Blood Flow Quantification

Oliver D. Kripfgans Ph.D.

Associate Professor

J. Brian Fowlkes
Ph.D.

Professor

Jonathan Rubin
M.D., Ph.D.

Professor Emeritus

Background

Significance

Blood flow delivers oxygen/nutrients and removes waste products. Medical tests often measure blood velocities but not flow, i.e., the amount of blood per time. Velocities, in units of centimeters per second, don't reflect (volumetric) flow, i.e., volume per time, for example milliliters per minute. Example: A fast moving single traffic lane may be less desired than a lower speed multi lane traffic if the amount of cars per time is higher. Standard cardio-vascular exams obtain blood pressure, which provides limited to no information about the amount of blood flow per time. Theoretically there can be blood pressure with zero blood flow.

Conservation

Blood flow is conserved. For example, blood entering an organ, e.g. a kidney, must equal the amount of blood exiting the same kidney. If not, blood would either be lost in the kidney (by bleeding into the collective system) or be generated in the kidney, which is impossible. Velocities however, can significantly vary between the arterial and the venous side of the kidney since the lumen sizes of arteries and veins generally differ.

Physics

Flow Estimation in 3D

Finite sum of Gauss's Theorem with a partial volume coefficient modification (wi). Ultrasound beams that are only partially within a blood vessel will have their associated area element limited to that fractional size.

Angle Independence

As long as the scanning (circular/oval) ultrasound beams fully intersect the blood vessel the flow assessment is angle independent. Area and velocity are both a function of the relative angle but in reciprocal ways to each other.

Partial Volume Effect

Gauss's Theorem assumes infinitive small ultrasound beams. For (realistic) finite sized beams a partial volume modification (wi) is needed. Ultrasound beams that are only partially within a blood vessel will have their associated area element limited to that fractional size.

Current Research

Bedside Cardiovascular Monitoring of Neonates with Patent Ductus Arteriosus

(Co-PIs: Kripfgans and Rubin)

The goals of this project are to employ our 3D ultrasound blood volume flow method to measure blood flow and the consequences thereof in patent ductus arteriosus (PDA) shunts in very low birth weight (VLBW) infants. Supported by the American Society of Echocardiography and the American Institute for Ultrasound in Medicine (E21 Research Grant for Clinician-Scientist and Engineering Partnership)

Reference: https://pubmed.ncbi.nlm.nih.gov/36182604/

Assessment of Placental Blood Volume Flow and Function in IUGR Using a Transfer Function Model

(PI: Rubin)

In this project, we will develop a 3D ultrasound-based method that uses the blood flow dynamics in the umbilical arteries and vein to quantitatively assess placental function. The technique is totally benign, can be applied throughout pregnancy, and has the potential to detect placental based abnormalities, such as intrauterine growth restriction (IUGR), earlier in gestation than standard ultrasound Doppler based methods. Supported by the National Institutes of Health R21 HD095501.

References: https://pubmed.ncbi.nlm.nih.gov/34935157/
https://pubmed.ncbi.nlm.nih.gov/37699274/

3D Umbilical Venous Blood Flow: A New Paradigm for Improving the Assessment of Fetal Growth Restriction

(Co-PIs: Fowlkes and Lee)

The delivery of a small for gestational age baby impacts families and health care systems alike although a critical challenge is distinguishing those that are born constitutionally small from those with intrauterine undernourishment that are at increased risk for adverse outcomes. We have developed a new approach for measuring umbilical venous blood flow using 3D ultrasound and Doppler technology across all trimesters of pregnancy. In this proposal, we explain how we will determine accuracy, reproducibility, normal reference standards, and circulatory findings in small fetuses, based on 3D umbilical venous blood flow, to improve our ability for detecting and monitoring pregnancies with suspected growth abnormalities from intrauterine undernourishment. Supported by the National Institutes of Health R01 HD097756. The grant is joint with Baylor College of Medicine (Dr. Wesley Lee) and in collaboration with the NIH Perinatal Branch in Detroit (Dr. Roberto Romero ).

News

Front Cover of IEEE Ultrasonics, Ferroelectrics, and Frequency Control

IEEE Ultrasonics, Ferroelectrics, and Frequency Control. November 2019, Volume 66, Number 11, ISSN 0885-3010

Partial Volume Effect and Correction for 3-D Color Flow Acquisition of Volumetric Blood Flow. Color flow images (axial-lateral) from an X6-1 2-D matrix array probe operating at the frequency of 2.6 MHz on a Philips EPIQ 7 clinical scanner. Volumetric flow was computed by applying Gauss’ Theorem in the lateral-elevational c-surface. Velocities vi were obtained from the color flow beams, and areas, Ai, from the associated c-surface voxel areas. Voxels that contain only partial flow were accounted for by using color flow power to derive weights, wi (partial volume correction). By this approach, flow, Q, could be computed over a large range of color flow gain settings (31%, 35%, 40%, 45%, 51%, 55%, 60%, and 71%) with associated biases of −20%, −18%, −13%, −11%, 2%, −4%, −3%, and 0%, respectively. Flow, Q, computed without partial volume correction weights, w, showed biases of 3%, 22%, 44%, 70%, 116%, 238%, 409%, 361% for the aforementioned color flow gain settings. Volume flow measurements with partial volume correction were observed to be more independent of user-selected color flow gain, which minimizes bias over a wider range of gain settings.

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Publications

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