Abstract: This invention relates to refrigerated superconducting MR magnets having integrated cryogenic gradient coils. In particular, the amount of eddy currents produced by the magnet are substantially reduced while reducing the size and weight, and, therefore, the cost of the superconducting magnet required to produce an acceptable MR image.

Abstract: In a magnet system with two coil systems of different mean diameter arranged coaxially with respect to the longitudinal axis of the system defined by the direction of the field in the homogeneity region, which are rotationally symmetrical and are arranged symmetrically about the transverse median plane of the system perpendicular to the longitudinal axis and can carry exciting currents which result in overlapping magnetic fields that compensate, at least approximately, for the dipole fields of the two coil systems, an operating mode selector switch device (22) configured as a superconducting network is provided, by means of which the magnet system (10) can also be switched, as an alternative to the operating mode which provides considerable dipole-field compensation in the outer space of the magnet system (10), to that operating mode in which the magnetic fields generated by the two coil systems (11 and 12) at the center thereof are aligned in the same direction. In a special configuration, the ratio B.sub.

Abstract: In a magnetic resonance apparatus, a coil system is added to a gradient coil system, as a result of which a measuring field range is adapted to the geometry of an object to be examined. For example, by addition of a Bo coil system to be activated simultaneously with the z-gradient system, an asymmetry is realized in the z-gradient field, as a result of which return of disturbing resonance signals from an object part located outside the gradient field operating range is avoided. Further, by addition of additional arc conductors, the z-gradient linearity range is displaced in the z-direction.

Abstract: A magnetic field generating apparatus for a magnetic resonance imaging (MRI) apparatus, including soft ferrite disposed adjacently to a gradient magnetic field coil which is disposed in a gap and serves to form a static magnetic field. The soft ferrite has saturated magnetic flux density (Rs) more than 0.4 T, coersive force (He) less than 50 A/m, and specific resistance .rho. more than 10.sup.-5 .OMEGA..multidot.cm. The magnetic field generating apparatus thus constructed has a magnetic circuit arrangement that a pair of permanent magnetic bodies which are disposed so as to confront each other and define the gap are magnetically connected through a yoke, and pole pieces are fixedly secured to the surfaces of the respective permanent magnetic bodies facing the gap, thereby generating the magnetic field in the gap.

Abstract: A pair of serially-connected coils detect noise variations in an MRI background magnetic field. Although the coils are closely coupled to the primary background magnetic field generator of the MRI system, they are disposed so as to be substantially de-coupled from rapidly changing MRI gradient magnetic fields. The noise detecting loops drive a negative feedback loop including a low pass filter, amplifier and controlled current source driving a large correcting loop. The device attenuates background magnetic field noise during MRI data acquisition over a frequency band extending from a few millihertz to more than 100 Hz. It is preferably used with existing field stabilization software that otherwise compensates for fluctuations in an overlapping frequency band which starts at d.c. Thus, when used together, background magnetic field noise may be attenuated (or compensated for in subsequent MRI data processing) over a frequency band that extends from d.c. to more than 100 Hz.

Abstract: A magnet system for generating a uniform magnetic field in an examination zone (5) in an accommodation space of magnetic resonance apparatus is formed by a first, approximately cylindrical electromagnetic coil system (1) which encloses the examination zone and which is symmetrically arranged relative to a symmetry axis (9) and relative to a asymmetry plane (11) extending perpendicularly to the symmetry axis, and a second, approximately cylindrical electromagnetic coil system (7) which is arranged so as to be symmetrical relative to the symmetry axis and relative to the symmetry plane and which is arranged so as to be concentric with the first coil system, the magnetic dipole moments of the first and the second coil system being oppositely directed and substantially equal.

