Robert J. Witte

Scalar Localization of the Electrode Array After Cochlear Implantation: A Cadaveric Validation Study Comparing 64-slice Multidetector Computed Tomography With Microcomputed Tomography

Hypothesis: Improved resolution available with 64-slice multidetector computed tomography (MDCT) could potentially be used clinically to localize the cochlear implant (CI) electrode array within the basal turn. Background: In CI surgery, the electrode array should be inserted into and remain within the scala tympani to avoid injury to Reissners membrane and the scala media. Correlating the position of the electrode in the basal turn with surgical technique and implant design could be helpful in improving outcomes. Methods: After a standard left mastoid exposure of the round window niche through the facial recess performed on a cadaver head, an electrode array from a Nucleus Softip Contour CI was fully inserted through a cochleostomy. The head was then scanned axially on a 64-slice MDCT with 0.4-mm slice thickness and reconstructed into the oblique axial, oblique coronal, and oblique sagittal planes of the cochlea. The temporal bone was then harvested and imaged on a microcomputed tomographic scanner using 20-&mgr;m slice thickness. Identical reconstructions were made and compared with the 64-slice images to confirm exact location of the electrode array. Results: The 64-slice MDCT accurately localized the electrode array to the scala tympani. This was best demonstrated in the oblique sagittal plane, identifying the electrode array in the posterior inferior portion of the basal turn, posterior to the spiral lamina. Conclusion: This ex vivo validation study suggests that 64-slice MDCT has the potential to allow accurate localization of the CI electrode array within the basal turn of the cochlea.

Scalar localization of the electrode array after cochlear implantation: clinical experience using 64-slice multidetector computed tomography.

Objective: To use the improved resolution available with 64-slice multidetector computed tomography (MDCT) in vivo to localize the cochlear implant electrode array within the basal turn. Study Design: Sixty-four-slice MDCT examinations of the temporal bones were retrospectively reviewed in 17 patients. Twenty-three implants were evaluated. Setting: Tertiary referral facility. Patients: All patients with previous cochlear implantation evaluated at our center between January 2004 and March 2006 were offered a computed tomographic examination as part of the study. In addition, preoperative computed tomographic examinations in patients being evaluated for a second bilateral device were included. Intervention: Sixty-four-slice MDCT examination of the temporal bones. Main Outcome Measure: Localization of the electrode array within the basal turn from multiplanar reconstructions of the cochlea. Results: Twenty-three implants were imaged in 17 patients. We were able to localize the electrode array within the scala tympani within the basal turn in 10 implants. In 3 implants, the electrode array was localized to the scala vestibuli. Migration of the electrode array from scala tympani to scala vestibuli was observed in three implants. Of the 7 implants in which localization of the electrode array was indeterminate, all had disease entities that obscured the definition of the normal cochlear anatomy. Conclusions: Sixty-four-slice MDCT with multiplanar reconstructions of the postoperative cochlea after cochlear implantation allows for accurate localization of the electrode array within the basal turn where normal cochlear anatomy is not obscured by the underlying disease process. Correlating the position of the electrode in the basal turn with surgical technique and implant design could be helpful in improving outcomes.

Temporal Bone CT: Improved Image Quality and Potential for Decreased Radiation Dose Using an Ultra-High-Resolution Scan Mode with an Iterative Reconstruction Algorithm

