Characterisation of computed tomography devices and optimisation of clinical protocols based on mathematical observers

The technological evolutions of diagnostic X-ray imaging modalities enable to radiologists improve diagnosis quality and patient care. In this context, the number of X-ray examinations like conventional radiography, fluoroscopy or computed tomography (CT), is increasingly used in patient care. The risk associated with the use of ionizing radiation in medical imaging is the risk of inducing cancer, a risk which is by the Linear No-Threshold model traditionally developed for patient radiation protection. In addition, CT imaging contributes to roughly 70 % of the total annual effective dose delivered by X-ray imaging to the population. Because of this, many efforts have been made to decrease patient exposure to ensure that the risk benefit balance clearly lies on the benefit side. Nevertheless, while the risk of inducing cancer cannot be neglected, the major risk for the patient, if the justification process is respected, was the non-detection of a pathological lesion. The goal of this work was to propose a strategy to optimise patient exposure while maintaining diagnostic accuracy using a task-based methodology that is pertinent in a clinical context when dealing with CT imaging. In this context, objective image quality should be developed and should take into account the following four elements: (1) It should be linked to a task; (2) the properties of signals and backgrounds have to be defined in accordance with their statistical properties; (3) the observer should be specified and (4) a figure of merit should be precisely defined and quantified. In this sense, model observers, which are mathematical tools potentially used as a surrogate for human observers are well suited to objectively estimate image quality at the diagnostic accuracy level. They can indeed perform a task (e.g. lesion detection) for a given type of image and signal (e.g. noisy uniform background) and allow a quantitative performance estimation using for example the area under the receiver operating characteristic curve. In addition, the advantage of model observers is that they are economical, both in terms of time and money and they are consistent unlike the human observers. This work shows that using a task-based approach to benchmark CT units and clinical protocols in terms of image quality and patient exposure becomes feasible with model observers. Such an approach may be useful for adequately and quantitatively comparing clinically relevant image quality and to estimate the potential for further dose reductions offered by the latest technological developments. The methodology developed during this PhD thesis enables medical physicists to convert clinically relevant information defined by radiologists into task-based image quality criteria

Photon-Counting Detector CT for Liver Lesion Detection-Optimal Virtual Monoenergetic Energy for Different Simulated Patient Sizes and Radiation Doses

OBJECTIVES The aim of this study was to evaluate the optimal energy level of virtual monoenergetic images (VMIs) from photon-counting detector computed tomography (CT) for the detection of liver lesions as a function of phantom size and radiation dose. MATERIALS AND METHODS An anthropomorphic abdominal phantom with liver parenchyma and lesions was imaged on a dual-source photon-counting detector CT at 120 kVp. Five hypoattenuating lesions with a lesion-to-background contrast difference of -30 HU and -45 HU and 3 hyperattenuating lesions with +30 HU and +90 HU were used. The lesion diameter was 5-10 mm. Rings of fat-equivalent material were added to emulate medium- or large-sized patients. The medium size was imaged at a volume CT dose index of 5, 2.5, and 1.25 mGy and the large size at 5 and 2.5 mGy, respectively. Each setup was imaged 10 times. For each setup, VMIs from 40 to 80 keV at 5 keV increments were reconstructed with quantum iterative reconstruction at a strength level of 4 (QIR-4). Lesion detectability was measured as area under the receiver operating curve (AUC) using a channelized Hotelling model observer with 10 dense differences of Gaussian channels. RESULTS Overall, highest detectability was found at 65 and 70 keV for both hypoattenuating and hyperattenuating lesions in the medium and large phantom independent of radiation dose (AUC range, 0.91-1.0 for the medium and 0.94-0.99 for the large phantom, respectively). The lowest detectability was found at 40 keV irrespective of the radiation dose and phantom size (AUC range, 0.78-0.99). A more pronounced reduction in detectability was apparent at 40-50 keV as compared with 65-75 keV when radiation dose was decreased. At equal radiation dose, detection as a function of VMI energy differed stronger for the large size as compared with the medium-sized phantom (12% vs 6%). CONCLUSIONS Detectability of hypoattenuating and hyperattenuating liver lesions differed between VMI energies for different phantom sizes and radiation doses. Virtual monoenergetic images at 65 and 70 keV yielded highest detectability independent of phantom size and radiation dose

Objective assessment of low contrast detectability in computed tomography with Channelized Hotelling Observer

