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.     

Le contrôle de qualité externe en Biologie de la Reproduction de 1992 à 1996

Clinical efficiency of laboratory results in spermiology needs to have reliable data, and a quality assurance in their determinations. This could be done by creating an External Quality Control, each laboratory analyzing the same specimens. We transferred in spermiology methodologies currently used in Quality Control in Biochemistry and results presented here referred to the 1992–1996 period. Volountary participation of 37 laboratories who recieved two slides issuing from the same ejaculate. Coloration was made with that used in their own laboratory. Two parameters were specially studied: the total normal sperm count and the degree of teratospermia by evaluation of the Multiple Abnormalities Index (MAI). An area around the target value of 15% is actually retained and results in terms of precision and accuracy are interpreted with the Youden’s diagram. For the total normal sperm count, the disperson remains important during the 4 years (about 30 and 40%) with a poor percentage of laboratories in the area of accuracy. For the MAI, results are better as soon as the dispersion falls from 25 to 15% during the same time and the percentage of laboratories in the accuracy area rises from 10% to 68%. After four years of external quality control, such a protocol is very useful. But the quality results of some parameters must be more extensively explored to reduce interlaboratory dispersion and to improve the clinical efficiency of laboratory data in the spermiology approach.     

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.     

Testostérone et contrôle central de l’érection

Testosterone orchestrates the perinatal organization and activation of cerebral and spinal neuronal structures involved in the expression of male sexual behaviour in adults. The present review briefly describes testosterone effects in the regulation of sexual motivation and erection, as well as the genetic models developed to date in order to unravel its central mechanisms of action.     

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.     

Les mécanismes de contrôle de la méiose dans la lignée germinale mâle

In 1883, it was discovered that whereas the fertilized egg of a particular worm (Parascaris Equorum) contains four chromosomes, the nucleus at the egg and that of the sperm each contains only two chromosomes. This finding implied that germ cells must be formed by a special kind of nuclear division in which the chromosome complement is precisely halved. This type of division is called meiosis. Meiosis and mitosis share many regulatory elements. Among them, are the cyclindependent kinases (CDK) and the cyclins which control all transitions of the cell cycle. The activity of the CDKs is regulated by their association to specific cyclines and by phosphorylation/dephosphorylation reactions. Moreover, recent reports reveal the existence of a variety of small proteins which bind to and modulate G1/S CDK-cyclin complexes: the CKI. Two more proteins appear of great importance in regulating the cell cycle: Rb and p53. The central role of MPF (maturation producing factor=M-phase promoting factor) has been established, mostly by studies conducted on either invertebrates oocytes and eggs that resume the meiotic division. MPF is the cyclin B-p34cdc2 kinase. As for the cytostatic factor (CSF), it is reasonably certain that it is, in part or entirely, MOS. The cell cycle signalling mechanisms in oocytes include cAMP, Ca⁺⁺ and the agonists of PKC. Much less informations on the control of meiosis in spermatogenesis are available. Indeed, it is difficult to get rather high number of germ cells at some precise steps of their maturation and there is a lack of culture system allowingin vitro germ cell differentiation. However, most of the genes involved in the regulation of the cell cycle are expressed in the testis (c-mos, cyclins, CDK, cdc 25…). Their expression has striking cellular, lineage and developmental specificity. It has also been shown that FSH, interleukin-1a, and MIP-1a enhance stagespecific DNA synthesis in rat seminiferous tubule segments, while interleukin-6 decreases it. In our laboratory, we have settled recently two cell culture systems allowing the expression of germ cell specific genes for 2 to 3 weeks. This should help to study more easily the genetic control of meiosis during spermatogenesis and to understand better which growth factors and/or cytokines are really important for the regulation of this process.     

Activité des corpora allata et contrôle photopériodique de la maturation ovarienne chez Locusta migratoria

Locusta migratoria migratoria females of the ‘Kazalinsk’ strain show a sustained inhibition of ovarian maturation when submitted to long-day photoperiodic conditions ($\text{17}\text{hr}\text{24}\text{hr}$). A full ovarian cycle can be initiated at any time throughout adult life by implantation of corpora allata (CA) taken from egg-laying females. Therefore, in inhibited females, the gonadotropic activity of the CA fail to allow normal vitellogenesis. However, if such females receive CA taken from females conditioned in the same way, a full ovarian cycle still occurs. If CA taken from 5-week-old, either mature or immature, females are implanted into 5-day-old females reared without males under long-day lighting, a single ovarian cycle results, no matter what the state of the donor females. The possibility is discussed that in L. migratoria females neurosecretory material may be involved in the functional development of adult CA, whereas the gonadotropic hormone is released from the CA under nervous control, as far as a photoperiod-sensitive strain is concerned.