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The application of selective saturation (or solvent suppression) techniques in nuclear magnetic resonance (NMR) imaging offers the opportunity to significantly expand the range of NMR studies. Data acquired at 1.44 T are presented using a two-dimensional spin-echo sequence preceded by a selective (saturating) radiofrequency pulse. Individual water or lipid proton resonances were eliminated (greater than 90% reduction in signal intensity) resulting in images of H2O or -CH2- distribution with resolution and imaging time equivalent to conventional proton images. Data are also presented demonstrating the feasibility of using selective saturation to image proton metabolites at low concentrations with a three-dimensional chemical shift imaging approach. Lactate was investigated because of its importance in the pathophysiology of ischemic insult. Phantom studies without solvent suppression failed to detect lactate at 80 mM; however, with solvent suppression, lactate at 40 mM was imaged in a reasonable time (approximately 50 min). With the favorable NMR characteristics of the methyl protons of lactate and with improvements in imaging systems, this technique may play an important role in the noninvasive evaluation of tissue ischemia using 1H NMR.

Techniques for subtraction angiography with magnetic resonance imaging have been extended from two to three dimensions, and a novel method that reduces the expected data acquisition time by at least an order of magnitude is presented. Electrocardiogram-gated three-dimensional (3D) images are acquired by Fourier transform technique, and flow contrast is obtained by subtracting pairs of images acquired at different points in the cardiac cycle. The vascular tree is shown in 3D perspective by means of a surface detection and a 3D display program. Isotropic 3D angiography requires determining the disposition of the blood vessels in a matrix of cubical voxels. Using orthodox Fourier transform technique, for an image matrix with 256 voxels to the edge, a data acquisition with 256 X 256 = 65 K phase-encodings would be needed. If gated, this would require approximately 1 day. In this study we abbreviate the data acquisition by doing only 1/64 of the usual set of phase-encoding gradient pulses. Spatial resolution is undiminished, but aliasing or "wraparound" results in each of the two phase-encoded coordinates of the 3D image. This aliasing is rectified in a two stage process. First, 64 copies of the undersampled 3D arteriogram are juxtaposed in a two-dimensional grid pattern. This assembles many copies of the complete vascular tree. Because they occupy only a small fraction of ambient volume, these copies are unlikely to overlap or collide with one another. Second, a single copy of the vascular tree is isolated by a surface detection program that takes advantage of the fact that the vascular tree is topologically connected. Studies of the abdominal aorta are presented.

The ability of the nuclear magnetic resonance signal to encode information about macroscopic motion has been recognized since the works of Hahn and Carr and Purcell. In the medical imaging setting this ability has led to a variety of ingenious magnetic resonance flow imaging schemes that ultimately may become competitive with X-ray angiography in sensitivity and specificity while remaining radically noninvasive. This work demonstrates that conventional spin-echo Fourier transform image acquisitions naturally encode a component of flow velocity that lies within the image plane. By displacing just the real part of the complex image data (phase display), the velocity distribution within the subject is revealed in image form. This method of flow imaging requires neither special pulse sequences nor image reconstruction and format software for its implementation. Further, images that intersect a flow channel longitudinally, demonstrating in-plane flow, yield an unusually large quantity of physiologic information per image. Phantom and in vivo flow images are presented. Also described is a phantom based on a rotating disk that enables calibration of the velocity/phase-shift constant for an untested pulse sequence.

The paramagnetic metal complex iron(III) ethylenebis-(2-hydroxyphenylglycine) [Fe(EHPG)-] is an effective hepatobiliary contrast agent for liver enhancement in magnetic resonance (MR) imaging. The intravenous administration of 0.2 mmol/kg of Fe(EHPG)- to rats yields a 200% increase in the signal intensity of the liver when using a T1-weighted inversion recovery pulse sequence on a 1.4 T imaging system. Biodistribution studies in rats and a rabbit, along with imaging studies in a dog at 0.6 T, confirm that the complex has significant hepatocellular uptake and appears to be excreted unaltered into the bile. Control experiments with a different iron complex, iron(III) diethylenetriaminepentaacetic acid, reveal little hepatic affinity and poor enhancement capability due to its extracellular distribution. This initial evaluation of Fe(EHPG)- demonstrates that paramagnetic metal complexes with hepatobiliary specificity are well suited for enhancement of normal liver parenchyma and may increase the sensitivity of MR in the detection of liver disease.