Reduction of Radiation Dosage in Visualization of Paranasal Sinuses in Daily Routine.

Background. Preoperative imaging of the nose and paranasal sinus is standard in otorhinolaryngology. Previous studies on phantoms demonstrated the potential for dose reduction of cone beam computed tomography (CBCT) by varying the application parameters. Methodology. Based on previous studies, the standard protocol of paranasal sinus imaging by CBCT was altered. One hundred and fifty examinations using the old protocol (01/2010-01/2011, high dosage) and 150 examinations using the new protocol (09/2012-09/2013, low dosage) were evaluated and compared for the visibility of 17 anatomical structures, the Lund-Mackay Score, and technical parameters. Results. Alteration of the protocol resulted in a significant reduction in dosage (6.64 mGy versus 2.88 mGy). Both groups showed the same amount of pathology (Lund-Mackay Score: 4.95 ± 3.79 versus 5.26 ± 5.77; p = 0.558). There was a significant better visibility of the anatomical structures (all visible = 1, nothing visible = 4) (results: 1.25 versus 1.17; p = 0.001) in the low-dosage group. Conclusion. Despite a significant reduction in the applied dosage, reliable visualization of the bony anatomy of the anterior skull base is possible by CBCT. This demonstrates the need for the discussion of the required clinical imaging quality.

Visualization of anatomy in normal and pathologic middle ears by cone beam CT.

Cone beam computed tomography (CBCT, syn. digital volume tomography = DVT) was introduced into ENT imaging more than 10 years ago. The main focus was on imaging of the paranasal sinuses and traumatology of the mid face. In recent years, it has also been used in imaging of chronic ear diseases (especially in visualizing middle and inner ear implants), but an exact description of the advantages and limitations of visualizing precise anatomy in a relevant number of patients is still missing. The data sets of CBCT imaging of the middle and inner ear of 204 patients were analyzed regarding the visualization of 18 different anatomic structures. A three-step scale (excellent visible, partial visible, not visible) was taken. All analyses were performed by two surgeons experienced in otology and imaging. The indications for imaging were chronic middle ear disease or conductive hearing loss. Previously operated patients were excluded to rule out possible confounders. In dependence of a radiological pathology/opacity of the middle ear, two groups (with and without pathology) were built. Regarding the possibility of excellent visualization, significant differences were only found for small bony structures: incu-stapedial joint (25.8 vs. 63.5 %), long process of incus (42.7 vs. 88.8 %), head of stapes (27.0 vs. 62.6 %), anterior crus of stapes (16.9 vs. 40.9 %) and posterior crus of stapes (19.1 vs. 42.6 %). The other structures (semicircular canals, skull base at mastoid and middle ear, jugular bulb, sinus sigmoideus, facial nerve) could be visualized well in both groups with rates around 85-100 %. Even CBCT shows little limitations in visualization of the small structures of the middle and inner ear. Big bony structures can be visualized in normal as well as in pathologic ears. Overall, due to pathology of middle ear, an additional limitation of evaluation of the ossicular chain exists. In future, studies should focus on comparative evaluation of different diseases and different radiological modalities and be performed by radiologists and otologists together to improve the quality of reports and to answer clinical questions more satisfactorily.

Indications of cone beam CT in head and neck imaging.

CONCLUSION: Cone Beam Computed Tomography (CBCT) can be widely used in imaging of bony structures of the anterior and lateral skull base. Significant differences of applied dosages result from the different protocols of the various indications. OBJECTIVES: CBCT is increasingly being used in head and neck imaging. Until now, no precise knowledge about its dedicated usage existed. METHODS: All CBCT of 2012 and 2013 were analysed with regard to the technical parameters, the performance, and the indication for imaging. RESULTS: In total, 1862 patients were examined in 2012 and 2013. The top eight indications of the anterior skull were (1) chronic rhinosinusitis with disturbed nasal breathing (30.3%); (2) chronic rhinosinusitis (17.6%); (3) midfacial traumatology (13.7%); (4) disturbed nasal breathing (12.8%); (5) acute rhinosinusitis (7.9%); (6) polyposis nasi (6.3%); (7) search for focus (3.9%); and (8) persistent rhinorrhea (1.2%). For the lateral skull base, the top eight were (1) control after cochlear implantation (28.4%); (2) cholesteatoma (19.7%); (3) visualization of ear anatomy (8.7%); (4) chronic otitis media mesotympanalis (6.3%); (5) conductive hearing loss (5.1%); (6) suspected mastoiditis (4.8%); (7) pathology of external auditory canal (4.8%); and (8) otosclerosis (3.3%). Applied dosage for the anterior skull base was significantly lower than for the lateral skull base (2.90 mGy vs 5.92 mGy, p < 0.05); 2.4% and 3.6% of patients' images, respectively, had to be repeated.

