Average thickness of the bones of the human neurocranium: development of reference measurements to assist with blunt force trauma interpretations

A database of magnetic resonance imaging-transcranial ultrasound co-registration

PURPOSE

As a portable and cost-effective imaging modality with better accessibility than Magnetic Resonance Imaging (MRI), transcranial sonography (TCS) has demonstrated its flexibility and potential utility in various clinical diagnostic applications, including Parkinson's disease and cerebrovascular conditions. To better understand the information in TCS for data analysis and acquisition, MRI can provide guidance for efficient imaging with neuronavigation systems and the confirmation of disease-related abnormality. In these cases, MRI-TCS co-registration is crucial, but relevant public databases are scarce to help develop the related algorithms and software systems.

ACQUISITION AND VALIDATION METHODS

This dataset comprises manually registered MRI and transcranial ultrasound volumes from eight healthy subjects. Three raters manually registered each subject's scans, based on visual inspection of image feature correspondence. Average transformation matrices were computed from all raters' alignments for each subject. Inter- and intra-rater variability in the transformations conducted by raters are presented to validate the accuracy and consistency of manual registration. In addition, a population-averaged MRI brain vascular atlas is provided to facilitate the development of computer-assisted TCS acquisition software.

DATA FORMAT AND USAGE NOTES

The dataset is provided in both NIFTI and MINC formats and is publicly available on the OSF data repository: https://osf.io/zdcjb/.

POTENTIAL APPLICATIONS

This dataset provides the first public resource for the development and assessment of MRI-TCS registration with manual ground truths, as well as resources for establishing neuronavigation software in data acquisition and analysis of TCS. These technical advancements could greatly boost TCS as an imaging tool for clinical applications in the diagnosis of neurological conditions such as Parkinson's disease and cerebrovascular disorders.

Sex differences in caloric nystagmus intensity: Should reference values be updated?

Bithermal caloric irrigation of the horizontal semicircular canals is a key method of neurotological diagnostics, allowing the detection of peripheral vestibular hypofunction in the low-frequency range. Current diagnostic criteria for unilateral vestibulopathy (UVP), bilateral vestibulopathy (BVP), and presbyvestibulopathy (PVP) rely on gender-neutral absolute or relative metrics. Here, we analyzed all bithermal water caloric examinations performed in the German Center for Vertigo and Balance Disorders (DSGZ) between 07/2018 and 01/2024 and calculated the total caloric reactivity (TR). Patient age and sex were collected as covariates. For UVP, BVP, and PVP diagnoses, international diagnostic criteria were applied. In total, 11,332 patients (6219 females, mean age 55.97±17.52 years) were included. Females displayed a higher TR (mean difference: 6.41°/s, p<0.001). The frequency of UVP, BVP, and PVP diagnoses based on absolute cut-off values showed a significant male predominance (UVP: n = 1144, 548 females, odd ratio [OR] -0.32, p<0.001; BVP: n = 305, 138 females, OR -0.40, p<0.001; PVP: n = 813, 378 females, OR -0.37, p<0.001). However, the rate of UVP based on relative asymmetries showed no sex differences (n = 2971, 1595 females, OR -0.08, p = 0.06). Diagnostic criteria for UVP, BVP, or PVP, which utilize absolute caloric excitability cut-offs, might need to be updated to address sex-specific differences of caloric excitability.

From digital to physical model: the use of 3D-printed models in wound ballistic reconstruction

Synthetic models (also called "surrogates") simulating human tissues are widely used in wound ballistics. Although there are a large number of commercial models showing interesting properties, these are limited to generic shapes. The result of the interaction between the projectile and the target varies based on several parameters; therefore, using a case-specific, custom-shaped synthetic model would enhance the accuracy of the findings. For this purpose, the authors created, based on Post-Mortem Computed Tomography (PMCT) measurements, case specific 3D-printed synthetic models. The first ballistic tests were performed on simple plates printed with different materials and compared against polyurethan Synbone® products in order to select the most suited materials for synthetic head models. Further tests were realised on head models printed with PLA (polylactic acid), PETG (polyethylene terephthalate glycol-modified) and TPU (thermoplastic polyurethane) polymers as well as on two head models composed of powder and resin. The bullet's behaviour, its deformation, the wound channel and other qualitative aspects were directly compared to the findings of the real case reported in Riva et al in Int J Legal Med 135:2567-2579, 2021, as well as to the "open shape" head model created by Riva et al in Forensic Sci Int 294:150-159, 2019. Finally, although the results of this study did not completely fulfil the requirements to simulate human bones, its concept in reproducing case specific head models with easily available 3D printing materials, is very promising.

