Abstract: A method for providing a nuclear magnetic resonance (NMR) angiographic image substantially only of moving spins associated with fluid flow in a living organism sample having a cardiac cycle at a cardiac rate, and immersed in a main static magnetic field, commences by nutating the spins by a preselected amount .alpha. less than 90.degree., in the initial part of each of a pair of imaging sequences. The repetition time interval T.sub.R between sequential nutations occurs at a rate greater than the cardiac rate. After each nutation, a pair of alternating-polarity flow-encoding signal pulses are generated in a first magnetic field gradient impressed upon the sample, with each of the flow-encoding pulses in the first sequence of each pair having a polarity opposite to the polarity of the like-positioned flow-encoding pulse in the second sequence of each pair.

Abstract: Several sequences of radio-frequency and magnetic field gradients are presented for obtaining from a sample multiple response echo signals from which to obtain a plurality of independent angiograms, which can be combined or separately analyzed to provide more information than an individual angiogram, but in substantially the same amount of time as a single angiogram. For example, a series of angiograms, each with a different projection axis, can be obtained in the time required to obtain a single angiogram using a single echo method. If the view angle of each echo is the same, then the acquired angiograms can be added to enhance the signal-to-noise ratio. Anothe pulse sequence simultaneously obtains two or more angiograms, each sensitive to one of two orthogonal flow components of the overall blood flow, the angiograms are then added to give an angiogram which is sensitive to total flow in all directions. Multiple velocity ranges are accommodated in a fourth sequence form.

Abstract: Apparatus for shifting the phase of a phase-quadrature signal pair, in at least one of the transmitter and receiver of an NMR system, uses a circuit for shifting the phase of each of the pair of signals by a substantially similar amount responsive to a control signal, and a microcontroller for programmably establishing the control signal data to provide a desired phase shift. Typically, the control signal is of digital data nature and the phase shifter operates to shift signal phase through an angle equal to a selected multiple N of a basic angle. The basic angle is selected such that a plurality of equal angle increments are established by the resolving properties of the data signal. A plurality of phase shifters can be controlled by a single microcontroller.

Abstract: Magnetic field gradient and radio-frequency (RF) pulse signal sequences permitting moving nuclear spins to be selectively detected and then displayed as projected angiographic data in a nuclear magnetic resonance (NMR) image, without the use of contrast agents. The method allows the intensity of an image pixel to be determined by the macroscopic detected spin velocity and can provide essentially complete suppression of non-moving spins. Resulting images have high signal-intensity dynamic range for detected vessels. The selected detection of moving flows is not dependent upon pulsatile flow so that venous and arterial structures are equally as well visualized in high-resolution NMR angiographic images.

Abstract: A method for suppressing undesired NMR response signals from uncoupled resonances while obtaining desired NMR signals from a sample containing like nuclei which are coupled to one another, precedes each NMR response-signal-evoking excitation signal sequence with a pulse sequence having radio-frequency (RF) pulses providing a 90.degree. rotation of the spin magnetization about a first axis and then providing a 180.degree. degree rotation of the spin magnetization about a second axis, substantially orthogonal to the first axis, in the plane of magnetization rotation, prior to the alternating presence of a second 90.degree. RF pulse causing rotation about the first axis prior to the start of an associated imaging sequence. Time intervals T, of substantially alike duration related to the coupling constant J of the coupled nuclei, occur between each of the pulses; that one of the alternating sequences which is devoid of the second 90.degree.

Abstract: A method of suppressing at least one undesired resonance response signal while facilitating reception of at least one other desired NMR response signal from a coupled spin resonance in NMR spectroscopy, utilizes a pair of alternating sequences of RF signal pulses, with each sequence having an initial .pi./2 RF pulse, followed by a .pi. RF signal pulse having a temporal midpoint at a time interval T after the temporal midpoint of the initial pulse (where T=n/4J, with n being an odd integer and J being the spin coupling constant of the hydrogen nuclei) and a final .pi. RF signal pulse with a temporal midpoint at twice the time interval T after the temporal midpoint of the first .pi. RF signal pulse in that sequence. Only one of the pair of sequences is provided with a polarization transfer narrowband .pi. RF signal pulse symmetrically disposed about a temporal midpoint located at substantially a time interval T after the first .pi.

Abstract: Methods for generating non-single-quantum coherences and suppress single-quantum coherences, such as from water molecules, use a pulse subsequence, prior to a normal excitation/response signal sequence in Nuclear Magnetic Resonance imaging and/or spectroscopy, to constructively sum image signals exhibiting multiple quantum behavior, while subtracting pairs of response signals originating in noncoupled-spin systems. A variety of multistep phase-cycling programs for achieving zero-quantum and multiple-quantum filtering are disclosed.