Thin-slice Computed Tomography Scans Research Articles

CT Radiomics for Predicting Pathological Complete Response of Axillary Lymph Nodes in Breast Cancer After Neoadjuvant Chemotherapy: A Prospective Study.

The diagnostic effectiveness of traditional imaging techniques is insufficient to assess the response of lymph nodes (LNs) to neoadjuvant chemotherapy (NAC), especially for pathological complete response (pCR). A radiomics model based on computed tomography (CT) could be helpful. Prospective consecutive breast cancer patients with positive axillary LNs initially were enrolled, who received NAC prior to surgery. Chest contrast-enhanced thin-slice CT scan was performed both before and after the NAC (recorded as the first and the second CT respectively), and on both of them, the target metastatic axillary LN was identified and demarcated layer by layer. Using pyradiomics-based software that was independently created, radiomics features were retrieved. A pairwise machine learning workflow based on Sklearn (https://scikit-learn.org/) and FeAture Explorer was created to increase diagnostic effectiveness. An effective pairwise auto encoder model was developed by the improvement of data normalization, dimensionality reduction, and features screening scheme as well as the comparison of the prediction effectiveness of the various classifiers. A total of 138 patients were enrolled, and 77 (58.7%) in the overall group achieved pCR of LN after NAC. Nine radiomics features were finally chosen for modeling. The AUCs of the training group, validation group, and test group were 0.944 (0.919-0.965), 0.962 (0.937-0.985), and 1.000 (1.000-1.000), respectively, and the corresponding accuracies were 0.891, 0.912, and 1.000. The pCR of axillary LNs in breast cancer following NAC can be precisely predicted using thin-sliced enhanced chest CT-based radiomics.

Direct Comparison Between the Kawase Approach and Retrosigmoid Intradural Suprameatal Corridor to Access the Petroclival Region Using Computed Tomography Quantitative Volumetric Analysis: A Cadaveric Study

The anterior petrosectomy, also known as the Kawase approach, and the retrosigmoid intradural suprameatal approach (RISA) have both been used to reduce the petrous apex and access the petroclival region. Our goal was to compare the volumes and 3-dimensional shapes of bony resection obtained through each approach while trying to resemble realistic surgical settings. Five cadaveric specimens totaling 10 sides were dissected and analyzed. In every specimen, 1 side was used for the Kawase approach while the opposite side was used for the RISA. Petrosectomy volumes were assessed by comparing preoperative and postoperative thin-sliced computed tomography scans. Petrosectomy volumes were significantly larger through the Kawase approach than through the RISA (0.82 ± 0.11 vs. 0.49 ± 0.07 cm3, P < 0.001). In addition, surgical maneuverability and freedom were greater in the Kawase operative variant. Lastly, the morphology of the bony window achieved through each approach was clearly different: trapezoid for the anterior petrosectomy versus elongated ellipsoid for the RISA. The Kawase approach invariably results in larger volumes of bony removal than the RISA operative variant, and the volume of petrosectomy that is spatially congruent is only partially identical. The Kawase corridor is best suited for middle fossa lesions that extend into the posterior fossa, while the RISA is suitable for pathologies mainly residing in the posterior fossa and extending into the Meckel cave.

Preliminary Study of CT Three-dimensional Reconstruction Combined with Ground Glass Nodules of Natural Lung Collapse in Thoracoscopic Pulmonary Segmental Resection

背景与目的计算机断层扫描（computed tomography, CT）三维重建技术越来越多地被应用于肺磨玻璃结节（ground glass nodule, GGN）肺癌患者术前规划中，但术中如何准确定位结节和保证安全切除边缘依然是临床医生面对的难题。本研究旨在探讨全胸腔镜下肺段切除术中，CT三维重建联合术中肺自然萎陷定位方法的准确性、便捷性及切缘的安全性。方法选取2019年7月-2019年12月收治入院的45例影像学表现有肺GGN的患者为研究组，45例患者均接受薄层CT扫描并术前进行三维重建，于麻醉后快速打开胸腔小操作口和患者气道，利用压强差使肺快速自然萎陷，根据自然标志线进行GGN定位，3-0 prolene线标记，然后行三维重建指导下的胸腔镜肺段切除术。标本摘除后测量GGN与缝线标识的距离、GGN与切缘的距离并常规送检切缘。统计患者一般临床资料、病理资料与术后并发症，并与同期采用hookwire定位针进行定位的连续45例患者进行比较。结果CT三维重建联合术中无创式肺自然萎陷GGN定位，平均定位时间为6.9 min，定位准确率为90.6%。术中发现广泛胸腔粘连2例，肺气肿1例。术后病理均证实为肺腺癌，切缘送检均呈阴性。肺段切除后均无严重并发症的发生。结论CT三维重建联合术中肺自然萎陷GGN定位，缩短了术中寻找GGN的时间，保障了切缘的安全性，是一种更经济、实惠、便捷的定位方法，使肺段切除更加精准。

