed2004

Spin-echoes in nitrogen-14 quadrupolar spin-system with axially symmetric electric field gradient tensor.

The behaviour of the magnetisation in the spin-1 system with the axial symmetry of the electric field gradient (EFG) tensor was analysed theoretically. The behaviour of the NQR signals in hexamethylenetetramine (C6H12N4) was also studied experimentally using the pulse NQR technique and sensitive equipment. It was shown that the axial symmetry of the EFG in a sample could not be the reason why spin-echo signals were not observed in conventional pulse experiments for the same type of sample. A very short spin-spin relaxation time T2 seems to be the reason of that. The signal-to-noise ratio was sufficient for measuring T2 in C6H12N4, which had not been reported earlier. Experimental results of applying certain pulse sequences to the 14N NQR in a sample are also presented.

Journal Article↗

PubMed2004

Study of quasistationary and stationary states in the short-repetition-time sequences in the NQR of nitrogen.

Experimental and theoretical study of quasistationary and stationary states that are established in the quadrupolar spin system subjected to the steady-state sequences which consist of a chain of identical pulses and can be preceded by a preparatory pulse. We have obtained theoretical expressions for the magnetisation of the spin system that take into account off-resonance conditions during the effect of the pulses. Frequency dependencies of the NQR signal in the quasistationary and stationary states are shown for C3H6N6O6 (RDX) and NaNO2, and compared with theoretical results.

Journal Article↗

PubMed2004

Modified steady-state free precession pulse sequences for the detection of pure nuclear quadrupole resonance.

Modifications of the steady-state free precession multi-pulse technique for the effective detection of the nuclear quadrupole resonance (NQR) signals are proposed. These modifications are based on the use of composite pulses and enable the suppression of the coherent noise signals such as the magneto-acoustic and piezo-electric signals or the ringing signal from the NQR probe. Experimental results of applying the proposed technique to nitrogen-14 NQR in the sample of C6H12N4 are also presented and convincingly demonstrate its effectiveness.

Journal Article↗

PubMed2004

Comparative experimental analysis of composite pulses in 14N NQR.

Experimental results of comparing composite pulses in nitrogen-14 NQR, that are analogous to common 90 degrees RF pulses in powder, are presented. All tested pulses have been taken from publications in journals. Comparative diagrams of the measurement results for induction signals and echo signals are presented. The results of the measurements demonstrate that the best outcomes are achieved when the composite pulse (45)0(95)180(164)0 is used.

Nitrogen Isotopes↗

PubMed2003

The transient processes in multi-pulse nitrogen-14 NQR.

It has been demonstrated that transient processes, observed in a single crystal of NaNO2 acted upon by pulse sequences MW-2 and MW-4 and their modifications with 180 degrees flip angle of the pulses (Solid State Nucl. Magn. Resonance 10 (1997) 63; Sov. Phys.-JETP 88(5) (1999) 1580), which manifest themselves in the oscillating form of the NQR signals envelope, can be explained in the frames of a two-particle model. It has been proved that the nature of echo signals in the effective field of multi-pulse sequences received by the inversion of the phase of the sequence pulses or by introducing an additional 180 degrees pulse is connected with re-focusing of accumulated digressions of the flip angle from the ideal 180 degrees pulse. Experimental results of observing single and multiple echoes in a number of powdered nitrogenated substances in the effective field of various sequences at room temperature have been presented.

Journal Article↗