title: Lower receiving frequencies than transmitting frequencies could yield improved results for contrast imaging: an in vivo study in closed chest canines.
abstract: BACKGROUND
  Ultrasonic imaging methods of receiving at higher frequencies, which are multiples of the transmitting frequencies (harmonic imaging), are well established as a means of improving myocardial visualization in association with intravenous contrast administration. This exploratory study examined the effect of using receive frequencies that were lower than the transmit frequencies while imaging closed chest dogs with an Ensemble wideband, phase inversion contrast program on a modified Siemens Elegra scanner.
  
  
  METHODS
  Intravenous bolus injections of 0.75 mL Definity and 1 mL QW7437 were administered to six anesthetized dogs. Intermittent imaging for contrast visualization was performed using either a broadband array, transmitting at 1.4 MHz and receiving at 2.6-3.2 MHz or a broadband 4-7.5 MHz transducer transmitting at 6.0 MHz and receiving at 4.2-4.5 MHz. Contrast enhancement was measured by videodensitometry, sampling mid-cavity and within the myocardium before and after injection. The changes in videodensity from control to after injection were calculated for each method.
  
  
  RESULTS
  There was no significant difference in the change in intracavity videodensity between the two imaging strategies although there was near full intracavity saturation in all cases. However, the change in myocardial density was significantly greater for both contrast agents when using receiving frequencies lower than transmitting frequencies (P = 0.02 and 0.03). The difference in duration of the myocardial blush did not reach statistical significance but it tended to persist for longer with the lower receiving frequencies.
  
  
  CONCLUSIONS
  Delivering sound energy at a slightly higher frequency and receiving at lower than the transmit frequency may be an advantageous method of enhancing myocardial perfusion signals during intravenous contrast echocardiography.
authors.affiliation: Oregon Health & Science University, Portland, USA.
authors.forename: Rosemary A
authors.initials: RA
authors.lastname: Rusk
authors.forename: Yoshiki
authors.initials: Y
authors.lastname: Mori
authors.forename: Xiaokui
authors.initials: X
authors.lastname: Li
authors.forename: Zuhua
authors.initials: Z
authors.lastname: Mao
authors.forename: Patrick L
authors.initials: PL
authors.lastname: von Behren
authors.forename: Diane
authors.initials: D
authors.lastname: Paine
authors.forename: Antoinette
authors.initials: A
authors.lastname: Kenny
authors.forename: David J
authors.initials: DJ
authors.lastname: Sahn
mesh_terms: D000818:Animals; D003287:Contrast Media; D004285:Dogs; D004452:Echocardiography / Q000379:methods; D005466:Fluorocarbons; D008863:Microspheres
chemical_list: D003287:Contrast Media; D005466:Fluorocarbons; C109298:QW7437; C042852:perflutren