Biomedical subjects

T van Doorn

Publications and source records attributed to T van Doorn.

24 records · Page 2Linked to original sources

PubMed1995

Optical transmission properties of homogenised milk used as a phantom material in visible wavelength imaging.

Using the collimated output beam from a Helium-Neon laser, operating at 632.8 nm, transmission intensities through various thicknesses and concentrations of homogenised milk have been measured for the purpose of determining the suitability of milk as a phantom for visible wavelength imaging. Also, theoretical predictions to the laser beam attenuation in milk based on diffusion theory have been calculated, giving substantial agreement with experiment for milk concentrations greater than 10%. The transmission properties of milk have been compared with a commonly used optical phantom, namely Intralipid, and the scattering coefficient mu(s) measured for each phantom. The scattering coefficients for undiluted milk and 20% solids Intralipid are 52 +/- 1, and 139 +/- 6 mm-1, respectively. With appropriate normalisation of the physical parameters, the effective physical properties of the phantom materials vis a vis light transmission become the same within limits imposed by experimental error. Comparison of measured transmission properties of homogenised milk with tissue confirm its suitability as a phantom vis a vis scattering properties determined by mu(s) and its mean cosine of scatter g, but that its absorption coefficient mu(a) is approximately two orders of magnitude less than for tissue. Appropriate attenuators, such as India Ink, have been suggested as additives to increase the value of mu(a).

Animals↗

PubMed1994

The efficacy of K-edge filters in diagnostic radiology.

The application of K-edge filters in diagnostic radiology has been investigated by many workers for over twenty years. These investigations have analysed the effects of such filters on image quality and radiation dose as well as the practicalities of their application. This paper presents a synopsis of the published works and concludes that K-edge filters do not perceptibly improve image quality and make only limited reductions in patient dose. K-edge filters are also costly to purchase and potentially result in a reduction in the cost effectiveness of x-ray examinations by increasing the x-ray tube loading. Equivalent contrast enhancement and dose reductions can be achieved by the assiduous choice of non-selective filters.

Adult↗

PubMed1993

Performance characteristics of a laser based planar imaging system.

With the advent of lasers and high sensitivity detectors, there has been a recent renewed interest in medical imaging at visible wavelengths. This paper reports on the investigation of the spatial resolution of a prototype laser based planar imaging system by examining the transmission of the laser beam through a phantom medium having similar absorption and scattering properties to that of soft tissue. The results of this work, whilst supporting the conclusions of other recent publications, have demonstrated a previously unreported phenomenon. With the experimental configuration described in this paper, opaque objects, in the form of thin wires, are equally well resolved at similar distances from both the input and exit boundaries of the scattering medium. The spatial resolution is a maximum nearest these boundaries.

Breast↗

PubMed1993

Absorbance measurement with a helium-neon laser for chemical dosimetry.

A laser-based system for absorbance measurement has been developed for use in chemical dosimetry as an alternative to the spectrophotometer. The system incorporating a Helium-Neon laser operating at 543.5 nm is designed specifically for measurement of absorbed doses below 10 Gy with the ferrous sulphate-benzoic acid-xylenol orange (FBX) dosimeter. Absorbance measurement for the FBX dosimeter is normally carried out at 540 nm with a spectrophotometer. The performance of the laser-based system in measurement of absorbance is comparable to that of a standard spectrophotometer and it is concluded that the absorbance measurement technique is not the limiting factor in the sensitivity of the FBX dosimeter for absorbed doses below 1 Gy.

Absorption↗

PubMed1987

Localization and treatment of familial malignant nonfunctional paraganglioma with iodine-131 MIBG: report of two cases.

Two cases of familial, malignant, nonfunctional paraganglioma are reported. Uptake of iodine-131 metaiodobenzylguanidine ([131I]MIBG) by the tumors and metastases was demonstrated. In the first case, with multicentric and locally invasive disease, [131I]MIBG correctly localized a right carotid body paraganglioma which had been missed arteriographically. In the second case, with widespread, symptomatic metastatic disease, a therapeutic dose of [131I]MIBG produced palliation of bone pain after the failure of radio- and chemotherapy. Uptake of [131I]MIBG by paragangliomas does not correlate with catecholamine secretory activity. Iodine-131 MIBG should be considered as a therapeutic option in unresectable, malignant paragangliomas which take up this radiopharmaceutical.

3-Iodobenzylguanidine↗

PubMed1982

A comparison of serum thyroglobulin measurements and whole body 131I scanning in the management of treated differentiated thyroid carcinoma.

Serum thyroglobulin levels were measured by a sensitive radioimmunoassay in 76 patients whose differentiated thyroid carcinoma had been treated by surgery with or without subsequent administration of radioactive iodine (131I). Examination of the results of 105 concomitant whole body 131I scan results and serum thyroglobulin levels showed a high degree (83.8%) of concordance between these two techniques. A significant correlation (r = 0.670, p less than 0.001) was found between serum thyroglobulin levels and quantitative 131I uptake in the neck and/or metastases in 42 patients in whom this was measured. Although a high degree of congruence was found between the results of 131I scans and the presence or absence of circulating thyroglobulin, 13 patients with negative scans using conventional doses of 131I had measurable levels of thyroglobulin. Eight of these patients had or subsequently developed evidence of residual thyroid tissue or metastatic carcinoma. The measurement of serum thyroglobulin levels in patients previously treated for differentiated carcinoma offers a more convenient and more sensitive method of detecting residual normal or neoplastic thyroid tissue than does whole body scanning in 131I.

Carcinoma↗