AbstractPurposeIterative algorithms introduce new challenges in the field of image quality assessment. The purpose of this study is to use a mathematical model to evaluate objectively the low contrast detectability in CT.Materials and methodsA QRM 401 phantom containing 5 and 8 mm diameter spheres with a contrast level of 10 and 20 HU was used. The images were acquired at 120 kV with CTDIvol equal to 5, 10, 15, 20 mGy and reconstructed using the filtered back-projection (FBP), adaptive statistical iterative reconstruction 50% (ASIR 50%) and model-based iterative reconstruction (MBIR) algorithms. The model observer used is the Channelized Hotelling Observer (CHO). The channels are dense difference of Gaussian channels (D-DOG). The CHO performances were compared to the outcomes of six human observers having performed four alternative forced choice (4-AFC) tests.ResultsFor the same CTDIvol level and according to CHO model, the MBIR algorithm gives the higher detectability index. The outcomes of human observers and results of CHO are highly correlated whatever the dose levels, the signals considered and the algorithms used when some noise is added to the CHO model. The Pearson coefficient between the human observers and the CHO is 0.93 for FBP and 0.98 for MBIR.ConclusionThe human observers' performances can be predicted by the CHO model. This opens the way for proposing, in parallel to the standard dose report, the level of low contrast detectability expected. The introduction of iterative reconstruction requires such an approach to ensure that dose reduction does not impair diagnostics

PATIENT EXPOSURE OPTIMISATION THROUGH TASK-BASED ASSESSMENT OF A NEW MODEL-BASED ITERATIVE RECONSTRUCTION TECHNIQUE

The goal of the present work was to report and investigate the performances of a new iterative reconstruction algorithm, using a model observer. For that, a dedicated low-contrast phantom containing different targets was scanned at four volume computed tomography dose index (CTDIvol) levels on a Siemens SOMATOM Force computed tomography (CT). The acquired images were reconstructed using the ADMIRE algorithm and were then assessed by three human observers who performed alternative forced choice experiments. Next, a channelised hotelling observer model was applied on the same set of images. The comparison between the two was performed using the percentage correct as a figure of merit. The results indicated a strong agreement between human and model observer as well as an improvement in the low-contrast detection when switching from an ADMIRE strength of 1-3. Good results were also observed even in situations where the target was hard to detect, suggesting that patient dose could be further reduced and optimised

Plk4 Regulates Centriole Asymmetry and Spindle Orientation in Neural Stem Cells

Defects in mitotic spindle orientation (MSO) disrupt the organization of stem cell niches impacting tissue morphogenesis and homeostasis. Mutations in centrosome genes reduce MSO fidelity, leading to tissue dysplasia and causing several diseases such as microcephaly, dwarfism, and cancer. Whether these mutations perturb spindle orientation solely by affecting astral microtubule nucleation or whether centrosome proteins have more direct functions in regulatingMSO is unknown. To investigate this question, we analyzed the consequences of deregulating Plk4 (the master centriole duplication kinase) activity in Drosophila asymmetrically dividing neural stem cells. We found that Plk4 functions upstream of MSO control, orchestrating centriole symmetry breaking and consequently centrosome positioning. Mechanistically, we show that Plk4 acts through Spd2 phosphorylation, which induces centriole release from the apical cortex. Overall, this work not only reveals a role for Plk4 in regulating centrosome function but also links the centrosome biogenesis machinery with the MSO apparatus.ERC starting grant CentroStemCancer [242598]; Institut Curie; CNRS; NCI [P30CA23074]; NIGMS [R01 GM110166, GM126035]; FRM; IC; FRM installation grant; ATIP grantOpen access articleThis item from the UA Faculty Publications collection is made available by the University of Arizona with support from the University of Arizona Libraries. If you have questions, please contact us at [email protected]

Discovery of two L & T binaries with wide separations and peculiar photometric properties

We present spatially resolved photometric and spectroscopic observations of two wide brown dwarf binaries uncovered by the SIMP near-infrared proper motion survey. The first pair (SIMP J1619275+031350AB) has a separation of 0.691" (15.2 AU) and components T2.5+T4.0, at the cooler end of the ill-understood J-band brightening. The system is unusual in that the earlier-type primary is bluer in J-Ks than the later-type secondary, whereas the reverse is expected for binaries in the late-L to T dwarf range. This remarkable color reversal can possibly be explained by very different cloud properties between the two components. The second pair (SIMP J1501530-013506AB) consists of an L4.5+L5.5 (separation 0.96", 30-47 AU) with a surprisingly large flux ratio (Delta J =1.79 mag) considering the similar spectral types of its components. The large flux ratio could be explained if the primary is itself an equal-luminosity binary, which would make it one of the first known triple brown dwarf systems. Adaptive optics observations could not confirm this hypothesis, but it remains a likely one, which may be verified by high-resolution near-infrared spectroscopy. These two systems add to the handful of known brown dwarf binaries amenable to resolved spectroscopy without the aid of adaptive optics and constitute prime targets to test brown dwarf atmosphere models.Comment: accepted for publication in Ap

Bibliothèque : faire société (La)

