The value of three-dimensional photogrammetry in isolated sagittal synostosis: Impact of age and surgical technique on intracranial volume and cephalic index─a retrospective cohort study

3D Analysis of the Cranial and Facial Shape in Craniosynostosis Patients: A Systematic Review

With increasing interest in 3D photogrammetry, diverse methods have been developed for craniofacial shape analysis in craniosynostosis patients. This review provides an overview of these methods and offers recommendations for future studies. A systematic literature search was used to identify publications on 3D photogrammetry analyses in craniosynostosis patients until August 2023. Inclusion criteria were original research reporting on 3D photogrammetry analyses in patients with craniosynostosis and written in English. Sixty-three publications that had reproducible methods for measuring cranial, forehead, or facial shape were included in the systematic review. Cranial shape changes were commonly assessed using heat maps and curvature analyses. Publications assessing the forehead utilized volumetric measurements, angles, ratios, and mirroring techniques. Mirroring techniques were frequently used to determine facial asymmetry. Although 3D photogrammetry shows promise, methods vary widely between standardized and less conventional measurements. A standardized protocol for the selection and documentation of landmarks, planes, and measurements across the cranium, forehead, and face is essential for consistent clinical and research applications.

3D-2D Distance Maps Conversion Enhances Classification of Craniosynostosis

OBJECTIVE

Diagnosis of craniosynostosis using photogrammetric 3D surface scans is a promising radiation-free alternative to traditional computed tomography. We propose a 3D surface scan to 2D distance map conversion enabling the usage of the first convolutional neural networks (CNNs)-based classification of craniosynostosis. Benefits of using 2D images include preserving patient anonymity, enabling data augmentation during training, and a strong under-sampling of the 3D surface with good classification performance.

METHODS

The proposed distance maps sample 2D images from 3D surface scans using a coordinate transformation, ray casting, and distance extraction. We introduce a CNN-based classification pipeline and compare our classifier to alternative approaches on a dataset of 496 patients. We investigate into low-resolution sampling, data augmentation, and attribution mapping.

RESULTS

Resnet18 outperformed alternative classifiers on our dataset with an F1-score of 0.964 and an accuracy of 98.4%. Data augmentation on 2D distance maps increased performance for all classifiers. Under-sampling allowed 256-fold computation reduction during ray casting while retaining an F1-score of 0.92. Attribution maps showed high amplitudes on the frontal head.

CONCLUSION

We demonstrated a versatile mapping approach to extract a 2D distance map from the 3D head geometry increasing classification performance, enabling data augmentation during training on 2D distance maps, and the usage of CNNs. We found that low-resolution images were sufficient for a good classification performance.

SIGNIFICANCE

Photogrammetric surface scans are a suitable craniosynostosis diagnosis tool for clinical practice. Domain transfer to computed tomography seems likely and can further contribute to reducing ionizing radiation exposure for infants.

Craniometric and Aesthetic Outcomes in Craniosynostosis Surgery: A Systematic Review and Meta-Analysis

OBJECTIVE

To systematically review the published comparative aesthetic outcomes, and its determinants, for craniosynostoses surgically treated by minimally-invasive cranial procedures and open cranial vault remodeling (CVR).

DESIGN

PRISMA-compliant systematic review.

SETTING

Not-applicable.

PATIENTS/PARTICIPANTS

Articles were included if they compared spring cranioplasty, strip minimally-invasive craniectomy or CVR for outcomes related to aesthetics or head shape. Forty-two studies were included, comprising 2402 patients.

INTERVENTIONS

None.

MAIN OUTCOME MEASURE(S)

The craniometric and PROM used to determine surgical outcomes.

RESULTS

Twenty-five studies (59%) evaluated sagittal craniosynostosis, with metopic (7;17%) and unicoronal (4;10%) the next most prevalent. Thirty-eight studies (90%) included CVR, 24 (57%) included strip craniectomy with helmeting, 9 (22%) included strip craniectomy without helmeting, 11 (26%) included spring cranioplasty, and 3 (7%) included vault distraction. A majority of studies only used 1 (43%) or 2 (14%) craniometric measures to compare techniques. In sagittal synostosis, 13 (59%) studies showed no difference in craniometric outcomes, 5 (23%) showed better results with CVR, 3 (14%) with strip craniectomy, and 1 (5%) with springs. In studies describing other synostoses, 10/14 (71%) were equivocal. Subjective outcome measures followed similar trends. Meta-analysis shows no significant difference in cranial index (CI) outcomes between CVR and less invasive procedures in patients with sagittal synostosis.

