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Objective: The work aimed to describe the etiological and evolutionary aspects of cardiogenic shock in the intensive care unit of the cardiology department (USIC) of the G-spot hospital in Bamako, Mali. Materials and Methods: This was a descriptive cross-sectional study from January 1, 2018 to April 30, 2019 that included all patients admitted to the USIC during this period. Each patient benefited from individual data support with systematic recording of socio-demographic, clinical, complementary and therapeutic data and analyzed with the SOFTWARE SPSS 20.0 French version. Results: The study involved 40 patients out of 311 patients hospitalized in USIC, representing a hospital frequency of 12.86%. Males were the most affected (60%) with a sex ratio of 1.50. The modal class was 41 - 60 years with extremes at 18 years and 89 years. Cardiovascular risk factors were dominated by HTA (27.50%), diabetes and tobacco, each with 22.50%. The general signs were tachycardia (90%), oxygen desaturation (77.50%), impregnable blood pressure (62.50%), agitation (52.50%) and an oliguria (70%). At the electrocardiogram the rhythm was sinus (80%), it was an atrial fibrillation (15%), a ventricular tachycardia (10%) and signs of coronary ischemia (necrosis in 35% and ST over shifted in 20% of cases). At cardiac doppler ultrasound,the left ventricle was dilated (50%), the right cavities dilated (30%), segmental kinetic disorder (40%), the left ventricular systolic function (FEVG) impaired (75%) and valve disease (10%). Biology noted hyper-creatinemia (65%), hyper-glycemia (12.50%), anemia and hyponatremia with 20% frequency each. Among etiology, ischemic heart disease accounted for 57.50% followed by pulmonary embolism 20%, dilated valve cardiomyopathy 7.50% and chronic pulmonary heart 2.50%. The trend in the majority of cases was unfavorable with 60% of deaths. Chronic pulmonary heart and pulmonary embolism were the deadliest with a frequency of 100% and 87.50% respectively. Conclusion: Cardiogenic shock is an infrequent condition with a high mortality of a prognosis. Ischemic heart disease is the most common etiology of the disease.

Introduction: Peripartum cardiomyopathy (PPCM) is a heart failure whose etiology is still unknown. The aim of work was to study peripartum cardiomyopathy in its epidemiological, clinical, paraclinical and therapeutic aspects at the Tombouctou hospital. Methods: This is a descriptive cross-sectional study carried out in the Medicine Department of the Timbuktu hospital from January 1 to December 31, 2019. It concerned patients who presented heart failure between the 8th month of pregnancy and the first 5 months postpartum. Results: During the study,23 patients were collected. Average age of the patients was 23.50 ± 3.50 years with extremes of 16 and 34 years. Incidence of Peripartum cardiomyopathy (PPCM) was 1/345 pregnancies. Average parity was 3.20 with extremes of 1 and 8. Symptoms appeared at postpartum with 87% of cases. A significant delay in diagnosis was observed. Global heart failure was the mode of decompensation with 70%. Electrocardiographic signs were mainly sinus tachycardia (87%) and left ventricular hypertrophy (83%). Cardiac ultrasound showed in all cases dilated cardiomyopathy and it was associated with thrombus in left ventricle cavity for three cases. Left ventricular ejection fraction was severely impaired in 70% of cases. Pulmonary hypertension was significant in 52%. Most commonly drugs we used in our series at acute stage were duretics: furosemide 100% and spironolactone 70% (100% and 70%) and ACE inhibitors (90%). Beta-blockers (bisoprolol and carvedilol) were used in 15 patients. Bromocriptine (prolactin inhibitor) was used for 2 patients. Conclusion: Peripartum cardiomyopathy is a serious cardiac complication of pregnancy of unknown cause, common in the African population.

