Abstract: According to the invention, a magnetic field gradiometer detector for detecting a material of interest positioned in a detecting region outside the detector includes a transmitter for generating an output signal at a selected frequency, a receiver for detecting the signal, a probe, and a switch coupling the receiver and transmitter with the probe that alternately connects and disconnects the receiver and transmitter to the probe, switching between transmitting and receiving. The probe includes tuning elements and a gradiometer coil array. The gradiometer coil array includes a first surface coil and a second surface coil wound in an opposite sense, the probe having a first side and an opposite second side, with the first and second surface coils configured asymmetrically such that the probe projects a magnetic field in the outside detecting region adjacent to the first side while being self-shielded on the second side.

Abstract: This invention involves an apparatus to measure the nuclear quadrupole (NQR) response of a specimen using three frequencies. Three-frequency NQR involves excitation of at least two transitions that causes an observed signal at a third transition frequency. Thus, the transition excited and detected is not irradiated at all. This reduces undesirable interfering signals due to the excitation, for example as a result of acoustic ringing and/or tank circuit ring-down, since the excitation is not applied at the frequency that is detected. This invention will be particularly useful to detect substances selected from the group consisting of explosives and narcotics using nitrogen NQR.

Abstract: This invention involves an apparatus to measure the nuclear quadrupole (NQR) response of a specimen using three frequencies. Three-frequency NQR involves excitation of at least two transitions that causes an observed signal at a third transition frequency. Thus, the transition excited and detected is not irradiated at all. This reduces undesirable interfering signals due to the excitation, for example as a result of acoustic ringing and/or tank circuit ring-down, since the excitation is not applied at the frequency that is detected. This invention will be particularly useful to detect substances selected from the group consisting of explosives and narcotics using nitrogen NQR.

Abstract: A nuclear quadrupole resonance (NQR) method and probe for generating RF magnetic fields in different directions to distinguish NQR from acoustic ringing induced in a sample. Generally, an RF magnetic field is generated along an axis towards a sample to induce a resonance signal in the sample. The resonance signal includes NQR and acoustic ringing. The resonance signal is detected along the RF magnetic field axis. The acoustic ringing is detected along a direction orthogonal to the RF magnetic field axis. As a result, the NQR in the resonance signal can be distinguished from the acoustic ringing in the resonance signal.

Abstract: A nuclear quadrupole resonance (NQR) method and probe for generating RF magnetic fields in different directions to distinguish NQR from acoustic ringing induced in a sample. Generally, an RF magnetic field is generated along an axis towards a sample to induce a resonance signal in the sample. The resonance signal includes NQR and acoustic ringing. The resonance signal is detected along the RF magnetic field axis. The acoustic ringing is detected along a direction orthogonal to the RF magnetic field axis. As a result, the NQR in the resonance signal can be distinguished from the acoustic ringing in the resonance signal.

Abstract: An apparatus which includes a probe for detecting a resonance signal induced in a sample. The probe and the resonance signal each have a respective, corresponding Q, and the ratio, Q′, of the Q of the probe to the Q of the resonance signal is relatively large. Preferably, Q′ is greater than, or equal to, 1.

Abstract: A method and apparatus for screening samples to determine which samples include a target material. Generally, the samples are pre-screened to determine which of the samples have a piezoelectric resonance when irradiated with an electric field, to thereby indicate the presence of the target material. The samples that have the piezoelectric resonance are then further screened by a different process to confirm the presence of the target material. For example, samples that have the piezoelectric resonance are further screened for a specific nuclear quadrupole resonance (NQR), a specific nuclear magnetic resonance (NMR) or a specific visual characteristic, to confirm the presence of the target material in the sample. The apparatus and method can be used, for example, to search luggage at ports of entry for the presence of cocaine hydrochloride or heroin hydrochloride.

Abstract: A Nuclear Quadrupole Resonance (NQR) method and apparatus for detecting the presence of a nitramine explosive, with a reduced probability of spurious triggering of consumer electronics. In the method and apparatus, a signal is emitted towards a nitramine explosive so that a nitro group in the namine explosive produces an NQR resonance signal. The NQR resonance signal is then detected to thereby detect the presence of the nitramine explosive. If the nitramine explosive is RDX, the NQR resonance signal of the nitro group is at a frequency which is either 502.3 kHz, 500.5 kHz, 405.1 kHz, 396.2 kHz or 384.1 kHz. Such frequencies are much lower than those in conventional detection techniques. As a result, the probability of the undesirable spurious triggering of electronic items exposed to the NQR RF pulses will be reduced, due to the reduction in induced voltage at lower frequency. The detection sensitivity is also reduced, but in many cases will still be adequate to detect nitramine explosives.

Abstract: A noise immune gradiometer split shield coil for use in magnetic resonance etection, such as in Nuclear Magnetic Resonance (NMR) and Nuclear Quadrupole Resonance (NQR). The coil is formed by a transmission line configured as a magnetic field gradiometer. The transmission line has a conductor which is electrically continuous through the coil, and a shield which is split at a position that causes the gradiometer to be electrically balanced. In this manner, the coil provides a high degree of internal shielding to reduce the effects of environmental noise pick-up. Such coils are also less sensitive to the effects of nearby conducting media.

