3D CT imaging method for measuring temporal bone aeration

OBJECTIVE: 3D volume reconstruction of CT images can be used to measure temporal bone aeration. This study evaluates the technique with respect to reproducibility and acquisition parameters. MATERIAL AND METHODS: Helical CT images acquired from patients with radiographically normal temporal bones using standard clinical protocols were retrospectively analyzed. 3D image reconstruction was performed to measure the volume of air within the temporal bone. The appropriate threshold values for air were determined from reconstruction of a phantom with a known air volume imaged using the same clinical protocols. The appropriate air threshold values were applied to the clinical material. RESULTS: Air volume was measured according to an acquisition algorithm. The average volume in the temporal bone CT group was 5.56 ml, compared to 5.19 ml in the head CT group (p = 0.59). The correlation coefficient between examiners was > 0.92. There was a wide range of aeration volumes among individual ears (0.76-18.84 ml); however, paired temporal bones differed by an average of just 1.11 ml. CONCLUSIONS: The method of volume measurement from 3D reconstruction reported here is widely available, easy to perform and produces consistent results among examiners. Application of the technique to archival CT data is possible using corrections for air segmentation thresholds according to acquisition parameters.     

Computerized assessment of the mastoid air cell system

There have been many arguments on the development of pneumatization of temporal bone. However, a technique for direct volume measurement from high resolution computed tomography has never been reported. The aim of this paper is to develop a technique by using digital image processing to measure the volume of the mastoid air cell system. Forty three ears of 26 healthy subjects (13 males and 13 females) without a history of chronic or exudative otitis media, clear signs of Meniere's disease, severe sensorineural hearing impairment or malformation of temporal bone were eligible for enrolment in this study. Using a digital image processing technique, only the black air cells and tympanic cavity on the CT films are easily selected. Then, after image processing, only areas of these extracted black pneumatized parts are calculated. Consequently, the volume of pneumatized parts of temporal bone could be calculated separately as total volume and as partial volume that divided by several CT planes. The average volume of pneumatization in 43 temporal bones was 5.97 ml. However, since the volume of pneumatization in the temporal bone has traditionally been estimated by analyzing areas on X-ray films, the new method described in this study is significant for its ability to directly measure the volume of pneumatization in the temporal bone.     

Detection of labyrinthine fistulas in human temporal bone by virtual endoscopy and density threshold variation on computed tomographic scan

OBJECTIVE: To assess the sensitivity of the routine computed tomographic (CT) scan of the temporal bone coupled to a virtual endoscopy, with density threshold variation, in detecting small fistulas in human temporal bone specimens. DESIGN: Single-blind, before-after trial. SETTING: This study was carried out in a research laboratory in collaboration with a radiology department. PATIENTS: Five human adult temporal bone specimens were included. INTERVENTIONS: The fistulas were created with calibrated burrs (0.3, 0.5, and 0.8 mm) in the 3 semicircular canals and in the promontory of 3 temporal bones. Two other temporal bones served as controls. All bones underwent CT scan (1-mm section thickness) before and after dissection. Three-dimensional images were obtained from CT scan native axial views at different density reconstruction thresholds. The virtual endoscope was placed in the middle ear cavity looking to the inner ear wall. The threshold at which a bony defect appeared on virtual endoscopic images (opening threshold in Hounsfield units [H]) was noted for each location. MAIN OUTCOME MEASURES: Opening thresholds before and after dissection. RESULTS: On standard axial views, fistulas smaller than 0.5 mm were not visualized. By virtual endoscopy, all fistulas could be visualized. The opening threshold decreased after fistula creation in the semicircular canals (1244 +/- 50.5 H [n = 36] vs 778 +/- 52.4 H [n = 34]; P<.001; 1-way analysis of variance and Dunnett multiple comparisons posttest) and in the promontory (1541 +/- 37.8 H [n = 12] vs 1334 +/- 35.1 H [n = 8]; P<.001). The opening thresholds in the control specimens remained unchanged after dissection. CONCLUSION: Virtual endoscopy with variation of reconstruction threshold allows the detection of small labyrinthine fistulas with diameters of 0.3 mm or smaller.     

