Abstract: A method and apparatus for determining the propensity of fuel materials to leave deposits in compression ignition engines is disclosed. The apparatus consists of a closed chamber fitted with conduits to supply fuel composition, air, and other test fluids to its interior, and arranged to contain or substantially contain a substrate. Substrate is placed in the chamber to provide interaction between a fluid passing through and the substrate. Substrate may be a monolithic machined element or a collection of discrete bodies. The chamber conduits are connected to at least two metering devices, one controlling fuel and one air flow, whereby the substrate is exposed to measured quantities of fuel compositions and air. Heating devices are in thermal communication with the substrate and the source of air provided to the chamber, thus providing a method of controlling the temperature of the substrate and air flowing through the chamber.

Abstract: A technique for producing multiple spin echo signals following an initial excitation pulse is provided. A first inverting pulse is applied a given time interval following the initial excitation pulse, resulting in the formation of the usual first spin echo signal after passage of the given time interval. At a later point in time, a second inverting pulse is applied. The time interval between the initial excitation pulse and this second inverting pulse is not required to be harmonically related to the first given time interval. This results in the production of at least a second, later occurring spin echo signal which does not contain harmonically-related artifact components of the earlier pulses and spin echo signals.

Abstract: In a magnetic resonance imaging system, the same reference signal is used for both radio frequency transmission and phase sensitive detection. The use of the same reference signal for both transmission and reception prevents phase unlock between the two events. However, this technique results in variation in the demodulated, frequency encoded information, which is corrected by digitally filtering the received signal information as a function of the demodulation frequency used.

Abstract: In a magnetic resonance imaging system, a multiplexing technique is used to image volumetric regions by performing a number of scans within the recovery time of the spin systems. The multiple scans acquire signal information from sub-regional volumes by phase-encoding in the direction of the excitation gradient.

Abstract: The null point in the gradient field of an NMR imaging system is offset from its nominal position in the static magnetic field by application of a bias field to the gradient field. The bias field produces a substantially uniform offset in the field intensity at every point in the gradient field. Alternatively, null point offset may be achieved by controllably superimposing two gradient fields of separately located null points.

Abstract: The effects of motion in a given direction of particles being imaged in an NMR imaging system are substantially reduced by using gradients in the given direction produced by gradient pulse sequences which exhibit a zero value first moment relative to the point in time at which phase determination of the particles occurs. This point in time is generally taken at the time at which the longitudinal magnetization is translated to the transverse plane, as that is the phase reference for the NMR signals produced by the particles.

Abstract: The effects of particle motion or flow within a sample may be measured by applying a motion-encoding gradient to the sample, along with spatial encoding gradients. The motion-encoding gradient applies two gradient fields of respective opposite sense to the spins of the sample so as to encode motion as a net phase component resulting from the two fields. Two image data sequences, one with motion encoding and one without, may be compared to measure the effects of motion, or a plurality of image data sequences may be taken, each with a different value motion-encoding gradient. A Fourier transformation performed on the sequence data in the latter case with respect to the variation in the motion-encoding gradient pulses will yield a plurality of images, each representing the amount of material which exhibits a different velocity.

Abstract: Apparatus for imposing a gradient magnetic field intensity on a static magnetic field intensity in a nuclear-magnetic-resonance (NMR) system. The gradient field has a predetermined error relationship with respect to a desired characteristic of the gradient field within a selected region. The selected region is substantially smaller in volume than the volume "enclosed" by a surface or surfaces on which electrical conductors are distributed to generate the gradient field. The surface current densities in a grid-like pattern of differential areas on the surfaces are chosen such that, within the selected region, the predetermined error relationship results. The gradient field intensity outside of the selected region generally does not have the characteristic desired within the region. The predetermined error relationship can be established in a linearly-varying field intensity in a spherical volume enclosed by a cylindrical surface.