Clinical Features and Temporal Lung Radiographic Changes in 25 Patients Recovering from COVID-19 Pneumonia: A Retrospective Case-Control Study.

BackgroundLittle is known of the changes in lung radiographic characteristics over time in patients recovering from COVID-19. This study analyzed the clinical features and temporal lung radiographic changes in patients with moderate and severe COVID-19 pneumonia who did not require invasive mechanical ventilation during the acute and convalescent periods.Material/MethodsThe data of 25 patients with COVID-19 pneumonia from January 29, 2020, to November 24, 2020, who did not require invasive mechanical ventilation and who were followed up were retrospectively collected. The 25 patients were divided into severe and moderate groups. Clinical characteristics and computed tomography (CT) manifestations were compared. A total of 121 consecutive thin-slice CT scans were collected at 4 weeks, 2 months, and 5 months after admission to evaluate lung abnormalities in the patients. The CT score was used to assess disease severity.ResultsThe severe group had a lower rate of nucleic acid conversion within 10 days of admission and higher D-dimer, creatine kinase, and lactate dehydrogenase values. In the severe group, hospital stay was longer and hospitalization costs were higher. The average CT score of the severe group peaked in the second week, while the moderate group peaked in the first week and then decreased over time. There were no statistically significant differences in the average CT score between the 2 groups at the 5-month follow-up.ConclusionsThe pulmonary lesions of patients recovering from COVID-19 and who do not require invasive mechanical ventilation were gradually absorbed and resolved over time.

A Customized Technique of Cranioplasty for Patients with Large Skull Defects: A Technical Note

In our technical note, we have presented a technique of cranioplasty for large skull defects. A thin-slice computed tomography scan is performed. A model of the skull is constructed using a desktop 3-dimensional printer from the computed tomography scan. The skull model is filled with towels of soft cotton and inserted in a sterile thin plastic bag. The implant is molded intraoperatively on the skull model under sterile conditions. After surgical exposure of the skull defect, the implant is inserted and fixed using miniplates and miniscrews. The technique was used in 6 patients and described in 2 representative cases. The required time and cost are significantly lower than those for other techniques used for preoperative manufacture of implants. No technique-related complications occurred. The radiological and cosmetic results were satisfactory. In the present case series, no early or delayed complications occurred. The presented technique is simple, safe, and time- and cost-effective. The technique and results are reproducible.

Solid component ratio influences prognosis of GGO-featured IA stage invasive lung adenocarcinoma

BackgroundThe computed tomography (CT) characteristic of ground glass opacity (GGO) were shown to be associated with clinical significance in lung adenocarcinoma. We evaluated the prognostic value of the solid component ratio of GGO IA invasive lung adenocarcinoma.MethodsWe retrospectively analyzed the records of GGO IA patients who received surgical resection from April 2012 to December 2015. The solid component ratio was calculated based on thin-slice CT scans. Baseline features were compared stratified by the ratio. Cox proportional hazard models and survival analyses were adopted to explore potential prognostic value regarding overall survival (OS) and disease-free survival (DFS).ResultsFour hundred fifteen patients were included. The higher ratio was significantly associated with larger tumor diameter, pathological subtypes and choice of surgical type. There was a significantly worse DFS with a > 50% ratio. The subgroups of 0% and ≤ 50% ratio showed close survival curves of DFS. Similar trends were observed in OS. Multivariate analyses revealed that the ratio was a significant predictor for DFS, but not for OS. No significant prognostic difference was observed between lobectomy and limited resections.ConclusionA higher solid component ratio may help to predict a significantly worse prognosis of GGO IA lung adenocarcinoma.

