Abstract: A method to model the NMR signal and/or noise functions as stochastic processes. Locally relevant statistics for the signal and/or noise processes are derived directly from the set of individual coil images, in the form of array correlation matrices, by averaging individual coil image cross-products over two or more pixel locations. An optimal complex weight vector is computed on the basis of the estimated signal and noise correlation statistics. The weight vector is applied to coherently combine the individual coil images at a single pixel location, at multiple pixel locations, or over the entire image field of view (FOV).

Abstract: A Fourier transformation in a measured data matrix (MD) with the discrete measured data (x.sub.j,k) is implemented for all k=0 . . . N-1, respectively in the following steps, whereby it is defined: w=e.sup.-2i.pi./Na) The measured signals (x.sub.j,k) are acquired with an rf-phase modulation of the nuclear magnetic resonance signals according to a chirp function w.sup.j.spsp.2.sup./2,b) The arising data are convoluted with a second chirp (w.sup.-(j-k).spsp.2.sup./2) and entered into an auxiliary data matrix (HD),c) The image data matrix is acquired from the auxiliary data matrix (HD) by Fourier transformation in at least one further direction.

Abstract: An apparatus and method for obtaining samples of pristine formation or formation fluid, using a work string designed for performing other downhole work such as drilling, workover operations, or re-entry operations. An extendable element extends against the formation wall to obtain the pristine formation or fluid sample. While the test tool is in a standby condition, the extendable element is withdrawn within the work string, protected by other structure from damage during operation of the work string. The test apparatus is mounted on a sliding, non-rotating, sleeve on the work string.

Abstract: Eddy current compensation for magnetic field transients arising from electric current transients is obtained by digital computation of the time dependence of the eddy current magnetic effect, reversing the sense thereof to obtain a corrective signal portion, converting both the corrective portion and the basic signal profile to analogue form, summing same and directing the pre-compensated electric current through an inductive element.

Abstract: A head mounted tracker is placed in the operator area near the operator. The tracker has the capability to map the operator area without manual assistance. These operations are performed by processing low and high frequency components, based on the frequency of an alternating current generating the magnetic field, of the magnetic field in the operator area.

Abstract: A method of correcting for magnetic field inhomogeneity caused by various factors, such as implanted metal and air/tissue interfaces, in magnetic resonance imaging (MRI) is provided. Geometric distortion due to inhomogeneity in a static magnetic field B.sub.0 is corrected for by addition of a compensation gradient. The compensation gradient is applied in the slice selection direction Z, has a timing substantially identical to the standard frequency encoding gradient G.sub.x, and has an amplitude identical to the slice selection gradient G.sub.z that is applied during the initial RF excitation. Inhomogeneity in an RF field B.sub.1 is compensated for by utilizing an RF coil that is large enough in size as compared with a metal implant to make the volumetric percentage of the metal in the coil insignificant. Inhomogeneity in a gradient field G=(G.sub.x, G.sub.y, G.sub.z) is corrected for by a treatment of the most significant error factor G.sub.z that causes slice thickness error.

Abstract: The invention relates to a method of obtaining phase information in magnetic resonance imaging (MRI) and employing this information to produce an enhanced image. In the past, magnetic resonance imagers have obtained data which contains phase as well as magnitude information. Often the phase information has been discarded in order to avoid image artifacts, which are usually attributable to motion. The present invention employs a technique in which this phase information is used in order to improve image quality, in an analogous method to that used in optical microscopy.

Abstract: A workstation computer system, and its associated method and program storage device, stores a novel software package known as "Variance Cube". The computer system is responsive to a plurality of seismic signals propagating through a cubic volume of an earth formation for generating a cube, representing said cubic volume of earth, where the cube includes a plurality of seismic data samples and where each seismic data sample has a corresponding "variance value" assigned thereto. The computer system also generates one or more maps, such as a time slice map, representing one or more slices through the cube. Each map displays and is used to determine certain geologic features which exist along the corresponding slice through the cube, each map including a plurality of the variance values representing the geologic features, each such variance value being defined as the degree to which an amplitude of each seismic data sample in the cube at a particular reflection time "t" varies about an average amplitude.

