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Harmonic imaging with gas‐filled microspheres: Initial experiences
Author(s) -
Forsberg Flemming,
Goldberg Barry B.,
Wu Yunqiu,
Liu JiBin,
Merton Daniel A.,
Rawool Nandkumar M.
Publication year - 1997
Publication title -
international journal of imaging systems and technology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.359
H-Index - 47
eISSN - 1098-1098
pISSN - 0899-9457
DOI - 10.1002/(sici)1098-1098(1997)8:1<69::aid-ima9>3.0.co;2-r
Subject(s) - second harmonic imaging microscopy , harmonic , acoustics , doppler effect , biomedical engineering , clutter , materials science , microbubbles , ultrasound , contrast (vision) , optics , physics , medicine , second harmonic generation , computer science , radar , laser , telecommunications , astronomy
The introduction of safe and efficacious ultrasound contrast agents, which significantly enhance the backscattered signals, has allowed previously inaccessible areas of slow flow to be imaged. However, imaging organ perfusion or small deep‐lying vessels remains difficult. The ability of harmonic imaging to resolve these problems has been investigated. Harmonic imaging uses the nonlinear properties of microbubble‐based agents by transmitting at the fundamental frequency but receiving at the second harmonic. In vitro measurements revealed a harmonic response 15 dB below the fundamental for a driving frequency of 2.5 MHz at an acoustic pressure of 50 kPa for one particular contrast medium. In vivo , two different gas‐filled microbubble agents were administrated to 10 dogs and three rabbits. Three different scanners were used to obtain images of kidneys, liver, heart, and vessels in harmonic and conventional gray‐scale, pulsed Doppler, and color Doppler modes. Enhancement lasted significantly longer in harmonic than in conventional modes (94 s; P = 0.00003). Harmonic images were less susceptible to artifacts, such as acoustic shadowing, and a wider range of dosages could therefore be used. A clear increase in the (flow) signal‐to‐clutter ratio was observed. Harmonic images were, however, very dependent on focal zone settings. These preliminary results demonstrate the potential of contrast‐enhanced harmonic imaging, but further studies are required to establish clinical efficacy. © 1997 John Wiley & Sons, Inc. Int J Imaging Syst Technol, 8, 69–81, 1997