Bone-Selective MRI as a Nonradiative Alternative to CT for Craniofacial Imaging

Computed tomography (CT) is the clinical gold-standard for high-resolution 3D visualization of cortical bone structures. However, ionizing radiation is of concern, particularly for pediatric patients. This study evaluates the feasibility of producing 3D human skull renderings using a novel bone-selective magnetic resonance imaging technique. A dual-radiofrequency pulse, dual-echo, 3D ultrashort echo time sequence was applied for scanning of a cadaver skull and five healthy adult subjects. Scans were each completed within 6 minutes. Semiautomatic segmentation of bone voxels was performed using ITK-SNAP software, leading to 3D renderings of the skulls. For comparison, thin-slice head CT scans were performed. Mimics software was used to measure eight anatomic distances from 3D renderings. Lin's Concordance Correlation test was applied to assess agreement between measurements from MR-based and CT-based 3D skull renderings. The 3D rendered MR images depict most craniofacial features (e.g., zygomatic arch), although some voxels were erroneously included or excluded in the renderings. MR-based measurements differed from CT-based measurements by mean percent difference ranging from 2.3%-5.0%. Lin's Concordance Correlation Coefficients for MR-based vs CT-based measurements ranged from 0.998-1.000. The proposed dual-radiofrequency dual-echo 3D ultrashort echo time imaging technique produces high-resolution bone-specific images within a clinically feasible imaging time, leading to clear visualization of craniofacial skeletal structures. Concordance coefficients suggest good reliability of the method compared to CT. The method is currently limited by time and manual input necessary for segmentation correction. Further investigation is needed for more accurate 3D renderings and for scanning of pediatric patients.

Anatomical reduction and precise internal fixation of intra-articular fractures of the distal radius with virtual X-ray and 3D printing

To evaluate and precisely internal fix intra-articular distal radial fracture (IDRF) using the virtual X-ray and three-dimensional (3D) printing technologies. Twenty-one patients with IDRF were recruited, and the data from digital design group (DDG) and real surgery group (RSG) were collected and analyzed. In DDG, the data from thin-slice computed tomography scan, virtual X-ray measurement parameters, including volar tilt, palmar tilt, radius length (D1), ulnar variation (D2), locking plate position parameter (D3) and distance between key nail and joint surface (D4) were collected. The bone was virtually fixed with the locking plate, and the final model of radius with the screw was obtained by 3D printing. In RSG, the locking plate was precisely pre-bended and used in surgery. During the surgery, the key K-wire was accurately placed and the locking plate was adjusted with the aid of the U-shaped navigation arm. The C-arm was used to observe the positions of key K-wires and the locking plate, and the same above-mentioned parameters were measured intra- and post-operatively. The data from RSG and DDG were compared statistically by t test. This approach proved to be successful in all 21 patients, and none of the screws pierced through the wrist joint surface. All the measured parameters, including the volar tilt, palmar tilt, D1–4, in RSG were not significantly different from preoperative DDG data. Virtual X-ray measurement of anatomical reduction parameters and 3D printing can help the anatomical reduction and precise internal fixation by providing quantitative references, preoperatively, intraoperatively and postoperatively.

The effects of physics-based data augmentation on the generalizability of deep neural networks: Demonstration on nodule false-positive reduction.

An important challenge for deep learning models is generalizing to new datasets that may be acquired with acquisition protocols different from the training set. It is not always feasible to expand training data to the range encountered in clinical practice. We introduce a new technique, physics-based data augmentation (PBDA), that can emulate new computed tomography (CT) data acquisition protocols. We demonstrate two forms of PBDA, emulating increases in slice thickness and reductions of dose, on the specific problem of false-positive reduction in the automatic detection of lung nodules. We worked with CT images from the lung image database consortium (LIDC) collection. We employed a hybrid ensemble convolutional neural network (CNN), which consists of multiple CNN modules (VGG, DenseNet, ResNet), for a classification task of determining whether an image patch was a suspicious nodule or a false positive. To emulate a reduction in tube current, we injected noise by simulating forward projection, noise addition, and backprojection corresponding to 1.5mAs (a "chest x-ray" dose). To simulate thick slice CT scans from thin slice CT scans, we grouped and averaged spatially contiguous CT within thin slice data. The neural network was trained with 10% of the LIDC dataset that was selected to have either the highest tube current or the thinnest slices. The network was tested on the remaining data. We compared PBDA to a baseline with standard geometric augmentations (such as shifts and rotations) and Gaussian noise addition. PBDA improved the performance of the networks when generalizing to the test dataset in a limited number of cases. We found that the best performance was obtained by applying augmentation at very low doses (1.5mAs), about an order of magnitude less than most screening protocols. In the baseline augmentation, a comparable level of Gaussian noise was injected. For dose reduction PBDA, the average sensitivity of 0.931 for the hybrid ensemble network was not statistically different from the average sensitivity of 0.935 without PBDA. Similarly for slice thickness PBDA, the average sensitivity of 0.900 when augmenting with doubled simulated slice thicknesses was not statistically different from the average sensitivity of 0.895 without PBDA. While there were cases detailed in this paper in which we observed improvements, the overall picture was one that suggests PBDA may not be an effective data enrichment tool. PBDA is a newly proposed strategy for mitigating the performance loss of neural networks related to the variation of acquisition protocol between the training dataset and the data that is encountered in deployment or testing. We found that PBDA does not provide robust improvements with the four neural networks (three modules and the ensemble) tested and for the specific task of false-positive reduction in nodule detection.

