"Black bone" MRI: a potential alternative to CT when imaging the head and neck: report of eight clinical cases and review of the Oxford experience

Three contrasts in 3 min: Rapid, high-resolution, and bone-selective UTE MRI for craniofacial imaging with automated deep-learning skull segmentation

PURPOSE

Ultrashort echo time (UTE) MRI can be a radiation-free alternative to CT for craniofacial imaging of pediatric patients. However, unlike CT, bone-specific MR imaging is limited by long scan times, relatively low spatial resolution, and a time-consuming bone segmentation workflow.

METHODS

A rapid, high-resolution UTE technique for brain and skull imaging in conjunction with an automatic segmentation pipeline was developed. A dual-RF, dual-echo UTE sequence was optimized for rapid scan time (3 min) and smaller voxel size (0.65 mm3). A weighted least-squares conjugate gradient method for computing the bone-selective image improves bone specificity while retaining bone sensitivity. Additionally, a deep-learning U-Net model was trained to automatically segment the skull from the bone-selective images. Ten healthy adult volunteers (six male, age 31.5 ± 10 years) and three pediatric patients (two male, ages 12 to 15 years) were scanned at 3 T. Clinical CT for the three patients were obtained for validation. Similarities in 3D skull reconstructions relative to clinical standard CT were evaluated based on the Dice similarity coefficient and Hausdorff distance. Craniometric measurements were used to assess geometric accuracy of the 3D skull renderings.

RESULTS

The weighted least-squares method produces images with enhanced bone specificity, suppression of soft tissue, and separation from air at the sinuses when validated against CT in pediatric patients. Dice similarity coefficient overlap was 0.86 ± 0.05, and the 95th percentile Hausdorff distance was 1.77 ± 0.49 mm between the full-skull binary masks of the optimized UTE and CT in the testing dataset.

CONCLUSION

An optimized MRI acquisition, reconstruction, and segmentation workflow for craniofacial imaging was developed.

Cranial bone imaging using ultrashort echo-time bone-selective MRI as an alternative to gradient-echo based "black-bone" techniques

OBJECTIVES

CT is the clinical standard for surgical planning of craniofacial abnormalities in pediatric patients. This study evaluated three MRI cranial bone imaging techniques for their strengths and limitations as a radiation-free alternative to CT.

METHODS

Ten healthy adults were scanned at 3 T with three MRI sequences: dual-radiofrequency and dual-echo ultrashort echo time sequence (DURANDE), zero echo time (ZTE), and gradient-echo (GRE). DURANDE bright-bone images were generated by exploiting bone signal intensity dependence on RF pulse duration and echo time, while ZTE bright-bone images were obtained via logarithmic inversion. Three skull segmentations were derived, and the overlap of the binary masks was quantified using dice similarity coefficient. Craniometric distances were measured, and their agreement was quantified.

RESULTS

There was good overlap of the three masks and excellent agreement among craniometric distances. DURANDE and ZTE showed superior air-bone contrast (i.e., sinuses) and soft-tissue suppression compared to GRE.

DISCUSSIONS

ZTE has low levels of acoustic noise, however, ZTE images had lower contrast near facial bones (e.g., zygomatic) and require effective bias-field correction to separate bone from air and soft-tissue. DURANDE utilizes a dual-echo subtraction post-processing approach to yield bone-specific images, but the sequence is not currently manufacturer-supported and requires scanner-specific gradient-delay corrections.

Can Craniosynostosis be Diagnosed on Physical Examination? A Retrospective Review

Craniosynostosis is a developmental craniofacial defect in which one or more sutures of the skull fuse together prematurely. Uncorrected craniosynostosis may have serious complications including elevated intracranial pressure, developmental delay, and blindness. Proper diagnosis of craniosynostosis requires a physical examination of the head with assessment for symmetry and palpation of sutures for prominence. Often, if craniosynostosis is suspected, computed tomography (CT) imaging will be obtained. Recent literature has posited that this is unnecessary. This study aims to address whether physical examination alone is sufficient for the diagnosis and treatment planning of single suture craniosynostosis. Between 2015 and 2022, the Divisions of Pediatric Neurosurgery and Pediatric Plastic Surgery at UTHealth Houston evaluated 140 children under 36 months of age with suspected craniosynostosis by physical examination and subsequently ordered CT imaging for preoperative planning. Twenty-three patients received a clinical diagnosis of multi-sutural or syndromic craniosynostosis that was confirmed by CT. One hundred seventeen patients were diagnosed with single suture craniosynostosis on clinical examination and follow-up CT confirmed suture fusion in 109 (93.2%) patients and identified intracranial anomalies in 7 (6.0%) patients. These patients underwent surgical correction. Eight (6.8%) patients showed no evidence of craniosynostosis on CT imaging. Treatment for patients without fused sutures included molding helmets and observation alone. This evidence suggests that physical examination alone may be inadequate to accurately diagnose single suture synostosis, and surgery without preoperative CT evaluation could lead to unindicated procedures.

Susceptibility-weighted imaging to evaluate normal and abnormal vertebrae in fetuses:a preliminary study

OBJECTIVE

To evaluate the performance of Susceptibility-weighted imaging (SWI) in visualizing normal and abnormal fetal vertebrae in vivo and in utero.

METHODS

Ninety-seven women with normal fetal vertebrae and 127 women suspected fetal vertebral anomalies on ultrasound were included in our study. SWI, TrueFISP and HASTE of the fetal spine were performed on 1.5-T MRI. The image quality and diagnostic performance between HASTE/TrueFISP and SWI were compared. Pearson correlations to correlate the L1 centrum ossification center (COC) measurements with gestational age (GA) were performed.

RESULTS

The visibility of the fetal vertebral structures on the SWI images (3.58 ± 0.69) was significantly greater than those on the HASTE (1.98 ± 0.51, P < 0.001) and TrueFISP (2.63 ± 0.52, P < 0.001). The diagnostic accuracy of SWI (89.0%) was superior to HASTE/TrueFISP (48.0%) (P < 0.001) and the area under the curve (AUC) for SWI was 0.909 (P < 0.001). The height, transverse, sagittal diameter and area of L1 COC were linearly correlated with GA (all P < 0.001).