Differences of radiological artefacts in cochlear implantation in temporal bone and complete head.

OBJECTIVES: Accurate radiological evaluation of cochlear implants is essential for improvement of devices and techniques and also for assessing the position of the electrodes within the cochlea. Radiological study of implants has focused on isolated temporal bones. Previous studies showed relevant sizes of artefacts (dimensions of the radiological image compared with the actual dimensions of the electrode) in visualization of cochlear implants in computed tomography and cone beam computed tomography (CBCT). In this study, we aimed to obtain CBCT images of cochlear electrodes in isolated temporal bones and in whole heads and to assess the differences in image quality between the two. METHODS: Cochlear electrodes were implanted in three complete human heads. Radiological examinations were performed using a single CBCT scanner with varying x-ray tube currents, voltages, and rotation angles. The temporal bones were then removed and the same radiological examinations were repeated, with and without the receiver coils. Artefacts from a basal electrode (electrode 9) and an apical electrode (electrode 2) were calculated. These were compared with each other by measuring the diameter of the image of the electrode (electrode inclusive of imaging artefacts) and with the real electrode diameters from the manufacturer's data. Additionally, the radiological diameters (inclusive of artefact) of the electrodes were compared to the cross-sectional diameters of the basal and apical coils of the cochlea at the locations of these two electrodes. RESULTS: In comparison to the real electrode diameters, radiological artefact proportions of 51-58% for electrode 9 and 56-61% for electrode 2 were calculated. The differences between whole head images (group 1) and temporal bone images with and without the receiver coil (groups 2 and 3) were highly significant for each protocol (P < 0.001). DISCUSSION AND CONCLUSION: These results indicate that it is not possible reliably to determine the exact intracochlear positions of electrodes using CBCT. Imaging of isolated temporal bones produced significantly greater artefacts than imaging of the whole head. Evaluations of image quality based only on results for isolated temporal bones are not transferable to clinical situations, and should be assessed critically.

Visualisation of the Bonebridge by means of CT and CBCT.

BACKGROUND: With the Bonebridge, a new bone-anchored hearing aid has been available since March 2012. The objective of the study was to analyse the visualisation of the implant itself as well as its impact on the representation of the bony structures of the petrosal bone in CT, MRI and cone beam CT (CBCT). METHODS: The Bonebridge was implanted unilaterally in two completely prepared human heads. The radiological imaging by means of CBCT, 64-slice CT, 1.5-T and 3.0-T MRI was conducted both preoperatively and postoperatively. The images were subsequently evaluated from both the ENT medical and nd radiological perspectives. RESULTS: As anticipated, no visualisation of the implant or of the petrosal bones could be realised on MRI because of the interactive technology and the magnet artefact. In contrast, an excellent evaluability of the implant itself as well as of the surrounding neurovascular structures (sinus sigmoideus, skull base, middle ear, inner ear, inner auditory canal) was exhibited in both the CT and in the CBCT. CONCLUSION: The Bonebridge can be excellently imaged with the radiological imaging technologies of CT and CBCT. In the process, CBCT shows discrete advantages in comparison with CT. No relevant restrictions in image quality in the evaluation of the bony structures of the petrosal bones could be seen.

Analysis of pneumatization and neurovascular structures of the sphenoid sinus using cone-beam tomography (CBT).

