CT image representation

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CT image representation

Christoph Ammann
Hi,

I have a question about how CT images are defined/represented:

Let's say I take a 5 mm thick CT slice with a needle passing through it,
as shown in the left image.
The axial slice view may turn out like on the right, with line segment
P1-P2 representing the length of the needle appearing in the plane.
Also, the axial image will have some sagittal value like e.g. S = 100.

Is this sagittal  value taken in the front edge, middle, or back edge of
the slice?

What happens if the gantry is tilted such that the plane is oblique? Do
the corners of the image dictate the slice location? Again, are the
measurement for corner locations taken in the center of the voxel or at
one of the corners?


Thank you,

Christoph

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Re: CT image representation

lasso
Hi Christoph,

The reported slice position corresponds to the middle of the slice. You can
verify it by enabling "Slice intersections" display, turning off
interpolation for the volume display, and zoom in a lot in the slice viewer
window.

The slice positions might not be perfectly computed for volumes with oblique
slices (the slice intersection lines doesn't cross exactly the voxel
center), the issue is tracked in this item:
http://www.na-mic.org/Bug/view.php?id=757.

Andras

-----Original Message-----
From: [hidden email]
[mailto:[hidden email]] On Behalf Of Christoph Ammann
Sent: 2011-February-24 3:46 PM
To: [hidden email]
Subject: [slicer-devel] CT image representation

Hi,

I have a question about how CT images are defined/represented:

Let's say I take a 5 mm thick CT slice with a needle passing through it, as
shown in the left image.
The axial slice view may turn out like on the right, with line segment
P1-P2 representing the length of the needle appearing in the plane.
Also, the axial image will have some sagittal value like e.g. S = 100.

Is this sagittal  value taken in the front edge, middle, or back edge of the
slice?

What happens if the gantry is tilted such that the plane is oblique? Do the
corners of the image dictate the slice location? Again, are the measurement
for corner locations taken in the center of the voxel or at one of the
corners?


Thank you,

Christoph

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Re: CT image representation

pieper
Administrator
Hi Guys -

Andrey and I did some work on the oblique slice support - I added a note
to bug 757 because I think it's fixed now - if so we could close it.

Also, Christoph, slicer doesn't support gantry titled CT volumes (i.e.
where the volume is sheared, not just rotated).  This is because itk
does not support them.

-Steve

On 02/24/2011 05:00 PM, Andras Lasso wrote:

> Hi Christoph,
>
> The reported slice position corresponds to the middle of the slice. You can
> verify it by enabling "Slice intersections" display, turning off
> interpolation for the volume display, and zoom in a lot in the slice viewer
> window.
>
> The slice positions might not be perfectly computed for volumes with oblique
> slices (the slice intersection lines doesn't cross exactly the voxel
> center), the issue is tracked in this item:
> http://www.na-mic.org/Bug/view.php?id=757.
>
> Andras
>
> -----Original Message-----
> From: [hidden email]
> [mailto:[hidden email]] On Behalf Of Christoph Ammann
> Sent: 2011-February-24 3:46 PM
> To: [hidden email]
> Subject: [slicer-devel] CT image representation
>
> Hi,
>
> I have a question about how CT images are defined/represented:
>
> Let's say I take a 5 mm thick CT slice with a needle passing through it, as
> shown in the left image.
> The axial slice view may turn out like on the right, with line segment
> P1-P2 representing the length of the needle appearing in the plane.
> Also, the axial image will have some sagittal value like e.g. S = 100.
>
> Is this sagittal  value taken in the front edge, middle, or back edge of the
> slice?
>
> What happens if the gantry is tilted such that the plane is oblique? Do the
> corners of the image dictate the slice location? Again, are the measurement
> for corner locations taken in the center of the voxel or at one of the
> corners?
>
>
> Thank you,
>
> Christoph
>
> _______________________________________________
> slicer-devel mailing list
> [hidden email]
> http://massmail.spl.harvard.edu/mailman/listinfo/slicer-devel
> To unsubscribe: send email to [hidden email] with unsubscribe as the subject
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Re: CT image representation

Christoph Ammann
Thanks to all of you for the information.

Christoph

Steve Pieper wrote:

> Hi Guys -
>
> Andrey and I did some work on the oblique slice support - I added a
> note to bug 757 because I think it's fixed now - if so we could close it.
>
> Also, Christoph, slicer doesn't support gantry titled CT volumes (i.e.
> where the volume is sheared, not just rotated).  This is because itk
> does not support them.
>
> -Steve
>
> On 02/24/2011 05:00 PM, Andras Lasso wrote:
>> Hi Christoph,
>>
>> The reported slice position corresponds to the middle of the slice.
>> You can
>> verify it by enabling "Slice intersections" display, turning off
>> interpolation for the volume display, and zoom in a lot in the slice
>> viewer
>> window.
>>
>> The slice positions might not be perfectly computed for volumes with
>> oblique
>> slices (the slice intersection lines doesn't cross exactly the voxel
>> center), the issue is tracked in this item:
>> http://www.na-mic.org/Bug/view.php?id=757.
>>
>> Andras
>>
>> -----Original Message-----
>> From: [hidden email]
>> [mailto:[hidden email]] On Behalf Of Christoph
>> Ammann
>> Sent: 2011-February-24 3:46 PM
>> To: [hidden email]
>> Subject: [slicer-devel] CT image representation
>>
>> Hi,
>>
>> I have a question about how CT images are defined/represented:
>>
>> Let's say I take a 5 mm thick CT slice with a needle passing through
>> it, as
>> shown in the left image.
>> The axial slice view may turn out like on the right, with line segment
>> P1-P2 representing the length of the needle appearing in the plane.
>> Also, the axial image will have some sagittal value like e.g. S = 100.
>>
>> Is this sagittal  value taken in the front edge, middle, or back edge
>> of the
>> slice?
>>
>> What happens if the gantry is tilted such that the plane is oblique?
>> Do the
>> corners of the image dictate the slice location? Again, are the
>> measurement
>> for corner locations taken in the center of the voxel or at one of the
>> corners?
>>
>>
>> Thank you,
>>
>> Christoph
>>
>> _______________________________________________
>> slicer-devel mailing list
>> [hidden email]
>> http://massmail.spl.harvard.edu/mailman/listinfo/slicer-devel
>> To unsubscribe: send email to
>> [hidden email] with unsubscribe as the
>> subject

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