Abstract: A magnetic field correction device for enhancing the homogeneity of a magnetic field generated by a magnet of a magnetic resonance imaging device. The correction device includes a plurality of magnetic shim holders disposed at predetermined circumferential angles on a support cylinder coaxial with the magnet. Each shim holder accommodates a magnetic shim element consisting of a first and a second magnetic bar member of distinct lengths and a first and a second non-magnetic tube for accommodating the first and second magnetic bar members therein. The members are positioned by respective stoppers inserted into the tubes.

Abstract: A cantilevered trapezoidal-toroidal structure is provided in an active magnetic shielding system for a superconducting magnet to support the bucking magnet coils in spaced relationship to the main magnet coils.

Abstract: Disclosed is an MRI-dedicated magnetic field generating device for generating magnetic fields within an air gap, including: a pair of permanent magnet assemblies opposite to each other to form an air gap therebetween; yokes for magnetically linking the permanent magnet assemblies; and magnetic pole pieces fixed to air-gap-confronting surfaces thereof. Based on this construction, intensities of the magnetic fields are increased by disposing a plurality of magnetic material segments on the same circle or a concentric circle on the confronting surface thereof or decreased by disposing a plurality of permanent magnet segments having a magnetizing direction opposite to that of the permanent magnet assemblies on the same circle or the concentric circle on the confronting surface thereof; or alternatively both the magnetic material segments and the permanent magnet segments are disposed on the same circle or the concentric circle.

Abstract: This invention relates to refrigerated superconducting eddy current free MR magnets having integrated gradient coils. In particular, the amount of resultant eddy currents produced by the magnet are substantially reduced while reducing the size and weight, and, therefore, the cost of the superconducting magnet required to produce an acceptable MR image.

Abstract: An open access superconducting MRI magnet includes a ferromagnetic frame open on at least two sides and having upper and lower end plates and at least two support posts. A superconducting coil assembly is mounted to each end plate for generating a magnetic flux field in a patient receiving area located between the end plates. A magnetic flux field shaping means is associated with each end plate. The flux field shaping means includes rose shims, inner rings mounted within the rose shims, and removable segments mounted to the rose shims. Transition plates are located between the support ports and end plates for minimizing flux leakage. In addition the end plates are formed with a varying thickness such that a cross section taken perpendicular to a return path of magnetic flux is substantially constant.

Abstract: A magnet system to generate a static, uniform magnetic field in the examination chamber of a nuclear spin tomograph has a pair of outer field coils (1a, 1b) arranged on a common axis (a) at a mutual axial distance (g.sub.1) and a pair of inner field coils (2a, 2b) coaxial with the outer ones which are also equal to each other, in which both pairs of coils are arranged symmetrically to a central plane (E) perpendicular to the common axis (a). The axial distance (g.sub.1) between the outer field coils (1a and 1b) is 40 to 60% of their inside diameter (da.sub.2). The axial distance (g.sub.2) between the inner field coils (2a and 2b) is, with a maximum deviation of 15%, equal to that (g.sub.1) between the outer coils (1a and 1b). The magnet system forms an almost eight-order coil system and there is at least one transverse access aperture running across the direction of the uniform magnetic field and between the inner field coils (2a, 2b).

Abstract: A magnetic field generating assembly including self-contained modules formed from relatively high temperature superconducting material. A magnetic flux guide, such as a yoke, is positioned relative to the modules so that magnetic flux generated by the modules is coupled into the flux guide.

Abstract: A magnet apparatus has an active magnetic shield or a cancel coil disposed coaxially with a main coil at an end portion thereof so that the structure of the magnet apparatus is simplified and the both coils are easily assembled together. The outer diameter of the magnet apparatus is rendered small because it is unnecessary to increase the radius of the apparatus. No misalignment between the main coil and the cancel coil occurs due to an assembly error and/or a magnetomotive force generated when the coils are excited, whereby the static magnetic field is prevented from being distributed unevenly and the tomographic image is refrained from being deteriorated.

