It depends on the type of image you wish to show:
-MRIcron is actually excellent for extracting the VOI and displaying 2D images in a single plane or as orthogonal triplane images. I have found these steps helpful:

• First, create an intensity filter of the perfusion image from the Draw menu. This will allow you to "extract" the volume of the hyper (or hypo) perfusion clusters.
• Then mask the clusters in the perfusion image using the Draw menu. Open the image of the clusters, then open the intensity filter voi as a VOI in the Draw menu, then apply the mask and save the result.
• Finally open the masked perfusion cluster as an overlay on your T1. I favor the actc LUT/color map to show these results

BioimageSuite's ISAS overlays are also really nice 2D representations but I do not find their 3D view quite as nice as:

-The "nicest" 3D representation can be done with MeVisLab's View3D.

• Put the stripped T1 in as the main image,
• then add the perfusion cluster you created with the MRIcron method as an isocontour overlay. I attached a typical MeVisLab network to show the setup.
• You can clip the T1 in any plane to expose the deeper portions of the cluster or modify the transparency to do that.