afni.nimh.nih.gov

You could use XMedcon, but despite it creates
a multiframe dicom file from a single volume
you had to change some dicom header information to supply some missing data in
the AFNI.BRIK.
Also with this program is posible to convert
to and fro Acr/Nema 2.0, Analyze (SPM), Concorde/µPET, DICOM 3.0, Ecat/Matrix 6.4, InterFile3.3 and PNG or GIF7a/89a.
More info at
[xmedcon.sourceforge.net]

I hope it helps

Pablo Sau