On-board SPECT for localizing functional targets: a simulation study.
On-board SPECT for localizing functional targets: a simulation study.
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用于定位功能目标的机载 SPECT：模拟研究。
DOI：
10.1118/1.3113902
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发表时间：
2009
期刊：
影响因子：
3.8
通讯作者：
Yin,Fang-Fang
中科院分区：
文献类型：
--
作者：
Roper,Justin;Bowsher,James;Yin,Fang-Fang
为了定位功能靶点和分子靶点，研究了单光子发射计算机断层扫描(SPECT)在机载放射治疗机成像中的应用。一个电脑模拟的女性NCAT体模仰卧在平顶的治疗沙发上。在上半身确定了20个肿瘤位置。这8个肺肿瘤都受到呼吸运动的影响。肿瘤直径分别为10.8 mm、14.4 mm和21.6 mm，肿瘤与背景的比例分别为3：1和6：1，这是放射性示踪剂Sestamibi的特征。对于前半圆形轨迹，模拟了代表扫描时间为4、8和20min的投影图像。使用6个子集和5次迭代，利用有序子集期望最大化(OSEM)对图像进行衰减校正。计算了25张图像的对比噪声比(CNR)。使用与无噪声肿瘤模板的互相关来选择每个肿瘤周围14.4 mm半径搜索体积内最可疑的肿瘤位置，每个搜索体积中只有一个肿瘤。通过计算测量的肿瘤位置和真实的肿瘤位置之间的平均距离来评估定位的准确性。肿瘤相对于探测器轨迹的位置对定位精度和CNR有很大影响。例如，胸壁附近的CNR值比脊柱和肋骨附近的肿瘤大3.5倍，比6：1和3：1肿瘤摄取的CNR值相差1.6倍要大得多。典型地，6：1摄取的肿瘤与3：1摄取的肿瘤在扫描时间为4分钟时定位准确，而3：1摄取的肿瘤成像时间为20分钟。在4min扫描中，14.4 mm和21.6 mm 6：1摄取的前部肿瘤被定位在2 mm以内。这些结果表明，SPECT，即机载放射治疗机，可能是一种可行的方式，利用相对较短的扫描时间来定位某些功能和分子靶点。
Single photon emission computed tomography (SPECT) was investigated for imaging on‐board radiation therapy machines in order to localize functional and molecular targets. A computer‐simulated femaleNCATphantom was positioned supine on a flat‐top treatment couch. Twenty tumor locations were defined in the upper torso. The eight lung tumors were subject to the effects of respiratory motion. Tumor diameters of 10.8, 14.4, and 21.6 mm were simulated for tumor‐to‐background ratios of 3:1 and 6:1 that are characteristic of the radiotracer ‐sestamibi. Projection images representing scan times of 4, 8, and 20 min were simulated for an anterior, half‐circular trajectory. Images were reconstructed with attenuation correction by ordered‐subsets expectation maximization (OSEM) using six subsets and five iterations. Contrast‐to‐noise ratios (CNRs) were calculated from ensembles of 25 images. Cross correlation with a noise‐free tumor template was used to select the most suspicious tumor location within a 14.4‐mm‐radius search volume surrounding each tumor, with only that one tumor in each search volume. Localization accuracy was assessed by calculating average distances between measured and true tumor locations. Localization accuracy and CNRs were strongly affected by tumor location relative to the detector trajectory. For example, CNR values near the chest wall were greater by a factor of 3.5 than for tumors near the spine and posterior ribs, a much greater effect than the factor of 1.6 difference in CNR between 6:1 and 3:1 tumor uptakes. Typically, tumors of 6:1 uptake were localized as accurately with 4 min of scan time as tumors of 3:1 uptake that had been imaged for 20 min. Using 4 min scans, 14.4 and 21.6 mm anterior tumors of 6:1 uptake were localized within 2 mm. These results suggest that SPECT, on‐board radiation therapy machines, may be a viable modality for localizing certain functional and molecular targets using relatively short scan times.