Clinically relevant human temporal bone measurements using novel high-resolution cone-beam CT

Assessment of subjective image quality, contrast to noise ratio and modulation transfer function in the middle ear using a novel full body cone beam computed tomography device

BACKGROUND

Multi slice computed tomography (MSCT) is the most common used method in middle ear imaging. However, MSCT lacks the ability to distinguish the ossicular chain microstructures in detail resulting in poorer diagnostic outcomes. Novel cone beam computed tomography (CBCT) devices' image resolution is, on the other hand, better than MSCT resolution. The aim of this study was to optimize imaging parameters of a novel full body CBCT device to obtain optimal contrast to noise ratio (CNR) with low effective dose, and to optimize its clinical usability.

METHODS

Imaging of five anonymous excised human cadaver temporal bones, the acquisition of the effective doses and the CNR measurements were performed for images acquired on using Planmed XFI® full body CBCT device (Planmed Oy, Helsinki, Finland) with a voxel size of 75 µm. All images acquired from the specimens using 10 different imaging protocols varying from their tube current exposure time product (mAs) and tube voltage (kVp) were analyzed for eight anatomical landmarks and evaluated by three evaluators.

RESULTS

With the exception of protocol with 90 kVp 100 mAs, all other protocols used are competent to image the finest structures. With a moderate effective dose (86.5 µSv), protocol with 90 kV 450 mAs was chosen the best protocol used in this study. A significant correlation between CNR and clinical image quality of the protocols was observed in linear regression model. Using the optimized imaging parameters, we were able to distinguish even the most delicate middle ear structures in 2D images and produce accurate 3D reconstructions.

CONCLUSIONS

In this ex vivo experiment, the new Planmed XFI® full body CBCT device produced excellent 2D resolution and easily created 3D reconstructions in middle ear imaging with moderate effective doses. This device would be suitable for middle ear diagnostics and for e.g., preoperative planning. Furthermore, the results of this study can be used to optimize the effective dose by selecting appropriate exposure parameters depending on the diagnostic task.

Ultra-low-dose CBCT scan: rational map for ear surgery

PURPOSE

This study will evaluate the clinical quality and usability of peripheral image data from the temporal bone area obtained using a sinonasal ultra-low-dose (ULD) cone-beam computed tomography (CBCT) scan and compare them to those obtained using a high-resolution (HR) CBCT.

METHODS

The population consisted of 66 anatomical sites (ears of 33 subjects) imaged using two modalities: an HR CBCT (Scanora 3Dx scanner; Soredex, Tuusula, Finland) and a ULD CBCT (Promax 3D Mid scanner; Plandent, Helsinki, Finland). The image quality (IQ) for every anatomical site in each image was rated using a Likert scale from 0 to 5.

RESULTS

The quality of ULD CBCT scans was clinically sufficient in over 95% of the assessed images of the sigmoid sinus, jugular bulb, epitympanum and mastoid antrum as well as external acoustic meatus (all p > 0.05 compared to HR CBCT). The IQ was clinically sufficient in 75-94% of the assessed images of the scutum, mastoid segment of the facial nerve, cochlea and semicircular canals (all p < 0.05 compared to HR CBCT). The overall IQ of the HR CBCT scans was good or excellent.

CONCLUSION

CBCT imaging and the data at image margins are underutilized. CBCT can produce excellent structural resolution with conventional imaging parameters, even with off-focus images. Using ultra-low doses of radiation, the produced IQ is clinically sufficient. We encourage ear surgeons to check the patients' imaging history and to consider the use of imaging modalities that involve lower radiation doses especially when conducting repetitive investigations and with children.

Evaluation of morphological variations of petrotympanic fissure using computed tomography imaging of the temporal bone

PURPOSE

Petrotympanic fissure (PF) is important for both dentists and otolaryngologists to know the temporal anatomy well especially for pre-surgical radiological evaluations. Computed tomography (CT) is indispensable method for temporal bone imaging. The purpose of this study was to evaluate PF morphology and position using CT.

METHODS

CT scans of 300 patients (600 PFs) were retrospectively evaluated. PF types were recorded by dividing into 3 groups (Type 1,2 and 3). Length of the mandibular fossa (MF) and PF, vertical diameter (VD) of the PF at the MF level, midpoint and tympanic cavity (TC) level were measured. PF position types were subdivided as low, midline and high.

RESULTS

Type 1, 2 and 3 was found in 18.7%, 51.5% and 29.8% of the cases, respectively. The mean length of the MF and PF was 18.33 mm and 3.77 mm, respectively. The mean VD of the PF at the MF level, midpoint and TC level was 1.71, 0.98 and 0.97 mm, respectively. The low, midline and high position of PF was observed 14.5%, 54.3% and 31.2% of the cases, respectively.

CONCLUSION

Length of the MF and PF in males was significantly higher than females. VD of the PF at the MF level in Type 1 and Type 3 was significantly higher than type 2. In type 1,VD of the PF at the midpoint was significantly higher than type 2 and type 3. VD of the PF at the TC level in Type 1 and Type 3 was significantly higher than type 2.