Assessment of Sphenoid Sinus Variations and Its Related Neurovascular Structures Using Contrasted Thin Slice Computed Tomography Scan Of The Brain

Introduction: Sphenoid sinus is the most variable structure in human. The prevalence of anatomical variations varies with the population. Increasing endoscopic procedures around the sphenoid sinus and advances in imaging techniques, allowed precise evaluation of sinus anatomical variation in each population. This study measured the prevalences and described the variations of the sphenoid sinus using thin slice contrasted computed tomography scan of brain scans. Materials and Methods: A retrospective cross-sectional study of 250 brain scans of patients between 18-60 years old attending Hospital Tengku Ampuan Afzan, Kuantan, Pahang from 1st January to 31st December 2017. The sphenoid sinus pneumatization types, volume, optic nerve relation according to Delano’s classification, internal carotid artery relation, and the number of sinus septum and attachment site were studied. Results: Post sellar pneumatization type was most common (52%). The mean sinus volume was 19 cm³ which was significantly different between genders. Delano optic nerve type 1 was most frequent (43%) and most were seen bilaterally with significant differences between gender. The internal carotid artery was seen non-protruded 41.6% cases, protruded in 36.4% cases, and protrusion with wall dehiscence in 22% cases. Two septate sinuses were more prominent (44.3%), aseptate sinus in 2.4% cases. The principle septa attachment site was sella (28%), internal carotid artery related septa found in 10% cases and 3.2% of cases with optic nerve septal attachment. Conclusion: This study revealed the presence of all sphenoid sinus variations amongst the study population. The preoperative determination of these anatomical variations minimizes vital neurovascular structures injury.

Morphometric Measurements of the C1 Lateral Mass with Congenital Occipitalization of the Atlas

Unfamiliarity with the morphometry of the assimilated C1 lateral mass (C1LM) could make screw placement dangerous. In the present study, we defined the morphometric dimensions of the occipitalized C1LM to provide surgeons with valuable information for preoperative planning. Thin-slice computed tomography scanning data from 131 patients with occipitalization of the atlas (OA) and 50 control cases were imported into Mimics software for analysis. The widths and heights of the C1LM were fully measured in the different planes. The ideal inward angulation and the safe maximum cephalic angulation of C1 screw trajectory were evaluated. Except for the medial height, all the widths and heights of C1LM were significantly shorter in the OA group than those in the control group. The ideal inward angle (α) was significantly larger in the OA group (23.8° ± 8.3°) than that (15.3° ± 3.8°) in the control group; the corresponding screw length was also significantly longer in the OA group (20.9 ± 2.9 mm). The safe maximum cephalic angles (β) of the screw trajectory did not reach a significant difference between the 2 groups. All the widths and heights were shorter in the females than those in the males. The α angle also did not reach a significant difference between the sexes; however, the β angles in the males (35.9° ± 10.4°) was significantly larger than that in the females (32.0° ± 9.4°). Although the hypoplastic C1LM brings limitations to screw insertion to some extent, it is still broad enough to accommodate a screw safely in both female and male patients. Considering the irregularity of the C1LM in patients with OA, the preoperative imaging assessment is critical, and C1LM screw placement should be performed individually.

Forensic age estimation using computed tomography of the medial clavicular epiphysis: a systematic review.

