Trouble with DICOM values

Hi all,

Currently I am working with images from a Bioscan NanoSPECT/CT. When I use the 'readdicom(file)' command I get the dicom file loaded in MATLAB, but not with the original DICOM values, but with numbers from 0 to 2^16-1.

The images I load are SPECT with 0 to 1.5kBq emmision per voxel. But as soon as I load them in MATLAB I get 0 to 2^16-1.

In this way I can't analyse the values correctly (I'm working on dual-isotope crosstalk correction).

Can anyone help me getting my values back in kBq?

[mohd akmal masud]

you have to calibrate first your spect machine. because the pixel value is not represnt the kBq. It is a count.

Answer 1

[Walter Roberson]

You should be using the dicom RescaleSlope and RescaleIntercept. Convert the data to double, multiply by the slope, add the intercept.

Note: the properties are not present in all dicom files.

[mohd akmal masud]

Walter Roberson, I think spect dicom info does not mention the rescale slope and intercept.

And want to ask you,

What means convert the data to double?

[Walter Roberson]

double(YourMatrix)

The data is read in as an integer data type. If you do not convert it to floating point data type then you will get incorrect results when you rescale it.

[Walter Roberson]

I do not have a SPECT file to test with.

I found a CT dataset on the internet. The one I tested does have RescaleIntercept and RescaleSlope, but in that particular case the slope is 1 and the intercept is 0.

[Walter Roberson]

Have a look at DoseCalibrationFactor https://dicom.innolitics.com/ciods/pet-image/pet-image/00541322

Factor that was used to scale this image from counts/sec to Bq/ml using a dose calibrator. The value shall be one if no dose calibration was applied.