Cone-Beam CT Compared to Multi-Slice CT for the Diagnostic Analysis of Conductive Hearing Loss: A Feasibility Study

OBJECTIVES

Multislice computed tomography (MSCT) is commonly used as a diagnostic tool for patients with a conductive hearing loss. Recent studies indicate that cone-beam computed tomography (CBCT) may be used as a low-radiation dose alternative for temporal bone imaging. This study compares image quality and radiation dose between CBCT and MSCT when assessing anatomical landmarks related to conductive hearing loss.

MATERIALS AND METHODS

Five human cadaver heads (10 ears) were imaged on the NewTom 5G CBCT and the Discovery CT750 HD MSCT. Visibility of 16 anatomical landmarks of the middle and inner ear was assessed by two observers on a 4-point Likert scale. Furthermore, effective radiation dose was compared, and contrast-to-noise ratio and spatial resolution were measured with a phantom head.

RESULTS

Image quality of CBCT was assessed as superior to MSCT. Effective radiation dose of the high-resolution CBCT protocol was 30.5% of the clinical MSCT dose. High-resolution CBCT was reported as having a higher spatial resolution and superior contrast-to-noise perception in comparison with MSCT.

CONCLUSION

High-resolution CBCT was evaluated as superior to MSCT in the assessment of structures related to conductive hearing loss. Furthermore, CBCT imaging resulted in a considerably lower effective radiation dose.

[Progress of research on cone beam CT in cochlear implantation]

Cochlear implant, as the most successful artificial auditory implant, brings tens of thousands of patients with severe or profound sensorineural hearing loss back to the world of sound every year. With the expansion of surgical indications, a large number of difficult cases bring new challenges for cochlear implantation. As a new technology, cone beam CT has the double advantages of high spatial resolution and low radiation. It is considered as the second revolution of CT technology, which shows unique value in the application of cochlear implantation. This article reviews the basic principles of cone beam CT and its application and research progress in cochlear implantation.

Practicable assessment of cochlear size and shape from clinical CT images

There is considerable interpersonal variation in the size and shape of the human cochlea, with evident consequences for cochlear implantation. The ability to characterize a specific cochlea, from preoperative computed tomography (CT) images, would allow the clinician to personalize the choice of electrode, surgical approach and postoperative programming. In this study, we present a fast, practicable and freely available method for estimating cochlear size and shape from clinical CT. The approach taken is to fit a template surface to the CT data, using either a statistical shape model or a locally affine deformation (LAD). After fitting, we measure cochlear size, duct length and a novel measure of basal turn non-planarity, which we suggest might correlate with the risk of insertion trauma. Gold-standard measurements from a convenience sample of 18 micro-CT scans are compared with the same quantities estimated from low-resolution, noisy, pseudo-clinical data synthesized from the same micro-CT scans. The best results were obtained using the LAD method, with an expected error of 8-17% of the gold-standard sample range for non-planarity, cochlear size and duct length.

High Resolution Computed Tomography Atlas of the Porcine Temporal Bone and Skull Base: Anatomical Correlates for Traumatic Brain Injury Research

Brain injuries are a significant cause of morbidity and mortality worldwide. Auditory and vestibular dysfunction may occur following trauma to the temporal bone (TB), including the lateral skull base. The porcine model is a commonly used large animal model for investigating brain injury. Reports detailing porcine TB anatomy based on high resolution computed tomography (HRCT) imaging, however, are limited. Herein, we employ HRCT to evaluate and describe the bony anatomy of the porcine TB and lateral skull base. High-resolution multi-detector and cone beam CT were used to image porcine TBs (n = 16). TBs were analyzed for major anatomical structures and compared to human species. Porcine temporal bone anatomy was readily identifiable by HRCT. Although some variability exists, the ossicular chain, vestibule, cochlea, course of the facial nerve, and skull base are similar to those of humans. Major differences included position of the external auditory canal and mastoid, as well as presence of the petrous carotid canal. Study findings may serve as an atlas to evaluate the porcine middle and inner ear, as well as lateral skull base injuries for future porcine brain injury models or other studies that require CT-based analysis.

The radioanatomical assessment of the Körner's septum

PURPOSE OF THE STUDY

Körner's septum (KS) is a developmental remnant formed at the junction of mastoid and temporal squama, representing the persistence of the petrosquamosal suture. During mastoid surgery, it could be taken as a false medial wall of the antrum so that the deeper cells might not be explored. The aim of the study was to assess a Körner's septum prevalence and to analyze its topography.

METHODS

The study was performed on 80 sets of cone-beam computed tomography (CBCT) images of temporal bone (41 male, 39 female, 160 temporal bones). Körner's septum was identified and its thickness was measured on axial sections at three points: at the level of superior semicircular canal (SCC), at the level of head of malleus (HM) and at the level of tympanic sinus (TS).

RESULTS

KS was encountered at least in one point of measurements in 50 out of 80 sets of CBCT images (62.5%). The average thickness at the level of SCC was 0.87 ± 0.34 mm, at the level of HM was 0.99 ± 0.37 mm and at the level of TS was 0.52 ± 0.17 mm.

CONCLUSIONS

Körner's septum is a common structure in the temporal bone-air cell complex. It is more often encountered in men. In half of the patients, it occurs bilaterally. However, in most of the cases it is incomplete with anterior and superior portions being the most constant.