Medicolegal physicians are increasingly called upon to aid in determining the administrative age group affiliation of refugees with questionable unaccompanied minor claims. According to guidelines for forensic age assessment, age differentiation along the 18-year-old cut-off relies on clavicular ossification. The thin-slice computed tomography scan (TSCTs) of the medial clavicular epiphysis (MCE) is one of the methods contributing to this assessment, though it is not yet universally accepted. The aim of this systematic review was to identify scientific papers where age was assessed using TSCTs of the MCE and to observe whether this examination was reproducible and reliable in estimating a person's age relative to the 18-year-old threshold. A search algorithm was applied to several databases to identify articles in accordance with the PRISMA (Preferred Reporting Items for Systematic-Reviews and Meta-Analyses) statement. One boxplot per article was constructed, separating by stage of maturation and sex. The 13 articles selected represented a sample of 5605 individuals (3396 males, 2209 females) aged 10 to 35years. All individuals classified as stages 4 and 5 were aged 18years or older. The same result was obtained concerning stage 3c, except in one article. The results thus appear reliable and reproducible, in particular, with respect to the 18-year-old threshold; medicolegal physicians should be able to estimate that all individuals in stages 4 and 5 are at least 18years old. Additional studies applied to several other populations in the world should complement the selected studies.

Trabecular Anatomy of the Axis Vertebra: A Study of Shaded Volume-Rendered Computed Tomography Images.

To date, trabecular morphology studies have been conducted on thin-section computed tomography (CT) scans of cadaveric bone. Here we describe the trabecular anatomy of the axis vertebra as revealed by an innovative imaging tool. Ten patients who underwent thin-slice CT scans for suspected cervical spine injury were prospectively subjected to shaded volume-rendered 3-dimensional reconstruction of the images. The trabecular anatomy thus depicted was recreated, and the mechanical vectors were deduced independently by a senior radiologist and spine surgeon and then matched. The clinical implications were postulated. The most striking trabeculae are the vertical compression trabeculae connecting the C1 facet to the C3 body. The center of the body of C2 has a space with sparse trabeculae; similarly, the pars interarticularis also has a clear void. The dens contain predominantly tensile trabeculae that are retained even in older patients. Midline remnants of the odontoid body synchondrosis persist even into late adulthood. Shaded volume-rendered imaging appears to be an excellent tool for studying the trabecular anatomy of cancellous bone. The weight-bearing trabeculae run from the C1-2 facet to the C3 body; the inferior facet contributes little to weight-bearing.

A Multidisciplinary Technique Using Endonasal Endoscopic Approach with Intrathecal Fluorescin Under Neuronavigation Guidance in Patients with Cerebrospinal Fluid Leak

Background: Cerebrospinal fluid (CSF) is contained in an anatomic space, including cerebral ventricles and subarachnoid spaces and cisterns of brain and spine. Distraction of normal anatomy of any containing parts of this system will result in CSF leakage which could be associated with morbidity and mortality with variable degrees. In this study, we aimed to present 3 patients with history of blunt head trauma, who presented with delayed CSF leak and underwent endonasal endoscopic approach under image guided surgery using neuronavigation system with fluorescein illumination. Case Presentation: Three patients were referred to neurosurgery department of Shohada Tajrish Hospital with previous history of blunt head trauma, complained from CSF rhinorrhea. They underwent thin slice Computed Tomography scan and received intrathecal fluorescein for better visualization of leakage source under live endonasal endoscopic approach, using image guided neuronavigation technology. Autologous fat tissue and fascia was used to seal the leakage site. Clinical and imaging follow up at post-operative state as well as 1 st , 2 nd , 4 th and 8 th week revealed no post-operative complications and repeated CSF leakage. Conclusion: CSF rhinorrhea indicates abnormality in bony structure of skull base and is a major threat for ascending microbial infections and subsequent meningitis. Thus, identification of leakage site(s) and accurate surgical repair is necessary. We experienced a multidisciplinary approach which showed excellent results and no post-operative complications. Multidisciplinary approach with combination of endonasal endoscopic view under neuronavigation system improves accuracy and will minimize post-operative complications.

Three-dimensional spiral CT measurement of atlantal pedicle and its clinical application.