Rencontre organisée à l\u27enssib les 25 et 26 juin 2012 dans le cadre des Estivales. Thématiques du 25 juin : Bibliothèque, création et mémoire Thématiques du 26 juin : Bibliothèque, éducation et politique Comme l’école, après l’école, la bibliothèque peut être un instrument de connaissance du passé, d’analyse du présent et de construction de l’avenir. Qu’est-ce qui rend ce projet possible, légitime, nécessaire ? En quoi la bibliothèque et, plus généralement, les instances de partage du savoir et les institutions culturelles permettent d’être « parmi les hommes » ? Comment, inscrites dans l’épaisseur du temps, elles se nourrissent nécessairement de mémoire et d’histoire ? En quoi elles peuvent/doivent contribuer à la reconstruction d’un espace public, d’un débat public ? Quelle ambition politique, quel projet démocratique peuvent trouver un ancrage une assise, dans ces institutions et fonder leur raison d’être ? A travers ce colloque et ses intervenants, l’enssib a souhaité interroger quelques-unes de ses convictions et de ses exigences : la curiosité intellectuelle, la liberté de l’esprit, la mémoire partagée, la passion de la chose publique, le rôle politique de la bibliothèque. Une éthique de la bibliothèque

L’urgence comme catalyseur ? Les enjeux liés au développement du volet « langue et intégration » du programme Horizon académique

Depuis 2016, l’Université de Genève, en Suisse, dispose, avec « Horizon académique », d’un programme d’intégration académique et sociale visant à valoriser et à renforcer les compétences des réfugié-es de niveau universitaire et d’autres populations aux besoins similaires. Dans cet article, nous nous intéresserons plus particulièrement au cursus « langue et intégration », qui constitue le volet du programme dédié à l’apprentissage du français langue étrangère, enjeu majeur puisque le niveau B2 du CECRL est une exigence de l’Université de Genève pour entreprendre des études supérieures. Nous montrerons comment l’urgence, suscitée par les vagues migratoires de 2015, l’adoption des politiques publiques et, plus récemment, l’arrivée massive de réfugié-es ukrainien-nes, a fonctionné comme catalyseur pour le développement de ce cursus, qui accueille à ce jour 324 étudiant-es, réparti-es dans 18 classes. La notion d’urgence nous servira également de repère pour identifier les trois phases principales par lesquelles est passé le dispositif entre 2016 et aujourd’hui — conception, développement et stabilisation. Nous présenterons en détail chacune d’entre elles en soulignant les défis qu’elles suscitent et en explicitant les réponses didactiques apportées. Nous terminerons par exposer les défis liés à la pérennisation d’un dispositif conçu dans l’urgence et pour répondre à l’urgence et dont la grande force est de montrer que la maîtrise de la langue passe par l’intégration et non l’inverse.Since 2016, the University of Geneva, in Switzerland, has developed an academic and social integration program (Horizon académique), aimed at enhancing and strengthening the skills of university-level refugees and other populations, with similar needs. In this article, we will focus more particularly on the “language and integration” classes, which is the part of the program dedicated to learning French as a foreign language. Learning French is indeed a major challenge since the B2 level of the CEFR is a requirement of the University of Geneva to undertake higher education. We will show how the urgency, brought by the migratory waves of 2015, the adoption of public policies, and more recently, the massive arrival of Ukrainian refugees, worked as a catalyst for the development of this part of the Horizon académique program. 324 students are currently welcome in 18 classes. The notion of urgency will also serve as a benchmark for identifying the three main phases through which the system has passed between 2016 and today – design, development, and stabilization. We will present each of them in detail, highlighting the challenges they raise and explaining the didactic responses provided. We will then expose the challenges related to the sustainability of a pedagogical program designed in an emergency context and to respond to an emergency. We conclude by emphasizing the major strength of the "language and integration" program: mastering a language need to rest on integration and not the other way around

Konzepte zur Charakterisierung klinischer CT-Systeme unter Einbeziehung von Bildqualität und Dosis

In Germany, as in most Western countries, the exposure to the population due to CT examinations has increased over the last twenty years, despite major technological progresses which might lead to the expectation that doses would decrease. The last survey organized in Germany showed that in 2014 the average dose per inhabitant due to CT was 1.0 mSv compared to 0.8 mSv in 2007. Thus, the use of CT is a major source of concern for Public Health Authorities such as the “Bundesamts für Stahlenchutz” in Germany. Among the ways to control the population exposure creeping upwards one should ensure that the principle of justification is correctly applied and that the radiological examination and intervention are optimized in terms of the balance of low dose against required image quality. In the context of optimization, the units used should work efficiently to ensure that there is no waste of radiation in the imaging process. The aim of this project is to propose a way to benchmark CT units, allowing the assessment of the efficiency of CT units using clinically relevant protocols. The project was made of four work-packages. The first work-package was a review of the literature dedicated to image quality assessment in CT imaging. During this work-package the clinically relevant protocols used for benchmarking were also defined. The second work-package was dedicated to the set-up of the methodology to be used when dealing with the benchmarking of CT units using two different concepts. The third work-package was the application of these concepts on eight CT units; including two models from each of four manufacturers. Finally, the fourth work-package consisted in the analysis of the data with the proposal of a strategy to establish a dose efficiency index (DEI) to quantify the CT unit performances