computer-aided simulation of mastoidectomy

Objective To establish a three-dimensional model of the temporal bone using CT scan images for study of temporal bone structures and simulation of mastoidectomy procedures. Methods CT scan images from 6 individuals (12 temporal bones) were used to reconstruct the Fallopian canal, internal auditory canal, cochlea, semicircular canals, sigmoid sinus, posterior fossa floor and jugular bulb on a computer platform. Their anatomical relations within the temporal bone were restored in the computed model. The same model was used to simulate mastoidectomy procedures. Results The reconstructed computer model provided accurate and clear three-dimensional images of temporal bone structures. Simulation of mastoidectomy using these images provided procedural experiences closely mimicking the real surgical procedure. Conclusion Computeraided three dimensional reconstruction of temporal bone structures using CT scan images is a useful tool in surgical simulation and can aid surgical procedure planning.     

Evaluation of the mastoid air cell system by high resolution computed tomography: three-dimensional multiplanar volume rendering technique

The mastoid air cell system is an important contributor to the pathophysiology of middle-ear inflammatory disease. The mastoid cavity is not only an air reservoir, but also an active space for gas exchange. Various methods of temporal bone imaging have been designed to investigate mastoid pneumatization. In this study, we examined 100 normal temporal bones for the evaluation of mastoid pneumatization. Mastoid air cell systems were measured by reconstructed axial and coronal high resolution computed tomography (HRCT) images. The reconstructions were made by a three-dimensional multiplanar volume rendering (3D MPVR) technique. The mean volume of the mastoid air cell pneumatization was 7.9 cm(3) (4.0-14.0 cm(3), SD = 2.3 cm(3)). The ears were allocated to the groups with respect to measured mastoid air cell pneumatization. Twenty-eight per cent of the ears have small pneumatization with an air cell system not exceeding 6 cm(3). Fifty-two per cent had an air cell system between six and 10 cm(3), and 20 per cent had an air cell system exceeding 10 cm(3). With its excellent imaging quality and the ability to eliminate bone and soft tissue, HRCT is the best method for evaluating the mastoid air cell system. The 3D MPVR technique must be used to measure the temporal bone/mastoid pneumatization for the best results.     

Computer-aided surface area measurement of temporal bone pneumatization: histological sections]

Contention exists on the development of pneumatization of temporal bone. Many techniques to measure the volume of pneumatization have been reported, but no techniques for direct surface area measurement. We measured the surface area and volume of human mastoid air cells. Eight normal temporal bones removed at autopsy were analyzed and fixed in formalin fixative, decalcified, and embedded in celloidin, sectioned at 25 microns and stained with H-E for histological examination. Total surface area and the volume of human mastoid air cells were measured using a personal computer. The surface area of pneumatic spaces for the 8 temporal bone specimens ranged from 36.1 cm2 to 163.0 cm2 (mean +/- SD: 89.1 +/- 34.0 cm2). The volume of pneumatic spaces for the 8 specimens ranged from 1.53 ml to 6.03 ml (mean +/- SD: 4.12 +/- 0.97 ml). The surface area of temporal bone pneumatic spaces we determined could serve as useful basic data for determining the physiology of ventilation for the temporal bone and the function of mastoid cells.     

Three-dimensional reconstruction based on images from spiral high-resolution computed tomography of the temporal bone: anatomy and clinical application

The aim of this study was to investigate the usefulness of a three-dimensional (3D) reconstruction of computed tomography (CT) images in determining the anatomy and topographic relationship between various important structures. Using 40 ears from 20 patients with various otological diseases, a 3D reconstruction based on the image data from spiral high-resolution CT was performed by segmentation, volume-rendering and surface-rendering algorithms on a personal computer. The 3D display of the middle and inner ear structures was demonstrated in detail. Computer-assisted measurements, many of which could not be easily measured in vivo, of the reconstructed structures provided accurate anatomic details that improved the surgeon's understanding of spatial relationships. A 3D reconstruction of temporal bone CT might be useful for education and increasing understanding of the anatomical structures of the temporal bone. However, it will be necessary to confirm the correlation between the 3D reconstructed images and histological sections through a validation study.     

