University of Pennsylvania

Other

Carnegie Mellon University

Bell Communications Research, Inc.

Phospho-Energetics, Inc.

John S Leigh

David A Roberts

Britton Chance

Ravinder Reddy

Mitchell D Schnall

John Carl Schotland

Meir Shinnar

V Harihara Subramanian

John A Detre

Erik K Insko

Alan P Koretsky

Lizann Bolinger

Gadi Goelman

Donald S Williams

B Murat Eyuboglu

Oded Gonen

Scott M Eleff

A magnetic resonance-electrical impedance tomography (MREIT) technique for determining the local conductivity of an object. The MREIT technique combines magnetic resonance current density imaging (MRCDI) with electrical impedance tomography (EIT) in order to obtain the benefits of both procedures. The MREIT technique includes the step of current density imaging by performing the steps of placing a series of electrodes around the patient or object to be imaged for the application of current, placing the patient or object in a strong magnetic field, and applying an MR imaging sequence which is synchronized with the application of current through the electrodes. Next, the electric potentials of the surface of the object or patient are measured simultaneously with the MR imaging sequence, as in EIT. Then, the MR imaging signal containing information about the current and the measured potential are processed to calculate the internal conductivity (impedance) of the object or patient.

Magnetic resonance&mdash;electrical impedance tomography

Acquisition of three-dimensional image-guided localized proton spectroscopy (.sup.1 H-MRS) in the human brain is achieved on a standard clinical imager with a hybrid of chemical shift imaging (CSI) and transverse Hadamard spectroscopic imaging (HSI). 16.times.16.times.4 arrays of 3.5 and 1 ml voxels were obtained in 27 minutes. The spatially-selective HSI 90.degree. pulses were incorporated naturally into a PRESS double spin-echo sequence to subdivide the VOI into 4 partitions along its short axis. Two-dimensional CSI is performed along the other long axes. Because the hybrid excites the spins in the entire VOI, a .sqroot.N signal-to-noise-ratio (SNR) gain per given examination time is realized compared to sequentially interleaving N two-dimensional slices. A twofold gain in sensitivity is demonstrated in the brain for N=4.

Three-dimensional localized proton NMR spectroscopy using a hybrid of

A method for the direct reconstruction of an object from measurements of the transmitted intensity of the scattered radiation effected by irradiating the object. The transmitted intensity is related to the image by an integral operator. The image is directly reconstructed by executing a prescribed mathematical algorithm, as determined with reference to the integral operator, on the transmitted intensity.

Absorption imaging system and method using direct reconstruction of

A subtractive time of flight technique for MR angiography and quantitative blood flow measurement. Proton spins of water in the arterial supply to a tissue or organ are inverted in a steady-state fashion by applying constant amplitude off-resonance radio frequency pulses in the presence of a constant linear magnetic field gradient to effect adiabatic fast passage transport-induced inversion of spins which move in the direction of the gradient. An angiogram is formed by subtracting an image acquired with the arterial inversion pulse from a control image acquired with no arterial inversion. By inverting the spins in a steady-state manner, no cardiac gating is necessary for imaging organs. However, cardiac gating is desirable when imaging the heart so that spins of blood passing through the coronary arteries can be inverted during systole, when most of the blood is in the left ventricle, and imaged at end diastole, when most of the blood is in the coronary arteries. A coronary angiogram is then formed by subtracting images acquired with and without the inversion pulse. Also, by applying several inverting and imaging pulses during a cardiac cycle in accordance with the technique of the invention, a characteristic banding pattern may be formed in the fluid whereby each band corresponds to a population of spins that experienced inversion due to a single RF pulse. Since the width of the inversion band is proportional to the duration of the RF pulse and the velocity of the spin, measurement of the thickness of the inverted and uninverted bands allows for calculation of flow velocity. By gating such a pulse sequence to the cardiac cycle, time resolved in vivo velocity measurements may be made.

Quantitative blood flow measurement using steady-state transport-induced

Methods for measuring the perfusion of fluid in a substance are shown to include subjecting the fluid to electromagnetic energy so as to cause a response related to the magnetization of the fluid before it enters the substance, performing magnetic resonance measurements on the substance to generate intensity information and processing the intensity information to determine perfusion. In one embodiment of the invention, perfusion is measured by labeling atoms in the fluid at a base point, generating a steady state in the substance by continuing to label atoms until the effect caused by labeled atoms perfusing in the substance, reaches a steady state, generating image information for the substance and processing the image information to determine perfusion. It is preferred to label atoms by applying magnetic resonance perturbation. In one embodiment the labeling of atoms involves saturating spins associated with the atoms. In an especially preferred embodiment labeling involves inverting spins associated with the atoms continuously by adiabatic fast passage. Such inversion is preferably achieved by applying a radio frequency field virtually continuously. The invention is particularly useful where the substance is tissue and wherein the fluid is blood. In such an embodiment, labeling involves labeling the hydrogen atoms of water contained in the blood. It is also preferred for labeling to occur at a point between the heart and the tissue. It is also especially preferred for the generation of magnetic resonance images to involve generating a first image while labeling at the base point, labeling at a remote point, generating a second image while labeling at the remote point and generating a relaxation image. In such an embodiment, all of the images are processed in the determination of perfusion.

