Management of patient dose and image noise in routine pediatric CT abdominal examinations

The aim was to propose a strategy for finding reasonable compromises between image noise and dose as a function of patient weight. Weighted CT dose index (CTDIw) was measured on a multidetector-row CT unit using CTDI test objects of 16, 24 and 32cm in diameter at 80, 100, 120 and 140kV. These test objects were then scanned in helical mode using a wide range of tube currents and voltages with a reconstructed slice thickness of 5mm. For each set of acquisition parameter image noise was measured and the Rose model observer was used to test two strategies for proposing a reasonable compromise between dose and low-contrast detection performance: (1) the use of a unique noise level for all test object diameters, and (2) the use of a unique dose efficacy level defined as the noise reduction per unit dose. Published data were used to define four weight classes and an acquisition protocol was proposed for each class. The protocols have been applied in clinical routine for more than one year. CTDIvol values of 6.7, 9.4, 15.9 and 24.5mGy were proposed for the following weight classes: 2.5-5, 5-15, 15-30 and 30-50kg with image noise levels in the range of 10-15HU. The proposed method allows patient dose and image noise to be controlled in such a way that dose reduction does not impair the detection of low-contrast lesions. The proposed values correspond to high- quality images and can be reduced if only high-contrast organs are assesse

Repeated injections of 131I-rituximab show patient-specific stable biodistribution and tissue kinetics

Purpose: It is generally assumed that the biodistribution and pharmacokinetics of radiolabelled antibodies remain similar between dosimetric and therapeutic injections in radioimmunotherapy. However, circulation half-lives of unlabelled rituximab have been reported to increase progressively after the weekly injections of standard therapy doses. The aim of this study was to evaluate the evolution of the pharmacokinetics of repeated 131I-rituximab injections during treatment with unlabelled rituximab in patients with non-Hodgkin's lymphoma (NHL). Methods: Patients received standard weekly therapy with rituximab (375mg/m2) for 4 weeks and a fifth injection at 7 or 8 weeks. Each patient had three additional injections of 185MBq 131I-rituximab in either treatment weeks 1, 3 and 7 (two patients) or weeks 2, 4 and 8 (two patients). The 12 radiolabelled antibody injections were followed by three whole-body (WB) scintigraphic studies during 1 week and blood sampling on the same occasions. Additional WB scans were performed after 2 and 4 weeks post 131I-rituximab injection prior to the second and third injections, respectively. Results: A single exponential radioactivity decrease for WB, liver, spleen, kidneys and heart was observed. Biodistribution and half-lives were patient specific, and without significant change after the second or third injection compared with the first one. Blood T1/2β, calculated from the sequential blood samples and fitted to a bi-exponential curve, was similar to the T1/2 of heart and liver but shorter than that of WB and kidneys. Effective radiation dose calculated from attenuation-corrected WB scans and blood using Mirdose3.1 was 0.53+0.05mSv/MBq (range 0.48-0.59mSv/MBq). Radiation dose was highest for spleen and kidneys, followed by heart and liver. Conclusion: These results show that the biodistribution and tissue kinetics of 131I-rituximab, while specific to each patient, remained constant during unlabelled antibody therapy. RIT radiation doses can therefore be reliably extrapolated from a preceding dosimetry stud

Difference in performance between 3D and 4D CBCT for lung imaging: a dose and image quality analysis.

The study was to describe and to compare the performance of 3D and 4D CBCT imaging modalities by measuring and analyzing the delivered dose and the image quality. The 3D (Chest) and 4D (Symmetry) CBCT Elekta XVI lung IGRT protocols were analyzed. Dose profiles were measured with TLDs inside a dedicated phantom. The dosimetric indicator cone-beam dose index (CBDI) was evaluated. The image quality analysis was performed by assessing the contrast transfer function (CTF), the noise power spectrum (NPS) and the noise-equivalent quanta (NEQ). Artifacts were also evaluated by simulating irregular breathing variations. The two imaging modalities showed different dose distributions within the phantom. At the center, the 3D CBCT delivered twice the dose of the 4D CBCT. The CTF was strongly reduced by motion compared to static conditions, resulting in a CTF reduction of 85% for the 3D CBCT and 65% for the 4D CBCT. The amplitude of the NPS was two times higher for the 4D CBCT than for the 3D CBCT. In the presence of motion, the NEQ of the 4D CBCT was 50% higher than the 3D CBCT. In the presence of breathing irregularities, the 4D CBCT protocol was mainly affected by view-aliasing artifacts, which were typically cone-beam artifacts, while the 3D CBCT protocol was mainly affected by duplication artifacts. The results showed that the 4D CBCT ensures a reasonable dose and better image quality when mov-ing targets are involved compared to 3D CBCT. Therefore, 4D CBCT is a reliable imaging modality for lung free-breathing radiation therapy

