Objective: To construct swept source optical coherence tomography (SS-OCT) imaging system for root canal endoscopy, and to evaluate the accuracy of diagnosing artificial root fractures.
Methods: An ultra-high-speed (40 kHz) swept laser source was developed based on the piezoelectric tuning filter and the Fourier domain mode locking (FDML) swept laser technology (patent number: 200620135940.2). Ultra-miniature gradient index lens technology (patent number: 201320241218.7) was used to create a thin endoscopic probe with a diameter of 0.86 mm for real-time image transmission. The SS-OCT light source had a wavelength of 1 310 nm and a bandwidth of 100 nm. The axial and transverse image resolutions were 15 μm and 25 μm, respectively. Artificial fractures were created on human mandibular premolars with single root and the premolar roots were prepared to 41 horizontal sections (1 mm thick). 27 root sections with fractures (width: 52-284 μm) and 14 the sections without fractures were observed under an optical stereomicroscope with a cold light source as the gold standard. The horizontal root sections were scanned by self-developed SS-OCT imaging system for root canal endoscopy with a central wavelength of 1 310 nm and bandwidth of 100 nm. The data were reconstructed with 30 μm thick slices at an interval of 30 μm. Two observers, a radiologist and an endodontist, were trained and independently evaluated all the reconstructed images blindly. The diagnostic performance of SS-OCT imaging system was calculated, and statistical analysis was performed.
Results: SS-OCT root canal endoscopic imaging system composed of high-speed swept laser source, fiber coupler, endoscopic probe, reference arm and differential detector. Root sections could be scanned by SS-OCT and imaged in realtime at a depth of 1 to 2 mm. The kappa value for interobserver agreement was 0.792, and the intraobserver agreement was 1.000 and 0.709 for two observers respectively. All of 27 fractured root sections and 12 of 14 root sections without fractures were accurately diagnosed while 2 unfractured root sections were misdiagnosed. The sensitivity was 1.000 and the specificity was 0.857 for diagnosis of artificial root fractures by SS-OCT. The positive predictive value (PPV), negative predictive value (NPV) and the overall accuracy rate were 0.931, 1.000 and 0.951 respectively.
Conclusion: The swept source optical coherence tomography imaging system for root canal endoscopy is a promising imaging method for observing root fractures．.
目的: 建立扫频光学相干断层扫描(swept source-optical coherence tomography, SS-OCT)根管内窥影像系统,并评价该系统应用于诊断模拟根管内壁裂的准确性。
方法: 自主研发基于压电调谐滤波器并应用傅里叶(Fourier)域锁模技术构建的40 kHz超高速扫频激光光源系统(专利号200620135940.2),利用超微型梯度折射率透镜(专利号201320241218.7)制作极细根管内窥探头(直径0.86 mm),实现实时成像传输。构建的SS-OCT根管内窥影像系统扫频光源中心波长为1 310 nm,带宽为100 nm; 扫描图像的横向和纵向分辨率分别为25 μm和15 μm。利用人离体下颌前磨牙牙根制作人工模拟根裂(内壁裂),并制备高度1 mm的牙根横断面切盘。立体显微镜下观察发现,41个待测样本中有27个根管内壁裂样本(宽度在52~284 μm),另14个样本无根裂。应用上述构建的SS-OCT根管内窥影像系统扫描待测样本,重建图像的层厚为30 μm,层间距为30 μm。对1名口腔放射科医师和1名牙体牙髓科医师进行培训,判读SS-OCT扫描重建图像,判读根管内壁裂的有无及具体位置,评价两名观察者的自身一致性和观察者之间的一致性。以立体显微镜(组织学)检查结果作为金标准,评价应用SS-OCT根管内窥影像系统诊断模拟根管内壁裂的准确性。
结果: 两位观察者自身一致性的Kappa值分别为1.000和0.709,观察者之间的Kappa值为0.792。应用SS-OCT根管内窥影像系统扫描后27个根裂样本均被正确诊断,灵敏度为1.000,14个无根裂的样本有12个被正确判读,特异度为0.857, 2个无根裂样本被判读为有根裂,为假阳性。阳性预测值、阴性预测值分别为0.931、1.000,准确性为0.951。
结论: 扫频光学相干断层扫描根管内窥影像系统应用于观察根管内壁裂有临床应用前景。