BACKGROUND: The sphenoid sinus is a frequent target of paranasal sinus surgery. Because of the high risk of injuring the surrounding structures (e.g. internal carotid artery, optical nerve) a preoperative imaging is absolutely necessary. PURPOSE: To analyze the possibilities of cone-beam computed tomography (CBCT), which is especially quite a new technique in ENT, in the evaluation of the sphenoid sinus, its surrounding structures, and the corresponding anatomical variations. MATERIAL AND METHODS: This was a retrospective, single-centre study of 580 patients (1160 sides = cases). The Accu-I-Tomo-F17 was used. Pneumatization of sphenoid sinus, course of internal artery, course of optical nerve, and dehiscence of the bony canals were evaluated. RESULTS: In the case of pneumatization a type I (completely missing or minimal sphenoid sinus) was found in two patients (0.3%), type II (posterior wall of sphenoid sinus is in front of the anterior wall of the sella) in 38 patients (6.6%), type III (posterior wall is between anterior and posterior wall of sella) in 332 patients (57,2%), type IVa (posterior wall is behind the posterior wall of sella without air dorsal the sella) in 104 patients (17.9%), and type IVb (similar to type IVa but with air dorsal the sella) in 104 patients (17.9%). In 1025 cases (89.5%) a smooth course of the internal carotid artery was found whereas a free course could be detected in 120 cases (10.5%). Defects of the bony canal of the optical nerve were found in 16.7% and of the internal carotid artery in 2.7% of the cases. The optical nerve showed a free course through the sphenoid in 151 cases (13.7%) and a smooth course in 1007 cases (87.0%). CONCLUSION: CBCT could evaluate all relevant anatomic structures and answer the questions of different anatomical variants. A modified classification of the pneumatization of the sphenoid sinus could be described. Frequencies of anatomical variations are in accordance with the current literature of CT research.

Age-dependent differences of the anterior skull base.

OBJECTIVE: Imaging of the anterior skull base and paranasal sinuses is essential before surgery of the nose and paranasal sinuses. It is important to know individual anatomical variations to define a "dangerous ethmoid" to prevent complications such as considerable bleeding or injury to the brain. This study aimed to analyze the relevant parameters with special regard to age-dependent differences. METHODS: This was a retrospective, single center study of 865 patients. Data from cone beam computed tomography (CBCT) of 116 patients less than 18 years of age and 749 adult patients were analyzed. Keros type, the course of the anterior ethmoid artery, the course of the uncinate process and the angle between the lateral lamella and the cribriform of the olfactory fossa were evaluated. RESULTS: Different frequencies of the course of the uncinate process between young and adult persons could be shown: onset at the lamina papyracea 67% vs. 64%; onset at the skull base, 22% vs. 26%; and onset at the middle turbinate, 11% vs. 10%. Differences in the course of the anterior ethmoid artery could be evaluated in the same way: course at the skull base, 49% vs. 44%; free course with a distance to the skull base of less than 3mm, 11% vs. 19%; and free course with a distance to the skull base more than 3mm, 40% vs. 37%. Significant differences could be found in the frequencies of the height of the olfactory fossa: Keros type I, 28% vs. 16%; Keros type II, 51% vs. 60%; and Keros type III, 21% vs. 24%. The angle between the lateral lamella and the cribriform plate showed significant differences dependent on the course of the anterior ethmoid artery (skull base=123° vs. distance<3mm=117° vs. distance>3mm=110°) and dependent on the height of the olfactory fossa (Keros type I=135° vs. Keros type II=117° vs. Keros type III=104°). Analysis of the angle as a factor of age and Keros type showed a significant difference in Keros type I (125° vs. 132°) and Keros type II (105° vs. 110°). CONCLUSION: Cone beam computed tomography (CBCT) of the anterior skull base allows the assessment of individual anatomical-radiological risk profiles and the identification of a "dangerous ethmoid". Significant age-dependent differences in the frequencies of anatomic landmarks and the angles of the ethmoid roof could be evaluated and led to significantly different risk profiles between children and adults.

Analysis of the fossa olfactoria using cone beam tomography (CBT).

CONCLUSION: A cone beam tomography (CBT) examination of the olfactory area with its different variants allows development of an individual anatomical-radiological risk profile of the ethmoid and the identification of so-called 'dangerous ethmoids.' OBJECTIVE: Preoperative imaging performed with high-resolution CBT is imperative for analysis of the risk of injuring the olfactory fossa during sinus surgery. This study aimed to analyze the relevant parameters. METHODS: This was a retrospective, single-center study of 141 patients. The Accu-I-Tomo F17 was used. Keros type, the point of the anterior ethmoid artery, and the angle between the lateral lamella and the cribriform plate (α(lc)) were evaluated. RESULTS: The Keros types were distributed as follows: type I, 13% (α(lc): 131°); type II, 64% (α(lc): 116°); type III, 23% (α(lc): 108°) (p < 0.001). The angle of the olfactory fossa and the position of the anterior ethmoid artery (free course: α(lc)=112° vs integrated into the skull base: α(lc)= 120°) was significantly different. DISCUSSION: Surgical procedures in Keros type III where the height of the lateral lamella is much longer than in type II or type I, with an angle of nearly 107° between the lateral lamella and the cribriform plate, are expected to be safer in comparison with Keros type II with 116° and Keros type I with 131°.