Method and apparatus for detecting substance using nuclear resonance

Abstract

A method and apparatus for detecting a prescribed substance in a specimen, using nuclear quadrupole resonance or nuclear magnetic resonance. The nuclei of the specimen are irradiated with a modified steady state free precession RF pulse sequence comprising a plurality of pulses. The pulse sequence includes pairs of pulses offset from each other by a prescribed phase shift to produce a plurality of nuclear resonance echo signals from the prescribed substance, if present. The pulse sequence is constructed with pairs of pulses where phases of adjacent pulse pairs are offset by 90 DEG of the type: [tau / 2-(theta-Deltatau-theta)0 DEG -tau-(theta-Deltatau-theta)90 DEG -tau / 2]n, and where the transmit frequency has an offset relative to the resonant frequency of an irradiated nuclei of the prescribed substance. The echo signals are analyzed using Fourier transform and filtering techniques to register only those echo signals that are near the resonance frequencies of irradiated nuclei of the prescribed substance being detected. The registered echo signals are then compared with set reference values corresponding to the prescribed substance to determine whether the prescribed substance is present or not in the specimen. This type of detection method is not affected by temperature variations or other factors that create intensity anomalies. The pulse sequence creates additional echo signals, which increases the intensity of the observed signal and thus the signal to noise ratio. It also attenuates the effect of magneto-acoustic ringing.

Description

field of invention [0001] This invention relates to the practical use of nuclear resonance in material discrimination, and in particular the use of nuclear quadrupole resonance (NQR) and nuclear magnetic resonance (NMR) in the detection of, among other things, explosives and narcotics. [0002] In this specification, unless the context requires otherwise, the word "comprise" and its variations such as "comprises" and "comprising" will be understood to mean the inclusion of a stated integer or group of integers but also the exclusion of other integers. or an array of integers. Background technique [0003] By Carr in "steady-state free precession in nuclear magnetic resonance, Physical Review (steady-state free precession in nuclear magnetic resonance, physical review), vol.112, NO.5, 1958, p. 1693-1701" in the article As described, a given substance with a so-called "steady-state free precession (SSFP)" multi-pulse sequence generates a series of...

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Problems solved by technology

Assuming that the above phase correlation is not satisfied at Δf τ≠m, the signal will be further reduced because the proposed accumulation scheme is no longer optimal

[0032] In the application of NMR to detect matter, the intensity varies with drift and changes in the static magnetic field. This is also a problem. None of the pulse sequences mentioned above can overcome this problem.

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