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Biomedical subjects

D J Coleman

Publications and source records attributed to D J Coleman.

At least 55 records · Page 3Linked to original sources
PubMed1995

High frequency ultrasound imaging in pupillary block glaucoma.

BACKGROUND: The diagnosis of pupillary block glaucoma requires sufficient clarity of the ocular media. This is particularly important for assessment of both the presence and patency of an iridotomy, and the determination of central anterior chamber depth. METHODS: High frequency ultrasonography was used in three patients with suspected pupillary block to determine iris configuration, posterior chamber volume, and ciliary body conformation. RESULTS: All patients demonstrated high frequency ultrasonographic findings consistent with pupillary block: iris bombé, a formed posterior chamber, and a lack of anterior rotation of the ciliary processes. CONCLUSION: High frequency ultrasound imaging appears to be a valuable adjunct in making or corroborating the diagnosis of pupillary block glaucoma.

Aged↗
PubMed1995

High-frequency ultrasound spectral parameter imaging of anterior corneal scars.

High frequency (50-MHz) ultrasound allows greater resolution (approximately 30 microns) and improved tissue differentiation of the anterior ocular structures than conventional (8-10 MHz) ultrasonic techniques. Spectral analysis of tissue acoustic backscatter is sensitive to both the concentration and size of tissue inhomogeneities. We studied the healing process of experimentally induced corneal scars using high frequency ultrasound spectral analysis. Scatterer size and concentration parameter images of scarred corneas showed distinctive patterns that were correlated with histology over time. This quantitative technique offers a new, noninvasive, in vivo method for the assessment of the internal microarchitecture of surgically altered corneal tissue and its healing dynamics.

Animals↗
PubMed1994

Corneal pachymetric topography.

PURPOSE: The authors developed a system for producing topographic pachymetric maps of the corneal epithelium and anterior scar tissue. METHOD: The system uses high-frequency ultrasound scanning enhanced by digital signal processing. Ultrasonic echo data from consecutive parallel B-scans of the cornea spaced at 250-microns intervals are digitized and stored. Using the I-scan (obtained by computing the analytic signal magnitude of the deconvolved ultrasound signal), layer thickness measurements are made with a precision of 2 microns (standard deviation) at 120-microns intervals along each scan plane. The data are stored as an array, z(x,y), mapping thickness, z, onto horizontal and vertical (x,y) spatial coordinates. Pachymetric maps are then constructed by plotting local thickness, represented by a color scale, against measurement point position. RESULTS: Examples of a normal cornea, a contact lens-wearing cornea, Reis-Bückler dystrophy, and postphotorefractive keratectomy are presented. Areas with significant subepithelial scarring and general epithelial thickening in a subject with Reis-Bückler dystrophy are mapped. Unevenness in the epithelial thickness profile of the cornea in a subject after photorefractive keratectomy is shown, relative to the fellow (untreated) cornea. CONCLUSION: This technique provides the corneal surgeon with a new tool for the topographic evaluation of the thickness of anterior corneal layers in normal and pathologic corneas with high precision. In addition, the technique is not limited to optically transparent tissue.

Adult↗
PubMed1994

Epithelial and corneal thickness measurements by high-frequency ultrasound digital signal processing.

PURPOSE: The authors determine the mean central corneal and epithelial thickness in a group of normal human subjects using a new high-frequency ultrasound technique, incorporating digital signal processing. METHOD: Both eyes of ten volunteers (age range, 23-44 years) were scanned through a normal saline standoff. Digitized ultrasonic echo data were mathematically transformed to produce a plot, the I-scan, which optimally localizes acoustic interfaces to provide improved measurement precision. System precision was determined by analysis of variance of repeated measures. Central epithelial thickness was obtained by averaging multiple measurements. Central corneal thickness was determined by fitting measurements of apparent corneal thickness in consecutive parallel B-scans to a mathematically modeled cornea. A speed of sound of 1640 m/second was used. RESULTS: Epithelial pachymetric precision using A-scan and I-scan was 4.8 and 2.0 microns (standard deviation), respectively. The mean epithelial thicknesses for the right and left eyes were 50.7 +/- 3.7 microns and 50.3 +/- 3.4 microns, respectively. The mean corneal thicknesses in the right and left eyes were 514.6 +/- 38.4 microns and 516.2 +/- 37.8 microns, respectively. The root mean-square differences in epithelial and corneal thickness between the left and right eyes of each subject were 1.3 and 7.7 microns, respectively (neither was statistically significant). CONCLUSION: This system provides a pachymetric precision superior to current optical and ultrasound methods. Epithelial and corneal pachymetry is obtained noninvasively by a method that is not limited to optically clear media.