CONCLUSION

SWI proved to be a reliable method for depicting fetal vertebral structure and growth, which can significantly improve the diagnostic performance of vertebral anomalies in fetuses. This article is protected by copyright. All rights reserved.

Deep Learning for Synthetic CT from Bone MRI in the Head and Neck

BACKGROUND AND PURPOSE

Bone MR imaging techniques enable visualization of cortical bone without the need for ionizing radiation. Automated conversion of bone MR imaging to synthetic CT is highly desirable for downstream image processing and eventual clinical adoption. Given the complex anatomy and pathology of the head and neck, deep learning models are ideally suited for learning such mapping.

MATERIALS AND METHODS

This was a retrospective study of 39 pediatric and adult patients with bone MR imaging and CT examinations of the head and neck. For each patient, MR imaging and CT data sets were spatially coregistered using multiple-point affine transformation. Paired MR imaging and CT slices were generated for model training, using 4-fold cross-validation. We trained 3 different encoder-decoder models: Light_U-Net (2 million parameters) and VGG-16 U-Net (29 million parameters) without and with transfer learning. Loss functions included mean absolute error, mean squared error, and a weighted average. Performance metrics included Pearson R, mean absolute error, mean squared error, bone precision, and bone recall. We investigated model generalizability by training and validating across different conditions.

RESULTS

The Light_U-Net architecture quantitatively outperformed VGG-16 models. Mean absolute error loss resulted in higher bone precision, while mean squared error yielded higher bone recall. Performance metrics decreased when using training data captured only in a different environment but increased when local training data were augmented with those from different hospitals, vendors, or MR imaging techniques.

CONCLUSIONS

We have optimized a robust deep learning model for conversion of bone MR imaging to synthetic CT, which shows good performance and generalizability when trained on different hospitals, vendors, and MR imaging techniques. This approach shows promise for facilitating downstream image processing and adoption into clinical practice.

Zero-TE MRI: principles and applications in the head and neck

Zero echo-time (ZTE) MRI is a novel imaging technique that utilizes ultrafast readouts to capture signal from short-T2 tissues. Additional sequence advantages include rapid imaging times, silent scanning, and artifact resistance. A robust application of this technology is imaging of cortical bone without the use of ionizing radiation, thus representing a viable alternative to CT for both rapid screening and "one-stop-shop" MRI. Although ZTE is increasingly used in musculoskeletal and body imaging, neuroimaging applications have historically been limited by complex anatomy and pathology. In this article, we review the imaging physics of ZTE including pulse sequence options, practical limitations, and image reconstruction. We then discuss optimization of settings for ZTE bone neuroimaging including acquisition, processing, segmentation, synthetic CT generation, and artifacts. Finally, we examine clinical utility of ZTE in the head and neck with imaging examples including malformations, trauma, tumors, and interventional procedures.

Preliminary experience with black bone magnetic resonance imaging for morphometry of the mandible and visualisation of the facial skeleton

BACKGROUND

Children with orofacial deformity may require repeated imaging of the facial skeleton.

OBJECTIVE

To test the feasibility and accuracy of "black bone" magnetic resonance imaging (MRI) for assessing facial deformity in children.

MATERIALS AND METHODS

Three-dimensional (3-D) black bone gradient echo sequences (flip angle 5°, submillimetre spatial resolution) from 10 children (median age: 13 years, range: 2-16 years), who underwent MRI of the temporomandibular joints, were evaluated with multiplanar reconstruction and 3-D rendering tools. Intra- and inter-reader agreement was investigated for measuring the height of the mandibular ramus and condyle, basal length of the mandible, gonion angle and mandibular inclination angle by intraclass correlation coefficient (ICC) and Bland-Altman analysis. Absolute percentage error was calculated with the average of all measurements serving as reference.

RESULTS

Sixty linear and 40 angle measurements were obtained on reformatted multiplanar black bone images with excellent inter-reader agreement (ICC > 0.99, agreement bias < 1.4 mm/ < 1.5°) and small error (median absolute error < 3%). The black bone images required inversion of the signal intensity and removal of air before they could be processed with standard volume rendering tools. The diagnostic utility of 3-D views for assessing the facial skeleton was sufficient except for assessing dental relationship.

CONCLUSION

Morphometric measurements of the mandible can be obtained from black bone MRI with comparable inter-rater agreement to that reported for cone beam computed tomography (CT). With improvements of 3-D rendering techniques and software, black bone MRI may become a radiation-free alternative to CT in children with facial deformities.

Imaging in craniofacial disorders with special emphasis on gradient echo Black-Bone and Zero Time Echo MRI sequences

Context:

The well-known effects of ionizing radiation on brain cells have been a major driving force toward the use of non-ionizing methods of imaging in both elective and emergency settings. Pediatric neurosurgery has certainly leveraged on this shift in clinical practice, however patients with craniofacial disorders could not fully benefit from the adoption of magnetic resonance imaging (MRI) because computed tomography (CT) scans still retain superior imaging power on bone tissue.

Aims:

To explore the knowledge available on the use of MRI as surrogate for CT scan in the assessment of craniosynostosis.

Settings and Design:

A scoping review was designed to identify landmark studies and ongoing clinical trials exploring the accuracy of MRI-based bone imaging in the preoperative planning of pediatric patients with craniosynostosis.

Materials and Methods:

A total of 492 records were screened from Pubmed, Ovid Medline, Scopus, and Cochrane Library databases; while 55 records were retrieved from ClinicalTrials.gov register. Only clinical studies revolving around the use of Gradient Echo Black-Bone (BB) and Zero Time Echo (ZTE) MRI sequences for the preoperative planning of pediatric craniosynostosis were retained for inclusion.

Results and Conclusions:

This review identified only five clinical studies reporting a high accuracy of MRI-based 3D bone reconstruction in 47 pediatric candidates to surgical correction of craniosynostosis. Although promising, limited evidence (Level IV) exist that BB and ZTE MRI could help in the surgical planning for craniosynostosis management. The results of two ongoing randomized clinical trials, which are actively enrolling patients, will hopefully help answering this research question.

