Temporal changes of the apparent diffusion coefficients of water and metabolites in rats with hemispheric infarction: experimental study of transhemispheric diaschisis in the contralateral hemisphere at 7 tesla.

The purpose of the present study was to clarify the temporal changes of the apparent diffusion coefficients (ADCs) of cerebral metabolites during early focal ischemia using stimulated echo acquisition mode with short echo time at a 7 T magnet to assess the pathophysiology of the reduction in diffusion properties observed both in the ischemic cerebral hemisphere and in the contralateral hemisphere. The ADCs of metabolites in the infarcted hemisphere 1 hour and 3 hours after the onset of ischemia decreased with 25% and 29% for choline containing compounds (Cho), 16% and 26% for creatine and phosphocreatine (Cre), and 19% and 19% for N-acetylaspartate (NAA), respectively, compared with the ADC values 2 hours later in the contralateral hemisphere. There were decreases in the ADC of Cho, Cre, and NAA with 21%, 7%, and 18% 8 hours later, respectively, in the noninfarcted hemisphere, which suggested transhemispheric diaschisis in rats with focal cerebral ischemia. The present study proposed that the diffusion characteristics of the brain metabolites might offer new insights into circulatory and metabolic alteration in the cerebral intracellular circumstance.

Measurement of relative fat content by proton magnetic resonance spectroscopy using a clinical imager.

The aim of this study was to determine the applicability of a proton magnetic resonance (MR) spectroscopy-based technique using a clinical 1.5-T MR imager for assessment of relative fat content. Proton MR spectra were obtained from a trunk phantom and 23 volunteers using a single free induction decay measurement. The ratios of fat methyl and methylene proton resonance to the water proton resonance were compared with the ratio of oil weight to water weight for the phantom, and with the ratio of body fat to lean body mass estimated by bioelectrical impedance analysis for the human subjects. Good linear relationships were found between the MR metabolite ratio and the ratio of oil weight to water weight (r = 0.9989), and the ratio of body fat to lean body mass (r = 0.9169). This MR spectroscopy-based technique is sufficiently accurate and may be applicable to assessment of human body composition.

Simultaneous measurement of temperature and velocity maps by inversion recovery tagging method.

A new method, called the inversion recovery (IR) tagging method, for simultaneous measurement of temperature and velocity maps of flowing fluid has been developed. The present method employs a set of tagging pulses which acts as an inversion pulse of the conventional IR method, based on the temperature dependence of the spin-lattice relaxation of water proton in a fluid, and has the advantage of being able to compensate the reduction of the NMR signal intensity due to flow motion and to reduce the total time to measure these maps. First, the accuracy of the temperature measurement of stagnant doped water in a differentially heated cell using the conventional IR method, as the basic sequence of the IR tagging method, has been evaluated. The accuracy was within 10% of the temperature difference DeltaT = 17.2 degrees C and the measurable temperature resolution was within +/-0.5 degrees C. Then temperature and velocity maps of the flowing doped-water through a cooled pipe were measured simultaneously by the IR tagging method, and the accuracy of temperature measurement was evaluated. The accuracy obtained using the present method was within 15% of the temperature difference DeltaT = 15 degrees C.

High-pressure magnetic resonance imaging up to 40 MPa.

A high-pressure vessel designed for use with commercial magnetic resonance imaging equipment at up to 40 MPa of pressure was used and tested. Special features of the vessel are the following: 1) 12.6 mm sample chamber i.d.; 2) only non-magnetic parts; 3) visible sample from the outside; 4) resistant to corrosive chemicals, and; 5) sample could be manually translated and rotated in situ. This apparatus was demonstrated through observation of CO(2) clathrate-hydrate growth in a water droplet injected into liquid CO(2) at 20 MPa.

A method of RF inhomogeneity correction in MR imaging.

A direct postprocessing method for correcting RF inhomogeneity in MR imaging is proposed. First, two images with different flip-angles of theta and 2theta are obtained. Next, the spatial distribution maps of the sensitivity of the surface coil and the B1 field intensity are produced by employing those images. Finally, the correction of the MR image is achieved, dividing the original image by distribution maps of the coil sensitivity and the B1 field intensity. The method was applied to images obtained by a gradient echo sequence and the corrected image is presented.

[Study of diffusion phenomenon using an experimental magnetic resonance system (SIS 200/400) for small animals--reliability and apparent diffusion coefficient of normal animals].

