The drying process of concrete: a neutron radiography study.

The natural drying process of concrete, which has a significant effect on its characteristics, for example durability, was studied at the neutron radiography facility at SAFARI-1 nuclear research reactor, operated by Necsa. Monitoring of the movement of the water in concrete samples, which were wet cured for one day and covered on all the sides but one, was done by means of a CCD camera system. In this paper the methodology in observing the drying process will be described together with results obtained from this investigation. The measured water content and porosity results were quantified and compared reasonably well with conventional gravimetrical measurements.

A computerized implementation of a non-linear equation to predict barrier shielding requirements.

A non-linear equation to predict barrier shielding thickness from the work function of x- and gamma-ray generators is presented. This equation is incorporated into a model that takes into account primary, scatter, and leakage radiation components to determine the amount of shielding necessary. The case of multiple wall materials is also considered. The equation accurately models the radiation attenuation curves given in NCRP 49 for concrete and lead, thus eliminating the necessity to use graphical or tabular methods to calculate shielding thickness, which can be inaccurate.

Proposed semi-analytical formulae for the determination of (L/rho)medair and Prepl for electron beams as used in radiotherapy.

To convert an ionization measurement to absorbed dose, the TG-21, the IAEA, and the TG-25 protocols for the calibration of high energy electron therapy machines demand an accurate knowledge of the mean restricted collision mass stopping power ratio, (L/rho)medair, and the electron fluence correction factor, Prepl. This paper presents a semi-analytical expression to calculate (L/rho)medair at depths in the range of 0 to 30 g/cm2 and for any energy in the range of 4-60 MeV, for water, polystyrene, and acrylic relative to air, and another expression to calculate Prepl for any cylindrical ionization chamber with an inner diameter in the range of 3 to 7 mm. The published values for (L/rho)medair were fitted to a single analytical expression with 10 coefficients using a nonlinear least square routine. Another expression with 4 coefficients was used to fit the electron fluence correction factor, Prepl, for cylindrical ionization chambers, as a function of chamber diameter and the mean electron energy at depth of measurement. In the electron energy range of 4-60 MeV, and for all published depths, the calculated (L/rho)medair values agree with the published values within +/- 1% in 99% of the cases. The calculated Prepl values agree with the tabulated values within +/- 1% in all of the cases. The proposed equations now allow one to use a computer to calculate the values of (L/rho)medair and Prepl accurately, doing away with the time-consuming procedure of interpolating between values from tables during the routine calibration of high energy electron therapy machines.

Isotopes as host blood markers to measure blood intake by feeding ticks (Acari: Ixodidae).

We have modified an experimental technique in which two different isotopes (Cr51 and I125) were used simultaneously as blood markers for determining the amount of blood removed by feeding ticks. This method enables us to measure separately and directly the volumes of red blood cells and plasma in ticks and to calculate the ratio between the two parameters (concentrating ability). The concentration of red blood cells in nymphs of Amblyomma hebraeum Kock and Rhipicephalus appendiculatus Neumann and in females of these species plus in those of Hyalomma truncatum Kock were found to be twice the amount measured in the labeled blood of goats. Concentrations of plasma in the ticks were approximately two-thirds of that measured in samples taken directly from these same goats. Small nonsignificant differences between the ability of various tick species to concentrate red blood cells and dilute host plasma were found. The advantage of this method is compared with that of the colorimetric and gravimetric methods, and its potential use is discussed.

Central axis depth dose curve for electron beams.

In this article an analytical equation for electron depth dose is proposed electron energies from 6-20 MeV. The equation contains four parameters and it fits the build-up region, fall-off region as well as the bremsstrahlung background region. The calculated values from this equation fit within 1,5% of the measured data in the build-up region and in the fall-off region within 0,5 mm for the energy range 5-10 MeV and within 1 mm for the range 12-20 MeV. This equation can be applied beyond the practical range.

The assessment of mucociliary clearance using monodisperse 99mTc-tagged red blood cells.

To assess mucociliary clearance rates of the lungs using a monodisperse particle of constant volume, we investigated the possibility of using a patient's own red blood cells. The cells are tagged with 99mTechnetium. The procedure was performed on two groups of volunteers. The test was found to be very reliable (98%). A second group was studied with the administration of a placebo or 400 mg Aminophylline during the acquisition of the data. The expected response could be seen in 81% of the cases studied.

Normalisation of glomerular filtration rate measurements.

The result of a glomerular filtration rate (GFR) measurement on a particular patient is of limited use to the referring physician since normal GFR values vary widely with the patient's age and build, etc. To overcome this problem, it is usual to normalise the measured GFR by dividing it by the patient's surface area and multiplying the result by the surface area of a 'standard' man. This transforms the measurement onto a scale which applies to all patients, young and old, large and small, where normal values fall within a well-defined range and where the degree of renal impairment can be quantified. We have examined the generally accepted surface area (SA) and the less well-known extracellular volume (ECV) normalisation methods of GFR measurements in a series of 110 patients. The results show that both methods produce essentially the same result; however, ECV normalisation is theoretically more correct, can be found directly without the patient's ECV being measured and does not require the use of empirical formulae. Mathematical justification for ECV normalisation is presented, and a proposed distribution pattern for the normalised measurement is introduced. A simple mathematical model shows that accurate GFR measurements can be made in the presence of an enlarged ECV, but normalisation of these will produce misleading low values.

