Any voxel whose center is within 10mm of the coordinate entered will be included in the ROI. As your coordinate doesn't always fall in the same place with respect to the voxel center, then the ROIs will be different sizes because of the number of voxels within 10mm of coordinate.

Best Regards, Donald McLaren
=================
D.G. McLaren, Ph.D.
Research Fellow, Department of Neurology, Massachusetts General Hospital and
Harvard Medical School
Postdoctoral Research Fellow, GRECC, Bedford VA
Website: http://www.martinos.org/~mclaren
Office: (773) 406-2464
=====================
This e-mail contains CONFIDENTIAL INFORMATION which may contain PROTECTED
HEALTHCARE INFORMATION and may also be LEGALLY PRIVILEGED and which is
intended only for the use of the individual or entity named above. If the
reader of the e-mail is not the intended recipient or the employee or agent
responsible for delivering it to the intended recipient, you are hereby
notified that you are in possession of confidential and privileged
information. Any unauthorized use, disclosure, copying or the taking of any
action in reliance on the contents of this information is strictly
prohibited and may be unlawful. If you have received this e-mail
unintentionally, please immediately notify the sender via telephone at (773)
406-2464 or email.


On Fri, Jun 20, 2014 at 8:02 AM, Dhananjay kimothi <[log in to unmask]> wrote:
Dear SPmers,

When i am defining ROI's  in MARSBAR (sphere with coordinate -51 0 -39 ),volume covered is 4288 but when the coordinate is -52 -66 31 ,volume is 3984 but i defined the radius 10mm for both the cases.
I am not able to comprehend it,why it is happening??
I am attaching the figures herewith.


Regards,
Dhananjay Kimothi