Clinical application of "black bone" imaging in paediatric craniofacial disorders

For decades, CT has been the primary imaging modality for the diagnosis and surveillance of paediatric craniofacial disorders. However, the deleterious effects of ionising radiation in the paediatric population are well established and remain an ongoing concern. This is especially so in the head and neck region, which has relatively poor soft tissue shielding with many radiosensitive organs. The development of "black bone" imaging utilising low flip angles and short echo time (TE) has shown considerable promise in alleviating the use of ionising radiation in many cases of craniofacial disorders. In this review article, we share our experience of utilising "black bone" sequence in children with craniofacial pathologies, ranging from traumatic injuries to craniosynostosis and focal osseous/fibro-osseous lesions such as fibrous dysplasia and Langerhans cell histiocytosis (LCH). A detailed discussion on the technical aspects of "black bone" sequence, including its potential pitfalls and limitations, will also be included.

"Black bone": the new backbone in CAD/CAM-assisted craniosynostosis surgery?

BACKGROUND

Computer-assisted design and manufacturing (CAD/CAM) techniques have been implemented in craniosynostosis surgery to facilitate cranial remodeling. However, until now, computed tomography (CT) scans with ionizing radiation were necessary to plan the procedure and create guiding templates. The purpose of this study was to present our series using CAD/CAM techniques in planning and conducting fronto-orbital advancement surgery in patients with trigonocephaly with datasets acquired only by "black bone" magnetic resonance imaging (MRI).

METHODS

Six consecutively operated cases from 2019 were included in this study. All patients suffered from non-syndromic trigonocephaly with no primary surgeries. All patients underwent cranial MRI including black bone sequences. Preoperative planning and guides were created based on the DICOM datasets. We analyzed demographic data, clinical data, and outcome measured by Whitaker score.

RESULTS

In all cases, precise frontobasal advancement was possible with the CAD/CAM guides created by black bone MRI. The mean operation time and planning time were 222 and 32 min. The time on intensive and intermediate care unit (ICU/IMC) time was 4.5 days, respectively. All but one case were classified as Whitaker I.

CONCLUSION

In trigonocephaly treatment by frontobasal advancement, black bone MRI-based CAD/CAM craniosynostosis surgery is safe and feasible. It offers the major advantage of completely avoiding CT scans and ionizing radiation with superior imaging quality of intracranial structures. Thus, it improves intraoperative safety and-at the same time-has the potential to reduce operating room (OR) time.

Differences between 3D isovoxel fat suppression VIBE MRI and CT models of proximal femur osseous anatomy: A preliminary study for bone tumor resection planning

Purpose

To evaluate the osseous anatomy of the proximal femur extracted from a 3D-MRI volumetric interpolated breath-hold (VIBE) sequence using either a Dixon or water excitation (WE) fat suppression method, and to measure the overall difference using CT as a reference standard.

Material and methods

This retrospective study reviewed imaging of adult patients with hip pain who underwent 3D hip MRI and CT. A semi-automatically segmented CT model served as the reference standard, and MRI segmentation was performed manually for each unilateral hip joint. The differences between Dixon-VIBE-3D-MRI vs. CT, and WE-VIBE-3D-MRI vs. CT, were measured. Equivalence tests between Dixon-VIBE and WE-VIBE models were performed with a threshold of 0.1 mm. Bland–Altman plots and Lin’s concordance-correlation coefficient were used to analyze the agreement between WE and Dixon sequences. Subgroup analyses were performed for the femoral head/neck, intertrochanteric, and femoral shaft areas.

Results

The mean and maximum differences between Dixon-VIBE-3D-MRI vs. CT were 0.2917 and 3.4908 mm, respectively, whereas for WE-VIBE-3D-MRI vs. CT they were 0.3162 and 3.1599 mm. The mean differences of the WE and Dixon methods were equivalent (P = 0.0292). However, the maximum difference was not equivalent between the two methods and it was higher in WE method. Lin’s concordance-correlation coefficient showed poor agreement between Dixon and WE methods. The mean differences between the CT and 3D-MRI models were significantly higher in the femoral shaft area (P = 0.0004 for WE and P = 0.0015 for Dixon) than in the other areas. The maximum difference was greatest in the intertrochanteric area for both techniques.

Conclusion

The difference between 3D-MR and CT models were acceptable with a maximal difference below 3.5mm. WE and Dixon fat suppression methods were equivalent. The mean difference was highest at the femoral shaft area, which was off-center from the magnetization field.

Advanced Magnetic Resonance Imaging of the Skull Base

Magnetic resonance (MR) imaging is a crucial tool for evaluation of the skull base, enabling characterization of complex anatomy by utilizing multiple image contrasts. Recent technical MR advances have greatly enhanced radiologists' capability to diagnose skull base pathology and help direct management. In this paper, we will summarize cutting-edge clinical and emerging research MR techniques for the skull base, including high-resolution, phase-contrast, diffusion, perfusion, vascular, zero echo-time, elastography, spectroscopy, chemical exchange saturation transfer, PET/MR, ultra-high-field, and 3D visualization. For each imaging technique, we provide a high-level summary of underlying technical principles accompanied by relevant literature review and clinical imaging examples.

7-T MRI for brain virtual autopsy: a proof of concept in comparison to 3-T MRI and CT

The detection and assessment of cerebral lesions and traumatic brain injuries are of particular interest in forensic investigations in order to differentiate between natural and traumatic deaths and to reconstruct the course of events in case of traumatic deaths. For this purpose, computed tomography (CT) and magnetic resonance imaging (MRI) are applied to supplement autopsy (traumatic death) or to supplant autopsy (natural deaths). This approach is termed “virtual autopsy.” The value of this approach increases as more microlesions and traumatic brain injuries are detected and assessed. Focusing on these findings, this article describes the examination of two decedents using CT, 3-T, and 7-T MRI. The main question asked was whether there is a benefit in using 7-T over 3-T MRI. To answer this question, the 3-T and 7-T images were graded regarding the detectability and the assessability of coup/contrecoup injuries and microlesions using 3-point Likert scales. While CT missed these findings, they were detectable on 3-T and 7-T MRI. However, the 3-T images appeared blurry in direct comparison with the 7-T images; thus, the detectability and assessability of small findings were hampered on 3-T MRI. The potential benefit of 7-T over 3-T MRI is discussed.