We have developed a magnetic resonance (MR) spin echo method to obtain diffusion weighted imaging using motion probing gradient (MPG) pulses in orthogonal direction before and after a 180 degree pulse. Phantom models containing water, acetone, cupric sulfate and agar, and normal brains of Wistar rats and puppies were examined. MRI was performed using a SISCO SIS 200/400 MRI/MRS experimental system for small animals (4.7 tesla, 400 mm bore). The apparent diffusion coefficient (ADC) values, given in mm2/sec, were 2.19 +/- 0.02 x 10(-3) in water, 4.51 +/- 0.18 x 10(-3) in acetone, and the ADC of water was independent on longitudinal (T1) or transverse (T2) relaxation time. Time-dependent ADC changes were not demonstrated, however position-dependent ADC changes were significant. It is therefore important to set the sample at the same position for repeated MRI studies and for the evaluation of the time course of experimental studies. Mean ADC values of rat brains were 0.65 x 10(-3) for cortex, 0.69 x 10(-3) for caudate-putamen, 0.69 x 10(-3) (perpendicular to axon) for corpus callosum, 1.11 x 10(-3) (parallel to axon) for optic nerve, and 1.38 x 10(-3) (parallel to axon) for trigeminal nerve. Those of puppies were 1.14-1.42 x 10(-3) for gray matter, 1.17 (parallel to axon) and 0.89 (perpendicular to axon) x 10(-3) for white matter, 1.66 (parallel to axon) and 0.57 (perpendicular to axon) x 10(-3) for internal capsule, and 0.91-0.95 x 10(-3) for thalamus. On the in vivo ADC maps, white matter tracts successfully showed anisotropic diffusion. This technique has promising implications for the evaluation of the time course of cerebral damage and degenerative changes.

Carbon-13 magnetic resonance imaging of a human arm.

An image of naturally abundant carbon-13 of -CH2- chains of the fatty tissue in a human upper arm is presented. A slotted-tube resonator (STR) for the carbon-13 imaging is described with fabrication details. The carbon-13 image is compared with a proton -CH2- chemical shift image of the same upper arm.

Carbon-13 chemical shift imaging of [1-13C] glucose under metabolism in the rat head in vivo.

Carbon-13 chemical shift images (metabolic maps) of [1-13C] glucose in the heads of rats were obtained and compared with proton images of the same rats in terms of signal allocation. Wistar rats were kept awake or anesthetized. [1-13C] glucose was injected intravenously in a dose of 1 g per kg of body weight. The head of the Wistar rat was placed on or into circular coils. Carbon-13 images were obtained using a 7.05 Tesla system. A simple spin echo sequence was used with a chemical shift selective (CHESS) pulse. The frequency band width was set to cover the spectral breadth of the carbon-13 signal of [1-13C] glucose. The slice thickness of the image was 4 mm or 6 mm, and the field of view (FOV) was 60 mm x 60 mm, with a matrix size of 64 x 64. The total acquisition time was 36 minutes. Strong signals were observed from the scalp muscles and tissues outside the brain, but signal strength from the brain itself was minimal. This was presumably due to the metabolism of [1-13C] glucose in the brain. Little difference was recognized between [1-13C] glucose images of the heads of rats with and without anesthesia. Chemical shift imaging of carbon-13 could be useful methods for the in vivo study of physiochemical structures and metabolic pathways of living organs.

In vivo F-19 chemical shift imaging with FTPA and antibody-coupled FMIQ.

A mixture of perfluoromethyldecahydroisoquinoline (FMIQ) emulsion coupled with anti-CEA (carcinoembryonic antigen) antibody and perfluorotripropylamine (FTPA) was injected into a nude mouse inoculated with human colon carcinoma LS174T. Three days after the injection, in vivo fluorine-19 chemical shift images of the spectral signals of the two perfluorocarbons (PFCs) were obtained simultaneously. The signal intensities and distributions of FMIQ and FTPA were similar in the liver and spleen but different in the tumor. FMIQ was detected in almost the entire tumor, with scattered areas of high uptake. FTPA, however, was detected only in the center of the tumor. The results suggest that F-19 chemical shift imaging of two PFCs, one coupled to antibody and the other not, has potential application in tumor diagnosis.

Cerebral energy metabolism in experimental canine hydrocephalus.

