text: The measurement of Ki from dynamic PET scans require tracer kinetic modelling to obtain the model parameters describing the biological processes in bone, as described by Hawkins et al. Since this model has two tissue compartments, it is sometimes called a two-tissue compartmental model. Various different versions of this model exist; however, the most fundamental approach is considered here with two tissue compartments and four tracer-exchange parameters. The whole kinetic modelling process using Hawkins model can be summed up in a single image as seen on the right-hand-side. The following differential equations are solved to obtain the rate constants:
  The rate constant K (in units: ml/min/ml) describes the unidirectional clearance of fluoride from plasma to the whole of the bone tissue, k (in units: min) describes the reverse transport of fluoride from the ECF compartment to plasma, k and k (in units min) describe the forward and backward transportation of fluoride from the bone mineral compartment.
  K represents the net plasma clearance to bone mineral only. K is a function of both K, reflecting bone blood flow, and the fraction of the tracer that undergoes specific binding to the bone mineral k / (k + k). Therefore,  
  Hawkins et al. found that the inclusion of an additional parameter called fractional blood volume (BV), representing the vascular tissue spaces within the ROI, improved the data fitting problem, although this improvement was not statistically significant.