In Vivo Super Resolution Ultrasound Imaging using the Erythrocytes - SURE

Current super resolution imaging is conducted using ultrasound contrast agents, where a sparse distribution ofbubbles must be employed to separate individual targets. Thesparse targets make the acquisition time long in the range of1 to 10 minutes, and therefore demands an accurate motioncorrection over a long time. The employment of a contrastagent also lowers MI to below 0.2 to not disrupt the bubbles,with a corresponding lower signal-to-noise ratio in the images.A new method, SURE (SUper Resolution ultrasound imagingusing Erythrocytes), where erythrocytes are used as targets, issuggested to alleviate these problems. Perfused tissues containan abundance of targets, and the full clinical pressure rangecan be used. It is hypothesized that super resolution imagingbelow the diffraction limit can be attained in seconds usingSURE imaging. A SURE processing pipeline was developed withmodules for beamforming, tissue motion estimation, alignment,singular value decomposition for echo canceling, and subsequentpeak detection in the speckle pattern. The detected peaks weresummed in a high-resolution image for yielding the SURE image.Data were acquired using a 10 MHz linear array GE L10-18i probe (150 µm wavelength) and a Verasonics Vantage 256scanner. A synthetic aperture scan sequence with 12 emissionswas employed at a pulse repetition frequency of 5 kHz for a 417Hz frame rate. Kidneys of Sprague-Dawley rats were scanned for24 seconds and RF data stored for off-line processing. The excisedkidneys were micro-CT scanned for 11 hours for generatingreference maps of the vasculature with a voxel size of 21 µm.SURE images revealed vessels with sizes down to 50 µm. Fourierring correlations between independent images measured for 12s revealed a resolution between 25 to 49 µm, demonstrating thesuper resolution capability of the method. The SURE images areobtained in 1 to 12 seconds, demand no injection of intravenouscontrast agents, and can use the full pressure and intensityrange allowed in medical ultrasound, making the method easilyadaptable to clinical use.