shift_timings: Shift timings of TAC and Input

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

Shift timings of TAC and Input

Description

This function sorts out all the time shifting of the input and TAC so that they are in the same time. This function makes several 'editorial decisions'. i) If the TAC is shifted positively, all frames will be shifted positively, but the time=0 frame will remain at time=0, i.e. there are no extra frames added. Shifting of the TAC only occurs if the input is shifted negatively (and can be turned off using shifttac=F). ii) If the input is shifted, and is subsequently shorter than the TAC, an extra measurement will be added at max(t_tac) with the same value as the last measurement. iii) If the input is shifted positively, all interpolated times will be shifted by the specified amount, but an extra measurement is added at time=0 of 0,0,1 for blood, plasma and parent fraction respectively (followed by interpolation into default 6000 equally spaced time intervals in the new time window) i.e. not the same process as for the TACs: I figure that since the blood changes so quickly, this is likely more close to the true kinetics. Get in touch if you have suggestions for this.

Usage

shift_timings(t_tac, tac, input, inpshift, shifttac = T)

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.
tac	Numeric vector of radioactivity concentrations in the target tissue for each frame. We include zero at time zero: if not included, it is added.
input	Data frame containing the blood, plasma, and parent fraction concentrations over time. This can be generated using the blood_interp function.
inpshift	The number of minutes by which the times of the input data frame should be adjusted.
shifttac	Optional. Can the TAC be shifted. If the input is shifted negatively, it will then contain negative time values. If shifttac=TRUE, the TAC will be made later, but if shifttac=FALSE, the blood, plasma and parent fraction with negative values will be removed. Default is TRUE.

Details

Function to shift backwards and forwards the timings of the TAC vector and input data frame to make them consistent.

Value

A list containing the following after time shifting: the times of the TAC out$t_tac, the TAC out$tac, the input dataframe out$input, the interpolated time out$interptime (which is the same as the time in the input dataframe), and the interpolated TAC out$i_tac.

Author(s)

Granville J Matheson, [e-mail]

Examples

## Not run: 
inpshift <- 0.25 # 15 seconds
newValues <- shift_timings(t_tac, tac, input, inpshift)
t_tac <- newValues$t_tac
tac <- newValues$tac
input <- newValues$input

## End(Not run)

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