dcemriS4 (version 0.51)

Arterial Input Functions: Arterial Input Functions

Description

Parametric models for arterial input functions (AIFs) that are compatible with single compartment models for dynamic contrast-enhanced MRI (DCE-MRI).

Usage

aif.orton.exp(tt, AB, muB, AG, muG)
model.orton.exp(tt, aparams, kparams)
orton.exp.lm(tt, aif, guess=c(log(100),log(10),log(1),log(0.1)),
             nprint=0)

Arguments

tt

is a vector of acquisition times (in minutes) relative to injection of the contrast agent. Negative values should be used prior to the injection.

AB,muB,AG,muG

are parameters of the double exponential function that describe the AIF.

aparams

is the vector of parameters ($A_B$, $\mu_B$, $A_G$, $\mu_G$) associated with the AIF.

kparams

is the vector of parameters ($v_p$, $K^{trans}$, $k_{ep}$) associated with the extended Kety model for contrast agent concentration.

aif

is the vector of observed contrast agent concentrations (data) used to estimate the parametric model.

guess

Initial parameter values for the nonlinear optimization.

nprint

is an integer, that enables controlled printing of iterates if it is positive. In this case, estimates of par are printed at the beginning of the first iteration and every nprint iterations thereafter and immediately

Value

• aif.orton.exp and model.orton.exp return the AIF associated with the pre-specified parameter values.

  orton.exp.lm returns a list structure with

• AB
  The amplitude of the first exponential function.
• muB
  The decay rate of the first exponential function.
• AG
  The amplitude of the second exponential function.
• muG
  The decay rate of the second exponential function.
• info
  The success (or failure) code from the Levenburg-Marquardt algorithm nls.lm.
• message
  The text message associated with the info paramters.

Details

aif.orton.exp displays the exponential AIF from Orton et al. (2008) for a known set of AIF parameter values. model.orton.exp displays the exponential AIF from Orton et al. (2008) for a known set of AIF and compartmental model parameter values. orton.exp.lm estimates the AIF parameters, using nonlinear optimization, using a vector of observed contrast agent concentrations.

References

Orton, M.R., Collins, D.J., Walker-Samuel, S., d'Arcy, J.A., Hawkes, D.J., Atkinson, D. and Leach, M.O. (2007) Bayesian estimation of pharmacokinetic parameters for DCE-MRI with a robust treatment of enhancement onset time, Physics in Medicine and Biology 52, 2393-2408. Orton, M.R., d'Arcy, J.A., Walker-Samuel, S., Hawkes, D.J., Atkinson, D., Collins, D.J. and Leach, M.O. (2008) Computationally efficient vascular input function models for quantitative kinetic modelling using DCE-MRI, Physics in Medicine and Biology 53, 1225-1239.

See Also

dcemri.lm, extract.aif, nls.lm

Examples

data("buckley")
## Generate AIF params using the orton.exp function from Buckley's AIF
xi <- seq(5, 300, by=5)
time <- buckley$time.min[xi]
aif <- buckley$input[xi]
aifparams <- orton.exp.lm(time, aif)
aifparams$D <- 1 
unlist(aifparams[1:4])

aoe <- aif.orton.exp(time, aifparams$AB, aifparams$muB, aifparams$AG,
                     aifparams$muG)
with(buckley, plot(time.min, input, type="l", lwd=2))
lines(time, aoe, lwd=2, col=2)
legend("right", c("Buckley's AIF", "Our approximation"), lty=1,
       lwd=2, col=1:2)
cbind(time, aif, aoe)[1:10,]