Comparison of calculated and experimental NMR spectral broadening for lung tissue

Abstract

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.

Separation of Intra- and Extramyocellular Lipid Signals in Proton MR Spectra by Determination of Their Magnetic Field Distribution

“…The EMCL compartments are determined mainly by the more tubular structures of muscle fibers. For this reason the compartments of EMCL can show a rather inhomogenous and even asymmetrical distribution of the magnetic field due to a tube-like geometry combined with anisotropic susceptibility effects as was similarly found for geometric models of trabecular bone (13) and lung tissue (14).…”

Modeling the nuclear magnetic resonance behavior of lung: From electrical engineering to critical care medicine

“…For example, theoretical NMR lineshapes have been calculated for both the parenchymal and nonparenchymal lung tissues and compared with experimental lineshapes measured in excised unperfused rat lungs [Christman et al, 1996]. Good agreement has been observed between theoretical and experimental data.…”

“…Furthermore, the impact of pulmonary edema on lung function mainly depends on the extent of the pathologic changes involving the parenchymal lung tissue, although the nonparenchymal structures (e.g., the airways) are also affected [Hogg et al, 1972]. However, in a more recent study [Christman et al, 1996] the nonparenchymal lung structures have been simulated as cylindrical tubes, each corresponding to a bronchovascular branch with the surrounding interstitial tissue, and their NMR properties have been found to differ from those of the parenchymal pulmonary tissue.…”

“…Proton NMR lineshape determinations have been performed in sponge phantoms and in normal excised lungs (where they have been found to vary regionally) [Christman et al, 1996]. However, little information is available regarding the lineshape characteristics in edematous lungs .…”

“…4) The Wigner-Seitz model [Christman et al, 1996], consists of polyhedral (12-faced) air cells in a water medium, each representing an alveolus. These cells are similar to the Wigner-Seitz polyhedra used in solid state physics [Ashcroft and Mermin, 1976], with the exception that the walls are thickened to attain an arbitrary air/ tissue ratio and the corners are rounded to simulate the alveolar shape.…”