MR imaging of synchronous spin motion and strain waves
AssigneeMayo Foundation for Medical Education and Research
InventorRichard L. Ehman
Life of this patent
Estimating the term…
Abstract
A scan using an NMR imaging system is carried out while applying an oscillating stress to the object being imaged. An alternating magnetic field gradient synchronized with the applied stress is employed in the NMR imaging pulse sequence to detect and measure synchronous spin motion throughout the field of view. The direction of the alternating gradient and/or the applied stress may be changed to measure and image the elastic properties of the object.
Claims41
A method for producing an image indicative of a mechanical characteristic of tissues, the steps comprising:
- a) applying a polarizing magnetic field to the tissues;
- b) irradiating the tissues with an RF excitation field that produces transverse magnetization in spins in said tissues;
- c) applying a magnetic field gradient to the spins which alternates in polarity;
- d) applying a stress to the tissues which varies in magnitude in synchronism with the alternation in the magnetic field gradient polarity;
- e) acquiring an NMR signal produced by the transversely magnetized spins;
- f) repeating steps a) through e) to acquire a set of said NMR signals from which a first image may be reconstructed;
- g) repeating steps a) through f) to acquire NMR signals from which a second image may be constructed;
- h) producing a third image indicative of the difference in phase between the NMR signals acquired for said first and second images;
- and
- i) producing from said third image a fourth image which indicates a mechanical property of the tissues.
An NMR system for producing an image which indicates a mechanical characteristic of a subject placed within the field of view of the NMR system, which comprises:
- a transducer coupled to the subject for imparting mechanical wave motion to spins located in the subject;
- a magnet for producing a polarizing magnetic field in the field of view;
- an RF transmitter for producing transverse magnetization in the spins;
- an RF receiver for receiving NMR signals produced by the spins;
- magnetic field gradient means for producing a magnetic field in the field of view having a gradient in a first direction;
- a pulse generator for producing a pulse sequence in which the RF transmitter produces transverse magnetization in the spins, the magnetic field gradient means produces an alternating magnetic field gradient that imparts a phase shift in the NMR signals due to the wave motion of the spins, and the RF receiver receives the NMR signals produced by the spins;
- and
- an image reconstructor for reconstructing a phase image from the received NMR signals and which employs the phase information therein to indicate the mechanical characteristic of the subject at each pixel location in the image.
A method for producing an image with an NMR imaging system which indicates a mechanical characteristic of a subject within the field of view of the NMR imaging system, the steps comprising:
- a) imparting mechanical wave motion to spins located in the subject;
- b) conducting a scan of the subject with the NMR imaging system using a pulse sequence in which an alternating magnetic field gradient is employed to impart a phase shift in acquired NMR data due to the wave motion of the spins;
- and
- c) reconstructing a phase image from the NMR data acquired during the scan and employing the phase information therein to indicate the mechanical characteristic of the subject at each pixel location in the image.
A method for producing an image with an NMR imaging system which indicates a mechanical characteristic of a subject within the field of view of the NMR imaging system, the steps comprising:
- a) conducting a scan of the subject with the NMR imaging system to acquire a first and a second NMR data set, the first NMR data set being acquired by:
- i) imparting mechanical wave motion to spins located in the subject by energizing a transducer which applies an alternating stress to the subject;
- ii) performing an imaging pulse sequence with the NMR imaging system in which an alternating magnetic field gradient is employed to impart a phase shift in the acquired first NMR data set due to the wave motion of the spins;
- the second NMR data set being acquired by:
- iii) changing the energization of said transducer from that used during the acquisition of the first NMR data set;
- iv) performing substantially the same imaging pulse sequence used to acquire the first NMR data set;
- b) reconstructing a phase image by combining the first and second NMR data sets to indicate the difference in phase of the first and second NMR data sets at each pixel of the phase image;
- and
- c) displaying an image of a mechanical characteristic of the subject using the phase image.
Dependencies are inferred from the claim text.