Adult↗
PubMed1994

High-frequency ultrasound corneal pachymetry in the assessment of corneal scars for therapeutic planning.

We used high-frequency ultrasound B-scanning with digital signal processing for pachymetric analysis of corneal scars to help determine the optimal management strategy. Four patients were selected for this report. By an automated motor system, 12 consecutive, parallel ultrasound B-scans, each 2.5 to 3 mm wide at 0.25 mm intervals, were obtained from the central corneal area of three patients with anterior corneal scarring. In a fourth patient with near complete corneal scarring obscuring the view of the anterior chamber, a set of 15 mm wide B-scans was obtained. Digitized ultrasound signals were used to produce high-resolution images and I-scans enabling a pachymetric precision of +/- 2 microns (SD). Epithelial, scar, and corneal thickness measurements were made along each scan to determine the most significant zone of pathology. Pachymetry of the cornea and the individual layers was used to assess the suitability for either photorefractive or penetrating keratectomy. B-scan imaging of the full anterior segment provided useful information for the preoperative planning of anterior segment reconstruction and the prognostic evaluation of penetrating keratoplasty. This method provides a powerful tool for the corneal surgeon in management planning.

Adult↗
PubMed1994

Immunomodulation in choroidal melanoma: reversal of inverted CD4/CD8 ratios following treatment with ultrasonic hyperthermia.

It has long been suggested that malignant melanomas, cutaneous as well as uveal, are responsive to human immune-mediated host defenses. We report here 5 consecutive cases of posterior choroidal melanomas which were treated with hyperthermia generated by high-intensity focused ultrasound. Patient immune function was monitored by determination of T-cell helper/suppressor (CD4/CD8) ratios immediately before and approximately 1 week following hyperthermia treatment. All 5 patients had normal total T-cell counts as measured by the pan-T-cell marker CD3. Two patients were noted to have inverted CD4/CD8 ratios (< 1:1) before hyperthermia. In both these cases, the ratio reverted to normal (> 1:1) 1 week following treatment. One patient whose CD4/CD8 ratio was not inverted was noted to have a further increase in his CD4 T cells relative to his CD8 (37% increase). Two patients with initially normal CD4/CD8 demonstrated no significant change following hyperthermia. It appears that ultrasonic hyperthermia may induce a systemic immunomodulatory effect in patients with posterior choroidal melanoma and inverted T-cell helper/suppressor resulting in a normalization of T-cell subset ratios.

Aged↗
PubMed1993

High-frequency ultrasound quantitative analyses of corneal scarring following excimer laser keratectomy.

OBJECTIVE: To report objective grading and analysis of excimer laser-induced scarring using high-frequency ultrasound. METHODS: High-frequency ultrasound (50 MHz) corneal examination was performed on eight New Zealand white rabbits at different time points (10, 17, 24, and 74 days following phototherapeutic keratectomy). We used biometry and signal-processing techniques to determine corneal, epithelial, and scar thicknesses and to quantify the acoustic backscatter. RESULTS: Excimer laser-induced scarring showed an irregularly distributed acoustic hyperreflectivity that decreased through day 74. Corneal thickness remained reduced after ablation (mean, 318 microns compared with 419 microns for controls). Epithelial thickness averaged 62 microns and scar thickness, 87 microns. Scar peak and average anterior stroma acoustic backscatter ratios decreased from day 10 to day 74 (19.65 to 2.76, and 6.42 to 1.32, respectively). Histopathologic study showed increased keratocyte activity at early time points that correlated with acoustic backscatter ratios and imaging pattern. CONCLUSIONS: High-frequency ultrasound signal processing is a noninvasive method that quantitatively grades excimer laser-induced corneal scarring.

