[Insight-users] Dicom Series Read Series Write: change in intensity values

[Bill Lorensen]

Steve,

You are right, I meant each slice and not each pixel.

Bill

On Nov 28, 2007 6:08 PM, Steve M. Robbins <steve at sumost.ca> wrote:

> On Wed, Nov 28, 2007 at 08:55:15AM +0100, Mathieu Malaterre wrote:
> > On Nov 28, 2007 4:40 AM, Steve M. Robbins <steve at sumost.ca> wrote:
> > > On Mon, Nov 26, 2007 at 11:22:25PM +0100, Mathieu Malaterre wrote:
> > >
> > > >  To go into further details, PET for instance has a dynamic
> > > > slope/intersept.
> > >
> > > What do you mean by "dynamic slope/intercept"?  That the rescale
> > > slope and intercept are specified per-image, even when the image
> > > series forms a volume?  That's not limited to PT; CT has the
> > > same behaviour, doesn't it?
> >
> > Hum...
> > I have never seen this happen with CT images (due to the nature of
> > Houndsfield Units this is not typical to go beyond 16 bits well at
> > least for human composition, in which case a single rescale
> > slope/intercept should be enough).
>
> True.  I asked the question not because I have seen it in practice,
> but to make sure I understood what you and Bill were talking about.
> Somewhere in that conversation it was mentioned that PET scales each
> *pixel* individually, which made me wonder whether I understood DICOM
> correctly.  (I think the comment about scaling by pixel was an error
> and scaling by slice was intended.)
>
>
> > Do you have by any chance a sample dataset, or do you recall the
> > private vendor doing this ?
>
> I don't recall any CT series in which rescale slope and intercept
> change.
>
> However, let me tell you about a series I did come across in the wild.
> It was MR and it had different *Bits Stored* across the series: a few
> images had 12 bits, the next few had 13, some more had 14.  I have no
> idea why they needed to do this, but it did expose a bug in our code.
> I can't recall for certain, but I don't think this was a volumetric
> data set.
>
> The moral of the story is only that a DICOM reader ought to be
> prepared for almost anything and verify assumptions (such as "all
> rescales and slopes are equal") on the actual input.
>
> Regards,
> -Steve
>
>
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