Methods for measuring perfusion using magnetic resonance imaging

MR angiography using steady-state transport-induced adiabatic fast

A new geometry for a radio frequency coil design in which longitudinal conductors of the coil lie on two parallel planes. The currents in the conductors of one plane run in the opposite direction to those of the other plane. For the case of discrete conductors, field maps illustrate that the homogeneity and sensitivity of the biplanar design are superior to that of a saddle coil, and when the design is optimized, the homogeneity is almost as good as that for comparable discrete cosine or birdcage coil designs. The measured B1 map of an optimized, single-tuned biplanar coil in accordance with the invention thus compares favorably to that of an equivalent discrete cosine coil and demonstrates excellent homogeneity in the central region of the coil. However, the biplanar RF coils of the invention are advantageous in that the cost of the coils may be substantially reduced by reducing the number of conductors, in that the coil may be easily accessed on one of its sides as well as at both ends, and in that increased sensitivity is possible since the biplanar coils may be placed closer to the objects under investigation. This makes the coil of the present invention highly desirable for certain applications such as breast, shoulder, knee, wrist, neck and cardiac imaging.

Biplanar RF coils for magnetic resonance imaging or spectroscopy

Methods of constructing pulse sequences to selectively excite frequency bands in NMR imaging, spectroscopic and optical systems are disclosed. In preferred embodiments, selective .pi./2, .pi., and refocusing hard and soft pulses are constructed for perturbing the spins of the system. In NMR imaging, for example, the desired magnetization is written as an (N+1)th order Fourier series in .omega.t, where .omega. is the off-resonance frequency. In addition, if all pulses have the same phase, then the z magnetization is known to be symmetric in frequency, and the resulting hard pulse sequence can be written as an Nth order Fourier cosine series. Given this Fourier series representing the desired z magnetization, an inversion may be used to determine the hard pulse sequence of N pulses which will actually yield the desired response. In particular, if one starts with a specification of a desired z magnetization not as a Fourier series in .omega.t, but rather as having certain desired values over several frequency ranges, the techniques of finite impulse response filters may be applied to yield the desired Fourier series representing the z and xy magnetizations. The optimal hard pulse sequence which yields that Fourier series may then be mathematically determined and applied to the system to yield the desired response. In accordance with another feature of the invention, the synthesized hard pulse sequence may be used to generate a soft pulse which has a frequency response over a broad range which is the same as that of the synthesized hard pulse sequence. The methods of the invention thus allow for the generation of optimal pulse sequences without the use of linear Fourier transform approximations to intrinsically nonlinear systems.

Methods of generating pulses for selectively exciting frequencies

A multiple tuning NMR probe includes a radio frequency (RF) probe tuned by means of a circuit which creates a multiple pole circuit response in the probe, each of the poles being sufficiently separated from each other as to cause resonance of the probe at distinct frequencies. When tuning for nuclei with resonances substantially apart, this function may be accomplished using a parallel capacitor-inductor (L-C) trap with an impedance matching network. When tuning for nuclei with substantially closely spaced resonances, a tank circuit is used which has a single resonance which is split into two resonances by strongly coupling it to another tank circuit in resonance with the sample coil tank circuit.

Multiple tuning NMR probe

A nuclear magnetic resonance analytic apparatus for obtaining tissue metabolism information from a living body member. The apparatus consists of a large high-intensity electromagnet with an inner space having a uniform magnetic field, for receiving the body member. The space has a probe coil mounted therein with which the body member is engageable. For phosphorus-31 metabolite, there is provided a 24.33 MHz RF generator connected through a control logic section and a driver unit to the probe coil via a transmitter/receiver switching unit arranged to in effect switch the probe coil from a normal connection with a demodulation circuit to the driver unit responsive to a burst of RF pulse energy applied to the switching unit by the driver unit via the control logic section by command of a computer. The control logic section controls the system so as to first apply short pulses of the RF signal to the probe coil for a predetermined excitation time period, gating-off the demodulation unit. After this excitation period, the transmitter circuit is disabled, the demodulation circuit is gated-on, and the switching unit restores the normal connection of the probe coil to the demodulation unit, allowing the free induction decay signals sensed by the probe coil to be demodulated and furnished in analog form to the computer, which converts these analog signals into representations of the intensities versus frequency shift of the respective metabolite components of the tissue. Means is provided for applying a predetermined simulated free induction decay signal to the demodulation circuit for testing the apparatus.

Growing community of inventors

Philadelphia, PA, United States of America

John S Leigh