Congenital heart diseases are abnormalities of heart that occur during intrauterine life. Our work aimed to study the epidemiological and echocardiographic aspects of congenital heart disease with Cardiology Department of the Tombouctou hospital. This was a descriptive cross-sectional study from November 2018 to December 31, 2019 on Doppler echocardiography reports from patients admitted to the Cardiology department. The probes used were 3.5 and 5 MHz on an Esaote Mylab40 device. The inclusion criteria concerned patients of both sexes under the age of 16, hospitalized or followed in the cardiology department for cardiac symptoms and having benefited from a cardiac Doppler ultrasound. Results: During the study period, 370 echocardiographic examinations were performed and revealed 20 cases of congenital heart disease with a prevalence of 5.45%. The female sex was the majority 13/7 cases which makes a sex ratio of 0.54. Heart murmurs were the main reason for requesting cardiac Doppler ultrasound with the 13 out of 20 cases of congenital heart disease (65%). Interventricular communication was represented by 15 cases (75%). Congenital heart disease is a reality in Africa. Its frequency and reported series are underestimated due to the inaccessibility of Doppler echocardiography.

Introduction: Pulmonary embolism and aortic dissection are two formidable cardiovascular emergencies. Their exceptional association has a poor prognosis with very high mortality. The aim of our study was to report the case of a 31-year-old patient with pulmonary embolism associated with De Bakey’s type I aortic dissection, admitted to the cardiology department of Kati University Hospital. Case Presentation: We report the case of a young patient of 31 with no known cardiovascular history, on estrogen-progestogen contraception for 10 years, who consults for a left basal thoracic pain of increasing intensity, a whitish productive cough, hemoptysis and dyspnea stage III. She was admitted to the cardiology department, transthoracic cardiac ultrasound objectified aortic insufficiency, dissection of the aorta, the presence of the intimal flap, the false and the true channel, dilation of the right cavities with HTAP. The chest CT scan revealed bilateral lobar and segmental pulmonary embolism, De Bakey’s type I aortic dissection. Medical treatment was instituted for hemodynamic stabilization at the end of sending her to a center specializing in cardiovascular surgery for better management; unfortunately she succumbed before the preparations for her evacuation were finished. Conclusion: The pulmonary embolism associated with aortic dissection constitutes a medical emergence of rare incidence in a cardiological environment;if the diagnosis was quickly made in our patient, the lack of technical platform made management difficult.

Objective: The purpose of this work was to determine the epidemiological, clinical and evolutionary aspects of the pulmonary embolism of the young person in the cardiology department of the University Hospital Center (CHU) Point G in Bamako-Mali. Methodology: This was an analytical study from January 01, 2018 to December 31, 2018 in the CHU Point G cardiology department, including all patients hospitalized during this period. Results: Of 1379 hospitalized patients, 19 patients were concerned by pulmonary embolism of the young person. The prevalence of pulmonary embolism of the young person was 1.37%. The most affected age group was 21 - 30 (47.4%) of patients. The predominance was female (89.47%) with a gender ratio of 0.11 in favour of women. The average age in the series was 29.79 years with extremes of 16 years and 40 years. Factors predisposing to pulmonary embolism were dominated by peri partum, cardiomyopathy and obesity with 47.3%, 31.57% and 21.1%, respectively. The dominant signs were chest pain and dyspnea in 94.7% and 89.5% of cases respectively. Pulmonary embolism was unlikely in 60.52% according to the Geneva and Wells score simplified. At the thoracic angioscanner, the embolism was bilateral in 52.6% of cases and distal in 36.8% of patients; in 10 patients who performed cardiac ultrasound, pulmonary arterial hypertension (70%), dilation of the right ventricle (20%) and left ventricular dilation (40%). Hyper leucocytosis (47.4%), anemia and low prothrombin rate (TP) (22.2%) were the most found biological abnormalities. More than 2/3 (68.5%) our patients had an intermediate mortality risk according to the PESI (Pulmonary Embolism Severity Index) score. The average hospital stay was 10 days. Hospital mortality was 10.5%. Conclusion: The pulmonary embolism of the young person is a frequent, serious and multifactorial pathology and the female sex is most affected especially during peri partum periods, hence the need for preventive measures. Clinical signs are not specific and based on the assessment of clinical probability. Pulmonary angioscanner remains the confirmation review in our context.