Pin penetration depths in the neurocranium using a three-pin head fixation device

In estimated 10-15% of neurosurgical interventions employing a conventional three-pin head fixation device (HFD) the patient's head loses position due to slippage. At present no scientifically based stability criterion exists to potentially prevent the intraoperative loss of head position or skull fractures. Here, data on the skull penetration depth both on the single and two-pin side of a three-pin HFD are presented, providing scientific evidence for a stability criterion for the invasive three-pin head fixation. Eight fresh, chemically untreated human cadaveric heads were sequentially pinned 90 times in total in a noncommercially calibrated clamp screw applying a predefined force of 270 N (approximately 60 lbf) throughout. Three head positions were pinned each in standardized manner for the following approaches: prone, middle fossa, pterional. Titanium-aluminum alloy pins were used, varying the pin-cone angle on the single-pin side from 36° to 55° and on the two-pin side from 25° to 36°. The bone-penetration depths were directly measured by a dial gauge on neurocranium. The penetration depths on the single-pin side ranged from 0.00 mm (i.e., no penetration) to 6.17 mm. The penetration depths on the two-pin side ranged from 0.00 mm (no penetration) to 4.48 mm. We measured a significantly higher penetration depth for the anterior pin in comparison to the posterior pin on the two-pin side in prone position. One pin configuration (50°/25°) resulted in a quasi-homogenous pin depth distribution between the single- and the two-pin side. Emanating from the physical principle that pin depths behave proportionate to pin pressure distribution, a quasi-homogenous pin penetration depth may result in higher resilience against external shear forces or torque, thus reducing potential complications such as slippage and depressed skull fractures. The authors propose that the pin configuration of 50°/25° may be superior to the currently used uniform pin-cone angle distribution in common clinical practice (36°/36°). However, future research may identify additional influencing factors to improve head fixation stability.

Cranial Bone Changes Induced by Mild Traumatic Brain Injuries: A Neglected Player in Concussion Outcomes?

Mild traumatic brain injuries (TBIs), particularly when repetitive in nature, are increasingly recognized to have a range of significant negative implications for brain health. Much of the ongoing research in the field is focused on the neurological consequences of these injuries and the relationship between TBIs and long-term neurodegenerative conditions such as chronic traumatic encephalopathy and Alzheimer's disease. However, our understanding of the complex relationship between applied mechanical force at impact, brain pathophysiology, and neurological function remains incomplete. Past research has shown that mild TBIs, even below the threshold that results in cranial fracture, induce changes in cranial bone structure and morphology. These structural and physiological changes likely have implications for the transmission of mechanical force into the underlying brain parenchyma. Here, we review this evidence in the context of the current understanding of bone mechanosensitivity and the consequences of TBIs or concussions. We postulate that heterogeneity of the calvarium, including differing bone thickness attributable to past impacts, age, or individual variability, may be a modulator of outcomes after subsequent TBIs. We advocate for greater consideration of cranial responses to TBI in both experimental and computer modeling of impact biomechanics, and raise the hypothesis that calvarial bone thickness represents a novel biomarker of brain injury vulnerability post-TBI.

Automatic analysis of skull thickness, scalp-to-cortex distance and association with age and sex in cognitively normal elderly

Personalized neurostimulation has been a potential treatment for many brain diseases, which requires insights into brain/skull geometry. Here, we developed an open source efficient pipeline BrainCalculator for automatically computing the skull thickness map, scalp-to-cortex distance (SCD), and brain volume based on T 1 -weighted magnetic resonance imaging (MRI) data. We examined the influence of age and sex cross-sectionally in 407 cognitively normal older adults (71.9±8.0 years, 60.2% female) from the ADNI. We demonstrated the compatibility of our pipeline with commonly used preprocessing packages and found that BrainSuite Skullfinder was better suited for such automatic analysis compared to FSL Brain Extraction Tool 2 and SPM12- based unified segmentation using ground truth. We found that the sphenoid bone and temporal bone were thinnest among the skull regions in both females and males. There was no increase in regional minimum skull thickness with age except in the female sphenoid bone. No sex difference in minimum skull thickness or SCD was observed. Positive correlations between age and SCD were observed, faster in females (0.307%/y) than males (0.216%/y) in temporal SCD. A negative correlation was observed between age and whole brain volume computed based on brain surface (females -1.031%/y, males -0.998%/y). In conclusion, we developed an automatic pipeline for MR-based skull thickness map, SCD, and brain volume analysis and demonstrated the sex-dependent association between minimum regional skull thickness, SCD and brain volume with age. This pipeline might be useful for personalized neurostimulation planning.