FIACH (version 0.1.2)

boldContrast: Maximum Theoretical BOLD signal observable

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

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)