System and method for T1 relaxation enhanced steady-state MRI
A method for generating magnetic resonance (MR) images of a subject includes performing, using a magnetic resonance imaging (MRI) system, a steady-state pulse sequence to acquire MR data from a region of interest in the subject. The steady-state pulse sequence includes a contrast-modifying (CM) radio frequency (RF) pulse applied periodically at a predetermined time interval followed by a gradient spoiler pulse. The CM RF pulse has a flip angle with a value determined based on a minimum Ernst angle for a set of one or more background tissues in the region of interest that the CM RF pulse is configured to suppress with respect to a tissue of interest. The method further includes generating an image with Ti contrast based on the acquired MR data.
1 . A method for generating magnetic resonance (MR) images of a subject, the method comprising:
performing, using a magnetic resonance imaging (MRI) system, a steady-state pulse sequence to acquire MR data from a region of interest in the subject, the steady-state pulse sequence comprising a contrast-modifying (CM) radio frequency (RF) pulse for T 1 -weighting applied periodically at a predetermined time interval throughout an acquisition of a plurality of echo signals using a plurality of imaging RF pulses, the CM RF pulse applied at each predetermined time interval prior to acquisition of at least two of the plurality of echo signals, and the CM RF pulse having a flip angle with a value determined based on a minimum Ernst angle for a set of one or more background tissues in the region of interest that the CM RF pulse is configured to suppress with respect to a tissue of interest; and
generating an image with T 1 contrast based on the acquired MR data.
2 . The method according to claim 1 , further comprising displaying the generated image on a display.
3 . The method according to claim 1 , wherein the set of one or more background tissues includes a fluid and the tissue of interest is blood.
4 . The method according to claim 1 , wherein the set of one or more background tissues includes an unenhanced myocardium and the tissue of interest is enhanced myocardium.
5 . The method according to claim 1 , wherein the set of one or more background tissues includes normal tissue and the tissue of interest is an abnormally enhancing tissue.
6 . The method according to claim 5 , wherein the abnormally enhancing tissue is one of a tumor or inflammation.
7 . The method according to claim 1 , wherein the flip angle of the CM RF pulse has a value greater than half the minimum Ernst angle for the set of one or more background tissues in the region of interest that the CM RF pulse is configured to suppress with respect to the tissue of interest and is determined using:
α
CM
>
0.5
×
cos
-
1
(
e
-
τ
/
T
1
min
)
where α CM is the flip angle in degrees of the CM RF pulse, cos −1 is the inverse cosine function yielding degrees, e is the mathematical constant approximately equal to 2.71828, t is the predetermined time interval, and T 1 min is the shortest longitudinal relaxation time in the set of one or more background tissues the CM RF pulse is configured to suppress.
8 . The method according to claim 1 , wherein the steady-state pulse sequence further comprises an α/2 store RF pulse applied prior to the CM RF pulse and an α/2 restore RF pulse applied following to the CM RF pulse.
9 . The method according to claim 1 , wherein the CM RF pulse is slice selective.
10 . The method according to claim 1 , wherein the predetermined time interval is greater than 50 ms.
11 . A magnetic resonance imaging (MRI) system comprising:
a magnet system configured to generate a polarizing magnetic field about at least a portion of a subject;
a plurality of gradient coils configured to apply at least one gradient field to the polarizing magnetic field;
a radio frequency (RF) system configured to apply an excitation field to the subject and to receive MR data from the subject; and
a computer system programmed to:
perform, using the MRI system, a steady-state pulse sequence to acquire MR data from a region of interest in the subject, the steady-state pulse sequence comprising a contrast-modifying (CM) radio frequency (RF) pulse for T 1 -weighting applied periodically at a predetermined time interval throughout an acquisition of a plurality of echo signals using a plurality of imaging RF pulses, the CM RF pulse applied at each predetermine time interval prior to acquisition of at least two of the plurality of echo signals, and the CM RF pulse having a flip angle with a value determined based on a minimum Ernst angle for a set of one or more background tissues in the region of interest that the CM RF pulse is configured to suppress with respect to a tissue of interest; and
generate an image with T 1 contrast based on the acquired MR data.
12 . The system according to claim 11 , further comprising a display and wherein the computer system is further programmed to display the generated image on the display.
13 . The system according to claim 11 , wherein the set of one or more background tissues includes a fluid and the tissue of interest is blood.
14 . The system according to claim 11 , wherein the set of one or more background tissues includes unenhanced myocardium and the tissue of interest is enhanced myocardium.
15 . The system according to claim 11 , wherein the set of one or more background tissues includes a normal tissue and the tissue of interest is abnormally enhancing tissue.
16 . The system according to claim 15 , the abnormally enhancing tissue is one of a tumor or inflammation.
17 . The system according to claim 11 , wherein the flip angle of the CM RF pulse has a value greater than half the minimum Ernst angle for the set of one or more background tissues in the region of interest that the CM RF pulse is configured to suppress with respect to the tissue of interest and is determined using:
α
CM
>
0.5
×
cos
-
1
(
e
-
τ
/
T
1
min
)
where α CM is the flip angle in degrees of the CM RF pulse, cos −1 is the inverse cosine function yielding degrees, e is the mathematical constant approximately equal to 2.71828, t is the predetermined time interval, and T 1 min is the shortest longitudinal relaxation time in the set of one or more background tissues the CM RF pulse is configured to suppress.
18 . The system according to claim 11 , wherein the pulse sequence further comprises an α/2 store RF pulse applied prior to the CM RF pulse and an α/2 restore RF pulse applied following to the CM RF pulse.
19 . The system according to claim 11 , wherein the CM RF pulse is slice selective.
20 . The system according to claim 11 , wherein the predetermined time interval is greater than 50 ms.