Abstract: A phantom for use with magnetic resonance imaging (“MRI”) and, in particular, for calibrating quantitative diffusion MRI is provided. In general, the phantom includes a solution composed of a solvent that has diffusivity value higher than that of water, and a solute that when added to the solvent reduces the diffusivity of the solution. By varying the combined concentration of the solvent and solute, the diffusivity of the solution can be controlled to fall within a range of diffusivity values found in biological tissues in a variety of different physiological conditions or tissue environments.

Abstract: Phantoms for use in magnetic resonance imaging (“MRI”) and, in particular, for use in quantifying fat concentration, iron concentration, or both, are provided. The phantoms are constructed to accurately reflect in vivo magnetic resonance signal behavior in the presence of both fat and iron. The phantoms described here can thus be used for phantom-based validation of MRI techniques for the joint quantification of fat and iron concentration, for phantom-based validation of MRI techniques for quantifying fat concentration in the presence of iron overload, and for phantom-based validation of MRI techniques for quantifying iron concentration given the confounding presence of fat.

Abstract: An object-based approach is used to initialize the magnetic field inhomogeneity estimation for chemical species separation, such as water-fat separation, and other imaging applications. For example, a susceptibility distribution in the subject being imaged is estimated from images reconstructed from single-echo or multi-echo k-space data and used to initialize the magnetic field inhomogeneity estimation. This approach can be applied to any complex-based chemical shift encoded chemical species separation technique and to other imaging applications, such as susceptibility-weighted imaging and quantitative susceptibility mapping. The field map can also be used to correct for image distortions and to generate magnetic field shimming values.

Abstract: Systems and methods for simultaneously acquiring three-dimensional data from multiple different frequency bins with a magnetic resonance imaging (“MRI”) system, and without frequency-encoding gradients, are provided. A multiband radio frequency (“RF”) pulse is used to excite spins associated with multiple different resonance frequency offsets, and a fully phase-encoded acquisition is used to acquire data, which may be spectrally-resolved data, from magnetic resonance signals formed in response to the multiband RF pulse.

Abstract: A phantom for use with magnetic resonance imaging (“MRI”) and, in particular, for calibrating quantitative diffusion MRI is provided. In general, the phantom includes a solution composed of a solvent that has diffusivity value higher than that of water, and a solute that when added to the solvent reduces the diffusivity of the solution. By varying the combined concentration of the solvent and solute, the diffusivity of the solution can be controlled to fall within a range of diffusivity values found in biological tissues in a variety of different physiological conditions or tissue environments.

Abstract: Phantoms for use in magnetic resonance imaging (“MRI”) and, in particular, for use in quantifying fat concentration, iron concentration, or both, are provided. The phantoms are constructed to accurately reflect in vivo magnetic resonance signal behavior in the presence of both fat and iron. The phantoms described here can thus be used for phantom-based validation of MRI techniques for the joint quantification of fat and iron concentration, for phantom-based validation of MRI techniques for quantifying fat concentration in the presence of iron overload, and for phantom-based validation of MRI techniques for quantifying iron concentration given the confounding presence of fat.

Abstract: A system and method for acquiring spectrally-resolved three-dimensional data with a magnetic resonance imaging (“MRI”) system without frequency-encoding gradients are provided. An MRI system is directed to produce a radio frequency (“RF”) pulse that rotates net magnetization about an axis, after which a first phase-encoding gradient is established along a first direction, a second phase-encoding gradient is established along a second direction that is orthogonal to the first direction, and a third phase-encoding gradient is established along a third direction that is orthogonal to the first and second directions. Spectrally-resolved data are acquired at a point in k-space that is defined by the first, second, and third phase-encoding gradients, and is acquired by sampling a magnetic resonance signal at a plurality of time points during a period of time in which no magnetic field gradients are established by the MRI system.