Introduction: Acute myocardial infarction (IDM) occupies the first place in terms of mortality, among ischemic pathologies. Thrombolysis in the case of medical treatment for acute myocardial infarction (AMI) is undoubtedly the most revolutionary performed to date in this context, with a significant reduction in the mortality rate. The aim of our study was to describe the epidemiological aspects, the criteria for myocardial reperfusion post thrombolysis, the complications during thrombolysis and the complications of acute myocardial infarction in the cardiology department of the CHU Ernesto Guevara De La Serna of Las Tunas (Cuba). Methods: A retrospective cross-sectional descriptive study was carried out from June 2009 to December 2011. The patients hospitalized during this period in the USIC (coronary intensive care unit) for SCA ST(+) were included in the study. The variables studied were: Age, sex, myocardial reperfusion criteria, complications during thrombolysis and complications of myocardial infarction. Results: A total of 207 patients were included. The male sex represented 72.5% of the cases, giving a sex ratio of 2.63. The age group > 60 years was predominant with 54.2% of the cases. Thrombolysed patients represented 65.2% of the cases. Myocardial reperfusion criteria were observed in the majority of thrombolysed patients: relief of precordial pain (77%), regression of the ST segment to 50% of its previous level (81.5% of patients). Bleeding was observed in 1.5% of thrombolysed cases. Complications were encountered in 57% of non thrombolysed patients with a lethality of 5.6%. Conclusion: The male sex was the most affected. Thrombolysis was effective in the majority of patients. The post thrombolysis bleeding rate was low. More than half of the cases of SCA ST(+) not thrombolysed presented complications.

International audience; Fuel debris have a distinct neutron signature that can be detected to locate the said debris in a damaged nuclear power plant. Neutron measurement in a damaged PCV environment is however submitted to severe deployments constraints, including a high-dose-rate gamma background and limited available space. The study was therefore oriented towards small fission chambers (FC), with U-235-enriched active substrates. To investigate the expected performance of the FC in various irradiation conditions, a numerical model of the detector head was built. We describe the elaboration and experimental calibration of the numerical model and the Monte Carlo study of the fission rate inside U-235 coatings per generated neutron. The evaluation of a representative calibration coefficient then allowed us to carry out a multi-parameter performance study of a FC underwater, aiming at computing an explicit response function linking, on the one hand, the activity and spatial distribution of neutron emitters in a water container, with, one the other hand, the expected count rates measured by a fission chamber as a function of its radial and axial position inside the water volume. The FC underwater behavior was subsequently corroborated by a measurement campaign on a FC response, set at different positions inside a water drum, as a function of its axial and radial distance to a Cf-252 neutron source attached near the center of the container. We finally present an approach in which fuel debris localization is defined as an Inverse Problem, solvable with a Maximum-Likelihood Expectation Maximization (ML-EM) iterative algorithm. The projector matrix is built by capitalization on the results of the previously consolidated numerical studies. The ML-EM was tested on simulated data sets with a varying number of active voxels. Our first results indicate that, for a thermal neutron flux in the order of 10 n.cm−2.s−1 at the detector, originating voxels are identified with a spatial resolution in the radial plane in the order of 10 to 100 cm2.

Objective: The work aimed at describing an epidemioclinical, therapeutic and evolutionary characteristics of patients hospitalized for aortic dissection in the cardiology department in Point “G” Hospital University Center in Bamako—Mali. Methodology: It was a descriptive cross-sectional study from January 2010 to February 2017 in the CHU Point G cardiology department, including all patients hospitalized during this period. Results: Of 6912 hospitalized patients, 23 patients were concerned by aortic dissection. The prevalence of aortic dissection was 0.33%. The most affected age group was 50 - 69 (43.5%) of patients. The predominance was male with a sex ratio of 4.75. The cardiovascular risk factors were high blood pressure (73.9%) and smoking (60.9%). The major functional signs were chest pain (65.2%) and dyspnea (65.2%). Asphygmy (56.5%) and breath of aortic insufficiency (60.9%) were the dominant physical signs. The electrocardiogram recorded sinus tachycardia with 86.9% of patients. The radiographic of the frontal thorax showed mediastina widening (73.9%). At echocardiography, dilatation of the ascending aorta was described with 73.9% and the intimal veil (47.8%). Pericardial effusion was observed with 26.1% of patients. In the thoracic angioscan, the aortic dissection gave 43.5% for type A and 56.5% for type B. The aneurysm of the aorta was abdominal with 21.7%, ascending portion (13.0%) and descending with 8.7%. Complications were dominated by heart failure (47.8%) and aneurysm of the aorta (34.8%). The lethality was 52.2%. Conclusion: Aortic dissection is a medical and surgical emergency with poor prediction.

