Measuring submicrometer displacement vectors using high-frame-rate ultrasound imaging

Displacement analysis of myocardial mechanical deformation (DIAMOND) reveals segmental susceptibility to doxorubicin-induced injury and regeneration

Zebrafish are increasingly utilized to model cardiomyopathies and regeneration. Current methods evaluating cardiac function have known limitations, fail to reliably detect focal mechanics, and are not readily feasible in zebrafish. We developed a semiautomated, open-source method - displacement analysis of myocardial mechanical deformation (DIAMOND) - for quantitative assessment of 4D segmental cardiac function. We imaged transgenic embryonic zebrafish in vivo using a light-sheet fluorescence microscopy system with 4D cardiac motion synchronization. Our method permits the derivation of a transformation matrix to quantify the time-dependent 3D displacement of segmental myocardial mass centroids. Through treatment with doxorubicin, and by chemically and genetically manipulating the myocardial injury-activated Notch signaling pathway, we used DIAMOND to demonstrate that basal ventricular segments adjacent to the atrioventricular canal display the highest 3D displacement and are also the most susceptible to doxorubicin-induced injury. Thus, DIAMOND provides biomechanical insights into in vivo segmental cardiac function scalable to high-throughput research applications.

Photoacoustic imaging of sub-diffraction objects with spectral contrast

Photoacoustic imaging couples the chemical specificity of optical absorption with the viewing depth of ultrasound. Systems based on linear array transducers have the versatility to be applied in various (pre-) clinical scenarios but face a trade-off between viewing depth and image resolution depending on transducer frequency and aperture. We propose here a method to disentangle, with precision, small, closely spaced targets with optical spectral contrast, without impairing the imaging depth. Photoacoustic data sets were recorded at two different optical wavelengths. We accurately recovered object separation distances (mean error=2.3%±6%) from the phase difference between signals across the array, down to a spacing of 1/20th of the system's beam-formed lateral resolution. The proposed method may enable the translation of super-resolution microscopy to deep tissue imaging.