Abstract: A magnetic field control apparatus for establishing a uniform field of flux for use in magnetic resonance imaging has a pair of opposed magnetic poles mounted on end plates of variable thickness. A pair of substantially flat parallel pole faces are attached to the facing surfaces of the magnetic poles. The end plates are supported by connecting members. In addition, there is included a plurality of segments movably mounted to the periphery of the pole face for adjusting the density of the magnetic field. The top and bottom end plates may have substantially identical concave portions on the opposite outside surfaces thereof. The magnetic poles and pole faces are preferably in the shape of thin, flat, circular plates. In one embodiment, there is included one or more inner segmented concentric rings for further adjustably controlling the homogeneity of the uniform magnetic flux in the air gap between the opposing pole faces into which a patient can be inserted for magnetic resonance imaging.

Abstract: A medical NMR scanner having a primary field magnet assembly is disclosed. The scanner includes a ferromagnetic frame defining a patient-receiving space adapted to receive a human body. It also includes a pair of opposed polar regions aligned on a polar axis. The polar regions are disposed on opposite sides of the patient-receiving space. Structure including either electrical windings or a permanent magnet is provided in each of the polar regions for producing a magnetic field within the patient-receiving space. Windings positioned in proximity to each of the polar regions are provided for producing gradients in the magnetic field, when energized. A plurality of ferromagnetic elements positioned in side-by-side relation to one another in each of the polar regions is provided for limiting eddy current generation in the polar regions when the gradient producing auxiliary coils are energized. Each of the ferromagnetic elements has its shortest dimension oriented generally perpendicular to the polar axis.

Abstract: A magnetic field gradient coil system for use in a magnetic resonance imaging apparatus forming a magnetic field gradient in a direction of a Z-axis of an X, Y, Z orthogonal coordinate system having its origin at a selected position in the imaging apparatus comprises one pair of first coils and one pair of second coils having their centers on the Z-axis and having the same radius, the coils of each coil pair disposed symmetrically with respect to an XY plane including the origin, the coils of the second coil pair disposed more distant from the origin than the coils of the first coil pair, the coils of the first and second coil pairs disposed on one side of the origin supplied with current in the same direction, the coils disposed on the other side of the origin supplied with current opposite to the direction of current in the coils on the one side of the origin, each of the coils of the first coil pair disposed where the value of the Z-axis magnetic field component of first order at a selected position on the

Abstract: A medical NMR scanner having a primary field magnet assembly is disclosed. The scanner includes a ferromagnetic frame defining a patient-receiving space adapted to receive a human body. It also includes a pair of opposed polar regions aligned on a polar axis. The polar regions are disposed on opposite sides of the patient-receiving space. Structure including either electrical windings or a permanent magnet is provided in each of the polar regions for producing a magnetic field within the patient-receiving space. Windings positioned in proximity to each of the polar regions are provided for producing gradients in the magnetic field, when energized. A layer of an electrically resistive but magnetically permeable material such as a ferrite, a sintered metal or a metal containing composite, is positioned in each of the polar regions for limiting eddy current generation in the polar regions when the gradient producing auxiliary coils are energized.

Abstract: Shim holding independently accessible open cavities are attached to the magnet bore. The holding independently accessible open cavities are arranged in rows and columns to provide readily identifiable locations. The shim holding indpendently accessible open cavities increase the effeciency of shimming to improve the homogeneity of magnets in magnetic resonance systems.

Abstract: The fabrication of a flux source using magnetically rigid material is dissed for deriving a magnetic field of uniform density and enhanced magnitude within an enclosed cylindrical cavity thereof. In the preferred embodiments, segments of the magnetically rigid material are configured and arranged in the flux source to direct the magnetic field in parallel with the cyindrical axis of the cavity.

Abstract: A magnet assembly comprises an array of electrical coils (1-4) positioned side by side in the same sense and arranged such that in use when working currents are supplied to each coil (1-4) a magnetic field of control characteristics is continuously generated in a region (7) spaced from the coils.