Use of indium-111-labelled platelets in black stroke patients. A pilot study.

Human blood platelets labelled with indium-111 oxine have been shown to accumulate on damaged vascular surfaces and abnormal platelet deposition has been demonstrated in the carotid arteries of white stroke patients. Gamma scintigraphy of the carotid and cerebral arteries of 5 black stroke patients and 5 age- and sex-matched controls using 111In-labelled platelets showed no abnormal accumulation indicative of carotid artery disease.

A conjugate counting method to determine [75Se]SeHCAT retention in the human body.

To evaluate the functional integrity of the distal part of the ileum the retention of a gamma-labelled bile acid (SeHCAT) in the human body can be measured with a detector. Due to the lack of a whole body counter at our institution a two detector system was designed to measure SeHCAT retention and an evaluation of such a system has been made. The detectors are positioned on either side of a patient lying supine on a hospital trolley. The trolley is stepped forward in 100 mm steps, to determine the SeHCAT activity in the patient. With these counts the location of the SeHCAT activity and total activity present in the body can be determined. A water filled phantom and a phantom consisting of nine 1-L saline bags with 75Se activity placed in them was used to determine system performance. Four patients with no history of bowel disease were compared with published data for normals. Results showed that the system performed satisfactorily, and accurate quantitative measurements could be made, showing that this inexpensive system could be used where a whole body counter is not available.

Importance of cholescintigraphy and inferior vena cava flow studies in the differential diagnosis of hepatocellular carcinoma.

In order to assess the usefulness of inferior vena cava flow studies and cholescintigraphy complementary to the routine static liver scintigraphy in the differential diagnosis of hepatocellular carcinoma (HCC), we studied 37 patients with a proven diagnosis of HCC and 11 patients with a liver abcess or cyst. The procedure followed was 1) a 99mTc-colloid flow study of the inferior vena cava (IVC) and iliac veins followed by static liver imaging and 2) cholescintigraphy using a dynamic acquisition mode to determine the perfusion as well as the concentration/excretion of the liver and pathological area. The hepatic perfusion index (HPI) was calculated by the "slope" method of Sarper et al.: Radiology 141:179-184 (1981) and the "area" method of Biersack et al.: Fortschritte auf dem Gebiete der Rontgenstrahlen und der Nuklear medizin. Erganzungsband 126:47-52 (1977). The results were compared with data previously collected in patients without liver disease (control) and other liver pathologies.

Evaluation of different formulae for the study of platelet survival.

The International Committee of Standardization in Haematology has recommended in 1977 three methods for calculating the mean platelet survival time of isotope labelled platelets, although in recent years other mathematical equations were also suggested for the determination of platelet survival times. Seven different methods of calculating the mean survival time for normals were investigated and were compared with one another.

Ethnic differences in human lymphocytic cyclic AMP production after isoprenaline stimulation and propranolol blockade.

The stimulatory effects of isoprenaline on human lymphocytic cyclic AMP (cAMP) and blockade by propranolol were studied in vitro in healthy Black and White volunteers. Basal levels of lymphocytic cAMP were significantly higher in Blacks than in Whites. Stimulation with isoprenaline caused a dose-related increase in cAMP, which was in concentrations of 10(-9) to 10(-5)M significantly greater in Blacks than in Whites. Blockade by 10(-4)M propranolol did not affect basal cAMP levels significantly, but increases in cAMP levels were significantly smaller in both groups after 10(-9) to 10(-2)M isoprenaline, while differences between cAMP levels in Blacks and Whites were still significant at concentrations 10(-9) to 10(-3)M. The increased cAMP concentration in lymphocytes of Blacks probably reflects a higher degree of beta 2-adrenoceptor activity which could be due to either a greater number and/or greater sensitivity of lymphocytic beta 2-adrenoceptors in Blacks than in Whites.

Formulae for the determination of percentage depth dose of 8 and 16 megavolt x-rays by means of a computer.

Linear accelerators play an important role in the treatment of some cancer patients. These accelerators produce high-energy X-rays (in the megavolt (MV) range) and the effective penetration of the X-rays depends on the energy. The percentage depth dose at the central axis gives an indication of effective penetration. An attempt was made to derive formulae for the percentage depth dose for 8 and 16 MV X-rays in tissue. The formulae can be used for treatment planning purposes and also for calculating the integral absorbed dose. A further important application of the formulae is the calculation of the central absorbed dose for two opposing beams at non-standard treatment distances.