Retrospective reconstruction in CT?

rekex · Joined: 05 Mar 2006 Posts: 19

I've done a fair amount of reading on this but i'm still not sure.
So if any of you are able to help me with this, it would be fantastic!

I know that in multi-slice CT, once we have performed a scan, we are able to retrospectively reconstruct images with different slice thickness from the existing raw data without re-scanning the patient. But if you want to reconstruct a THINNER SLICE...the thickness of this slice is limited by the detector configuration that was selected.

From what I understand, you cannot retro-reconstruct smaller than the smallest detector width which was employed.
Is that right?
Could someone please clarify this for me.

If the detector configuration was 2x2.5mm can you reconstruct a 1.5mm slice??

any responses will be much appreciated. cheers!

ScrmnWoody · Joined: 22 Aug 2007 Posts: 40 Location: Bellingham, WA

I'm a little confused by your question. Here's why. We have a Toshiba Aquillion 32 slice scanner. Almost everything we scan (if helical) is scanned at 0.5x0.3mm.

Most things are reconstructed prospectively at 3mm. But, if we needed to go back and retrospectively reconstruct something smaller, we could. And, occasionally the radiologist will simply ask us to send the volume to PACS and they can review the 0.5x0.3.

It doesn't get much smaller than that.
_________________
Chris

rekex · Joined: 05 Mar 2006 Posts: 19

@ ScrmnWoody
Thanks 4 ur response

but i suppose i should clarify my question. What i am asking is:
For example with the 4-channel Siemens helical scanner, the detector array is designed as follows:
5mm, 2.5mm, 1.5mm, 1mm, 1mm, 1,5mm, 2.5mm, 5mm

If the detector configuration of 4 x 5mm is used. So the 2.5mm, 1.5mm & 1mm elements are grouped to form 5mm width.

then in this case we are acquiring 4 slices of 5mm section width. and if we wished to retrospectively reconstruct thinner slices, say 2.5mm or 1.5mm would it be possible?

From what I have read it seems that we cannot reconstruct any smaller than the effective detector thickness. But if we wanted to reconstruct 10mm in this case it would be possible. Is this correct??

I hope I've explained my question clearly.

papa · Posted: Fri Oct 12, 2007 3:23 pm Post subject:

sometimes it depends on the scanner. so you've got the seimens 4-slice, and you're trying to take 5mm slices and change them to 2.5mm slices. you need to scan the images in the 2.5mm slices. the scanner can fuse them together into a biger slice, but you can only reconstruct down to your smaller slice. so if you want 2.5mm slices, you need to change your set-up to 4 X 2.5 fused to 5.0mm or 2 X 5.0.

the reason you can't reconstruct those 2.5, 1.5, and 1.0 mm slices is that the entire scan needs to be performed in the smallest slice. the scanner can't take just those images and reconstruct smaller, because you would have image gaps all over the place.

another question is if you are scanning helically or axial. the scanner does both. if you are scanning helically, to get a thinner slice, make sure the "narrow collimation" is checked to on. then you can reconstruct down to like .75mm thick.
_________________
Mr. Green

papa RT(R)(CT) Mr. Green

Delusional Radiology
never meddle in the affairs of a dragon, for you are crunchy, and taste good with ketchup

rekex · Joined: 05 Mar 2006 Posts: 19

@ papa

Thanks for the response. i think i understand now Smile