Biomedical subjects

L J Filipow

Publications and source records attributed to L J Filipow.

6 recordsLinked to original sources

PubMed1997

Approximating the acoustic reflection coefficient of lossy biological tissues.

The amplitude acoustic reflection coefficient of an interface between two lossy biological tissues can be approximated as Rlossy approximately Rlossless + i delta/2 where Rlossless is the lossless acoustic reflection coefficient and delta is the change in alpha/kappa (absorption coefficient per wavenumber) across the tissue interface. This approximation is shown to be valid for both normal and oblique angles of incidence.

Acoustics↗

PubMed1990

131I treatment of thyroid papillary carcinoma in a patient with renal failure.

Procedures for 131I ablation in renal failure are not known. In one patient receiving dialysis, detailed dosimetry and health safety aspects were obtained. The results showed insignificant contamination of equipment, but a surprisingly significant reduction in biologic half-life of 131I due to efficient dialysis extraction. The data indicate that 131I ablation can be done safely and easily during dialysis but that much higher 131I doses must be used to achieve equivalent results to those obtained in patients with normal renal function.

Adult↗

PubMed1987

CT guided functional stereotaxic surgery.

One of the major problems in stereotaxic surgery is to identify the brain target. Since these do not show on any of the usual radiological studies they have to be located with reference to observable structures. Initially bony landmarks were used but later either positive or negative contrast ventriculograms were found to be more accurate. Often this involves additional needling of the brain or a spinal puncture with the added mortality and morbidity associated with these procedures. We have extended the use of CT guided stereotaxic surgery to functional conditions by measuring the target position in relation to the third ventricle and the AC-PC line as seen on the unaugmented CT scan. Our experience with 27 procedures in 23 patients (9 movement disorders, 13 pain and 1 insertion of depth electrode) would indicate it is at least as accurate as other techniques. The surgical time is usually shorter and patient tolerance is better.

Adult↗

PubMed1979

The measurement of the depth of a point source of a radioisotope from gamma ray spectra.

The spectrum of the scattered radiation from a 'point' source of 99Tcm located within a slab of tissue-like material has been studied with a 19-phototube gamma camera, a 7.5 cm x 7.5 cm sodium iodide detector and a Ge(Li) counter. Both backscatter and forward scattered radiation contribute to the spectra observed; 'infinite' backscatter is achieved at a thickness of 8 cm. The scattered radiation can be used to estimate the thickness of the overlying material. The scatter from 133Xe and 51Cr was also measured. The depth of a source could usually be determined to within a few millimetres from the proportion of scatter in the spectrum; it was more accurate with the 51Cr (320 keV) than with the lower-energy photopeaks of the other two isotopes. The variation in the spectrum as the source moved across the field of the gamma camera was recorded.

Chromium Radioisotopes↗

PubMedDate not supplied

Measurement of total body potassium in premature infants by means of a whole-body counter.

This paper describes a whole-body counter (WBC) specially designed to measured total body potassium (TBK) infants under 4,500 g. The counter is a "shadow shield" design and consists of a single 10 cm X 10 cm X 45 cm NaI(Tl) crystal, positioned lengthwise and shielded from environmental background radiation by a minimum of 10 cm of lead. The standard error of counting for a 2,000-s counting period is 19.9% for a 1,000-g infant and 11.9% for a 2,000-g infant. TBK of stillborn pigs, measured by the WBC, agreed to an average of 3% of TBK determined by carcass analysis in the same animals. A total of 118 measurements of TBK have been made in 50 premature infants ranging in weight between 1,100 and 3,600 g and in age between 2 and 75 days. The observed relationship of TBK with weight is described by the equation: TBK (mEq) = 0.0433Wt (g + 1.57 r = 0.92. Potassium retention per gram weight gain is estimated to be 0.043 mEq. The obtained TBK values agree well with values published by other workers but extend the range of measurement to 1,100 g.

Animals↗

PubMedDate not supplied

Analysis of the gamma ray spectra recorded in the use of Xenon-133 for cerebral blood flow studies.

A problem in the measurement of cerebral blood flow with 133Xenon is the presence of extra-cerebral counts in the total counts recorded with a collimated gamma ray detector looking at the brain. A method of studying qualitatively the contribution of this extra-cranial component in patients is described. This entails the sequential accumulation of gamma ray spectra recorded during the clearance phase of 133Xenon from the brain. It is shown that different CBF indices are obtained for various regions of the recorded gamma ray spectra. The principal component of the extra-cerebral counts at 15 minutes postinjection appears to be intra-cranial, and not the scalp as assumed previously in the spectrum subtraction method.

Brain↗