 |
 |
Hi there On Tue, 22 Jan 2002, Qingyan Guan wrote: > Hi, > > I have a question about avwstats tool. > > I need calculator a brain volume. I used avwstats for volume calculation. > >From its usage, I only can see the option of output. Is there any constraint > for input image, which steps it automatically processed? > For example, If I give a whole brain 3D image with skull and csf as input, > does the output for volume include skull of brain, or csf? > > For the accuracy, should I calculator the white, grey and csf class > seperatly, then add them up? avwstats input -v will just calculate the volume of the image - not the brain i.e. if you have an image 256 x 256 x 42 the first output will perform exactly that calculation = 2752512 voxels. The second output will be the volume in mm^3 (i.e. it takes account for the voxel size). avwstats input -V calculates the non-zero volume. i.e the first output is the number of non-zero voxels, and the second is the number of non-zero voxels multiplied by the volume of a single voxel. If you want to calculate the total brain volume, run Bet on your image then run: avwstats input_brain -V and then take the second output (in mm^3) If you want to exclude CSF from your volume estimate, run Fast on your image. At the end volume fractions are quoted for each class. I think the output will look something like Class: CSF tissue 1 tissue 2 brain percentage Volumes: 0.2 0.4 0.4 0.8 if you multiply the total brain volume (as calculated above) by the brain percentage quoted by Fast, it should give you a pretty good estimate of brain volume. You can obviously calculate the volume of each tissue type in a similar way. Hope this helps cheers Tim