Cone-beam CT versus Multidetector CT in Postoperative Cochlear Implant Imaging: Evaluation of Image Quality and Radiation Dose

High Spatial-Resolution Skull Base Imaging With Photon-Counting Computed Tomography and Energy-Integrating Computed Tomography: A Comparative Phantom Study

ABSTRACT

Photon-counting computed tomography (PCCT) offers better high-resolution and noise performance than energy integrating detector (EID) CT. In this work, we compared both technologies for imaging of the temporal bone and skull base. A clinical PCCT system and 3 clinical EID CT scanners were used to image the American College of Radiology image quality phantom using a clinical imaging protocol with matched CTDI vol (CT dose index-volume) of 25 mGy. Images were used to characterize the image quality of each system across a series of high-resolution reconstruction options. Noise was calculated from the noise power spectrum, whereas resolution was quantified with a bone insert by calculating a task transfer function. Images of an anthropomorphic skull phantom and 2 patient cases were examined for visualization of small anatomical structures. Across measured conditions, PCCT had a comparable or smaller average noise magnitude (120 Hounsfield units [HU]) to the EID systems (144-326 HU). Photon-counting CT also had comparable resolution (task transfer function f25 : 1.60 mm -1 ) to the EID systems (1.34-1.77 mm -1 ). Imaging results supported quantitative findings as PCCT more clearly showed the 12-lp/cm bars from the fourth section of the American College of Radiology phantom and better represented the vestibular aqueduct and oval and round windows when compared with the EID scanners. A clinical PCCT system was able to image the temporal bone and skull base with improved spatial resolution and lower noise than clinical EID CT systems at matched dose.

OPTIMISING THE PARAMETERS OF COCHLEAR IMPLANT IMAGING WITH CONE-BEAM COMPUTED TOMOGRAPHY

With computed tomography (CT), the delicate structures of the inner ear may be hard to visualise, which a cochlear implant (CI) electrode array can further complicate. The usefulness of a novel cone-beam CT device in CI recipient's inner ear imaging was evaluated and the exposure parameters were optimised to attain adequate clinical image quality at the lowest effective dose (ED). Six temporal bones were implanted with a Cochlear Slim Straight electrode array and imaged with six different imaging protocols. Contrast-to-noise ratio was calculated for each imaging protocol, and three observers evaluated independently the image quality of each imaging protocol and temporal bone. The overall image quality of the inner ear structures did not differ between the imaging protocols and the most relevant inner ear structures of CI recipient's inner ear can be visualised with a low ED. To visualise the most delicate structures in the inner ear, imaging protocols with higher radiation exposure may be required.

[Radiologic Imaging of Pediatric Hearing Loss]

Hearing loss in childhood has serious consequences for the entire development of the child. It is very important to make an accurate early diagnosis. The assessment usually includes physical, genetic, and radiological examination. In imaging diagnostics, CT, Cone Beam CT and or MRI of the petrous bone are the usual imaging modalities for the assessment of diseases of mastoid air cells, middle ear, external ear, the cochlea, the vestibulocochlear nerve, and the brain.

High-speed flat-detector computed tomography for temporal bone imaging and postoperative control of cochlear implants

PURPOSE

Flat-detector computed tomography (FD-CT) is the standard for cochlear implant (CI) imaging. FD-CT systems differ in technical characteristics. Our aim was an evaluation of two different FD-CT generations with different protocols and hardware regarding image quality, radiation dose, and scan time.

METHODS

Two temporal bone specimens (- / + CI = TB₀/TB₁) were scanned using three different scanners: two FD-CT systems with different scanning protocols (standard FD-CT: 20 s 70 kV, 20 s 109 kV; high-speed FD-CT [HS-FD-CT]: 7 s 109 kV, 9 s 109 kV, 14 s 72 kV) and MS-CT (5 s 120 kV). Acquired datasets were evaluated in consensus reading regarding qualitative and quantitative parameters: addressing CI- and cochlea-specific parameters, cochlea delineation, lamina spiralis ossea visibility, distinction of single CI electrodes, determination of intracochlear implant position, stapes delineation, and mastoidal septation were assessed. Addressing protocol-specific parameters, radiation dose (dose-length-product/DLP), and scan time were assessed.

