Keyhole acceleration for magnetic resonance acoustic radiation force imaging (MR ARFI).
MR ARFI measures the displacement induced by the ultrasonic radiation force and provides the location of the focal spot without significant heating effects. Displacements maps obtained with MR ARFI provide an indirect estimation of the acoustic beam intensity at the target. This measure is essential for dose estimation prior to focused ultrasound treatments (FUS) and adaptive focusing procedures of MR-guided transcranial and transribs FUS. In the latter case, the beam correction is achieved by maximizing the displacement at focus. A significant number of serial MR ARFI images are required and thus, a partial k-space updating method, such as keyhole appears as a method of choice. The purpose of this work is to demonstrate via simulations and experiments the efficiency of the keyhole technique combined with a two-dimensional spin-echo MR ARFI pulse sequence. The method was implemented in an ex vivo calf brain taking advantage of the a priori knowledge of the focal spot profile. The coincidence of the phase-encoding axis with the longest axis of the focal spot makes the best use of the technique. Our approach rapidly provides the focal spot localization with accuracy, and with a substantial increase to the signal-to-noise ratio, while reducing ultrasound energy needed during MR-guided adaptive focusing procedures.
ICM-Institut du Cerveau et de la Moelle épinière, CENIR-Centre de NeuroImagerie de Recherche, Groupe Hospitalier Pitié-Salpêtrière, 47 boulevard de l'hôpital, 75013 Paris, France; CRICM-Centre de Recherche de l'Institut du Cerveau et de la Moelle épinière, Université Pierre et Marie Curie (Paris 6)/INSERM UMR_S975/CNRS UMR 7225, Groupe Hospitalier Pitié-Salpêtrière, bâtiment ICM, 47 boulevard de l'hôpital, 75013 Paris, France.
Raphaël
R
Paquin
Alexandre
A
Vignaud
Laurent
L
Marsac
Youliana
Y
Younan
Stéphane
S
Lehéricy
Mickaël
M
Tanter
Jean-François
JF
Aubry
D000465:Algorithms; D000818:Animals; D001921:Brain / Q000033:anatomy & histology* / Q000502:physiology*; D002417:Cattle; D055119:Elastic Modulus / Q000502:physiology; D054459:Elasticity Imaging Techniques / Q000379:methods*; D007089:Image Enhancement / Q000379:methods*; D007090:Image Interpretation, Computer-Assisted / Q000379:methods*; D066298:In Vitro Techniques; D015203:Reproducibility of Results; D012680:Sensitivity and Specificity
Adaptive focusing; FUS; Keyhole; MR ARFI; Ultrasound; k-space substitution