# T2/T2* Map

Class: NodeT2Map

The node calculates a $$T_2$$ or $$T_2^*$$ map from spin echo or gradient echo data with multiple echo times. For notational simplicitly $$T_2$$ and $$T_2^*$$ will be refered to as $$T_2$$ below.

At least two images are required, however, more images are advised if a larger range of $$T_2$$ values are expected. For accurate results it is required that no other setting but TE varies between images.

An optional mask can also be provided to limit the calculations to a region. In addition to the $$T_2$$ map, a $$S_0$$ map which contains all weighting that is independent of $$T_2$$ is also produced. The parameter values are obtained by fitting the data to the signal equation

$$$S_i = S_0 e^{-TE_i/T_2}, ~~~i = 1, 2, ...,n \label{#eq:nonlin} \tag{1}$$$

where $$i$$ is an index over $$n$$ images with different echo times.

T2 example

## Inputs

#### Echo Series

One or several images are used as inputs. If the input contains timeseries the different time points are interpreted different echo times. Atleast two different echo times are needed for the node to function.

MetaData: The images must contain the field EchoTime.

Type: Image4DFloat, Required, Multiple

An (optional mask) that specifies which pixels to analyse.

Type: Image4DBool, Optional, Single

## Outputs

#### T2

A $$T_2$$ or $$T_2^*$$ map calculated for the voxels specified by the mask or in all voxels if no mask is provided. The map has the same unit as the echo time, typically given in ms.

Type: Image4DFloat

## Settings

#### Method Selection

Selects the method to use.

Values: Linear, NonLinear

## References

1. P.A. Boulby and F. Rugg-Gunn, “T2: the Transverse Relaxation Time,” in Quantitative MRI of the brain: Measuring changes caused by disease, P. S. Tofts, Ed. Wiley, 2003, pp. 143–201.