how to convert coordinates in pixel to mm?

 i have x,y,z coordinates of dicom in pixel.i have to convert them into mm?

Answer 1

[KSSV]

See this link for similar question and answer by Walter Roberson:

https://in.mathworks.com/matlabcentral/answers/215612-how-can-i-convert-pixels-to-mm-for-a-specific-dicom-image

[lovey chatha]

i need way to find out way to convert pixel coordinates into mm?

[KSSV]

It is mentioned in the link...what problem you facing?

Answer 2

[Image Analyst]

I know you've already accepted an answer but I just thought I'd include my code to do spatial calibration, if you still need it.

[lovey chatha]

I am not able to understand this code properly can u be specific to my question?

[Image Analyst]

Basically you have to measure something of a known length and compute the calibration scale factor in mm per pixel. Then whenever you measure any distance in pixels you multiply by the mm/pixel factor, the pixel units cancel out, and you're left with a length in mm. Doesn't that make sense? You have pixels, you want mm, so what do you do? You multiply by a factor with units of mm per pixel, right?

Or simply look in the metadata of the image and take the factor from there, if it's in there.

[tom coder]

Image Analyst,

I am confirming the pixel2mm factors for EPID of a linac. The phantom chosen is made of 3 BB with known diamter. Successfuly detect all 9 circles using imfindcircles in 3 dicom images but failed on the 4th (SID80, attached). The original dicom image is also zip-attached.

Any efficient algorithm to detect center of circle at subpixel level?

Thanks.

[Image Analyst]

Tom Coder:

Try thresholding:

binaryImage = grayImage < 3300;

See attached demo.