CONCLUSIONS

There is no difference in CI outcomes between CVR and less invasive procedures. The majority of literature comparing craniometric and aesthetic outcomes between CVR and less invasive procedures shows equivocal results for sagittal synostosis. However, the heterogeneity of data for other craniosynostoses did not allow meta-analysis.

Sagittal Craniosynostosis: Comparing Surgical Techniques Using 3D Photogrammetry

BACKGROUND

The aim of this study was to compare three surgical interventions for correction of sagittal synostosis-frontobiparietal remodeling (FBR), extended strip craniotomy (ESC), and spring-assisted correction (SAC)-based on three-dimensional (3D) photogrammetry and operation characteristics.

METHODS

Patients who were born between 1991 and 2019 and diagnosed with nonsyndromic sagittal synostosis who underwent FBR, ESC, or SAC and had at least one postoperative 3D photogrammetry image taken during one of six follow-up appointments until age 6 were considered for this study. Operative characteristics, postoperative complications, reinterventions, and presence of intracranial hypertension were collected. To assess cranial growth, orthogonal cranial slices and 3D photocephalometric measurements were extracted automatically and evaluated from 3D photogrammetry images.

RESULTS

A total of 322 postoperative 3D images from 218 patients were included. After correcting for age and sex, no significant differences were observed in 3D photocephalometric measurements. Mean cranial shapes suggested that postoperative growth and shape gradually normalized with higher occipitofrontal head circumference and intracranial volume values compared with normal values, regardless of type of surgery. Flattening of the vertex seems to persist after surgical correction. The authors' cranial 3D mesh processing tool has been made publicly available as a part of this study.

CONCLUSIONS

The findings suggest that until age 6, there are no significant differences among the FBR, ESC, and SAC in their ability to correct sagittal synostosis with regard to 3D photocephalometric measurements. Therefore, efforts should be made to ensure early diagnosis so that minimally invasive surgery is a viable treatment option.

CLINICAL QUESTION/LEVEL OF EVIDENCE

Therapeutic, III.

Photogrammetry Applied to Neurosurgery: A Literature Review

Photogrammetry refers to the process of creating 3D models and taking measurements through the use of photographs. Photogrammetry has many applications in neurosurgery, such as creating 3D anatomical models and diagnosing and evaluating head shape and posture deformities. This review aims to summarize the uses of the technique in the neurosurgical practice and showcase the systems and software required for its implementation. A literature review was done in the online database PubMed. Papers were searched using the keywords "photogrammetry", "neurosurgery", "neuroanatomy", "craniosynostosis" and "scoliosis". The identified articles were later put through primary (abstracts and titles) and secondary (full text) screening for eligibility for inclusion. In total, 86 articles were included in the review from 315 papers identified. The review showed that the main uses of photogrammetry in the field of neurosurgery are related to the creation of 3D models of complex neuroanatomical structures and surgical approaches, accompanied by the uses for diagnosis and evaluation of patients with structural deformities of the head and trunk, such as craniosynostosis and scoliosis. Additionally, three instances of photogrammetry applied for more specific aims, namely, cervical spine surgery, skull-base surgery, and radiosurgery, were identified. Information was extracted on the software and systems used to execute the method. With the development of the photogrammetric method, it has become possible to create accurate 3D models of physical objects and analyze images with dedicated software. In the neurosurgical setting, this has translated into the creation of anatomical teaching models and surgical 3D models as well as the evaluation of head and spine deformities. Through those applications, the method has the potential to facilitate the education of residents and medical students and the diagnosis of patient pathologies.

Comparison of the accuracy of different handheld-type scanners in three-dimensional facial image recognition

PURPOSE

Handheld-type scanners are widely used in clinical practice. This study examined the accuracy of handheld-type scanners using plaster statues to assess their performance in facial recognition.

METHODS

Twelve 4-mm zirconia balls as measuring points were attached to the facial portions of three types of plaster statue. Six digital facial images of each plaster statue were obtained using one of the following five handheld-type scanners: Artec Eva, Artec Spider, Bellus 3D FaceApp, SNAP, and Vectra H1. Four-millimeter spherical objects were manually placed at the measurement points on the scanned data generated using computer-aided design software and coordinate positions were measured using a contact-type high-resolution three-dimensional measurement device. Consequently, the discrepancy between the distance measured using the contact-type device and that measured using the handheld-type scanner was calculated. The scanning time, processing time, and deviation of the distance between the measuring points were analyzed using two-way analysis of variance and t-test with Bonferroni correction.

