- 2014-12-01 (x)
- Lewin, Jonathan S. (x)
- Search results
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Show moreBackground of the invention: The present invention relates to Magnetic Resonance Imaging (MRI) arts. More particularly, the invention relates to providing audio information as part of an imaging pulse sequence, to provide instructions and other information to a patient undergoing a MRI procedure. The basics of Magnetic Resonance Imaging are well known. In a typical MRI system an object, such as the human body, is placed within a gradient magnetic construction which forms a uniform magnetic field. When the object is subjected to this uniform magnetic field, the nuclei in the object attempt to align with the polarizing field, but precess about it in random order at their characteristic Larmor frequency. Thereafter, the object is excited by a pulse sequence which acts to tip the nuclei. When a pulse is switched off, the nuclei precess back toward their equilibrium position during which a response is emitted and detected by an RF receiver. Numerous unique pulse sequences exist for MRI investigations. When utilized to produce images, magnetic field gradients are employed. Typically, the region to be imaged is scanned by pulse sequences during which the field gradients vary according to the particular sequence used. The resulting set of received MRI signals are digitized and processed to reconstruct an image employing one of many well known reconstruction techniques. A pulse program generator or pulse sequence generator of the MRI system stores and uses the pulse sequences to provide signals that control the operation of the RF transmitters, RF receivers, gradient coils, etc. of a MRI system. Software code which defines different pulse sequences is loaded into writable control storage areas of the pulse program generator. The code, which includes instructions, is a type of computer program that is executed by the pulse program generator to specify pulse program generator outputs and also specifies the duration of such outputs. Since the program generator is writable, various MRI pulse sequences can be specified by simply downloading different instructions into the pulse program generator control storage. Thus, different instruction sequences corresponding to numerous MRI pulse sequences are able to be maintained on a host computer storage and downloaded for use by the MRI system. The pulse sequences which typically have been provided to a pulse program generator have been limited to those which are capable of being analytically expressed, such as those based on sine, cosine, tangent, and exponential functions. However, very recently, MRI systems have been developed which allow the downloading of arbitrary signal patterns to the pulse program generator, allowing an arbitrary pattern of signals to be used as the pulse sequence controlling the gradient coils of an MRI system.
http://www.google.com/patents?vid=USPAT5709207
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Show moreField of the invention: The present invention relates generally to the field of magnetic resonance imaging (MRI). More particularly, the present invention relates to the field of MRI chemical-shift excitation. Background of the invention: In a typical magnetic resonance imaging MRI) system, a subject such as a human body is placed in a static magnetic field such that selected nuclear magnetic dipoles of the subject preferentially align with the magnetic field. The MRI system then applies radio frequency (RF) pulsed magnetic fields to cause magnetic resonance of the preferentially aligned dipoles and detects RF magnetic resonance (MR) signals from the resonating dipoles for reconstruction into an image representation. The MRI system typically scans the region to be imaged by applying RF pulse sequences to the subject while imposing time-varying magnetic field gradients with the static magnetic field. In imaging most tissues with MRI, the hydrogen protons from water are preferably detected as most soft tissues are composed of greater than approximately eighty percent water. Unfortunately, fat is also largely composed of hydrogen protons and may therefore appear as an unwanted or unnecessary component in many hydrogen MR images. A variety of methods have been developed to help eliminate the effect of fat magnetization from hydrogen MR images and thereby improve the contrast between normal and pathologic tissue in a variety of anatomic locations such as, for example, the liver and pancreas, the orbits, the breast, bone marrow, and the coronary arteries. Water excitation methods apply an RF pulse sequence to tip water magnetization and not fat magnetization for detection. Fat suppression methods apply an RF pulse sequence to tip fat magnetization and not water magnetization, eliminate the fat magnetization, and then excite the water magnetization for detection. Such methods are able to tip water and fat magnetization in a selective manner because of the chemical shift difference in resonant frequency between water protons and protons in the methylene (--CH.sub.2) groups of fat molecules. The chemical shift difference between two chemical species in which excitation of one and elimination of the other is desired is given by .delta. in parts per million (ppm). For water and fat protons, the chemical shift difference is approximately 3.5 ppm in accordance with the following equations: ##EQU1##where .omega. is the Larmor frequency of the nuclei of interest, .gamma. is the gyromagnetic ratio of the nuclei of interest, and B.sub.0 is the applied static magnetic field. One common fat suppression method applies binomial sets of RF pulses at specific amplitudes and specific interpulse intervals to tip fat magnetization into the transverse or detection plane while restoring water magnetization to the longitudinal axis.
