Biomedical subjects

P Dimitriou

Publications and source records attributed to P Dimitriou.

At least 19 recordsLinked to original sources

PubMed2007

Optimization of doses received by the hospital staff and the members of the family of patients undergoing 111In-DTPA-D-Phe1-Octreotide therapy.

According to the Euratom Directives (96/29, 97/43), the doses received by the workers as well as the family of patients and third persons during medical exposures, should conform to the dose constraint levels (DCLs), established by the authorities for each group in the context of optimisation. This study deals with the implementation of a radiation protection protocol, concerning the aforementioned group members for patients undergoing treatment with 111In-DTPA-D-Phe1-Octreotide, after intra-arterial infusion. It is shown that by applying this protocol the annual doses to the medical and technical staff are considerably reduced and remain below the established DCLs. Following the post-release behaviour instructions given to the patient, doses to the family and third persons may be kept lower than the corresponding DCLs provided by the National Regulations.

Equipment Design↗

PubMed2005

Occupational exposure in Greek industrial radiography laboratories (1996-2003).

More than 40 industrial radiography laboratories are operating in Greece using X-ray or gamma-ray sources and more than 250 workers occupationally exposed to ionising radiation in these facilities are monitored on a regular basis. This study presents the evolution of individual doses received by radiographers during the past years. The mean annual dose (MAD) of all workers as well as of exposed workers is estimated, and correlated to the types of laboratories and practices applied. The MAD of the exposed workers in industrial radiography is compared with the doses of workers in other specialties and with the doses of radiographers in other countries. Furthermore, the study attempts to propose dose constraints for the practices in industrial radiography, according to the BSS European directive and the relevant Greek radiation protection legislation. The proposed value was defined as the dose below which the annual doses of 75% of the exposed radiographers are expected to be included.

Gamma Rays↗

PubMed2004

Discrimination of hip fractures by quantitative ultrasound of the phalanges and the calcaneus and dual X-ray absorptiometry.

The aim of the current study was to evaluate the ability of different techniques used for the assessment of bone status to discriminate between postmenopausal women with and without hip fracture. Fifty-one postmenopausal women (mean age 64.5 +/- 6.5) who had sustained a low energy hip fracture and 51 age-matched controls (mean age 64.6 +/- 6.0) were studied. Quantitative ultrasound (QUS) assessment was carried out using the Ubis 3000 device capable of measuring broadband ultrasound attenuation (BUA) and speed of sound at the calcaneus (SOSC) and the Sunlight Omnisense device capable of estimating speed of sound at the phalanges (SOSP). Femoral neck bone mineral density (BMD) was assessed using dual X-ray absorptiometry. Correlations between QUS variables ranged from r = 0.35 to 0.72 and between QUS variables and BMD from r = 0.30 to 0.36. BMD was the best discriminator of hip fractures (odds ratio = 3.61, area under curve = 0.824). All QUS variables were significant discriminators of hip fractures with odds ratios ranging from 1.88 to 2.63 and areas under the ROC curves ranging from 0.663 to 0.740. Among the QUS variables, the SOSP showed the best odds ratio and area under curve. Comparison between the areas under the ROC curve did not show any significant difference between SOSP, BUA and BMD. On the contrary, the difference between SOSC and BMD was significant (P < 0.05). In conclusion, BMD and QUS variables investigated in the current study were significant discriminators of hip fractures. The differentiation of the hip fractures by BMD was significantly better than that of BUA measured at the calcaneus. Moreover, BMD discriminated fractured patients better than BUA and SOS(P), although the difference did not reach statistical significance.

Absorptiometry, Photon↗

PubMed2001

Conceptus radiation dose and risk from cardiac catheter ablation procedures.

