Abstract: Methods for increasing the imaging accuracy of object density pixel values by forming linear combinations thereof to counteract spatial mixing of object density pixel value information, and by using an estimate of the object density pixel values to correct for the effects of variations in the object density. A measured variable M as a function of time t is related to the actual object density by M(t)=∫F((q),q,t) (q) dq, where q is the spatial variable. An estimated object density * is related to an actual object density by (q)=∫&Sgr;tE([],q,t)F(,q′,t) (q′) dq′, where E is an approximate inverse of F, and &Sgr;tE([],q,t)F(,q′,t) is defined as the kernel function A(q,q′). Due to the limited number of time samples, the kernel A only approximates the delta function &dgr;(q−q′), and values of (q′) away from q=q′ contribute to *(q).

Abstract: Method and apparatus for increased accuracy of an image of object density pixel values obtained by forming linear combinations thereof. A measured variable M is related to an integration of the actual object density .rho. over space q by a transform function F, i.e., M(t)=.intg.F(t, q).rho.(q)dq, and an estimated object density .rho.* is obtained by an approximate inversion of the transform function, i.e., .rho.*(q)=.SIGMA.E(t,q)M(t), where the sum is over the samples taken. (In the case of magnetic resonance imaging, M is the magnetization induced in a coil transverse to the main magnetization coil, the transform function F(t,q) includes sinusoidal components, and the inversion function G includes an inverse Fourier transform.) Therefore, the estimated object density .rho.* is related to the actual object density .rho. by.rho.*(q)=.intg..SIGMA.E(t,q)F(t,q').rho.(q')dq',and .SIGMA.E(t,q)F(t,q') is termed the kernel A(q,q').

Abstract: A simple, reliable, convenient and safe system for aiming a dental X-ray apparatus at an X-ray film plate. In the system of the present invention, magnetic field sensors, mounted on the dental X-ray apparatus, are used as a means of detecting the relative strength of a magnetic field of a magnet which is located next to an X-ray film plate within the mouth of a patient. By measuring and comparing the relative strengths of this magnetic field at each sensor, the system of the present invention can detect and indicate the condition of alignment or misalignment, including relative displacement in the x and y directions, as well as relative tilt about the x or y axes. Furthermore, the alignment system of the present invention can indicate misalignment of the X-ray film plate axes with the axes of the collimated X-ray beam. The present invention also provides a three-dimensional display by which the alignment or misalignment of the X-ray apparatus is conveniently indicated to the operator.

Abstract: Improved two dimensional nuclear magnetic resonance imaging methods of the present invention are presented which comprise sensitizing a two dimensional slice of an object by standard procedures in a static magnetic field wherein the magnetization of the spins is transverse to the static field, applying a time varying magnetic field gradient to the sensitized two dimensional slice, detecting radiated electromagnetic energy from the two dimensional slice, and reconstructing spin information for each element within a slice from the detected radiated electromagnetic energy. In one aspect, the improvement is the use of an appropriate weighting function in the reconstruction to weight the detected radiated electromagnetic energy signals to compensate for the use of time varying magnetic field gradients that do not sample equal area elements of phase space in equal time intervals.

Abstract: A method for obtaining a spatial mapping using nuclear magnetic resonance. A sample is subjected to time dependent magnetic gradient fields having linear components in the X and Y directions, normalized so that the time dependency is eliminated in the vicinity of a line X.sub.0,X.sub.0,Z. A time independent gradient field is applied along this line. An initial RF pulse is applied to rotate the magnetization 180 degrees. This is followed by a 90 degree pulse and then a series of 180 degree pulses. It has been determined experimentally that the relaxation times T.sub.1 and T.sub.2 for ischemic muscle tissue are longer than T.sub.1 and T.sub.2 for normal tissue. The above-described pulse pattern enhances the differentiation between the ischemic and normal tissue, and can provide useful data in applications wherein data can only be acquired during a short period of time.

Abstract: A dental x-ray aligning system in which various Hall effect sensors, mounted on a dental x-ray apparatus, detect the magnetic field strength resulting from a magnet which is attached to an x-ray film plate located within the mouth of a patient. By measuring and comparing the relative magnetic field strengths, the present invention can indicate when the dental x-ray apparatus is properly aligned, and can also indicate the direction in which the apparatus should be moved to obtain alignment, and the distance between the apparatus and the film plate. The present invention also includes means for adjusting the collimation of the dental x-ray apparatus.