Multichannel Pulsed Doppler Signal Processing for Vascular Measurements in Mice

Abstract

The small size, high heart rate, and small tissue displacement of a mouse require small sensors that are capable of high spatial and temporal tissue displacement resolutions and multichannel data acquisition systems with high sampling rates for simultaneous measurement of high fidelity signals. We developed and evaluated an ultrasound-based mouse vascular research system (MVRS) that can be used to characterize vascular physiology in normal, transgenic, surgically altered, and disease models of mice. The system consists of multiple 10/20MHz ultrasound transducers, analog electronics for Doppler displacement and velocity measurement, signal acquisition and processing electronics, and personal computer based software for real-time and offline analysis. In-vitro testing of the system showed that it is capable of measuring tissue displacement as low as 0.1 µm and tissue velocity (µm/s) starting from 0. The system can measure blood velocities up to 9 m/s (with 10 MHz Doppler at a PRF of 125 kHz) and has a temporal resolution of 0.1 milliseconds. Ex-vivo tracking of an excised mouse carotid artery wall using our Doppler technique and a video pixel tracking technique showed high correlation (R 2 =0.99). The system can be used to measure diameter changes, augmentation index, impedance spectra, pulse wave velocity, characteristic impedance, forward and backward waves, reflection coefficients, coronary flow reserve, and cardiac motion in murine models. The system will facilitate the study of mouse vascular mechanics and arterial abnormalities resulting in significant impact on the evaluation and screening of vascular disease in mice.

Doppler velocity measurements from large and small arteries of mice

“…By recording velocity signals from two sites, separated by a known distance, and measuring the difference in pulse arrival times, one can determine the pulse transit time and calculate PWV (21,24). Velocity can be measured sequentially from the two sites with a high-fidelity ECG used as a timing reference, or velocity can be measured from two sites simultaneously using two Doppler probes (48). Typically, we determine aortic PWV from velocities measured in the aortic arch and in the descending aorta about 4 cm distal.…”

Photoacoustic microscopy of blood pulse wave

“…2,3 Traditional Doppler ultrasound has been used for PWV measurements, however, it is limited to large trunk vessels. 1,4,5 Photoacoustic microscopy (PAM) is capable of high sensitivity, high resolution, and noninvasive vascular imaging in vivo, 6 extending PWV measurements to small peripheral vessels. In this letter, by simultaneously monitoring blood flow speed and cardiac pulsation using a combined PAM-electrocardiography (ECG) system, we demonstrated the first in vivo photoacoustic measurement of the PWV in the mouse peripheral vasculature.…”

Defective Association of the Platelet Glycoprotein Ib–IX Complex with the Glycosphingolipid-Enriched Membrane Domain Inhibits Murine Thrombus and Atheroma Formation

“…We treated mouse carotid arteries with 10% FeCl 3 (Fig. 3A, upper panel) and monitored the blood flow with a Doppler system (Fig.3A, lower panel) (12-15). We found that the mice expressing wild type GP Ibα occluded their vessels faster than the mutant mice, where the blood flow in 2 out of 14 mutant mice did not even stop (Fig.…”

“…After rinsing three times with phosphate-buffered saline, the blood flow and ECG signal were monitored using a PC-based high-speed real-time Doppler signal processing system (12-15). The occlusion time was counted as the period from removal of the filter paper to the time when the Doppler signal went to nearly zero.…”