title: Sensitive particle acoustic quantification (SPAQ): a new ultrasound-based approach for the quantification of ultrasound contrast media in high concentrations.
abstract: OBJECTIVE
  Ultrasound contrast media (USCM) consisting of gas-filled microparticles (MPs) can be detected in tissue in extremely small amounts using the stimulated acoustic emission effect (SAE), which occurs after the destruction of MPs in an acoustic field. Limited by the spatial resolution of ultrasound devices, the displayed size of individual MPs/SAEs is in the range of millimeters rather than micrometers. Thus, more than approximately 1000 microparticles per milliliter led to complete SAE saturation in the image and cannot be quantified. We have developed a method to quantify microparticles in high concentrations by increasing the resolution.
  
  
  METHODS
  We quantified gas-filled microparticles in an agar phantom containing 30,000 microparticles per mL with a defined overlap of consecutive images, thereby destroying the microparticles with high mechanical index and measuring the corresponding SAE effects using videodensitometry.
  
  
  RESULTS
  In each image, only those particles that had not been previously destroyed were detected. The thickness of the slices containing SAE signals was thus determined by frame-to-frame displacement. Based on the reduced slice thickness and the resulting improved spatial resolution, individual microparticles were detected even in high microparticle concentrations.
  
  
  CONCLUSIONS
  Sensitive particle acoustic quantification (SPAQ) allows the quantification of microparticles, even in high concentrations, based on a massive increase in resolution.
authors.affiliation: Schering AG, Research Laboratories, Berlin, Germany. michael.reinhardt@schering.de
authors.forename: Michael
authors.initials: M
authors.lastname: Reinhardt
authors.forename: Peter
authors.initials: P
authors.lastname: Hauff
authors.forename: Andreas
authors.initials: A
authors.lastname: Briel
authors.forename: Volkmar
authors.initials: V
authors.lastname: Uhlendorf
authors.forename: Ralf A
authors.initials: RA
authors.lastname: Linker
authors.forename: Mathias
authors.initials: M
authors.lastname: Mäurer
authors.forename: Michael
authors.initials: M
authors.lastname: Schirner
mesh_terms: D000818:Animals; D003287:Contrast Media / Q000032:analysis*; D005260:Female; D010316:Particle Size; D051381:Rats; D017208:Rats, Wistar; D012680:Sensitivity and Specificity; D014465:Ultrasonics; D014463:Ultrasonography / Q000379:methods*
chemical_list: D003287:Contrast Media