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Biomedical subjects

J Ripoll

Publications and source records attributed to J Ripoll.

13 recordsLinked to original sources
PubMed2001

Kirchhoff approximation for diffusive waves.

Quantitative measurements of diffuse media, in spectroscopic or imaging mode, rely on the generation of appropriate forward solutions, independently of the inversion scheme employed. For complex boundaries, the use of numerical methods is generally preferred due to implementation simplicity, but usually results in great computational needs, especially in three dimensions. Analytical expressions are available, but are limited to simple geometries such as a diffusive slab, a sphere or a cylinder. An analytical approximation, the Kirchhoff approximation, also called the tangent-plane method is presented for the case of diffuse light. Using this approximation, analytical solutions of the diffusion equation for arbitrary boundaries and volumes can be derived. Also, computation time is minimized since no matrix inversion is involved. The accuracy of this approximation is evaluated on comparison with results from a rigorous numerical technique calculated for an arbitrary geometry. Performance of the approximation as a function of the optical properties and the size of the medium is examined and it is demonstrated that the computation time of the direct scattering model is reduced at least by two orders of magnitude.

Journal Article↗
PubMed2001

Recovery of optical parameters in multiple-layered diffusive media: theory and experiments.

Diffuse photon density waves have lately been used both to characterize diffusive media and to locate and characterize hidden objects, such as tumors, in soft tissue. In practice, most biological media of medical interest consist of various layers with different optical properties, such as the fat layer in the breast or the different layers present in the skin. Also, most experimental setups consist of a multilayered system, where the medium to be characterized (i.e., the patient's organ) is usually bounded by optically diffusive plates. Incorrect modeling of interfaces may induce errors comparable to the weak signals obtained from tumors embedded deep in highly heterogeneous tissue and lead to significant reconstruction artifacts. To provide a means to analyze the data acquired in these configurations, the basic expressions for the reflection and transmission coefficients for diffusive-diffusive and diffusive-nondiffusive interfaces are presented. A comparison is made between a diffusive slab and an ordinary dielectric slab, thus establishing the limiting distance between the two interfaces of the slab for multiple reflections between them to be considered important. A rigorous formulation for multiple-layered (M-layered) diffusive media is put forward, and a method for solving any M-layered medium is shown. The theory presented is used to characterize a two-layered medium from transmission measurements, showing that the coefficients of scattering, mu'(s) , and absorption, mu(a) , are retrieved with great accuracy. Finally, we demonstrate the simultaneous retrieval of both mu;(s) and mu(a).

Diffusion↗
PubMed2000

Boundary conditions for light propagation in diffusive media with nonscattering regions

The diffusion approximation proves to be valid for light propagation in highly scattering media, but it breaks down in the presence of nonscattering regions. We present a compact expression of the boundary conditions for diffusive media with nonscattering regions, taking into account small-index mismatch. Results from an integral method based on the extinction theorem boundary condition are contrasted with both Monte Carlo and finite-element-method simulations, and a study of its limit of validity is presented. These procedures are illustrated by considering the case of the cerebro-spinal fluid in the brain, for which we demonstrate that for practical situations in light diffusion, these boundary conditions yield accurate results.

Journal Article↗
PubMed1981

[Influence of chloramphenicol on glutamic acid excretion in citrobacter intermedius C3 (author's transl)].

Chloramphenicol inhibits growth of C. intermedius C3 along with glutamic acid excretion, isocitrate dehydrogenase, glutamate dehydrogenase and the percentage of glutamic acid excreting colonies in solid medium. Repression of isocitrate dehydrogenase and glutamate dehydrogenase may explain the observed decrease in extracellular glutamic acid accumulation even when media were supplemented with 2-oxoglutarate, a known inducer of excretion in C. intermedius C3.

Cell Division↗
PubMed1979

The effect of 2-oxoglutarate and biotin in the release of amino acids by Citrobacter intermedius C3.

Excretion of amino acids by Citrobacter intermedius C3 was assayed in a mineral medium with glucose as carbon source. Glutamic acid is the main amino acid excreted in liquid medium and it is also detected at the colonial level in solid medium. Mutants with different behaviour with respect to the excretion of amino acids are studied. The presence of 2-oxoglutarate in the medium induced excretion in all strains. On the other hand when biotin was added to the culture media amino acid excretion was partially reduced.

Amino Acids↗
PubMed1978

[Metabolic studies in brothers affected by alcaptonuria (ochronosis)].

The case of two brothers affected by alcaptonurie is reported. The activity of the homogenthisycasa enzyme has been determined by the material obtained through percutaneous biopsy. Concentrations of the aminoacids producing fenilalanina and thiroxina in their parents' blood have been investigated, the tests showing lack of liver enzyme and normal concentration of the amount of aminoacids in blood. Some aspects of skin lesion have been briefly reported and methods for treatment presented.

Adult↗
PubMed1978

[Effect of L-tetramisol associated with rifampicin in patients with lepromatous leprosy. L-tetramisol in patients with lepromatous leprosy].

In this work are presented results obtained in the treament of thirty patients suffering of lepromatous leprosy. In a group of fifteen patients L-tetramisol was administrated in association to antimocrobian drugs. The control group received only the last medication. Immunological modifications were not observed in any case. However, in six patients treated with L-tetramisol associated to rifampicin during three months it was possible to observe a notable improvement of the clinical state. In the patients that received L-tetramisol associated to other drugs or in those that received only antimicrobian drugs the clinical improvement was very low or null.

Adolescent↗