Abstract: An apparatus using nuclear magnetic or quadrupole resonance to detect selected nuclei in a specimen (e.g., specimens containing a class of explosives or narcotics). The apparatus includes a pulsing unit to generate an RF pulse or a train of pseudo-random RF pulses used in stochastic NQR. Each of the pulses has an RF signal reaching a full amplitude within a quarter-cycle (substantially no pulse rise delay) and having a recovery delay of less than Q/.pi. cycles (substantially no recovery delay). The apparatus also includes a transmitter (e.g., a coil) to irradiate the specimen with a train of pseudo-random RF pulses and to detect after each pulse a resonance signal generated by the specimen in response to each corresponding pulse of the train of pseudo-random RF pulses. The pulsing unit has a capacitor connected to a DC power source by a first switch and connected to the coil by a second switch. When the first switch is closed, the DC power source charges the capacitor.

Abstract: One aspect of the present invention is a method for detecting a class of target species containing quadrupolar nuclei in a specimen by nuclear quadrupole resonance, comprising: (a) generating a random or pseudo-random train of rf pulses; (b) irradiating the specimen with the train of rf pulses; (c) detecting an NQR signal in response to irradiating the specimen; (d) cross-correlating the NQR signal with the random or pseudo-random train of rf pulses, thereby generating a free induction decay signal; and (e) converting the free induction decay signal into a frequency domain signal. Another aspect of the present invention is an apparatus for carrying out the method of the invention.

Abstract: Acoustic ringing and adverse effects from variations in the NQR detection of explosives and narcotics are minimized or eliminated. A specimen is irradiated with a modified steady state steady state free precession (SSFP) pulse sequence which combines a phase-alternated pulse sequence (PAPS) with a non-phase-alternated pulse sequence (NPAPS). The resulting signals from the PAPS and NPAS may then be coadded to cancel out the FID contributions to the signals. By canceling out the FID contributions to the signals, the effects of probe ringing and other extraneous responses, as well as the effect of temperature variation, are minimized or removed. The present method is especially effective in the detection of explosives and narcotics having .sup.14 N or .sup.35,37 Cl nuclei. A steady state free precession pulse which is especially useful with the method of the present invention is the strong off-resonance comb (SORC).

Abstract: The sensitive detection of explosives and narcotics by nuclear quadrupole resonance (NQR) is performed at low rf power by assuring that the rf field strength is larger than the local magnetic field. Additionally, it has been recognized that signal-to-noise ratio of a signal induced by a specimen of fixed size decreases by only the square root of the coil size. Thus, rather than scaling power linearly with coil size, as conventionally done to maintain the same rf field intensity, the power need only be increased by the square root of the increased coil size to assure maintenance of the same signal to noise ratio. This technique permits the use of larger coils than previously used. The invention is useful for both volume coils and surface coils.

Abstract: A method is provided for measuring the distribution of the extent of molear transport along two orthogonal directions, and further for measuring the anisotropy of molecular transport. For a sample which consists of compartments which contain mobile spins, such as round or cylindrical micelles, the distribution of compartment eccentricities can be calculated from this measurement. This method enables the anisotropy of molecular transport to be determined for a sample independently of any bulk orientation within the sample and thus the anisotropy of local geometries can be determined.

Abstract: An improved method and apparatus for nuclear magnetic resonance (NMR) imaging are provided by intercalating a magnetic field gradient in the form of short pulses into an NMR line-narrowing sequence. By inserting the short pulses into predetermined windows in the line-narrowing pulse sequence, the resolution of NMR images obtained thereby is increased and image artifacts from homogenous contributions to the natural linewidth are reduced. Furthermore, the short gradient pulses may be intercalated into known multiple pulse sequences or new multiple pulse sequences for specific imaging purposes which allows far more freedom in designing efficient and improved pulse cycles for NMR imaging.

Abstract: A system and method for detecting a class of explosives and narcotics containing nitrogen in a specimen by nuclear quadrupole resonance which improves the selectivity, sensitivity and spatial localization over conventional detection systems. As a result, sub-kilogram quantities of explosives and narcotics against a background of more benign materials may be detected by the nuclear quadrupole resonance system and method. Also, by the use of a meanderline surface coil, the electrical and magnetic fields will fall off rapidly over a short distance so that a localized region may be scanned and people may be scanned without depositing substantial RF power into the body. Furthermore, by using a strong off-resonance comb (SORC) irradiation sequence, the signal-to-noise ratio of the detected signal is improved for obtaining a more accurate detection signal from the specimen.

Abstract: A method and device of NMR spectroscopic analysis of liquids whereby magnzation of the spins of one nuclear species in spin-locked along a certain direction and the spin polarization of this species is transferred to a second species through the modulation of the amplitude and/or phase of rf fields applied to one or both species. The NMR signal can be detected directly from the second species.

Abstract: A method for obtaining a nuclear magnetic resonance image of a sample is performed by first placing the sample in a homogeneous static magnetic field excited with a homogeneous transmitter device. Spin magnetization in the sample is thus initially detected with an inhomogeneous receiver device such that an induced voltage in the receiver device depends on a spatial location of precessing nuclei in the sample. Then, a spatial coupling of the sample and the receiver device is varied and the spin magnetization in the sample is again detected with the inhomogeneous receiver device. The full spatial distribution of the spin density of the sample and hence an image of the sample is then determined with the spin magnetizations detected. Either the sample is moved relative to the receiver device, or the spatial coupling of the receiver device and the sample is electronically altered. Any spin interactions are eliminated by using coherent averaging techniques before the detecting steps.