MRI VISUALISATION -- Help/advice needed

[ohm]

Hello,

I have MRI data comprising of roughly 150 slices through a
persons neck. I need to extract a 3d model of the carotid
arteries (this artery bifurcates), from this data.

The data is basically a 256x256 array with showing intensity.
Because of this poor resolution the artery is only about 5x5
data points large. 

I plan to use some sort of thresholding to get the artery 
outline from which i can get a 3d mesh of its surface. 
However because of the low res, an automated method is not 
very predictable, and the arterial x-sections very ill-defined.

Anyway I would like to know if there are any software, 
(commercial although preferably not) or otherwise that could 
do this sort of thing. Or if there are any standard methods 
of doing this. In fact any pointers will be appreciated.

thanks