基于CT片的颞骨计算机三维重建及实体模型复制

目的利用快速成形技术复制基于颞骨CT片重建的颞骨三维模型，探讨其临床应用前景。方法利用GE16排螺旋CT扫描重建的正常人及5例干颞骨水平断层片和Materialise Mimics 6．3体绘制软件重建颞骨三维立体模型。利用Auro SLA光固化快速成形机复制颞骨实体模型并进行手术演练。结果成功重建并复制了颞骨立体模型，模型表面骨性标志明显，不同断面剖切显示内部精细结构清晰。手术演练证明该模型能较好地满足手术模拟的要求。结论快速成形技术能够成功复制颞骨实体模型并用于术前手术演练，在侧颅底外科有广阔的应用前景，对于设计手术入路和减少并发症发生具有重要意义。     

Three-dimensional images of the reuniting duct using cone beam CT

Conclusion. There is a bony groove under the course of the reuniting duct of the inner ear. Cone beam CT could show three-dimensional (3D) reconstruction images of this groove in a cadaver and living human subjects. Objective. To obtain simple and universal images of the reuniting duct in humans for clinical use. Materials and methods. We investigated the reuniting duct macroscopically by observing the temporal bone in cadavers and living human subjects using cone beam CT. 3D reconstruction images of the duct were analyzed by the rendering software IVIEW. Results. The reuniting duct showed a bony groove between the saccule and cecum of the hook portion of the cochlea that could be three-dimensionally visualized by cone beam CT. A bony groove image in a living human subject could also be visualized by cone beam CT.     

高分辨CT三维容积重建对颞骨骨质破坏的诊断价值

目的：探讨高分辨CT(HRCT)三维容积重建在颞骨骨质破坏中的诊断价值。方法：术前高分辨率轴位或冠状位CT上显示有颞骨骨质破坏或高度怀疑有骨质破坏的15例胆脂瘤型中耳炎患者，应用容积再现(VR)对病变区进行重建，术中观察病变范围并与重建图像比较。结果：与轴位或冠状位CT图像相比，所有重建图像均清晰地显示了骨质的破坏区域，并立体地显示了与周围骨质之间的关系，与手术结果相符合。结论：HRCT三维容积重建对颞骨骨质破坏诊断具有较高价值，并且有利于手术方式的制定。     

The Value of Measuring Eustachian Tube Aeration on Temporal Bone CT in Patients with Chronic Otitis Media

Objectives

To evaluate that the cross-sectional area of the air space in the Eustachian tube (ET) on computed tomography (CT) images could be useful for predicting the postoperative aeration of the middle ear.

Methods

The patient group consisted of 80 patients (80 ears) with chronic otitis media and who underwent middle ear surgery from 2006-2007 and who were followed up for more than 1 yr. The control group consisted of 100 ears of 50 individuals with normal tympanic membranes and who underwent CT for other causes (such as tinnitus or hearing loss). The largest cross-sectional areas of the aerated ET were measured on the coronal images of the temporal bone CT by a single otologist using the computer-based "Region of Interest" picture archiving and communications system. The patient group was divided into two subgroups, 1) those with good postoperative aeration and 2) those with poor postoperative aeration. The largest cross-sectional areas of the aerated ETs were compared between the patients and the controls, and between the patients with good aeration and the patients with poor aeration.

Results

The mean cross-sectional areas significantly differed between the patient group and the control group, and between the good and poor aeration subgroups (P<0.05 each). The mean area of the poor aeration subgroup was smaller than that of the control group (P<0.05), but the mean area of the good aeration subgroup did not significantly differ from that of the controls.

