An attenuation method for reducing count rate losses in preclinical PET during intratherapeutic imaging
Mellhammar, Emma LU ; Dahlbom, Magnus ; Evans-Axelsson, Susan LU
; Axelsson, Johan
; Tran, Thuy
LU
and Strand, Sven-Erik
LU
(2017)
2016 IEEE Nuclear Science Symposium, Medical Imaging Conference and Room-Temperature Semiconductor Detector Workshop, NSS/MIC/RTSD 2016
2017-January.
- Abstract
In pre-clinical imaging, tumor response to radionuclide therapy can be monitored with PET imaging. Radionuclides used for therapy such as 177Lu emit a significant amount of low energy photons. These photons may have an energy high enough to penetrate the imaged object and are the prone to be detected. Although these phtons are likely to be rejected electronically, they add dead-time to the system since they need to be processed by the electronics. This is a problem in high-sensitivity pre-clinical PET system with a low number of readout channels, such as the Genisys G8 investigated in this work. The low energy gammas may also affect image quality due to increased probability of pulse pile-up. The use of high-attenuating... (More)
In pre-clinical imaging, tumor response to radionuclide therapy can be monitored with PET imaging. Radionuclides used for therapy such as 177Lu emit a significant amount of low energy photons. These photons may have an energy high enough to penetrate the imaged object and are the prone to be detected. Although these phtons are likely to be rejected electronically, they add dead-time to the system since they need to be processed by the electronics. This is a problem in high-sensitivity pre-clinical PET system with a low number of readout channels, such as the Genisys G8 investigated in this work. The low energy gammas may also affect image quality due to increased probability of pulse pile-up. The use of high-attenuating shields designed to absorb most of the low energy photons emitted from the therapeutic radionuclide were investigated. Cylindrical led shields were constructed with thicknesses between 1 and 3 mm. A 3mm thick cylindrical shield was also constructed out of Rose metal (50% Bi, 28% Pb, and 22% Sn). The diameter of the shield was wide enough to accommodate a NEMA IQ phantom and a mouse. The attenuation of the shields for annihilation radiation was measured with a 22Na point source placed at the center of the FOV. Measurements of the coincidence rate were performed with the lead shields in place. At a of thicknesses of 1 and 3mm, the coincidence rate was reduced by a factor or 0.70 and 0.40, respectively. To study the effect of the presence of a background of low energy gammas on the coincidence count rate and the efficacy of the lead shields, 177Lu was added to a 1 cm diameter hollow sphere. In the presence of 100 MBq of 177Lu, the coincidence count rate was reduced by a factor 0.20 due to the detector dead-time. Although the count rate was reduced by a factor of 0.40 with the 3mm shield around the source, the dead-time effects due to the 177Lu background were less than 7%. 18F imaging of a NEMA phantom and a tumor bearing mouse showed dramatic image distortions in the presence of the 177Lu background. When imaging of with the 3mm shield in place, the image distortions were eliminated and were comparable in to the images acquired without the background activity.
(Less)
- author
- Mellhammar, Emma
LU
; Dahlbom, Magnus
; Evans-Axelsson, Susan
LU
; Axelsson, Johan
; Tran, Thuy
LU
and Strand, Sven-Erik
LU
- organization
- publishing date
- 2017-10-16
- type
- Chapter in Book/Report/Conference proceeding
- publication status
- published
- subject
- host publication
- 2016 IEEE Nuclear Science Symposium, Medical Imaging Conference and Room-Temperature Semiconductor Detector Workshop, NSS/MIC/RTSD 2016
- volume
- 2017-January
- article number
- 8069462
- publisher
- IEEE - Institute of Electrical and Electronics Engineers Inc.
- conference name
- 2016 IEEE Nuclear Science Symposium, Medical Imaging Conference and Room-Temperature Semiconductor Detector Workshop, NSS/MIC/RTSD 2016
- conference location
- Strasbourg, France
- conference dates
- 2016-10-29 - 2016-11-06
- external identifiers
-
- scopus:85041818922
- ISBN
- 9781509016426
- DOI
- 10.1109/NSSMIC.2016.8069462
- language
- English
- LU publication?
- yes
- id
- 55f834a5-c583-4ea6-9025-918040452f0a
- date added to LUP
- 2018-02-23 11:56:20
- date last changed
- 2022-03-09 17:11:10
@inproceedings{55f834a5-c583-4ea6-9025-918040452f0a,
abstract = {{<p>In pre-clinical imaging, tumor response to radionuclide therapy can be monitored with PET imaging. Radionuclides used for therapy such as <sup>177</sup>Lu emit a significant amount of low energy photons. These photons may have an energy high enough to penetrate the imaged object and are the prone to be detected. Although these phtons are likely to be rejected electronically, they add dead-time to the system since they need to be processed by the electronics. This is a problem in high-sensitivity pre-clinical PET system with a low number of readout channels, such as the Genisys G8 investigated in this work. The low energy gammas may also affect image quality due to increased probability of pulse pile-up. The use of high-attenuating shields designed to absorb most of the low energy photons emitted from the therapeutic radionuclide were investigated. Cylindrical led shields were constructed with thicknesses between 1 and 3 mm. A 3mm thick cylindrical shield was also constructed out of Rose metal (50% Bi, 28% Pb, and 22% Sn). The diameter of the shield was wide enough to accommodate a NEMA IQ phantom and a mouse. The attenuation of the shields for annihilation radiation was measured with a 22Na point source placed at the center of the FOV. Measurements of the coincidence rate were performed with the lead shields in place. At a of thicknesses of 1 and 3mm, the coincidence rate was reduced by a factor or 0.70 and 0.40, respectively. To study the effect of the presence of a background of low energy gammas on the coincidence count rate and the efficacy of the lead shields, <sup>177</sup>Lu was added to a 1 cm diameter hollow sphere. In the presence of 100 MBq of <sup>177</sup>Lu, the coincidence count rate was reduced by a factor 0.20 due to the detector dead-time. Although the count rate was reduced by a factor of 0.40 with the 3mm shield around the source, the dead-time effects due to the <sup>177</sup>Lu background were less than 7%. 18F imaging of a NEMA phantom and a tumor bearing mouse showed dramatic image distortions in the presence of the <sup>177</sup>Lu background. When imaging of with the 3mm shield in place, the image distortions were eliminated and were comparable in to the images acquired without the background activity.</p>}},
author = {{Mellhammar, Emma and Dahlbom, Magnus and Evans-Axelsson, Susan and Axelsson, Johan and Tran, Thuy and Strand, Sven-Erik}},
booktitle = {{2016 IEEE Nuclear Science Symposium, Medical Imaging Conference and Room-Temperature Semiconductor Detector Workshop, NSS/MIC/RTSD 2016}},
isbn = {{9781509016426}},
language = {{eng}},
month = {{10}},
publisher = {{IEEE - Institute of Electrical and Electronics Engineers Inc.}},
title = {{An attenuation method for reducing count rate losses in preclinical PET during intratherapeutic imaging}},
url = {{http://dx.doi.org/10.1109/NSSMIC.2016.8069462}},
doi = {{10.1109/NSSMIC.2016.8069462}},
volume = {{2017-January}},
year = {{2017}},
}