Trabecular Bone Assessment Using Magnetic-Resonance Imaging: A Pilot Study

The aim of this study was to assess trabecular bone morphology via magnetic-resonance imaging (MRI) using microcomputed tomography (µCT) as the control group. Porcine bone samples were scanned with T1-weighted turbo spin echo sequence imaging, using TR 25 ms, TE 3.5 ms, FOV 100 × 100 × 90, voxel size 0.22 × 0.22 × 0.50 mm, and scan time of 11:18. µCT was used as the control group with 80 kV, 125 mA, and a voxel size of 16 µm. The trabecular bone was segmented on the basis of a reference threshold value and morphological parameters. Bone volume (BV), Bone-volume fraction (BvTv), Bone specific surface (BsBv), trabecular thickness (TbTh), and trabecular separation (TbSp) were evaluated. Paired t-test and Pearson correlation test were performed at p = 0.05. MRI overestimated BV, BvTv, TbTh, and TbSp values. BsBv was the only parameter that was underestimated by MRI. High statistical correlation (r = 0.826; p < 0.05) was found for BV measurements. Within the limitations of this study, MRI overestimated trabecular bone parameters, but with a statistically significant fixed linear offset.

A novel concept of cam-type femoroacetabular impingement treatment with patient-specific template guided osteochondral deformity ablation

PURPOSE

To present a novel surgical concept for the cam-type femoroacetabular impingement (FAI) treatment and to assess and report the clinical outcomes.

METHODS

We performed a retrospective study of a single-surgeon case series of six hips in five consecutive male patients with symptomatic cam-type FAI, treated with the mini-open anterior hip approach with a patient-specific template (PST)-guided deformity ablation between 2015 and 2018. We assessed the hip range of motion, iHOT-33, Tegner, and EQ-5D before surgery and after a minimum follow-up of 30 months.

RESULTS

The average age was 37 ± 13.3 years, average BMI was 31.1 ± 3.3 kg/m², and average pre-surgery Tönnis hip osteoarthritis (OA) grade was 1 ± 1. The average surgery duration was 71 ± eight minutes. The average estimated blood loss was 83 ± 26 ml. After a mean follow-up of 50 ± 12 months, we observed no OA progression with no change in Tönnis hip OA grades. Hip flexion and internal rotation significantly improved (p = 0.007; p = 0.048) from mean 98° ± 9° and 14° ± 11° to mean 113° ± 8° and 23° ± 8°, respectively. iHOT-33, Tegner, and EQ-5D improved significantly (p = < 0.001; p = 0.004; p = < 0.001) from mean 44.7 ± 12.2, 3 ± 1, and 0.513420 ± 0.101389 to mean 94 ± 2.7, 5 ± 1, and 1.000000 ± 0, respectively. One patient needed revision surgery for heterotopic ossification removal, with no sequelae at the last follow-up.

CONCLUSION

Mini-open anterior hip approach with the PST-guided cam-type FAI deformity ablation presents an accurate and reproducible solution for cam-type FAI surgical treatment, with promising clinical outcomes. Using a PST in the cam-type FAI surgery may present a powerful additional tool in the existing open techniques armamentarium.

'Black Bone' magnetic resonance imaging as a novel technique to aid the pre-operative planning of posterior tympanotomy for cochlear implantation

Purpose: 'Black Bone' magnetic resonance imaging (BB MRI) is a novel sequence developed as an alternative to computed tomography (CT) for osseous imaging. We explored its potential utilisation in the pre-operative surgical planning of posterior tympanotomy for cochlear implantation through depiction of the mastoid facial nerve (mFN) canal and the posterior canaliculus of the chorda tympani (ChT), thus defining the facial recess. Methods: Twenty five adult patients were prospectively imaged with a dedicated BB MRI sequence. A consensus qualitative BB MRI 'visibility score' for the confidence of demonstration of the mFN canal and the posterior canaliculus of the ChT was recorded, as well as a 'corresponding score' to determine whether the neural structures on BB MRI corresponded to the paths of the nerves on a previous CT study. Results/discussion: The BB MRI sequence was able to clearly delineate the course of mFN in 100% of cases and that of ChT in 72%, with their courses corresponding to those depicted on CT in almost all cases. Maximum intensity projections with 7 mm slabs provided the optimal simultaneous demonstration of mFN, ChT and round window along the posterior tympanotomy surgical approach. Conclusion: The proposed BB MRI sequence reliably depicts mFN and ChT in the majority of cases, with a performance comparable to that of CT. It is proposed that it will be a useful adjunct to MRI protocols as part of cochlear implant assessment in those centres where CT is not routinely performed.

Automated Segmentation of the Craniofacial Skeleton With "Black Bone" Magnetic Resonance Imaging

Three-dimensional (3D) imaging of the craniofacial skeleton is integral in managing a wide range of bony pathologies. The authors have previously demonstrated the potential of "Black Bone" MRI (BB) as a non-ionizing alternative to CT. However, even in experienced hands 3D rendering of BB datasets can be challenging and time consuming. The objectives of this study were to develop and test a semi- and fully-automated segmentation algorithm for the craniofacial skeleton.Previously acquired adult volunteer (n = 15) BB datasets of the head were utilized. Imaging was initially 3D rendered with our conventional manual technique. An algorithm to remove the outer soft-tissue envelope was developed and 3D rendering completed with the processed datasets (semi-automated). Finally, a fully automated 3D-rendering method was developed and applied to the datasets. All 3D rendering was completed with Fovia High Definition Volume Rendering (Fovia Inc, Palo Alto, CA). Analysis was undertaken of the 3D visual results and the time taken for data processing and interactive manipulation.The mean time for manual segmentation was 12.8 minutes, 3.1 minutes for the semi-automated algorithm, and 0 minutes for the fully automated algorithm. Further fine adjustment was undertaken to enhance the automated segmentation results, taking a mean time of 1.4 minutes.Automated segmentation demonstrates considerable potential, offering significant time saving in the production of 3D BB imaging in adult volunteers. the authors continue to undertake further development of our segmentation algorithms to permit adaption to the pediatric population in whom non-ionizing imaging confers the most potential benefit.

3D pediatric cranial bone imaging using high-resolution MRI for visualizing cranial sutures: a pilot study

OBJECTIVE

There is an unmet need to perform imaging in young children and obtain CT-equivalent cranial bone images without subjecting the patients to radiation. In this study, the authors propose using a high-resolution fast low-angle shot golden-angle 3D stack-of-stars radial volumetric interpolated breath-hold examination (GA-VIBE) MRI sequence that is intrinsically robust to motion and has enhanced bone versus soft-tissue contrast.

