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Biomedical subjects

David Huang

Publications and source records attributed to David Huang.

At least 37 records · Page 2Linked to original sources
PubMed2005

Comparison of optical coherence tomography and ultrasound biomicroscopy for detection of narrow anterior chamber angles.

OBJECTIVE: To assess the accuracy of classification of narrow anterior chamber (AC) angles using quantitative imaging by optical coherence tomography (OCT) and ultrasound biomicroscopy (UBM). DESIGN: Observational comparative study. METHODS: A high-speed (4000 axial scans/s) anterior segment OCT prototype was developed using a 1.3-microm light source. Seventeen normal subjects (17 eyes) and 7 subjects (14 eyes) with narrow angle glaucoma were enrolled. All subjects underwent gonioscopy, OCT, and UBM. Quantitative AC angle parameters (angle opening distance, angle recess area, and the trabecular-iris space area [a new parameter we have defined]) were measured from OCT and UBM images using proprietary processing software. MAIN OUTCOME MEASURES: Specificity and sensitivity in identifying narrow angles with image-derived AC angle parameters. RESULTS: Eight of 31 eyes were classified as having narrow angles (Shaffer grade < or =1 in all quadrants). The AC angle parameters measured by both OCT and UBM had similar mean values, reproducibility, and sensitivity-specificity profiles. Both OCT and UBM showed excellent performance in identifying eyes with narrow angles. Areas under the receiver operating characteristic curves for these parameters were all in the range of 0.96 to 0.98. CONCLUSIONS: Optical coherence tomography was similar to UBM in quantitative AC angle measurement and detection of narrow angles. In addition, it was easier to use and did not require contact with the eye. Optical coherence tomography is a promising method for screening individuals at risk for narrow angle glaucoma.

Adult↗
PubMed2005

Characteristics of keratoconus and pellucid marginal degeneration in mean curvature maps.

PURPOSE: To characterize keratoconus and pellucid marginal degeneration (PMD) on mean curvature maps. DESIGN: Observational case series. METHODS: A retrospective analysis of clinical records of 19 keratoconus eyes and eight PMD eyes. Keratometric mean curvature maps were computed from a placido-disk-based corneal topography system. The peak location and amplitude of distortions were quantified by fitting two-dimensional Gaussian functions. Computer simulations of keratoconic corneal topography were used to help interpret the results. RESULTS: Keratoconus and PMD eyes had a characteristic localized increase in convexity (cone) on mean curvature maps. Computer simulations showed that the peak on the mean curvature map accurately represented the peak of the cone-like distortion. However, the peak location and appearance of the same conic distortion on axial and tangential maps were greatly influenced by coexisting astigmatism. The Gaussian function provided an excellent model of keratoconus on mean curvature maps, with a mean cross-correlation of 0.80. According to Gaussian fitting, the vertical cone peak locations were -1.10 +/- 0.43 mm (mean +/- SD) in keratoconus eyes and -1.94 +/- 0.53 mm in PMD eyes (P < .01). The locations of peaks on axial and tangential maps differed considerably from those on mean curvature maps. Advanced keratoconus tended to have higher cones (amplitude 13.31 +/- 6.87 diopters) than early keratoconus (amplitude 10.65 +/- 1.56 diopters). CONCLUSIONS: Gaussian fitting of mean curvature maps accurately quantifies the peak location and amplitude of the cone in keratoconus and PMD eyes. This new topographic analysis might be useful in the diagnosis and tracking of corneal ectatic diseases.

Computer Simulation↗
PubMed2005

High-speed optical coherence tomography of laser iridotomy.