Conclusion

The cross-sectional area of the aerated ET, as measured on the preoperative coronal images of temporal bone CT scans, may be useful for predicting the postoperative condition of the tympanic cavity.     

An experimental study for qualitatively diagnosing stapes lesions by helical 3-dimensional CT

To evaluate qualitative diagnosis of stapes lesions by 3-dimensional computed tomography (3D-CT) combined with superselective image processing (3D-SS) of stapes, we studied helical 3D-CT on a phantom model of the temporal bone. Two stapes models were used-1 made from the bone filler, Celatite, consistent in bone density but changing in cross sectional area, and the other made from an apacerum rod used in quantitative computed tomography (QCT), consistent in cross sectional area but changing in bone density. These stapes models were put into a skull phantom and analyzed by helical 3D-CT. The influence of the tympanic cavity conditions on CT images of stapes was evaluated by filling the phantom model with Vaseline following 3D selective reconstruction. In all stapes models, lowering the lower CT window width threshold resulted in an enlarged cross-sectional area of the model. The higher the bone density, the lower the increase in cross-sectional area in the image. The stapes model with lower density had greater influence on the imaging by tympanic cavity conditions and was likely to be misdiagnosed as showing higher bone density. Based on the experimental study, 3D-SS by helical 3D-CT appears to be a useful measure for qualitatively diagnosing stapes lesions.     

High-resolution petrous bone imaging using multi-slice computerized tomography

Multi-slice computerized tomography (MSCT) is considered to provide superior image quality. We defined a data acquisition protocol for high-resolution (HR) temporal bone imaging using MSCT and assessed its impact on data acquisition and post-processing (PP). The data acquisition protocol was defined in cadaveric phantom studies performed by MSCT and subsequently applied to 38 patients referred for temporal bone assessment. The parameters image quality and diagnostic value of MSCT data were assessed for the cross-sectional source images as well as for 2-dimensional (2D) reformations and 3-dimensional (3D) reconstructions by 3 radiologists by comparison with incremental HR scans of 17 patients with suspected middle ear disorders. The data acquisition protocol yielded HR images with an excellent detail resolution and a comparable image quality of cross-sectional scans and related orthogonal reformations. MSCT achieved higher scores for image quality and diagnostic value (p < 0.001, t-test) than incremental HR CT with regard to both 2D and 3D reconstructions. MSCT improves the image quality of HR cross-sectional scans as well as that of 2D and 3D PP techniques in petrous bone imaging. The radiation exposure of the eye lenses is increased by MSCT as gantry angulation is not yet possible in the helical scan mode.     

Accuracy of CT in the measurement of stapes prostheses using a temporal bone model

Objectives. Current 3D temporal bone models have either lacked the resolution (if volume‐rendered from imaging)¹ or lacked the interactivity (if surface‐rendered from sections)² necessary for surgical training. The objective was to produce a 3D volume‐rendered temporal bone model from serial sections. Method. High resolution images were acquired from serial histological sections of the temporal bone using a Canon SLR digital 8‐megapixel camera. Image registration was performed by aligning in Adobe Photoshop on a PC with a 256 Mb graphics card. Segmentation of surgically relevant anatomical structures was performed followed by 3D volumetric reconstruction. The model was finally checked for anatomical accuracy and interactivity by practicing otologists. Results. An anatomically accurate, high resolution 3D volume‐rendered model of the temporal bone was produced, containing many of the surgically relevant structures the otologist may come across during surgery. The course of the facial nerve, the labyrinth, internal carotid artery, jugular vein and all the ossicles where visualised (including the stapes footplate) along with the internal and external auditory meati and even the chorda tympani nerve in some projections. The model was interactive with the ability to rotate it in any plane, zoom into areas of interest and ‘cut’ volume to reveal underlying structures. Conclusions. To the best of our knowledge, this is the world's first 3D volume‐rendered model of the temporal bone from histological sections. At a time of difficulty in procuring cadaveric bones, this model could be a major aid to improving the future training of surgeons performing procedures on the temporal bone. References. 1 Wiet G.J., Schmalbrock P., Powell K. & Stredney D. (2005) Use of ultra‐high‐resolution data for temporal bone dissection simulation. Otolaryngol. Head Neck Surg. 133, 911–915 2 Mason T.P., Applebaum E.L., Rasmussen M., Millman A., Evenhouse R. & Panko W. (2000) Virtual temporal bone: creation and application of a new computer‐based teaching tool. Otolaryngol. Head Neck Surg. 122, 168–173     

