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Objectives: Symmetry is essential for computer-aided surgical (CAS) procedures in oral and maxillofacial surgery (OMFS). A critical step for successful CAS is mirroring the unaffected side to create a template for the virtual reconstruction of the injured anatomical structure. The aim was to identify specific anatomical landmarks of the midfacial skeleton, to evaluate the symmetry in a group of the real-world Central European population, and to use these landmarks to assess midfacial symmetry in CT scans., Material and Methods: The retrospective cross-sectional study defined landmarks of the midface's bony contour using viscerocranial CT data. The distances of the skeletal landmarks (e.g., the frontozygomatic suture and temporozygomatic suture) of the left and right sides from the midline were measured and statistically compared. Midfacial symmetry for reference points was defined as a difference within 0 mm and their mean difference plus one standard deviation., Results: We examined a total of 101 CT scans. 75% of our population shows symmetrical proportions of the midface. The means of the differences for the left and right sides ranged from 0.8 to 1.3 mm, averaging 1.1 ± 0.2 mm for all skeletal landmarks. The standard deviations ranged from 0.6 to 1.4 mm, with a computed mean of 0.9 ± 0.3 mm., Conclusion: We established a methodology to assess the symmetry of the bony midface. If the determined differences were equal to or lower than 2.5 mm in the mentioned midfacial skeletal landmarks, then the symmetry of the bony midface was considered present, and symmetry-based methods for CAS procedures are applicable., Clinical Relevance: Many CAS procedures require facial symmetry. We provide an easy-to-apply method to probe for symmetry of the midface. The method may be used for population-based research, to check for proper reduction of fractures after reposition or to screen for symmetry prior to CAS planning., (© 2023. The Author(s).)

Background: Only verbal pregnancy screening is recommended for post-menarcheal females undergoing pelvic radiographs. In contrast, usually, a urine/serum pregnancy test for pelvic computed tomographic (CT) exams is required out of concern for higher radiation exposure., Objective: To estimate patient-specific fetus absorbed dose to a potentially pregnant minor from an optimized dose CT of the pelvis for femoral version and surgical planning and provide evidence that such examinations of the pelvis can be performed with only verbal pregnancy screening., Methods and Methods: A retrospective study was performed on 102 female patients between 12-18 years of age (15.4 ± 2.1 years) who underwent optimized dose CT of the pelvis for orthopedic evaluation of femoral version and surgical planning. Optimized CT exams were performed with weight-adjusted kVp and tube current modulation. Patient-specific dose from the optimized dose CT was calculated using the National Cancer Institute Dosimetry System for CT (NCICT) database by matching each patient to a phantom from the NCI non-reference phantom library based on patient sex, weight, and height. The calculated absorbed uterus dose was used as a surrogate for the fetus dose. Furthermore, patient-specific organ doses were used to estimate the effective dose. The strengths of the linear relationships between the dose metrics and patient characteristics were assessed using Pearson correlation coefficients through linear regression., Results: The mean patient-specific effective dose for an optimized dose CT of the pelvis was 0.54 ± 0.20 mSv (range: 0.15-1.22 mSv). The mean estimated absorbed uterine dose was 1.57 ± 0.67 mGy (range: 0.42-4.81 mGy). Both effective dose and estimated uterine dose correlated poorly with patient physical characteristics (R = -0.26; 95% CI: [-0.43, -0.007] for age, R = 0.03; 95% CI: [-0.17, 0.22] for weight) but correlated strongly (R = 0.79, 95% CI: [0.7, 0.85]) with CTDI vol ., Conclusion: The estimated fetus dose in case of pregnancy was significantly lower than 20 mGy for urine/serum pregnancy screening, suggesting that the pregnancy screening protocols in minors undergoing optimized dose CT require reassessment and may be safely performed by verbal attestation only., (© 2023. The Author(s), under exclusive licence to Springer-Verlag GmbH Germany, part of Springer Nature.)