http://www.google.com/patents?vid=USPAT6404198
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Show moreBackground of the invention: The present invention relates to magnetic resonance ("MR") imaging. It finds particular application in conjunction with correcting MRI motion artifacts and main field fluctuation and will be described with particular reference thereto. It will be appreciated, however, that the invention is also amenable to other like applications. Magnetic resonance imaging is a diagnostic imaging modality that does not rely on ionizing radiation. Instead, it uses strong (ideally) static magnetic fields, radio-frequency ("RF") pulses of energy and magnetic field gradient waveforms. More specifically, MR imaging is a non-invasive procedure that uses nuclear magnetization and radio waves for producing internal pictures of a subject. Three-dimensional diagnostic image data is acquired for respective "slices" of an area of the subject under investigation. These slices of data typically provide structural detail having a resolution of one (1) millimeter or better. Programmed steps for collecting data, which is used to generate the slices of the diagnostic image, are known as an MR image pulse sequence. The MR image pulse sequence includes magnetic field gradient waveforms, applied along three (3) axes, and one (1) or more RF pulses of energy. The set of gradient waveforms and RF pulses are repeated a number of times to collect sufficient data to reconstruct the slices of the image. The data for each slice is acquired during respective excitations of the MR device. Ideally, there is little or no variations in the phase of the nuclear magnetization during the respective excitations. However, movement of the subject (caused, for example, by breathing, cardiac pulsation, blood pulsation, and/or voluntary movement) and/or fluctuations of the main magnetic field strength may change the nuclear magnetization phase from one excitation to the next. This change in the phase of the nuclear magnetization may degrade the quality of the MR data used to produce the images. A non-phase encoded additional echo signal, prior to or after the data echo used for image generation, may be used to detect view dependent global phase variations when two-dimensional Fourier transform encoding and reconstruction algorithms are used. This "Navigator" echo passes through the center of the data space (K-space) each time, while the MR image data is ordered sequentially and linearly. Then, computational methods are used to correct the undesired view-to-view phase variation, thereby eliminating a significant source of image artifacts. With reference to FIG. 1, a typical MR imaging pulse 10 includes a slice select (frequency encoding) gradient 12 and an RF pulse 14 (i.e., the actual MR image signal). The slice select gradient 12 and the RF pulse 14 define a spatial location in which the image data occurs.
http://www.google.com/patents?vid=USPAT6404196
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Show moreBackground: Magnetic Resonance Imaging (MRI) is one of the most important modern medical imaging modalities, with approximately 18 million procedures performed in 2001. MRI is currently used in three main areas: diagnostic imaging (dMRI), interventional imaging (iMRI), and quantitative imaging. Most commonly, it is used clinically for a variety of diagnostic procedures. These diagnostic procedures usually require high spatial resolution, high SNR, and low artifact levels. Additionally, it is important to have strong contrast between normal and pathological tissues. Available contrasts include: diffusion-weighted imaging for stroke; perfusion imaging for vascular tumors and infarction; spin-lattice (longitudinal) relaxation characteristic time constant T1 contrast; spin-spin (transverse) relaxation characteristic time T2 contrast; flow-sensitive imaging and MR angiography for detecting a variety of vascular pathologies, malformations and cardiac defects; and others. Many of the background concepts and terminology used herein to describe or refer to MR imaging systems and their principles may be found, for example, in the book, titled “Magnetic Resonance Imaging: Physical Principles and Sequence Design,” by Haacke, et al., John Wiley & Sons (Wiley-Liss), 1999. The raw data in MRI is acquired in k-space, which is the spatial frequency (also known as the Fourier domain) representation of the image or images of interest. In typical MRI data acquisition methods, k-space data are acquired—one line at a time—on a rectilinear (Cartesian) grid matrix. The image is then reconstructed, typically by using a fast Fourier transform (FFT) technique. However, rectilinear (Cartesian) data sampling methods are usually not time-efficient, and the reconstructed images may be affected by flow and motion artifacts. For this reason, some clinicians have proposed to use non-rectilinear (non-Cartesian) sampling paths, or trajectories, in k-space to acquire MRI data. One exemplary non-rectilinear trajectory is a spiral trajectory which permits acquisition of an MR image in 100 msec or less. Such spiral trajectories provide excellent immunity to flow artifacts and variable tissue contrast. However, since spiral trajectories sample only a limited number of points in k-space, such trajectories, if not properly selected, may introduce unwanted artifacts. Most current k-space trajectory design techniques essentially begin with a trajectory shape that is easy to visualize and realize. The properties of the trajectory are examined and the real-space MRI image obtained from the various trajectories is then examined by a clinician for unwanted artifacts, and to ensure a faithful rendition of the tissue image. Two of the more common classes of non-rectilinear trajectories are spiral and radial.
