SYSTEMS AND METHODS FOR ULTRASHORT ECHO TIME ACTUAL FLIP ANGLE IMAGING AND VARIABLE REPETITION TIME MAGNETIC RESONANCE IMAGING

• US 20190079154A1
• Filed: 09/07/2018
• Published: 03/14/2019
• Est. Priority Date: 09/08/2017
• Status: Active Grant

• Current Assignee: Regents of the University of California (University of California)
• Original Assignee: Regents of the University of California (University of California)
• Inventors: Du, Jiang, Ma, Yajun
• Granted Patent: US 10,641,853 B2
• Time in Patent Office: Days
• CPC Class Codes: G01R 33/246 Spatial mapping of the RF magnetic field B1
• CPC Class Codes: G01R 33/4816 NMR imaging of samples with ultrashort relaxation times such as solid samples, e.g. MRI using ultrashort TE [UTE], single point imaging, constant time imaging
• CPC Class Codes: G01R 33/50 based on the determination of relaxation times , e.g. T1 measurement by IR sequences; T2 measurement by multiple-echo sequences
• CPC Class Codes: G01R 33/5602 by filtering or weighting based on different relaxation times within the sample, e.g. T1 weighting using an inversion pulse
• CPC Class Codes: G01R 33/5608 Data processing and visualization specially adapted for MR, e.g. for feature analysis and pattern recognition on the basis of measured MR data, segmentation of measured MR data, edge contour detection on the basis of measured MR data, for enhancing measured MR data in terms of signal-to-noise ratio by means of noise filtering or apodization, for enhancing measured MR data in terms of resolution by means for deblurring, windowing, zero filling, or generation of gray-scaled images, colour-coded images or images displaying vectors instead of pixels image data processing or generation, in general G06T

Abstract

Disclosed are systems and methods for accurately measuring T1 in magnetic resonance imaging (MRI) for short T2 tissues by an integrative three-dimensional Ultrashort Echo Time Actual Flip Angle Imaging Variable TR (3D UTE-AFI-VTR) technique. Also, disclosed are systems and methods for accurately measuring T1 for T2 tissues by an integrative three-dimensional Ultrashort Echo Time Actual Flip Angle Imaging Variable Flip Angle (3D UTE-AFI-VFA) technique. The disclosed methods and systems can be implemented to allow accurate T1 mapping for T2 tissues, including menisci, ligaments, tendons, myelin in gray and white matter, cortical bone, and soft tissue in whole joints.

Claims

1. A magnetic resonance imaging (MRI) method for characterizing a tissue, comprising:

(a) acquiring magnetic resonance (MR) data from a tissue using an MRI system in accordance with an ultrashort echo time actual flip angle imaging (UTE AFI) procedure to produce a longitudinal magnetization mapping function of radio frequency (RF) pulses applied to the tissue, wherein the tissue includes a short T2 tissue region and a long T2 tissue region,

wherein the acquiring the MR data includes;

(i) applying an RF pulse sequence at the tissue using an interleaved ultrashort echo time (UTE) acquisition protocol that includes two or more differing TR parameters and two or more differing gradient crusher parameters, from which the acquired MR data includes (1) a first MR data set corresponding to a first TR parameter and first gradient crusher and (2) a second MR data set corresponding to a second TR parameter and second gradient crusher; and

(ii) generating the longitudinal magnetization mapping function of the applied RF pulses from the first MR data set corresponding to short T2 tissue and from the second MR data set corresponding to long T2 tissue within the target tissue;

(b) applying a T1 mapping for the short T2 tissue region and the long T2 tissue region using a variable repetition time (VTR) fitting procedure to produce a T1 measurement associated with at least a portion of the short T2 tissue region; and

(c) producing an image providing the T1 measurements with respect to the tissue indicative of the, at least portion of, short T2 tissue region of the tissue.

2. The method of claim 1, wherein the first TR parameter is in a range of 5 ms to 50 ms, and the second TR parameter in a range of 25 ms to 400 ms;

and wherein a parameter of the first gradient crusher is in a range of 5 mT·

ms/m to 500 mT·

ms/m, and a parameter of the second gradient crusher is in a range of 250 mT·

ms/m to 2500 mT·

ms/m.

3. The method of claim 1, wherein the first TR parameter is 20 ms, and the second TR parameter is 100 ms;

and wherein the first gradient crusher includes a parameter at 180 mT·

ms/m and the second gradient crusher includes a parameter at 900 mT·

ms/m.

4. The method of claim 1, wherein the applying the T1 mapping includes:

assigning the longitudinal magnetization mapping function based on a signal ratio (r) of the first and second MR data sets and a TR ratio (n) of the first and second TR parameters in accordance with (r n−

1)/(n−

r), where r is the signal ratio of the first MR data set and second MR data set (S1/S2), and n is the TR ratio of the first TR parameter and the second TR parameter (TR1/TR2);

combining the magnetization in thermal equivalent coefficient (M₀) and the transversal mapping function (f_xy,s(α

, τ

, T2)) into a single unknown parameter (g); and

determining the T1 measurement by fitting the acquired MR data with variable TR values.

5. The method of claim 4, wherein the fitting the acquired MR data with variable TR values includes calculating T1 values using

6. The method of claim 1, wherein the tissue includes menisci, ligaments, tendons, myelin in gray and white matter, or cortical bone.

