High-resolution microscopy coil MR-Eye

3T high-resolution magnetic resonance imaging, conventional ultrasonography and ultrasound biomicroscopy of the normal canine eye

Background

Advances in MRI coil technology and increased availability of high-field MRI in veterinary medicine enable the acquisition of images of increasingly high spatial resolution while preserving signal-to-noise ratio.The purpose of the present study was to compare 3T high-resolution magnetic resonance imaging (HR-MRI) with ultrasound (US) and ultrasound biomicroscopy (UBM) in the normal canine eye, to assess its potential to depict normal ocular anatomy.

Results

HR-MRI was compared with US and UBM in 10 eyes from 10 healthy beagle dogs. Ocular structures (cornea, anterior chamber, iridocorneal angle, iris, lens, ciliary body, choroid, vitreous body, posterior wall of the eye, optic nerve and optic nerve sheath, extraocular muscles) were assessed subjectively and central corneal thickness (CCT), anterior chamber depth (ACD), aqueous depth (AQD), anteroposterior, mediolateral and dorsoventral lens diameter (APLD, MLLD, DVLD), anteroposterior diameter of the globe including and excluding the scleroretinal rim (APDSRR, APD), vitreous chamber depth (VCD) and optic nerve sheath diameter (ONSD) were measured in HR-MRI and in US. Optic nerve diameter (OND) was measured in HR-MRI. HR-MRI and UBM appearance of the anterior segment were subjectively compared. Detailed reference high-resolution MRI images of normal eyes of Beagle dogs are provided.

Conclusions

HR-MRI allowed assessment of all structures identified with US and UBM. The MRI examinations were performed under general anesthesia with the addition of a neuromuscular blocking agent, while US and UBM examinations were performed in conscious animals. Visibility of the entire ocular wall, the lens, the structures caudal to the ciliary body and the optic nerve and its sheath was superior with HR-MRI. HR-MRI allowed the distinction of retina, choroid and sclera, and the delineation of structures not previously identified in canine eyes with MRI, including Tenon’s capsule and the sub-Tenon’s space.Plane selection was more accurate with HR-MRI compared to US. In general, the range of measurements was narrower for MRI than for US. CCT, AQD, APLD, MLLD, APD, APDSRR and ONSD differed significantly between HR-MRI and US, respectively (p = 0.005-0.027).Micro-MRI may be useful for the assessment of ocular pathologies in the future.

Role of Structural, Metabolic, and Functional MRI in Monitoring Visual System Impairment and Recovery

The visual system, consisting of the eyes and the visual pathways of the brain, receives and interprets light from the environment so that we can perceive the world around us. A wide variety of disorders can affect human vision, ranging from ocular to neurologic to systemic in nature. While other noninvasive imaging techniques such as optical coherence tomography and ultrasound can image particular sections of the visual system, magnetic resonance imaging (MRI) offers high resolution without depth limitations. MRI also gives superior soft-tissue contrast throughout the entire pathway compared to computed tomography. By leveraging different imaging sequences, MRI is uniquely capable of unveiling the intricate processes of ocular anatomy, tissue physiology, and neurological function in the human visual system from the microscopic to macroscopic levels. In this review we discuss how structural, metabolic, and functional MRI can be used in the clinical assessment of normal and pathologic states in the anatomic structures of the visual system, including the eyes, optic nerves, optic chiasm, optic tracts, visual brain nuclei, optic radiations, and visual cortical areas. We detail a selection of recent clinical applications of MRI at each position along the visual pathways, including the evaluation of pathology, plasticity, and the potential for restoration, as well as its limitations and key areas of ongoing exploration. Our discussion of the current and future developments in MR ocular and neuroimaging highlights its potential impact on our ability to understand visual function in new detail and to improve our protection and treatment of anatomic structures that are integral to this fundamental sensory system. LEVEL OF EVIDENCE 3:   TECHNICAL EFFICACY STAGE 3:  .

MR-Eye: High-Resolution Microscopy Coil MRI for the Assessment of the Orbit and Periorbital Structures, Part 2: Clinical Applications

In the first part of this 2-part series, we described how to implement microscopy coil MR imaging of the orbits. Beyond being a useful anatomic educational tool, microscopy coil MR imaging has valuable applications in clinical practice. By depicting deep tissue tumor extension, which cannot be evaluated clinically, ophthalmic surgeons can minimize the surgical field, preserve normal anatomy when possible, and maximize the accuracy of resection margins. Here we demonstrate common and uncommon pathologies that may be encountered in orbital microscopy coil MR imaging practice and discuss the imaging appearance, the underlying pathologic processes, and the clinical relevance of the microscopy coil MR imaging findings.