Objective: The aim of this study was to describe the epidemiological, clinical and Para clinical characteristics in patients hospitalized for pulmonary embolism in the cardiology department of Gabriel Toure University Hospital. Methodology: It was a retrospective and descriptive study from January 2011 to December 2014 and involved all patients hospitalized during the study period. Results: The study included 21 patients out of 1738 hospitalized patients, with a prevalence of 1.21%. The mean age was 38.57 years with extreme ages of 18 and 64 years. The sex ratio was 0.40. Risk factors found in the study were oral contraception (19.05%), overweight (19.05%), smoking (14.28%), HIV (4.76%) and heart failure (4, 76%). 61.90% (n = 13) had isolated pulmonary embolism, 38.09% (n = 8) had venous thrombosis and pulmonary embolism association. Through the chest angio-CT, 28.57% of obstructions were located at the left branch of the pulmonary artery, 9.52% at the right branch and 61.90% were bilateral obstructions. Four deaths were recorded, all in a context of massive pulmonary embolism, with a fatality rate of 19.05%. Conclusion: Pulmonary embolism is a serious and common disease, often difficult to diagnose. It is a cardiovascular emergency and requires immediate and adequate care.

Objective: To study hypertension and its manifestations in Out-patients’ Department of Cardiology of Kati. Methods: The study was traversal and it was based on a sample of 300 patients, reached during the interval of 12 (twelve) months (from June 2012 to June 2013). Results: The predominance was among the females with 68.7%. The average age was about 55.8 ± 12.2 years old. The extreme ages were about 21 and 90 years old. In the set, 66% of the patients lived in the town of Kati. The symptoms of Dieulafoy were predominantly the reasons for consultation with 55.7%. The cardiac frequency in the vast majority of cases was normal (85.3%). The left ventricular hypertrophy in the electrocardiogram was observed in more than half of the cases, that is to say, 51.3%. In a bit higher proportion, the echocardiography Doppler became normal, that is to say, 54%. Brain scanner done on 9 patients found out signs of cerebrovascular stroke in 8 patients, that is to say, a frequency of 88.9%. In 76% of cases of orthostatic hypotension, the patients were hypertensive. The blood pressure was normal during the passage of orthostatism in the cases of 258 of our patients, that is to say, 86.0% of the cases. However, the orthostatic hypotension (OH) was observed in the cases of 42 patients, that is to say, 14.0% of the cases. In this set of patients, 41.6% of the moans were due to cephalgias and dizziness’s. The monotherapy of patients with OH represented 47.6% of the cases. Blood pressure was not controlled in 66.7% of the cases of OH. The biological examinations required were normal in 52.4% of the cases. Conclusion: The hypertension is a disease which is frequently the reason for consultation in cardiology. The symptoms of Dieulafoy can be the signs of call. The complications are sometimes recurrent. The orthostatic hypotension should be found out even under monotherapy on a balanced or non-balanced hypertensive patient through treatment.