Abstract: A method for planning continuity logging surveys and for detecting the presence of a continuous or discontinuous low-velocity inclusion in a subterranean geological formation. To detect the presence of a continuous or discontinuous low-velocity inclusion, a seismic source is inserted into a source borehole located at either a boundary or a center of a low velocity inclusion. Seismic energy is generated coupled to the low-velocity inclusion using the seismic source. The seismic energy propagates as seismic waves through the low-velocity inclusion and is measured and recorded by at least one detector disposed in a receiver borehole. The seismic waves are analyzed for the presence of at least one seismic signature from which the distance of a discontinuity, if any, of the low-velocity inclusion with respect to the receiver borehole can be determined.

Abstract: The present invention is directed to a balance correcting method for scanning optical apparatus for deflection-scanning a light beam in such an arrangement that a drive motor is of an inner rotor type in which a rotary body having a drive magnet is disposed inside a stator and a rotary polygon mirror is mounted on the rotary body so as to enable deflection scanning of the light beam, wherein a mechanical part having the rotary body is arranged as separable from an electric circuit part having the stator, the mechanical part having the rotary body is separated from the electric circuit part upon balance correction, only the mechanical part is then mounted on a balance corrector, the mechanical part is rotated by a stator as a rotating device preliminarily provided in the balance corrector, and an amount of unbalance is measured and adjusted.

Abstract: An MRI system acquires NMR signals at a fixed sample rate. The acquired NMR signals are decimated to produce an output NMR signal at a prescribed sample rate. The acquired NMR signal is converted to a two-dimensional array and then transformed to the frequency domain by performing a DFT along one dimension of the array and a FFT along the other dimension. The resulting frequency domain data is filtered to the prescribed bandwidth and Fourier transformed back to the time domain.

Abstract: In order to provide a magnetic resonance imaging method and apparatus which avoids artifacts due to the motion of a subject when the imaging is conducted with the interval between time phases reduced, a two-dimensional Fourier space is divided into a plurality of regions A,A'-D,D' symmetrically with respect to the frequency axis kx, and data acquisitions for the peripheral regions B and B', C and C', and D and D' are sequentially conducted with the data acquisition for the central regions A and A' interposed each time. At this time, the data acquisition is conducted alternately for each TR in a pair of symmetric regions, thereby minimizing the time difference between symmetric data.

Abstract: The analysis or evaluation circuit for analyzing an alternating voltage or current signal that includes a D.C. voltage or D.C. current component includes a window comparator having a circuit portion for comparing the alternating voltage or current signal to an upper threshold and a lower threshold and another circuit portion for adjusting the upper and lower threshold when one of the upper and the lower thresholds is reached by the alternating voltage or current signal. By means of a VCL output signal that switches when a threshold adjustment occurs, a frequency dependent signal may be produced that can be analyzed to obtain a rotational speed of a rotational body from which the input alternating voltage or current is derived.

Abstract: A method and apparatus for determining gas corrected porosity using nuclear magnetic resonance (NMR) and density measurements is disclosed. The total porosity (TCMR) or an earth formation is determined using an NMR tool. A log output is generated that indicates the density of the formation. The density porosity of the formation is determined from the log output. The difference between the TCMR-density porosity log accurately indicates the presence of gas. A gas corrected porosity, .phi., and gas saturation, S.sub.g, are determined based upon the density porosity and TCMR.

