PubMed Health⌕ Search

Biomedical subjects

K T Shimizu

Publications and source records attributed to K T Shimizu.

9 recordsLinked to original sources
PubMed2002

Surface-enhanced emission from single semiconductor nanocrystals.

The fluorescence behavior of single CdSe(ZnS) core-shell nanocrystal (NC) quantum dots is dramatically affected by electromagnetic interactions with a rough metal film. Observed changes include a fivefold increase in the observed fluorescence intensity of single NCs, a striking reduction in their fluorescence blinking behavior, complete conversion of the emission polarization to linear, and single NC exciton lifetimes that are >10(3) times faster. The enhanced excited state decay process for NCs coupled to rough metal substrates effectively competes with the Auger relaxation process, allowing us to observe both charged and neutral exciton emission from these NC quantum dots.

Journal Article↗
PubMed2000

Correlation between fluorescence intermittency and spectral diffusion in single semiconductor quantum dots.

We find a correlation between the dynamics of fluorescence intermittency and spectral diffusion in the spectroscopy of single CdSe nanocrystal quantum dots (QD). A statistical analysis of the data suggests two populations of blinking events: blinking followed by large spectral diffusion shifts and blinking with small or no spectral shifts. Although unexpected from earlier studies, the correlation between blinking and spectral shifting is consistent with a model of QD ionization as the mechanism for the blinking event, followed by a redistribution of local electric fields that results in spectral shifting.

Journal Article↗
PubMed1998

Restoration of irradiated patients using osseointegrated implants: current perspectives.

STATEMENT OF PROBLEM: The success rates of osseointegrated implants used to restore patients who were irradiated for head and neck tumors are influenced by radiation-induced changes in the hard and soft tissues. PURPOSE: This article examined, by review of the literature, current perspectives on the restoration of irradiated patients using osseointegrated implants. RESULTS: In published reports that investigated both intraoral and extraoral applications, irradiation decreased implant success rates and the amount of reduction was dependent on the location within the craniofacial skeleton. The limited number of implants and patients in these studies precludes definitive conclusions regarding the efficacy of placing implants into irradiated tissues. The implants placed into the irradiated anterior mandible have demonstrated an acceptable implant success rate of 94% to 100% with a minimal risk of osteoradionecrosis. The efficacy of implants in the posterior mandible has not been examined. Implant success rates ranged from 69% to 95% in the irradiated maxilla for intraoral applications. Extraoral applications demonstrated excellent implant success rates in the temporal bone (91% to 100%). The rates in the anterior nasal floor have varied from 50% to 100%. The implant success rates in the frontal bone decreased as the length of the studies increased (96% to 33%). The long-term efficacy of implants in the irradiated frontal bone is poor.

Animals↗
PubMed1995

Craniopharyngioma: treatment in the CT and MR imaging era.

PURPOSE: To determine optimal treatment in patients with craniopharyngiomas. MATERIALS AND METHODS: In 1977-1990, 49 patients (age range, 3-67 years; median age, 35 years; 25 female, 24 male) with craniopharyngiomas were examined. Follow-up was 5-17 years (median, 8 years). Fifteen patients were aged younger than 18 years. RESULTS: All patients underwent surgical resection. Complete resection was achieved in 19. Seven patients underwent additional surgery for recurrent disease. Rate of mortality due to surgical complications was 10% (n = 5). Eight patients had marked perioperative or long-term morbidity. Twenty-five patients judged to have undergone subtotal resection underwent postoperative radiation therapy (RT). RT doses were 4,600-6,287 cGy administered in fractions of 180-200-cGy/d. Actuarial 5-year progression-free survival in patients who underwent complete resection was 63% (12 of 19 patients) versus 96% (24 of 25 patients) in patients who underwent subtotal resection followed by RT (P = .04). No RT dose response was observed. Patient functional status has not been substantially affected by adjuvant RT. CONCLUSION: RT achieves excellent tumor control after subtotal resection of craniopharyngiomas.