PURPOSE: To describe high-speed (4000 axial scans/s) optical coherence tomography (OCT) findings in a patient with narrow angles. DESIGN: Interventional case report. METHODS: A 56-year-old woman was found to have occludable narrow angles on OCT screening. This was confirmed by gonioscopy. Bilateral iridotomy was performed. Imaging of the angles was performed with a high-speed OCT prototype before and after iridotomy. RESULTS: OCT showed narrow angle bilaterally. Cornea, sclera, scleral spur, trabecula, iris, and iris recess were visualized. After iridotomy, the OCT showed reduction of iris concavity and patent iridotomies. Quantitative measurements of trabecula-iris space area on the OCT images showed widening of the angles to nonoccludable values. CONCLUSIONS: A 1.3-microm wavelength OCT allows noncontact quantitative assessment of the angle and may be useful in the management of narrow-angle glaucoma.

Diagnostic Techniques, Ophthalmological↗
PubMed2005

Optical coherence tomography imaging of the anterior chamber angle.

Primary angle closure glaucoma is a common cause of visual loss worldwide. Gonioscopy and other current methods of assessment of the anatomy of the anterior segment relevant to the diagnosis of this disease, such as ultrasound biomicroscopy, have significant limitations. Anterior segment optical coherence tomography, with its rapid, noncontact, and high-resolution image acquisition, seems to be a promising tool for the evaluation of the anterior chamber angle configuration, including changes induced by illumination and laser peripheral iridotomy. It has the potential for use as a rapid screening tool for detection of occludable angles. Ongoing clinical studies should help to evaluate its efficacy in this regard.

Anterior Chamber↗
PubMed2005

Anterior chamber width measurement by high-speed optical coherence tomography.

OBJECTIVE: To measure anterior chamber (AC) width and other dimensions relevant to the sizing of phakic intraocular lenses (IOLs) with a high-speed optical coherence tomography (OCT) system. DESIGN: Cross-sectional observational study. PARTICIPANTS: Both eyes of 20 normal volunteers. METHODS: A novel high-speed (4000 axial scans/second) OCT prototype was developed for anterior segment scanning. The system uses long wavelength (1310 nm) for deeper angle penetration, rectangular scanning for undistorted imaging, and short image acquisition time (0.125 seconds) to reduce motion error. Three horizontal cross-sectional OCT images (15.5 mm wide and 6 mm deep) of the anterior segment were obtained from each eye with real-time image display to guide centration on the corneal apex. Image processing software was developed to correct for image warping resulting from index transitions. Anterior chamber dimensions were measured using computer calipers by 3 expert raters (ophthalmologists). Analysis of variance was used to determine interrater, interimage, right versus left eye, and intersubject standard deviation (SD) of OCT measurements. MAIN OUTCOME MEASURES: Anterior chamber width (recess to recess), AC depth, and crystalline lens vault as measured by OCT; external white-to-white (WTW) corneal diameter (CD) as measured by Holladay-Godwin gauge. RESULTS: The mean AC width was 12.53+/-0.47 mm (intereye SD), and the mean corneal diameter was 11.78+/-0.57 mm. Optical coherence tomography measurement of AC width has good repeatability from image to image (SD, 0.134 mm), but there was significant difference between raters (SD, 0.215 mm). Estimation of AC width from WTW CD by linear regression was relatively inaccurate (residual SD, 0.41 mm). The mean AC depth was 2.99+/-0.323 mm (intereye SD), with repeatability of less than 0.001 mm (interimage SD), and the mean crystalline lens vault was 0.39+/-0.27 mm with 0.023 mm repeatability. CONCLUSIONS: Reproducible OCT AC biometry was demonstrated using a high-speed OCT prototype. Further improvement in reproducibility may be achieved by automating the measurements with a computer. Direct OCT AC width measurement may improve sizing of angle-supported AC IOLs over conventional estimation by WTW CD. The measurement of AC depth and lens vault also may be useful for other types of phakic AC IOLs.

Adult↗
PubMed2005

Mean curvature mapping for detection of corneal shape abnormality.

Corneal topography is used to measure the anterior surface of the cornea. It is conventionally represented as radial slope, radial curvature, and elevation. In this paper, we introduce the application of mean curvature mapping as an alternative representation of the corneal topography. The purpose is to improve the detection of keratoconus and other diseases characterized by local increase in corneal curvature. Both simulated keratoconic cornea and real keratoconus data exported from the corneal topography system were analyzed. Four representations of corneal topography were generated and compared. It was found that mean curvature mapping provided the most precise cone location in simulated keratoconus. In both actual and simulated keratoconus cases, the appearance of the cone-like distortion is more consistent on mean curvature maps. Mean curvature mapping may improve the detection and localization of corneal shape abnormalities.

