Measurement of muon capture on the proton to 1% precision and determination of the pseudoscalar coupling gP

The MuCap experiment at the Paul Scherrer Institute has measured the rate Λ(S) of muon capture from the singlet state of the muonic hydrogen atom to a precision of 1%. A muon beam was stopped in a time projection chamber filled with 10-bar, ultrapure hydrogen gas. Cylindrical wire chambers and a segmented scintillator barrel detected electrons from muon decay. Λ(S) is determined from the difference between the μ(-) disappearance rate in hydrogen and the free muon decay rate. The result is based on the analysis of 1.2 × 10(10) μ(-) decays, from which we extract the capture rate Λ(S) = (714.9 ± 5.4(stat) ± 5.1(syst)) s(-1) and derive the proton's pseudoscalar coupling g(P)(q(0)(2) = -0.88 m(μ)(2)) = 8.06 ± 0.55.

Measurement of the muon capture rate in hydrogen gas and determination of the proton's pseudoscalar coupling gP

The rate of nuclear muon capture by the proton has been measured using a new technique based on a time projection chamber operating in ultraclean, deuterium-depleted hydrogen gas, which is key to avoiding uncertainties from muonic molecule formation. The capture rate from the hyperfine singlet ground state of the microp atom was obtained from the difference between the micro(-) disappearance rate in hydrogen and the world average for the micro(+) decay rate, yielding Lambda(S)=725.0+/-17.4 s(-1), from which the induced pseudoscalar coupling of the nucleon, g(P)(q(2)=-0.88m(2)(micro))=7.3+/-1.1, is extracted.

Comparison of calculated and experimental NMR spectral broadening for lung tissue

NMR lineshapes were calculated for a model of lung, and NMR proton spectra were measured for individual voxels in an excised inflated rat lung. NMR lines for parenchymal lung regions containing alveoli, alveolar ducts, and capillaries were calculated using a computer simulation of the NMR signal from a three-dimensional honeycomb-like structure, a collection of modified Wigner-Seitz cells. These cells were modified by rounding the corners and increasing the thickness of the boundaries to model various degrees of lung inflation and lung water. NMR lineshapes were also calculated for the central or nonparenchymal lung regions containing bronchi and large blood vessels. A comparison of theoretical lineshapes with those measured in individual voxels both in the parenchymal and in the central (largely nonparenchymal) regions in excised rat lungs at an inflation pressure of 30 cm of water shows excellent agreement. These results indicate that the NMR lineshape reflects the underlying lung geometry. This research constitutes the first calculations and measurements of NMR lineshapes in lung. The appendix describes a new method for calculating the magnetic field inside a weakly diamagnetic material of arbitrary shape placed in an otherwise uniform external magnetic field. This new method does not require either solution of simultaneous equations or evaluation of integral expressions.

Rapid line scan technique for artifact-free images of moving objects

Moving objects (e.g., heart, lung, chest wall, etc.) typically cause artifacts to appear in two-dimensional Fourier transform ("spin warp") images. The rapid line scan (RLS) technique is a simple inexpensive technique that can rapidly produce artifact-free images of moving objects, without requiring enormous magnetic field gradients or periodic motions. The basic concepts and potential industrial applications of the RLS technique are described.

Regional effects of repetition time on NMR quantitation of water in normal and edematous lungs

It is well known that pulmonary edema is, in general, spatially nonuniform. Since the NMR spin-lattice relaxation time (T1) is increased by lung edema, the spatial distribution of T1 will be nonuniform. When the repetition time (TR) is short relative to the T1 of edematous lung, lung water content will be underestimated and this underestimation will be spatially nonuniform as well. Therefore, technical artifacts which are a complex function of lung edema and its spatial distribution are expected. We compared overall and regional (topographic) lung water density measurements obtained from living rats (with normal or edematous lungs) using repetition times of 2.0 and 6.2 s (at a magnetic field of 1 T), to quantify this uneven T1 effect for normal and edematous lungs. NMR measurements at TR = 2.0 s underestimated whole lung water density (-rho H2O) TR = 6.2 s) by an average of 7.2% in normal rats and 22.5% in rats with pulmonary edema. Regional -rho H2O underestimation (%delta-rho H2O) varied from 2.2 to 8.8% (groups means) in normal lungs and from 7.3 to 30.8% in edematous lungs. As a result, the interquartile range (of the voxel distribution as a function of rho H2O) underestimated the spatial nonuniformity of lung water density by 28.0% in edematous lungs, likely because of greater loss of NMR signal from high-water-density, long-T1 lung regions. Both %delta-rho H2O and T1 were significantly correlated with -rho H2O at TR = 6.2 s.(ABSTRACT TRUNCATED AT 250 WORDS)

Assessment of lung water distribution by nuclear magnetic resonance. A new method for quantifying and monitoring experimental lung injury

We have developed a new analytical method that uses nuclear magnetic resonance (NMR) imaging data to quantify lung water content and distribution. This new method generates a distribution of lung water density in which the fraction of voxels corresponding to a given water density is plotted on the vertical axis as a function of water density on the horizontal axis, thereby complementing the spatial information provided by the NMR image. We obtained reproducible lung water distribution data at comparable lung volumes in normal excised lungs and in intact living rats. In normal excised unperfused rat lungs, the distribution varied with the degree of inflation, but the changes were small compared with those associated with lung edema. The lung water density distribution changed markedly after induction of lung edema by intrabronchial saline instillation, intravenous oleic acid injection, and rapid intravenous saline infusion. Lung water density distribution data were well correlated (correlation coefficient = 0.948 for the excised lungs and 0.823 for the intact living rats) with gravimetric lung water measurements. The new analytical method is noninvasive, provides easily repeatable measurements, and is as sensitive as the gravimetric technique to lung water changes.