Abstract: Described here is a system and method for estimating apparent transverse relaxation rate, R2*, while simultaneously performing chemical species separation (e.g., water-fat separation) using magnetic resonance imaging (“MRI”). A homodyne reconstruction of k-space datasets acquired using a partial k-space acquisition is used and the chemical species separation of the resultant images takes into account the spectral complexity of the chemical species in addition to magnetic resonance signal decay associated with transverse relaxation. Full resolution maps of R2* are thus capable of being produced while also allowing for the production of images depicting the separated chemical species that are corrected for transverse relaxation associated signal decays.

Abstract: Systems and methods for simultaneously acquiring three-dimensional data from multiple different frequency bins with a magnetic resonance imaging (“MRI”) system, and without frequency-encoding gradients, are provided. A multiband radio frequency (“RF”) pulse is used to excite spins associated with multiple different resonance frequency offsets, and a fully phase-encoded acquisition is used to acquire data, which may be spectrally-resolved data, from magnetic resonance signals formed in response to the multiband RF pulse.

Abstract: An object-based approach is used to initialize the magnetic field inhomogeneity estimation for chemical species separation, such as water-fat separation, and other imaging applications. For example, a susceptibility distribution in the subject being imaged is estimated from images reconstructed from single-echo or multi-echo k-space data and used to initialize the magnetic field inhomogeneity estimation. This approach can be applied to any complex-based chemical shift encoded chemical species separation technique and to other imaging applications, such as susceptibility-weighted imaging and quantitative susceptibility mapping. The field map can also be used to correct for image distortions and to generate magnetic field shimming values.

Abstract: A method for measuring transverse relaxation rate, R2*, corrected for the presence of macroscopic magnetic field inhomogeneities with a magnetic resonance imaging (MRI) system is provided. The method accounts for additional signal decay that occurs as a result of macroscopic variations in the main magnetic field, B0, of the MRI system, and also mitigates susceptibility-based errors and introduction of increased noise in the R2* measurements. Image data are acquired by sampling multiple different echo signals occurring at respectively different echo times. A B0 field inhomogeneity map is estimated by fitting the acquired image data to an initial signal model. Using the estimated field map, a revised signal model that accounts for signal from multiple different chemical species and for signal decay resulting from macroscopic variations in the B0 field is formed. Corrected R2* values for the different chemical species are then estimated by fitting the acquired image data to the revised signal model.

Abstract: Described here is a system and method for estimating apparent transverse relaxation rate, R2*, while simultaneously performing chemical species separation (e.g., water-fat separation) using magnetic resonance imaging (“MRI”). A homodyne reconstruction of k-space datasets acquired using a partial k-space acquisition is used and the chemical species separation of the resultant images takes into account the spectral complexity of the chemical species in addition to magnetic resonance signal decay associated with transverse relaxation. Full resolution maps of R2* are thus capable of being produced while also allowing for the production of images depicting the separated chemical species that are corrected for transverse relaxation associated signal decays.

Abstract: A system and method for acquiring spectrally-resolved three-dimensional data with a magnetic resonance imaging (“MRI”) system without frequency-encoding gradients are provided. An MRI system is directed to produce a radio frequency (“RF”) pulse that rotates net magnetization about an axis, after which a first phase-encoding gradient is established along a first direction, a second phase-encoding gradient is established along a second direction that is orthogonal to the first direction, and a third phase-encoding gradient is established along a third direction that is orthogonal to the first and second directions. Spectrally-resolved data are acquired at a point in k-space that is defined by the first, second, and third phase-encoding gradients, and is acquired by sampling a magnetic resonance signal at a plurality of time points during a period of time in which no magnetic field gradients are established by the MRI system.

Abstract: Methods are disclosed for calculating a fat fraction corrected for noise bias of one or more voxels of interest using a magnetic resonance imaging (MRI) system. A plurality of image data sets are obtained each corresponding to NMR k-space data acquired using a pulse sequence with an individual associated echo time tn. A system of linear equations is formed relating image signal values to a desired decomposed calculated data vector having a component such as a water and fat combination having zero mean noise, or having a real fat component and a real water component. A fat fraction is calculated from at least one component of the decomposed calculated data vector. In another embodiment, the system of linear equations is normalized and can directly estimate a fat fraction or a water fraction having reduced noise bias.

