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High Resolution Minimal Scan Technique for Localized Magnetic Resonance Chemical Shift Imaging

IP.com Disclosure Number: IPCOM000037046D
Original Publication Date: 1989-Nov-01
Included in the Prior Art Database: 2005-Jan-29
Document File: 3 page(s) / 53K

Publishing Venue

IBM

Related People

Feig, E: AUTHOR

Abstract

A method for providing a chemical shift image of a windowed chemical slice by using high resolution magnetic resonance is provided. The reconstructed image is localized by windowing in two dimensions, and the method for accomplishing the same generally comprises: with a coherent detector tuned so that the proton peak for fat is set to zero,

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High Resolution Minimal Scan Technique for Localized Magnetic Resonance Chemical Shift Imaging

A method for providing a chemical shift image of a windowed chemical slice by using high resolution magnetic resonance is provided. The reconstructed image is localized by windowing in two dimensions, and the method for accomplishing the same generally comprises: with a coherent detector tuned so that the proton peak for fat is set to zero,

(a) selectively exciting a body along a desired plane;

(b) encoding along a first direction (x) by waiting for a period tk and then providing a linear gradient (A), and along a perpen dicular direction (y) by waiting for period tk and providing a fixed linear gradient;

(c) reexciting the body with a spin-echo;

(d) measuring the induced free induction decay in the presence of a time varying gradient which is a superposition of the fixed linear gradient and a cosinusoidal gradient with a first predetermined amplitude and frequency in the second (y) direction, and a cosinusoidal gradient with a predetermined amplitude and frequency in the first direction;

(e) tuning the coherent detector so that tkw2 = f, where w2 is the proton peak for water, and repeating steps (a) through (d); and (f) processing the measured free induction decays by multiplying the measurements by ei(ma + nb)t, low-pass filtering the results according to a filter which is dictated by the desired windows, and Fourier transforming the filtered values with respect to the linear gradient (A) to provide a reconstruction of sums and differences of chemical shift images of a slice of the body which is windowed in two dimensions.

(g) adding and subtracting the two images to separate the individual chemical shift componets. The provided method limits the number of voltage inputs into the magnetic resonance system which are required to obtain a localized reconstruction. As a result, scanning time is significantly reduced.

The excitation, encoding, and induced free induction decay measurement of a body having a three dimensional density function d(x,y,w) is indicated in the figure, where w is a chemical shift coordinate. It is recognized that the chemical shift spectrum of protons has two distinct peaks, w1 and w2, corresponding to fat and water. As shown by pulse 10, a desired plane of the body is selectively excited. At 15, a delay of tk is inserted prior to encoding. At 20, the excited plane is encoded along the x direction with a linear gradient A which is varied over time (i.e., from scan to scan), and along the y direction with a fixed linear gradient. A refocusing spin-echo pulse is applied at 30, and measurements f(A,tk,t) over time are made at 40 as the applied voltage in the x and...