Cerebral energy metabolism, its relationship to the stage and extent of hydrocephalus, and the effect of cerebrospinal fluid (CSF) removal on it were studied in experimental canine hydrocephalus produced by intracisternal injection of kaolin by using phosphorus-31 (P-31) magnetic resonance (MR) spectroscopy and MR imaging. P-31 MR spectra were serially obtained before and after CSF removal, maximally on eight occasions over a period of nearly 5 h. There was a decrease in the ratio of creatine phosphate to inorganic phosphate, used as an indicator of the bioenergetic state, in acute and subacute stages of hydrocephalus as compared with the control. An animal in the subacute stage, when periventricular edema was most prominent, exhibited the most predominent decrease in this ratio at 14 days after hydrocephalic insult. The recovery of the ratio toward the control level was seen in the chronically hydrocephalic animal. There was no change in adenosine triphosphate (ATP) levels in any stage of hydrocephalus. Serial spectra obtained after the withdrawal of ventricular CSF showed no change in the bioenergetic state of the brain in any stage of hydrocephalus. There was no relationship between either the extent of hydrocephalus or the ventricular CSF pressure and the change in the bioenergetic state or the levels of any of the phosphorus compounds. These findings may indicate the alteration of the mitochondrial energy metabolism in hydrocephalus, which may explain the mechanism of hydrocephalic syndrome.

Changes in free water content and energy metabolism of the brain in experimental hydrocephalus.

In acute and subacute hydrocephalus periventricular oedema is most prominent. At these stages of hydrocephalus, the free water content is increased and the bound water content, to the contrary, significantly decreased in the periventricular white matter. The bioenergetic state is also altered. In the chronic stage the ratio of free-to-bound water content returns to a level near the control value, leading to a decrease of periventricular oedema by formation of alternative pathways of CSF absorption. The bioenergetic state was slightly altered at this stage.

Spectroscopic imaging by dephasing amplitude changing (SIDAC).

A technique for spectroscopic imaging based on a new concept of dual encoding (i.e., both phase and frequency encoding) of position along the direction of the read-out gradient is proposed. The phase encoding is produced by changing the amplitude of the dephasing gradient as in conventional phase encoding. High-resolution spectroscopic images of a normal human thigh obtained by a 2.0 Tesla whole body MR imaging system are presented.

Movement of water in conjunction with plant movement visualized by NMR imaging.

The water distribution in the pulvinus of Mimosa can be visualized by an NMR imaging technique. After stimulation of a Mimosa plant, water in the lower half of the main pulvinus disappeared, the water previously contained in this area seeming to be transferred to the upper half of the main pulvinus. Movement of the water in conjunction with Mimosa movement was visualized sequentially by a non-invasive NMR imaging procedure.

31P NMR spectroscopy of the stomach by zig-zag coil.

Phosphorus-31 (31P) nuclear magnetic resonance (NMR) spectroscopic investigations of the rat stomach were performed utilizing a 1-cm2, three-turn, zig-zag coil. A zig-zag coil of this dimension produced an effective B1 field that extends only within a 4-mm distance from the plane of the surface coil, rendering it possible to obtain high-resolution 31P spectra localized to the stomach without contamination from surrounding tissues. Normal stomach showed a characteristic spectral pattern with resonances reflecting inorganic phosphate (Pi), phosphocreatine (PCr), and the alpha-, beta-, and gamma-phosphates of adenosine triphosphate (ATP). Ischemia-induced changes in Pi, PCr, and ATP resonances were readily followed in vivo with a time resolution of 2.13 min. Indomethacin-induced ulcer revealed a low intracellular pH and a decrease in the PCr to Pi ratio indicating the partially ischemic conditions of ulcerative lesions of the stomach as has been previously suggested. The present studies indicate that 31P NMR spectroscopy utilizing a zig-zag coil is a powerful tool to study local pathology of the gastrointestinal (GI) tract. Since zig-zag coils suitable for fiberscopic devices are easily constructed, clinical applications of the present technique are apparent.

Tumor imaging with anti-CEA antibody labeled 19F emulsion.

The possibility of using 19F MRI for detection of tumors using a 2-T NMR system was examined in animals. Anticarcino-embryonic antigen (CEA) antibody conjugated with perfluorochemical (perfluorotributylamine, FTBA) was administered to nude mouse inoculated with LOVO, a CEA-producing human cancer cell line. Tumor imaging based on the 19F NMR was examined after excision of the tumors from nude mice (ex vivo). The imaging pattern of the tumor coincided with the antibody distribution determined immunohistologically.

Semiquantitative analysis of fatty liver using spectroscopic imaging by dephasing amplitude changing (SIDAC).

The potential utility of spectroscopic imaging by dephasing amplitude changing (SIDAC) was evaluated in fatty infiltration in rats induced by cholesterol and ethanol. There was an excellent correlation between the in vivo fat-to-water ratio obtained from SIDAC and that in liver specimens from in vitro measurement (r = 0.97). SIDAC is a promising method for semiquantitative analysis of fatty infiltration of the liver.