- Wendt, Michael (x)
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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 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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