Tran-Gia Johannes, Denis-Bacelar Ana M, Ferreira Kelley M, Robinson Andrew P, Bobin Christophe, Bonney Lara M, Calvert Nicholas, Collins Sean M, Fenwick Andrew J, Finocchiaro Domenico, Fioroni Federica, Giannopoulou Katerina, Grassi Elisa, Heetun Warda, Jewitt Stephanie J, Kotzasarlidou Maria, Ljungberg Michael, Lourenço Valérie, McGowan Daniel R, Mewburn-Crook Jamie, Sabot Benoit, Scuffham James, Sjögreen Gleisner Katarina, Solc Jaroslav, Thiam Cheick, Tipping Jill, Wevrett Jill, Lassmann Michael
Department of Nuclear Medicine, University Hospital Würzburg, Oberdürrbacher Str. 6, 97080, Würzburg, Germany.
National Physical Laboratory, Hampton Road, Teddington, UK.
EJNMMI Phys. 2023 Nov 23;10(1):73. doi: 10.1186/s40658-023-00582-3.
Commissioning, calibration, and quality control procedures for nuclear medicine imaging systems are typically performed using hollow containers filled with radionuclide solutions. This leads to multiple sources of uncertainty, many of which can be overcome by using traceable, sealed, long-lived surrogate sources containing a radionuclide of comparable energies and emission probabilities. This study presents the results of a quantitative SPECT/CT imaging comparison exercise performed within the MRTDosimetry consortium to assess the feasibility of using Ba as a surrogate for I imaging.
Two sets of four traceable Ba sources were produced at two National Metrology Institutes and encapsulated in 3D-printed cylinders (volume range 1.68-107.4 mL). Corresponding hollow cylinders to be filled with liquid I and a mounting baseplate for repeatable positioning within a Jaszczak phantom were also produced. A quantitative SPECT/CT imaging comparison exercise was conducted between seven members of the consortium (eight SPECT/CT systems from two major vendors) based on a standardised protocol. Each site had to perform three measurements with the two sets of Ba sources and liquid I.
As anticipated, the I pseudo-image calibration factors (cps/MBq) were higher than those for Ba for all reconstructions and systems. A site-specific cross-calibration reduced the performance differences between both radionuclides with respect to a cross-calibration based on the ratio of emission probabilities from a median of 12-1.5%. The site-specific cross-calibration method also showed agreement between Ba and I for all cylinder volumes, which highlights the potential use of Ba sources to calculate recovery coefficients for partial volume correction.
This comparison exercise demonstrated that traceable solid Ba sources can be used as surrogate for liquid I imaging. The use of solid surrogate sources could solve the radiation protection problem inherent in the preparation of phantoms with I liquid activity solutions as well as reduce the measurement uncertainties in the activity. This is particularly relevant for stability measurements, which have to be carried out at regular intervals.
核医学成像系统的调试、校准和质量控制程序通常使用装有放射性核素溶液的空心容器来执行。这导致了多个不确定性来源，其中许多可以通过使用含有能量和发射概率相当的放射性核素的可溯源、密封、长寿命替代源来克服。本研究展示了在MRTDosimetry联盟内进行的定量SPECT/CT成像比较实验的结果，以评估使用钡作为碘成像替代物的可行性。
在两个国家计量机构制作了两组四个可溯源的钡源，并封装在3D打印的圆柱体中（体积范围为1.68 - 107.4 mL）。还制作了相应的用于填充液态碘的空心圆柱体以及用于在Jaszczak体模内进行可重复定位的安装底板。基于标准化方案，联盟的七名成员（来自两个主要供应商的八个SPECT/CT系统）之间进行了定量SPECT/CT成像比较实验。每个站点必须使用两组钡源和液态碘进行三次测量。
正如预期的那样，对于所有重建和系统，碘伪图像校准因子（计数每秒/兆贝可）都高于钡的校准因子。特定站点的交叉校准相对于基于发射概率中位数之比的交叉校准，将两种放射性核素之间的性能差异从12%降低到了1.5%。特定站点的交叉校准方法还表明，对于所有圆柱体体积，钡和碘之间具有一致性，这突出了使用钡源计算部分容积校正恢复系数的潜在用途。
本次比较实验表明，可溯源的固态钡源可作为液态碘成像的替代物。使用固态替代源可以解决使用液态碘活度溶液制备体模时固有的辐射防护问题，同时减少活度测量中的不确定性。这对于必须定期进行的稳定性测量尤为重要。
