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Quantitative proton chemical‐shift imaging
Author(s) -
Buxton Richard B.,
Wismer Gary L.,
Brady Thomas J.,
Rosen Bruce R.
Publication year - 1986
Publication title -
magnetic resonance in medicine
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.696
H-Index - 225
eISSN - 1522-2594
pISSN - 0740-3194
DOI - 10.1002/mrm.1910030609
Subject(s) - phase (matter) , proton , nuclear magnetic resonance , range (aeronautics) , relaxation (psychology) , analytical chemistry (journal) , chemistry , mathematics , physics , materials science , chromatography , psychology , social psychology , organic chemistry , quantum mechanics , composite material
Abstract Recently W. T. Dixon ( Radiology 153 , 189 (1984)) introduced a simple method of proton chemical‐shift imaging which requires only two images, a conventional (in‐phase) image and an image in which fat and water protons are 180° out of phase during signal acquisition, to separate the signals from fat and water protons. We have tested the application of this method to the quantitative determination of fat content and fat and water longitudinal relaxation times, and analyzed the effects of random and systematic errors. Ten phantoms were constructed with a range of fat contents (0–50% by weight) and water T 1 's (300–800 ms). Fat and water T 1 's were measured with a 0.6‐T clinical imaging system in two ways: (1) using the system as a spectrometer with all gradients off, and (2) from least‐squares fits to in‐phase and out‐of‐phase image data made with six values of T R . The image‐derived values of water T 1 agreed well with spectrometer‐derived values ( r = 0.97) and the image derived fat fraction correlated strongly with the fat fraction by weight ( r = 0.995). The effects of random and systematic errors were analyzed for a minimum data set of four images: in‐phase and out‐of‐phase images at two values of T R . The pair of T R values which minimize the variance in water T 1 were calculated, and for these pulse sequences the effects of two potential systematic errors were calculated: (1) inhomogeneities in the main field, which will reduce the intensity in out‐of‐phase images compared to in‐phase images even for pure water samples, and (2) an incorrect shift of the 180° pulse in the out‐of‐phase pulse sequence, corresponding to an inaccurate assumed chemical shift. With careful attention to such systematic effects the Dixon method is capable of producing reliable quantitative measurements. © 1986 Academic Press, Inc.