VAI - Introduction

The Vessel Architectural Imaging (VAI) module is developed for analysis of double echo Gradient Echo (GRE) and Spin Echo (SE) dynamic multi-echo dynamic susceptibility contrast (DSC) MRI data. In addition to the generation of standard perfusion related maps (CBV, CBF, MTT) the module can generate VAI-specific maps when double echo GRE/SE data is provided.

The overall aim of the module is to provide a better interface between structural data (used to define tumor/lesion/volume of interest) and double echo perfusion data to enable fast and efficient definition of tumor volume as well as generation of multi-parametric functional maps.
The module has the following main features:

• Multi-planar reconstruction (MPR) views of structural dataset used to define lesion / volume of interest.
• Additional view of perfusion (dynamic multi-echo) data in separate panel; shown either as time-intensity curves or GRE/SE hysteresis curves.
• User friendly and fast definition of lesion volume from MPR views using a combination of seed growing and morphometric operations.
• Co-registration of structural and functional data.
• Fast generation of VAI parametric maps with possibility of interactive visualization of dynamic response.
• Fast and automated generation of statistical output (incl histogram analysis) of all perfusion metrics generated
• User friendly and highly interactive user interface (based on VTK) allowing efficient MPR interaction as well as full volume rendering and MIP rendering of structural data.

The module can also be used for standard DSC analysis, to utilize the user friendly MPR view and lesion segmentation tool capabilities.

Sequence requirements for VAI

In order to perform VAI analysis, a double echo EPI sequence is needed where the first echo is a GRE readout (typical TE 20-30 ms) and the second echo is a SE readout (typical TE 80-120 ms). The temporal resolution should be as high as possible (more important than for standard DSC-MRI) and should preferably be at least 1.5 sec.  It should be noted that the SE and GRE parts cannot (currently) be acquired as two separate scans but need to be integrated in a single EPI acquisition. Based on the literature, VAI-compatible sequences are available as research options from most major vendors.