RESULTS

Two HS-FD-CT protocols (14 s/9 s) provide higher or equivalent diagnostic information regarding CI- and cochlea-specific parameters compared to both standard FD-CT protocols. The fastest HS-FD-CT protocol (7 s)-providing inferior diagnostic information compared to all other FD-CT protocols-still exceeds MS-CT. The highest DLP was recorded for the 14 s HS-FD-CT protocol (TB₁ = 956 mGycm); the lowest DLPs were recorded for the 7 s HS-FD-CT protocol (TB₀ = 188 mGycm) and for MS-CT (TB₀ = 138 mGycm), respectively. HS-FD-CT allows a significant reduction of scan time compared to standard FD-CT.

CONCLUSION

High-speed FD-CT improves visualization of temporal bone anatomy and postoperative assessment of CIs by combining excellent image quality, fast scan time, and reasonable radiation exposure.

Visualization of Different Types of Cochlear Implants in Postoperative Cone-Beam CT Imaging

RATIONALE AND OBJECTIVES

To evaluate cone-beam computed-tomography (CBCT) images of the temporal bone for radiological delineation, metal artifacts, and accuracy for localization of six different electrode arrays after cochlear device implantation.

MATERIALS AND METHODS

This retrospective study included 116 patients who underwent CBCT (120kV, 7.1mA) within 24 hours after cochlear device implantation. Exclusion criteria were anatomical abnormalities, and electrode misinsertion. Six different CI electrodes were implanted: Advanced Bionics HiFocus Mid-Scala, Cochlear Contour Advance, Cochlear Slim-Straight, Cochlear Slim-Modiolar, MED-EL Flex 24 and MED-EL Flex 28. Two radiologists rated independently presence of metal artifacts, overall image quality, as well as dedicated visualization of the osseous spiral lamina, inner and outer cochlear wall, single electrode contacts, and electrode position using 5-point-Likert scales. Inter-rater agreement was calculated by using Cohen's kappa and intraclass correlation.

RESULTS

Of 116 patients, 94 (81.0%; 56.1 ± 16.9 years; age range, 13-86 years; 49 [52.1%] females) were included in the study. Overall image quality was rated good for all electrode models without significant differences (p = 0.061). Depiction of electrode contacts was rated significantly better for Advanced Bionics HiFocus Mid-Scala, Cochlear Slim-Straight, and MED-EL Flex 24 and 28 compared to Cochlear Contour Advance and Slim-Modiolar (p < 0.001). Depiction of the osseous spiral lamina (p = 0.20), inner (p = 0.42) and outer cochlear wall (p = 0.35), metal artifacts (p = 0.18), and electrode position (p = 0.31) did not show significant differences between electrode models. Inter-rater agreement varied from substantial to almost perfect (0.70-0.93).

CONCLUSION

CBCT provides excellent visualization of all evaluated CI electrode types, in particular electrode arrays with greater spacing between contacts and contact size allow improved radiologic evaluation.

Measuring 3D Cochlear Duct Length on MRI: Is It Accurate and Reliable?

BACKGROUND AND PURPOSE

Prior studies have evaluated cochlear length using CT to select the most suitable cochlear implants and obtain patient-specific anatomy. This study aimed to test the accuracy and reliability of cochlear lateral wall length measurements using 3D MR imaging.

MATERIALS AND METHODS

Two observers measured the cochlear lateral wall length of 35 patients (21 men) with postlingual hearing loss using CT and MR imaging. The intraclass correlation coefficient (with 95% confidence intervals) was used to evaluate intraobserver and interobserver reliability for the 3D cochlear measurements.

RESULTS

The mean age of the participants was 39.85 (SD, 16.60) years. Observer 1 measured the mean lateral wall length as 41.52 (SD, 2.25) mm on CT and 41.44 (SD, 2.18) mm on MR imaging, with a mean difference of 0.08 mm (95% CI, -0.11 to 0.27 mm), while observer 2 measured the mean lateral wall length as 41.74 (SD, 2.69) mm on CT and 42.34 (SD, 2.53) mm on MR imaging, with a mean difference of -0.59 mm (95% CI, -1.00 to -0.20 mm). An intraclass correlation coefficient value of 0.90 (95% CI, 0.84-0.94) for CT and 0.69 (95% CI, 0.46-0.82) for MR imaging was obtained for the interobserver reliability for the full-turn cochlear lateral wall length.

CONCLUSIONS

CT-based 3D cochlear measurements show excellent intraobserver and interobserver reliability, while MR imaging-based lateral wall length measurements have good-to-excellent intraobserver reliability and moderate interobserver reliability. These results corroborate the use of CT for 3D cochlear measurements as a reference method and demonstrate MR imaging to be an alternative acquisition technique with comparably reliable results.