Abstract: A field gradient generator in an NMR imaging apparatus comprises three sets of field gradient generating coils for respectively generating field gradients in three orthogonal directions in a space to be observed. Each set of coils includes a plurality of unit coils through which individual currents respectively flow. There are prepared a plurality of unit drivers which are for exclusive uses of the respective unit coils or are connected arbitrarily to each unit coil. Thereby, the lowering of an allowable operating voltage is implemented by use of a parallel operation of the unit drivers.

Abstract: In one aspect of the present invention a superconductive magnet for use in a magnetic resonance imaging and spectroscopy is provided. The magnet comprises a cylindrical coil form having a plurality of superconductive coils situated coaxially on the cylinder, spaced apart from one another. A plurality of pairs of thermal bridges each comprising a bar shaped section connecting a first and second end portion is also provided. The first end section has a greater surface are than the second end section. Each of the pairs of thermal bridges is situated between a respective pair of adjacent coils. The bar section of each of the thermal bridges extends axially between the adjacent coils. In each pair, the first end of one of the pair and the second end of the other of the pair are in thermal contact with one of the adjacent coils, the second end of one of the pair and the first end of the other of the pair are in thermal contact with the other coil of the adjacent pair.

Abstract: Magnetic field generators used in magnetic resonance imaging instruments (MRI) need an extremely uniform and wide magnetic field space. With the annulus of a field-generating annular magnet composed of a plurality of permanent magnet blocks arranged annularly, non-magnetic hold plates may be arranged in correspondence with each of the permanent magnet blocks, and field-regulating permanent magnet pieces may be fixed at stated positions of the hold plated, thereby obtaining a uniform magnetic field space.

Abstract: An actively shielded, superconducting magnet of a nuclear magnetic resonance tomography apparatus has an inner coil system and an outer coil system connected in series to avoid an increase in the external field upon the quench of one of the coil systems. To avoid losing the protection of the shielding effect from external magnetic field disturbances, a superconducting current limiter having a low critical current-carrying capability is connected in the coil system to guide a difference current between the inner coil system and the outer coil system. To avoid an unwanted increase in the external field in the event of a quench of one of the coil systems, the current limiter becomes normally conductive in the presence of a current difference larger than a prescribed value.

Abstract: A magnet apparatus for use in magnetic resonance imaging systems comprises a superconducting coil which produces a main magnetic field in a working volume defined in the bore in which a patient is accommodated and a cryostat accommodating the superconducting coil and keeping the superconducting coil in the superconducting state. This cryostat includes only one thermal radiation shield and is configured with a smaller volume than that of conventional cryostats with no reduction in the heat insulation effects. Therefore, the dimensions of the bore are determined to comply with 1.0.ltoreq.L/B<1.9 where L is the length along the Z axis of the bore and B is its diameter. Thus, the length L along the Z axis of the bore is determined to be relatively short while the dimensions of the working volume necessary for diagnosis is secured in the bore, with the result that the oppressive sensation that the patient has in the bore is lessened.

Abstract: A shim coil for a nuclear magnetic resonance imaging apparatus capable of being independent of influences from time varying magnetic fields generated by gradient coil. The shim coil includes primary coil for producing an extra magnetic field in accordance with a direct current to be supplied, and compensatory coil for producing a compensatory magnetic field which cancels a magnetic field produced by the primary coil means in response to an induced current due to the time varying gradient magnetic fields.

Abstract: A magnetic field generating system for use in a magnetic resonance imaging system to apply a static magnetic field and additionally a gradient field and a high frequency field to a body under examination in order to excite a magnetic resonance and to collect magnetic resonance data about the magnetic resonance. The field generating system comprises a superconducting including magnet a superconducting coil for generating the static magnetic field, a gradient coil for generating the gradient field and a high frequency coil for generating the high frequency field. At least part of the superconducting magnet is made of a metal member, and at least part of the metal member is interposed between the superconducting coil the gradient coil provided with non-conductive sections for impeding an eddy current.

