Magnetic resonance imaging of amyloid plaque in the brain
Amyloid plaque in the brain of a subject is imaged in an MRI system with or without the use of a contrast agent. Contrast is achieved using a spin-echo pulse sequence that is both respiratory gated and cardiac gated to reduce motion artifacts at the very high image resolution required to see plaque. A preparatory pulse sequence is used to insure longitudinal magnetization remains constant for all the acquired views even if the effective TR changes during the scan due to irregular breathing.
1. A method for acquiring an in vivo, high resolution magnetic resonance image from a subject, the steps comprising:
a) producing a trigger signal when the subject is in a preselected phase of the subject's respiratory cycle;
b) performing a pulse sequence to acquire an NMR signal when the trigger signal is produced, the pulse sequence including:
b)i) performing a preparatory pulse sequence to create uniform view-to-view longitudinal magnetization in the presence of non-uniform view-to-view trigger times in which the longitudinal magnetization in a region of interest in the subject is set to a preset amount by applying an rf nulling pulse with a substantially 90° flip angle followed by a preset null recovery time (TN);
b)ii) producing transverse magnetization in the region of interest by applying an rf excitation pulse after step b)i);
b)iii) producing an NMR echo signal at a preselected time (TE) after application of the rf excitation pulse;
b)iv) acquiring the NMR echo signal in the presence of a readout magnetic field gradient;
c) changing a magnetic field gradient in the pulse sequence and repeating step b) to acquire another NMR signal; and
d) repeating step c) until sufficient NMR echo signals are acquired to reconstruct an image.
2. The method as recited in claim 1 in which the region of interest is in the subject's brain.
3. The method as recited in claim 2 in which the region of interest is in a portion of the subject's brain containing amyloid plaque and the NMR echo signal is produced in step b)iii) by producing an rf refocusing pulse.
4. The method as recited in claim 1 in which the rf nulling and rf excitation pulses are adiabatic half-passage RF pulses that flip substantially all of the longitudinal magnetization into the transverse plane.
5. The method as recited in claim 1 in which the pulse sequence performed in step b) further includes:
producing a first selective RF refocusing pulse in the presence of a first gradient after step b)ii) to refocus the transverse magnetization in a first slice through the region of interest; and
producing a second selective RF refocusing pulse in the presence of a second gradient after step b)ii) to refocus the transverse magnetization in a second slice through the region of interest.
6. The method as recited in claim 5 in which the selective RF refocusing pulses are hyperbolic scant type pulses.
7. A method for acquiring an in vivo, high resolution magnetic resonance image from a subject, the steps comprising:
a) producing a first trigger signal when the subject is in a preselected phase of the subject's respiratory cycle;
b) performing a preparatory pulse sequence when the first trigger signal is produced by applying an rf nulling pulse followed by a preset null recovery time (TN);
c) producing a second trigger signal when the subject is in a preselected phase of the subject's cardiac cycle;
d) performing an imaging pulse sequence to acquire an NMR echo signal from a selected region of interest in the subject after the second trigger signal is produced; and
e) repeating steps a) through d) until sufficient NMR echo signals are acquired to reconstruct an image.
8. The method as recited in claim 7 in which the rf nulling pulse has a substantially 90° flip angle.
9. The method as recited in claim 7 in which step d) includes:
d)i) producing transverse magnetization in the region of interest by applying an rf excitation pulse;
b)ii) producing an NMR echo signal at a preselected time (TE) after application of the rf excitation pulse; and
d)iii) acquiring the NMR echo signal in the presence of a readout magnetic field gradient.
10. The method as recited in claim 9 in which the region of interest is in a portion of the subject's brain containing amyloid plaque and the NMR echo signal is produced in step d)ii) by producing an rf refocusing pulse.
11. The method as recited in claim 10 in which step d) further includes:
producing a first selective RF refocusing pulse in the presence of a first gradient after step d)i) to refocus the transverse magnetization in a first slice through a region of interest; and
producing a second selective RF refocusing pulse in the presence of a second gradient after step d)i) to refocus the transverse magnetization in a second slice through the region of interest.