Adolescent↗
PubMed1994

Mucosal melanoma of the head and neck: the impact of local control on survival.

The management for mucosal melanoma of the head and neck is controversial in view of the poor prognosis. Thirty-five patients seen from 1955 to 1991 were analyzed retrospectively. Almost all (34/35) presented with localized disease. Primary treatments included radical surgery (15), local resection (11), radiation therapy (6), or systemic treatment (2). While the rate of local recurrence was high (27/34), only 5 patients developed distant disease before local relapse. Furthermore, only 5/21 achieved successful local salvage. Patients with their disease controlled locally had significantly longer survival than those with persistent local disease (P = .0001). The 5-year disease-specific survival was 45%. The authors conclude that mucosal melanoma of the head and neck is not necessarily incurable. When local control is achieved, survival rate is significantly improved. Aggressive local treatments should be initiated at presentation of this disease.

Actuarial Analysis↗
PubMed1994

Primary central nervous system lymphoma. Results at the University of California at Los Angeles and review of the literature.

The authors report 24 patients with primary central nervous system lymphoma (PCNSL) treated from 1977 to 1992. There were 13 females and 11 males. Median age was 57 (range: 17-84). Patients were symptomatic for a median of 3 months. Headache was the most common complaint. Median Karnofsky performance score was 70. There were 19 patients with solitary PCNSL, and 5 had multiple deposits. Disease was confined to the supratentorium in 23 patients. Cerebrospinal fluid cytology was positive in 5 of 22 patients examined. All patients received whole-brain irradiation with or without supplemental tumor boost. Tumor doses ranged from 10 to 60 Gy. Intrathecal chemotherapy was administered to 16 patients and 7 received systemic agents. After follow-up ranging from 1 to 66 months, median survival and progression-free survival were each 8 months. One- and 3-year actuarial survival rates were 50% and 36%, respectively. One- and 3-year actuarial progression-free rates were 41% and 15%, respectively. Relapse occurred in 18 patients, and in 17 there was a component of local progression. Lesions recurred in the spinal meninges in 1 patients and in the vitreous in 1. Patients with Karnofsky performance status > or = 70 demonstrated median progression-free survival of 27 months, compared to 4 months for patients < 70 (p = .024). No other significant patient or treatment-related prognostic factors were identified. Clinical dementia occurred in 2 of 11 patients surviving at least 1 year. Review of the literature indicates PCNSL demonstrates relative radioresistance. The most immediate improvement in prognosis for patients with PCNSL can be achieved by properly sequencing systemic and intrathecal chemotherapy with radiation therapy.

Actuarial Analysis↗
PubMed1993

Management of oligodendrogliomas.

To define optimum treatment and delineate recurrence patterns and prognostic factors in oligodendrogliomas, the authors reviewed the records of 49 patients who received treatment for these rare tumors between 1957 and 1990; 41 patients had at least 5 years follow-up. Age, race, gender, performance of computed tomography (CT), tumor location and grade, histologic findings, calcifications, surgery with or without postoperative radiation therapy, and the doses and fields used in radiation therapy were evaluate for prognostic relevance by means of chi 2 and Wilcoxon log-rank tests. Metaanalysis of relevant literature was also performed. Actuarial survival at 5, 10, and 15 years was 61%, 41%, and 24%, respectively. The pattern of recurrence was predominantly local alone (30 of 31 patients [97%] with recurrence). Age younger than 40 years, low-grade tumor, calcifications, and performance of CT were statistically significant prognostic factors. A trend existed toward improved 5-year survival in patients who underwent postoperative radiation therapy (P = .067); at stratification for subtotal resection, this improvement became significant (74% vs 25%, P = .019). Metaanalysis demonstrated a survival advantage for surgery with radiation therapy versus surgery only (56% vs 42%, P < .01).

Adolescent↗