Mitochondrial DNA parameters in blood of infants receiving lopinavir/ritonavir or lamivudine prophylaxis to prevent breastfeeding transmission of HIV-1

Children who are human immunodeficiency virus (HIV)-exposed but uninfected (CHEU) accumulate maternal HIV and antiretroviral exposures through pregnancy, postnatal prophylaxis, and breastfeeding. Here, we compared the dynamics of mitochondrial DNA (mtDNA) parameters in African breastfed CHEU receiving lopinavir/ritonavir (LPV/r) or lamivudine (3TC) pre-exposure prophylaxis during the first year of life. The number of mtDNA copies per cell (MCN) and the proportion of deleted mtDNA (MDD) were assessed at day 7 and at week 50 post-delivery (PrEP group). mtDNA depletion was defined as a 50% or more decrease from the initial value, and mtDNA deletions was the detection of mtDNA molecules with large DNA fragment loss. We also performed a sub-analysis with CHEU who did not receive a prophylactic treatment in South Africa (control group). From day seven to week 50, MCN decreased with a median of 41.7% (interquartile range, IQR: 12.1; 64.4) in the PrEP group. The proportion of children with mtDNA depletion was not significantly different between the two prophylactic regimens. Poisson regressions showed that LPV/r and 3TC were associated with mtDNA depletion (reference: control group; LPV/r: PR = 1.75 (CI95%: 1.15–2.68), p < 0.01; 3TC: PR = 1.54 (CI95%: 1.00–2.37), p = 0.05). Moreover, the proportion of children with MDD was unexpectedly high before randomisation in both groups. Long-term health impacts of these mitochondrial DNA parameters should be investigated further for both CHEU and HIV-infected children receiving LPV/r- or 3TC- based regimens.http://www.mdpi.com/journal/jcmpm2021Paediatrics and Child Healt

Les structures de performance en français : caractérisation et prédiction

Summary : Characterizing and predicting performance structures in French. Over the past fifteen years, considerable attention has been paid to the performance structures of sentences, that is those structures based on experimental data such as pausing or parsing values. These structures are characterized by a number of properties (hierarchy, symmetry and basic units of equal size) and can best be predicted by algorithms which take into account the prosodic structure of the sentence. Research on performance structures, which has mainly concentrated on English, has recently influenced the decelopment of prosodic rules in text-to-speech synthesis. In this study, we turn to the performance structures of French. First we describe the structures obtained by means of an oral reading task and show some interesting differences with English (the prosodic status of postposed adjectives, the bundling of certain function words to heads on the left, etc.). Then we attempt to predict these structures by means of slightly modified versions of the algorithme originally developed for English and show that the predictions obtained are not jully satisfactory. Finally we propose a new algorithm, specifically designed for French, and demonstrate that it is a far better predictor of the data obtained. Key-words : psycholinguistics, production, speech, performance structures, prediction algorithms.Résumé Les recherches réalisées jusqu'à maintenant dans le but d'étudier l'évolution de la représentation gestuelle d'actions en tant qu'activité figurative avaient des difficultés à dégager des niveaux d'évolution cohérents. De là l'hypothèse, formulée par certains auteurs, d'une évolution indépendante de ce type d'activités figuratives par rapport au développement cognitif général. La recherche présentée ici montre que ces difficultés sont liées à l'absence de prise en compte, dans l'analyse des catégories, du signifiant et du signifié des gestes. Les modifications introduites dans le paradigme expérimental ont permis de dégager une évolution cohérente des comportements dans un échantillon de 320 enfants âgés de 4 à 12 ans ; 4 niveaux, sont en effet observés, chacun d'eux pouvant se définir comme une structure, c'est-à-dire comme composé d'un certain nombre d'éléments reliés entre eux par des rapports hiérarchiques dans un réseau représentationnel. Mots clés : représentation gestuelle, réseau représentationnel, activité figurative, structure.Monnin Pascal, Grosjean F. Les structures de performance en français : caractérisation et prédiction. In: L'année psychologique. 1993 vol. 93, n°1. pp. 9-30