Algorithms↗
PubMed2005

Optical coherence tomography: a new method to assess aneurysm healing.

OBJECT: Aneurysmal subarachnoid hemorrhage affects approximately 10/100,000 people per year. Endovascular coil embolization is used increasingly to treat cerebral aneurysms and its safety and durability is rapidly developing. The long-term durability of coil embolization of cerebral aneurysms remains in question; patients treated using this modality require multiple follow-up angiography studies and occasional repeated treatments. METHODS: Optical coherence tomography (OCT) is an emerging imaging modality that uses backscattered light to produce high-resolution tomography of optically accessible biological tissues such as the eye, luminal surface of blood vessels, and gastrointestinal tract. Vascular OCT probes in the form of imaging microwires are presently available--although not Food and Drug Administration-approved--and may be adapted for use in the cerebral circulation. In this study the authors describe the initial use of OCT to make visible the neck of aneurysms created in a canine model and treated with coil embolization. Optical coherence tomography images demonstrate changes that correlate with the histological findings of healing at the aneurysm neck and thus may be capable of demonstrating human cerebral aneurysm healing. CONCLUSIONS: Optical coherence tomography may obviate the need for subsequent follow-up angiography studies as well as aid in the understanding of endovascular tissue healing. Data in this study demonstrate that further investigation of in vivo imaging with such probes is warranted.

Animals↗
PubMed2004

Group index of the human cornea at 1.3-microm wavelength obtained in vitro by optical coherence domain reflectometry.

The group index of the cornea, rather than the phase refractive index, is required for thickness calculations with optical coherence tomography. Recent advances with high-speed optical coherence tomography at 1.3 microm make index measurement at this wavelength of great interest. Group indices of three human corneas from an eye bank were measured in vitro with optical coherence domain reflectometry. Measurements were made in a calibrated cuvette filled with a preservation medium to maintain proper corneal hydration. Group indices were calculated from the optical path lengths measured. The corneal group index was 1.389 +/- 0.004 (average +/- standard deviation). The average group index of a balanced salt solution, an approximation to aqueous humor, was 1.343 +/- 0.001.

Chondroitin Sulfates↗
PubMed2004

LASIK for hyperopia, hyperopic astigmatism, and mixed astigmatism: a report by the American Academy of Ophthalmology.

OBJECTIVE: To describe LASIK for hyperopia, hyperopia with astigmatism, and mixed astigmatism and to examine the evidence to answer questions about the safety and efficacy of the procedure. METHODS: A literature search conducted for the years 1968 to 2002 retrieved 118 citations. During review and preparation of this article, an additional 2 articles were included. The panel members selected 36 articles for the panel methodologist to review and rate according to the strength of evidence. A level I rating is assigned to properly conducted, well-designed, randomized clinical trials; a level II rating to well-designed cohort and case-control studies; and a level III rating to case series, case reports, and poorly designed prospective and retrospective studies. RESULTS: This assessment describes 5 nonrandomized interventional trials (level II), 3 nonrandomized comparative trials (level III), and 20 noncomparative case series (level III). Additionally, 6 single-case reports (level III) were included because they reported relevant complications, and 2 theoretical analyses (level III) were also considered. This assessment does not compare studies because many variables such as range of hyperopia, follow-up periods, lasers, microkeratomes, techniques, and surgeon experience have not been controlled. CONCLUSIONS: For low (<3 diopters [D]) to moderate (3-5 D) hyperopia, results from published studies (levels II and III evidence) have shown that LASIK is effective and predictable in achieving very good to excellent uncorrected visual acuity, achieving postoperative refractions within 1 D of emmetropia, and is safe in terms of minimal loss of best-corrected spectacle vision. Although there are fewer data for hyperopic astigmatism, the results available seem to mirror the data for low to moderate hyperopia (levels II and III evidence). The postoperative results for both uncorrected vision and safety are less compelling, as greater amounts of hyperopia are treated (>4 to 5 D). Utilizing hyperopic LASIK for the treatment of consecutive hyperopia and astigmatism is also effective, although the ability to reduce hyperopic astigmatism after radial keratotomy is limited. Although a variety of ablation profiles can be used to treat mixed astigmatism, very good visual results have been reported (levels II and III evidence). Serious adverse complications leading to permanent visual loss are possible but, fortunately, very rare. There are insufficient data to compare one laser system with another or one ablation profile with another.

