Sensitive Particle Acoustic Quantification (SPAQ): A New Ultrasound-Based Approach for the Quantification of Ultrasound Contrast Media in High Concentrations

RATIONALE AND OBJECTIVES: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. CONCLUSION:Sensitive particle acoustic quantification (SPAQ) allows the quantification of microparticles, even in high concentrations, based on a massive increase in resolution.