Biomedical subjects

D Spielman

Publications and source records attributed to D Spielman.

6 recordsLinked to original sources

PubMed1992

Inhomogeneity correction for in vivo spectroscopy by high-resolution water referencing.

One of the most common sources of distortion in in vivo spectroscopy is the inhomogeneity of the main magnetic field. This effect is particularly problematic when performing spectroscopic imaging, as the shim cannot be simultaneously optimized for all voxels. In this paper we present a technique to measure inhomogeneity rapidly, then show how to use the measurement to improve the analysis of the spectrum. This technique can be applied in conjunction with any spectroscopic localization method and any spectral quantitation algorithm. We present results from spectroscopic imaging of phantoms, then show application to a single-voxel water-suppressed proton brain study. We find that the quantitation of the in vivo spectrum is made immune to inhomogeneous line broadening.

Brain↗

PubMed1991

1H spectroscopic imaging using a spectral-spatial excitation pulse.

Excellent water suppression is required to perform in vivo 1H spectroscopic experiments. However water suppression is difficult due to both B0 and RF inhomogeneities. These inhomogeneities are particularly troublesome in spectroscopic imaging experiments where water suppression is required throughout some large region of interest. In this paper, we propose the use of spectral-spatial excitation pulses for such experiments. These two-dimensional pulses are shown to provide water suppression that is insensitive to a range of B0 and RF variations while simultaneously providing spatial localization. Experimental results including images (with voxel volumes ranging from 3.4 to 1.5 cc) of various brain metabolites from both a normal volunteer and a patient with a metastatic lung carcinoma are presented.

Brain↗

PubMed1991

Spectroscopic imaging with multidimensional pulses for excitation: SIMPLE.

Proton spectroscopy and spectroscopic imaging in the human brain require the elimination of both water and lipid signals. Strong lipid signals from subcutaneous fat are usually eliminated by confining the excited volume to lie wholly within the skull. Water suppression, however, can be difficult due to both B0 and RF inhomogeneities, which are particularly troublesome in imaging experiments where a relatively large region-of-interest (ROI) is typical. In this paper, we discuss the use of multidimensional selective-excitation pulses (e.g., pulses that are simultaneously selective along two axes) to both define the ROI and provide the necessary water suppression. Pulse sequences providing three-dimensional localization along with water suppression that is insensitive to a range of B0 and RF inhomogeneities are described. Spectra and spectroscopic images (voxel volume = 3.4 cc. acquisition time = 38 min) of various 1H metabolites from a patient with an astrocytoma show clear differences between normal and cancerous tissues and demonstrate the ability of these techniques to be used in vivo.

Astrocytoma↗

PubMed1989

Water referencing for spectroscopic imaging.

A water referencing algorithm for addressing the spectroscopic imaging problems of low SNR and main field inhomogeneities is proposed. Using the location of the water peak from each voxel and additional a priori information results in a parametric estimation problem. Optimum estimates of the desired metabolite concentration can then be computed and displayed in an image format. The algorithm is shown to be very stable in the presence of noise and is insensitive to Bo inhomogeneity. A detailed error analysis as well as extensions to the basic data model are also discussed. Results from both 1H and 31P experiments are presented to verify the predicted good performance even with extremely low signal-to-noise ratio data.

Algorithms↗

PubMed1989

A fast spectroscopic imaging method using a blipped phase encode gradient.

Many methods of chemical shift imaging have been described recently. In most cases, these methods couple resolution and imaging time. The most flexible methods use time-varying gradients to cover a large region of k space on each excitation. We present here a new time-varying gradient method that offers a decrease in scan time (when SNR is sufficient), simplifies the reconstruction problem by retaining an essentially rectilinear sampling grid, and makes efficient use of scan time by minimizing gradient reversals. Implementation on a standard high-field imaging system (GE Signa) is discussed, and experimental results are shown. An application of the method to the generation of water reference data sets is described.

Fourier Analysis↗

PubMed1986

In vivo spectroscopic magnetic resonance imaging using estimation theory.

The ability to map spectroscopic components for in vivo application is a highly desirable goal. Thusfar it has been unavailable because of the low SNR inherent in the measurement of each voxel. In this paper we deal with this low SNR in two ways. First, estimation theory, using a priori data, is used to estimate the amplitudes in each voxel. Second, the resultant estimates are presented in an image format so that they are readily correlated with anatomical and physiological patterns. A computer simulation is presented of a case where the SNR is -10 dB. At this level, conventional Fourier transform spectroscopy provides meaningless results. Using estimation theory and an imaging format, a simulated lesion is readily seen.

Computers↗