Biomedical subjects

Guillermo Sanchez

Publications and source records attributed to Guillermo Sanchez.

3 recordsLinked to original sources

PubMed2003

Mathematical techniques for solving analytically large compartmental systems.

The flow of radioactive particles inside the body from internally deposited radioisotopes in people exposed to inhalation, ingestion, injection, or other ways is usually evaluated using compartmental models. The biokinetic models included in the documents of the International Commission on Radiological Protection such as International Commission on Radiological Protection 66 and 78 involve many compartments. Usually numeric methods are applied. Very often analytical solutions are not possible. New computer programs that include symbolic capability can be used to solve compartmental systems. In this paper some techniques are developed in order to make feasible a computer program that gives not only faster and more accurate solutions, but also analytic solutions for these kind of models. The main idea is to make a partition of subsystems and solve them sequentially. The concept of pseudotrap compartments in a subsystem is crucial at this point. Impulse (acute), constant, and continuous (such as exponential) intakes are considered. This technique has been applied to develop a computer code called Humorap to solve the International Commission on Radiological Protection 66 and 78 models.

Air Pollutants↗

PubMed2003

Planar photonic crystal structure with inherently single-mode waveguides.

A planar photonic crystal that allows inherently gap-guided single-mode waveguides is proposed and discussed. This novel structure consists of a two-dimensional lattice of silicon rods embedded on a thin silica slab sandwiched between two silica claddings whose refractive indices are slightly lower than the index of the silica core. The physical parameters of the structure, i.e., rod radius and core thickness, are optimized to maximize the bandgap width for odd modes. Lossless guided modes inside the bandgap and below the claddings' light cone are obtained by reducing the radius of a row of rods. The waveguide bandwidth can be increased by inserting a thin silicon dielectric waveguide instead of the row of rods. The proposed approach may overcome many of the common drawbacks in conventional holes-on-dielectric planar photonic crystal waveguides.

Journal Article↗

PubMed2002

Giant anterior cervicothoracic arachnoid cyst.

STUDY DESIGN: A case report with a review of the literature is presented demonstrating the imaging findings of a patient with recent onset, progressive spinal cord compression at T6 caused by a giant arachnoid cyst that was successfully treated. OBJECTIVE: To present the imaging findings of a giant anterior cervicothoracic intradural arachnoid cyst using several methods before and after treatment. SUMMARY OF BACKGROUND DATA: This case demonstrates the imaging findings of the largest described anterior cervical arachnoid cyst straddling the cervicothoracic junction. It presented with spinal cord compression in a 26-year-old diagnosed by MRI and successfully treated surgically. METHODS: The patient experienced progressive left-sided sensory and motor deficits below T6. Pain and temperature sensation were decreased. Reflexes were increased in both lower extremities with clonus. Preoperative MRI was followed by laminectomy and cyst fenestration with subsequent postoperative myelogram and CT. RESULTS: Imaging confirmed the presence of a giant arachnoid cyst straddling the cervicothoracic junction. Postoperative imaging documented relief of spinal cord compression. Symptoms improved progressively after surgery. By the time of discharge all residual neurologic deficits had resolved. CONCLUSION: Anterior arachnoid cysts straddling the cervicothoracic junction have yet to be reported, and arachnoid cysts involving the cervical region are extremely rare. Imaging demonstrated the cyst and its response to treatment. This patient responded well to surgery and was discharged without neurologic sequelae.

Adult↗