Animals↗
PubMed1993

The role of the contractile fibroblast in the capsules around tissue expanders and implants.

The occurrence, structure and contractility of myofibroblasts in the capsules around tissue expanders and static implants has been studied in the rat, pig and humans. The capsules showed a characteristic layered structure with myofibroblasts being the predominant cell type. Capsular strips contract in vitro in a manner characteristic of fibroblast contraction. The contractile ability decreased with the time since expander insertion; and increased with expander exposure, peri-expander infection and clinical evidence of adverse capsular contracture. An hypothesis is proposed that capsular contracture is analogous to wound contraction, and that intraimplant pressure usually inhibits capsular contraction. Evidence is shown from intraexpander pressure measurements to support this hypothesis. The clinical implications for tissue expansion and breast augmentation are discussed.

Animals↗
PubMed1993

High-frequency ultrasound imaging and spectral analysis in traumatic hyphema.

PURPOSE: High-frequency (50-MHz) ultrasound allows high-resolution imaging of anterior ocular structures. Spectrum analysis of acoustic backscatter is sensitive to the concentration, size, and density of tissue inhomogeneities. The authors sought to determine whether acoustic imaging and spectrum analysis of hyphema would allow them to distinguish organized from fluid hyphema and recent from old hemorrhage in the eye. METHODS: Trauma-induced hyphemas were followed by slit-lamp photography and high-frequency ultrasonography in six New Zealand white rabbits. The blood collections were analyzed using the normalized power spectra of the digitized radio frequency ultrasound data and compared with in vitro references. RESULTS: The 50-MHz acoustic images permitted differentiation between fluid (diffuse) and clotted (organized) blood. Spectrum analysis allowed quantitative characterization of the degree of blood organization. Significant changes were observed in spectral properties during the time course of absorption both for initial and after-rebleeding hemorrhages. The characteristics of a human postsurgical hyphema also were examined and found to be similar to those seen in the experimental model. CONCLUSION: Spectrum analysis of high-frequency ultrasound data was able to distinguish organized from recent hemorrhage, which is clinically helpful for planning hyphema therapy.

Animals↗
PubMed1993

Measurement of ocular tumor volumes from serial, cross-sectional ultrasound scans.

A system has been developed to determine intraocular tumor volume, a characteristic that has been estimated in previous studies from linear dimensions using a variety of models. Volume was determined by tracing tumor boundaries in sequential, parallel ultrasound scans, adding the areas and multiplying by the interslice interval. The in vitro accuracy of the technique was within +/- 2%. The mean difference between volumes determined from replicate in vivo scans of intraocular tumors was 4.3%. Serial scan volumes were, on average, 19% smaller than volumes computed from an ellipsoidal model and 13% smaller than area-rotational volumes. Differences of as much as 50% were observed between serial scan volumes and volumes computed with these models. The results indicate that methods based on either linear measurements or the tumor area in a single cross-section will tend to both systematically overestimate tumor volume and suffer from unpredictable, nonsystematic errors.

Humans↗
PubMed1993

Using high-frequency ultrasound to characterize intraocular foreign bodies.

We scanned uniformly-sized particles of brass, aluminum, glass, and plastic at ultrasonic frequencies of 10 and 50 MHz to determine the effects of material type and transducer frequency on the ultrasonographic appearance of these particles. The particles were scanned in vitro against both anechoic and echoic backgrounds and in vivo, implanted in the angle of rabbit eyes. Both the metals and glass produced reverberations against an anechoic background; the plastic particles appeared as discrete objects, with no reverberations. Against an echoic background, the plastic particles created prominent shadows, while the metal ones did not. When placed in the angle of a rabbit eye, with the exception of the plastic at 10 MHz, all the materials could be differentiated from surrounding tissues at both frequencies. However, the appearance of the foreign body and the surrounding tissues, as well as their exact location and size, were most obvious with the 50-MHz system. In general, the particles produced more reverberations at 10 than at 50 MHz, and more prominent shadowing at 50 than at 10 MHz. In summary, high-frequency imaging enabled superior characterization of all the particles.