BACKGROUND: The aim of the current study was to estimate the conceptus radiation dose and risk associated with fluoroscopic imaging during a catheter ablation procedure for supraventricular tachycardia performed on the expectant mother. METHODS AND RESULTS: Exposure parameters and fluoroscopy times for each projection of the cardiac ablation procedure performed in 20 female patients of childbearing age were recorded. Radiation doses for a potential conceptus were estimated by using dose data obtained in anthropomorphic phantoms simulating pregnancy at the first, second, and third trimesters. Dose measurements were carried out using thermoluminescent dosimeters. For a typical examination, the average radiation dose to the conceptus was <1 mGy in all periods of gestation. Average excess fatal cancer was 14.5/10(6) unborn children irradiated during the first postconception weeks. Corresponding values for the second and third trimesters were 30 and 55.7/10(6), respectively. The risk for hereditary effects in future generations was 1.5/10(6) cases for conceptus irradiation during the first postconception weeks. Corresponding values for the second and third trimesters were 3.0 and 5.6/10(6), respectively. Formulas and dose data are presented for estimating the conceptus risk from any technique and x-ray system used for catheter ablation procedures. CONCLUSIONS: A typical catheter ablation procedure results in a very small increase in risk of harmful effects to the conceptus. However, estimation of conceptus dose from catheter ablation procedures is always needed to assess the risk to the individual developing in utero.

Adult↗

PubMed2001

Dose constraints to the individual annual doses of exposed workers in the medical sector.

The study is an attempt, within the process of the optimization of radiation protection, to propose constraints to the individual annual doses of classified workers employed in the medical sector of ionizing radiation applications in Greece. These exposed workers were grouped according to their specialties, i.e. medical doctors, technicians and nurses and their occupational category with common or similar tasks, such as diagnostic radiology, interventional radiology, nuclear medicine and radiotherapy. The last 5 years' annual dose distributions of these occupational groups, coming from the National Dose Registry Information System (NDRIS) of the Greek Atomic Energy Commission (GAEC) were analyzed. The proposed dose constraints (DCs) were set at levels, below which the annual doses of the 70 or 75% of the exposed workers per category are expected to be included. At the present stage the derived values may be considered achievable ceiling values referring to acceptably applied practices rather than to optimized ones, taking into account social and economic criteria.

Allied Health Personnel↗

PubMed2001

Estimation of doses received by patients undergoing radiological examinations in Greece.

This study deals with the estimation of doses received by patients undergoing radiological examinations in order to establish diagnostic reference levels (DRLs) within the process of optimisation of patients' exposure in Greece. Six large hospitals in Athens were selected and 385 patients made up the sample. The entrance surface doses (ESDs) to patients undertaking five common X ray examinations (chest, cervical spine, lumbar spine AP and LAT, pelvis) were estimated using both thermoluminescence dosemeters (TLDs) attached to the patient's skin and an ionisation chamber for air kerma measurements. Exposure settings and patient's data were recorded. Results concerning the kilovoltage and focus-to-film-distance (FFD) settings and the ESD values were analysed and compared to those recommended by the EU. Discrepancies in the patient doses and techniques used for the examinations studied were found among the different hospitals denoting the importance of establishing a national quality assurance programme and examination protocols to ensure patient doses are kept as low as possible. All the examinations studied fulfilled the EU recommendations except that for the chest where the doses were considerably higher due to the use of low kVP settings.

Adolescent↗

PubMed2001

Bladder wall dosimetry for 131I administered activities.

Detailed dosimetric calculations of bladder dose from 131I accumulations are presented, using Monte Carlo simulations and the dynamic bladder model proposed in the recent revision of MIRD Pamphlet No 14. Penetrating radiation and electron dose to the bladder wall inner surface, as well as within the bladder wall, per unit of 131I activity accumulated in the bladder, are calculated for various bladder filling volumes. The effect of backscatter was taken into account for photon dose calculations while electron dose was determined for all the beta spectral components of 131I. Dosimetric results were used to derive simple parameterisation functions of photon and electron dose with respect to bladder filling volume in combination with any bladder physiology model. Calculations of bladder dose per unit of 131I-OIH and 131I-NaI administered activity, using the derived parametrisations, differ by less than 12% from corresponding results given in the recent revision of MIRD Pamphlet No 14.

Computer Simulation↗

PubMed1995

Immunolocalization of transitional cell carcinoma of the bladder with intravesically administered technetium-99m labelled HMFG1 monoclonal antibody.

