A nuclear magnet resonance (NMR) system probes samples using a stochastically pulsed radio-frequency magnetic field. The NMR system uses active shims to compensate for spatial inhomogeneity in the bias magnetic field applied by a small permanent magnet. The active shim, made of a flexible conductor, creates a magnetic field when current is passed through it. The magnetic field created by the active shim can compensate for a first, second or third order spherical harmonic spatial inhomogeneity. The NMR system may have an array of active shims, with each active shim compensating for a spherical harmonic spatial inhomogeneity. The array of active shims may be arranged within the NMR system so as to increase power efficiency. The NMR system can accommodate a standard NMR sample tube and can be used to measure nuclear spin density or acquire an NMR spectrum.

A whole measurement process includes a plurality of step combinations. Each of the step combinations is composed of a solution-state measurement step and a solid-state measurement step. In the solution-state measurement step, solution-state NMR measurement is performed such that magnetization that is to be used in the solid-state measurement step remains. In the solid-state measurement step, solid-state NMR measurement is performed by using the magnetization that remains. No waiting time for recovering magnetization is provided between the solution-state measurement step and the solid-state measurement step. The solid-state measurement step may be performed earlier, and the solution-state measurement step may be performed later. Alternatively, the two steps may be performed simultaneously.

A nuclear magnet resonance (NMR) system probes samples using a stochastically pulsed radio-frequency magnetic field. The NMR system uses active shims to compensate for spatial inhomogeneity in the bias magnetic field applied by a small permanent magnet. The active shim, made of a flexible conductor, creates a magnetic field when current is passed through it. The magnetic field created by the active shim can compensate for a first, second or third order spherical harmonic spatial inhomogeneity. The NMR system may have an array of active shims, with each active shim compensating for a spherical harmonic spatial inhomogeneity. The array of active shims may be arranged within the NMR system so as to increase power efficiency. The NMR system can accommodate a standard NMR sample tube and can be used to measure nuclear spin density or acquire an NMR spectrum.

A protocol to determine chemical shift-specific Ti constants in inhomogeneous magnetic fields is provided. Based on intermolecular double-quantum coherences and spatial encoding techniques, the method can resolve overlapped NMR spectral peaks in inhomogeneous magnetic fields acquired using conventional methods. With inversion recovery involved, the amplitude of spectral peak will be modulated by inversion recovery time. After fitting the spectral peak amplitude variation curve, the corresponding longitudinal relaxation time can be achieved. With the measured T.sub.1 values in inhomogeneous magnetic fields, insights into chemical exchange rates, signal optimization, and data quantitation can be obtained.

Embodiments of a compact portable nuclear magnetic resonance (NMR) device are described which generally include a housing that provides a magnetic shield; an axisymmetric permanent magnet assembly in the housing and having a bore, a plurality of magnetic elements that together provide a well confined axisymmetric magnetization for generating a near-homogenous magnetic dipole field B.sub.0 directed along a longitudinal axis and providing a sample cavity for receiving a sample, and high magnetic permeability soft steel poles to improve field uniformity: a shimming assembly with coils disposed at the longitudinal axis for spatially correcting the near homogenous magnetic field B.sub.0; and a spectrometer having a control unit for measuring a metabolite in the sample by applying magnetic stimulus pulses to the sample, measuring free induction delay signals generated by an ensemble of hydrogen protons within the sample; and suppressing a water signal by using a dephasing gradient with frequency selective suppression.

Embodiments of a compact portable nuclear magnetic resonance (NMR) device are described which generally include a housing that provides a magnetic shield; an axisymmetric permanent magnet assembly in the housing and having a bore, a plurality of magnetic elements that together provide a well confined axisymmetric magnetization for generating a near-homogenous magnetic dipole field B.sub.0 directed along a longitudinal axis and providing a sample cavity for receiving a sample, and high magnetic permeability soft steel poles to improve field uniformity: a shimming assembly with coils disposed at the longitudinal axis for spatially correcting the near homogenous magnetic field B.sub.0; and a spectrometer having a control unit for measuring a metabolite in the sample by applying magnetic stimulus pulses to the sample, measuring free induction delay signals generated by an ensemble of hydrogen protons within the sample; and suppressing a water signal by using a dephasing gradient with frequency selective suppression.

Embodiments of a compact portable nuclear magnetic resonance (NMR) device are described which generally include a housing that provides a magnetic shield; an axisymmetric permanent magnet assembly in the housing and having a bore, a plurality of magnetic elements that together provide a well confined axisymmetric magnetization for generating a near-homogenous magnetic dipole field Bo directed along a longitudinal axis and providing a sample cavity for receiving a sample, and high magnetic permeability soft steel poles to improve field uniformity: a shimming assembly with coils disposed at the longitudinal axis for spatially correcting the near homogenous magnetic field Bo; and a spectrometer having a control unit for measuring a metabolite in the sample by applying magnetic stimulus pulses to the sample, measuring free induction delay signals generated by an ensemble of hydrogen protons within the sample; and suppressing a water signal by using a dephasing gradient with frequency selective suppression.

An imaging method may include obtaining imaging data associated with a region of interest (ROI) of an object. The imaging data may correspond to a plurality of time-series images of the ROI. The imaging method may also include determining, based on the imaging data, a data set including a spatial basis and one or more temporal bases. The spatial basis may include spatial information of the imaging data. The one or more temporal bases may include temporal information of the imaging data. The imaging method may also include storing, in a storage medium, the spatial basis and the one or more temporal bases.

Described here are systems and methods for volumetric excitation in magnetic resonance imaging (“MRI”) using frequency modulated radio frequency (“RF”) pulses. In general, quadratic phase modulation along the slice encoding direction is implemented for additional spatiotemporal encoding, which better distributes signal content in the slice direction and enables higher acceleration rates that are robust to slice-undersampling.

A method is presented for controlling a spin system in an external magnetic field. The method includes sending a first pulse to a resonator over a first period. The resonator generates a magnetic field in response to receiving the first pulse. Moreover, the resonator applies the magnetic field to the spin system and the first pulse maintains the magnetic field in a transient state during the first period. The method also includes sending a second pulse to the resonator over a second period immediately following the first period. The resonator alters a magnitude of the magnetic field to zero in response to receiving the second pulse. Other methods are presented for controlling a spin system in an external magnetic field, including systems for controlling a spin system in an external field.