Re: Minimum thickness of CT/MRI data

From: Bob Yancey (
Date: Thu Jul 10 1997 - 23:00:57 EEST

On 11 Jul 1997, J. Hur wrote:

>Hi, RP'ers
>I'm working and researching on the medical RP model using CT or MRI data.
>Generally, we take a set of CT/MRI slice data with a thickness of 5 mm in
>our medical center.
>I wonder if the number of CT/MRI data is enough to reconstruct the surface
>model or STL data.
>You know, because of the maximum permissible exposure to radiation or
>something, we cannot take a thinner slice of MRI/CT data for a patient.
>I need your advice or experiences of surface/STL reconstruction job using
>MRI/CT data.
>Thanks in advance.
>Junghoon Hur
>Ph.D Candidate
>CAD Lab. Dept. of Mechanical Design & Production Engineering
>Seoul National University, San 56-1
>Shilimdong, Kwanakgu,
>Seoul, 151-742, Korea

Our experience has been that with smoothly varying objects (such as with
the human anatomy), the accuracy of the surface/STL file is more dependent
on the slice spacing rather than the slice thickness. A CT data set with a
5 mm slice thickness and a slice spacing of 1 mm is as good or better than
a data set with 1 mm slice thickness and 1 mm slice spacing. The reason
that it might be better is that your will have a better signal-to-noise
ratio in the image with a 5 mm slice thickness versus a 1 mm slice
thickness. This may not solve your limitations with radiation exposure,
however, since both data sets will contain the same number of slices and
therefore the same radiation exposure to the patient. In general, the
accuracy of your surface/STL model will only be as good as the accuracy of
your data. If your slices are spaced every 5 mm, then your surface/STL
model will only be acccurate to within 5 mm in the slice direction.

Bob Yancey

Advanced Research and Appplications Corporation (ARACOR)
514 E. Dayton-Yellow Springs Road
Fairborn, OH 45324

(937) 879-4200
(937) 879-3934 (FAX)

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