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Attenuation Effects of MR Headphones During Brain PET/MR Studies
Aaron Ferguson1, Jonathan McConathy2, Yi Su2
1Department of Medical Imaging and Radiation Therapeutics, Saint Louis University, St. Louis, Missouri; and laforestr@mir.wustl.edu aaroneferguson@yahoo.com.
Unlabelled:
PET/MR offers potential advantages over PET/CT that are currently under investigation. One of the challenges of PET/MR is attenuation correction, as there is no simple correlation between MR signal intensity and the attenuation of 511-keV photons detected in PET. Currently, dedicated MR sequences are used to segment voxels into categories that are then assigned a predetermined attenuation coefficient. MR hardware such as the imaging table, coils, and headphones are also sources of attenuation. The purpose of this study was to evaluate the effect of MR-compatible headphones on average activity concentration measured with PET/MR. We also present a practical approach to correct for the attenuation effect of headphones using a CT-derived attenuation map.
Methods:
Phantom studies were performed using a 3-L cylindric phantom containing 55 MBq of (18)F-FDG and water. Images were acquired on a PET/MR device in 2 settings-one with the PET/MR headphones on and one with the headphones off. Phantom images were analyzed to compare activity concentration with headphones on and off. A high-resolution CT and (57)Co transmission scan was obtained to construct a PET attenuation map of the headphones. The resulting attenuation map was registered to the phantom data to evaluate the ability to correct for headphone attenuation. One human subject was scanned to evaluate the clinical impact of headphone attenuation and the accuracy of the proposed correction.
Results:
Activity concentrations measured in the phantom were reduced by as much as 13.2% with headphones on compared with headphones off. Using the modified attenuation maps that account for attenuation from the headphones resulted in a decrease in the headphone attenuation effect from a maximum of 13.2% to 1.9%. Comparable attenuation effects were observed in the human brain and were similarly reduced with correction using the modified attenuation maps.
Conclusion:
MR-safe headphones were a source of attenuation on our PET/MR phantom and human studies. Attenuation effects of headphones should be considered and can be corrected during quantitative brain PET/MR studies.
Insights
MR-safe headphones cause attenuation in PET/MR imaging, reducing activity concentration. A CT-derived map corrects this, minimizing the effect from 13.2% to 1.9% in phantom and human studies.
Area of Science:
- Medical Imaging
- Nuclear Medicine
- Magnetic Resonance Imaging
Background:
- Positron Emission Tomography/Magnetic Resonance (PET/MR) imaging offers advantages over PET/CT.
- Attenuation correction in PET/MR is challenging due to the lack of direct correlation between MR signal and photon attenuation.
- MR hardware, including headphones, can introduce significant attenuation artifacts.
Purpose of the Study:
- To evaluate the impact of MR-compatible headphones on activity concentration measurements in PET/MR.
- To develop and assess a practical method for correcting headphone-induced attenuation using CT-derived maps.
Main Methods:
- Phantom studies using an (18)F-FDG filled phantom were conducted with and without MR-safe headphones.
- Activity concentrations were compared between the two settings.
- A CT-derived attenuation map of the headphones was created and applied to phantom and human brain data for correction.
Main Results:
- Headphones reduced measured activity concentrations by up to 13.2% in phantom studies.
- The proposed correction method reduced the maximum attenuation effect to 1.9%.
- Similar attenuation effects and successful correction were observed in human brain imaging.
Conclusions:
- MR-safe headphones are a notable source of attenuation in quantitative PET/MR brain imaging.
- A CT-based attenuation correction approach effectively mitigates headphone-induced artifacts.
- Accurate attenuation correction is crucial for reliable quantitative PET/MR studies.
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