Galileo锥形束CT影像线性测量放大率的研究

Magnification of liner measurement on the image of Galileo CBCT scan

目的:研究Galileo锥形束CT影像的放大率。方法:使用数控机床加工实验模具在有机玻板平面制备72条标准凹槽,充填氧化锌水门汀形成阻射线。定义与扫描视野冠、矢状面平行的线为X、Y轴向线,与水平面垂直者为Z轴向线。观测平面内两个轴线垂直相交形成4个象限,各象限内含两个方向的轴向线各9条。模具置于CBCT扫描视野(FOV)中,使观测平面与FOV中心水平面一致,两平面中心重合后,记为H平面;使观测平面与FOV中心水平面垂直、冠状面平行,两平面中心重合后,记为C平面;H、C平面分别扫描5次。定义R值为阻射线中心偏离FOV中心的距离。影像三维重建后,测量各阻射线影像的长度6次,计算其放大率。结果:X、Y、Z轴向线放大率的最大值为3.4%、3.3%、3.3%;对称分布的阻射线的放大率差异不显著(P>0.05);不同平面间,同名阻射线间相比:远离中心平面的影像放大率大于近中心平面(P<0.05);同一平面内,不同线段止点间相比:远离平面中心点的阻射线影像放大率大于接近平面中心点(P<0.05);X轴向放大率明显大于Y、Z轴向(P<0.05),而Y与Z轴向的放大率较为接近(P>0.05);放大率与R值显著正相关(P<0.05)。结论:锥形束CT影像较实体放大,放大率与被测物体偏离FOV中心的距离显著正相关。

AIM： To investigate the magnification on cone beam computed tomography（CBCT） images.METHODS： A homemade polymethylmethacrylate plate with 72 grooves filled with zinc oxide cement radiopaque lines was prepared by the CNC machine tools. The lines parallel with the coronal plane,sagittal plane and perpendicular to the horizontal plane were defined as X-,Y- and Z-axis lines respectively. Every 2 axes divided the plane into 4 quadrants and each quadrant contained 2 axial lines and 9 lines on each axis. First,the mould was put into FOV of CBCT and the observation surface was consistent with the horizontal plane of FOV. The center of the observation surface was coincided with the center of FOV. This observation surface was called plane H,and then the plane upper and lower at 20 mm and40 mm to plane H was scanned respectively for 5 times. Second,the observation surface was made perpendicular to the horizontal plane and parallel to the coronal plane and the center of the observation surface coincided with the center of FOV. This surface was called plane C,and then the plane anterior and posterior at 20 mm and 40 mm to plane C was scanned for 5 times. The distance of the center of radiopaque lines departing from the FOV center was defined as R. The length of each radiopaque line was measured for 6 times,and the magnification was calculated. RESULTS： The maximum magnification of X-axis,Y-axis and Z-axis lines were 3. 4%,3. 3% and 3. 3% respectively（ P〈0. 05）. For the same line,the magnification of its image that stayed away from the center plane was larger than that close to center plane（P〈0. 05） and as for different lines in the same plane,the magnification of the lines staying away from the center of the plane was larger than that close to it（ P〈0. 05）. X-axis magnification was greater than Y-axis or Z-axis（ P〉0. 05）,while the Y- axis and Z- axis magnification was closer（ P〉0. 05）. Magnification was positively associated with R（P〈0. 05）. CONCLUSION： CBCT images may have a certain magnification of the scanned objects,which is positively associated with the distance from the objects to the FOV center.