Abstract: An automated magnetic field shimming process for magnetic resonance spectroscopic imaging (MRSI) uses doubly phase encoded NMR spin echo responses in conjunction with multiple fourier transformation to derive a spectroscopic plot for each voxel in a three-dimensional array of voxels in an image volume (including portions of a living subject) which is to be subsequently subjected to MRSI using NMR FID or spin echo responses. The thus derived hydrogen peak frequency is taken as a measurement of existing static magnetic field intensity within that voxel and adjusted shim coil currents are calculated so as to reduce or minimize nonuniformity of the static magnetic field. A nonexistent pseudo shim coil having an assumed uniform shim contribution may enhance the resulting field homogeneity. The auto shimming procedure may be applied iteratively as required to achieve the predetermined degree of field uniformity.

Abstract: A magnetic resonance apparatus is provided with a detection system comprising a coil, which may be part of a shim coil system. Signals detected by this system are used for a dynamic control of a shim coil system in order to mitigate dynamically adverse influences of eddy currents on the magnetic field homogenity in at least a region of interest within the coil system of the apparatus.

Abstract: An RF coil arrangement (23) in a magnetic resonance apparatus wherein a static magnetic field for application to a body under examination is produced in a gap (3) between a pair of pole pieces (5). The RF coil arrangement comprises at least one coil (45 or 47) having a first part (49,51) fixed secured to a part (5) of the apparatus adjacent the gap and a further part (53) which is detachably electrically connected to the first part to provide easy access to the gap when placing in, or removing from, the gap a body to be imaged. The further part of the coil may be wholly detachable from the first part or pivotally mounted on a first portion (49) of the first part and detachable from a second portion (51) of the first part on pivotal movement of the further part with respect to the first portion of the first part.

Abstract: In a gradient coil system for a magnetic resonance apparatus arc conductors of notably X coils and Y coils are stacked axially or radially so as to form rigid stacks. The arc conductors are interconnected by means of electrical conductors and the stacks are also interconnected, so that a rigid, self-supporting coil system is obtained. Because the coil system is composed of rigid elements, is comparatively open and does not require a coil former, the production of noise in a magnetic resonance apparatus comprising such a coil system is substantially reduced and field disturbances due to coil deformations are also reduced.

Abstract: Magnet coil system for nuclear spin tomography has superconducting coils for generating a homogeneous magnetic base field and nonsuperconducting coils within an interior region defined by the base field coils for developing magnetic field gradients. At least one cooled radiation shield of electrically and thermally conductive material is arranged between the gradient coils and the superconducting base field coils. To prevent eddy currents started in the radiation shield from distorting the gradient fields, the radiation field contains superconducting material of a "second kind" that is a high temperature superconductor. The superconductor is in a nonsuperconducting state at the start of an excitation process for the base field coils and in a superconducting state during the undisturbed operation of the magnet coil system.

Abstract: A magnetic resonance system having a compact magnet configuration for generating a static magnetic field. The magnet and platform carrying the patient to be examined are so arranged as to be arbitrarily moved relative to one another. The resulting small size field-homogeneous space may be freely moved to various portions of the patient body to permit a wide range of whole body measurements.

Abstract: Apparatus such as high resolution nuclear magnetic resonance apparatus is provided which includes a large volume having a homogeneous static magnetic field generated by a solenoid magnet within which a plurality of stationary samples can be analyzed concomitantly. The static magnetic field is rendered homogeneous by means of a plurality of radial and axial coils connected to a controlled power supply.

Abstract: A nuclear magnetic resonance imaging apparatus has a superconducting coil which generates a static magnetic field, an electrically-conducting tubular heat shield which surrounds the superconducting coil, and a pair of confronting circular coils which are coaxial with the longitudinal axis of the cylindrical thermal shield and generate a gradient field in the longitudinal direction of the heat shield. The magnetic field generated by the circular coils induces eddy currents in the heat shield, and the eddy currents generate magnetic fields which form a composite magnetic field together with the magnetic field generated by the circular coils. The circular coils are positioned such that the terms in the expression for the magnetic flux density of the composite magnetic field which are proportional to the cube of the distance in the longitudinal direction of thermal shield cancel one another.

