boldContrast: Maximum Theoretical BOLD signal observable

In FIACH: Retrospective Noise Control for fMRI

Description

This function returns a theoretical threshold beyond which BOLD signal changes are likely to be artefactual based on the models presented in Yablonskiy and Haacke(1994).

Usage

boldContrast(B0, te, plot = TRUE, random = TRUE, alpha = 0.38, hct = 0.4, cbf.base = 55, 
             chi = 1.8e-07, e.base = 0.4, w0 = 267500000,e.act=.1,cbf.act=2*cbf.base)

Arguments

B0	Magnetic field strength specified in Tesla.
te	Echo Time specified in ms
plot	Logical indicating whether or not to plot results.
random	Logical indicating if the theoretical model assumes the cylinders embedded in the medium are randomly orientated. If false the cylinders are assumed to be in parallel.
alpha	Power to which cbf.base is raised to estimate Cerebral Blood Volume.
hct	Hematocrit expressed as a real number between 0 and 1.
cbf.base	Cerebral Blood Flow at rest, specified in ml per mg per minute.
chi	Volume susceptibility difference between oxygenated and de-oxygenated blood specified in cgs units.
e.base	1- oxygenation fraction during rest. ranging between 0 and 1
w0	Gyromagnetic ratio of the proton expressed in radians per second per tesla
e.act	1- oxygenation fraction during activation. ranging between 0 and 1. Defaults to .1 to produce a conservative threshold. A value of .2 might produce a more realistic threshold.
cbf.act	Cerebral Blood Flow during activation, specified in ml per mg per minute

Value

A threshold expressed in percent signal change is returned

Author(s)

Tim Tierney

Examples

## magnetic field strength of 1.5T and TE of 30ms
## assuming parallel orientation of cylinders.
boldContrast(1.5,30,plot=TRUE,random=FALSE) 

## magnetic field strength of 1.5T and TE of 
## 30ms assuming random orientation of cylinders
boldContrast(1.5,30,plot=TRUE,random=TRUE)   

FIACH documentation built on May 1, 2019, 8:02 p.m.