title: Conditionally Increased Acoustic Pressures in Nonfetal Diagnostic Ultrasound Examinations Without Contrast Agents: A Preliminary Assessment.
abstract: The mechanical index (MI) has been used by the US Food and Drug Administration (FDA) since 1992 for regulatory decisions regarding the acoustic output of diagnostic ultrasound equipment. Its formula is based on predictions of acoustic cavitation under specific conditions. Since its implementation over 2 decades ago, new imaging modes have been developed that employ unique beam sequences exploiting higher-order acoustic phenomena, and, concurrently, studies of the bioeffects of ultrasound under a range of imaging scenarios have been conducted. In 2012, the American Institute of Ultrasound in Medicine Technical Standards Committee convened a working group of its Output Standards Subcommittee to examine and report on the potential risks and benefits of the use of conditionally increased acoustic pressures (CIP) under specific diagnostic imaging scenarios. The term "conditionally" is included to indicate that CIP would be considered on a per-patient basis for the duration required to obtain the necessary diagnostic information. This document is a result of that effort. In summary, a fundamental assumption in the MI calculation is the presence of a preexisting gas body. For tissues not known to contain preexisting gas bodies, based on theoretical predications and experimentally reported cavitation thresholds, we find this assumption to be invalid. We thus conclude that exceeding the recommended maximum MI level given in the FDA guidance could be warranted without concern for increased risk of cavitation in these tissues. However, there is limited literature assessing the potential clinical benefit of exceeding the MI guidelines in these tissues. The report proposes a 3-tiered approach for CIP that follows the model for employing elevated output in magnetic resonance imaging and concludes with summary recommendations to facilitate Institutional Review Board (IRB)-monitored clinical studies investigating CIP in specific tissues.
authors.affiliation: Department of Biomedical Engineering, Duke University, PO Box 90281, Durham, NC 27708 USA.
authors.forename: Kathryn R
authors.initials: KR
authors.lastname: Nightingale
authors.affiliation: National Center for Physical Acoustics and Department of Physics and Astronomy, The University of Mississippi, University, MS 38677 USA.
authors.forename: Charles C
authors.initials: CC
authors.lastname: Church
authors.affiliation: US Food and Drug Administration (Retired), Current Address: 132 S Van Buren St, Rockville, MD 20850 USA.
authors.forename: Gerald
authors.initials: G
authors.lastname: Harris
authors.affiliation: US Food and Drug Administration, 10903 New Hampshire Ave, Building 62, Room 2104, Silver Spring, MD 20993-0002 USA.
authors.forename: Keith A
authors.initials: KA
authors.lastname: Wear
authors.affiliation: Center for Industrial and Medical Ultrasound, Applied Physics Laboratory, University of Washington, 1013 NE 40th St, Seattle WA 98105 USA.
authors.forename: Michael R
authors.initials: MR
authors.lastname: Bailey
authors.affiliation: Department of Radiology, University of Michigan Health System, 3218C Med Sci I, B Wing SPC 5667, Ann Arbor, MI 48109-5667 USA.
authors.forename: Paul L
authors.initials: PL
authors.lastname: Carson
authors.affiliation: Fujifilm SonoSite, 21919 30th Dr SE, Bothell, WA 98021 USA.
authors.forename: Hui
authors.initials: H
authors.lastname: Jiang
authors.affiliation: Samsung Medison Co, Ltd, Building, 42, Teheran-ro, 108-gil, Gangnam-gu, Seoul 135-851, Korea.
authors.forename: Kurt L
authors.initials: KL
authors.lastname: Sandstrom
authors.affiliation: Department of Biomedical Engineering, Boston University, 44 Cummington Mall, Boston, MA 02215 USA.
authors.forename: Thomas L
authors.initials: TL
authors.lastname: Szabo
authors.affiliation: Emeritus Professor of Radiology and Medical Physics, Temple University School of Medicine, Philadelphia, PA 19140 USA.
authors.forename: Marvin C
authors.initials: MC
authors.lastname: Ziskin
mesh_terms: D000162:Acoustics; D000818:Animals; D004869:Equipment Safety; D006801:Humans; D008962:Models, Theoretical; D017410:Practice Guidelines as Topic; D011312:Pressure; D014463:Ultrasonography / Q000592:standards*; D014481:United States; D014486:United States Food and Drug Administration