Fast two-point mapping of the bound pool fraction and cross-relaxation rate constant for mri
AssigneeUniversity of Washington
InventorVasily Yarnykh
Life of this patent
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Abstract
A two-point reconstruction technique provides an efficient clinical method for measuring parametric bound pool fraction and cross-relaxation rate constant spatial distributions in biological objects from two experimental measurements based on magnetization transfer effect obtained in magnetic resonance imaging (MRI). The method is based on linearization of an analytical pulsed magnetization transfer mathematical model so that spatial distribution maps of the bound pool fraction and cross-relaxation rate constant can be obtained in a time-efficient manner by using only two experimental magnetization transfer images of the bio-logical object in which water and macromolecules are present.
Claims51
A method for efficiently determining spatial distribution images of a macromolecular proton fraction and a cross-relaxation rate constant, in a biological object, comprising the steps of:
- (a) producing a first and a second magnetic resonance (MR) image with magnetization transfer contrast characterized by a first and a second signal intensity;
- (b) producing a reference MR image without magnetization transfer;
- (c) calculating a first and a second saturation rate respectively corresponding to the first and second MR images;
- (d) producing a T1 map for the spatial distribution of the longitudinal relaxation time of the biological object;
- and
- (e) determining said spatial distribution images of the macromolecular proton fraction and the cross-relaxation rate constant based on said first and second MR images, said reference MR image, said first and second saturation rates, and said T1 map, such that additional magnetic resonance images are not required to construct the macromolecular proton fraction and the cross-relaxation rate constant spatial distribution images, thereby substantially reducing a time required to produce the spatial distribution images of the macromolecular proton fraction and the cross-relaxation rate constant in the biological object.
A two-point magnetic resonance image reconstruction method for producing parametric maps of an object including water and macromolecules, comprising the steps of:
- (a) causing a magnetization transfer effect to take place between free protons of water and bound protons of macromolecules at a first and a second measurement point;
- (b) determining a first signal intensity based on said first measurement point, and a second signal intensity based on said second measurement point;
- (c) computing a first value of a linear variable based on the first signal intensity, and a second value of said linear variable based on the second signal intensity, such that said first and second values of said linear variable define a linear function of a saturation variable;
- and
- (d) constructing spatial distribution images of a bound pool fraction and a cross-relaxation rate constant, based on results of the step of computing, in an efficient and timely manner.
A method for simultaneous measurement of spatial distributions of a macromolecular proton fraction and a cross-relaxation rate constant in an object by magnetic resonance imaging, comprising the steps of:
- (a) acquiring:
- (i) a first magnetic resonance (MR) image using a pulse sequence with a first off-resonance saturation;
- (ii) a second MR image using a pulse sequence with a second off-resonance saturation that is different from the first off-resonance saturation;
- (iii) a reference MR image using a pulse sequence without off-resonance saturation;
- and
- (iv) a plurality of MR images for use in determining longitudinal relaxation times in the object;
- (b) determining a spatial distribution of the longitudinal relaxation times in the object;
- (c) determining a first and a second saturation rate corresponding to the first and the second MR images produced using the pulse sequence with the first off-resonance saturation and the second off-resonance saturation;
- and
- (d) producing images of the spatial distributions of the macromolecular proton fraction and the cross-relaxation rate constant in the object based on:
- (i) said MR images;
- (ii) said image of the spatial distribution of the longitudinal relaxation times;
- and
- (iii) said first and second saturation rates.
A system for producing spatial distribution images of a bound pool fraction and a cross-relaxation rate constant spatial in a biological object, comprising:
- (a) a magnetic resonance imaging (MRI) apparatus adapted for producing magnetic resonance (MR) images of the biological object and for causing a magnetization transfer effect to take place;
- and
- (b) a controller coupled to the MRI apparatus to control it, said controller carrying out a plurality of functions, including:
- (i) producing a first MR image, a second MR image, and a reference MR image of the biological object;
- (ii) approximating a plurality of linear functions corresponding to said first and second MR images;
- and
- (iii) determining said spatial distribution images of the bound pool fraction and the cross-relaxation rate constant based on said plurality of linear functions, such that an additional series of MR images is not required to construct the bound pool fraction and the cross-relaxation rate constant spatial distribution images, thereby substantially reducing the time required to produce the spatial distribution images of the bound pool fraction and the cross-relaxation rate constant in the biological object.
A two-point measurement method for determining a bound pool fraction and a rate constant of magnetic cross-relaxation between a bound pool and a free pool in an object containing at least two pools of magnetic nuclei with substantially different mobility, comprising the steps of:
- (a) applying a first radiofrequency (RF) saturation with a first predefined power and a first predefined frequency;
- (b) detecting a first nuclear magnetic resonance (NMR) signal produced after applying the first RF saturation;
- (c) applying a second RF saturation with a second predefined power and a second predefined frequency such that either the second predefined power or the second predefined frequency is substantially different from the first predefined power or the first predefined frequency, respectively;
- (d) detecting a second NMR signal produced after applying the second RF saturation;
- (e) measuring a longitudinal relaxation time T1 of the object;
- (f) determining a reference NMR signal;
- (g) computing a first saturation rate of the bound pool from the first predefined power, the first predefined frequency, and a predefined transverse relaxation time of the bound pool;
- (h) computing a second saturation rate of the bound pool from the second predefined power, the second predefined frequency, and the predefined transverse relaxation time of the bound pool;
- (i) computing a first saturation rate of the free pool from the first predefined power, the first predefined frequency, and a predefined transverse relaxation time of the free pool;
- (j) computing a second saturation rate of the free pool from the second predefined power, the second predefined frequency, and the predefined transverse relaxation time of the free pool;
- (k) computing a first value of a linear variable that is an algebraic function of the first normalized NMR signal, the reference NMR signal, the first saturation rate of the bound pool, the first saturation rate of the free pool, and the longitudinal relaxation time T1, such that said linear variable is a substantially linear function of a saturation rate of the bound pool;
- (l) computing a second value of said linear variable that is an algebraic function of the second normalized NMR signal, the reference NMR signal, the second saturation rate of the bound pool, the second saturation rate of the free pool, and the longitudinal relaxation time Ti;
- and
- (m) computing the bound pool fraction and the rate constant of magnetic cross-relaxation in the object based on the first value of the linear variable, the second value of the linear variable, the first saturation rate of the bound pool, the second saturation rate of the bound pool, and the longitudinal relaxation time T1.
A method for efficiently determining a macromolecular proton fraction and a cross-relaxation rate constant, in a biological object, for use in a clinical environment, comprising the steps of:
- (a) producing a first magnetic resonance (MR) image with a magnetization transfer contrast characterized by a first signal intensity, and a second MR image with a magnetization transfer contrast characterized by a second signal intensity;
- (b) producing a reference MR image without magnetization transfer;
- (c) calculating a first saturation rate, and a second saturation rate respectively corresponding to the first MR image, and the second MR image;
- (d) producing a T1 map for a spatial distribution of a longitudinal relaxation time of the biological object;
- and
- (e) determining the macromolecular proton fraction, and the cross-relaxation rate constant based on said first and second MR images, said reference MR image, said first and second saturation rates, and said T1 map, to aid in diagnosing a disease by detecting abnormal values of either the macromolecular proton fraction or the cross-relaxation rate constant in the biological object.
Dependencies are inferred from the claim text.