The aim of this study was the immunolocalization of transitional cell carcinoma of the bladder with a radiolabelled murine tumour-associated monoclonal antibody and the measurement of the absolute uptake of the antibody by the tumour. Fourteen patients with transitional cell carcinoma of the bladder received 3-6 mCi (111-222 MBq) of technetium-99m labelled HMFG1 monoclonal antibody intravesically and one patient, 2 mCi (74 MBq) of iodine-131 labelled 11.4.1, which is a non-tumour-specific monoclonal antibody. Four of the 15 patients were evaluated with single-photon emission tomography (SPET) 1 1/2 to 2 h post administration. All patients underwent transurethral resection of the bladder tumour within 12-20 h following intravesical administration of the radiolabelled antibody. The radioactivity of biopsy specimens from normal urothelium and tumour areas were counted in a gamma counter. The mean uptake of the radiolabelled antibodies from normal and tumour sites was expressed as a percentage of the administered dose per kilogram of tissue. Conventional histology and immunohistochemistry using HMFG1 monoclonal antibody were performed on paraffin sections of the biopsy specimens. Although our results are preliminary, it can be concluded that: (a) bladder tumours are well imaged by SPET when using 99mTc-HMFG1; (b) intravesically administered radiolabelled antibody remains on the bladder tissue and does not escape into the systemic circulation; (c) the wide range of tumour uptake values (0%-9.3% administered dose/kg) observed probably can be attributed to heterogeneity of the antigenic expression of the tumour; (d) values of 99mTc-HMFG1 monoclonal antibody uptake by the tumour do not justify future attempts at radioimmunotherapy.

Administration, Intravesical↗

PubMed1995

The contribution of hypogonadism to the development of osteoporosis in thalassaemia major: new therapeutic approaches.

OBJECTIVE: The osteoporosis seen in thalassaemia major is of multifactorial origin. The aim of the study was to evaluate the contribution of hypogonadism to the development of this osteoporosis and to assess the efficacy of new sex hormone replacement therapy regimens. DESIGN AND PATIENTS: Sixty-seven patients were studied: 12 were hypogonadal, 32 had been on previous hormone replacement therapy (conjugated oestrogens plus medroxyprogesterone for females, depot testosterone esters for males); 10 had received continuous courses of treatment and 22 3-monthly on/off courses, and 22 were eugonadal without previous replacement therapy. Twenty-seven of the above patients were evaluated prospectively at 16 and 32 months during different therapeutic approaches (12 without treatment, 7 on continuous replacement and 8 on/off schemes followed by continuous therapy during the second observation period). The continuous schemes comprised either transdermal oestradiol (100 micrograms) plus medroxyprogesterone for females or hCG to produce serum testosterone concentrations within normal range, for males. MEASUREMENTS: Bone mineral density (BMD) and bone mineral content (BMC) of lumbar spine and distal end of radius were measured by dual-energy X-ray absorptiometry. RESULTS: Spinal BMD was found to be more than 30% lower than that of controls matched for sex and age with no difference between sexes. Radial BMD was less impaired and showed significantly (P < 0.01) higher levels in males (decrease of 5.8% +/- 2.3, mean +/- SD) than in females (-14.5 +/- 3.4%, mean +/- SD). In the retrospective evaluation it was found that the hypogonadal group had the lowest (P < 0.0001) BMD levels (0.62 +/- 0.01, mean +/- SE) and the highest were observed on the continuous replacement group (0.83 +/- 0.04), whereas the values of the other groups were similar. In a multiple regression analysis model it was found that only sex steroid levels were related to the BMD measurements (for oestradiol t = 2.6, P = 0.01 and for testosterone t = 6.5, P = 0.0001), whereas parameters related to haemolytic anaemia and desferrioxamine treatment were not. In the prospective study the continuous replacement group increased BMD and BMC values more than the on/off treatment courses (P = 0.01). CONCLUSIONS: Hypogonadism seems to play an important role in the development of osteopenia-osteoporosis in thalassaemia major; continuous hormone replacement therapy with transdermal oestrogen for females or hCG for responding males best improves the bone density parameters.

Adult↗

PubMed1989

[A clinical and epidemiological study of Tori mandibularis].