METHODS

Patients younger than 11 years of age, who underwent clinical head CT scanning for craniosynostosis or other cranial malformations, were eligible for the study. 3D reconstructed images created from the GA-VIBE MRI sequence and the gold-standard CT scan were randomized and presented to 3 blinded reviewers. For all image sets, each reviewer noted the presence or absence of the 6 primary cranial sutures and recorded on 5-point Likert scales whether they recommended a second scan be performed.

RESULTS

Eleven patients (median age 1.8 years) underwent MRI after clinical head CT scanning was performed. Five of the 11 patients were sedated. Three clinicians reviewed the images, and there were no cases, either with CT scans or MR images, in which a reviewer agreed a repeat scan was required for diagnosis or surgical planning. The reviewers reported clear imaging of the regions of interest on 99% of the CT reviews and 96% of the MRI reviews. With CT as the standard, the sensitivity and specificity of the GA-VIBE MRI sequence to detect suture closure were 97% and 96%, respectively (n = 198 sutures read).

CONCLUSIONS

The 3D reconstructed images using the GA-VIBE sequence in comparison to the CT scans created clinically acceptable cranial images capable of detecting cranial sutures. Future directions include reducing the scan time, improving motion correction, and automating postprocessing for clinical utility.

Enhancing Distraction Osteogenesis With Carbon Fiber Reinforced Polyether Ether Ketone Bone Pins and a Three-Dimensional Printed Transfer Device to Permit Artifact-Free Three-Dimensional Magnetic Resonance Imaging

OBJECTIVES

To: (1) design an artifact-free 3D-printed MR-safe temporary transfer device, (2) engineer bone-pins from carbon fiber reinforced polyether ether ketone (CFR-PEEK), (3) evaluate the imaging artifacts of CFR-PEEK, and (4) confirm the osteointegration potential of CFR-PEEK, thus enhancing 3D-planning of bony advancements in hemifacial microsomia using sequential magnetic resonance imaging (MRI).

STUDY DESIGN

Engineered CRF-PEEK bone pins and a 3D printed ex-fix device were implanted into a sheep head and imaged with MRI and computed tomography . The osseointegration and bony compatibility potential of CFR-PEEK was assessed with scanning electron microscopy images of MC3T3 preosteoblast cells on the surface of the material.

RESULTS

The CFR-PEEK pins resulted in a signal void equivalent to the dimension of the pin, with no adjacent areas of MR-signal loss or computed tomography artifact. MCT3 cells adhered and proliferated on the surface of the discs by forming a monolayer of cells, confirming compatibility and osseointegration potential.

CONCLUSION

A 3D printed transfer device could be utilized temporarily during MRI to permit artifact-free 3D planning. CFR-PEEK pins eliminate imaging artifact permitting sequential MRI examination. In combination, this has the potential to enhance distraction osteogenesis, by permitting accurate three-dimensional planning without ionizing radiation.

Automated 3D MRI rendering of the craniofacial skeleton: using ZTE to drive the segmentation of black bone and FIESTA-C images

Purpose

Automated bone segmentation from MRI datasets would have a profound impact on clinical utility, particularly in the craniofacial skeleton where complex anatomy is coupled with radiosensitive organs. Techniques such as gradient echo black bone (GRE-BB) and short echo time (UTE, ZTE) have shown potential in this quest. The objectives of this study were to ascertain (1) whether the high-contrast of zero echo time (ZTE) could drive segmentation of high-resolution GRE-BB data to enhance 3D-output and (2) if these techniques could be extrapolated to ZTE driven segmentation of a routinely used non bone-specific sequence (FIESTA-C).

Methods

Eleven adult volunteers underwent 3T MRI examination with sequential acquisition of ZTE, GRE-BB and FIESTA-C imaging. Craniofacial bone segmentation was performed using a fully automated segmentation algorithm. Segmentation was completed individually for GRE-BB and a modified version of the algorithm was subsequently implemented, wherein the bone mask yielded by ZTE segmentation was used to initialise segmentation of GRE-BB. The techniques were subsequently applied to FIESTA-C datasets. The resulting 3D reconstructions were evaluated for areas of unexpected bony defects and discrepancies.

Results

The automated segmentation algorithm yielded acceptable 3D outputs for all GRE-BB datasets. These were enhanced with the modified algorithm using ZTE as a driver, with improvements in areas of air/bone interface and dense muscular attachments. Comparable results were obtained with ZTE+FIESTA-C.

Conclusion

Automated 3D segmentation of the craniofacial skeleton is enhanced through the incorporation of a modified segmentation algorithm utilising ZTE. These techniques are transferrable to FIESTA-C imaging which offers reduced acquisition time and therefore improved clinical utility.

Magnetic resonance imaging artifacts produced by dental implants with different geometries

OBJECTIVES

The purpose of this study was to evaluate the MRI-artifact pattern produced by titanium and zirconia dental implants with different geometries (diameter and height).

METHODS

Three titanium (Titan SLA, Straumann) and three zirconia (Pure Ceramic Implant, Straumann) dental implants differing on their design (diameter x height) were installed in porcine bone samples. Samples were scanned with a MRI (3T, T1W turbo spin echo sequence, TR/TE 25/3.5ms, voxel size 0.22×0.22×0.50 mm, scan time 11:18). Micro-CT was used as control group (80kV, 125mA, voxel size 16µm). Artifacts' distribution was measured at vestibular and lingual sites, mesial and distal sites, and at the apex. Statistical analysis was performed with Within-ANOVA (p=0.05).

RESULTS

Artifacts distribution measured 2.57 ± 1.09 mm for titanium artifacts and 0.37 ± 0.20 mm for zirconia artifacts (p<0.05). Neither the measured sites (p=0.73) nor the implant geometries (p=0.43) influenced the appearance of artifacts.

CONCLUSION

Artifacts were higher for titanium than zirconia implants. The artifacts pattern was similar for different dental implant geometries.