3D printed temporal bone as a tool for otologic surgery simulation

PurposeIn this face validity study, we discuss the fabrication and utility of an affordable, computed tomography (CT)–based, anatomy-accurate, 3-dimensional (3D) printed temporal bone models for junior otolaryngology resident training.Materials and methodsAfter IRB exemption, patient CT scans were anonymized and downloaded as Digital Imaging and Communications in Medicine (DICOM) files to prepare for conversion. These files were converted to stereolithography format for 3D printing. Important soft tissue structures were identified and labeled to be printed in a separate color than bone. Models were printed using a desktop 3D printer (Ultimaker 3 Extended, Ultimaker BV, Netherlands) and polylactic acid (PLA) filament. 10 junior residents with no previous drilling experience participated in the study. Each resident was asked to drill a simple mastoidectomy on both a cadaveric and 3D printed temporal bone. Following their experience, they were asked to complete a Likert questionnaire.ResultsThe final result was an anatomically accurate (XYZ accuracy = 12.5, 12.5, 5 μm) 3D model of a temporal bone that was deemed to be appropriate in tactile feedback using the surgical drill. The total cost of the material required to fabricate the model was approximately $1.50. Participants found the 3D models overall to be similar to cadaveric temporal bones, particularly in overall value and safety.Conclusions3D printed temporal bone models can be used as an affordable and inexhaustible alternative, or supplement, to traditional cadaveric surgical simulation.     

High-resolution Petrous Bone Imaging Using Multi-slice Computerized Tomography

Multi-slice computerized tomography (MSCT) is considered to provide superior image quality. We defined a data acquisition protocol for high-resolution (HR) temporal bone imaging using MSCT and assessed its impact on data acquisition and post-processing (PP). The data acquisition protocol was defined in cadaveric phantom studies performed by MSCT and subsequently applied to 38 patients referred for temporal bone assessment. The parameters image quality and diagnostic value of MSCT data were assessed for the cross-sectional source images as well as for 2-dimensional (2D) reformations and 3-dimensional (3D) reconstructions by 3 radiologists by comparison with incremental HR scans of 17 patients with suspected middle ear disorders. The data acquisition protocol yielded HR images with an excellent detail resolution and a comparable image quality of cross-sectional scans and related orthogonal reformations. MSCT achieved higher scores for image quality and diagnostic value (p &lt; 0.001, t-test) than incremental HR CT with regard to both 2D and 3D reconstructions. MSCT improves the image quality of HR cross-sectional scans as well as that of 2D and 3D PP techniques in petrous bone imaging. The radiation exposure of the eye lenses is increased by MSCT as gantry angulation is not yet possible in the helical scan mode.     

颞骨CT三维重建面神经立体解剖定位

目的:探讨基于PC机的颞骨CT三维重建在面神经解剖定位中的方法和应用价值,总结出一套量化的研究面神经定位的方法,以便指导耳科及侧颅底手术。方法:使用3D-DOCTOR软件对成人轴位CT影像进行三维重建,显示颞骨内各重要结构的形态及其相互间复杂的立体关系。并用软件自带的功能测量面神经及其毗邻结构之间的距离和相对角度。分析测得的数据,总结面神经与其毗邻解剖标志结构之间的相对关系。结果:重建获得清晰的三维图像,包括面神经、鼓环、听小骨、匙突、锥隆起、内听道、耳蜗、半规管、颈静脉球窝、颈内动脉管等颞骨内结构。准确测量三维模型所得的面神经及其毗邻结构之间的相关参数并发现一定的规律性,这非常有益于手术中进行面神经快速定位和手术入路的设计。结论:基于PC机的颞骨CT三维重建可以准确地显示其内部各解剖结构及其相互间的空间立体关系,并可进行测量定位。     