This is a study aiming at: a) reviewing the information found in the relevant literature as regards the etiology, incidence, distribution, implication and management of the tori mandibularis, b) evaluating the incidence, location and morphology of this bony mass in a sample of Greek population and c) comparing the findings with those of other investigators. The material consisted of 357 patients, from 20 years old and onwards, who had consecutively visited the Clinic of Removable Prosthodontics for some problem. After clinical examination and tabulation of the findings, the following conclusions were drawn: a) the etiology of appearance of tori mandibularis remains unknown; b) in our sample, 12.8% had this condition; c) the incidence was higher in men (60.4%) than in women (39.5%); d) in our sample, the higher percentage of individuals showing the condition originated from Thraci (Northern Greece) while the lower came from Hepiros; e) No indication of a heredity factor was found; f) this condition is more often bilateral than unilateral and g) the torus mandibularis was extending from the canine to the area of the first premolar in 54.4% of the cases.

Adult↗

PubMed1988

Function of reticuloendothelial system in splenectomised thalassemics.

The activity of reticuloendothelial system (RES) was estimated in 19 patients with beta-thalassemia major, 20 +/- 4 years old, who had undergone successful splenectomy 6 +/- 5 years previously. The kinetics of 125I denatured human serum albumin in low and large doses was applied for this purpose and the parameters derived (effective RES blood flow-ERBF- and maximum phagocytic capacity-PCmax) were compared to those of nonsplenectomized thalassemics, detected in previous works, as well as to those of 13 healthy controls. In splenectomised thalassemics both parameters of RES activity were found significantly lower than those of nonsplenectomized patients (p less than 0.001). Compared to those of healthy controls, PCmax of splenectomised thalassemics was found not to be significantly different, while ERBF was significantly lower (p less than 0.001). No correlation was noted between the above parameters of RES function and the age of the patients, the age at which splenectomy was performed, the time lapsed since the operation, the amount of blood transfused to the patients after splenectomy or their serum ferritin levels. A pilot study performed in 6 out of the 19 splenectomised patients did not reveal any effect of blood transfusion on RES function parameters, by contrast to observations in nonsplenectomized thalassemics. The results of this study suggest that in splenectomised thalassemics the remaining RES reacts to the continuing hemolytic stimulus in a manner different than that of splenic RES of nonsplenectomized patients and account for, at least in part, the predisposition of the former group to infections.

Adolescent↗

PubMed1988

Assessment of splenic and RES function of patients with thalassemia major long after partial splenic embolization: in vivo clearance study.

The activity of the remaining reticuloendothelial system (RES) and the function of the splenic remnants was estimated in 5 thalassemic patients who had undergone successful partial splenic embolization (PSE) 6 yr previously. The kinetics of 125I-heat-denatured human albumin as well as that of 51Cr-heat-damaged homologous red blood cells were applied for this purpose and the parameters derived were compared to those of nonsplenectomized as well as splenectomized thalassemics with the following results: (a) The parameters of splenic function in embolized thalassemics were found to be within the limits observed in nonsplenectomized patients. (b) Their maximum phagocytic capacity was significantly lower, not only than that found in nonsplenectomized, but also than in thalassemic patients splenectomized at about the same time. It is concluded that, 6 yr after PSE has been performed, a reorientation of the altered circulatory dynamics has taken place in the splenic remnants allowing previously blockaded areas to gain normal function. It therefore seems that, despite the continuing hemolytic stimulus, RES hyperplasia is prevented, resulting in the stable, low-level transfusion requirements that have been observed in embolized thalassemics.

Adolescent↗

PubMed1987

Radiation dose to the bladder wall and the gonads from direct radionuclide cystography in children.

A dynamic spherical bladder model, previously developed in our laboratory, was implemented to evaluate the absorbed dose to the bladder wall from 99mTc-pertechnetate and direct radionuclide cystography (DRC). This model takes into account the flow rate of normal saline into the bladder and the bladder volume as a function of the filling time. The DRC examinations of 36 children were analysed and calculations were carried out in order to estimate (a) the absorbed dose to the bladder during and following the DRC examination and (b) the gonadal dose. It is shown that the estimated dose to the bladder wall is much greater than that estimated by static models. It is also shown that the absorbed dose to the bladder due to the activity in the residual urine following the examination is even greater than the dose received during the DRC procedure. Our results indicate that in order to reduce the radiation burden, besides the so far proposed precautions, concerning the shortening of the DRC procedure, the patient should also be well hydrated and encouraged to void frequently after the examination.

