Accurate Blood Flow Measurements: Are Artificial Tracers Necessary?

Abstract

Imaging-based blood flow measurement techniques, such as particle image velocimetry, have become an important tool in cardiovascular research. They provide quantitative information about blood flow, which benefits applications ranging from developmental biology to tumor perfusion studies. Studies using these methods can be classified based on whether they use artificial tracers or red blood cells to visualize the fluid motion. We here present the first direct comparison in vivo of both methods. For high magnification cases, the experiments using red blood cells strongly underestimate the flow (up to 50% in the present case), as compared to the tracer results. For medium magnification cases, the results from both methods are indistinguishable as they give the same underestimation of the real velocities (approximately 33%, based on in vitro reference measurements). These results suggest that flow characteristics reported in literature cannot be compared without a careful evaluation of the imaging characteristics. A method to predict the expected flow averaging behavior for a particular facility is presented.

Optical detection of nanoparticle agglomeration in a living system under the influence of a magnetic field

“…In previous studies the blood flow in heart [7] and blood vessels [9] of chicken embryos has been studied using fluorescent artificial tracers injected into a candled egg placed in a water bath. In the present work, we selected a different setup using a shellless, planar embryo model demonstrating several advantages.…”

“…The influence of the magnification as key optical parameter in mPIV measurements was investigated for particle transport in chicken egg vessels [9]. Deviations in the measured velocities of blood cells and fluorescent polymer beads at different magnifications increase with higher magnification, caused by differences between centerline velocity and depth-averaged velocity.…”

Quantification of Blood Flow and Topology in Developing Vascular Networks

“…A relatively large DOC compared to the blood vessel diameter can cause a severe underestimation of the measured centerline velocity (see [24]), since the measured velocity is an average of all flow velocities along the viewing direction. With the present magnification of 5× and the largest blood vessels diameter measuring 200 µ m, the measurements were in the depth-saturated regime [20]. In this case, the actual centerline velocity could easily be retrieved by applying a correction factor.…”

Hemodynamics in the Microcirculation and in Microfluidics

“…Thus, there are some advantages to ignoring the biological interactions and side effects of the animal conditions in in vivo experiments. The nano-tracer particles were more suitable for measuring flow velocities near the wall than RBCs as tracer particles, in vitro 117 as well in vivo, 121 because the cell-free layers near the wall have no traceable RBCs due to lateral migration. Poelma et al 121 also mentioned that the velocities at the center of the micro vessel measured using tracer particles or RBCs tended to be almost the same in the case of high-magnication observations, depending on the numerical aperture of the objective lens.…”

“…The nano-tracer particles were more suitable for measuring flow velocities near the wall than RBCs as tracer particles, in vitro 117 as well in vivo, 121 because the cell-free layers near the wall have no traceable RBCs due to lateral migration. Poelma et al 121 also mentioned that the velocities at the center of the micro vessel measured using tracer particles or RBCs tended to be almost the same in the case of high-magnication observations, depending on the numerical aperture of the objective lens. Some groups have succeeded in measuring the blood flow in in vivo experiments using lPIV methods with respect to the hearts of a zebra fish, 63 the embryonic venous vessels of a chicken, 61,82 and the vitelline network of a chicken.…”