Abstract: A method for producing an image of a subject with a magnetic resonance imaging (MRI) system is provided. Image data is acquired at a sequence of multiple echo times occurring within two or more repetition times (TRs). Odd-numbered echoes are sampled during odd-numbered TRs, and even-numbered echoes are sampled during even-numbered TRs. Images are reconstructed and used to calculate the respective signal contributions of two or more chemical species using, for example, an IDEAL separation technique. The respective signal contributions are then used to produce images that depicts substantially only one of the chemical species. For example, separated water and fat images may be produced.

Abstract: A method for measuring transverse relaxation rate, R2*, corrected for the presence of macroscopic magnetic field inhomogeneities with a magnetic resonance imaging (MRI) system is provided. The method accounts for additional signal decay that occurs as a result of macroscopic variations in the main magnetic field, B0, of the MRI system, and also mitigates susceptibility-based errors and introduction of increased noise in the R2* measurements. Image data are acquired by sampling multiple different echo signals occurring at respectively different echo times. A B0 field inhomogeneity map is estimated by fitting the acquired image data to an initial signal model. Using the estimated field map, a revised signal model that accounts for signal from multiple different chemical species and for signal decay resulting from macroscopic variations in the B0 field is formed. Corrected R2* values for the different chemical species are then estimated by fitting the acquired image data to the revised signal model.

Abstract: A method for producing an image of a subject with a magnetic resonance imaging (MRI) system is provided. Image data is acquired at a sequence of multiple echo times occurring within two or more repetition times (TRs). Odd-numbered echoes are sampled during odd-numbered TRs, and even-numbered echoes are sampled during even-numbered TRs. Images are reconstructed and used to calculate the respective signal contributions of two or more chemical species using, for example, an IDEAL separation technique. The respective signal contributions are then used to produce images that depicts substantially only one of the chemical species. For example, separated water and fat images may be produced.

Abstract: Methods are disclosed for calculating a fat fraction corrected for noise bias of one or more voxels of interest using a magnetic resonance imaging (MRI) system. A plurality of image data sets are obtained each corresponding to NMR k-space data acquired using a pulse sequence with an individual associated echo time tn. A system of linear equations is formed relating image signal values to a desired decomposed calculated data vector having a component such as a water and fat combination having zero mean noise, or having a real fat component and a real water component. A fat fraction is calculated from at least one component of the decomposed calculated data vector. In another embodiment, the system of linear equations is normalized and can directly estimate a fat fraction or a water fraction having reduced noise bias.

Abstract: Methods are disclosed for calculating a fat fraction corrected for noise bias of one or more voxels of interest using a magnetic resonance imaging (MRI) system. A plurality of image data sets are obtained each corresponding to NMR k-space data acquired using a pulse sequence with an individual associated echo time tn. A system of linear equations is formed relating image signal values to a desired decomposed calculated data vector having a component such as a water and fat combination having zero mean noise, or having a real fat component and a real water component. A fat fraction is calculated from at least one component of the decomposed calculated data vector. In another embodiment, the system of linear equations is normalized and can directly estimate a fat fraction or a water fraction having reduced noise bias.

Abstract: A method for producing images of a subject containing M spin species using a magnetic resonance imaging (MRI) system includes obtaining N k-space data matrices from N k-space data sets acquired with the MRI system using a pulse sequence with an individual associated echo time. The k-space data matrices each include corresponding data at the same plurality of k-space locations and time stamps are tracked for each k-space location. For each k-space location, a set of linear equations in k-space is solved. The set of linear equations relates corresponding data from the N k-space data matrices, echo times and time stamps to desired calculated k-space data. Calculated data in k-space which is corrected for chemical shift is produced corresponding to each k-space location and aggregated to obtain a k-space calculated data set. The k-space calculated data set is transformed to image space to obtain a corresponding image.