http://www.google.com/patents?vid=USPAT7078899
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Show moreField of the invention: The present invention relates to the image processing arts and more particularly to improving magnetic resonance imaging (MRI) system images. The invention will also have application to other imaging systems like X-ray, CT, single photon emission computed tomography (SPECT), positron emission tomography (PET), and others. Background: Magnetic resonance imaging systems acquire diagnostic images without relying on ionizing radiation. Instead, MRI employs strong, static magnetic fields, radio-frequency (RF) pulses of energy, and time varying magnetic field gradient waveforms. MRI is a non-invasive procedure that employs nuclear magnetization and radio waves for producing internal pictures of a subject. Two or three-dimensional diagnostic image data is acquired for respective “slices” of a subject area. These data slices typically provide structural detail having, for example, a resolution of one millimeter or better. Programmed steps for collecting data, which is used to generate the slices of the diagnostic image, are known as a magnetic resonance (MR) image pulse sequence. The MR image pulse sequence includes generating magnetic field gradient waveforms applied along up to three axes, and one or more RF pulses of energy. The set of gradient waveforms and RF pulses are repeated a number of times to collect sufficient data to reconstruct the image slices. Data is acquired during respective excitations of an MR device. Ideally, there is little or no variation in the nuclear magnetization during the respective excitations. However, movement of the subject caused, for example, by breathing, cardiac pulsation, blood pulsation, and/or voluntary movement, may change the nuclear magnetization from one excitation to the next. This change of the nuclear magnetization may degrade the quality of the MR data used to produce the images. Acquiring an MRI image takes a period of time. The period of time is determined, at least in part, by the number of scans that are taken and the number of data acquisitions in each scan. If the object being imaged moves during the scan then artifacts can be introduced into the image. Very small motions (e.g., 1 mm, 1° of rotation) can introduce artifacts like blurring and ghosting. Some patients may have difficulties lying completely still, which can lead to MRI images of these patients being degraded by a rotational motion. Furthermore, some types of motion (e.g., heartbeat, respiration) require additional technologies for reducing the effects on imagery. Since these technologies may not yield ideal results, they too can lead to the degradation of MRI images due to rotational motion. Summary: The following presents a simplified summary of methods, systems, APIs, data packets, and computer readable media for improving MRI images that are degraded by an object's rotational motion during MRI, to facilitate providing a basic understanding of these items.
http://www.google.com/patents?vid=USPAT7002342
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Show moreBackground: Off-resonance effects (e.g., field inhomogeneity, susceptibility, chemical shift) cause artifacts in magnetic resonance imaging (MRI). The artifacts appear as positional shifts along the readout direction in rectilinearly sampled acquisitions. Usually, they are insignificant because of short readout times in normal spin-echo (SE) and gradient-echo (GRE) sequences. However, off-resonance artifacts sometimes appear as severe geometric distortion because of the relatively long readout time in echo planar imaging (EPI).Over the past decade, spiral imaging techniques have gained in popularity due to their short scan time and insensitivity to flow artifacts. However, off-resonance effects cause blurring artifacts in the reconstructed image. Most spiral off-resonance correction methods proposed to date are difficult to apply to correct for blurring artifacts due to the fat signals, since the fat-water frequency shift is typically much greater than that due to main magnetic field (B0) inhomogeneity across the field of view (FOV). As such, off resonance artifacts remain one of the main disadvantages of spiral imaging. Currently, off-resonance artifacts due to fat signals are most commonly avoided by use of spatially and spectrally selective radio-frequency (RF) excitation pulses (SPSP pulses) since they excite only water spins, thereby eliminating the off-resonance fat signals and thus avoiding artifact generation. Yet, SPSP pulses may not lead to satisfactory fat signal suppression in the presence of large B0 inhomogeneity. Excitation of only water spins could be achieved through application of chemical shift presaturation pulses [e.g., CHESS pulses] prior to normal spatially selective excitation. However, the effectiveness of these frequency selective RF excitation pulses is dependent on main magnetic field homogeneity. Alternatively, Dixon techniques have been investigated for water-fat decomposition in rectilinear sampling schemes. In the original Dixon technique, water and fat images were generated by either addition or subtraction of the “in-phase” and “out-of-phase” data sets. Water and fat separation is unequivocal using this technique when magnetic field inhomogeneity is negligible over the scanned object. However, when B0 inhomogeneity cannot be neglected, the original Dixon technique fails to accurately decompose water and fat signals. Therefore, modified Dixon techniques using three data sets (i.e., three-point Dixon (3PD) technique) or four data sets were developed to correct for B0 inhomogeneity off-resonance effects and microscopic susceptibility dephasing. New versions of the Dixon technique use two data sets with B0 inhomogeneity off-resonance correction, i.e., the two-point Dixon (2PD) technique.
http://www.google.com/patents?vid=USPAT7042215
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