Patients with baseline temporal bone CT scans acquired by using a z-axis ultra-high-resolution protocol and a follow-up scan by using the ultra-high-resolution–iterative reconstruction technique were identified. Images of left and right temporal bones were reconstructed in the axial, coronal, and Poschl planes. Spatial resolution was comparable (Poschl) or slightly better (axial and coronal planes) with ultra-high-resolution–iterative reconstruction than with z-axis ultra-high-resolution. Paired t test indicated that noise was significantly lower with ultra-high-resolution–iterative reconstruction than with z-axis ultra-high-resolution. BACKGROUND AND PURPOSE: Radiation dose in temporal bone CT imaging can be high due to the requirement of high spatial resolution. In this study, we assessed whether CT imaging of the temporal bone by using an ultra-high-resolution scan mode combined with iterative reconstruction provides higher spatial resolution and lower image noise than a z-axis ultra-high-resolution mode. MATERIALS AND METHODS: Patients with baseline temporal bone CT scans acquired by using a z-axis ultra-high-resolution protocol and a follow-up scan by using the ultra-high-resolution–iterative reconstruction technique were identified. Images of left and right temporal bones were reconstructed in the axial, coronal, and Poschl planes. Three neuroradiologists assessed the spatial resolution of the following structures: round and oval windows, incudomallear and incudostapedial joints, basal turn spiral lamina, and scutum. The paired z-axis ultra-high-resolution and ultra-high-resolution–iterative reconstruction images were displayed side by side in random order, with readers blinded to the imaging protocol. Image noise was compared in ROIs over the posterior fossa. RESULTS: We identified 8 patients, yielding 16 sets of temporal bone images (left and right). Three sets were excluded because the patient underwent surgery between the 2 examinations. Spatial resolution was comparable (Poschl) or slightly better (axial and coronal planes) with ultra-high-resolution–iterative reconstruction than with z-axis ultra-high-resolution. A paired t test indicated that noise was significantly lower with ultra-high-resolution–iterative reconstruction than with z-axis ultra-high-resolution (P < .001), with a mean noise reduction of 37% (range, 18%–49%). CONCLUSIONS: The ultra-high-resolution–iterative reconstruction scan mode has similar or slightly better resolution relative to the z-axis ultra-high-resolution mode for CT of the temporal bone but significantly (P < .01) lower image noise, which may enable the dose to be reduced by approximately 50%.

F178. Epilepsy and temporal encephaloceles: Presurgical evaluation and surgical outcomes

Introduction Temporal encephalocele (TE) is an under-recognized surgically-remediable cause of medically refractory temporal lobe epilepsy. This study assessed preoperative evaluations [MRI, FDG-PET, routine and prolonged video scalp EEG, intraoperative and extraoperative electrocorticography (ECog)] and short-term surgical outcomes in patients with medically refractory temporal lobe epilepsy due to TE. Methods Patients with medically refractory temporal lobe epilepsy who underwent surgical intervention for known TE at the Mayo Clinic Rochester between January 2008 and July 2017 were identified. Additional patients who underwent surgery for temporal lobe epilepsy were found retrospectively on review of PET-CT or PET-MRI by an experienced neuroradiologist. Minimum required follow-up was 3 months. Results Fifteen patients were identified (female 80%, median age 42.1 years, interquartile range (IQR) 19.3–54.9 years). TE was identified in 7 patients prior to surgery (left 3, right 2, bilateral 2), from radiology re-review in 7 (left 1, right 1, bilateral 5), and intraoperatively in 1 (right). Temporal hypometabolism was present on FDG-PET in 7 of 10 patients, including 5 initial MRI reviews not suggestive of TE. Routine EEG was normal in 7 patients (47%). Prolonged video EEG showed interictal discharges and ictal onset ipsilateral to the TE in all unilateral cases. In bilateral TE, temporal interictal discharges were lateralized in 4 patients and focal ictal onset present in 5 patients. Intraoperative or extraoperative ECog showed widespread mesial and neocortical temporal discharges in 12 of 14 patients. Three patients (20%) underwent focal TE resection, 11 patients (73.3%) anterior temporal lobectomy (ATL), and 1 patient amygdalohippocampal laser ablation. Eight patients (53.3%) were seizure-free at last follow-up (median follow-up duration 7.1 months, IQR 4.2–41.9, 1 focal TE resection, 7 ATL). Focal TE resection was performed only in recent years (median duration of follow-up in focal TE resection 7.2 months, IQR 7–13.8, versus ATL 18.7 months, IQR 4.1–48.8), and comparison of surgical outcome between surgical groups was limited to short-term follow-up. At 6 months, seizure-freedom was achieved in 2 of 3 patient with focal TE resection and 4 of 6 patients with ATL (p > 0.05). Conclusion TE is an easily overlooked etiology of medically refractory temporal lobe epilepsy. Normal routine EEG and unrevealing initial MRI review were seen in nearly half of the patients. Although prolonged video scalp EEG provided concordant localizing information consistent with TE, ECog often showed epileptogenic discharges extending beyond regions around the TE and should be interpreted with caution as short-term follow up remained favorable despite focal TE resection. Long-term follow-up is needed to clarify which surgical approach optimizes seizure outcome while minimizing resection.

