 the average model values by ROI for 
its voxelwise binding potential (BPnd) models, such as Logan, SRTM, etc.
This function reads the .voistat file and returns a data.frame with the
ROI as rows and the model value as the column. Optionally, the ROIs can be
combined into larger ROIs if ROI_def is specified, just as with TAC loading.</p>
    
    </div>

    <pre class="usage"><span class='fu'>load_voistat</span>(<span class='no'>filename</span>, <span class='kw'>ROI_def</span> <span class='kw'>=</span> <spa