大橋 剛介¹, 大矢 晃久², 跡部 オスカル³, 名取 道也⁴, 中島 真人¹

Gousuke OHASHI¹, Akihisa OHYA², Oscal Atobe³, Michiya NATORI ⁴, Masato NAKAJIMA¹

¹慶應義塾大学理工学部電気工学科中島研究室, ²筑波大学電子情報工学系, ³慶應義塾大学医学部産婦人科学教室, ⁴国立大蔵病院臨床研究部

¹Nakajima Laboratory Department of Electrical Engineering Keio University, ²Institute of Information Science and Electronics University of Tsukuba, ³Department of Obstetrics and Gynecology Keio University School of Medicine, ⁴Department of Clinical Research National Ohkura Hospital

キーワード : Boundary extraction, Bubble filling, Fetal bladder, Volume measurement

We attempted to develop an accurate, automatic method for determining the volume of internal organs. Our method has three steps. In the first step, three-dimensional sonographic data are obtained from an organ. In the second step, organ boundaries are accurately defined. For this purpose, we designed a neural network system with which we classified each voxel as liquid, soft tissue, or boundary. Because this system alone may not always be accurate, however, we devised step three, the ‘bubble filling methods.’ With the combination of the neural network system and the bubble filling method, we were able to determine the area of the target organ. Volume was obtained by calculating the number of voxels inside the determined area. To evaluate the accuracy of this method, we prepared seven phantoms of different volumes, ranging from 0.31 to 39 ml, and compared volumes computed by this method with these actual values. Mean difference between actual and computed volume was 0.729 ml (3.38%). We then computed the volumes obtained with another method, in which we estimated the boundaries on visual inspection of three-dimensional sonograms (manual method). Mean difference between actual volume and volume estimated by the manual method was 0.641 ml. We treated volumes obtained with the manual method as standard values, because actual organ volume was unknown. Fifty three-dimensional fetal bladder images were obtained from eight fetuses. We used this method to compute fetal bladder volume (y) and compared the values obtained with those obtained with the manual method (x). The linear regression line of y=-0.0741+1.02x indicates that this method may be sufficiently accurate to use in calculating the volume of the fetal bladder.