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Feasibility of 177Lu activity quantification using a small portable CZT-based gamma-camera

Roth, Daniel LU orcid ; Larsson, Erik ; Strand, Joanna LU ; Ljungberg, Michael LU and Sjögreen Gleisner, Katarina LU (2024) In EJNMMI Physics 11(1).
Abstract

Background: In image processing for activity quantification, the end goal is to produce a metric that is independent of the measurement geometry. Photon attenuation needs to be accounted for and can be accomplished utilizing spectral information, avoiding the need of additional image acquisitions. The aim of this work is to investigate the feasibility of 177Lu activity quantification with a small CZT-based hand-held gamma-camera, using such an attenuation correction method. Methods: A previously presented dual photopeak method, based on the differential attenuation for two photon energies, is adapted for the three photopeaks at 55 keV, 113 keV, and 208 keV for 177Lu. The measurement model describes the count rates... (More)

Background: In image processing for activity quantification, the end goal is to produce a metric that is independent of the measurement geometry. Photon attenuation needs to be accounted for and can be accomplished utilizing spectral information, avoiding the need of additional image acquisitions. The aim of this work is to investigate the feasibility of 177Lu activity quantification with a small CZT-based hand-held gamma-camera, using such an attenuation correction method. Methods: A previously presented dual photopeak method, based on the differential attenuation for two photon energies, is adapted for the three photopeaks at 55 keV, 113 keV, and 208 keV for 177Lu. The measurement model describes the count rates in each energy window as a function of source depth and activity, accounting for distance-dependent system sensitivity, attenuation, and build-up. Parameter values are estimated from characterizing measurements, and the source depth and activity are obtained by minimizing the difference between measured and modelled count rates. The method is applied and evaluated in phantom measurements, in a clinical setting for superficial lesions in two patients, and in a pre-clinical setting for one human tumour xenograft. Evaluation is made for a LEHR and an MEGP collimator. Results: For phantom measurements at clinically relevant depths, the average (and standard deviation) in activity errors are 17% ± 9.6% (LEHR) and 2.9% ± 3.6% (MEGP). For patient measurements, deviations from activity estimates from planar images from a full-sized gamma-camera are 0% ± 21% (LEHR) and 16% ± 18% (MEGP). For mouse measurements, average deviations of − 16% (LEHR) and − 6% (MEGP) are obtained when compared to a small-animal SPECT/CT system. The MEGP collimator appears to be better suited for activity quantification, yielding a smaller variability in activity estimates, whereas the LEHR results are more severely affected by septal penetration. Conclusions: Activity quantification for 177Lu using the hand-held camera is found to be feasible. The readily available nature of the hand-held camera may enable more frequent activity quantification in e.g., superficial structures in patients or in the pre-clinical setting.

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author
; ; ; and
organization
publishing date
type
Contribution to journal
publication status
published
subject
keywords
Lu, Activity quantification, CZT, Hand-held gamma-camera, Molecular imaging
in
EJNMMI Physics
volume
11
issue
1
article number
2
publisher
Springer
external identifiers
  • pmid:38167976
  • scopus:85181247910
ISSN
2197-7364
DOI
10.1186/s40658-023-00602-2
project
Metoder för strålningsdosimetri inom preklinisk radionuklidterapi
language
English
LU publication?
yes
id
63fad1ae-ade9-41f6-b571-ab172a1ed88b
date added to LUP
2024-02-12 10:23:45
date last changed
2024-04-14 01:52:52
@article{63fad1ae-ade9-41f6-b571-ab172a1ed88b,
  abstract     = {{<p>Background: In image processing for activity quantification, the end goal is to produce a metric that is independent of the measurement geometry. Photon attenuation needs to be accounted for and can be accomplished utilizing spectral information, avoiding the need of additional image acquisitions. The aim of this work is to investigate the feasibility of <sup>177</sup>Lu activity quantification with a small CZT-based hand-held gamma-camera, using such an attenuation correction method. Methods: A previously presented dual photopeak method, based on the differential attenuation for two photon energies, is adapted for the three photopeaks at 55 keV, 113 keV, and 208 keV for <sup>177</sup>Lu. The measurement model describes the count rates in each energy window as a function of source depth and activity, accounting for distance-dependent system sensitivity, attenuation, and build-up. Parameter values are estimated from characterizing measurements, and the source depth and activity are obtained by minimizing the difference between measured and modelled count rates. The method is applied and evaluated in phantom measurements, in a clinical setting for superficial lesions in two patients, and in a pre-clinical setting for one human tumour xenograft. Evaluation is made for a LEHR and an MEGP collimator. Results: For phantom measurements at clinically relevant depths, the average (and standard deviation) in activity errors are 17% ± 9.6% (LEHR) and 2.9% ± 3.6% (MEGP). For patient measurements, deviations from activity estimates from planar images from a full-sized gamma-camera are 0% ± 21% (LEHR) and 16% ± 18% (MEGP). For mouse measurements, average deviations of − 16% (LEHR) and − 6% (MEGP) are obtained when compared to a small-animal SPECT/CT system. The MEGP collimator appears to be better suited for activity quantification, yielding a smaller variability in activity estimates, whereas the LEHR results are more severely affected by septal penetration. Conclusions: Activity quantification for <sup>177</sup>Lu using the hand-held camera is found to be feasible. The readily available nature of the hand-held camera may enable more frequent activity quantification in e.g., superficial structures in patients or in the pre-clinical setting.</p>}},
  author       = {{Roth, Daniel and Larsson, Erik and Strand, Joanna and Ljungberg, Michael and Sjögreen Gleisner, Katarina}},
  issn         = {{2197-7364}},
  keywords     = {{Lu; Activity quantification; CZT; Hand-held gamma-camera; Molecular imaging}},
  language     = {{eng}},
  number       = {{1}},
  publisher    = {{Springer}},
  series       = {{EJNMMI Physics}},
  title        = {{Feasibility of <sup>177</sup>Lu activity quantification using a small portable CZT-based gamma-camera}},
  url          = {{http://dx.doi.org/10.1186/s40658-023-00602-2}},
  doi          = {{10.1186/s40658-023-00602-2}},
  volume       = {{11}},
  year         = {{2024}},
}