Norio Iriguchi

Impedance magnetic resonance imaging: A method for imaging of impedance distributions based on magnetic resonance imaging

Magnetic resonance imaging (MRI) techniques have become important tools in medicine and biology. Conventional MRI, however, produces no information about the electrical properties of the body. This article proposes a new and noninvasive method for imaging electrical properties such as conductivity and impedance based on MRI techniques. The basic idea is to use the shielding effects of induced eddy currents in the body on spin precession. Two types of methods are introduced; (i) a large flip angle method, and (ii) a third coil method. The large flip angle method enhances the shielding effects of conducting tissues at the given Larmor frequency. The third coil method detects the shielding effects of conducting tissues at an arbitrary frequency. Both phantom and animal experiments have been carried out to verify this concept using a MRI system of 7.05 T with a bore size of 183 mm in diameter.

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.

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.

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.

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. J. Magn. Reson. Imaging 2000;11:330–335.

The power sensitivity of magnetic resonance experiments

On the basis of formulae given by Hoult and Lauterbur [J. Magn. Res. 34, 425 (1979)] for magnetic resonance in conductive samples, formulae for the signal‐to‐noise ratio (SNR) and the SNR per unit input power are presented.

Principles and Horizons of Magnetic Resonance Imaging

Magnetic resonance imaging (MRI) is a way of making tomographic images of the body non-invasively. Protons in the body can act like tiny bar magnets, with a north pole and a south pole. When an external magnetic field is applied across a part of the body, each little magnet lines up with the external magnetic field. If a radiofrequency (rf) wave is then transmitted into the tissues, some of the magnets are induced by the energy from the rf wave. The if wave is then turned off, and subsequently the magnets rebroadcast a signal of the same frequency as the original rf wave. A rf coil picks up the signal from the atomic magnets, and a computer can process the signal and reconstruct an image from the signal.

The NMR sensitivity achievable with a slotted-tube resonator

The signal-to-noise ratio achievable with the slotted-tube resonator (STR), a fundamental type of high radiofrequency coil for nuclear magnetic resonance (NMR) experiments, was formulated in an equation. This equation is based on formulae presented by Hoult and Richards [J Magn Reson24, 71 (1976)] and Hoult and Lauterbur [J Magn Reson34, 425 (1979)]. The equation assumes that the sample is positioned within the homogeneous region of magnetic fluxB1 generated by the STR, and involves no unknown factors. The NMR sensitivity of an experiment with an STR can therefore be predicted, and the equation is applicable to any nuclear species, static field strength, and dimensions of the sample and STR.

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.