Rapid prototyping of temporal bone for surgical training and medical education

OBJECTIVE: The skills of ear surgery are best developed by dissecting a temporal bone. However, only a limited number of trainees can be afforded this opportunity because of the scarcity of available bones. The aim of this study was to investigate the validity of a prototype temporal bone model for surgical training and education. MATERIAL AND METHODS: A simulated 3D model of a human temporal bone was made using a selective laser sintering method. The powder layers were laser-fused based on detailed CT data and accumulated to create a 3D structure. Conventional surgical instruments were used to dissect the model under a microscope. RESULTS: The model was as hard as real bone and surface structures were accurately reproduced. The model could be shaved using a surgical drill, burr and suction irrigator in the same way as a real bone. The malleus and incus were reproduced. The semicircular canals and the oval and round window niches were identified. Cavity structures, such as the semicircular canal, vestibule, antrum and air cells, were filled with powder which had to be removed using a pick and suction irrigator during dissection. A magnified model was useful for educating medical students. CONCLUSION: This prototype 3D model made using selective laser sintering serves as a good educational tool for middle ear surgery.     

Evaluation of mastoid air cell system by three-dimensional reconstruction using sagittal tomography of the temporal bone

The mastoid air cell system has been recognized as an important contributor to the pathophysiology of middle ear inflammatory diseases. Various methods of temporal bone imaging have been designed to investigate the correlation between middle ear disease and mastoid pneumatization. In this study, the mastoid air cell system was reconstructed three-dimensionally from sagittal tomographic images of the temporal bone on X-ray films, using a personal computer to evaluate the mastoid pneumatization in a total of 29 patients with chronic otitis media, adhesive otitis media, adhesive-type cholesteatoma, attic cholesteatoma and cholesterol granuloma, and in five normal subjects as controls. Reconstructed three-dimensional images of the mastoid air cell system and its volume were analyzed. The reconstructed images were helpful in recognizing the three-dimensional solid appearance of the mastoid air cell system. The volume of the reconstructed mastoid air cell system was significantly reduced compared with that in the controls in each of the patient groups. Mastoid pneumatization in the patients with adhesive-type cholesteatoma was significantly suppressed compared with that in the adhesive otitis media patients. Interestingly, the adhesive otitis media group showed cell development at the tip of mastoid process, whereas the group of adhesive-type cholesteatoma did not, suggesting a difference in the pathophysiology in the two diseases. We found that three-dimensional reconstruction of the temporal bone using sagittal tomographic images was useful in evaluating the state of mastoid air cell system development in individual cases and in investigating the pathophysiology in middle ear disease.     

内耳及毗邻结构三维形态学研究

目的基于颞骨CT三维重建,研究内耳及其毗邻结构的三维解剖关系,对内耳及其毗邻结构的空间立体关系进行测量定位,总结规律,为指导耳科及侧颅底手术提供参考。方法使用3D-DOCTOR软件对34例成人颞骨轴位CT影像进行三维重建,显示内耳及其毗邻各重要结构的形态及其相互间复杂的空间关系。并用软件自带的功能测量内耳及其毗邻结构之间的距离和相对角度,总结内耳及其毗邻各重要结构的距离及相对角度的规律性。结果重建获得了清晰的耳蜗、半规管、听小骨、面神经、内听道、颈静脉球窝、颈内动脉管等颞骨内重要结构三维图象。测量三维模型后准确获得了耳蜗及半规管与面神经、颈内动脉、颈静脉球之间相对关系的参数。结论颞骨CT三维重建可以明确地显示其内部各解剖结构及其相互间的空间立体关系。