Physiologicomathematical model for studying human exposure to organic solvents: kinetics of blood/tissue n-hexane concentrations and of 2,5-hexanedione in urine.

The physiologicomathematical model with eight compartments described allows the simulation of the absorbtion, distribution, biotransformation, excretion of an organic solvent, and the kinetics of its metabolites. The usual compartments of the human organism (vessel rich group, muscle group, and fat group) are integrated with the lungs, the metabolising tissues, and three other compartments dealing with the metabolic kinetics (biotransformation, water, and urinary compartments). The findings obtained by mathematical simulation of exposure to n-hexane were compared with data previously reported. The concentrations of n-hexane in alveolar air and in venous blood described both in experimental and occupational exposures provided a substantial validation for the data obtained by mathematical simulation. The results of the urinary excretion of 2,5-hexanedione given by the model were in good agreement with data already reported. The simulation of an exposure to n-hexane repeated five days a week suggested that the solvent accumulates in the fat tissue. The half life of n-hexane in fat tissue equalled 64 hours. The kinetics of 2,5-hexanedione resulting from the model suggest that occupational exposure results in the presence of large amounts of 2,5-hexanedione in the body for the whole working week.

"Dynamic" biological exposure indexes for n-hexane and 2,5-hexanedione, suggested by a physiologically based pharmacokinetic model.

Biological exposure index (BEI) of n-hexane was studied for accuracy using a physiologically based pharmacokinetic (PB-PK) model. The kinetics of n-hexane in alveolar air, blood, urine, and other tissues were simulated for different values of alveolar ventilations and also for constant and variable exposures. The kinetics of 2,5-hexanedione, the toxic n-hexane metabolite, were also simulated. The ranges of n-hexane concentrations in biological media and the urinary concentrations of 2,5-hexanedione are discussed in connection with a mean n-hexane exposure of 180 mg/m3 (50 ppm) (threshold limit value [TLV] suggested by American Conference of Governmental Industrial Hygienists [ACGIH] for 1988-89). The experimental and field data as well as those predicted by simulation with the PB-PK model were comparable. The physiological-pharmacokinetic simulations are used to propose the "dynamic" BEIs of n-hexane and 2,5-hexanedione. The use of simulation with PB-PK models enables a better understanding of the limits, advantages, and issues associated with biological monitoring of exposures to industrial solvents.

[Liquid radioactive waste in health activities: annual dosage to the population]. / Rifiuti radioattivi liquidi nelle attività sanitarie: dosi annue alla popolazione.

A survey was taken of the amount of radionuclides, acquired, utilized, and released in one year's time, in the Adige river by the USL (Local Division of the National Public Health System) of Verona. The critical pathways of environmental pollution were analyzed and the individual and collective doses of some critical population groups and the population as a whole were compiled. Some suggestions to reduce the collective doses both from radioactive releases and diagnostic use of radionuclides are given.

Biological exposure index of styrene suggested by a physiologico-mathematical model.

We used a physiologico-mathematical model to study the biological exposure index of styrene correlated to the Threshold Limit Value (TLV) suggested by the ACGIH for 1986-87. This model allows the solvent concentrations in blood, alveolar air, fat tissue, and in other biological media to be estimated and simultaneously the kinetics of its metabolites to be followed when a specific exposure is settled. The comparison between the results obtained from the mathematical model and the numerous research projects documented in the literature suggests a reciprocal validation. Moreover, some biological parameters (particularly the alveolar ventilation) can explain the variability of results obtained from studies concerning the solvent pollution of the factories, which used biological monitoring. The ranges of styrene concentrations in blood and alveolar air and the urinary concentrations of its metabolites (mandelic and phenylglioxylic acids) are discussed in connection with the exposure at 215 mg/m3. Important differences correlated to the definition of set-levels of TLV and Biological Exposure Index (BEI) have been found: particularly the TLVs lead to different solvent uptakes according to some biological parameters; the BEI can better explain the individual solvent uptake and body burden.

Methyl ethyl ketone exposure in industrial workers. Uptake and kinetics.

Exposure to methyl ethyl ketone (MEK) was studied in workers occupationally exposed in industrial workplaces. Alveolar concentrations of MEK were compared with environmental exposure and with blood MEK concentrations. Urinary excretion of MEK and its metabolite, acetylmethylcarbinol , were compared with environmental exposure. The solubility of MEK was also studied in human body tissues which allowed us to estimate the distribution and kinetics of MEK by means of data computing on a multicompartimental mathematic model. The alveolar MEK concentration was correlated with the environmental MEK concentration and corresponded to 30% of it. Blood MEK concentration was correlated with alveolar MEK concentration and corresponded to 104-116 times the alveolar concentration and 31-35 times the environmental concentration. Urinary MEK excretion was correlated with environmental MEK exposure and the urinary excretion of acetylmethylcarbinol . The mean urinary MEK concentration was 4.8 times the mean environmental MEK concentration. The MEK solubility in the human tissues (brain, kidney, lung, fat, heart, muscles and liver) turned out to be similar to that found in blood (blood/air = 183). The amount of MEK and its metabolite, acetylmethylcarbinol , eliminated by the kidney corresponded together to 0.1% of the alveolar MEK uptake.

A new volumetric CT machine for dental imaging based on the cone-beam technique: preliminary results.

The objective of this paper is to present a new type of volumetric CT which uses the cone-beam technique instead of traditional fan-beam technique. The machine is dedicated to the dento-maxillo-facial imaging, particularly for planning in the field of implantology. The main characteristics of the unit are presented with reference to the technical parameters as well as the software performance. Images obtained are reported as various 2D sections of a volume reconstruction. Also, measurements of the geometric accuracy and the radiation dose absorbed by the patient are obtained using specific phantoms. Absorbed dose is compared with that given off by spiral CT. Geometric accuracy, evaluated with reference to various reconstruction modalities and different spatial orientations, is 0.8-1% for width measurements and 2.2% for height measurements. Radiation dose absorbed during the scan shows different profiles in central and peripheral axes. As regards the maximum value of the central profile, dose from the new unit is approximately one sixth that of traditional spiral CT. The new system appears to be very promising in dentomaxillo-facial imaging and, due to the good ratio between performance and low cost, together with low radiation dose, very interesting in view of large-scale use of the CT technique in such diagnostic applications.

The choice of radiographic film-screen systems: quality evaluation and purchasing specifications drafting. Report on A.I.F.B. Working Group activity.

The comparative evaluation of radiographic screen-film systems presents several problems from both the theoretical and the experimental points of view. From the theoretical point of view the main difficulties are related to the choice of the parameters best suited to express the "overall quality" of a system. This quantity is expressed as a product of image quality index and system sensitivity. As image quality index we assumed the signal-to-noise power ratio: this index depends in an explicit way on contrast, resolution and noise of the system. From the experimental point of view the main problem is that to measure some basic quantities, sophisticated and expensive equipment, like computer-controlled microdensitometers, is generally required. In this paper, we report the Italian Association of Biomedical Physicists Task group suggestions for measuring the basic physical parameters (with particular reference to the use of cost-effective equipment and for purchasing specification drafting). Using synthetic quality indices, the evaluation criteria of radiographic materials are directly derived from the general theory of radiographic image perception.