Academies and Institutes↗
PubMed2004

Optical coherence tomography of the anterior segment of the eye.

Optical coherence tomography is a versatile tool for visualization and measurement of corneal and anterior segment anatomy. Keratorefractive surgery, anterior chamber biometry, and angle assessment are some of the applications that should benefit from this technology.

Anterior Eye Segment↗
PubMed2004

Relationship between drug treatment services, retention, and outcomes.

OBJECTIVE: This longitudinal study conducted path analyses to examine the relationships between treatment processes and outcomes among patients in community-based drug treatment programs. METHODS: A total of 1,939 patients from 36 outpatient drug-free and residential treatment programs in 13 California counties were assessed at intake, discharge, three months after admission, and nine months after admission. Path analyses were conducted to relate the quantity and quality of services that were received in the first three months of treatment to treatment retention and outcomes at the nine-month follow-up. Patients were determined to have a favorable outcome if for at least 30 days before the follow-up assessment they did not use drugs, were not involved in criminal activity, and lived in the community. The path analyses controlled for patients' baseline characteristics. RESULTS: Greater service intensity and satisfaction were positively related to either treatment completion or longer treatment retention, which in turn was related to favorable treatment outcomes. Patients with greater problem severity received more services and were more likely to be satisfied with treatment. These patterns were similar for patients regardless of whether they were treated in outpatient drug-free programs or residential programs. CONCLUSIONS: The positive association between process measures-that is, greater levels of service intensity, satisfaction, and either treatment completion or retention-and treatment outcome strongly suggests that improvements in these key elements of the treatment process will improve treatment outcomes.

Adolescent↗
PubMed2004

Achieving normothermia in patients with febrile subarachnoid hemorrhage: feasibility and safety of a novel intravascular cooling catheter.

INTRODUCTION: Fever is common and difficult to control in patients with subarachnoid hemorrhage (SAH). We have previously shown an inverse relationship between fever and outcome in patients with SAH. MATERIALS/METHODS: This was a prospective, single-arm, feasibility trial in which nine patients with SAH underwent temperature management using an intravascular cooling catheter (ICC) to restore and maintain 24 hours of normothermia (36.5 degrees+/-0.2 degrees C). Enrollment occurred after development of a fever of at least 38.3 degrees C within 7 days of SAH that was refractory to acetaminophen treatment. The ICC was placed at the bedside through an introducer sheath via the femoral vein into the inferior vena cava (IVC). Portable X-ray confirmed placement. RESULTS: Normothermia was achieved in seven of the nine patients treated (78%); it was achieved in 100% of the patients with a 14F catheter (n=4) and in 60% of the patients with a 9F catheter (n=5). The two patients not reaching normothermia were not adequately treated for shivering. All other patients reached normothermia irrespective of intubation status. Overall, normothermia was well tolerated and not discontinued because of discomfort or adverse events. Two incidences of deep vein thrombosis were diagnosis by ultrasound that were not associated with clinical sequelae, and IVC filters were placed. No unanticipated adverse events occurred. DISCUSSION: We have demonstrated that fever can be safely and effectively controlled in patients with SAH for at least 24 hours using an ICC. Future studies are needed to assess the effect of such sustained therapy on outcome in patients with SAH.

Adult↗
PubMed2003

Gender comparisons of drug abuse treatment outcomes and predictors.

