Recent studies have used computer s

Recent studies have used computer simulations to betterpredict the temperature increase in targets in individual skullsby modeling the skull efficiency with properties extractedfrom CT, in particular the HU (36, 37), an arbitrary unit ofradio density. Although the HU has widespread applicability,it is still dependent on various other factors (38), and sostandardization of CT parameters should optimize the use ofHU as a rigorous diagnostic tool for evaluating skull adequacyfor MRgFUS lesioning. Recently, researchers reported the useof a novel method employing microbubbles as an ultrasoundcontrast agent; this technique allowed acoustic echoes to modifyphase corrections and thereby narrow the acoustic focus. Thismethod, called “echo focusing,” provided sonication efficiencyfor lesion formation that was superior to that obtained withCT-based aberration correction (24, 39). In these studies,an echo-focusing phase aberration correction technique wasincorporated by measuring returning acoustic signals fromintravenously injected microbubbles around the intended targetregion during sonication (40, 41). With echo focusing, successfullesion formation was achieved in 12 patients with ET, including3 patients in whom MRgFUS thalamotomy treatment usingCT-based aberration correction had failed (24). In anotherstudy, 8 patients with low SDR (mean SDR = 0.35) weresuccessfully treated using the echo-focusing method by raisingthe temperature to >54◦C in patients with ET and to >52◦Cin patients with PD; these temperatures were sufficient forlesion formation (39). This echo-focusing technique could beparticularly beneficial for patients with low SDR and for thosewith a target that is more lateral than the thalamus, as thisresearch demonstrated permanent lesion formation in cases ofpallidotomy in patients with an SDR