Zero TE MRI for Craniofacial Bone Imaging

Zero TE MR imaging is a novel technique that achieves a near-zero time interval between radiofrequency excitation and data acquisition, enabling visualization of short-T2 materials such as cortical bone. Zero TE offers a promising radiation-free alternative to CT with rapid, high-resolution, silent, and artifact-resistant imaging, as well as the potential for "pseudoCT" reconstructions. In this report, we will discuss our preliminary experience with zero TE, including technical principles and a clinical case series demonstrating emerging applications in neuroradiology.

Syndromic Craniosynostosis

Management strategies for syndromic craniosynostosis patients require multidisciplinary subspecialty teams to provide optimal care for complex reconstructive approaches. The most common craniosynostosis syndromes include Apert (FGFR2), Crouzon (FGFR2), Muenke (FGFR3), Pfeiffer (FGFR1 and FGFR2), and Saethre-Chotzen (TWIST). Bicoronal craniosynostosis (turribrachycephaly) is most commonly associated with syndromic craniosynostosis. Disease presentation varies from mild sutural involvement to severe pansynostoses, with a spectrum of extracraniofacial dysmorphic manifestations. Understanding the multifaceted syndromic presentations while appreciating the panoply of variable presentations is central to delivering necessary individualized care. Cranial vault remodeling aims to relieve restriction of cranial development and elevated intracranial pressure and restore normal morphology.

Non-invasive three-dimensional bone-vessel image fusion using black bone MRI based on FIESTA-C

AIM

To evaluate the image quality of bone-vessel fused volume-rendering (VR) images reconstructed by three-dimensional "black bone" magnetic resonance imaging (MRI) based on the fast imaging employing steady-state acquisition cycled phases (FIESTA-C) sequence and time-of-flight magnetic resonance angiography (TOF-MRA).

MATERIALS AND METHODS

Seventeen patients were analysed in this retrospective study. All patients underwent both MRI techniques including FIESTA-C and TOF-MRA and computed tomography angiography (CTA). MRI- and CT-based bone-vessel VR images were reconstructed. Visual depictions of frontal and parietal branches from the superficial temporal artery (STA) were independently scored by three experienced radiological technologists using a four-grade system.

RESULTS

In the visual evaluation, the scores of the both right and left frontal branches in MRI-based VR image were significantly larger those at CT (p<0.01, respectively). The scores of both the right and left parietal branches tended to be larger in MRI-based than that in CT-based VR imaging, but were not significantly so (p=0.06, 0.13 respectively). In the interobserver agreement analysis, κ values were all good (range: 0.6-0.76) for STA branch evaluation in MRI-based VR images.

CONCLUSION

MRI bone-vessel fused VR imaging can non-invasively depict STA frontal branches with better visibility compared to the CT-based VR imaging. This technique may be useful for the preoperative evaluation of donor branches for STA-middle cerebral artery bypass surgery.

Sphenoid Dysplasia in Neurofibromatosis: Patterns of Presentation and Outcomes of Treatment

BACKGROUND

Sphenoid wing dysplasia in patients with neurofibromatosis type 1 may result in challenging and significant changes, including ultimately vision loss. The authors describe the radiographic patterns of sphenoid dysmorphology with time and age, and the impact of surgical intervention on preservation of vision.

METHODS

A retrospective study was performed at a single pediatric hospital, identifying subjects with neurofibromatosis type 1. Records were reviewed in their entirety for each subject, with attention to ophthalmologic evaluation. Radiographic images were digitally analyzed and scored for sphenoid transformations on a grade of 0 to 3.

RESULTS

Fifty-two subjects were identified. On initial imaging, 42.31 percent had a normal sphenoid (grade 0), 32.69 percent had an abnormal contour (grade 1), 11.54 percent had thinning (grade 2), and 13.46 percent had a gross defect (grade 3). Among the 45 subjects with serial imaging, 55.56 percent demonstrated progression of the deformity of at least one grade. Deformity progression correlated with length of imaging interval. Enucleation was noted to occur more often in subjects with a gross sphenoid defect (p < 0.0001). Of subjects identified as having a gross sphenoid defect, 26.7 percent were managed using orbitosphenoid reconstruction with titanium mesh and cranial bone graft, and 33.3 percent were managed with soft-tissue debulking and canthopexy only. Vision was more likely to be preserved with early orbitosphenoid reconstruction (p < 0.05).

CONCLUSIONS

Sphenoid dysplasia is a progressive disease. Loss of vision is associated with a gross defect, and appears to be better preserved with early orbitosphenoid reconstruction with titanium mesh and cranial bone graft.

Use of black-bone MRI in the diagnosis of the patients with posterior plagiocephaly

PURPOSE

Ionising radiation exposure is especially harmful to brain development. The purpose of this study was to evaluate whether black-bone (BB) magnetic resonance imaging (MRI), a non-ionising imaging method, offers an alternative to ionising imaging methods such as computed tomography (CT) in the examination of cranial deformities.

METHODS

From 2012 to 2014, a total of 408 children were referred to the Craniofacial Centre at the Helsinki University Hospital for further examination due to flatness of the posterior skull. Fifteen of these patients required further diagnostic imaging. To avoid ionising radiation, we used an MRI protocol that included sequences for evaluation of both brain anatomy and skull bone and sutures by BB-MRI. A semi-automatic skull segmentation algorithm was developed to facilitate the visualisation. Two patients with scaphocephaly were included in the study to confirm the ability to differentiate synostosis with BB-MRI.

RESULTS

We obtained informative 3D images using BB-MRI. Seven patients (7/15, 46.7%) had plagiocephaly on the right side and seven on the left side (7/15, 46.7%). One patient (1/15, 6.7%) had symmetric posterior flatness affecting both sides. Neither structural nor signal-intensity alterations of the brain were detected in visual analysis.

CONCLUSION

BB-MRI provides an alternative to CT when imaging craniofacial deformities. BB-MRI provides not only high-quality 3D-reconstructed imaging of the bony structures and sutures but also information on brain structure in one imaging session. With further development, this method could replace ionising radiation-based methods in analysing deformities of the skull.

