Comparison of dose from radiological examination for scoliosis in children among two pediatric hospitals by Monte Carlo simulation.

The radiation exposures of children undergoing full spine radiography were investigated in two pediatric hospitals in Greece. Entrance surface kerma (Ka,e) was assessed by thermoluminescence dosimetry and patient's effective dose (E) was estimated by Monte Carlo simulation. All required information regarding patient age and sex, the irradiation geometry, the x-ray spectra, and other exposure parameters (tube voltage and current) were registered as well. Values of Ka,e were measured to range from 0.22 mGy to 2.12 mGy, while E was estimated to range from 0.03 mSv to 0.47 mSv. In general, all values were greater in one of the two hospitals, as higher tube currents and exposure times were used in the examinations because of the difference in radiographers' training and practice. Moreover, dose to red bone marrow was found to be between 0.01 to 0.23 mSv and dose to breast ranged between 0.02 and 1.05 mSv depending on the age, projection, and hospital. These values are comparable with literature sources.

The effect of hydration on the dose to the urinary bladder wall during technetium-99m diethylene triamine penta-acetic acid renography.

A spherical bladder dynamic model for the estimates of the radiation dose to the bladder walls from intravenously injected radionuclides was implemented to investigate in theory the effect of hydration on the reduction of the bladder dose in technetium-99m diethylene triamine penta-acetic acid (99mTc) DTPA renography. This model gives due consideration to the variation with time of the urine flow rate to the bladder, following a known fluid load. According to the model, the estimated dose depends on the renal function, the fluid load, the time elapsed from the fluid load to the i.v. DTPA injection, the micturition volume and the residual urine volume. Experimental data concerning the values of these parameters for normal individuals were obtained from the literature. Calculations cover the time period from i.v. injection up to the time of the ninth postinjection void. Results show that the patient's condition of hydration is critical for the radiation protection of the bladder. It is shown that optimum combinations of the values of the parameters involved in the calculations exist, which minimize the radiation dose. On the basis of these results, a general protocol is proposed, referring to the hydration conditions under which the renal dynamic study may be normally carried out, with a minimal absorbed dose to the bladder walls (less than 0.045 mGy/MBq).

The effect of blood transfusion on 51Cr-red blood cells surface-counting data in homozygous beta-thalassaemia.

The effect of blood transfusion on 51Cr-red blood cells surface-counting patterns was studied in 22 patients with homozygous beta-thalassaemia being transfused during erythrocyte survival study. Surface-counting patterns of 15 thalassaemics who had not been submitted to blood transfusion during the erythrocyte survival study were served as controls. In 17 of the transfused patients (group A), spleen excess counts (SEC) appeared decreasing after blood transfusion, reaching a minimum (about 50% of the initial value) 3-4 days later, and increasing thereafter to reach again their initial value on 8th to 10th posttransfusion day. The SEC pattern of the remaining 5 transfused patients (group B) presented a continuously ascending curve. Corresponding changes were observed in excess liver counts and heart counts patterns. As a result of these changes spleen/liver ratio (S/L) was found significantly affected by blood transfusion in the majority of thalassaemic patients which were transfused during the erythrocyte survival study. Furthermore, the mean age of group A patients (12.1 +/- 5.5 years) has been found to be significantly lower than that of group B (21.8 +/- 3.3 years). On the contrary, in the control group the SEC pattern appeared permanently increasing and the S/L was found unaltered during the whole duration of the erythrocyte survival study. In conclusion, as far as the surface-counting data represent indexes for splenectomy in thalassaemic patients, the results of this study signify that the influence of blood transfusion on these has to be taken into account.

Kinetics of heat-damaged homologous erythrocytes. A five-compartmental analysis.

A new theoretical five-compartmental model (5CM) was developed for analysis of the clearance of heat-damaged erythroctes (HDE) labelled with chromium 51. Besides the HDE-spleen interaction, this new model also takes into account the interaction between extrasplenic reticuloendothelial (RES) sites and HDE, i.e. the hepatic clearance of fragmented erythrocytes (FE). Accordingly, HDE clearance curves are analysed into three exponential components, the fastest of which describes the RES-FE interaction, whereas the others describe the splenic clearance of spherocytes. Therefore, an estimation of the effective liver blood flow for HDE (ELBF) was achieved, along with a series of parameters describing splenic function. The 5CM proved to be more efficient than a previously proposed three-compartmental model (3CM) in the mathematical description of HDE clearance. Comparison was made by applying both models to 37 experimental curves obtained from 20 patients with congenital hemolytic anemias. The values for the splenic function parameters calculated by 5CM analysis and the strong correlations observed among them offer evidence that this model provides an adequate approximation to the real conditions under which HDE clearance takes place. Furthermore, a detailed quantitative analysis of the pooling of spherocytes within the spleen was attempted in this work, and this phenomenon was found to compete with splenic irreversible spherocyte trapping. The ELBF proved to be closely correlated with the hemodynamic splenic parameters, following first-order kinetics, as do low-dose colloids.

Mathematical analysis of 51Cr-labelled red cell survival curves in congenital haemolytic anaemias.

The parameters of 51Cr labelled red cell survival curves were calculated in 33 patients with homozygous beta-thalassaemia, 8 with sickle-cell anaemia and 3 with s -- beta-thalassaemia, using a non-linear weighted least squares analysis computer program. In thalassaemic children the calculated parameters denote that the shortening of the mean cell life is due to early senescence alone, while there is some evidence that in thalassemic adults additional extracellular destruction mechanisms participate as well. Red cell survival curves from patients with sickle-cell anaemia and s -- beta-thalassaemia resemble each other, while their parameters indicate an initial rapid loss of radioactivity, early senescence and the presence of extracellular red cell destruction factors.

Colloid clearance rate changes in children with homozygous-beta-thalassemia in relation to blood transfusion.

The plasma clearance rate of heat denatured human serum albumin (DHAI-125, 5 mg/kg body weight) was studied in 20 children with homozygous-beta-thalassemia before and 7--10 days after blood transfusion. A significant increase of the DHAI-125 clearance rate (P less than 0.02) was found 7--10 days after blood transfusion while the spleen presented its minimum size. This finding may be relevant to the improved intrasplenic blood circulation after blood transfusion due to the release of the blood trapped within the spleen.