[Insight-users] MI registration update

[Lydia Ng]

Hi John,

> I was wondering if anyone had suggestions
> for trying to tighten the uncertainty in the rotation, perhaps =
increasing
> the rotation scale parameter?

Some optimizers allow you to scale between the parameters. E.g.

  typedef OptimizerType::ScalesType       OptimizerScalesType;
  OptimizerScalesType optimizerScales( =
transform->GetNumberOfParameters() );

  /* set optimizerScales here */

  optimizer->SetScales( optimizerScales );


Are you scaling you doing any scaling now?

One experiment you could try is to set hold the scaling for the rotation
parameters fixed and vary the translation parameters.
The smaller the translation parameter scales the "tighter" the allowed
rotation.=20

- Lydia


> -----Original Message-----
> From: Dill, John [mailto:john-dill at uiowa . edu]
> Sent: Monday, December 01, 2003 12:20 PM
> To: 'insight-users at itk . org'
> Subject: [Insight-users] MI registration update
>=20
> I have finished looking at the results of an experiment I did for
> observing
> the effect of the sample size on the mi search algorithm with sample =
size
> of
> 50, 100, 250, 500, 750, 1000.  It was done over nine patients and here =
are
> some things I have questions about.
>=20
> Out of the 18 registrations (ap and lat), there were 7 that were not =
good.
> About half of these I think I can account for by claiming data faults,
> where
> a significant portion of the DRR was missing and hence was biased by
> mis-information in the drr.  The others are not particularly clear why =
the
> registrations failed, perhaps artifacts from the treatment table are =
the
> cause.  All of my lateral registrations were good (except for the one
> which
> had half the drr missing).  I think I can correct those bad =
registrations
> with a proper window.
>=20
> In the registrations that worked, the sample sizes of 250, 500, 750, =
and
> 1000 all converged to the same x and y translation within about +/-0.2
> pixels, but what differed was the rotation component, which varied =
about
> +/-3 degrees in the extreme cases.  I found that out of those 4 sample
> sizes, the registration I preferred (not always though) typically had =
a
> rotation component closer to 0.  I was wondering if anyone had =
suggestions
> for trying to tighten the uncertainty in the rotation, perhaps =
increasing
> the rotation scale parameter?  I saw a tightening of the rotation
> variability when I increases the sample size, but not enough to be =
within
> say +/- 0.5 degree if possible, but could live with 1.  I can not have =
a
> +/-
> 3 degree uncertainty for sure.
>=20
> Thanks,
> John
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