Optimisation of three-dimensional lower jaw resection margin planning using a novel Black Bone magnetic resonance imaging protocol

BACKGROUND

MRI is the optimal method for sensitive detection of tumour tissue and pre-operative staging in oral cancer. When jawbone resections are necessary, the current standard of care for oral tumour surgery in our hospital is 3D virtual planning from CT data. 3D printed jawbone cutting guides are designed from the CT data. The tumour margins are difficult to visualise on CT, whereas they are clearly visible on MRI scans. The aim of this study was to change the conventional CT-based workflow by developing a method for 3D MRI-based lower jaw models. The MRI-based visualisation of the tumour aids in planning bone resection margins.

MATERIALS AND FINDINGS

A workflow for MRI-based 3D surgical planning with bone cutting guides was developed using a four-step approach. Key MRI parameters were defined (phase 1), followed by an application of selected Black Bone MRI sequences on healthy volunteers (phase 2). Three Black Bone MRI sequences were chosen for phase 3: standard, fat saturated, and an out of phase sequence. These protocols were validated by applying them on patients (n = 10) and comparison to corresponding CT data. The mean deviation values between the MRI- and the CT-based models were 0.63, 0.59 and 0.80 mm for the three evaluated Black Bone MRI sequences. Phase 4 entailed examination of the clinical value during surgery, using excellently fitting printed bone cutting guides designed from MRI-based lower jaw models, in two patients with oral cancer. The mean deviation of the resection planes was 2.3 mm, 3.8 mm for the fibula segments, and the mean axis deviation was the fibula segments of 1.9°.

CONCLUSIONS

This study offers a method for 3D virtual resection planning and surgery using cutting guides based solely on MRI imaging. Therefore, no additional CT data are required for 3D virtual planning in oral cancer surgery.

Does the Addition of a "Black Bone" Sequence to a Fast Multisequence Trauma MR Protocol Allow MRI to Replace CT after Traumatic Brain Injury in Children?

BACKGROUND AND PURPOSE

Head CT is the current neuroimaging tool of choice in acute evaluation of pediatric head trauma. The potential cancer risks of CT-related ionizing radiation should limit its use in children. We evaluated the role of MR imaging, including a "black bone" sequence, compared with CT in detecting skull fractures and intracranial hemorrhages in children with acute head trauma.

MATERIALS AND METHODS

We performed a retrospective evaluation of 2D head CT and brain MR imaging studies including the black bone sequence of children with head trauma. Two experienced pediatric neuroradiologists in consensus created the standard of reference. Another pediatric neuroradiologist blinded to the diagnosis evaluated brain MR images and head CT images in 2 separate sessions. The presence of skull fractures and intracranial posttraumatic hemorrhages was evaluated. We calculated the sensitivity and specificity of CT and MR imaging with the black bone sequence in the diagnosis of skull fractures and intracranial hemorrhages.

RESULTS

Twenty-eight children (24 boys; mean age, 4.89 years; range, 0-15.5 years) with head trauma were included. MR imaging with the black bone sequence revealed lower sensitivity (66.7% versus 100%) and specificity (87.5% versus 100%) in identifying skull fractures. Four of 6 incorrectly interpreted black bone MR imaging studies showed cranial sutures being misinterpreted as skull fractures and vice versa.

CONCLUSIONS

Our preliminary results show that brain MR imaging complemented by a black bone sequence is a promising nonionizing alternative to head CT for the assessment of skull fractures in children. However, accuracy in the detection of linear fractures in young children and fractures of aerated bone remains limited.

Age-Dependent Subchondral Bone Remodeling and Cartilage Repair in a Minipig Defect Model

After cartilage injury and repair, the subchondral bone plate remodels. Skeletal maturity likely impacts both bone remodeling and inherent cartilage repair capacity. The objective of this study was to evaluate subchondral bone remodeling as a function of injury type, repair scenario, and skeletal maturity in a Yucatan minipig model. Cartilage defects (4 mm) were created bilaterally in the trochlear groove. Treatment conditions included a full thickness chondral defect (full chondral defect, n = 3 adult/3 juvenile), a partial thickness (∼50%) chondral defect (PCD, n = 3/3), and FCD treated with microfracture (MFX, n = 3/3). At 6 weeks postoperatively, osteochondral samples containing the lesion site were imaged by micro-computed tomography (CT) and analyzed by histology and immunohistochemistry. Via micro-CT, FCD and MFX groups showed increased bone loss in juveniles compared with adults. Quantification of histology using the ICRS II scoring system showed equal overall assessment for the FCD groups and better overall assessment in juvenile animals treated with MFX compared with adults. All FCD and MFX groups were inferior to control samples. For the PCD injury, both age groups had values close to the control values. For the FCD groups, there were greater alterations in the subchondral bone in juveniles compared with adults. Staining for collagen II showed more intense signals in juvenile FCD and MFX groups compared with adults. This large animal study of cartilage repair shows the significant impact of skeletal maturity on the propensity of subchondral bone to remodel as a result of chondral injury. This will improve selection criteria for animal models for studying cartilage injury, repair, and treatment.

Improved methods for acrylic-free implants in nonhuman primates for neuroscience research

Traditionally, head fixation devices and recording cylinders have been implanted in nonhuman primates (NHP) using dental acrylic despite several shortcomings associated with acrylic. The use of more biocompatible materials such as titanium and PEEK is becoming more prevalent in NHP research. We describe a cost-effective set of procedures that maximizes the integration of headposts and recording cylinders with the animal's tissues while reducing surgery time. Nine rhesus monkeys were implanted with titanium headposts, and one of these was also implanted with a recording chamber. In each case, a three-dimensional printed replica of the skull was created based on computerized tomography scans. The titanium feet of the headposts were shaped, and the skull thickness was measured preoperatively, reducing surgery time by up to 70%. The recording cylinder was manufactured to conform tightly to the skull, which was fastened to the skull with four screws and remained watertight for 8.5 mo. We quantified the amount of regression of the skin edge at the headpost. We found a large degree of variability in the timing and extent of skin regression that could not be explained by any single recorded factor. However, there was not a single case of bone exposure; although skin retracted from the titanium, skin also remained adhered to the skull adjacent to those regions. The headposts remained fully functional and free of complications for the experimental life of each animal, several of which are still participating in experiments more than 4 yr after implant.NEW & NOTEWORTHY Cranial implants are often necessary for performing neurophysiology research with nonhuman primates. We present methods for using three-dimensional printed monkey skulls to form and fabricate acrylic-free implants preoperatively to decrease surgery times and the risk of complications and increase the functional life of the implant. We focused on reducing costs, creating a feasible timeline, and ensuring compatibility with existing laboratory systems. We discuss the importance of using more biocompatible materials and enhancing osseointegration.