International audience; This work aims at assessing the performance of a 235U enriched fission chamber in order to localize fuel debris, prior to dismantling operations, in a flooded primary containment vessel of a damaged nuclear reactor such as Fukushima Daiichi. Based on both a comprehensive scan of the environment and the detection of neutrons emitted by the melted core, fuel debris can be localized. In this paper, we carry out a simulation study using the MCNP6 code to investigate fission chamber response in the frame of fuel debris localization measurements in a damaged nuclear reactor. The CFUF34 fission chamber (manufactured by PHOTONIS) and the primary containment vessel of Fukushima Daiichi Unit 1 were chosen to conduct this work. Impact of different parameters were investigated with MCNP6, such as: neutron energy, water temperature, fission chamber position (altitude, lateral shift, and rotation), and sensitivity loss due to sediments potentially covering fuel debris. In summary, we show that fuel debris should be sought by their thermal neutron signature at a distance of a few centimeters and that potential rotational movements of the fission chamber up to 60° have a limited impact on signals measured. We also show that sensitivity loss due to sediments potentially covering fuel debris has been evaluated on the order of a factor 10 considering a 30 cm-thick sediment layer. On the other hand, experiments were performed to assess the impact of a strong gamma dose rate on fission chamber measurements. These irradiation trials involved a CFUE32 fission chamber (also manufactured by PHOTONIS) available in our laboratory and three different irradiation means: an X-ray tube, an 192Ir source, and a linear electron accelerator. These experiments enable to draw the conclusion that the fission chamber is not impacted by the gamma dose rate up to 104 Gy h−1, which is in good agreement with specifications provided by the manufacturer (PHOTONIS). In addition, no performance degradation was observed after an integrated gamma dose of 2200 Gy on the fission chamber in a 10 min irradiation. However, when the fission chamber is irradiated by gamma dose rates above 104 Gy h−1 (upper limit of the operating domain specified by PHOTONIS), a significant gamma background is observed. Nevertheless, as the gamma dose rates at Fukushima Daiichi should not exceed 103 Gy h−1, fission chamber measurements performed towards fuel debris localization in the primary containment vessels of the units would not be affected by the severe gamma-ray irradiation.

International audience; Monte Carlo (MC) simulation is widely used in gamma-ray spectrometry, however, its implementation is not always easy and can provide erroneous results. The present action provides a benchmark for several MC software for selected cases. The examples are based on simple geometries, two types of germanium detectors and four kinds of sources, to mimic eight typical measurement conditions. The action outputs (input files and efficiency calculation results, including practical recommendations for new users) are made available on a dedicated webpage.

Holmium-166 is a high-energy β−-emitter radionuclide (~ 1.8 MeV) with a short half-life ( ~ 26.8 h ) that offers great potential as an alternative to 90Y for the treatment of liver cancer based on radioembolization. The possibility of quantitative Single Photon Emission Computed Tomography (SPECT) imaging of the main γ-ray emission at 80.6 keV, in addition to strong paramagnetic properties suitable for Magnetic Resonance Imaging (MRI), complement this therapeutic potential. The present paper describes the measurements carried out in three European radionuclide metrology laboratories for primary standardization of 166Ho and new determinations of X- and γ-ray photon-emission intensities in the framework of the European EMPIR project MRTDosimetry. New half-life measurements were also performed.

International audience; Well-type re-entrant ionization chambers (IC) are used in radionuclide metrology for secondary measurements of radioactive sources. Generally this technique is used for solutions of gamma-emitting radionuclides, but was also extended to high-energy beta-emitting radionuclides like 90Y. In this case, the energy transfer to the gas is made through Bremsstrahlung photons. The measurement of gaseous 222Rn sources with an IC was also undertaken in the framework of the Système International de Référence (SIR) of the Bureau International des Poids et Mesures (BIPM). In this case, we observed an important influence of the thickness of the walls of the glass container of the source. We analysed this effect as the consequence of the direct interaction of high-energy electrons from 214Bi (maximum beta energy of 3.27 MeV) with the counting gas. As the efficiency of the direct ionization of a gas by electrons is several orders of magnitude more important than ionization by Bremsstrahlung, and as energy absorption in the walls of the ampoule is much more sensitive to the thickness of the walls than absorption of the Bremsstrahlung, this could explain the observed phenomenon. It is worth noticing that direct interaction of electrons with the IC gas is never expected when measuring solutions, and this phenomenon was to our knowledge, never addressed in the past. In order to analytically study this phenomenon, we undertook a Monte Carlo simulation of a Vinten 671 IC, with a radon source in a glass vial, where the solid daughters in secular equilibrium with the radon are adsorbed on the internal walls of the gas ampoule. The influence of the glass wall thickness on the response of the IC was studied vs. the wall thickness using the PENELOPE 2016 package and allowed us to determine the acceptable variability of the thickness of the ampoules. Similar simulations were also undertaken with metal gas containers, showing that they could solve measurement problems of 222Rn in the SIR system.

