Imagerie hybride : principe,dosimétrie et contrôle de qualité

The recent introduction of hybrid systems combining a SPECT and a CT in nuclear medicine, greatly improved the diagnostic accuracy for particular clinical indications, due to the possible attenuation and/or scatter correction of the SPECT functional images and the availability of helpful anatomic information. Although the gamma cameras performances are noticeably comparable, the associated CT furnished by the manufacturer are relatively different from each other. Whatever the system is, the introduction of CT in the nuclear diagnostic process results in a significant increase of the patient dose. This dose increase should be justified and optimized considering both the clinical question and the CT settings available on these systems. The installation of a hybrid system must be accompanied by the management of a documentary quality insurance program, jointly developed by the technologists, physicists and physicians, both covering its clinical use and the associated dosimetry issues as monitoring its performances. Particular quality control procedures have to be defined because of the coupling between the two devices.     

Mise en œuvre du contrôle de qualité en médecine nucléaire

Like in many nuclear medicine centers, the AFSSAPS decision of November 25, 2008, has slightly changed our habits. The centers with medical physicist already made most of these controls, and this concept was not new for them. But what about the other centers? Sometimes, measures were made as expected, other times the manufacturers were expected to do them during the maintenance time, often nothing was formalized, and even in some cases nothing was done. Our experience in quality control in nuclear medicine is relatively recent, but we find interesting to raise some issues, including the duration for all these controls, the possible delegations, the means necessary to build them and difficulties in applying these controls.     

Préparation et contrôle de qualité de la solution injectable de gallium-68 édotréotide (DOTATOC (68Ga))

Radiopharmacists of the Nuclear Medicine department of hospital Tenon have prepared and controlled the ⁶⁸Ga-labeled DOTATOC, for 4 years, as part of a clinical research study. The aim of this article is to share our experience, since this activity is not yet developed in France. Radiolabelling of DOTATOC (⁶⁸Ga) requires the settling of a ⁶⁸Ge/⁶⁸Ga generator, which is connected to an automated PC-controlled radiopharmaceutical labelling device (Elusynth ⁶⁸Ga, Iason) and comprises several steps. Performed quality controls (QC) are those commonly used for radiopharmaceuticals including: appearance, pH, radiochemical purity (RCP), radionuclide purity (PRN) and determination of the physical half-life. Bacterial endotoxins and sterility tests are systematically done. We obtained a mean value of radiolabelling yield around 45%. The results of QC are always in accordance with the specifications. The preparation failed in 7% of the 195 DOTATOC (⁶⁸Ga), over the last 4 years. It is important to note that the preparation of DOTATOC (⁶⁸Ga) monopolizes the radiopharmacist during 3 hours. This radiolabelling technique can be easily applied to other peptides, in order to develop other ⁶⁸Ga-labelled PET tracers.     

Etiologie de 350 cas de stérilité masculine. Effet de divers traitements sur la qualité du sperme et analyse de leur rôle dans la survenue de 100 grossesses

Etiologic factors of male sterility and the effect of different treatments on sperm quality have been evaluated in 350 men consulting for primary or secondary infertility of more than one year. Environmental factors represent 12% of the etiologies, acquired diseases such as varicoele and prostatitis 36.8%, testicular failure 23%, endocrinopathy 1,4%, sexual dysfunction 1,4%, abnormality of sperm transport 7,4%. and idiopathic cases 19%. A conventionnal treatment has been tempted in 50% of the cases and evaluated in 101 patients. A normalisation of the sperm (defined by a total motile sperm count (TMS) higher than 16 millions) has been observed in a variable proportion of the cases: 80% after hormonotherapy, 37% after varicocelectomy, and 30% after antiinflammatory treatment. Among 100 pregnancies, 39% occurred either spontanously or after ovulation induction, 32% after classical andrological treatment and 26% after assisted reproductive techniques (ART) such as in vitro fertilization, intracytoplasmic sperm injection or intrauterine insemination. The efficiency of these different treatments according to the TMS and the utility of the clinical investigation of the infertile male are discussed. The risk faced by the wife because of ART are underlined.     

Évaluation des paramètres et méthode de contrôle de qualité de la correction d’atténuation en tomographie par émission de positons

ObjectiveThe aim of this study is to evaluate the performance of the Computed Tomography based Attenuation Correction (CTAC) for Positron Emission Tomography (PET) data. Attenuation maps containing linear attenuation coefficients at 511 keV (LAC_511 keV) are calculated by trilinear conversion of Hounsfield Units (HU) obtained from CT slices after matrix size-reduction and gaussian filtering. Our work focusses on this trilinear conversion.Materials and methodsCT slices of an electron density phantom, composed of 17 cylindrical inserts made of different tissue-equivalent materials, were acquired using a Discovery ST4^® PET-CT. Data were processed with a customized version of CT quality control software, giving automatically the experimental conversion function: LAC_511 keV = f(HU). Furthermore, data from patient datasets were assessed using both smoothed CT slices and attenuation maps.ResultsLAC_511 keV extracted from phantom data are in good correlation with the expected theoretical values, except for the standard 10 mm diameter dense bone insert, where the obtained CTAC values are underestimated. Assuming a sample size issue, similar acquisitions were performed with a special 30 mm-diameter dense bone insert, confirming the underestimation as a consequence of the sample size. This effect, caused partly by a too smooth Gaussian filter of the CT images, could be limited by reducing the strength of the filter. Measurements from patients’ data showed the same underestimation of CAL_511 keV for high-density tissues.ConclusionWe assessed an underestimation of the CTAC obtained-values related to the sample size of the insert. A quality control was developed to this effect.     

Comparaison de deux techniques de prélèvement du zooplancton,le filet et la trappe de Schindler,en lagune Ebrié (Côte d'Ivoire)

The analysis of net (bottom to surface vertical hauls) and trap samples taken at night shows that net hauls underestimate abundance of all planktonic organisms from nauplii and mollusc larvae to adult calanids. There is no obvious explanation for this. The underestimation probably results from low net filtering efficiency. The mean ratio between trap and net observed densities is 1.46 (1.2 to 1.9) and does not change significantly according to the organisms.

     

Répartiteur de dose des médicaments radiopharmaceutiques : contrôle qualité sur deux sites hospitaliers et comparaison avec la législation en vigueur en France

An increasing number of nuclear medicine departments are equipped with automated measurement systems for the preparation of radiopharmaceuticals, with the main aim of minimising technician's irradiation. However, the automatic measurement of the patient activity differs from the manual measurement in material and method. In this context, the objective of the present study was to test the performances of one of these systems, the Unidose by TRASIS^®, in two newly equipped hospitals. The particularity of these systems is they are made up of two dose calibrators: the entrance calibrator (well chamber) and the exit calibrator (probe). Controls were performed on both of these dose calibrators. The results obtained, as well as the methodology employed, were then compared with the regulatory requirements in France. The results found are coherent between the two sites and have highlighted several non-conformities compared to the current regulations, part of which concerning the carpule dose calibrator, which is actually a probe. These results raise the question of a suitable regulation for the new automated measurement systems in nuclear medicine.