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

3D Reconstruction of the Blood Supply in an Elephant's Forefoot Using Fused CT and MRI Sequences

Being the largest still-living terrestrial mammal on earth, an elephant's feet play an important role in its health status. The musculoskeletal structures in the forefoot are well described in the literature, but information about vascularization is limited. The novel aim of this work is to provide anatomical guidance to structures found in the forefoot, focusing on the arterial system. Initially, native CT and MRI sequences were taken of the left forefoot of a deceased 6-year-old female Asian elephant; the foot was then filled with an iodine-containing contrast medium through the a. mediana and the CT scans were repeated in the same position. The images obtained were processed with 3D Slicer software for the 3D reconstruction of the bones and arteries. The results clearly showed the palmar blood supply of the forefoot. A so far undescribed vessel was revealed, stemming from the a. metacarpea, supplying the first digit and the digital cushion. The course of the deep palmar arch's terminal section was also established. This paper provides the first description of the exact disposition of the arteries in the palmar aspect of an elephant's forefoot and may be used in planning surgeries in clinically affected animals.

Imaging of Bone in the Head and Neck Region, is There More Than CT?

Purpose of Review

The objective of this review is to document the advances in non-ionising imaging alternatives to CT for the head and neck.

Recent Findings

The main alternative to CT for imaging bone of the head and neck region is MRI, particularly techniques which incorporate gradient echo imaging (Black Bone technique) and ultra-short or zero-echo time imaging. Since these techniques can provide high resolution isometric voxels, they can be used to provide multi-planar reformats and, following post processing, 3D reconstructed images of the craniofacial skeleton. As expected, the greatest advancements in recent years have been focused on enhanced image processing techniques and attempts to address the difficulties encountered at air-bone interfaces.

Summary

This article will review the imaging techniques and recent advancements which are bringing non-ionising alternatives to CT imaging of the bone of the head and neck region into the realm of routine clinical application.

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.

'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 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.