Comparison of imaging modalities for quantification of cyanoacrylate microbubble concentration

Abstract

Excessive neovascularisation of tissue (angiogenesis) is a significant indicator for various disease states. Molecular ultrasound imaging of targeted cyanoacrylate microbubbles (CMB) has demonstrated the ability to assess angiogenic markers. Monitoring the response to anti-angiogenic therapy requires a precise quantification of microbubbles. Power Doppler (PD) is an established method for quantitative measurements of stationary CMB by imaging their destruction. Pulse Inversion (PI) is mainly used in nondestructive imaging at low Mechanical Index (MI) levels. However, the echo change between two consecutive pulses caused by destruction of CMBs will also be visible in PI images. Thus PI imaging might also be an adequate method for quantitative destruction imaging. In this study PI and PD are compared regarding their ability to correctly quantify the destruction of stationary CMBs. To assess the performance of these methods for quantification a gelatine phantom with experimental CMBs was imaged using Sensitive Particle Acoustic Quantification (SPAQ), a technique for quantifying high concentrations of microbubbles. The phantom was imaged with SPAQ increments from 10 μm to 100 μm using a Sonix RP clinical ultrasound system (Ultrasonics) with a 7.5 MHz linear-array transducer. The results show that both methods are capable of imaging the destruction of single microbubbles. PI images displayed a significant portion of nonlinear signals not due to bubble destruction that could be eliminated by background subtraction. The average area of single destruction events is significantly lower for PI and than for PD images. PI offers better resolution but requires repeated scanning for quantification. © 2009 Springer Berlin Heidelberg.