A research-type 4 T whole-body magnet, built by Siemens AG, Erlangen, FRG, was used to investigate magnetic resonance at high field strengths. Designs for head and body coils operating at 170 MHz are described. Proton images of the human head and body are degraded by dielectric resonances and penetration effects. The nature of the dielectric resonances was demonstrated in phantoms containing distilled and saline doped water. Radiation damping at 170 MHz generates secondary echoes after a spin echo sequence. This effect was observed in phantoms and with reduced amplitude in the human head. Hydrogen spectra of the human head were selected utilizing stimulated and spin echoes. The latter technique allows the volume size to be reduced to 1 cm3. Examples of brain tumors that have been routinely investigated with volumes of 8 cm3 are given. Natural abundance carbon and phosphorus spectra of muscle and liver demonstrate the expected increase in spectral resolution and signal to noise ratio. Carbon spectra from the liver show the glycogen signal. Fluorine spectroscopy was used to study the time course of the absorption and emptying of a fluorinated antibiotic from the human stomach.

The clinical potential and limitations of magnetic resonance imaging and spectroscopy at 4 T were investigated with the use of a newly constructed system, which has been in use since January 1987. The magnet has a warm bore that measures 1.25 m in diameter, and its homogeneity in a sphere with a diameter of 50 cm is better than +/- 2.5 ppm. It was hypothesized that the improvement in the signal-to-noise ratio (S/N) afforded by the higher field strength would be useful in reducing imaging time and in improving spatial resolution. In experiments in human volunteers, believed to be the first in which an entire human body was exposed to a magnetic flux density of that magnitude, the subjects were exposed to 4 T for 10-30 minutes. They showed no changes in well-being or heart activity. The expected gain in spectral resolution due to chemical-shift scaling was achieved with the 4-T system, and an improvement in S/N was verified for phosphorus at 34 and 68 MHz. In sodium imaging, the high flux density appears to be useful in reducing imaging time, which should increase the usefulness of sodium imaging in evaluating brain tumors and strokes. In spectroscopy, the increase in flux density improves the quality of the spectra.

In 27 patients with low and high grade gliomas (n = 17), meningiomas (n = 4), and other supratentorial tumors and lesions (n = 6), the results of sodium-23 MR imaging with high spatial resolution were compared to CT and proton MRI. The Na MR studies were performed with a 4.0-T whole-body MR system and an isotropic 3D-Flash sequence (TR 70 ms, TE 11 ms), which depicts the long T2 component of sodium. All patients tolerated the sodium study at 4.0 T well. The sodium images revealed almost all lesions, but the resolution was inferior to that of the reference methods. Two small meningiomas did not show up at all in the sodium study. Furthermore in one case small hemorrhages and calcifications within one of the tumors could not be found. Sodium imaging of the long T2 component did not provide any additional information regarding the histology, grading, size, and differentiation of the tumor from the surrounding edema which had not already been provided by CT or H MRI.

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