Shapiro Boris, Zanin Dolores E A, Schipper Roman
Department of Nuclear Medicine, Bronovo Hospital, The Hague, The Netherlands.
Nucl Med Commun. 2014 Apr;35(4):382-90. doi: 10.1097/MNM.0000000000000071.
An easy-to-implement scintigraphic method that enables the assay of thyroid iodine uptake with improved accuracy and without the use of a reference source was developed with an aim to avoid unnecessary high radiation burden to patients undergoing (131)I treatment for benign thyroid disease.
Dual-energy (123)I planar imaging involving simultaneous recording of both the primary (159 keV) and scatter (130 keV) frames was followed by generation of subtraction 'scatter-free' images. A uniform cutoff level of 15% was chosen to delineate the functional thyroid tissue with the help of isocontour regions of interest, which in turn enabled quantitation of the scatter-free thyroid counts. The ratio of the total counts being recorded in each of the above frames, the 'primary-to-Compton' ratio, was determined and compared with the uniform absorption-free ratio ascribed to all of the thyroid images. This enabled determination of the upscaling factor needed to restore the scatter-free counts to their unmoderated level. The corrected count content was subsequently converted to the iodine dose accumulated by the thyroid with the help of the camera-specific net detection efficiency. As a result, the true uptake value could be determined without the need to image a reference source or phantom.
Clinical evaluation of the proposed reference-free method was carried out by reviewing the 24-h uptake values obtained for the 32 patients suffering from Graves' disease, multinodular struma, or autonomous nodule. A comparison with concurrently assayed thyroid uptake values derived from the counts of the 24-h urine samples measured by the well-type scintillation counter (direct assay method) revealed very good linear correlation (r > 0.96). Furthermore, a comparison with uptake values determined using the 159 keV images of the patient as well as those of the reference sample in a commonly used so-called 'classic' manner was also carried out. The outcomes of the classic assay were found on average to underestimate the thyroid uptake in absolute terms by ∼ 25% because of unattended scatter and absorption-induced count losses. In contrast, the results of the reference-free method exhibited slight overestimation only, which on average amounted to less than 2%. However, because of the time-related fluctuations of the gamma camera and the dose calibrator as well as uncertainties induced by the scatter and absorption corrections, the average relative error associated with thyroid uptake values as determined by the proposed reference-free method was found to amount to nearly 10%.
Strong evidence in support of the validity of the reference-free method designed to measure thyroid uptake with improved accuracy and without relating to a reference phantom image was produced in a clinical setting. As a result, the unnecessary high radiation burden to patients undergoing (131)I therapy because of systematic uptake underestimation could be avoided.
开发一种易于实施的闪烁扫描法，该方法能够在不使用参考源的情况下提高甲状腺碘摄取测定的准确性，旨在避免接受良性甲状腺疾病（131）I治疗的患者承受不必要的高辐射负担。
进行双能（123）I平面成像，同时记录初级（159 keV）和散射（130 keV）图像帧，随后生成相减的“无散射”图像。借助感兴趣的等轮廓区域选择15%的统一截止水平来描绘功能性甲状腺组织，这进而能够对无散射的甲状腺计数进行定量。确定上述每个图像帧中记录的总计数之比，即“初级与康普顿”比，并与归因于所有甲状腺图像的统一无吸收比进行比较。这使得能够确定将无散射计数恢复到其未调节水平所需的放大因子。随后，借助相机特定的净探测效率将校正后的计数含量转换为甲状腺积累的碘剂量。结果，无需对参考源或体模进行成像即可确定真实摄取值。
通过回顾32例患有格雷夫斯病、结节性甲状腺肿或自主性结节患者的24小时摄取值，对所提出的无参考方法进行了临床评估。与通过井型闪烁计数器测量的24小时尿液样本计数得出的同时测定的甲状腺摄取值（直接测定法）进行比较，显示出非常好的线性相关性（r>0.96）。此外，还与以常用的所谓“经典”方式使用患者的159 keV图像以及参考样本确定的摄取值进行了比较。发现经典测定的结果由于未注意到的散射和吸收引起的计数损失，平均在绝对值上低估甲状腺摄取约25%。相比之下，无参考方法的结果仅表现出轻微高估，平均不到2%。然而，由于伽马相机和剂量校准器的时间相关波动以及散射和吸收校正引起的不确定性，发现所提出的无参考方法确定的甲状腺摄取值的平均相对误差接近10%。
在临床环境中提供了有力证据，支持所设计的无参考方法在不涉及参考体模图像的情况下提高甲状腺摄取测量准确性的有效性。结果，可以避免因系统摄取低估而给接受（131）I治疗的患者带来不必要的高辐射负担。
