SU1485094A1 - Method for determining time of nuclear relaxation in radio spectrometers - Google Patents

Description

The invention relates to nuclear magnetic resonance (NMR). The purpose of the invention is to improve the accuracy and

The invention relates to the field of nuclear magnetic resonance (NMR), namely to NMR introscopy to measure local relaxation parameters, and can be used in medical diagnostics, as well as in science and technology when it is necessary to determine the relaxation parameters of various parts of the object under study. without destroying its integrity, namely physics, chemistry, biology.

The aim of the invention is to improve the accuracy and speed of the method.

. The drawing shows the dependence of the amplitude of the M ^ (C) NMR signal on the duration / s high hour2

reliability of the method. The method consists in that at the output of the device a constant component of the quasi-stationary NMR signal is extracted for each value of the durations' and RF pulses ranging from zero to the durations corresponding to 180-degree pulses, an additional polarizing field H _o is created at the sample location, which coincides in the direction of the main magnetic field Io, turn off the additional field H ¹ and allocate a constant coO

put the NMR signal, tending to its quasistationary value, and then determine the ratio of relaxation times T, / T ₄ by the slope of the tangent at the point {Г = 180 ° according to М (у) £, where Mu (€ ") is the amplitude of the NMR signal with a duration HF impulses ^. 1 ill.

total pulses, (HF), where C, is the abscissa of the intersection point of the tangent to Μ ^ ί'ο) with a duration £, ^, = 180 and a straight line drawn parallel to the abscissa axis through the point of the ordinate axis corresponding to the maximum of the NMR signal M ^ (C ) max.

The definition of relaxation times in the method is based on the fact that the amplitude of the constant component of a quasi-stationary NMR signal excited by a sequence of high-frequency pulses depends on both the ratio of relaxation times /, / Τ ^ and the duration of the exciting high-frequency pulses (T, is the spin-lattice relaxation time ; 511,. ,, 1485094 A1

3

1485094

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spin-spin relaxation time). Therefore, by measuring the amplitude of the constant component of the signal for different values of the duration of the high-frequency pulses, it is possible to avoid determining the absolute. values of such parameters as the equilibrium magnetization M _o , the average transverse projection of the magnetization M ^, and associate the desired value T, / T ^ directly with the magnitude of the voltage emitted by the constant component of the NMR signal.

In addition, from the relation of times T | and Td depends not only on the steady-state amplitude of the quasi-stationary NMR signal, but also on the time to establish the observed amplitude of the signal.

Example, In a test sample placed in an NMR-introscope sensor, a NMR signal is excited in the form of a stationary free procession (SSP) using a periodic (with period T) HF pulse sequence in which the filling phase of adjacent pulses differs by 180 °. If pulses with a duration of 'c are applied in the direction of the X axis of the rotating coordinate system and the condition T <gT _{2 is} met, then the magnitude of the NMR signal ζΐ ^ ζΐ ^- ) for RF pulses C, which is determined by the average transverse component of magnetization, can be determined by the formula

2М ₀ '51ПоС- 5ΪΠ β „

where M _o - determines the equilibrium magnetization}

o4 is the nutation angle of the magnetization vector for the duration of the pulse θ ',

[5 = 5ω ^Γ Γ, & ω is a detuning, i.e.

= ω- with ₀ .

Next, build an experimental graph of the dependence of the amplitude of the NMR signal on the pulse duration £ and at the transition point of the graph through

zero, which corresponds to 180-degree pulses, conduct a tangent to the resulting curve. The slope of the tangent is determined by the ratio T, / T ^ ,. therefore, it is possible to determine the ratio of relaxation times by the formula following from expression (1)

The advantage of the proposed method in comparison with the known is the possibility of pre-polarization with the inclusion of an additional magnetic field. This allows you to increase the signal-to-noise ratio, and therefore, to increase the sensitivity of the method, the accuracy and reliability of the information received.

Claims (1)

Claim The method for determining nuclear relaxation times in radio spectrometers, which consists in applying a main polarizing constant magnetic field to a sample, excites in the sample a periodic sequence of high-frequency pulses of quasi-stationary nuclear magnetic resonance (NMR) signals in the form of a free induction decay signal and spin echo signals, differing The fact that, in order to improve the accuracy and speed of the method, the constant component of the quasi-stationary NMR signal is isolated , / ί ") for each value of the durations of high-frequency pulses ranging from zero to durations corresponding to 180-n pulses, create at the location of the sample an additional polarizing constant magnetic field that coincides in direction with the main polarizing constant magnetic field, turn off the additional polarizing constant magnetic field, allocate a constant component of a quasi-stationary NMR signal, tending to its quasi-stationary value, and then determine the ratio of time spin-p sublattice relaxation to the spin-spin relaxation slope of the tangent at the point of the M * 's), for which the duration is equal to 180 pulses of high frequency. 1485094