Daniel Fiat

Determination of regional cerebral oxygen consumption in the human: 17O natural abundance cerebral magnetic resonance imaging and spectroscopy in a whole body system.

17O natural abundance imaging in a whole body imager is demonstrated using standard MRI spectrometer and 1H imaging methods. A novel design of a highly sensitive 17O/1H doubly tuned surface head coil is shown. The head probe allows simultaneous acquisition of 17O and 1H images using a single coil. The relatively low 17O signal intensity due to the low natural abundance of 17O (0.037 atom percent) is partially compensated by fast repetition of the pulse sequence, achievable due to the short spin lattice relaxation time, T1. A small number of signal averages (e.g., NEX = 50) is sufficient for obtaining images having signal to noise of about 5:1. Due to the short longitudinal relaxation time of 17O, i.e., 2-5 msec, short TR values can be used. 128 phase encoding steps with TR = 10-25 msec correspond to total acquisition time of 1 to 2.5 min. Due to the small gyromagnetic ratio of 17O and the relatively small gradients in a standard whole body system, i.e. 0.5 G/cm, the image in-plane resolution is about 3 mm and a slice thickness of 15 mm. In vivo 17O MRS and MRI natural abundance spectroscopic signals and images of human brain have been observed. The transverse relaxation time, T2 was found to be 2.00 +/- 0.17 msec at 1.5 T. MRS 17O measurements of signal intensity in the occipital cortex during inhalation of oxygen gas, 21.8% 17O enriched, showed a maximum signal enhancement of 25% within the inhalation period. The rate of the metabolism of oxygen (CMRO2) in the occipital cortex was found to be 1.5 mumole/(g tissue) in good agreement with the value of 1.435 mumole/(g tissue) given in the literature. Current measurements using higher 17O enrichments and larger quantities of 17O enriched oxygen gas will enhance resolution and provide more accurate determination of the rate of oxygen metabolism rate and blood flow. The potential of 17O imaging is thus demonstrated in physiological in vivo studies of cerebral metabolism of oxygen and blood flow.

Determination of the rate of cerebral oxygen consumption and regional cerebral blood flow by non-invasive 17O in vivo NMR spectroscopy and magnetic resonance imaging: Part 1. Theory and data analysis methods Daniel Fiat and Seho Kang

Theory and novel data analysis methods of 17O inhalation measurements are presented for the calculation of CMRO2, regional cerebral blood flow (rCBF), the reflow (R), the arterial venous difference (AVD) and the partition coefficient (lambda). Several of the methods proposed for the determination of CMRO2 do not require measurements of regional cerebral blood flow and H2(17)O arterial concentration. All methods of analysis are based on the Kety-Schmidt approach.

17O magnetic resonance imaging of the human brain

Abstract Here we show the first example of in vivo oxygen-17 (17O) magnetic resonance imaging of the human in natural abundance. Two-dimensional fast multi-planar gradient recalled 90 deg echo (FMPGR/90) pulse sequence and three-dimensional projection reconstruction pulse sequence methods were used.

Hydrogen bonds in the tripeptide Pro-Leu-Gly-NH217O and 1H studies

17O-NMR measurements of labeled Pro-Leu-Gly-NH2 were carried out at different pH levels and in mixed solvents of water/acetonitrile. Complementary studies of the amide protons were carried out in acetonitrile-d3. Only the prolyl C = 17O group was sensitive to the pH level. Protonation of the amine group resulted in an upfield chemical shift of 18 ppm. The chemical shifts of each of the three oxygen sites was sensitive to the ratio water:acetonitrile. Solvent composition dependence of the chemical shift and linewidth suggests that the prolyl C = 17O is involved in intramolecular hydrogen bond formation when Pro-Leu-Gly-NH2 is dissolved in acetonitrile, while in water there is no intramolecular H bond.

17O NMR investigation of the hydration of L-Alanine and L-Proline in water/Me2SO mixtures

The hydration state of L-Alanine and L-Proline has been assessed via 17O NMR. At neutral and basic pH, two water molecules are hydrogen bonded at the carboxylate group, one to each oxygen, whereas a third water molecule is hydrogen bonded to the protonated COOH group at acidic pH, via the hydroxyl hydrogen. The possible formation of dimers and/or higher complexes in DMSO is indicated not only from the chemical shift but also from the linewidth of the amino acids.

