Notice bibliographique
Résumé
The flat-panel image detectors capture an X-ray image electronically, and enable a smooth clinical transition to digital radiography by replacing traditional film/cassette based system. They provide excellent X-ray images and have been commercialized for different X-ray imaging modalities. However, there still remain significant scientific challenges in these detectors associated with dark current and ghosting which constitute critical performance requirements for modalities such as digital fluoroscopy. This doctoral dissertation involves both experimental characterization and physics-based theoretical modelling of time and bias dependent dark current behaviour and X-ray induced change in sensitivity (ghosting) in X-ray imaging detectors. The theoretical investigations are based on the physics of the individual phenomenon and a systematic solution of physical equations in the photoconductor layer; (i) semiconductor continuity equations (ii) Poisson’s equation, and (iii) trapping rate equations. The theoretical model has been validated with the measured and published experimental results. \n \nThe developed dark current model has been applied to a-Se and poly-HgI2 based detectors (direct conversion detectors), and a-Si:H p-i-n photodiode (indirect conversion detectors). The validation of the model with the experimental results determines the physical mechanisms responsible for the dark current in X-ray imaging detectors. The dark current analysis also unveils the important material parameters such as trap center concentrations in the blocking layers, trap depths, and effective barrier heights for injecting carriers. The analysis is important for optimization of the dark current consistent with having good transport properties which can ultimately improve the dynamic range of the detector. \n \nThe physical mechanisms of sensitivity reduction (ghosting) and its recovery has been investigated by exposing a-Se detector at high dose and then monitoring the recovery process under (i) resting the samples (natural recovery), (ii) reversing the bias polarity and magnitude, and (iii) shining light. The continuous monitoring of the sensitivity as a function of exposure and time reveals the ghosting mechanisms in a-Se mammography detectors. This research finds a faster sensitivity recovery by reversing the bias during the natural recovery process. The sensitivity recovery mechanisms (e.g., recombination between trapped and oppositely charged free carrier, trapping of oppositely charged free carriers, or relaxation of trap centers) have been qualitatively investigated by validating the simulation results with the experimental data. The ghost removal mechanisms and techniques are important to improve the image quality which can ultimately lead to the reduction of the patient exposure consistent with better diagnosis for different X-ray imaging modalities.
Récupéré en direct depuis OpenAlex et désinversé. Les résumés ne sont pas conservés dans cette base de données : les index inversés représentent 8,6 Go des 9,3 Go de texte de la base, et le serveur dispose de 13 Go libres.
Comment cette classification a été obtenuedéplier
Prédiction distillée sur la base complète
Imitation des enseignantsNi prévalence calibrée, ni vérité terrain. Validation humaine à venir. Apprise à partir de 10 348 étiquettes directes de Codex et de 10 348 étiquettes directes de Gemma. Le mode candidate est l'union des têtes enseignantes seuillées; le consensus est leur intersection. Ces sorties portent le statut machine_predicted_unvalidated et ne sont ni des étiquettes humaines ni des étiquettes directes de modèles de pointe.
Scores Codex et Gemma par catégorie
| Catégorie | Codex | Gemma |
|---|---|---|
| Métarecherche | 0,000 | 0,000 |
| Méta-épidémiologie (sens strict) | 0,000 | 0,000 |
| Méta-épidémiologie (sens large) | 0,000 | 0,000 |
| Bibliométrie | 0,001 | 0,000 |
| Études des sciences et des technologies | 0,000 | 0,000 |
| Communication savante | 0,000 | 0,000 |
| Science ouverte | 0,000 | 0,000 |
| Intégrité de la recherche | 0,000 | 0,000 |
| Charge utile insuffisante (le modèle a refusé de juger) | 0,000 | 0,000 |
Scores machine (provisoires)
Les deux têtes enseignantes du modèle étudiant, lues sur ce travail. Un score ordonne la base pour la relecture; il n'affirme jamais une catégorie, et le statut de validation accompagne chaque rangée tel quel.
Scores de référence d'un modèle non mature (critères de maturité non atteints, 7 itérations). Un score ordonne; il n'affirme jamais une catégorie.
score_only:v0-immature-baseline · tel quel depuis la passe de notation : score_only signifie que le nombre peut ordonner les travaux, et qu'aucune étiquette de catégorie n'en découleClassification
machine, non validéePrédiction automatique; un appel candidat d’une seule tête enseignante, pas un consensus.
Le détail, modèle par modèle et score par score, se trouve en fin de page sous « Comment cette classification a été obtenue ».