Animals↗
PubMed1992

Computer model of ultrasonic hyperthermia and ablation for ocular tumors using B-mode data.

Computer simulations have been conducted to examine hyperthermia and ablation for treating ocular tumors. An interactive software package has been implemented that permits relevant tissue dimensions to be determined from B-mode data. This package also permits interactive beam positioning, and it provides image displays depicting computed absorbed doses and temperature rises. Results are presented showing how hyperthermia temperature patterns are influenced by beam position, beam geometry and frequency. Images showing ablative temperature rises at various time intervals are also presented. For hyperthermia, geometric models of beam profiles showed that a non-uniform beam pattern (with a central low-intensity region) can produce more uniform heating of small ocular tumors than a beam with a uniform intensity profile. For a given tumor, the uniformity of hyperthermia temperatures was found to be a function of frequency, with 4.75 MHz providing reasonably uniform results for typical tumor heights (near 7 mm). For ablation, diffraction computations were employed to calculate beam intensity profiles; results show an initially rapid rise in temperature levels with subsequent, slower heating beyond the -3-dB limits of the focal volume. The model is now being refined, and additional phenomena, including nonlinear propagation, will be incorporated.

Body Temperature↗
PubMed1992

Computer simulations of ultrasonic heating for ocular therapy.

Computer simulations are being performed to model the temperature patterns produced during ultrasonically induced hyperthermia of ocular tumours. The software package for these simulations incorporates operator interaction and uses tissue geometry obtained from B-mode data. Previous studies used geometric approximations for the incident beams used for hyperthermia. In the current study, these beams were computed using diffraction analysis to obtain more realistic simulations of clinical exposures.

Body Temperature↗
PubMed1992

Ophthalmic ultrasonography.

Definition and differentiation of ocular structures and abnormalities necessitates the use of high-frequency, high-resolution, and high-definition ultrasound. Frequencies of 10 to 100 MHz are being employed. Color Doppler imaging, tissue characterization, parameter image staining, and three-dimensional volume rendering are new and useful adjuncts to ocular diagnosis.

Eye↗
PubMed1991

Ultrasonic tissue characterization of uveal melanoma and prediction of patient survival after enucleation and brachytherapy.

We performed survival studies on 136 patients with uveal malignant melanoma who were examined with ultrasonic tissue characterization before treatment with cobalt-60 brachytherapy (74 patients) or enucleation (62 patients). Mean follow-up time was 58.7 months for the brachytherapy group and 59.0 months for the enucleated group. The maximal follow-up time was nearly ten years. Univariate survival analysis showed that patients with small tumors (less than 250 mm3, 49 patients) had a higher five-year survival when treated with brachytherapy than when treated with enucleation. No patients in this study with tumor volumes greater than 1,500 mm3 (13 patients) were treated with brachytherapy. For tumors of intermediate size (74 patients), survival analysis did not indicate appreciable differences between the treatment options. However, multivariate models including two ultrasonic tissue characterization variables, scatterer size and concentration, showed appreciable intergroup differences in the dependence of survival on these factors. Results suggest that tissue properties detectable with ultrasonic techniques are related to differences in patient survival and may be used for treatment planning for tumors of intermediate size.

Brachytherapy↗
PubMed1991

Therapeutic ultrasound for the treatment of glaucoma.

A multicenter clinical trial of therapeutic ultrasound for the treatment of glaucoma included 20 centers in the United States in which 1,117 treatments were performed on 880 eyes. The study was limited to patients with refractory glaucoma who had not benefited from conventional medical and surgical techniques. Approximately 782 of 1,117 treatments (70%) showed an initial decrease in intraocular pressure from a pretreatment mean of 38.1 mm Hg to 22 mm Hg or less. By Kaplan-Meier survival analysis, the single treatment success rate (intraocular pressure between 6 and 22 mm Hg) was 48.7% at six months posttreatment. When retreatment was used subsequent to failure, the one-year multitreatment success rate was 79.3%. The most common complications were an immediate posttreatment intraocular pressure increase lasting a few hours and mild iritis. Other complications included scleral thinning in 28 of 1,117 treatments (2.5%) and phthisis bulbi in 12 of 1,117 treatments (1.1%).

Adolescent↗