MAGNETIC FIELD GRADIENTS IN THE MRI SUITE AND THEIR EFFECTS ON ANEURYSM CLIPS

We studied magnetic field intensity in the magnetic resonance imaging suite at our hospital and its possible effect on several different types of aneurysm clips, including one Heifetz 17-7 PH, six Heifetz Elgiloy, one Mayfield, six Perneczky, fifteen Sugita, one Sundt-Kees Variangle, four Variangle-McFadden and fifteen Yasargil clips. We carefully observed the clips for any translational or rotational movements along the path from the door towards the magnetic resonance imaging gantry. The magnetic field strength was 0.04 kiloGauss at the entrance of the room, with an acute increase of magnetic strength at 310 cm away from the entrance to the room, 90 cm to the entrance of the gantry. The magnetic strength continued to increase at a rate of 1.0-1.5 kiloGauss for every 20 cm up to the entrance to the gantry. No movement was observed in any of the clips at the entrance to the suite except for the Heifetz 17-7 PH clip, which showed small movement in the longitudinal plane of the clip. At the entrance to the gantry, the Heifetz 17-7 PH, Sundt-Kees Variangle, and Mayfield clips were aligned on the walls of the test container perpendicular to the magnetic bore. The, Heifetz Elgiloy, Perneczky, Sugita, Variangle-McFadden, and Yasargil clips showed no movement throughout the path of the stretcher or near the gantry.

17O and 14N NMR studies of the Co(II), Cu(II) and Mn(II) complexes of l-proline in aqueous solution

Abstract The 17 O and 14 N paramagnetic transverse relaxation time and chemical shift of proline as well as of water, in aqueous solutions of Co(II), Cu(II) and Mn(II) were measured as a function of pH, temperature, and metal ion concentration. The relaxation results were fitted to a theoretical equation linking the Swift-Connick equation to the stability constants of the major complexes in equilibrium. Stability constants for the major complexes of the three ions in this work were determined, along with thermodynamic parameters for some of the complexes. Two complexes of Co(II) were detected directly by 17 O NMR at basic pH, and were assigned to CoPrO 2 and CoPro 3 − . The hyperfine coupling constant for these two complexes, A / h , was determined directly from the isotropic shift and was found to be −0.63 and −0.31 MHz, respectively. CoPrO 2 could be detected in the pH range 6–12, for Co(II) concentrations greater than 0.04 M, and its chemical shift was around 700 ppm downfield from free proline, at 300 K. CoPro 3 − was detected only at pH 11, in the temperature range 275–284 K, with a chemical shift of 390 ppm downfield from free proline.

In vivo natural-abundance17O/1H MRI of rhesus monkey body in a whole-body scanner

In vivo natural-abundance17O and1H magnetic resonance imaging (MRI) techniques were combined to image the whole body of a rhesus monkey. The results demonstrate the feasibility of acquiring consecutive fast17O and1H images with a standard MRI scanner. The method has applications in the field of functional MRI and in17O MRI measurements of metabolism rate.

Combined17O/1H MRI study in a whole-body scanner

A simple method of obtaining consecutive1H and natural-abundance17O images is described with a scanner’s original body resonator (for1H) and a homemade linear birdcage (for17O). Two kinds of experiments were performed to test the method. In the first experiment, a proton image of the phantom was acquired with a whole-body resonator. In the second experiment, the phantom was inserted into an oxygen birdcage resonator and imaged again with a whole-body resonator. The intensities of images resulting from the experiments were analyzed. Although theB1 field homogeneity is disturbed, the proton images acquired with a whole-body resonator when the oxygen resonator is present are of acceptable quality for use in the combined17O/1H imaging.

Comparison of models for parameter estimation in broad-line NMR spectra

Abstract The effects of finite acquisition time, improperly chosen sampling time, and spectrometer dead time on broad-line NMR spectra are examined. A discrete Fourier-transform model equation for a nonlinear least-squares analysis that overcomes these limitations is derived. A nonlinear regression method is used to perform the nonlinear least-squares fit of the simulated and experimental data. The accuracy of the proposed model is compared with those of the conventional Lorentzian and the time-domain models. It is shown that the proposed discrete Fourier-transform model yields higher accuracy than the conventional Lorentzian line. The accuracy of the estimation of the proposed discrete Fourier-transform model is similar to that of time-domain model; however, its uncertainty level is lower.