阈值法三维体积测量肺结节的64排CT实验研究

Three-dimensional volumetric measurement of pulmonary nodules by 64-MSCT with segmentation threshold algorithm:experimental study

目的通过64排螺旋CT(LightspeedVCTGE)对肺结节模型进行三维体积测量的研究,探讨阈值法测量肺结节三维体积的可行性及最佳阈值。方法在肺组织模型上放置17枚大小范围10～45mm的模拟肺结节并在64排螺旋CT上使用表面遮盖法(SSD)三维重建成像。以模拟肺结节CT值与周围模拟肺组织CT值平均值为基准值(S),将基准值设为下限阈像,上限阈值为大于模拟肺结节最高像素的CT值(300HU),使用阈值分割技术,分割并测量模拟肺结节三维体积。上限阈值不变,改变下限阈值(基准值+100、基准值+200、基准值-100、基准值-200)。下限阈值为基准值,改变上限阈值(350HU、400HU、450HU),重新分割、测量模拟肺结节三维体积,通过与排水法测量的模拟肺结节真实体积进行配对比较。采用ALA软件对模拟肺结节进行自动体积测量,并与阈值法进行比较。结果以基准值为下限阈值,大于模拟肺结节最高像素的值为上限阈值,所测得三维体积与真实体积无统计学差异,P值>0.05,并且与真实体积配对差值最小。下限阈值越大,测量体积越小,下限阈值越小,测量体积越大。大于模拟肺结节最高像素的不同CT值作为上限阈值对测量结果无影响。ALA软件不能对直径大于30mm模拟肺结节进行测量。结论阈值法可以准确测量模拟肺结节三维体积,较ALA软件适用范围广。阈值法测量模拟肺结节三维体积的最佳阈值:下限值为模拟肺结节CT值及周围模拟肺组织的平均值,上限值为大于模拟肺结节最高像素值的CT值。

Objective To evaluate the feasibility of three-dimensional volumetric measurement of synthetic pulmonary nodules（SPNs）with segmentation threshold algorithm（STA）and searched the optimal threshold by scanning pulmonary nodule model on 64-MSCT.Methods Synthetic pulmonary nodules of seventeen different diameter（10-45 mm）on lung model was scanned and reconstruction with surface shaded display（SSD）on 64-MDCT.The standard threshold（S）was the average of attenuation of SPNs and the background.SPNs were separated and measured by STA with S as the lower threshold and 300 HU as the upper threshold.The volume of each nodule was measured again by adjusting lower thresholds（S＋100,S＋200,S-100,S-200）with fixed upper threshold and adjusting upper thresholds（350 HU,400 HU,450 HU）with fixed lower threshold.The difference between the measurement volume acquired by STA with different thresholds and the real volumes（measurement according to fluid displacement）of SPNs were evaluated by paired t-test.Meanwhile,the volume of nudules measured by ALA（Advanced Lung Analysis）software,was also compared with measurement by STA.Results No statistic significant difference on the paired t-test was demonstrated between volumes measurement of nodules which had minimal paired mean difference by STA with lower threshold using S and upper threshold using 300 HU and real volumes.For lower limit threshold,the lower threshold used,the bigger volumes obtained and vice versa.For upper threshold,different threshold exceed the highest attenuation of nodules did not influence the measurement.There are not all synthetic pulmonary nodules could be measured by ALA software.Conclusion Method of STA in three-dimensional volume measurement of nodules is feasibility.Applicability of STA is better than that of ALA software.The average attenuation of nodules and background is the optimal lower threshold of 3D volume measurement of nodules and upper threshold could be value exceed the highest attenuation of pulmonary nodules.