refLogan: Non-Invasive Logan Plot

In mathesong/kinfitr: Kinetic Modelling of PET Time Activity Curves

Non-Invasive Logan Plot

Description

Function to fit the non-invasive Logan plot model of Logan et al. (1996) to data.

Usage

refLogan(
  t_tac,
  reftac,
  roitac,
  k2prime,
  tstarIncludedFrames,
  weights = NULL,
  dur = NULL,
  frameStartEnd = NULL
)

Arguments

t_tac	Numeric vector of times for each frame in minutes. We use the time halfway through the frame as well as a zero. If a time zero frame is not included, it will be added.
reftac	Numeric vector of radioactivity concentrations in the reference tissue for each frame. We include zero at time zero: if not included, it is added.
roitac	Numeric vector of radioactivity concentrations in the target tissue for each frame. We include zero at time zero: if not included, it is added.
k2prime	Value of k2prime to be used for the fitting, i.e. the average tissue-to-plasma clearance rate. This can be obtained from another model, or set at a specified value. If using SRTM to estimate this value, it is equal to k2 / R1.
tstarIncludedFrames	The number of frames to be used in the regression model, i.e. the number of frames for which the function is linear after pseudo-equilibrium is reached. This is a count from the end of the measurement, so a value of 10 means that last 10 frames will be used. This value can be estimated using refLogan_tstar.
weights	Optional. Numeric vector of the weights assigned to each frame in the fitting. We include zero at time zero: if not included, it is added. If not specified, uniform weights will be used.
dur	Optional. Numeric vector of the time durations of the frames. If not included, the integrals will be calculated using trapezoidal integration.
frameStartEnd	Optional: This allows one to specify the beginning and final frame to use for modelling, e.g. c(1,20). This is to assess time stability.

Value

A list with a data frame of the fitted parameters out$par, the model fit object out$fit, a dataframe containing the TACs of the data out$tacs, a dataframe containing the TACs of the fitted values out$fitvals, a vector of the weights out$weights, the specified k2prime value out$k2prime, and the specified tstarIncludedFrames value out$tstarIncludedFrames

Author(s)

Granville J Matheson, [e-mail]

References

Logan J, Fowler JS, Volkow ND, Wang GJ, Ding YS, Alexoff DL. Distribution volume ratios without blood sampling from graphical analysis of PET data. Journal of Cerebral Blood Flow & Metabolism. 1996 Sep 1;16(5):834-40.

Examples

data(simref)

t_tac <- simref$tacs[[2]]$Times
reftac <- simref$tacs[[2]]$Reference
roitac <- simref$tacs[[2]]$ROI1
weights <- simref$tacs[[2]]$Weights

fit <- refLogan(t_tac, reftac, roitac, k2prime = 0.1, tstarIncludedFrames = 15, weights = weights)

mathesong/kinfitr documentation built on Jan. 15, 2024, 11:07 p.m.