P1B-11 A 2D-Array for Transcranial Ultrasound Focusing Using Shear-Mode Conversion: A Numerical Study
Notice bibliographique
Résumé
An incident ultrasonic acoustic wave with a frequency around 1 MHz creates longitudinal and shear waves inside the skull. Both waves propagate independently through the skull and create two longitudinal waves after the skull: a purely longitudinal wave and a longitudinal-shear-longitudinal wave. The process of the last wave is identified here as the shear-mode conversion (Sc). The interest of developing ultrasound techniques based on Scresides in the fact that the transmitted wave due to Sc has less phase-shift. The present study shows the feasibility of focusing ultrasound after the skull using a 2D-array (ScTX) conceived to take advantage of the Sc and with dimensions comparable to near-flat skull regions such as the anterior part of the frontal bone. The ScTX array is composed of two columns of 44 times 7 elements each one separated of 3 cm following its length. The configuration in column is aimed to produce an entering wavefront favorable to the shear-mode conversion. Each element is independently driven at 1 MHz and square-shaped with a length of 1.5 mm. The space between elements is 0.4 mm. The length and width of the device are, respectively, 9.7 and 5.9 cm. The new device was compared to a conventional 2D-array (CnTX) which has the same specifications of the ScTX device, with the exception of the inter-column space. The degree of focus steering of both devices was compared for depths of 1, 2, 4 and 6 cm from the inner face of the skull (dfs). For each depth, and assuming X and Y perpendicular to the sound propagation axis Z, four focal spots were tested at (x,y)=(0, 0), (2 cm, 0), (0, 2 cm) and (2 cm, 2 cm). A prismatic volume of 10.7 times 6.5 times 0.9 cm, located 1 cm from the device, was used to simulate the skull bone. The required phase of elements was calculated using a back-propagation (BP) method. Tests were done with the corrected phase calculated with only shear-mode BP (ScBP), only longitudinal BP (LnBP) and sum of both back-propagated waves (ScBP+LnBP). The resulting acoustic field for each focal point considered the forward-propagation due to the longitudinal and shear-mode transmissions. ScTX with ScBP produced the most focused fields for targets found close to the face of the skull (dfs= 1 cm) and steered following the X direction. For deeper targets (d/s= 2 cm, 4 cm, 6 cm), the correction ScBP+LnBP was more effective to focus ultrasound. For the same targets, the correction ScBP produced focal zones located closer to the device than expected. Calculation of surface area at -3 dB on XZ and YZ planes indicated that the ScTX device created more focused fields for most of tested cases, excepting a few cases involving steering following the Y direction. In conclusion, Focusing using shear mode conversion is feasible using a simple device that is compatible with the geometry of the frontal human bone. Using the proposed device, this focusing is limited to tissues located about 1 cm from the inner face of the skull.
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Comment cette classification a été obtenuedéplier
Prédiction machine sur la base complète
Imitation des enseignantsNi prévalence calibrée, ni vérité terrain. Validation humaine à venir. Le volet Gemma est une étiquette directe du modèle pour chaque travail de la base, lue sur la notice réduite au titre. Le volet Codex est un classifieur appris des 10 348 étiquettes directes de Codex et calibré sur les taux pondérés de l'échantillon; les champs sans appui suffisant ne portent aucun appel Codex. Le mode candidate est l'union des deux volets; le consensus est leur intersection. Ces sorties portent le statut machine_predicted_unvalidated et ne sont pas des étiquettes humaines.
Scores du classifieur distillé par catégorie (deux têtes)
| Catégorie | Codex | Gemma |
|---|---|---|
| Métarecherche | 0,000 | 0,001 |
| Méta-épidémiologie (sens strict) | 0,000 | 0,000 |
| Méta-épidémiologie (sens large) | 0,000 | 0,000 |
| Bibliométrie | 0,000 | 0,000 |
| Études des sciences et des technologies | 0,000 | 0,000 |
| Communication savante | 0,001 | 0,000 |
| Science ouverte | 0,001 | 0,000 |
| Intégrité de la recherche | 0,001 | 0,000 |
| Charge utile insuffisante (le modèle a refusé de juger) | 0,007 | 0,001 |
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 source (Gemma direct ou Codex distillé), 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 ».