This is really not an important point, but I will pitch in anyway.
Arguably, ROI is actually pronounced "arr - oh - eye" (the names of the
letters), so it does start with a vowel.


On Mon, Dec 23, 2013 at 12:02 PM, Samuel St-Jean
<notifications@github.com>wrote:

> In doc/examples/streamline_tools.py:
>
> > +streamline_generator = EuDX(csapeaks.peak_values, csapeaks.peak_indices,
> > +                            odf_vertices=peaks.default_sphere.vertices,
> > +                            a_low=.05, step_sz=.5, seeds=seeds)
> > +affine = streamline_generator.affine
> > +streamlines = list(streamline_generator)
> > +
> > +"""
> > +The first of the tracking utilities we'll cover here is ``target``. This
> > +function takes a set of streamlines and a region of interest (ROI) and returns
> > +only those streamlines that pass though the ROI. The ROI should be an array
> > +such that the voxels that belong to the ROI are ``True`` and all other voxels
> > +are ``False`` (this type of binary array is sometimes called a mask). This
> > +function can also exclude all the streamlines that pass though an ROI by
> > +setting the ``include`` flag to ``False``. In this example we'll target the
> > +streamlines of the corpus callosum. Our ``labels`` array has a sagittal slice
> > +of the corpus callosum identified by the label value 2. We'll create an ROI
>
> ROI starts with a consonant, and according to your link it should be a.
>
> An often repeated guideline is to use “a” when the word that follows
> starts with a consonant and to use “an” when word that follows starts with
> a vowel. Examples include “a book,” “an old book,” “an elephant,” and “a
> gray elephant.
>
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>