Abstract: External field compensation is provided for MRI apparatus which is in a magnetically noisy environment such as that caused by nearby subway trains. By means of a magnetometer type sensor, the external field fluctuation is sensed and after being adjusted for the filtering effect of the magnet structure of the MRI device itself, the master oscillator of the MRI device is adjusted to compensate for the external field fluctuation. Alternatively the current of the magnet coil is adjusted.

Abstract: A flexible, conformally fitted coil for imaging of the human shoulder and topologically similar specimens is in the form of a band of flexible conductive foil covered by a soft flexible insulating material. The geometry of the coil is such that it can pass under the arm and over the top of the shoulder, providing high sensitivity for magnetic resonance imaging (MRI) studies of the shoulder in MRI apparatus having either a vertical or horizontal axial magnetic field. The flexibility of the coil and the generality of its geometry makes it suitable for examination of patients in a wide variety of sizes. Radio Frequency (RF) Power is delivered to and/or received from the coil via a matching network. The matching network may include a transformer to reduce the necessary current delivered to the coil, or RF current may be injected directly into and extracted directly from the coil.

Abstract: A magnetic resonance imaging (MRI) method imposes void planes on tissue to be imaged, which may form a grid pattern of lines which, when later imaged, produces a reference void in the image. This is especially useful in studies of the heart where the contraction and relaxation of the heart can thus be measured. Also for static tissue the method is useful for radiation therapy port planning. The grid reference or void planes are formed by a simple use of an RF pulse in conjunction with the use of a slice select gradient which provides sufficient power so that those protons in the grid are saturated so that in the later imaging step there will be significant spin echo signal difference between the grid imposed areas and the remaining regions of the tissue.

Abstract: A head or body coil assembly for picking up signals in an MRI system is provided. It includes a band of conductive material which surrounds the specimen to be tested but which forms a gap substantially parallel to the axis of the curved band. An overlapping conductive section overlaps the gap at the adjacent ends to form respective capacitors with these ends. A ground connection in taken off from the overlapping section and a signal output lead is attached to one of the ends. Auxiliary variable capacitors are provided for balancing the system and for tuning it into resonance.

Abstract: A head or body coil assembly for picking up signals in an MRI system is provided. It includes a thin band of conductive material which surrounds the specimen having a thickness comparable to the skin depth at the frequency of the spin echo signals of the MRI system but being transparent to gradient waveform frequencies. The thin band is in the form of a cylinder which acts as a flux tube for the RF signals to automatically provide for a homogeneous magnetic field.

Abstract: In an MRI method for optimizing flip angles for unequal delay times, a mathematical relationship is derived where RF flip angles can be determined to provide output signals which are constrained to be equal in amplitude and maximized in a sequence of MRI imaging.

Abstract: Quadrature coils for magnetic resonance imaging (MRI apparatus) are in the form of loops constructed of foil bands of conductive material with their respective axes forming an angle with each other to provide the quadrature phase signals. Trapezoidal cutouts are in each loop to allow for entry of the head of a human being or other large specimen. The angle between the coils is adjusted to compensate for the cutouts to provide and maintain the quadrature phase signals. Inductive coupling between the coils is minimized by three rectangular trim foils which are parallel to the main magnetic field and placed adjacent to the coils.

Abstract: An improved image restoration technique for an MRI method is provided where after the corrected location of image points is determined, an improved interpolation technique is used in determining the intensity value of that image point utilizing the surrounding pixels, e.g., 4 or 16. The interpolation technique provides for a uniform noise variance by using a weighted average interpolation technique with the added constraint that the sum of the squares of the interpolation weighting functions is substantially equal to a constant. The resulting image may be sharpened by a hybrid convolution technique which separately processes border regions.

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: A pickup coil for magnetic resonance imaging (MRI) includes a single thin metal copper sheet which is covered with cloth-like material with the interior of the two ends of the coil being covered with VELCRO-type connective material so that they adhere together. Thus, this provides a conforming fit to various specimens of varying diameters and configurations. The two ends of the coil are held by and inserted in a capacitive tuning unit which compensates for the resistive loading caused by the specimen and also for implementing the needed resonance condition.

Abstract: Magnetic resonance imaging apparatus having a structure with an opening adapted to receive an object to be imaged. An object platform is provided which is sized so that it can be moved into the opening in the magnet structure. Structure is provided for supporting the platform and for moving the platform along x, y and z axes.

Abstract: In an improved NMR imaging method for forming images of a subject by determining the relative densities of nuclei within the subject, three orthogonal gradient fields are generated by digitally storing three gradient waveforms for each orthogonal direction, with each waveform being individually compensated and calibrated with respect to an axis with which it is associated. Nine associated matrix multiplying functions which determine the coordinates of a desired slice in its rotated plane are also stored by an external input (by computer or by the clinician operating the system.) Then, in a sequential fashion, digital words for each gradient waveform are read out, multiplied by pairs with the appropriate multiplying function and the three terms are added to form a digital word. These words are converted to an analog value and applied to the respective gradient coils.

Abstract: In an improved NMR imaging method, where three-nominally orthogonal gradient fields are generated, the quantization error of the phase encode gradient is reduced without the necessity of a digital to analog converter of higher bit capacity. This is accomplished in one embodiment by providing a second smaller gradient waveform which is relatively narrow compared to the primary gradient waveform, the ratio of the waveforms being proportional to the improved resolution. The second waveform can occur either before or after the 180.degree. excitation pulse used to produce a spin-echo signal. In another embodiment pulse width modulation is used to vary the area of the phase encode waveform in discrete increments.

Abstract: Magnet assembly having a magnet yoke formed of a magnet material and providing a generally rectangular opening and having first and second spaced apart parallel pole faces which are facing each other. First and second coil assemblies are disposed in the opening in the yoke. Each coil assembly comprises first and second spaced apart generally parallel bundles of nested U-shaped members formed of conducting material. The bundles have legs at opposite ends. First and second sets of cross pieces are bonded to the legs of the U-shaped members. Insulating material is disposed between the U-shaped members and the cross pieces so that the bonded together U-shaped members and the cross pieces form a continuous current conductor for each coil assembly.