International audience; The NUCLEIDE database provides comprehensive and accurate data recommended by the Decay Data Evaluation Project (DDEP). The module NUCLEIDE++, written in C++, and designed to work in conjunction with the GEANT4 Monte Carlo toolkit has been developed to simulate the complete decay scheme for a given radionuclide by randomly selecting the decay pathways, using data from NUCLEIDE. The nuclear de-excitation of the potential daughters can also be treated in the same run. The initial energies of the electron and positron in the case of beta-emitting radionuclides are sampled from spectra calculated with the BetaShape program developed at LNE-LNHB. The aim of this work is to propose to GEANT4 users the possibility to run with the recommended NUCLEIDE data and a more detailed model. The reliability of NUCLEIDE++ is shown by comparing the coincident particles cascades to the ones obtained with PENNUC and GEANT4.

Metrological non-destructive characterization of intense ( α , n) neutron sources (emission rate between 107 and 3 × 108 s−1 into 4 π sr solid angle) is a challenge for nuclear applications. In this article, we will present the design, development and in situ validation of two measurement cells especially dedicated to this characterization. The main goal consists in determining the absolute neutron emission rate of this type of neutron sources with relative uncertainties less than 5% (k=1). Another purpose is related to the qualitative and quantitative analysis of fission products present in irradiated neutron sources. Because of experimental constraints, acquisitions were carried out underwater which required a full remote control of the measurement cells. Neutron emission rate is assessed using three different non-destructive techniques: (i) global neutron counting, (ii) neutron activation using gold dosimeters and (iii) gamma-ray spectrometry. We will successively present the design step and associated constraints, main characteristics of measurement cells and associated laboratory characterization as well as experimental results obtained during the final in situ measurement campaign. The latter shows an excellent agreement regarding the neutron emission rate values provided by the three different non-destructive techniques and a relative combined standard uncertainty less than 5% (k=1) for the investigated neutron sources.

Proceedings of the 20th International Conference on Radionuclide Metrology and its Applications (ICRM), 8-11 June 2015, Vienna, Austria. Organizer TU Wien. Editors Franz-Josef Maringer, Dirk Arnold, Uwe Wätjen.; International audience; The present paper addresses the calibration of well-type ionization chambers (ICs) used at LNE-LNHB as standard transfer instruments to calibrate hospitals in the case of SIR-Spheres $^{90}$Y resin microspheres (Sirtex, Australia). Developed for interventional oncology, this radiopharmaceutical is directly injected in the liver for cancer treatment via a selective internal radiation therapy. The present work was carried out in the framework of the European project “Metrology for molecular radiotherapy” (MetroMRT). As commonly performed in radionuclide metrology for radiopharmaceuticals, the objective is to ensure the metrological traceability of SIR-Spheres to hospitals. Preceding studies were focused on primary measurements of SIR-Spheres based on the TDCR (Triple to Double Coincidence Ratio) method, applied after the dissolution of the $^{90}$Y-labeled resin microspheres. As $^{90}$Y is a high-energy β$^-$-emitter, the IC response strongly depends on the transport of electrons in the radioactive solution and surroundings (vial, chamber liners and materials). The variability of the IC-response due to the geometry dependence is investigated by means of measurements and Monte Carlo simulations in the case of a Vinten IC. The aim of the present study was also to propose a reliable uncertainty for ICs calibrations for the standard transfer of SIR-Spheres to hospitals.

