Biomedical subjects

Yong S Park

Publications and source records attributed to Yong S Park.

2 recordsLinked to original sources

PubMed2006

Reoperation for persistent or recurrent hemifacial spasm after microvascular decompression.

OBJECTIVE: The objective of this study was to investigate the outcome of reoperation for persistent or recurrent hemifacial spasm (HFS) after microvascular decompression (MVD). METHODS: Repeat MVD was performed on 13 patients with an HFS between June 1994 and May 2004. Patients who had compressing offending vessels identified on postoperative (prerevision) three-dimensional short-range magnetic resonance angiography were selected for repeat MVD. RESULTS: Six patients were found to have no improvement in HFS with the first MVD. All of these patients exhibited excellent improvement after the second MVD. In one patient who had mild improvement with the first MVD, but with more than 50% of remaining spasm, complete abolition of spasm occurred immediately after the second MVD. Six patients showed initial relief and subsequent aggravation of HFS after the first MVD. Of these patients, four had excellent results with the second MVD, one had a good result, and one had a fair outcome. Adverse effects after the second MVD were found in two patients (one patient with permanent mild facial weakness and one patient with hearing impairment). There was no serious morbidity associated with the second MVD. CONCLUSION: Our data suggest that repeat MVD of the facial nerve may be sufficient to resolve symptoms in selected patients with persistent or recurrent HFS. Additionally, three-dimensional short-range magnetic resonance angiography may help to identify the offending vessels and to select the patients with persistent or recurrent HFS.

Adult↗

PubMed2002

Temperature increases associated with polymerization of irradiated PAG dosimeters.

Polyacrylamide gel (PAG) dosimeters show considerable promise as three-dimensional dosimeters for the verification of complex dose distributions associated with conformal therapy. However, the potential of PAG dosimeters has not yet been borne out in clinical practice and it is apparent that basic investigations of these dosimeters are still required. The polymerization reactions in PAG dosimeters are exothermic and the heat given off by the reactions may influence polymerization reaction kinetics. We report the results of in situ measurements of local temperature increases in irradiated PAG resulting from heat generated by the radiation-induced exothermic polymerization reactions. Temperature changes proportional to the absorbed dose were observed in the irradiated gels, reaching a maximum of 12 degrees C under high-dose conditions, depending on the thermal boundary conditions. This has practical implications, for example, using small vials of PAG to calibrate large phantoms may not be appropriate since temperature differences during irradiation between the calibration vials and phantom may alter the morphology and quantity of the polymer formed, even when irradiated to the same dose. The inhibition of radiation-induced polymerization associated with low-level oxygen contamination is manifested by a delay in the onset of temperature rise during irradiation. The observed temperature changes are used to estimate the percentage conversion of double bonds from the bis/acrylamide monomers by polymerization reactions.

Acrylic Resins↗