[Gate-users] Multi-isotope energy blurring

[Matthew Strugari]

Hi everyone,

Please disregard my previous questions. I made a mistake and failed to remove the listed energies for technetium when I copied my energy spectrum file for iodine.  : )

On a related note, could anyone share how to obtain only the primary unscattered radiation generated directly within the source distribution from the root output? The mask I applied for each source j was (sourceID == j and comptonPhantom == 0 and comptonCrystal == 0) but there still appears to be counts below the photopeak.

Positively,
Matthew



From: Gate-users <gate-users-bounces at lists.opengatecollaboration.org> on behalf of Matthew Strugari <matthew.strugari at dal.ca>
Date: Saturday, February 6, 2021 at 14:47
To: gate-users at lists.opengatecollaboration.org <gate-users at lists.opengatecollaboration.org>
Subject: [Gate-users] Multi-isotope energy blurring
Hi all,

I hope you are all having a relaxing weekend.

Does anyone have any experience with multi-isotope SPECT acquisitions with GATE? I seem to be having difficulties configuring the energy resolution properly in the digitizer. I have specified the energy resolution according to the inverse square law using the commands:
/gate/digitizer/Singles/insert blurring
/gate/digitizer/Singles/blurring/setLaw inverseSquare
/gate/digitizer/Singles/blurring/inverseSquare/setResolution 0.15
/gate/digitizer/Singles/blurring/inverseSquare/setEnergyOfReference 140.5 keV

In a simple test using two capillary tubes of Tc-99m/I-123, I would expect the energy resolution for I-123 to be around 14.1% centered at 159 keV according to the inverse square law. However, when I separate the multi-isotope data according to their respective sources, I am finding that the energy resolution for I-123 is much larger than the expected 14.1% and the peak appears to be pushed towards 140 keV which causes excessive counts to be excluded from the energy window (see attached energy spectra). I can confirm that the counts are still associated with I-123 since reconstruction of the primary window counts reveals only one line source in the dataset.

I have also tried specifying independent resolutions for each energy of reference, but this causes the photopeaks to become blurred multiple times. My next attempt would be replacing the inverse square law with the linear law but I am not convinced that this will introduce the expected functionality.

How can I specify the energy resolution so that blurring is automatically and correctly applied to each photopeak in the acquisition? Is this an issue with GATE due to undefined functionality for multiple photopeaks?

Regards,

Matthew



--

Matthew Strugari
Biomedical Translational Imaging Centre - BIOTIC,
5890 University Ave,
Halifax, NS, B3K 6R8
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