University College London Hospitals NHS Foundation Trust, United Kingdom.
Colchester Hospital University NHS Foundation Trust, United Kingdom.
Phys Med. 2019 Mar;59:158-162. doi: 10.1016/j.ejmp.2019.03.006. Epub 2019 Mar 11.
A PET/CT scan of a uniformly filled Ga phantom resulted in an unexpectedly low SUV of 0.88. A potential contributing cause of underestimation of Ga SUV is overestimation of Ga activity in the Radionuclide Calibrator associated with the PET/CT scanner. To investigate this, a Radionuclide Calibrator cross-calibration exercise was performed.
A source of Ga was measured in 5 Capintec CRC-55tR calibrators using the pre-set Ga calibrator factor of 416, and a Veenstra VDC-505 calibrator using a factor recommended by the manufacturer. The source was then measured in an externally located Fidelis Secondary Standard Radionuclide Calibrator. Manual adjustments were made to the Capintec calibrator factors to match the decay corrected Fidelis measurement, followed by a repeat PET/CT scan of a uniform Ga phantom.
The cross-calibration results showed that the 5 Capintec calibrators systematically overestimated Ga activity by 7.8-9.4% (mean 8.5%) compared to the Fidelis. The calibrator factors were adjusted to 456-464 to match the Fidelis measurement, and the repeat phantom scan resulted in a SUV of 0.97, within the local tolerance of 1.00 ± 5%. The result for the Veenstra calibrator was within the tolerance of ±5%.
Underestimation of Ga SUV was primarily caused by overestimation of Ga activity using the pre-set calibrator factor setting on a Capintec CRC-55tR. Improvement in quantification accuracy was achieved by adjusting the Ga calibrator factor based upon a cross-calibration exercise. We recommend SUV checks using a uniform phantom and regular calibrator cross-calibration exercises for all isotopes used for quantitative PET/CT imaging.
对均匀充满镓的 Ga 体模进行 PET/CT 扫描，结果发现 SUV 值异常低，为 0.88。造成 Ga SUV 值低估的一个潜在原因是与 PET/CT 扫描仪相关的放射性核素校准器高估了 Ga 活度。为了研究这个问题，进行了放射性核素校准器的交叉校准。
使用预设的 Ga 校准器系数 416 对 5 个 Capintec CRC-55tR 校准器中的 Ga 源进行测量，并使用制造商推荐的系数对 Veenstra VDC-505 校准器中的 Ga 源进行测量。然后，在外部的 Fidelis 次级标准放射性核素校准器中测量该源。对 Capintec 校准器系数进行手动调整，以匹配经过衰变校正的 Fidelis 测量值，然后重复对均匀 Ga 体模进行 PET/CT 扫描。
交叉校准结果表明，与 Fidelis 相比，5 个 Capintec 校准器系统地高估了 Ga 活度 7.8-9.4%（平均 8.5%）。将校准器系数调整为 456-464 以匹配 Fidelis 测量值，重复体模扫描得到的 SUV 值为 0.97，在本地 1.00±5%的公差范围内。Veenstra 校准器的结果在±5%的公差范围内。
Ga SUV 值的低估主要是由于在 Capintec CRC-55tR 上使用预设的校准器系数设置高估了 Ga 活度。通过基于交叉校准进行 Ga 校准器系数调整，提高了定量准确性。我们建议对所有用于定量 PET/CT 成像的同位素使用均匀体模和定期的校准器交叉校准来检查 SUV 值。
