CT Image Analysis method

Please see the two photos above taken from a Cambridge International Physics Textbook
I have not a clue what is going on here.
we start with letters w x y z which are intensity levels and then after scanning we end up with the same values after dividing by 3
I am missing the point
Please help

Reply 1

moffs

Original post by swinroy

I am not completely sure if this is the answer you are looking for however,
I believe the point of the steps given is to show a simplified process that happens during the scanning process
In this process it is important to scan from multiple angles so the scanner/computer can figure out exactly where a certain density (tissue type) is in that slice
If it were to take one scan then -say from an arbitrary axis ,X- (as shown in step one by it's results of w+x,etc) it wouldn't be able to find out figure out where in a another axis ,y those two tissues/densities are found (the voxels could be organised w, x or x, w along this axis, X)
By taking multiple scans from different angles the computer can find the exact location in 3D space of specific voxels by finding where all the axis that that voxel lies on intersects
For example if we continue our original example, we can't know where in y w and X lie but if we take a second scan along y and we detect w then we know w lies in the intersection of the two axis along which we scanned (w and X)
So despite seeming useless here in reality we wouldn't know the exact location/order of the voxels without taking multiple scans

I hope this was the answer you were looking for and that I explained it in a way that made sense :smile:

(edited 5 months ago)

Reply 2

swinroy

Original post by moffs

I am not completely sure if this is the answer you are looking for however,
I believe the point of the steps given is to show a simplified process that happens during the scanning process
In this process it is important to scan from multiple angles so the scanner/computer can figure out exactly where a certain density (tissue type) is in that slice
If it were to take one scan then -say from an arbitrary axis ,X- (as shown in step one by it's results of w+x,etc) it wouldn't be able to find out figure out where in a another axis ,y those two tissues/densities are found (the voxels could be organised w, x or x, w along this axis, X)
By taking multiple scans from different angles the computer can find the exact location in 3D space of specific voxels by finding where all the axis that that voxel lies on intersects
For example if we continue our original example, we can't know where in y w and X lie but if we take a second scan along y and we detect w then we know w lies in the intersection of the two axis along which we scanned (w and X)
So despite seeming useless here in reality we wouldn't know the exact location/order of the voxels without taking multiple scans
I hope this was the answer you were looking for and that I explained it in a way that made sense :smile:

Hi Moffs:You have nailed this. Great explanation and I thank you. As an example suppose the following
North West Voxel 8
North East Voxel 2
South West Voxel 6
South East Voxel 4
Horizontal sum scan from the East give 10 in both North and South (8+2) and (6+4) = The same but no precise info found.

Imagery is all about CONTRAST. If there is no contrast there is no image. Two slabs of colour next to each other merge into one larger coloured object of the same colour so there is no detail.

Using other directions and taking a calculation will pinpoint the actual values.
I really do applaud the Author of this book as I have ofter marvelled at how Tomography works

Reply 3

moffs

Original post by swinroy

Hi Moffs:You have nailed this. Great explanation and I thank you. As an example suppose the following
North West Voxel 8
North East Voxel 2
South West Voxel 6
South East Voxel 4
Horizontal sum scan from the East give 10 in both North and South (8+2) and (6+4) = The same but no precise info found.
Imagery is all about CONTRAST. If there is no contrast there is no image. Two slabs of colour next to each other merge into one larger coloured object of the same colour so there is no detail.
Using other directions and taking a calculation will pinpoint the actual values.
I really do applaud the Author of this book as I have ofter marvelled at how Tomography works