Imaging elastic properties of the lung with magnetic resonance elastography
View Patent ↗A noble gas is administered to a subject to fill the lungs and magnetic resonance elastography image data is acquired while vibrations are applied to the chest wall. Shear waves are established in the gas-filled lungs by the vibrations and a shear modulus image is reconstructed from the MRE image data that may be used in the diagnosis of lung disease.
1. A method for producing an image of the lung of a subject with a magnetic resonance imaging (MRI) system, the steps comprising:
a) acquiring image data from the lung using the MRI system and a pulse sequence that solicits an NMR response from lung tissue;
b) reconstructing a lung density map from the image data acquired in step a) that indicates the density of lung tissue at each image pixel;
c) filling the lung with a gas that includes a NMR responsive gas;
d) acquiring magnetic resonance elastography (MRE) image data from the lung using the MRI system and a second pulse sequence that solicits an NMR response from the NMR responsive gas;
e) reconstructing a spatial frequency map from the MRE image data acquired in step d) that indicates frequency of a strain wave at each image pixel; and
f) calculating a shear modulus image from the lung density map and the spatial frequency map that indicates mechanical stiffness at each image pixel.
2. The method as recited in claim 1 in which the pulse sequence used in step b) indicates the density of hydrogen protons.
3. The method as recited in claim 1 in which the NMR responsive gas is a noble gas.
4. The method as recited in claim 3 in which the NMR responsive gas is hyperpolarized helium.
5. The method as recited in claim 1 in which step d) includes;
d)i) applying an oscillating stress to the lung at a selected frequency;
d)ii) acquiring MRE image data with the second pulse sequence;
d)iii) acquiring MRE reference image data with the second pulse sequence and without applying the oscillating stress; and
step e) includes:
e)i) reconstructing a phase image with the MRE image data acquired in step d)ii);
e)ii) reconstructing a reference phase image with the MRE reference image data acquired in step d)iii);
e)iii) producing a phase difference image by subtracting the reference phase image from the phase image; and
e)iv) calculating the spatial frequency map from the phase difference image.
6. The method as recited in claim 1 in which step d) includes:
d)i) placing an acoustic device against a chest wall containing the lung;
d)ii) energizing the acoustic device during acquisition of MRE image data to produce longitudinal stress waves in the chest wall at a selected frequency.
7. The method as recited in claim 6 in which the selected frequency is in the range of 50 to 200 Hz.
8. The method as recited in claim 6 in which the acoustic driver is placed against the axilla of the subject.