mrtm1: Ichise's Multilinear Reference Tissue Model

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

Ichise's Multilinear Reference Tissue Model

Description

Function to fit MRTM1 of Ichise et al. (2003) to data. This model is often used alongside MRTM2: MRTM1 is run on a high-binding region to obtain an estimate of k2prime, and this k2prime value is used for MRTM2.

Usage

mrtm1(
  t_tac,
  reftac,
  roitac,
  tstarIncludedFrames = NULL,
  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.
tstarIncludedFrames	Optional. The number of frames to be used in the multiple regression. 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 mrtm1_tstar. Note that this tstar differs from that of the non-invasive Logan plot (which is the point at which pseudo-equilibrium is reached). Rather, with MRTM1 and MRTM2, all frames can be used provided that the kinetics in the target tissue can be described by a one tissue compartment (1TC) model (like SRTM). If this is not the case, a t* is required. If the number of included frames is greater than the number of frames minus 2, then the par output will also include R1 and k2 values. These parameters are only applicable if 1TC dynamics can be assumed.
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$weights, and the specified tstarIncludedFrames value out$tstarIncludedFrames

Author(s)

Granville J Matheson, [e-mail]

References

Ichise M, Liow JS, Lu JQ, Takano A, Model K, Toyama H, Suhara T, Suzuki K, Innis RB, Carson RE. Linearized Reference Tissue Parametric Imaging Methods: Application to [11C]DASB Positron Emission Tomography Studies of the Serotonin Transporter in Human Brain. Journal of Cerebral Blood Flow & Metabolism. 2003 Sep 1;23(9):1096-112.

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 <- mrtm1(t_tac, reftac, roitac, weights = weights)

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