Gender differences in drug treatment outcomes and predictors were examined among a sample of 511 patients recruited from drug treatment programs across Los Angeles County. Face-to-face interviews were conducted at baseline and at 1-year follow-up. Results showed that women and men started their drug use and treatment careers at similar ages, but men reported greater drug use and criminal involvement at baseline. There were no significant differences by gender in drug use and alcohol use at follow-up but men reported more crimes than women. Separate logistic regression analyses showed that for both women and men, longer treatment retention was associated with drug abstinence and crime desistence at follow-up. Additional baseline predictors of abstinence at follow-up included use of multiple drugs and readiness for treatment for women, and spousal drug use for men. For crime desistence, significant predictors include legal involvement and treatment readiness for women, and legal involvement, use of multiple drugs, and living with children for men. For both women and men, participation in 12-step groups and no spousal drug use during follow-up were related to abstinence. There were both similarities and differences in predictors of treatment outcome for women and men.

Adolescent↗
PubMed2003

The prognostic significance of Gleason Grade in patients treated with permanent prostate brachytherapy.

PURPOSE: To assess the difference in biochemical freedom from relapse (BFR) between patients with clinically localized prostate cancer having Gleason Grade (GG) 3 + 4 vs. 4 + 3 disease treated with permanent prostate brachytherapy (PPB). METHODS AND MATERIALS: One thousand twenty-nine consecutive T1/T2 patients underwent PPB with Gleason sum 6, 7, or 8 adenocarcinoma of the prostate. Treatment consisted of transperineal ultrasound-guided implant as monotherapy or in combination with external beam radiation and/or neoadjuvant androgen ablation (NAAD). The Kattan modification of the ASTRO consensus definition that censors patients with rising follow-up PSA values early was used to measure BFR. Kaplan-Meier actuarial survival was calculated and compared using the log-rank test. Cox proportional hazards regression was performed to assess the role of Gleason grade, initial PSA value, stage, the addition of external beam radiotherapy, and the addition of NAAD. RESULTS: The median follow-up for all 1029 patients is 46 months (range: 3-108 months) with a BFR at 5 years of 78.2% and at 7 years of 76.2%. The 7-year BFR for patients with GG 3 + 3 was 81.8%, GG 3 + 4 was 78.4%, GG 4 + 3 was 56.7%, and GG 4 + 4 was 50.7% (p < 0.0001). Cox regression analysis identified that the Gleason grade (p < 0.0001), initial PSA value (p = 0.001), D90% (p < 0.0001), and clinical stage (p = 0.016) were associated with biochemical recurrence, whereas NAAD (p = 0.057) and external beam radiotherapy (p = 0.356) were not. CONCLUSIONS: Gleason sum 7 tumors in patients treated with PPB represent a heterogeneous group of patients based on the differentiation of Gleason Grade 3 + 4 tumors vs. 4 + 3 disease. This information confirms similar conclusions identified in patients treated with external beam radiation and is useful when determining prognosis after PPB.

Adenocarcinoma↗
PubMed2003

Comparison of treatment plans using intensity-modulated radiotherapy and three-dimensional conformal radiotherapy for paranasal sinus carcinoma.

PURPOSE: To compare intensity-modulated radiotherapy (IMRT) treatment planning with three-dimensional conformal radiotherapy (3D-CRT) planning for paranasal sinus carcinoma. MATERIALS AND METHODS: Treatment plans using traditional 3-field technique, 3D-CRT planning, and inverse planning IMRT were developed for a case of paranasal sinus cancer requiring adjuvant radiotherapy. Plans were compared with respect to dose conformality, dose-volume histograms, doses to critical normal tissues, and ease of treatment delivery. RESULTS: The inverse-planned IMRT technique was more conformal around the tumor target volume than conventional techniques. The dose-volume histograms demonstrated significantly better critical normal-tissue sparing with the IMRT plans, while able to deliver a minimum dose of 60 Gy to the clinical tumor volume and 70 Gy to the gross tumor volume. Acute toxicities in our analysis were minimal. CONCLUSIONS: IMRT planning provided improved tumor target coverage when compared to 3D-CRT treatment planning. There was significant sparing of optic structures and other normal tissues, including the brainstem. Inverse planning IMRT provided the best treatment for all paranasal sinus carcinomas, but required stringent immobilization criteria. Further studies are needed to establish the true clinical advantage of this modality.