Abstract: A magnetic resonance apparatus wherein an excitation pulse and refocusing pulse are applied to the spins of 1.sub.H and a return pulse is applied at an echo time. A plurality of inversion pulses having different frequency bands from each other are applied, at an interval between the excitation pulse to the spins of 1.sub.H and the return pulse, to the spins of 13.sub.C spin-spin coupled to 1.sub.H. By doing so, a polarization transfer occurs from the spins of the 1.sub.H to the spines of the 13.sub.C. And an excitation pulse is applied to the spins of the 13.sub.C simultaneously with or after the return pulse to the spins of the 1.sub.H. By doing so, magnetic resonance signal of the 13.sub.C is enhanced through the polarization transfer. There are sometimes the cases where, through the returning of the polarization from the 13.sub.C to the 1.sub.H, it is possible to receive the information on the spins of 13.sub.C from the spins of the 1.sub.H.

Abstract: In order to perform an ECG-gating imaging MR scan with an exact ECG-gating time predetermined, in an MRI system and MR imaging method, an ECG signal of a patient is acquired. A preparing MR scan with a region containing an object to be imaged of the patient starts at each of a plurality of time instants when a plurality of different delay times elapse respectively from a plurality of reference waves included and repeated in series in the signal, thus a plurality of preparing images being produced. An appropriate or optimum ECG-gating time instant is determined using the plurality of preparing images. The imaging MR scan with the region of the patient is then performed in synchronization with the appropriate or optimum ECG-gating time instant. For example, both of the preparing MR scan and the imaging MR scan are based on the same type of pulse sequences. The pulse sequences include a fast SE sequence, a sequence rooted in the fast SE sequence, or a segmented fast FE sequence.

Abstract: A pair of gradient field pulses of the same applied time and the same intensity are applied before and after a radio-frequency (RF) refocusing pulse (180.degree. pulse) as additional gradient field pulses to enhance the phase shift of a transverse magnetization spin, caused by the diffusion of a molecule including a target nuclide. To compensate for image deterioration caused by an unnecessary field distribution which is produced by the additional gradient field pulses, a compensation gradient field pulse dGcp and a compensation offset gradient field dGoffset are applied and a center frequency at the time of receiving and detecting an echo signal is shifted by df.sub.0.

Abstract: A rotational speed-detecting device of the present invention drives a sensor means 11, which includes a detecting unit that connects magneto-electric elements in series. A comparison voltage generator connects comparison voltage resistors in series, and is connected in parallel with the detecting unit, with a constant voltage by a constant-voltage control means 13, to which constant voltage is supplied by a constant-voltage generating means 14. The constant voltage means 14 controls a constant current of the constant-current means 15 with an on-and-off output from a comparison means 12 so as to superpose and flow a rectangular wave current in a power supply line between Vcc and VR.

Abstract: A permeability estimator is constructed from the lambda parameter, .LAMBDA., which is the size of dynamically connected pores. For simple pore geometries at high permeabilities, .LAMBDA. should theoretically be proportional to the pore volume-to-surface area ratio. Further, at high permeabilities, the permeability is proportional to .LAMBDA..sup.2 /F where F is the formation factor. Core data are used to establish the proportionality constant. At permeabilities less than about 100 md, the estimated permeability is seen to overestimate the actual permeability by a factor related to the estimate. Thus, a corrected second estimate can be readily made and is shown to match measured permeabilities on a diverse set of sands and shaly sands with a correlation coefficient of 0.89 for log k. The estimate can also be made using NMR relaxation time data with a correlation coefficient of 0.92 for the same data set.

Abstract: Technique and apparatus are disclosed for identifying characteristics of hydrocarbons, such as distinguishing light and heavy formation oil, in formations surrounding an earth borehole. The technique and apparatus can also be used for determining residual oil saturation, permeability, and bound water volume. An embodiment of the method of the invention includes the following steps: providing a nuclear magnetic resonance logging device that is moveable through the borehole; providing, from the logging device, a polarizing magnetic field and cycles of a magnetic pulse sequence, and receiving magnetic resonance spin echoes from the formations; processing the received spin echoes to produce a T.sub.2 distribution; computing a magnetic resonance porosity from the T.sub.2 distribution; deriving a measure of total porosity of the formations; and comparing the magnetic resonance porosity with the total porosity.