# cbf¶

cbf module computes the mean CBF and CBF timeseries by subtracting label-conttol pairs and modeled by the kinetic model. The module requires some parameters to be specified and standard parameters are supplied if those parameters are not provided.

## cbf_first_tagged¶

Volume label The cbf_first_tagged identifies which pair of volume is label or control volume. If cbf_first_tagged is 1, that means the first of pair volume is label and the second is control and vice versa.:

# the first volume is label
cbf_first_tagged[cxt]=1

# the first volume is control
cbf_first_tagged[cxt]=0


## cbf_perfusion¶

Labelling approach methods.

As of now, only two popular label strategies are implemente in xcpEngine .:

# for pulsed ASL (PASL)
cbf_perfusion[cxt]=pasl

# for pseudio-continous ASL (CASL/PASL)
cbf_perfusion[cxt]=casl


PASL is default if none is supply.

## cbf_m0_scale¶

M0 scale.

If the M0 scan is included and acquired at different scale to ASL acquisition, the user can supply the M0 scale. if there is no M0, cbf_m0_scale is set to 1, and average control volume is used as reference:

# scale
cbf_m0_scale[cxt]=1


## cbf_lambda¶

The lambda is the blood-brain partition coefficient that scales the signal intentisty of the tissues to that of the blood. The common or standard value is ƛ=0.90 ml/g.:

#
cbf_lambda[cxt]=0.9


## cbf_pld, cbf_tau¶

These two parameters are applicable to only CASL/PCASL. the cbf_tau is the label duration and cbf_pld is the post

labeling delay time. Both are expressed in seconds.:

#
cbf_tau[cxt]=1.8
cbf_pld[cxt]=1.8


## cbf_t1blood, cbf_alpha¶

cbf_t1blood is the longitutdinal relaxation time of the blood in seconds and the standard value denpends on the field strength of MRI machine. For 3T and 1.5T, the standard cbf_t1blood values are 1.650s and 1.350s respectively. The cbf_alpha is the labelling efficiency and values are different for PASL and CASL/PCASL. The standard value is 0.85 for CASL/PCASL and 0.98 for PASL.:

#
cbf_t1blood[cxt]=1.65 # for 3T MRI
cbf_alpha[cxt]=0.85 # for PCASL


## Expected output`¶

The main outputs are::
• prefix_cbf.nii.gz # mean cbf
• prefix_cbf_ts.nii.gz # cbf time series
• prefix_cbfR.nii.gz # relative mean cbf
• prefix_cbfZ.nii.gz # zscore mean cbf
• prefix_sub-1_cbf_tsnr.nii.gz # temporal signal to noise ratio of cbf