Abstract: A background field magnet for image transmitting devices of nuclear spin tomography is designed for the generation of a magnetic background field of predetermined first field strength and contains on a tubular coil support, and six super-conductive single coils which are arranged in pairs symmetrically with respect to a plane of symmetry at predetermined median distances from the plane. The coil support is also suitable for the generation of a second field strength which is smaller than the first field. According to the invention, it is provided that on the coil support (25) the coils (11, 12, 14) are applied with the same median distances (z.sub.1, z.sub.2. z.sub.4) with respect to the plane of symmetry (S), however, with reduced winding numbers N.sub.1 ', N.sub.2 ', N.sub.2 '), that additionally a pair (P3) of serially switched auxiliary coils (13) is provided which each is placed in the vicinity of the outer single coils (14) on the coil former (25) and that with given reduced winding number (N.sub.

Abstract: Magnetic imaging apparatus having a magnet providing a generally rectangular opening for receiving the object to be imaged and having first and second spaced apart substantially planar pole faces which are facing each other. First and second coil assemblies are disposed in the opening and provide a main magnetic field. First and second spaced apart substantially planar gradient field structures are disposed in the opening adjacent the pole faces and are adherent to the pole faces.

Abstract: The invention relates to a method and an apparatus for determining the cut (percentage) of one component of a multiphase fluid flowing in a pipeline, for example, oil or other hydrocarbon in a fluid flow that comprises oil, water, gas, and soil components, by use of NMR analysis. The fluid is flowed through an apparatus specifically designed to perform the analysis on the flowing fluid. Carefully sequenced 90.degree. pulse series are used to take advantage of the different spin relaxation times of the selected atomic species when they are constituent parts of molecules having inherently different levels of random molecular motion. The timing between pulses in a series and between series of pulses is chosen so that NMR emissions from unwanted matter do not occur, and FID peaks from the desired matter are registered.

Abstract: A magnet assembly for use in a magnetic resonance imaging system includes an outer cylindrical casing composed of a plurality of axially separate, connectable cylinder blocks, a plurality of air core coils arrayed in each of the cylinder blocks for generating a static magnetic field, a plurality of bases supporting each of the cylinder blocks, two discs attached respectively to axially opposite ends of the outer cylindrical casing, a plurality of three-dimensional adjustment bolts mechanisms disposed in the cylinder blocks and on the discs and having bolts hend endwise against the air core coils for positionally adjusting the coils independently in three directions with respect to axes of the cylinder blocks, and a plurality of connectors interconnecting the cylinder blocks into the outer cylindrical casing.

Abstract: A medical nuclear magnetic resonance system is provided with a primary field magnet assembly having a ferromagnetic frame. The system resists field variations caused by coil movement and confines the field within the frame.

Abstract: An NMR instrument incorporating a cryogenic magnet includes a constant pressure device to maintain the pressure of cryogenic vapors at a constant value whereby a stable magnetic environment is maintained.

Abstract: The axial dimensions of the usual "saddle" coils used to create transverse magnetic gradients in the static magnetic field of a magnetic resonance imaging system are substantially foreshortened. The outer arc of the saddle coil is moved axially inward while still leaving it at a position which produces negligible net transverse gradient contribution. While this new position of the outer arc can be expected to produce a significant second (third) derivative of the transverse gradient with respect to Z (the orientation of the static magnetic field) at the predetermined observation point, the inner arc of the saddle coil may be moved slightly away from the observation point so as to produce a second (third) derivative which substantially cancels that of the relocated outer arc. In this manner, the desired condition of having a net zero second (third) derivative may still be maintained even though the axial dimension of the saddle coil has been substantially reduced (e.g.

