Mueller matrix approach for determination of optical rotation in chiral turbid media in backscattering geometry.

For in vivo determination of optically active (chiral) substances in turbid media, like for example glucose in human tissue, the backscattering geometry is particularly convenient. However, recent polarimetric measurements performed in the backscattering geometry have shown that, in this geometry, the relatively small rotation of the polarization vector arising due to the optical activity of the medium is totally swamped by the much larger changes in the orientation angle of the polarization vector due to scattering. We show that the change in the orientation angle of the polarization vector arises due to the combined effect of linear diattenuation and linear retardance of light scattered at large angles and can be decoupled from the pure optical rotation component using polar decomposition of Mueller matrix. For this purpose, the method developed earlier for polar decomposition of Mueller matrix was extended to incorporate optical rotation in the medium. The validity of this approach for accurate determination of the degree of optical rotation using the Mueller matrix measured from the medium in both forward and backscattering geometry was tested by conducting studies on chiral turbid samples prepared using known concentration of scatterers and glucose molecules.

Polar decomposition of 3 x 3 Mueller matrix: a tool for quantitative tissue polarimetry.

The polarization properties of any medium are completely described by the sixteen element Mueller matrix that relates the polarization parameters of the light incident on the medium to that emerging from it. Measurement of all the elements of the matrix requires a minimum of sixteen measurements involving both linear and circularly polarized light. However, for many diagnostic applications, it would be useful if the polarization parameters can be quantified with linear polarization measurements alone. In this paper, we present a method based on polar decomposition of Mueller matrix for quantification of the polarization parameters of a scattering medium using the nine element (3 x 3) Mueller matrix that requires linear polarization measurements only. The methodology for decomposition of the 3 x 3 Mueller matrix is based on the previously developed decomposition process for sixteen element (4 x 4) Mueller matrix but with an assumption that the depolarization of linearly polarized light due to scattering is independent of the orientation angle of the incident linear polarization vector. Studies conducted on various scattering samples demonstrated that this assumption is valid for a turbid medium like biological tissue where the depolarization of linearly polarized light primarily arises due to the randomization of the field vector's direction as a result of multiple scattering. For such medium, polar decomposition of 3 x 3 Mueller matrix can be used to quantify the four independent polarization parameters namely, the linear retardance (delta ), the circular retardance (psi), the linear depolarization coefficient (Delta) and the linear diattenuation (d) with reasonable accuracy. Since this approach requires measurements using linear polarizers only, it considerably simplifies measurement procedure and might find useful applications in tissue diagnosis using the retrieved polarization parameters.

Laparoscopic splenectomy.

PURPOSE: To study the safety and efficacy of laparoscopic splenectomy (LS) in patients with hematologic disorders requiring surgical intervention. PATIENTS AND METHODS: A series of 103 consecutive adult patients underwent LS between 1992 and 1997 at our teaching hospital. Data were collected prospectively. The indications for splenectomy included idiopathic thrombocytopenic purpura (ITP), hereditary spherocytosis, autoimmune hemolytic anemia, and thrombotic thrombocytopenic purpura. RESULTS: The mean spleen size was 14 cm (range 8.5-24 cm) and the mean weight was 263 g (range 40-210 g). Accessory spleens were detected in 12 patients with ITP and 17 patients in the study overall. In 12 patients, LS was combined with a laparoscopic cholecystectomy for gallstones. There were four conversions to open splenectomy, all for hemorrhage and all occurred in the first 50 patients. We have not converted a single patient in the last 2 years. The mean operative time was 161 minutes and was greater in the first 10 cases than the last 10. There were no deaths. Postoperative complications occurred in six patients, one necessitating a second procedure for a small-bowel obstruction. The average length of stay in the hospital was 2.5 days. After surgery, thrombocytopenia resolved in 84% of patients with ITP and anemia resolved in 92% of the patients with hereditary spherocytosis. After a mean follow-up of 38 months (range 2-565 months), four patients (6%) showed a relapse of ITP, three within 12 months of surgery. CONCLUSIONS: Laparoscopic splenectomy can be performed safely and effectively in a teaching institution. LS in comparison with open surgery offers the same efficacy in the control of hematologic disease with the additional benefits of a minimally invasive approach. Laparoscopic splenectomy should therefore be considered the technique of choice and should prompt earlier consideration of surgery for patients with selected hematologic disorders.