Standardization of Thresholding for Binary Conversion of Vocal Tract Modeling in Computed Tomography

• Published in: Journal of voice Vol. 24; no. 4; pp. 503 - 509
• Main Authors: Inohara, Ken, Sumita, Yuka I, Ohbayashi, Naoto, Ino, Shuichi, Kurabayashi, Tohru, Ifukube, Tohru, Taniguchi, Hisashi
• Format: Journal Article
• Language: English
• Published: United States Mosby, Inc 01.07.2010
• Subjects: Adipose Tissue - diagnostic imaging; Aged; Buccal fat pad; Fat tissue; Female; Head and neck cancer patient; Head and Neck Neoplasms - surgery; Humans; Imaging, Three-Dimensional - methods; Imaging, Three-Dimensional - standards; Male; Maxilla - surgery; Maxillectomy; Middle Aged; Models, Anatomic; Mouth Mucosa - diagnostic imaging; Osteotomy; Otolaryngology; Postoperative Complications - diagnostic imaging; Rapid prototyping; Reconstructive Surgical Procedures; Reference Standards; Regression Analysis; Resins, Synthetic; Speech Disorders - diagnostic imaging; Threshold for binary conversion; Tomography, X-Ray Computed - methods; Tomography, X-Ray Computed - standards; Vocal Cords - diagnostic imaging; Vocal tract; X-ray computed tomography (CT); Vocal tract; Threshold for binary conversion; X-ray computed tomography (CT); Rapid prototyping; Buccal fat pad; Head and neck cancer patient; Maxillectomy; Fat tissue
• ISSN: 0892-1997; 1873-4588
• DOI: 10.1016/j.jvoice.2008.10.013

Summary Postoperative head and neck cancer patients suffer from speech disorders, which are the result of changes in their vocal tracts. Making a solid vocal tract model and measuring its transmission characteristics will provide one of the most useful tools to resolve the problem. In binary conversion of X-ray computed tomographic (CT) images for vocal tract reconstruction, nonobjective methods have been used by many researchers. We hypothesized that a standardized vocal tract model could be reconstructed by adopting the Hounsfield number of fat tissue as a criterion for thresholding of binary conversion, because its Hounsfield number is the nearest to air in the human body. The purpose of this study was to establish a new standardized method for binary conversion in reconstructing three-dimensional (3-D) vocal tract models. CT images for postoperative diagnosis were secondarily obtained from a CT scanner. Each patient's minimum settings of Hounsfield number for the buccal fat-pad regions were measured. Thresholds were set every 50 Hounsfield units (HU) from the bottom line of the buccal fat-pad region to −1024 HU, the images were converted into binary values, and were evaluated according to the three-grade system based on anatomically defined criteria. The optimal threshold between tissue and air was determined by nonlinear multiple regression analyses. Each patient's minimum settings of the buccal fat-pad regions were obtained. The optimal threshold was determined to be −165 HU from each patient's minimum settings of the Hounsfield number for the buccal fat-pad regions. To conclude, a method of 3-D standardized vocal tract modeling was established.