The LNE-LNHB, in charge of the French standards for radionuclide metrology, develops primary measurement methods intended for the calibration of secondary measuring instruments, such as used in hospitals, to determine the activity of radiopharmaceuticals injected into patients. The triple-to-double coincidence ratio ( TDCR) method, based on liquid scintillation counting, is widely implemented for radio nuclides which are pure beta and electron capture emitters. This technique requires the mixing of the radioactive solution with a scintillator cocktail. When preparing samples, the existence of physicochemical processes such as chemi-luminescence can require to delay the measurements to achieve the necessary stability conditions, which is not always compatible for short half life radio nuclides. To avoid this constraint, a new approach using Cerenkov radiation as a method of light production is presented in this paper, applied to the standardization of the short-lived radiopharmaceutical 11 C ( T1/2 ~ 20 min). The method is based on comprehensive modeling of the TDCR counter (the experimental equipment) using a Geant4 toolkit in order to calculate the detection efficiency.

International audience; In the field of radionuclide metrology, the TDCR method is a primary technique based on liquid scintillation using a threephotomultiplier instrumentation. The application of the TDCR model classically implemented in laboratories is investigated in the case of low-energy deposition in the liquid scintillator. For that purpose, the condition of stochastic independence between photomultipliers is introduced in order to express the classical probabilistic relations used for the detection efficiencies of coincidences. Experimentally observed in the case of $^3$H standardization, the time dependence arises when the coincidence resolving time is shorter than the time distribution of scintillation photons. The geometric dependence is also investigated because of the sensitivity of coincidence counting with the position of light emission inside the volume of the liquid scintillator. For that purpose, a new TDCR modeling using the Monte Carlo code Geant4 has been implemented in order to simulate the propagation of photons from their creation in the optical chamber to the production of photoelectrons in liquid scintillation counter. In both cases of stochastic dependence, the influence on the calculation of detection efficiencies and thus on the activity determination is presented. The new TDCR-Geant4 model was also developed to take into account Cherenkov emission; it has been applied to confirm the emission of Cherenkov photons subsequently created by Compton scattering in the photomultiplier windows. Using the TDCR-Geant4 model, a new primary technique is also presented by implementing the TDCR method using the Cherenkov emission. This new technique has been applied to the standardization of the short-lived radiopharmaceutical $^{11}$C ($_{T1/2}$ about 20 min).; En métrologie de l’activité, la méthode RCTD (Rapport des Coïncidences Triples à Doubles) est une technique primaire fondée sur la scintillation liquide, utilisant une instrumentation spécifique à trois photomultiplicateurs. Le modèle RCTD statistique de l’émission lumineuse permettant le calcul des rendements de détection des coïncidences est étudié dans le cas de dépôts de basses énergies dans le liquide scintillant. Pour cela, l’indépendance stochastique entre les photomultiplicateurs est introduite comme condition préalable à l’écriture des relations classiques du modèle statistique. Deux phénomènes pouvant conduire à la non-validité de cette condition sont décrits. Mise en évidence expérimentalement avec la mesure d’activité du tritium ($^3$H), la dépendance stochastique de type temporel se manifeste par une perte systématique de coïncidences lorsque le temps de résolution est trop court comparé à la distribution temporelle des photons de scintillation. La dépendance stochastique de type géométrique est également étudiée en raison de la sensibilité du comptage des coïncidences selon le point d’origine de l’émission lumineuse dans le volume du liquide scintillant. Cette étude a été possible grâce au développement d’une nouvelle modélisation avec le code Monte-Carlo Geant4 intégrant la simulation de la propagation des photons optiques jusqu’à la production des photoélectrons dans le détecteur. Dans les deux cas de dépendance stochastique, l’influence sur le calcul des rendements de détection des coïncidences et par suite sur la détermination de l’activité est exposée. Le nouveau modèle RCTD-Geant4 intègre aussi l’émission de photons Cherenkov ; il a permis la confirmation de l’émission de lumière « parasite » sous forme de photons Cherenkov suite à la diffusion Compton dans les faces d’entrée des photomultiplicateurs. Une nouvelle technique primaire RCTD-Cherenkov a également été développée grâce au modèle RCTD-Geant4 ; elle a été notamment appliquée à la mesure d’activité du carbone-11 (radiopharmaceutique à durée de vie courte, $T_{1/2}$ de l’ordre de 20 min).