RESULTS

The scanning and processing times ranged from 15.2 to 42.2 s and 20.7 to 234.2 s, respectively. Overall, 97% of all measured distances by Spider were within ±1.00% deviation; 79%, Vectra; 73%, Eva; 70%, Bellus; and 42%, SNAP.

CONCLUSIONS

The performance of handheld-type scanners using plaster statues varied among the different scanners. The scanning time of Eva and the processing time of Bellus were significantly shorter than those of other scanners. Furthermore, Spider exhibited the best accuracy, followed by Eva, Vectra, Bellus, and SNAP.

A Radiation-Free Classification Pipeline for Craniosynostosis Using Statistical Shape Modeling

Background: Craniosynostosis is a condition caused by the premature fusion of skull sutures, leading to irregular growth patterns of the head. Three-dimensional photogrammetry is a radiation-free alternative to the diagnosis using computed tomography. While statistical shape models have been proposed to quantify head shape, no shape-model-based classification approach has been presented yet. Methods: We present a classification pipeline that enables an automated diagnosis of three types of craniosynostosis. The pipeline is based on a statistical shape model built from photogrammetric surface scans. We made the model and pathology-specific submodels publicly available, making it the first publicly available craniosynostosis-related head model, as well as the first focusing on infants younger than 1.5 years. To the best of our knowledge, we performed the largest classification study for craniosynostosis to date. Results: Our classification approach yields an accuracy of 97.8 %, comparable to other state-of-the-art methods using both computed tomography scans and stereophotogrammetry. Regarding the statistical shape model, we demonstrate that our model performs similar to other statistical shape models of the human head. Conclusion: We present a state-of-the-art shape-model-based classification approach for a radiation-free diagnosis of craniosynostosis. Our publicly available shape model enables the assessment of craniosynostosis on realistic and synthetic data.

Design of 3D Additively Manufactured Hybrid Structures for Cranioplasty

A wide range of materials has been considered to repair cranial defects. In the field of cranioplasty, poly(methyl methacrylate) (PMMA)-based bone cements and modifications through the inclusion of copper doped tricalcium phosphate (Cu-TCP) particles have been already investigated. On the other hand, aliphatic polyesters such as poly(ε-caprolactone) (PCL) and polylactic acid (PLA) have been frequently investigated to make scaffolds for cranial bone regeneration. Accordingly, the aim of the current research was to design and fabricate customized hybrid devices for the repair of large cranial defects integrating the reverse engineering approach with additive manufacturing, The hybrid device consisted of a 3D additive manufactured polyester porous structures infiltrated with PMMA/Cu-TCP (97.5/2.5 w/w) bone cement. Temperature profiles were first evaluated for 3D hybrid devices (PCL/PMMA, PLA/PMMA, PCL/PMMA/Cu-TCP and PLA/PMMA/Cu-TCP). Peak temperatures recorded for hybrid PCL/PMMA and PCL/PMMA/Cu-TCP were significantly lower than those found for the PLA-based ones. Virtual and physical models of customized devices for large cranial defect were developed to assess the feasibility of the proposed technical solutions. A theoretical analysis was preliminarily performed on the entire head model trying to simulate severe impact conditions for people with the customized hybrid device (PCL/PMMA/Cu-TCP) (i.e., a rigid sphere impacting the implant region of the head). Results from finite element analysis (FEA) provided information on the different components of the model.

Photogrammetry as an alternative for acquiring digital dental models: A proof of concept

Photogrammetry is a mathematical technique that generates three-dimensional coordinates of specific points identified from multiple images of the same object obtained at different angles. This technique may be a low-cost alternative for traditional scanning. The objective of this proof of concept was to evaluate the accuracy and precision in obtaining digital models (DM) from a plaster model (PM) using photogrammetry. Five DM were generated from 50 photographs taken surrounding the PM. The photographs were taken by a single operator on five consecutive days using natural light. The images obtained were processed on 3DF Zephyr Free software. The height and width of all teeth were recorded on both PM and DM, as well as the distance between the canine cusps (C-C) and between the mesiobuccal cusps of the first molars (1 M-1 M). For the PM the measurements were taken with a digital caliper, whereas the DM was measured using the software Blender. The DM and PM measurements presented a limit of agreement between -0.433 and 0.611 mm. The accuracy of DM measurements showed a SD of ±0.171 mm and a repeatability coefficient of 0.474. In the superimposition of all DM, it was possible to notice a greater discrepancy in the posterior region of the arch and palate, but this difference decreased when the region was segmented. It can be concluded that photogrammetry appears to be a viable technique for the digitization of dental models. Further studies need to be performed to evaluate its clinical application.