Calculate the dose in voxels of PET image

PET image variable was exported from the DICOM browser as PET.mat 256x256x74. Its resized to 135x135x74 and rescaled using rescale slope and intercept values. The resized,rescaled PET image was convolved with 135x135x74kernel with voxel size 3x3x3mm^3 same as the image. Then the output PET shows the dose per voxel. I wan't select a volume and see the dose in that volume in the output image. Please suggest. I tried to convert output to .dcm files and use 3D slicer to view but 3D shows different values, may be there some problem

[Rik]

Are you sure you will get the dose that way? Don't you need to use the actual activity administered to convert the SUV to dose?

[Bhagya]

Rescaled PET image (Bq per voxel) was convolved with a DPK (Gy/Bq), so the result gives the dose.

[Rik]

And how exactly do you want to select a portion of the image? Because it sounds like you just need a viewer with a value monitor.

[Bhagya]

By registering the processed PET image with CT and selcting a ROI. The ROI could be 1cm^3, 2cm^3 etc.

Answer 1

[aditi bagora]

Hello Bhagya,

I understand that you want to determine the dose within a selected ROI from your PET image. It seems that your PET image already contains SUV values with a voxel size of 3x3x3 mm³. You are seeking a method to select an ROI and obtain the corresponding dosage value.

To calculate the dosage value for a volume, it is necessary to aggregate the values within a specific region. In the field of medical imaging, one commonly used approach is maximum intensity projection (MIP) applied to a specified thickness. Here, thickness refers to the depth of the volume.

To aggregate values for the desired thickness, you can follow these steps:

• Determine the number of slices required to apply MIP on the image. For example, if each slice of your PET image has a thickness of 2mm and you want to aggregate over a thickness of 10mm, you can apply maximum intensity projection to 5 slices.
• Iterate through all the slices and calculate MIP for the desired number of slices.
• Store the MIP data for your image.

To find the dosage for an ROI, you can follow the below steps:

• Draw the ROI on the image.
• Calculate the mean, minimum, and maximum values of all the SUV values within the ROI.
• The mean value will provide an approximate dosage value within the ROI for the given thickness.

It is important to note that the image is not a true 3D image but rather a stack of 2D images. Therefore, when determining the dosage of a dynamic volume, approximations need to be made due to the nature of the image representation. Also, when applying maximum intensity projection, it should be done on the desired number of slices rather than the entire volume.

Please refer to the following documentation to know more about on how to calculate maximum intensity projection:

How to calculate Maximum Intensity Projection (MIP) of a 3D image - MATLAB Answers - MATLAB Central (mathworks.com)

Hope this information helps!

Regards,

Aditi

[Bhagya]

ok thanks.