Comparison of a photon-counting-detector CT with an energy-integrating-detector CT for temporal bone imaging: A cadaveric study

BACKGROUND AND PURPOSE: Evaluating abnormalities of the temporal bone requires high-spatial-resolution CT imaging. Our aim was to assess the performance of photon-counting-detector ultra-high-resolution acquisitions for temporal bone imaging and compare the results with those of energy-integrating-detector ultra-high-resolution acquisitions. MATERIALS AND METHODS: Phantom studies were conducted to quantify spatial resolution of the ultra-high-resolution mode on a prototype photon-counting-detector CT scanner and an energy-integrating-detector CT scanner that uses a comb filter. Ten cadaveric temporal bones were scanned on both systems with the radiation dose matched to that of the clinical examinations. Images were reconstructed using a sharp kernel, 0.6-mm (minimum) thickness for energy-integrating-detector CT, and 0.6- and 0.25-mm (minimum) thicknesses for photon-counting-detector CT. Image noise was measured and compared using adjusted 1-way ANOVA. Images were reviewed blindly by 3 neuroradiologists to assess the incudomallear joint, stapes footplate, modiolus, and overall image quality. The ranking results for each specimen and protocol were compared using the Friedman test. The Krippendorff α was used for interreader agreement. RESULTS: Photon-counting-detector CT showed an increase of in-plane resolution compared with energy-integrating-detector CT. At the same thickness (0.6 mm), images from photon-counting-detector CT had significantly lower (P < .001) image noise compared with energy-integrating-detector CT. Readers preferred the photon-counting-detector CT images to the energy-integrating-detector images for all 3 temporal bone structures. A moderate interreader agreement was observed with the Krippendorff α = 0.50. For overall image quality, photon-counting-detector CT image sets were ranked significantly higher than images from energy-integrating-detector CT (P < .001). CONCLUSIONS: This study demonstrated substantially better delineation of fine anatomy for the temporal bones scanned with the ultra-high-resolution mode of photon-counting-detector CT compared with the ultra-high-resolution mode of a commercial energy-integrating-detector CT scanner.

Cochlear Implant Electrode Localization Using an Ultra-High Resolution Scan Mode on Conventional 64-Slice and New Generation 192-Slice Multi-Detector Computed Tomography

HYPOTHESIS A new generation 192-slice multi-detector computed tomography (MDCT) clinical scanner provides enhanced image quality and superior electrode localization over conventional MDCT. BACKGROUND Currently, accurate and reliable cochlear implant electrode localization using conventional MDCT scanners remains elusive. METHODS Eight fresh-frozen cadaveric temporal bones were implanted with full-length cochlear implant electrodes. Specimens were subsequently scanned with conventional 64-slice and new generation 192-slice MDCT scanners utilizing ultra-high resolution modes. Additionally, all specimens were scanned with micro-CT to provide a reference criterion for electrode position. Images were reconstructed according to routine temporal bone clinical protocols. Three neuroradiologists, blinded to scanner type, reviewed images independently to assess resolution of individual electrodes, scalar localization, and severity of image artifact. RESULTS Serving as the reference standard, micro-CT identified scalar crossover in one specimen; imaging of all remaining cochleae demonstrated complete scala tympani insertions. The 192-slice MDCT scanner exhibited improved resolution of individual electrodes (p < 0.01), superior scalar localization (p < 0.01), and reduced blooming artifact (p < 0.05), compared with conventional 64-slice MDCT. There was no significant difference between platforms when comparing streak or ring artifact. CONCLUSION The new generation 192-slice MDCT scanner offers several notable advantages for cochlear implant imaging compared with conventional MDCT. This technology provides important feedback regarding electrode position and course, which may help in future optimization of surgical technique and electrode design.

Indium-111 labeled leukocyte imaging following hepatic artery embolization.

The use of In-111 labeled leukocytes for abscess localization is becoming well established. The first report of In-111 imaging following hepatic embolization is presented. A 45-year-old man with adenocarcinoma of the colon and metastatic liver disease was treated for intractable pain using particulate embolization of the hepatic artery. In-111 leukocyte imaging was performed to rule out abscess formation. The distribution of the labeled leukocytes demonstrated hepatic uptake commensurate with Tc-99m sulfur colloid (SC) images. Areas of embolization did not accumulate tracer. Pathologic examination at autopsy correlated with the distribution of the labeled leukocytes. Thus, therapeutic embolization did not alter the normal distribution of this tracer in functional hepatic tissue.