title: Influence of transducer frequency and imaging modality on the intraoperative assessment of myocardial perfusion with transesophageal echocardiography.
abstract: OBJECTIVE
  To determine factors that improve intraoperative myocardial perfusion assessment with conventional ultrasound imaging and intravenous ultrasound agents.
  
  
  METHODS
  Prospective cohort study with repeated interventions on each patient.
  
  
  METHODS
  Single university hospital.
  
  
  METHODS
  Fourteen patients scheduled for elective coronary artery bypass graft surgery.
  
  
  METHODS
  Myocardial perfusion was evaluated with contrast transesophageal echocardiography during conventional imaging after central venous injections of the contrast agent Optison (0.3 mL) before cardiopulmonary bypass. Eight patients received the injection during continuous sampling at each of 4 transducer frequency settings (3.5, 5.0, 6.0, 7.0 MHz). In another 6 patients, injections were administered during continuous and intermittent sampling (electrocardiogram-gated) at 3.5 and 5.0 MHz. Generalized estimating equations were used to compare mean responses, with p < or = 0.05 considered significant.
  
  
  RESULTS
  All recorded images were analyzed with off-line videodensitometry. Background-corrected peak pixel intensity (PPI(corr)) and rate of change in pixel intensity (PPI(corr)/T(PPI)) were determined for each injection. PPI(corr) was greater at 3.5 MHz than at 5.0, 6.0, and 7.0 MHz (p < 0.001). PPI(corr)/T(PPI) was greater at 3.5 MHz than at 5.0 (p < 0.001), 6.0 (p = 0.003), and 7.0 MHz (p < 0.001). PPI(corr) was greater for gated than for nongated sampling conditions at 3.5 (p < 0.05) and 5.0 MHz (p < 0.05).
  
  
  CONCLUSIONS
  To optimize myocardial contrast opacification, intraoperative transesophageal echocardiography should be performed with intermittent sampling at a transducer frequency close to the intrinsic frequency of the contrast agent.
authors.affiliation: Department of Anesthesia and Critical Care, University of Chicago, 5841 S. Maryland Avenue, Chicago, IL 60637, USA. fdupont@airway.uchicago.edu
authors.forename: F W
authors.initials: FW
authors.lastname: Dupont
authors.forename: A M
authors.initials: AM
authors.lastname: Fisher
authors.forename: A
authors.initials: A
authors.lastname: Toledano
authors.forename: S
authors.initials: S
authors.lastname: Aronson
mesh_terms: D000418:Albumins; D003287:Contrast Media; D001026:Coronary Artery Bypass; D003326:Coronary Circulation; D017548:Echocardiography, Transesophageal; D004562:Electrocardiography; D005466:Fluorocarbons; D006801:Humans; D007432:Intraoperative Period; D011446:Prospective Studies; D014159:Transducers
chemical_list: D000418:Albumins; D003287:Contrast Media; C099458:FS 069; D005466:Fluorocarbons