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Biomedical subjects

B C Wilson

Publications and source records attributed to B C Wilson.

16 recordsLinked to original sources
PubMed1992

Magnetic resonance imaging of interstitial laser photocoagulation in brain.

Magnetic resonance (MR) imaging can be used to monitor the development of thermal lesions induced in tissue using interstitial laser photocoagulation (ILP). A potential application for ILP is the treatment of surgically inaccessible brain tumors. For the successful clinical application of MR-monitored ILP, it is necessary to relate MR images of ILP lesions to the actual induced lesions. In this preliminary study we performed ILP in the normal brains of anesthetized cats by delivering interstitially 1.0, 1.5, and 2.0 W of continuous-wave Nd:YAG laser energy (1,064 nm) for 1,000 s via a plane-cut 400 microns core optical fiber. At 48 h post-irradiation the lesions consisted of four sharply demarcated concentric zones of thermal damage. Lesion diameter increased linearly with delivered power. T2-weighted proton spin-echo images acquired during ILP showed a region of complete or near signal loss that underestimated the actual lesion at 48 h. Gadolinium-enhanced T1-weighted spin-echo images acquired immediately post-irradiation showed the actual lesion precisely.

Animals↗
PubMed1992

Optical properties of Intralipid: a phantom medium for light propagation studies.

Intralipid is an intravenous nutrient consisting of an emulsion of phospholipid micelles and water. Because Intralipid is turbid and has no strong absorption bands in the visible region of the electromagnetic spectrum, and is readily available and relatively inexpensive, it is often used as a tissue simulating phantom medium in light dosimetry experiments. In order to assist investigators requiring a controllable medium that over a finite range of wavelengths is optically equivalent to tissue, we have compiled previously published values of the optical interaction coefficients of Intralipid, most of which were measured at a wavelength of 633 nm. We have extended the measurements of the absorption and reduced scattering coefficients from 460 to 690 nm and the total attenuation coefficient from 500 to 890 nm. These measurements show that, for stock 10% Intralipid, the absorption coefficient varies from 0.015 to 0.001 cm-1 between 460 and 690 nm, the reduced scattering coefficient varies from 92 to 50 cm-1 between 460 and 690 nm, the total attenuation coefficient varies from 575 to 150 cm-1 between 500 and 890 nm, and the average cosine of scatter varies from 0.87 to 0.82 between 460 and 690 nm. With these data, we discuss the design of an optically tissue-equivalent phantom consisting of Intralipid and black India ink.

Absorption↗
PubMed1992

Interstitial laser photocoagulation: Nd:YAG 1064 nm optical fiber source compared to point heat source.

Interstitial laser photocoagulation (ILP) was performed in vitro in lean bovine and chicken muscle by delivering 1.6 W of continuous-wave Nd:YAG laser energy (1064 nm) from a 400-microns core optical fiber for 300s. The resulting thermal coagulation lesion was consistently larger when the delivered energy was deposited into a small steel sphere than when it was delivered freely into the tissue. Mathematical modelling confirms this result. This preliminary study suggests that a point heat source produces a larger volume of thermal coagulation than a point optical source (1064 nm) delivering the same power.

Animals↗
PubMed1992

Sonographic changes during hepatic interstitial laser photocoagulation. An investigation of three optical fiber tips.

RATIONALE AND OBJECTIVES: Interstitial laser photocoagulation (ILP) destroys tumors thermally, using laser energy delivered from implanted optical fibers. The objectives of the study are to identify a fiber tip/delivered energy combination which produces lesions of useful size, visible on ultrasound (US) during ILP, and to compare ILP lesions and their US images. METHODS: Hepatic ILP was performed at laparotomy in six pigs, using three different fiber tips (cylindrical diffusing, spherical diffusing, plane-cut). US images were obtained during ILP, immediately after ("early" images), and before the animals were killed (2-2.5 hours, "late" images). Actual lesions were assessed histopathologically. RESULTS: Few US changes were seen around cylindrical diffusing and spherical diffusing tips until tip destruction. Plane-cut tips, at 1.5 to 2.0 W, produced prominent US images of the 1- to 2-cm thermal lesions. Early images tended to overestimate necrosis. Late images approximated necrosis. CONCLUSION: For US-controlled ILP, plane-cut tips are better than currently available cylindrical diffusing or spherical diffusing tips. Lesion image growth periods might enable control of lesion size. Further studies are needed to determine the consistency of the described relationship between lesion images and actual lesions.

Animals↗
PubMed1992

Effects of light beam size on fluence distribution and depth of necrosis in superficially applied photodynamic therapy of normal rat brain.

The light fluence distributions of 632.8 nm light incident on the exposed surface of normal rat brain in vivo have been measured using an interstitial, stereotactically-mounted optical fiber detector with isotropic response. The dependence of the relative fluence rate on depth and the spatial distribution of fluence were compared for incident beam diameters of 3 and 5 mm. The fluence rate at depth of 1-6 mm along the optical axis within the brain tissue was approximately 70% greater for a 5 mm diameter beam than for a 3 mm beam, at the same incident fluence rate, although the plots of the relative fluence rate vs depth were parallel over the depth range 1-6 mm. The depths of necrosis resulting from photodynamic treatment of brain tissue using the photosensitizer Photofrin and irradiation by 632 nm light with 3 and 5 mm incident beams were also measured. The observed difference in necrosis depths was consistent with the measured difference in fluence. The importance of beam size in photodynamic treatment with small diameter incident light fields is discussed.

