title: Standing-wave suppression for transcranial ultrasound by random modulation.
abstract: Low-frequency transcranial ultrasound (<<1 MHz) is being investigated for a number of brain therapies, including stroke, tumor ablation, and localized opening of the blood-brain barrier. However, lower frequencies have been associated with the production of undesired standing waves and cavitation in the brain. Presently, we examine an approach to suppress standing waves during continuous-wave (CW) transcranial application. The investigation uses a small randomization in the frequency content of the signal for suppressing standing waves. The approach is studied in an ex-vivo human skull and a plastic-walled chamber, representing idealized conditions. The approach is compared to single-frequency CW operation as well as to a swept-frequency input. Acoustic field scans demonstrate that the swept-frequency method can suppress standing waves in the plastic chamber and skull by 3.4 and 1.6 times, respectively, compared to single-frequency CW excitation. With random modulation, standing waves were reduced by 5.6 and 2 times, respectively, in the plastic chamber and skull. It is expected that the process may play a critical role in providing a safer application of the ultrasound field in the brain and may have application in other areas where standing waves may be created.
authors.affiliation: Focused Ultrasound Laboratory, Harvard Medical School and Brigham and Women's Hospital, Boston, MA 02466, USA. sct@bwh.harvard.edu
authors.forename: Sai Chun
authors.initials: SC
authors.lastname: Tang
authors.forename: Gregory T
authors.initials: GT
authors.lastname: Clement
mesh_terms: D000465:Algorithms; D006801:Humans; D012815:Signal Processing, Computer-Assisted; D012886:Skull / Q000000981:diagnostic imaging; D017585:Ultrasonography, Doppler, Transcranial / Q000379:methods*
references.citation: J Ultrasound Med. 2005 Aug;24(8):1117-25
references.pmid: 16040827
references.citation: Eur J Ultrasound. 2002 Nov;16(1-2):121-30
references.pmid: 12470857
references.citation: Front Neurol Neurosci. 2006;21:150-161
references.pmid: 17290134
references.citation: Int J Hyperthermia. 2007 Mar;23(2):193-202
references.pmid: 17578343
references.citation: J Neurosurg. 2006 Sep;105(3):445-54
references.pmid: 16961141
references.citation: Neurology. 1956 Oct;6(10):693-704
references.pmid: 13369651
references.citation: IEEE Trans Med Imaging. 2005 Oct;24(10):1249-55
references.pmid: 16229412
references.citation: Stroke. 2005 Jul;36(7):1441-6
references.pmid: 15947262
references.citation: Ultrasound Med Biol. 2007 Feb;33(2):263-9
references.pmid: 17306697
references.citation: Eur J Radiol. 2006 Aug;59(2):149-56
references.pmid: 16716552
references.citation: Ultrasound Med Biol. 2008 Oct;34(10):1578-89
references.pmid: 18456391
references.citation: Radiology. 2001 Sep;220(3):640-6
references.pmid: 11526261
references.citation: J Neurosurg. 1981 May;54(5):659-63
references.pmid: 7014793
references.citation: IRE Trans Med Electron. 1960 Jul;ME-7:166-81
references.pmid: 13702332
references.citation: Circ J. 2007 Oct;71(10):1643-8
references.pmid: 17895565