Abstract: A nuclear spin tomograph comprises a magnet system with a, preferably, elongated holder (19,20) for a test object arranged in its one axis to slide in the longitudinal direction. The test object is further surrounded by coil systems for generating gradient fields and for irradiating a radio-frequency field. The magnet system is provided with a yoke iron body (10) enclosing a longitudinal opening (11) for receiving the test object, with outer marginal areas of the longitudinal opening (11) accommodating coil sections (12, 12'; 13, 13') which extend in the direction of the longitudinal opening (11), which are bent over at the ends thereof and which close above the opening (11) (FIG. 1).

Abstract: A two coil system is described which produces a linear gradient field inside and an arbitrarily low field outside the two coil set. By eliminating the field outside the gradient coils, interaction between the gradient coils and external structure can be eliminated. A reduction in eddy current effects of greater than a factor 100 are readily obtained. Two coils are required for each gradient axis instead of one so that some increase in power supply capability may be required.

Abstract: The invention relates to a coil arrangement for nuclear magnetic resonance examinations. The coil arrangement has conductors surrounded by a cylindrical shield. It is achieved by additional shields enclosing the openings of the coil arrangement for partly or entirely introducing the patient that the magnetic field in the longitudinal direction of the coil is highly constant.

Abstract: A coil arrangement for producing a static magnetic field comprising a central coil and two outer coils disposed on opposite sides of the central coil. The positions and dimensions of the coils are so selected that each term contained in the Taylor series of the function of the magnetic field in the axial direction (z axis) of the coil arrangement in minimized. The current density in the central portion of the central coil is made to be higher than at other portions. The inventive coil arrangement is smaller in size, lighter in weight, and consumers a smaller amount of power than the prior art for the same magnetic strength and with a better homogeneous magnetic field.

Abstract: An NMR scanner apparatus uses a permanent magnet comprised of an assembly of magnetic material formed of a substantial number of low energy permanent magnetic elements producing magnetic flux and arranged in at least one row of columns. A frame of magnetically soft material provides a return path for the magnetic flux and provides a surface from which the columns of magnetic elements extend. A flux concentrator plate is disposed adjacent to a surface of the assembly and recessed a sufficient distance from the edge of the assembly to inhibit the loss of magnetic flux. The flux concentrator plate and the frame sandwich the magnetic assembly therebetween. A pole piece consisting of a soft magnetic material is disposed adjacent to a surface of the flux concentrator plate. The pole piece defines a scanning area substantially smaller than the area of the adjacent surface of the flux concentrator plate such that the pole piece exhibits parallel lines of magnetic flux for inducing polarization in living tissue.

Abstract: An NMR imaging system includes apparatus for producing a uniform magnetic field in a predetermined volume. Such apparatus includes a ring assembly having an axial extent L defined by a plurality of nonmagnetic rings, each having an axis and positioned side-by-side so that the axes of the rings are colinear and define the axis of the ring assembly. A plurality of discrete permanent magnet segments are angularly mounted within each ring for defining a central coaxial aperture. Each segment in a ring has a easy axis of magnetization whose orientation is functionally related to the angular position of the segment in the ring. Each segment has inner and outer edges that are nominally located at distances r.sub.1 and r.sub.2, respectively, from the axis of the ring from which it is mounted. The inner free ends of the segments of all of the rings define a central aperture of length L within the ring assembly. Finally, an adjustment is provided for moving the segments in each ring such that the distance r.sub.

Abstract: A magnetic resonance diagnostic device has a coil for generating a fundamental magnetic field of constant magnitude in which an examination subject is placed, a coil for generating a number of gradient magnetic fields in which the patient is also disposed, a device for detecting changes in the nuclear magnetic resonance of the patient from an equilibrium position, with the direction of the fundamental magnetic field being continuously changed during examination for inducing the changes in nuclear magnetic resonance which are measured.