Child↗

PubMed1986

Kinetics of heat-damaged homologous red blood cells in patients with homozygous beta-thalassemia in relation to blood transfusion.

The kinetics of heat-damaged homologous red blood cells (HDE) was studied prior to and 7-10 d following blood transfusion in 14 patients with homozygous beta-thalassemia. On the basis of our results, beta-thalassemic patients were classified into two distinct groups. In the first group the pretransfusion HDE extraction efficiency of the spleen was significantly lower than that of the second group and it increased dramatically following blood transfusion. On the contrary, the relatively higher pretransfusion HDE extraction efficiency of the patients of the second group showed a significant decrease after blood transfusion. These differences between the two groups of beta-thalassemics might be attributed to the different qualitative as well as quantitative alterations of the splenic vascular bed occurring in these patients during the course of their disease. Furthermore, there was convincing evidence that part of the HDE mixture was extracted by RES sites outside the spleen, a function which is also affected by blood transfusion.

Adolescent↗

PubMed1986

RES phagocytosis in children with homozygous beta-thalassemia in relation to blood transfusion.

In order to investigate the effect of blood transfusion on the RE cell function in thalassemia major, 14 children with homozygous beta thalassemia were studied prior to and 7 to 10 d following blood transfusion, when, according to previous studies, spleen reaches its minimum size. The denatured human albumin (DHA) low and large dose clearance techniques were used in order to estimate the maximum RES phagocytic capacity. It is shown that, despite the confirmed post-transfusion high hepatosplenic circulation, the RE cell phagocytic capacity is not significantly affected. Furthermore the RES phagocytic capacity of beta-thalassemics is shown to be significantly higher than that of normal controls, and this can probably be attributed to the RES hyperplasia accompanying the disease.

Adult↗

PubMed1984

Fitting of radioactivity data to exponential functions by weighted least squares analysis.

The weighted least squares analysis ( WLS ) was compared with the commonly used least squares analysis in the fitting of radioactivity data to an exponential equation. The results show that the two methods present the same accuracy in estimating the parameters of exponential functions, while the WLS analysis offers a much higher reliability, permitting a considerable shortening of the sample counting time.

Humans↗

PubMed1984

Effect of scatter radiation on the planar source sensitivity of a collimated detector.

A theoretical model is proposed to describe the effect of a scattering medium on the plane-source sensitivity of a collimated detector. According to this model the scatter fraction fs(z) of the system is a linear function of the thickness z of the scattering medium and for any collimator geometry depends on the photopeak energy and the window settings as well as on the geometrical and physical characteristics of the scintillation detector. To calculate the parameters of the linear function fs(z), physical constants from the literature were used. The validity of the model was verified by experimental data. The computed parameters were found to differ slightly from the experimental ones and the differences were attributed to several approximations made during the theoretical analysis. The approach used for the determination of these parameters has contributed to a better understanding of the physical meaning of the factors affecting the generation of the scattered radiation and its detection by scintigraphic imaging systems.

Mathematics↗

PubMed1984

Grading of vesicoureteral reflux by radionuclide cystography.

Thirty-six children with urinary tract infection aged 6 months to 14 years (mean age 4 1/2 years) were studied sequentially using direct radionuclide (RNC) and conventional voiding cystourethrography (VCU). Vesicoureteral reflux (VUR) was detected equally well by both methods. Twenty-seven refluxing ureters were found by RNC, 23 by VCU and 22 by both methods. Radiologic grade of reflux may be determined approximately with the isotope technique from the volume of regurgitating urine and duration of reflux, at a much decreased radiation exposure. Residual urine was also measured by RNC and found to be higher in children with VUR. RNC is a reliable method for detecting and grading VUR and should effectively replace VCU as the follow-up examination of choice.

Adolescent↗