Li Q, Katsuragawa S, Doi K
Department of Radiology, The University of Chicago, Illinois 60637, USA.
Med Phys. 2000 Aug;27(8):1934-42. doi: 10.1118/1.1287112.
A contralateral subtraction technique has been developed to assist radiologists in the detection of asymmetric abnormalities such as lung nodules on a single chest radiograph. With this technique, a contralateral subtraction image is obtained by subtracting a right/left reversed "mirror" image from the original one. The lesions in the subtraction image may be enhanced because most of the symmetric skeletal structures, such as peripheral ribs, are eliminated. Although the quality of the previous contralateral subtraction images is relatively good, severe misregistration artifacts, mainly due to serious asymmetry of the ribs in the two lungs of the original image, were observed in some cases, and minor misregistration artifacts were also observed in many cases. In this study, we employed three image warping techniques. An initial global warping technique was applied to reduce severe misregistration artifacts in the subtraction image caused by asymmetric rib structures. Additional two iterative warping techniques based on an elastic matching technique were used for accurate registration of the local structures of ribs, so that minor artifacts present in many subtraction images obtained with the previous technique were greatly reduced. With the new technique, the percentage of chest images, which were rated as being of adequate, good, or excellent quality of subtraction images by use of a subjective evaluation method, was improved from 91% to 97%. In particular, the number of cases with excellent quality was greatly increased from 15% to 42%. The contralateral subtraction technique can be used for detection of asymmetric abnormalities, such as lung nodules, pneumothorax, pneumonia, and emphysema, on peripheral lungs in single chest radiographs, and it therefore has potential utility in a large proportion of abnormal chest images.
已开发出一种对侧相减技术，以帮助放射科医生在单张胸部X光片上检测不对称异常，如肺结节。通过这种技术，通过从原始图像中减去左右反转的“镜像”图像来获得对侧相减图像。相减图像中的病变可能会增强，因为大多数对称的骨骼结构，如外周肋骨，被消除了。尽管先前的对侧相减图像质量相对较好，但在某些情况下观察到严重的配准伪影，主要是由于原始图像中两肺肋骨严重不对称，并且在许多情况下也观察到轻微的配准伪影。在本研究中，我们采用了三种图像变形技术。应用一种初始全局变形技术来减少由不对称肋骨结构引起的相减图像中的严重配准伪影。另外两种基于弹性匹配技术的迭代变形技术用于肋骨局部结构的精确配准，从而大大减少了用先前技术获得的许多相减图像中存在的轻微伪影。使用新技术，通过主观评估方法被评为减法图像质量为足够、良好或优秀的胸部图像百分比从91%提高到了97%。特别是，质量优秀的病例数从15%大幅增加到了42%。对侧相减技术可用于在单张胸部X光片上检测外周肺的不对称异常，如肺结节、气胸、肺炎和肺气肿，因此在很大比例的异常胸部图像中具有潜在的实用价值。
