Blood tracer kinetics in the arterial tree

Area of Science:

• Physiology
• Biophysics
• Medical Imaging

Background:

• Organ blood supply evaluation uses tracers, but tracer kinetics are empirically modeled without considering vascular morphology.
• Current methods lack a direct link between observed tracer concentration and the underlying arterial tree structure.

Purpose of the Study:

• To establish a theoretical relationship between tracer kinetics and vascular morphology in the arterial tree.
• To develop a novel approach for in vivo assessment of vascular structure using experimentally determined response functions.

Main Methods:

• Developed a theoretical model relating tracer impulse response functions to vascular morphology.
• Analyzed tracer transport in individual vessel segments, considering laminar flow approximations.
• Applied the model to analyze regional cerebral blood flow measurements using arterial spin labeling data.

Main Results:

• Demonstrated that arterial tree response functions can be reduced to individual vessel segment properties under good mixing conditions.
• Showed that geometric scaling of the vascular tree simplifies the derived expressions.
• Identified the analysis of tracer concentration dependence on measurement principles in vessel segments.
• Obtained explicit expressions for response functions in major arterial segments with laminar flow.
• Predicted a ~20% underestimation in regional cerebral blood flow measurements, aligning with experimental data.

Conclusions:

• Tracer kinetics provide a window into vascular morphology, enabling new in vivo imaging possibilities.
• The inverse problem of accessing vascular morphology from response functions is ill-posed.
• The developed theory offers a more accurate framework for analyzing blood flow and vascular structure, improving upon current empirical methods.