The study aimed to establish the safe placement area and corresponding entry angle of atlantal pedicle screw using axial computed tomography (CT) measurement of atlas, in order to guide the clinical operation. Spiral thin-slice CT scan of atlas and three-dimensional reconstruction of 38 patients were randomly selected. Screw placement space was defined as the distance between the tangent lines of entry channel on the atlantal cross section and inner edge of transverse foramen and outer edge of spinal canal. Before operation, spiral CT measurement was used to determine the safe placement area, and the pipeline dredge method was used to conduct the internal fixation of atlantal pedicle screw for 7 patients. In CT measurements, the width of pedicle was 9.15±2.57 mm, which could safely accommodate screws with the diameter of 3.5 mm. The safe placement area was located in posterior arch of atlas (18.35±2.86 to 25.26±1.76 mm) away from the posterior tubercle, the entry angle ranged from 9.09±7.45° outward to 18.72±17.42° inward, and the length of screw channel ranged from 26.20±2.69 to 27.04±2.51 mm. The width of the safe placement area was up to 6.91±7.66 mm, and the angle of inclination on cross section was up to 27.81±10.32°. In conclusion, we identified a safe placement area for atlantal pedicle screw, where the screw was implanted inwards and outwards according to different entry points within the safe placement area. The detailed preoperative image measurement, determination of safe placement area and individual screw placement were found to be the key to a successful surgery.

MA12.05 Can Tumor Spread through Air Spaces (STAS) in Lung Adenocarcinomas Be Predicted Pre- and Intraoperatively?

We and others have reported the prognostic impact of tumor spread through air spaces (STAS) in lung adenocarcinomas. The goal of this study is to investigate preoperative predicting factors for STAS and to determine whether STAS can be detected by intraoperative frozen section analysis. In a cohort of 874 patients with small (≤2cm) stage I adenocarcinoma (1995-2012), we reviewed preoperative computed tomography (CT) and positron emission tomography (PET) scans. According to the 2016 Fleischner Society’s criteria, radiological whole tumor size, consolidation size, as well as C/T ratio (consolidation/whole tumor diameter) were determined using thin slice (<3mm) CT scans where available (n=174). Clinico-radiological prediction of STAS was evaluated by logistic regression model. Using the frozen section slides with adequate adjacent lung parenchyma surrounding tumor without artifact (n=48), the presence of STAS was evaluated by five pathologists who are unaware of the radiological findings or the pathological information on permanent slides. The kappa statistic was calculated to measure the agreement between two pathologists. In univariable model for predicting STAS, current smoker, larger consolidation tumor size, C/T ratio, and SUVmax were significant variables. In multivariable model, current smoker and C/T ratio were independent risk factors for the presence of STAS (p=0.027 and p<0.001, respectively; Table 1a). The sensitivity and the specificity of frozen section for prediction of STAS were 71% (95% confidence interval: 52-91%), 92.4% (81-100%) respectively, and the accuracy was 80% (71-89%). The kappa statistics were 0.40-0.74 (Table 1b) with 8/10 being moderate or substantial agreement. Smoking status and C/T ratio were independent predictors for the presence of STAS in patients with small lung adenocarcinomas. Frozen section prepared with adequate surrounding normal lung tissue may help identify STAS intraoperatively.

Improved CT Imaging for Mastoid Emissary Vein Visualization Prior to Posterior Fossa Approaches.

Background The clinical relevance of emissary veins (EVs) is often neglected. However, for posterior fossa approaches, especially in semisitting positions, these transosseous connections become potentially life threatening. Therefore, knowledge of the presence and configuration of EVs is essential in preoperative planning. We report on the use of preoperative computed tomography (CT) imaging techniques to visualize EVs reliably. Methods A total of 100 consecutive patients were evaluated by helical CT in bone window mode reconstructed using the standard technique (4.5-mm slices) and the high-resolution technique (1 mm) for the posterior fossa. The presence and size of the EVs, their entry point in the sigmoid sinus, their predilection site, and their visibility using either CT technique were evaluated. Statistical analyses included a comparison of the data from both sides of the head. Results We noted impressive anatomical variations (high standard deviations) in the number, size, and intraosseous length of the EVs among the study population and between the sides (right and left) of an individual patient; however, no statistical significance was observed for any of these parameters. The detection rate of EVs in thin-slice CT scans versus standard CT scans is significantly different (p = 0.0001 on both sides). Conclusions Thin-slice CT is essential in the preoperative planning of posterior fossa approaches to identify the presence and the course of EVs, reducing preventable approach-related morbidity during surgery.

