Imaging of cerebral and brain stem amyloidomas.

CNS amyloidomas are rare. We describe a 51-year-old man with isolated amyloidomas in the cerebral white matter and in the pons. CT and MR imaging showed a heterogeneous, enhancing mass in the deep cerebral white matter. A second, much smaller linear serpiginous lesion was present in the pons.

Hypertensive encephalopathy: complication in children treated for myeloproliferative disorders--report of three cases.

We routinely perform echo-planar diffusion-weighted sequences in all brain magnetic resonance (MR) imaging studies. When three children undergoing chemotherapy for acute leukemia presented with seizures, conventional MR images demonstrated what appeared to be acute, posterior, parasagittal infarcts. However, diffusion-weighted images were normal. These MR imaging findings were consistent with those of hypertensive encephalopathy. Early recognition and treatment of minimal hypertension in these patients allows reversal of encephalopathy.

Absolute quantitation of short TE brain 1H-MR spectra and spectroscopic imaging data.

A method for determining the concentrations of the materials that produce the well-resolved singlet signals in short TE brain 1H MR spectroscopic examinations is presented. Concentration determination is achieved by a water-referencing procedure. The ratios of the areas of the choline, total creatine, and N-acetyl signals to that of the water signal from the same volume of interest (VOI) are determined using acquisitions with and without water suppression. The tissue concentrations of the molecules producing the three signals can then be determined if the water concentration in the VOI can be found. This is done with a density-weighted MR study. The MR study provides the ratio of the mean MR signal amplitude from the VOI to that from an external standard containing a known water concentration. The method's flexibility is illustrated by using it with two different single-volume localization schemes and spectroscopic imaging. Preliminary evaluations of accuracy and reproducibility are made in phantom, animal, and limited human studies. The method's advantages and limitations are discussed.

Alveolar air-tissue interface and nuclear magnetic resonance behavior of lung.

Inflated lungs are characterized by a short nuclear magnetic resonance (NMR) free induction decay (rapid disappearance of NMR signal), likely due to internal (tissue-induced) magnetic field inhomogeneity produced by the alveolar air-tissue interface. This phenomenon can also be detected using temporally symmetric and asymmetric NMR spin-echo sequences; these sequences generate a pair of NMR images from which a difference signal (delta) is obtained (reflecting the signal from lung water experiencing the air-tissue interface effect). We measured delta in normal excised rat lungs at inflation pressures of 0-30 cmH2O for asymmetry times (a) of 1-6 ms. Delta was low in degassed lungs and increased markedly with alveolar opening when measured at a = 6 ms (delta 6 ms); delta 6 ms varied little during the rest of the inflation-deflation cycle. Delta 1 ms (a = 1 ms) did not vary significantly on inflation and deflation. Measurements of delta at a = 3 and 5 ms generally lay between those of delta 1 ms and delta 6 ms. These findings, which are consistent with theoretical predictions, suggest that measurements of delta at appropriate asymmetry times are particularly sensitive to alveolar opening and may provide a means of distinguishing alveolar recruitment from alveolar distension in the pressure-volume behavior of the lung.