Determination of lung water content and distribution by nuclear magnetic resonance imaging

NMR imaging techniques are applicable to the assessment of lung water content and distribution because the NMR signal is, under certain conditions, proportional to tissue proton density. NMR imaging is noninvasive, easily repeatable, free from ionizing radiation, and particularly suitable for the assessment of spatial lung water distribution. Lung water content and distribution have been estimated in excised animal lungs and in intact dead or living animals, under normal conditions and in various types of experimental pulmonary edema. Excised human lungs and human subjects have also been studied. Published data indicate that measurements of lung water content by NMR imaging techniques are feasible. These techniques estimate lung water spatial distribution with satisfactory accuracy and excellent resolving power. The application of NMR imaging techniques poses several problems and limitations, but available data suggest that most of the problems can be solved. NMR imaging has the potential to become a powerful tool for lung water research. Prospects of clinical application are also encouraging; numerous applications can be foreseen, although lack of mobility of NMR imaging systems may be a significant limitation in critical care medicine.

Asymmetric spin echo sequences. A simple new method for obtaining NMR 1H spectral images

The nuclear magnetic resonance (NMR) signal decay produced by reversible tissue-induced dephasing of the magnetization components in the transverse plane (reversible tissue-induced dephasing) was measured and expressed as a function of a new transverse relaxation time T'2 (T2 prime) for samples of rat liver, retroperitoneal fat, inflated lung, and corn oil. Simple exponentials did not adequately describe the observed NMR signal decay. Inflated lung demonstrated the most rapid signal decay (T'2 = 4.8 ms) followed by retroperitoneal fat (T'2 = 16 ms). No reversible tissue-induced dephasing was observed in liver (T'2 immeasurably long). In tissues which contain both fat and water, the chemically shifted 1H resonance peaks from -OH and -CH-are in phase with symmetric spin echo sequences but out of phase with asymmetric sequences. The interference of these two peaks produces a beat pattern with asymmetric sequences. Subtraction images obtained from paired symmetric- and asymmetric-sequence images accurately (r = .96) reflect T'2 and can be used to indicate the presence of fat. In vivo subtraction images of ethionine-induced fatty rat livers were significantly different from similar in vivo images of normal rat livers (P less than .0005). Since for each pixel of a subtraction image, the magnitude of the difference signal should be approximately proportional to the ratio of hydroxyl and alkyl protons, this simple spin echo sequence modification may obviate the need for more time-consuming 3-dimensional Fourier transform proton chemical shift images.

Manganese protoporphyrin IX. A potential intravenous paramagnetic NMR contrast agent: preliminary communication

An endogenous, biological chelating substance--protoporphyrin--has been studied in vitro and in vivo for potential usefulness as an MRI contrast agent. In vitro data show that manganese protoporphyrin IX (Mn PP) maintains strong paramagnetic properties. Limited in vivo studies suggest that Mn PP causes marked reduction of T1 in the liver, with less pronounced effects on other body tissues.

A new nuclear magnetic resonance property of lung

Inflated lung has a nuclear magnetic resonance (NMR) free-induction decay (FID) which is short compared with that of collapsed lung and those of other body tissues. An almost identically short FID is obtained from a slurry of 5-micron alumina particles in water. Interfaces between air and water in lung and between alumina and water in the slurry appear to be the source of spatial internal magnetic inhomogeneities which produce NMR line broadening and the short FID. Paired images that included lung, taken with paired symmetric and asymmetric NMR spin-echo sequences, permit the generation of an image, by subtraction, of the lung isolated from surrounding tissue. These new lung images are neither proton density, T1 (spin-lattice relaxation time), nor T2 (spin-spin relaxation time) images. They complement current NMR images and provide information about regional lung inflation. This previously unrecognized NMR property of lung tissue has potential application in NMR imaging, in quantitative determination of lung water and its distribution, and in the quantitation of regional lung inflation.

Determination of lung water content and distribution by nuclear magnetic resonance

The present study was designed to determine the value of nuclear magnetic resonance (NMR) imaging as a technique for quantifying lung water distribution and to estimate the degree of spatial resolution achieved by this technique. The spatial distribution of water was determined in six small (0.76 ml) rat lung tissue specimens by an NMR line-scan technique. After NMR imaging, each lung specimen was frozen and subdivided into slices; the gravimetric lung water content for each lung slice was compared with the integrated NMR water content over the volume corresponding to the same lung slice. In each tissue specimen, NMR and gravimetric lung water values were significantly correlated; the correlation coefficient for the pooled data for all six lung specimens was 0.91 (P less than 0.01). In two lung specimens, NMR values tended to be slightly higher than the gravimetric values. The magnitude of the difference between NMR and gravimetric values was generally less than 20% and only occasionally exceeded 25%. Our results suggest that the NMR-imaging method provides satisfactory estimates of lung water content and its distribution; the resolving power of the technique is excellent, as shown by its ability to detect water content differences between lung tissue slices of volume as small as 0.076 ml.

Lung water quantitation by nuclear magnetic resonance imaging

Nuclear magnetic resonance imaging was used to determine quantitatively the water distribution of saline-filled and normal rat lungs in both isolated lung and in situ preparations. Regional lung edema was easily detected. Studies of an isolated lung fragment indicate an accuracy of better than 1 percent and images of H2O/D2O phantoms indicate an average error of 2.7 percent.