I.  Level Set Segmentation

Code:
levelSet.m
 
 

II.  3D Seeded Region Growing
 
 

Code:
SeedSlice.m
SeededRegion.m
 
 

III. Comparison/Discussion

Quick inspection will illustrate that 3D region growing has considerably more complications than 2D seeded region growing.  Unfortunately, segmentation is a procedure where nearly perfect results are necessary to achieve levels necessary for most applications.  The advantage of 3D segmentation over its 2D counterpart is that you aren't required to seed every slice.  However, reasonable results do require a certain level of seeding - not to mention that seeding in the 3D domain is a bit of an art.  Considering the only slight time advantage gained in reduced seeding and the large degradation in results, the indication would seem to be that 2D seeded region growing is the superior method for two and three dimensions.