Suppression of the CT Beam Hardening Streak Artifact Using Predictive Correction on Detector Data

The purpose of the research was to develop an automated program incorporating a predictive artifact correction technique (PACT) to correct for the signal deviations from metal beam hardening artifacts in Computed Tomography (CT) detector raw data. Thin-slice sequential CT scans were performed on a dosimetry head phantom using a Somatom Sensation 16 scanner to establish a ground truth image. Metal pins were then affixed to either side of the phantom at the three and nine o’clock positions to cause streak artifact in detector raw data and a subsequent streak image. The program automatically detected the extent of the overlap peaks in the detector raw data causing the artifact. It profiled a correction using adjacent projections so that the peak error could be corrected rather than simply being removed or smoothed by interpolation. The PACT algorithm modified raw data was then reconstructed on a SYNGO CT reconstruction workstation. This image was then compared against ground truth and that produced by commercially available metal artifact reduction projection completion and also a research based iterative technique. Qualitative results illustrate superior suppression of streak artifact in images using PACT when compared directly to tested projection completion methods but inferior to iterative reconstruction. Recovery of voxel data underlying the streak is also demonstrated to be quantitatively superior with PACT when referenced to the original ground truth image. Limitations were however detected with the threshold technique for initial localisation of the streak sources. The work still demonstrates the feasibility of this predictive artifact correction technique in correcting beam hardening affected voxel data without recourse to expensive additional options such as iterative reconstruction or dual energy that are not so commonly available in the clinical setting.

Petrosectomy and Topographical Anatomy in Traditional Kawase and Posterior Intradural Petrous Apicectomy (PIPA) Approach: An Anatomical Study

To compare the anatomical exposure and petrosectomy extent in the Kawase and posterior intradural petrous apicectomy (PIPA) approaches. Kawase and PIPA approaches were performed on 4 fixed cadaveric heads (3 alcohol-fixed, 1 formaldehyde-fixed silicone-injected; 4 Kawase and 4 PIPA approaches). The microsurgical anatomy was examined by means of Zeiss Opmi CS/NC-4 microscopes. HD Karl Storz Endoscopes (AIDA system) were used to display intradural exposure. Petrosectomy volumes was assessed by comparing pre- and postoperative thin-slice computed tomography scans (Analyze 12.0; AnalyzeDirect Mayo Clinic). The Kawase approach exposed the rhomboid fossa with Meckel's cave extradurally, the upper half of the clivus, superior cerebellopontine angle, ventrolateral brainstem, the intrameatal region, basilar apex, and the preganglionic root of cranial nerve (CN) V, CN III-IV-VI intradurally. The PIPA approach exposed the cerebello-pontine angle with CN VI-XII, Meckel's cave, CN III-V, and the middle and lower clivus intradurally from a posterior view. The area of surgical exposure is wide in both approaches; however, the volume of petrosectomy, the working angle, and surgical corridor differ significantly. The Kawase approach allows wide exposure of the middle cranial fossa (MCF) and posterior cranial fossa, requiring extradural temporal lobe retraction and an extradural petrosectomy with preservation of the internal acoustic meatus and cochlea. No temporal lobe retraction and direct control of neurovascular structures make the PIPA approach a valid alternative for lesions extending mostly in the Posterior cranial fossa with minor extension in the MCF. The longer surgical corridor, cerebellar retraction, and limited exposure of the anterior brainstem make this approach less indicated for lesions with major extension in the MCF and the anterior cavernous sinus.

Assessing bone volume for orthodontic miniplate fixation below the maxillary frontal process.

The maxillary bone below the frontal process is used for orthodontic anchorage; indications have included skeletally anchored protraction of the maxilla for treating Class III malocclusions or the intrusion of teeth in patients with a deep bite. This study was conducted to assess the condition of bone before cortically implanting miniplates in that area of the maxilla. A total of 51 thin-sliced computed tomography scans of 51 fully-dentate adult patients (mean age 24.0 ± 8.1 years; 27 men and 24 women) obtained prior to third-molar osteotomy were evaluated. Study parameters included total bone thickness, thickness of the facial cortical plate, and width of the nasal maxillary buttress. All these parameters were measured at different vertical levels. The bone volume adjacent to the piriform aperture was most pronounced at the basal level and decreased progressively toward more cranial levels. The basal bone structure had a mean total thickness of 7.8 mm, facial cortical plate thickness of 1.9 mm, and nasal maxillary buttress width of 9.2 mm. At 16 mm cranial to the aperture base, these values fell to 5.6 mm, 1.3 mm, and 5.8 mm, respectively. These bone measurements suggest that screws 7 mm in length can be inserted at the base level of the piriform aperture and screws 5 mm long at the cranial end of the bone.