Introduction

For the full usage of VERBENA type verbena at the command line. A typical usage of VERBENA would be:

verbena -i data.nii.gz -a aif.nii.gz -o output_directory -m mask.nii.gz

This would process the 4D DSC data in data.nii.gz using the AIFs supplied in aif.nii.gz using the modified Vascular Model to estimate (relative) perfusion, commonly referred to as cerebral blood flow (rCBF), along with the mean transit time (MTT) and the transit time distribution parameter lambda; maps of which are placed in the output directory. Analysis is only performed within the mask supplied (mask.nii.gz) which will normally have been derived from a brain extraction using BET or other equivalent tool.

AIFs

VERBENA takes as an input a 4D Nifti file containing the Arterial Input Functions (AIFs) this should have identical dimensions to the data and thus should have a single AIF time course for every single voxel (within the mask), often this will be a single global AIF replicated for every single voxel. However, VERBENA allows for different AIFs to be specified for individual brain regions should a local AIF be available. We do not currently include a tool for the selection or identification of the AIF. Often the AIF time course will be manually selected from the DSC data by the identification of a major artery, various automated methods have been developed in the literature and it may be possible to find tools that implement them online.

Macro vascular contamination

By adding the --mv option an additional component will be added to the model (based on the AIF) to account for macro vascular contamination contrast in large arteries, see Theory. When this option is included a further image will be produced in the output directory that maps the Arterial Blood Volume (rABV) in relative units. By default the additional macro vascular component is added when the concentration time course of the voxel is calculated, optionally addition of the tissue and macro vascular component can be done as signal time courses using the --sigadd option.

'Model-Free' Analysis

VERBENA takes a model-based approach to perfusion quantification. It is possible to use a more conventional Singular Value Decomposition deconvolution method by choosing the --modelfree option. This 'model-free' quantification can also be used to create initial estimates for the main model-based VERBENA analysis using the --modelfreeinit option, which may lead to more robust results in some cases.