Transcranial ultrasonic brain therapy at frequencies higher than 500kHz requires adaptive focusing to compensate for the aberrations induced by the skull bone. This can be achieved by using multi-element arrays driven by a dedicated electronics. A growing number of elements was used to improve the focusing: 64 elements in 2000 , 300 in 2003 , 1024 in 2013 , and with more to come. We will present some of the salient results obtained pre-clinically and clinically with such multi-element transcranial devices. Nevertheless, we will show that comparable transcranial focusing can be achieved with a novel approach in rupture with the current trend. It consists in a single- element covered with a 3D acoustic lens of variable and controlled thickness. Similar lenses have been introduced in the past to perform single or multiple focusing patterns in homogenous propagating media  but recent 3d printing and milling capabilities make tailor-made 3D lenses a feasible option for transcranial adaptive focusing and 3D beam shaping, allowing to create holograms in the brain. Such lenses can furthermore allow beam steering around the target by taking advantage of the transkull isoplanatic angle.
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