"Black Bone" MRI: a novel imaging technique for 3D printing

OBJECTIVES

Three-dimensionally printed anatomical models are rapidly becoming an integral part of pre-operative planning of complex surgical cases. We have previously reported the "Black Bone" MRI technique as a non-ionizing alternative to CT. Segmentation of bone becomes possible by minimizing soft tissue contrast to enhance the bone-soft tissue boundary. The objectives of this study were to ascertain the potential of utilizing this technique to produce three-dimensional (3D) printed models.

METHODS

"Black Bone" MRI acquired from adult volunteers and infants with craniosynostosis were 3D rendered and 3D printed. A custom phantom provided a surrogate marker of accuracy permitting comparison between direct measurements and 3D printed models created by segmenting both CT and "Black Bone" MRI data sets using two different software packages.

RESULTS

"Black Bone" MRI was successfully utilized to produce 3D models of the craniofacial skeleton in both adults and an infant. Measurements of the cube phantom and 3D printed models demonstrated submillimetre discrepancy.

CONCLUSIONS

In this novel preliminary study exploring the potential of 3D printing from "Black Bone" MRI data, the feasibility of producing anatomical 3D models has been demonstrated, thus offering a potential non-ionizing alterative to CT for the craniofacial skeleton.

Foetal "black bone" MRI: utility in assessment of the foetal spine

OBJECTIVE

Foetal CT has recently been added to the foetal imaging armamentarium, but this carries with it the risks of ionizing radiation, both to the mother and the foetus. Foetal "black bone" MRI is a new technique that allows assessment of the foetal skeleton without the risk of exposure to ionizing radiation and is a potential new sequence in foetal MRI examination.

METHODS

Retrospective review of all foetal MRI studies over the past 4- to 5-year period identified 36 cases where susceptibility weighted imaging was used. Cases were selected from this group to demonstrate the potential utility of this sequence.

RESULTS

This sequence is most frequently useful not only in the assessment of spinal abnormalities, most commonly the bony abnormalities in myelomeningocele, but also in cases of scoliosis, segmentation anomalies and sacrococcygeal teratoma.

CONCLUSION

Although the utility of this sequence is still being evaluated, it provides excellent contrast between the mineralized skeleton and surrounding soft tissues compared with standard half Fourier acquisition single-shot turbo-spin echo sequences. Further assessment is required to determine whether black bone MRI can more accurately evaluate the level of bony defect in spina bifida aperta, an important prognostic factor. Potential further uses include the assessment of skeletal dysplasias, evaluation of the skull base and craniofacial skeleton in certain congenital anomalies and the post-mortem evaluation of the foetal skeleton potentially obviating the need for necropsy.

ADVANCES IN KNOWLEDGE

Foetal black bone MRI can be performed using susceptibility weighted imaging and allows better demonstration of the mineralized skeleton compared with standard sequences.

Evaluation of four different optimized magnetic-resonance-imaging sequences for visualization of dental and maxillo-mandibular structures at 3 T

OBJECTIVES

The purpose of this study was to evaluate four in-house optimized, non-contrast enhanced sequences for MRI-investigation of maxillo-mandibular and dental structures by use of 3 T.

METHODS

12 volunteers with different dental status were examined by using a 3 T MRI with a 20-channel standard head-and-neck coil. All images performed were evaluated by using 3D-techniques, with different slice-thicknesses, in 3D T1- and T2-weighted sequences, as well as by using new techniques of image depictions. In addition phantom measurements were performed to estimate the extent of image artefacts caused by retainers and metal implants.

RESULTS

Mean age of the participants was 33 years (range, 25.5-62.75 years), and the sex ratio was 5 females to 7 males. We identified different techniques to improve osseous and dental structures, despite problems caused by dental implants, tooth crowns or braces.

CONCLUSION

The sequences evaluated offered excellent visualization in 2D and 3D of osseous and dental structures. Anatomical, osseous and dental structures were described at their ROI, in relation to patients with dental and head and neck pathologies. The ability to detect and distinguish pathological processes as soon as possible in 3D with excellent image quality avoiding ionizing radiation remains a challenging domain.

"Black Bone" MRI: a potential non-ionizing method for three-dimensional cephalometric analysis--a preliminary feasibility study

OBJECTIVES

CT offers a three-dimensional solution to the inaccuracies associated with lateral cephalogram-based cephalometric analysis. However, it is associated with significant concerns regarding ionizing radiation exposure. MRI offers a non-ionizing alternative, but this has been less well investigated. We present a novel gradient echo MRI sequence ("Black Bone") and highlight the potential of this sequence in cephalometric analysis.

METHODS

After regional ethics approval, "Black Bone" imaging was obtained in eight patients in whom lateral cephalograms were available. "Black Bone", T1 and T2 weighted spin echo imaging were obtained in the mid-sagittal plane, and measurements were compared with those obtained on the lateral cephalogram using both the Advantage Windows Workstation (GE Medical Systems, Buckinghamshire, UK) and the Dolphin(®) cephalometric software (v. 11.5.04.23, Premium; Dolphin Imaging, Chatsworth, CA) by one assessor. Further assessment was made by scoring the ease of landmark identification on a ten-point scale.

RESULTS

"Black Bone" imaging surpassed T1 and T2 weighted imaging in terms of cephalometric landmark identification. A number of mid-sagittal cephalometric landmarks could not be clearly identified on T2 weighted imaging, making analysis impossible. Measurements on "Black Bone" demonstrated the smallest discrepancy when compared with those obtained on the lateral cephalogram. The discrepancy seen between measurements completed on mid-sagittal MRI and the lateral cephalogram was compounded by inherent inaccuracies of the lateral cephalogram. The overall mean discrepancy between distance measurements on "Black Bone" imaging and those on the lateral cephalogram was 1-2 mm.

CONCLUSIONS

Overall, "Black Bone" MRI offered an improved method of cephalometric landmark identification over routine MRI sequences, and provides a potential non-ionizing alternative to CT for three-dimensional cephalometrics.