th  - 1987 - 51st ENC Conference

WF62
CONVOLUTION CHEMICAL SHIFT IMAGING
M.D. COCKMAN- (a,b) and T.H. MARECI (b,c)
Departments of (a)Chemistry, (b)Radiology, and (c)Physics
University of Florida, Gainesville, FL 32610
One of the challenges of NMR imaging is the simultaneous
collection of spatial and chemical information. However,
non-selectlve Fourier chemical shift imaging methods, in
which spatial information is obtained for every chemical
resonance in a spectrum, hmve been time-consuming and require
at least a three-dlmensional Fourier transformation
algorithm. By a straightforward modification of the method of
Sepponen and coworkers (1), we have developed a new method of
non-selectlve chemical shift imaging which requires less
total data acquisition time and a simpler processing scheme.
The new method is accomplished in part by requiring that
the controlled inhomogeneity introduced by the gradients be
smaller than the inherent inhomogeneity which gives rise to
the chemical shift effect. The use of small gradient
strengths has the benefit of increasing the S/N ratio of the
resulting image. A second requirement of our method is that
the magnitudes of a time delay, during which chemical shift
encoding occurs, and a gradient, during which spatial
encoding occurs, are changed in concert with each other. This
simultaneous stepping has the effect of creating a modulation
function whose Fourier transform is the convolution of a
function of spatial position and a function of chemical shift
frequency. Our technique has therefore been named
aconvolution chemical shift imaging'. This imaging scheme
introduces spectral information into all spatial imaging
dimensions. Thus a three-dimensional chemical shift imaging
experiment can be reduced to a two-dimensional convolution
chemical shift imaging experiment which retains the same
information.
Convolution chemical shift imaging requires that the
spatial field of view in frequency units must be on the order
of or smaller than the chemical shift separation of interest
if one wishes to resolve a spatial image from each chemical
shift species. Therefore the method is best suited for small
objects at high field.
The convolution chemical shift imaging method has been
implemented on a General Electric CSI-2 imager/spectrometer.
Examples of the imaging of phantoms using the method are
presented.
This research was supported in part by the NIH Biotechnology
Resource Grant (P41-RR-02278) and the Veterans Administration
Medical Research Service.
(1) R.E. Sepponen, J.T. Sipponen, and J.I. Tanttu,
Assist. Tomogr. 8, 585 (1984).
J. Comput.