Get Dicom tags from dcm image

Hello.

I have a problem receiving Dicom tags. Iam working on a program for analyzing the image quality of a DICOM image.

One part will is to measure objects of known size in the image to see if the magnification is correct. To measure distance I need to convert pixel into real world measurements.

Therfore I need the pixel spacing value. As I have understood there are serveral names for the pixelspacing, depending on the treatment and imaging technique.

I tried to get the group and element tags of the pixel spacing value, but it won't work.

What I tried is the following:

[group, element] = dicomlookup('Filename');

I just get an empty 0x0 double in return.

What am I doing wrong?

Thanks in advance,

Mike