This study aimed to evaluate the impact of attenuation and scatter correction on the contrast to noise ratio values of SPECT and SPECT/CT images in sentinel lymph nodes scintigraphy. In addition, the effect of using an iterative reconstruction algorithm with variable iterations number and fixed subsets was also investigated. 35 patients with a total of 44 lymph nodes were recruited in the current study. SPECT/CT scans were performed 3–4 h following peri-tumoral ^99mTc-nanocolloid injection (≈1 mCi) at four points. Two image types were generated including SPECT with attenuation and scatter correction (AC–SC) and SPECT without any correction (NoAC–NoSC). The acquired projections were repeatedly reconstructed with eight subsets and 10, 20, 30 and 40 iterations. Afterwards, the calculated contrast to noise ratio values were used to investigate the effect of number of iteration and to compare the image quality of SPECT/CT and SPECT only. The mean contrast to noise (CNR) values of SPECT/CT scans were found to be 19,737, 26,418, 34,282 and 31,187 at 10, 20, 30 and 40 iterations, respectively. Whereas, the mean CNR values in SPECT (NoAC–NoSC) were as low as 8506, 10,582, 13,791 and 12,143 at 10, 20, 30 and 40 iterations, respectively. The CNR values of both SPECT and SPECT/CT improved with increasing number of iterations up to 30 iterations and then slightly decreased after 30–40 iterations. Likewise, no significant difference was found between 10 and 20 iterations (P_value = 0.06) in SPECT/CT, while a statistically significant difference was observed between 10 iterations and both 30 and 40 iterations (P_value < 0.05). It is concluded that the attenuation and scatter correction in SPECT/CT optimized the CNR values up to threefold compared to SPECT alone. Thus, a considerable improvement in the CNR values and the image quality can be obtained by increasing the iterations number to peak of 30 iterations.

本研究旨在评估衰减和散射校正对前哨淋巴结闪烁扫描中 SPECT 和 SPECT/CT 图像的对比度值的影响。此外，还研究了使用具有可变迭代次数和固定子集的迭代重建算法的效果。本研究招募了 35 名患者，共有 44 个淋巴结。在肿瘤周围^{99m 后}3-4 小时进行 SPECT/CT 扫描在四个点注射 Tc-纳米胶体 (≈1 mCi)。生成了两种图像类型，包括带衰减和散射校正的 SPECT (AC-SC) 和不带任何校正的 SPECT (NoAC-NoSC)。使用八个子集和 10、20、30 和 40 次迭代重复重建获得的投影。之后，计算出的对比度噪声比值用于研究迭代次数的影响，并仅比较 SPECT/CT 和 SPECT 的图像质量。在 10、20、30 和 40 次迭代时，发现 SPECT/CT 扫描的平均噪声对比度 (CNR) 值分别为 19,737、26,418、34,282 和 31,187。而 SPECT (NoAC–NoSC) 中的平均 CNR 值分别在 10、20、30 和 40 次迭代时低至 8506、10,582、13,791 和 12,143。SPECT 和 SPECT/CT 的 CNR 值随着迭代次数的增加而提高，达到 30 次迭代，然后在 30-40 次迭代后略有下降。同样，在 10 次和 20 次迭代之间没有发现显着差异（ 在 SPECT/CT 中P_值= 0.06），而在 10 次迭代和 30 次和 40 次迭代之间观察到统计学上的显着差异（P_值 < 0.05）。得出的结论是，与单独的 SPECT 相比，SPECT/CT 中的衰减和散射校正将 CNR 值优化了三倍。因此，通过将迭代次数增加到 30 次迭代的峰值，可以获得 CNR 值和图像质量的显着改善。