ACOSTA RODOLFO HECTOR
Congresos y reuniones científicas
Título:
Optimization of Resolution in Gas MRI
Autor/es:
R. H. ACOSTA; L. AGULLES-PEDRÓS; P. BLÜMLER; H.W. SPIESS
Lugar:
Paris, Francia
Reunión:
Congreso; 7th International Conference of Magnetic Resonance in Porous Media; 2004
Resumen:
found an important clinical application in the diagnostics of lungs [1]. While many authors
emphasize the fact that the signal (hence the resolution) in such images is increased by 4-5 orders of
magnitude, only a small number of publication considers the problem of the extremely high
diffusion coefficients in gases and their destructive influence on the MRI-signal.
Typically the influence of diffusion on MRI-signals is minimized by reducing the timing of the
sequence, but technical limits are quickly reached in the case of gases. On the other hand the
diffusion time controls also the diffusion contrast by selecting structures, which then show restricted
or free diffusion.
For imaging structures with various pore sizes, such as lungs, two very different approaches can be
followed. Firstly, the whole of all air spaces should be visible independent of their size and
secondly a certain size should be selectable, so that only structures smaller than this will contribute
to the image (see Fig. 1). We demonstrate that this goal can only be reached if both the timing of the
sequence and the diffusion coefficient is controlled. The latter can be realized by the use of buffer
gases of various molar weight.
However, to understand the influence on the signal-to-noise of the resulting image, the theory of
diffusion coefficients in gas mixtures has to be revised due to isotope specific measurements. Signal
changes by external excitation and radiation damping have to be addressed as well. These
influences are discussed in theory and experiments on phantoms and animal lungs using
hyperpolarized 3He and 129Xe.
emphasize the fact that the signal (hence the resolution) in such images is increased by 4-5 orders of
magnitude, only a small number of publication considers the problem of the extremely high
diffusion coefficients in gases and their destructive influence on the MRI-signal.
Typically the influence of diffusion on MRI-signals is minimized by reducing the timing of the
sequence, but technical limits are quickly reached in the case of gases. On the other hand the
diffusion time controls also the diffusion contrast by selecting structures, which then show restricted
or free diffusion.
For imaging structures with various pore sizes, such as lungs, two very different approaches can be
followed. Firstly, the whole of all air spaces should be visible independent of their size and
secondly a certain size should be selectable, so that only structures smaller than this will contribute
to the image (see Fig. 1). We demonstrate that this goal can only be reached if both the timing of the
sequence and the diffusion coefficient is controlled. The latter can be realized by the use of buffer
gases of various molar weight.
However, to understand the influence on the signal-to-noise of the resulting image, the theory of
diffusion coefficients in gas mixtures has to be revised due to isotope specific measurements. Signal
changes by external excitation and radiation damping have to be addressed as well. These
influences are discussed in theory and experiments on phantoms and animal lungs using
hyperpolarized 3He and 129Xe.