Aged↗
PubMed2003

Importance of implant dosimetry for patients undergoing prostate brachytherapy.

OBJECTIVES: To evaluate the disease and treatment-related factors for predicting biochemical freedom from recurrence (BFR) in patients with clinically localized prostate cancer undergoing permanent prostate brachytherapy. METHODS: Between November 1992 and June 1998, 883 consecutive patients with T1-T2 prostate cancer underwent permanent prostate brachytherapy. Computed tomography-based dosimetry was performed, and the minimal dose to 90% of the prostate volume relative to the prescribed dose (D(90)) was calculated. BFR was defined as three prostate-specific antigen (PSA) rises from nadir, with patients having one or two PSA rises censored early. Follow-up was calculated by censored events. Kaplan-Meier actuarial outcome was determined, and multivariate Cox regression analysis was performed to assess the significance of the D(90), initial PSA value, Gleason score, addition of external beam radiotherapy, addition of hormonal therapy, and isotope selection. RESULTS: The mean follow-up was 55 months (range 3 to 125). The 10-year BFR rate was 79.1%. Cox proportional analysis identified D(90) as a predictor of BFR (P <0.0001), along with Gleason score, initial PSA level, and clinical stage (P = 0.001, P = 0.001, and P = 0.011, respectively). The addition of external beam radiotherapy, hormonal therapy, and isotope selection did not have an impact on BFR (P = 0.128, P = 0.399, and P = 0.224, respectively). CONCLUSIONS: The quality of permanent prostate brachytherapy as measured by the D(90) was the most significant predictor for BFR in this study cohort at 10 years. Furthermore, adding external beam radiotherapy and/or hormonal therapy as adjuvant therapies did not independently predict for BFR. Overall, the reported 10-year BFR rates in this study were favorable. Strategies for ensuring the best quality implant should be used and, when reporting brachytherapy outcomes, the implant quality should be noted.

Adenocarcinoma↗
PubMed2003

Mathematical model of corneal surface smoothing after laser refractive surgery.

PURPOSE: To construct a quantitative model of corneal surface smoothing after laser ablation for refractive correction. DESIGN: Experimental study, interventional case series, and meta-analysis of literature. METHODS: A theory of epithelial smoothing in response to corneal contour change is derived from differential equations that describe epithelial migration, growth, and loss. Computer simulations calculate the effects on postoperative epithelial thickness, topography, refraction, and spherical aberration. Model parameter is matched with laser in situ keratomileusis (LASIK) outcome in literature and in a retrospective study of primary spherical myopic (77 eyes) and hyperopic (19 eyes) corrections. Surgically induced refractive change was the main outcome measure. RESULTS: Simulated epithelial remodeling after myopic ablation produces central epithelial thickening, reduction in achieved correction, and induction of oblate spherical aberration. Simulation of hyperopic ablation shows peripheral epithelial thickening, a larger reduction in correction, and induction of prolate spherical aberration. Simulation using a minus cylinder laser ablation pattern shows decreased astigmatism correction and increased hyperopic shift. In the LASIK series, linear regression of achieved correction vs ablation setting in hyperopic and minus cylinder corrections shows slopes of 0.97, 0.71, and 0.74, respectively. These clinical results match model predictions when the smoothing constant is set at 0.32, 0.63, and 0.55 mm, respectively. CONCLUSIONS: Epithelial thickness modulations after ablation can be modeled mathematically to explain clinically observed regression and induction of aberration. The cornea appears to smooth over ablated features smaller than approximately 0.5 mm. The model provides an approach for designing ablation patterns that precompensate for the smoothing to improve final outcome.

Astigmatism↗