Lecture 17: Tracer Kinetics Flashcards
What are the three methods for structural and functional medical imaging?
- Static
- Tomographic
- Dynamic
How and why do medical physicists analyse medical images?
They analyse the images by turning them into graphs and numbers that can be easily interpreted because clinicians don’t have time to do so.
What is tracer kinetics?
The movement of tracers to different organs via the bloodstream.
Describe the delivery of a tracer to and from an organ
What is the Fick equation?
Q = blood flow
M = amount of tracer in organ
t = time
C_a = concentration of tracer in arterial blood
C_v = concentration of tracer in venous blood
How can the blood flow to an organ be calculated using tracer kinetics?
dM/dt can be measured directly using functional imaging and the concentration of tracer in the blood can be measured by taking blood samples so blood flow can be calculated using the Fick equation.
Give the dilution equation (the tracer concentration in an organ)
C = concentration
M = amount of tracer in organ
V = organ volume
What is the equation for the transit time of a tracer through an organ (the average time a molecule of tracer spends in the organ)?
T = transit time
V = organ volume
Q = blood flow
What does the perfusion equation represent?
The blood flow per unit volume.
What is the perfusion equation?
f = blood flow per unit volume
Q = blood flow
V = organ volume
What is compartmental analysis?
A model of the body that separates it into a small number of distinct compartments though which a radiotracer is distributed.
What is a compartment (in compartmental analysis)?
A component of the body, such as an organ (e.g. kidneys or liver) or something more diffuse (e.g. blood), that is used in compartmental analysis.
What are the two basic assumptions made on compartmental modelling?
1) The mixing of the tracer within each compartment is complete and instantaneous (the tracers are freely diffusable).
2) The flow of a tracer out of a compartment is proportional to the concentration of tracer in that compartment (the more tracer in a compartment, the faster it flows out).
Give an example of when compartmental analysis is completed for a single, closed compartment.
Measuring the plasma volume in blood.
How is the plasma volume measured in blood?
Compartmental analysis is completed for a single, closed compartment.
A known quantity of I-131 (iodine), labelled Albunin, is injected into the bloodstream as it does not readily leave the blood plasma. After equilibration, a blood sample is removed and the concentration of I-131 is determined, then use to determine the total plasma volume.