Ophthalmic Magnetic Resonance Imaging: Where Are We (Heading To)?

Magnetic resonance imaging of the eye and orbit (MReye) is a cross-domain research field, combining (bio)physics, (bio)engineering, physiology, data sciences and ophthalmology. A growing number of reports document technical innovations of MReye and promote their application in preclinical research and clinical science. Realizing the progress and promises, this review outlines current trends in MReye. Examples of MReye strategies and their clinical relevance are demonstrated. Frontier applications in ocular oncology, refractive surgery, ocular muscle disorders and orbital inflammation are presented and their implications for explorations into ophthalmic diseases are provided. Substantial progress in anatomically detailed, high-spatial resolution MReye of the eye, orbit and optic nerve is demonstrated. Recent developments in MReye of ocular tumors are explored, and its value for personalized eye models derived from machine learning in the treatment planning of uveal melanoma and evaluation of retinoblastoma is highlighted. The potential of MReye for monitoring drug distribution and for improving treatment management and the assessment of individual responses is discussed. To open a window into the eye and into (patho)physiological processes that in the past have been largely inaccessible, advances in MReye at ultrahigh magnetic field strengths are discussed. A concluding section ventures a glance beyond the horizon and explores future directions of MReye across multiple scales, including in vivo electrolyte mapping of sodium and other nuclei. This review underscores the need for the (bio)medical imaging and ophthalmic communities to expand efforts to find solutions to the remaining unsolved problems and technical obstacles of MReye, with the objective to transfer methodological advancements driven by MR physics into genuine clinical value.

The value of preoperative high-resolution MRI with microscopy coil for facial nonmelanoma skin cancers

BACKGROUND

The extent and depth of facial nonmelanoma skin cancers and the involvement of adjacent structures are critical features for surgical planning, but they are difficult to assess clinically. High-resolution MRI (HR-MRI) with microscopy coil may facilitate detailed evaluation of skin lesions. The authors performed this prospective study to determine the value of high-resolution microscopy coil MRI in the preoperative evaluation of nonmelanoma skin cancer.

MATERIALS AND METHODS

Between October 2018 and August 2019, 16 lesions from fifteen consecutive patients with facial nonmelanoma skin cancer were evaluated using high-resolution microscopy coil MRI about tumor extent, depth, margins, characteristic, and their spatial relationship with adjacent structures. The preoperative HR-MRI results were compared with the intraoperative findings and with the histopathology, with special note to the depth of invasion.

RESULTS

Among the 16 lesions, HR-MRI imaging was found to provide accurate evaluation of tumor extent, depth, and margins and determine whether there was involvement of adjacent structures. The tumor depth measured on HR-MRI showed good correlation with histopathologic results (CCC: 0.973), and Bland-Altman analysis finding no significant bias existed between the two measurements. All lesions except one were completely resected with primary excision. Only one lesion required further excision. During follow-up for 3-15 months, no tumor recurrence was observed in any case.

CONCLUSIONS

HR-MRI is an accurate, noninvasive imaging technique that can be used as preoperative evaluation tool for facial nonmelanoma skin cancer. It can accurate predict tumor depth, margins, and involvement of structure. The valuable information it provided facilitates surgeons optimize surgical planning.

MR-Eye: High-Resolution Microscopy Coil MRI for the Assessment of the Orbit and Periorbital Structures, Part 1: Technique and Anatomy

Microscopy coil MR imaging of the orbits has been described previously as a technique for anatomic depiction. In the first part of this 2-part series, the improvement in spatial resolution that the technique offers compared with conventional MR imaging of the orbits is demonstrated. We provide a guide to implementing the technique, sharing pearls and pitfalls gleaned from our own practice to make implementation of microscopy coil MR imaging at your own center easy. As a quick reference guide to the small-scale structures encountered when reading the studies, a short anatomy section is included, which doubles as a showcase for the high-quality imaging that can be obtained. In the second part, our experience of microscopy coil MR imaging in day-to-day clinical practice takes it far beyond being a useful anatomic educational tool. Through a series of interesting cases, we highlight the added benefit of microscopy coil MR imaging compared with standard orbital MR imaging.

