On Sat, Mar 06, 2010 at 03:09:54PM -0500, Judd Storrs wrote: > On Fri, Mar 5, 2010 at 1:36 AM, Søren Hauberg <so...@hauberg.org> wrote: > > 2. It would be nice if the help text more clear explains what a > > 'phantom' is. Personally, I don't know what it is. > > FYI, > > A "phantom" is basically a non-human object used to assess image > reconstruction quality in medical imaging. The Shepp-Logan is a > digital 3D phantom that is designed to have grossly brain-like > features but also at the same time have a precisely defined > mathematical structure so that reconstruction algorithms can be tested > by simulation and comparision to the known ground truth. (The concept > of truth is problematic in medical imaging because there are multiple > (if not infinite) plausible images that correspond to the acquired > data) I think Shepp-Logan is in designed to even be analytically > useful.
Not quite. The original Shepp-Logan phantom is a 2D phantom, showing a slice through the head: http://bigwww.epfl.ch/thevenaz/shepplogan/ This is what is (hopefully) implemented in phantom.m (the fastest way is looking whether the description talks about 'ellipses' versus 'ellipsoids'). There is an extension to the 3D case, where a certain slice through the head has the properties of the 2D original. Shepp-Logan is characterized by very small jumps in density, making it difficult for algorithms at that time (in other words, a real challenge). Unfortunately, instead of improving their algorithms, people started creating 'modified' phantoms, with higher jumps to get more contrast in their results. Thomas ------------------------------------------------------------------------------ Download Intel® Parallel Studio Eval Try the new software tools for yourself. Speed compiling, find bugs proactively, and fine-tune applications for parallel performance. See why Intel Parallel Studio got high marks during beta. http://p.sf.net/sfu/intel-sw-dev _______________________________________________ Octave-dev mailing list Octave-dev@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/octave-dev