Animals↗
PubMed1992

The effect of light fluence rate in photodynamic therapy of normal rat brain.

This paper reports the effect of incident light fluence rate on the depth to which necrotic lesions are produced by photodynamic therapy (PDT) in the brains of normal Fisher rats. The rats were injected intraperitoneally with Photofrin (12.5 mg kg-1) 48 h prior to PDT with a fixed incident fluence of 35 J cm-2. The treatment was performed at 10, 50, 100, and 200 mW cm-2 and also in a periodic manner (30 s "on" at 100 mW cm-2, 30 s "off"). The depth to which necrosis occurred was determined 24 h after treatment by microscopic examination of tissue sections. No differences were found in the depth to which necrosis was produced by any of the five irradiation schedules. This finding is discussed in the context of other published dose-rate experiments.

Animals↗
PubMed1979

Impact of computerized tomography on neuroradiological investigations in South Australia.

Although there has been a reduction in cerebral angiographic (33%), pneumoencephalographic (70%) and radionuclide brain scanning (28%) investigations since the introduction of computerized tomography in South Australia, there has been a significant increase (56%) in the total number of neuroradiological investigations performed. At the same time, the number of patients who underwent neuroradiological investigations has risen by 75%. This is equivalent to approximately one person in every 290 per year.

Australia↗
PubMed1975

Neuropsychologic function of children with severe hearing impairment.

A neuropsychologic and medical study was carried out on a selected sample of 34 hearing-impaired children aged seven to 10 years at the onset of the study. In 16 children the cause of the hearing loss was thought to be exogenous. Eight of these had evidence for organic brain dysfunction. Nine children were thought to have genetic etiologies, and in nine no cause could be determined (sporadic hearing loss). Medical examination revealed several unsuspected abnormalities, particularly visual ones. Motor and visual motor deficits were frequent among hearing-impaired children with brain damage. The Performance Scale of the Wechsler Intelligence Scale for Children, and Raven's Coloured Progressive Matrices, as well as the Paper Folding item of the Hiskey-Nebraska Test of Learning Aptitude appeared sensitive to the presence of brain damage. The mean score for the WISC Performance Scale fell within the average range for hearing children, supporting previous findings of cognitive competence of the deaf. In this sample, Hiskey-Nebraska scores tended to be lower than WISC scores. Reasons for this discrepancy were suggested and did not appear to be accounted for by brain damage. Deficits in items requiring visual memory, sequencing, and categorization were relatively prevalent but showed no etiologic predilection. They were thought to be related to the consequence of hearing loss rather than to brain damage. Difficulty with stereognosis highlighted the problem of deciding why a hearing-impaired child might fail a particular task. This difficulty suggested that failure might not indicate a deficit in the function the task was designed to measure, but rather, reliance on an inefficient strategy for success.

Audiometry↗
PubMed1975

Digital reconstruction of point sources imaged by a zone plate camera.

Zone plate cameras are used for high sensitivity imaging of X- and gamma-ray sources. The image thus obtained requires decoding and numerical techniques are devised for this purpose. The response function and the signal-to-noise ratio for a single point source have been evaluated for zone plates with varying numbers of zones. Autocorrelation is the best of the methods examined, and the results are in good aggreement with those obtained using Monte Carlo techniques. The autocorrelation method can give a gain of 50% in signal-to-noise for a single point source over the maximum obtainable with optical decoding. Criteria for the choice of number of zones are discussed.

Computers↗
PubMed1975

Digital processing of images from a zone plate camera.

A method for the digital decoding of data obtained with a gamma camera fitted with a zone plate aperture is described. Taking a line source as the object, computer simulations have been used to examine the effects of noise, solid angle variations, shape of detector and detector resolution and methods of dealing with these effects are considered. Using an Anger gamma camera and a zone plate aperture both a line source and a thyroid phantom containing 99Tcm have been well reconstructed. The behaviour of the system with regard to resolution, signal-to-noise ratio and tomographic capability is discussed.

Computers↗
PubMed1975

Gemistocytic astrocytes in gliomas. An autoradiographic study.

Tritiated thymidine (3-H-T) was administered intravenously to seven patients with cerebral gliomas. Autoradiographs of biopsy specimens excised within the next four hours and of autopsy specimens from three of these patients obtained three weeks to six months after the single pulse of 3-H-T revealed the following: (a) no gemistocytic astrocytes and only a few giant astrocytes were labeled in biopsy specimens, despite a high overall labeling index of 5-10% (percentage of cells labeled in the total cell population); and (b) scattered foci of labeled genistocytes occurred in autopsy specimens, despite a sharp drop in overall labeling index. In histologic sections of these same specimens, genistocytes and giant cells occurred as the major cell types in an irradiated tumor, in large clusters near foci of degeneration, and as isolated cells in anaplastic foci. These findings suggest that: 1) gemistocytes and giant astrocytes are similar in origin and growth potential regardless of minor variations in morphology; 2) these cells multiply slowly, if at all, and are closely related to regressive changes within the tumor; 3) these cells may reflect profound proliferative activity in adjacent neoplastic cells; and 4) the labeling index and malignant potential of the tumor as a whole depend upon the more rapidly dividing tumor elements. Thus, if genistocytes and giant cells indicate malignancy, they do so secondarily, and the biologically harmless gemistocyte may be the loser in an intense competition for the substrates needed in cell proliferation.

Adolescent↗