*Department of Medical Engineering, School of Applied Health and Social Sciences, University of Applied Sciences Upper Austria, Linz, Austria; †Department of Otolaryngology-Head and Neck Surgery, Johns Hopkins University School of Medicine, Baltimore, Maryland, U.S.A.; ‡Faculty of Engineering and Natural Sciences, Johannes Kepler University Linz, Austria; §Siemens Corporation, Corporate Technology, Princeton, New Jersey;||Siemens Healthcare, Alpharetta, Georgia, U.S.A.; and ¶Escuela de Medicina Ignacio A. Santos, Instituto Tecnológico y de Estudios Superiores de Monterrey, Mexico.
Otol Neurotol. 2014 Feb;35(2):329-37. doi: 10.1097/MAO.0000000000000199.
We investigated if current-generation computed tomographic (CT) scanners have the resolution required to objectively detect bone structure defects as small as 0.1 mm. In addition, we propose that our method is able to predict a possible dehiscence in a semicircular canal.
In semicircular canal dehiscence (SCD), the bone overlying the superior canal (SC) is partially absent, causing vertigo, autophony, hyperacusis or hearing loss. Diagnosis of SCD is typically based on multi-slice computed tomography (MSCT) images combined with the consideration of clinical signs and symptoms. Recent studies have shown that MSCT tends to overestimate the size of dehiscences and may skew the diagnosis towards dehiscence when a thin bone layer remains. Evaluations of CT scans for clinical application are typically observer based.
We developed a method of objectively evaluating the resolution of CT scanners. We did this for 2 types of computed tomography: MSCT, and cone beam computed tomography (CBCT), which have been reported to have a higher resolution for temporal bone scans. For the evaluation and comparison of image accuracy between different CT scanners and protocols, we built a bone cement phantom containing small, well-defined structural defects (diameter, 0.1-0.4 mm). These small inhomogeneities could reliably be detected by comparing the variances of radiodensities of a region of interest (i.e., a region containing a hole) with a homogenous region. The Fligner-Killeen test was used to predict the presence or absence of a hole (p ≥ 0.05). For our second goal, that is, to see how this technique could be applied to the detection of a possible dehiscence in a SC, a cadaveric head specimen was used to create an anatomic model for a borderline SCD; the SC was drilled to the point of translucency. After semi-automatically fitting the location of the canal, our variance-based approach allowed a clear, significant detection of the thin remaining bone layer.
Our approach of statistical noise analysis on bone cement phantoms allowed us to distinguish real irregularities from measured image noise or reconstruction errors. We have shown that with computed tomography, an approach comparing radiodensity variance in regions of interest is capable of detecting inhomogeneities down to 0.1 mm (p ≤ 0.0001).
Our analysis of data from the cadaveric head specimen demonstrates that this approach can be used to objectively detect thin layers of bone overlying an SC. This should provide the basis for using this approach for a semi-automated, objective detection of SCD.
我们研究了当前一代的计算机断层扫描（CT）扫描仪是否具有能够客观检测小至 0.1 毫米的骨结构缺陷的分辨率。此外，我们提出我们的方法能够预测半规管中可能出现的裂隙。
在半规管裂（SCD）中，覆盖上半规管（SC）的骨部分缺失，导致眩晕、自体音、听觉过敏或听力损失。SCD 的诊断通常基于多层 CT（MSCT）图像，并结合临床体征和症状进行考虑。最近的研究表明，MSCT 往往会高估裂隙的大小，并且当剩余的骨层很薄时，可能会使诊断偏向于裂隙。CT 扫描的临床应用评估通常基于观察者。
我们开发了一种客观评估 CT 扫描仪分辨率的方法。我们对 2 种类型的计算机断层扫描进行了评估：MSCT 和锥形束 CT（CBCT），据报道这两种 CT 对颞骨扫描具有更高的分辨率。为了评估和比较不同 CT 扫描仪和协议的图像准确性，我们构建了一个包含小而明确结构缺陷（直径 0.1-0.4 毫米）的骨水泥模型。通过比较感兴趣区域（即包含孔的区域）的放射密度方差与均匀区域的放射密度方差，可以可靠地检测到这些小的不均匀性。Fligner-Killeen 检验用于预测孔的存在与否（p≥0.05）。为了实现我们的第二个目标，即了解该技术如何应用于检测 SC 中可能出现的裂隙，我们使用尸体头部标本创建了一个边界性 SCD 的解剖模型；将 SC 钻到半透明的程度。在半自动拟合管腔位置后，我们基于方差的方法能够清晰、显著地检测到剩余的薄骨层。
我们对骨水泥模型进行的统计噪声分析方法使我们能够将真实的不规则性与测量的图像噪声或重建误差区分开来。我们已经表明，使用计算机断层扫描，一种比较感兴趣区域放射密度方差的方法能够检测到小至 0.1 毫米的不均匀性（p≤0.0001）。
我们对头骨标本数据的分析表明，该方法可用于客观检测覆盖 SC 的薄骨层。这应为使用该方法进行半自动化、客观的 SCD 检测提供基础。