7. A magnetic resonance imaging (MRI) system for characterizing a tissue, comprising:

an MRI acquisition system including a magnet to generate a principal magnetic field (B₀), a radio frequency (RF) subsystem to apply a plurality of RF pulses to a tissue and to detect an echo signal, and a gradient subsystem to apply a plurality of gradient fields to the tissue, wherein the tissue includes a short T2 tissue region and a long T2 tissue region; and

a data processing device in communication with the MRI acquisition system and including a processor and memory, the data processing device configured to;

(a) cause the MRI acquisition system to acquire magnetic resonance (MR) data of the tissue in accordance with an ultrashort echo time actual flip angle (UTE-AFI) procedure, (b) process the acquired MR data to produce a longitudinal magnetization mapping function of the plurality of RF pulses applied to the tissue; and

(b) apply a T1 mapping for the short T2 tissue region and the long T2 tissue region using a variable repetition time (VTR) fitting procedure to produce a T1 measurement associated with at least a portion of the short T2 tissue region,

wherein the data processing device acquires the MR data by applying an RF pulse sequence at the tissue using an interleaved ultrashort echo time (UTE) acquisition protocol that includes two or more differing TR parameters and two or more differing gradient crusher parameters, from which the acquired MR data includes (1) a first MR data set corresponding to a first TR parameter and first gradient crusher and (2) a second MR data set corresponding to a second TR parameter and second gradient crusher, and

wherein the data processing device processes the acquired MR data by generating the longitudinal magnetization mapping function of the applied RF pulses from the first MR data set corresponding to short T2 tissue and from the second MR data set corresponding to long T2 tissue within the target tissue.

8. The system of claim 7, wherein the first TR parameter is in a range of 5 ms to 50 ms, and the second TR parameter in a range of 25 ms to 400 ms;

and wherein a parameter of the first gradient crusher is in a range of 5 mT·

ms/m to 500 mT·

ms/m, and a parameter of the second gradient crusher is in a range of 250 mT·

ms/m to 2500 mT·

ms/m.

9. The system of claim 7, wherein the first TR parameter is 20 ms, and the second TR parameter is 100 ms;

and wherein the first gradient crusher includes a parameter at 180 mT·

ms/m and the second gradient crusher includes a parameter at 900 mT·

ms/m.

10. The system of claim 7, wherein the data processing device applies the T1 mapping by:

assigning the longitudinal magnetization mapping function based on a signal ratio (r) of the first and second MR data sets and a TR ratio (n) of the first and second TR parameters in accordance with (r n−

1)/(n−

r), where r is the signal ratio of the first MR data set and second MR data set (S1/S2), and n is the TR ratio of the first TR parameter and the second TR parameter (TR1/TR2);

combining the magnetization in thermal equivalent coefficient (M₀) and the transversal mapping function (f_xy,s(α

, τ

, T2)) into a single unknown parameter (g); and

determining the T1 measurement by fitting the acquired MR data with variable TR values.

11. The system of claim 10, wherein the fitting the acquired MR data with variable TR values includes calculating T1 values using

12. The system of claim 7, wherein the tissue includes menisci, ligaments, tendons, myelin in gray and white matter, or cortical bone.

13. A magnetic resonance imaging (MRI) method for characterizing a tissue, comprising:

(a) acquiring magnetic resonance (MR) data from a tissue using an MRI system in accordance with an ultrashort echo time actual flip angle imaging (UTE AFI) procedure to produce a B1 inhomogeneity map of the tissue, wherein the tissue includes a short T2 tissue region and a long T2 tissue region,

wherein the acquiring the MR data includes;

(i) applying an RF pulse sequence at the tissue using an interleaved ultrashort echo time (UTE) acquisition protocol that includes two or more differing TR parameters and two or more differing gradient crusher parameters, from which the acquired MR data includes (1) a first MR data set corresponding to a first TR parameter and first gradient crusher and (2) a second MR data set corresponding to a second TR parameter and second gradient crusher; and

(ii) generating the B1 inhomogeneity map from the first MR data set corresponding to short T2 tissue and from the second MR data set corresponding to long T2 tissue within the target tissue;

(b) applying a T1 mapping for the short T2 tissue region and the long T2 tissue region using a variable flip angle (VFA) fitting procedure to produce a T1 measurement associated with at least a portion of the short T2 tissue region; and

(c) producing an image providing the T1 measurements with respect to the tissue indicative of the, at least portion of, short T2 tissue region of the tissue.

14. The method of claim 13, wherein the first TR parameter is in a range of 5 ms to 50 ms, and the second TR parameter in a range of 25 ms to 400 ms;

and wherein a parameter of the first gradient crusher is in a range of 5 mT·

ms/m to 500 mT·

ms/m, and a parameter of the second gradient crusher is in a range of 250 mT·

ms/m to 2500 mT·

ms/m.

15. The method of claim 13, wherein the first TR parameter is 20 ms, and the second TR parameter is 100 ms;

and wherein the first gradient crusher includes a parameter at 180 mT·

ms/m and the second gradient crusher includes a parameter at 900 mT·

ms/m.

16. The method of claim 13, wherein the applying the T1 mapping includes:

assigning the B1 inhomogeneity map based on a nominal flip angle, a signal ratio (r) of the first and second MR data sets, and a TR ratio (n) of the first and second TR parameters in accordance with arc cosine of ((r n−

1)/(n−

r)) divided by the nominal flip angle, where r is the signal ratio of the first MR data set and second MR data set (S1/S2), and n is the TR ratio of the first TR parameter and the second TR parameter (TR1/TR2); and

determining the T1 measurement by fitting the acquired MR data with variable flip angle values.

17. The method of claim 16, wherein the fitting the acquired MR data with variable TR values includes calculating T1 values using

18. The method of claim 13, wherein the tissue includes soft tissue in a whole joint.

19. The method of claim 18, wherein the whole joint includes a knee joint, and the soft tissue includes one or more of cartilage, meniscus, quadriceps tendon, patellar tendon, anterior cruciate ligament, posterior cruciate ligament, marrow or muscle.