IMAGE QUANTIFICATION FOR RADIATION DOSE CALCULATIONS-LIMITATIONS AND UNCERTAINTIES
IMAGE QUANTIFICATION FOR RADIATION DOSE CALCULATIONS-LIMITATIONS AND UNCERTAINTIES
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DOI：
10.1097/hp.0b013e3181e28cdb
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发表时间：
2010-11-01
期刊：
影响因子：
2.2
通讯作者：
Forrester, J. W.
中科院分区：
文献类型：
--
作者：
Pereira, J. M.;Stabin, M. G.;Forrester, J. W.
核医学中的辐射剂量计算依赖于通过平面和/或层析成像方法对辐射活性进行量化。然而，这两种方法都有固有的局限性，并且活动估计的准确性随对象大小、背景水平和其他变量而变化。本研究的目的是评估平面和单光子发射计算机断层扫描（SPECT）方法定量成像的局限性，重点是用于计算正常器官和肿瘤吸收剂量估计的活性量化。为了做到这一点，我们研究了一系列不同几何复杂性的幻影，其中有三种放射性核素，其衰变方案从简单到复杂。四种水溶液浓度的Tc-99m、I-131和in -111（74、185、370和740 kBq mL(-1)）被放置在四种不同大小的球体中，在周围的水中具有三种不同的活性水平。在现代SPECT/计算机断层扫描（CT）系统上获得了这些幻影的平面和SPECT图像。这些放射性核素和浓度/背景研究使用心脏模型和改良的躯干模型重复进行，其中肝脏和“肿瘤”区域含有放射性核素浓度并具有相同的不同背景水平。平面量化采用几何平均法、衰减校正（AC）、散射校正（SC和NSC）和不散射校正（SC和NSC）。用衰减图（AM）重建SPECT图像；在图像重建过程中使用散射窗进行SC。对于具有校正数据的球形源，对于最大的球体（11.5 mL）以及使用Tc-99m和I-131的平面和SPECT方法，观察到良好的精度（通常在已知值的+/- 10%以内），但对于较小的物体，最明显的是In-111，精度最差，偏离已知值。在较小的物体中，SPECT定量受到部分体积效应的影响，在这些情况下，所有放射性核素的定量结果通常比平面结果显示更大的误差。对于心脏幻像，结果是所有放射性核素实验中最准确的。背景减法是影响这些结果的重要因素。散射光子的贡献在I-131的量化中是重要的；如果不考虑散射，使用平面量化方法往往会高估活度。对于躯干幻像实验，结果表明，与先前所有放射性核素的球形源实验相比，明显低估了活度。尽管随着背景水平的增加，观察到一些变化，但SPECT结果在不同的活动浓度下更加一致。在最先进的伽玛相机上进行平面或SPECT量化，并进行适当的定量处理，对于大型物体和适度的目标-背景浓度，可以提供优于10%的精度；然而，当使用较小的物体时，在较高的背景下，对于具有更复杂衰变方案的核素，SPECT量化方法通常会产生更好的结果。中华医学杂志，2009 (5):688-701；2010
Radiation dose calculations in nuclear medicine depend on quantification of activity via planar and/or tomographic imaging methods. However, both methods have inherent limitations, and the accuracy of activity estimates varies with object size, background levels, and other variables. The goal of this study was to evaluate the limitations of quantitative imaging with planar and single photon emission computed tomography (SPECT) approaches, with a focus on activity quantification for use in calculating absorbed dose estimates for normal organs and tumors. To do this we studied a series of phantoms of varying complexity of geometry, with three radionuclides whose decay schemes varied from simple to complex. Four aqueous concentrations of Tc-99m, I-131, and In-111 (74, 185, 370, and 740 kBq mL(-1)) were placed in spheres of four different sizes in a water-filled phantom, with three different levels of activity in the surrounding water. Planar and SPECT images of the phantoms were obtained on a modern SPECT/computed tomography (CT) system. These radionuclides and concentration/background studies were repeated using a cardiac phantom and a modified torso phantom with liver and "tumor" regions containing the radionuclide concentrations and with the same varying background levels. Planar quantification was performed using the geometric mean approach, with attenuation correction (AC), and with and without scatter corrections (SC and NSC). SPECT images were reconstructed using attenuation maps (AM) for AC; scatter windows were used to perform SC during image reconstruction. For spherical sources with corrected data, good accuracy was observed (generally within +/- 10% of known values) for the largest sphere (11.5 mL) and for both planar and SPECT methods with Tc-99m and I-131, but were poorest and deviated from known values for smaller objects, most notably for In-111. SPECT quantification was affected by the partial volume effect in smaller objects and generally showed larger errors than the planar results in these cases for all radionuclides. For the cardiac phantom, results were the most accurate of all of the experiments for all radionuclides. Background subtraction was an important factor influencing these results. The contribution of scattered photons was important in quantification with I-131; if scatter was not accounted for, activity tended to be overestimated using planar quantification methods. For the torso phantom experiments, results show a clear underestimation of activity when compared to previous experiment with spherical sources for all radionuclides. Despite some variations that were observed as the level of background increased, the SPECT results were more consistent across different activity concentrations. Planar or SPECT quantification on state-of-the-art gamma cameras with appropriate quantitative processing can provide accuracies of better than 10% for large objects and modest target-to-background concentrations; however when smaller objects are used, in the presence of higher background, and for nuclides with more complex decay schemes, SPECT quantification methods generally produce better results. Health Phys. 99(5):688-701; 2010