Purpose: Many patients receive magnetic resonance (MR) and computed tomography (CT) scans post-operatively to review screw placement. Traditionally, CT is diagnostic but as metal artefact reduction sequences are advancing in MR, the necessity for both MR and CT scans is questionable. The objective is to establish the statistical agreeability of MR and CT for evaluation of adequate screw placement in posterior lumbar interbody fusion., Methods: This opportunistic retrospective study of 58 patients investigated 297 images of 296 implanted screws. Post-operative MR and CT images were scrutinised for depiction of lumbar pedicle screw position using a 5-point scale. Kappa value for statistical agreeability tested MR against CT., Results: The 297 images of screws resulted in strong to near-perfect agreement between MR and CT (n = 297 k = 0.8042 p < 0.025). MRI resulted in high sensitivity (88.7%) and positive predictive value (78.3%). MRI demonstrated very high specificity (96.2%) and negative predictive value (98.2%). MR depicted screws (mean 12.6 mm diameter, mean 65.3 mm length) with 50% error in diameter and 30% in length from susceptibility artefact compared to manufacturer dimensions (6.5-7.5 mm diameter, 40-50 mm length). Adequate screw placement was high despite this (85.8%). On MR, the cortex border visibility was 60.7% and the spinal canal visibility was 74.6%., Conclusion: There is strong to near-perfect agreement between MR and CT for evaluating adequate screw position in PLIF surgery. MR alone is useful for analyzing screw placement and should be considered first-line imaging in uncomplicated cases with CT analysis reserved for cases of uncertainty., Level of Evidence: Level III retrospective cohort study.

Purpose: To develop and evaluate a technical approach for CT-guided periradicular infiltration using quantitative needle access and guidance parameters extracted from CT scout images., Methods: Five 3D-printed phantoms of the abdomen mimicking different patients were used to develop a technical approach for scout-guided periradicular infiltration. The needle access point, puncture depth, and needle angulation were calculated using measurements extracted from anterior-posterior and lateral CT scout images. Fifty needle placements were performed with the technique thus developed. Dose exposure and number of image acquisitions were compared with ten procedures performed using a conventional free-hand technique. Data were analyzed with the Mann-Whitney U test., Results: Parameters derived solely from scout images provided adequate guidance for successful and reliable needle placement. Needle guidance was performed with the same equipment as the standard periradicular infiltration. Two scout images and 3.5 ± 2.3 (mean ± SD) single-shot images for needle positioning were acquired. Mean DLP ± SD was 3.8 ± 2.5 mGy cm. The number of single-shot acquisitions was reduced by 68% and the overall dose was reduced by 84% in comparison with the conventional free-hand technique (p < 0.0001)., Conclusion: Scout-guided needle placement for periradicular infiltration is feasible and reduces radiation exposure significantly.

Purpose: To describe the features of a novel patient-mounted system for CT-guided needle navigation, the Puncture Cube System (PCS), and to evaluate the accuracy and efficiency of the PCS by (a) applying numerical simulations and (b) by conducting punctures using the system in comparison to punctures using the free-hand method (FHM)., Methods: The PCS consists of a self-adhesive cube that is attached to the patient, with multiple through-holes in the upper and lower template plate and dedicated software that, using a computer vision algorithm, recognizes the cube in a planning scan. The target in the image dataset is connected by a line, here "virtual needle," which passes through the cube. For any chosen path of the virtual needle, the entry points for the needle into the cube are displayed by the software for the upper and lower template on-the-fly. The possible exactness of the system was investigated by using numerical simulations. Next, 72 punctures were performed by 6 interventionists using a phantom to compare for accuracy, time requirement, and number of CT scans for punctures with the system to the FHM ex vivo (phantom study)., Results: The theoretical precision to arrive at targets increased with the distance of the target but remained low. The mean error for targets up to 20 cm below the lower plate was computed to be well below 0.5 mm, and the worst-case error stayed below 1.3 mm. Compared to a conventional free-hand procedure, the use of the navigation system resulted in a statistically significantly improved accuracy (3.4 mm ± 2.3 mm versus FHM 4.9 mm ± 3.2 mm) and overall lower intervention time (168 s ± 28.5 s versus FHM 200 s ± 44.8 s). Furthermore, the number of CT scans was reduced to 2.3 versus FHM 2.8)., Conclusion: The PCS is a promising technique to improve accuracy and reduce intervention time in CT-guided needle navigations compared to the FHM.