High-Resolution Microscopy-Coil MR Imaging of Skin Tumors: Techniques and Novel Clinical Applications

High-resolution magnetic resonance (MR) imaging performed with a microscopy coil is a robust radiologic tool for the evaluation of skin lesions. Microscopy-coil MR imaging uses a small surface coil and a 1.5-T or higher MR imaging system. Simple T1- and T2-weighted imaging protocols can be implemented to yield high-quality, high-spatial-resolution images that provide an excellent depiction of dermal anatomy. The primary application of microscopy-coil MR imaging is to delineate the deep margins of skin tumors, thereby providing a preoperative road map for dermatologic surgeons. This information is particularly useful for surgeons who perform Mohs micrographic surgery and in cases of nasofacial neoplasms, where the underlying anatomy is complex. Basal cell carcinoma is the most common nonmelanocytic skin tumor and has a predilection to manifest on the face, where it can be challenging to achieve complete surgical excision while preserving the cosmetic dignity of the patient. Microscopy-coil MR imaging provides dermatologic surgeons with valuable preoperative anatomic information that is not available at conventional clinical examination.

Lid wiper epitheliopathy

Some recent research has resulted in a hypothesis that there is a common 'lid wiper' region that is apposite to the ocular surface or anterior lens surface (where contact lenses are worn), responsible for spreading tears during blinking. In the upper eyelid, it extends about 0.6 mm from the crest of the sharp posterior (inner) lid border (i.e. the mucocutaneous junction, or line of Marx) to the subtarsal fold superiorly and from the medial upper punctum to the lateral canthus horizontally. Histologically, it is seen as an epithelial elevation comprising of stratified epithelium with a transitional conjunctival structure of (moving posteriorly) squamous cells then cuboidal cells, with some parakeratinised cells and goblet cells. Lid wiper epitheliopathy (LWE) denotes staining of the lid wiper observed after instillation of dyes such as fluorescein, rose bengal or lissamine green. There have been some reports of higher rates of LWE in dry eye patients and contact lens wearers, but others have failed to find such associations. The primary cause of LWE is thought to be increased friction between the lid wiper and ocular or anterior contact lens surface due to inadequate lubrication, which could be caused by dry eye and may be exacerbated by factors such as abnormal blinking patterns, poor contact lens surface lubricity and adverse environmental influences. Recent evidence suggests that LWE is associated with sub-clinical inflammation. LWE has the potential to provide the missing mechanistic link between clinical observation and symptoms associated with dry eye and contact lens wear. Clinical and fundamental research into LWE is still in its infancy and in many instances equivocal; however, it is an idea that provides a potentially important new avenue for further investigation of anterior eye discomfort associated with ocular dryness and contact lens wear.

Uveal melanoma: evaluation of extrascleral extension using thin-section MR of the eye with surface coils

PURPOSE

This study was done to evaluate the role of high-resolution magnetic resonance (MR) imaging with special surface coils in selecting the correct therapeutic approach (eye enucleation or follow-up) in patients with suspected extrascleral extension of uveal melanoma.

MATERIALS AND METHODS

This prospective study involved 12 patients with suspected extrascleral extension of uveal melanoma on orbital ultrasonography. All patients were studied with thin-section MR imaging of the eye using surface coils.

RESULTS

High-resolution MR imaging of the eye excluded extrascleral extension of disease in 8/12 patients: in 4/8 cases it revealed vascular ectasia and in the other 4/8 cases the linear hypointensity of the sclera was unbroken. Seven of these eight patients were followed up by ultrasound, which showed stability of melanoma for at least 2 years, while the last patient underwent enucleation, and the histological examination confirmed the MR diagnosis. In 4/12 patients, high-resolution MR suggested a diagnosis of extrascleral extension of melanoma, which was confirmed at histological examination after enucleation.

CONCLUSION

High-resolution MR imaging of the eye with surface coils allowed us to evaluate extrascleral extension of uveal melanoma and choose the correct therapeutic approach, avoiding unnecessary enucleation in 7/12 patients.

Experimental differentiation of intraocular masses using ultrahigh-field magnetic resonance imaging--a case series

PURPOSE

The case reports presented here were compiled to demonstrate the potential for improved diagnosis and monitoring of disease progress of intraocular lesions using ultrahigh-field magnetic resonance microscopy (MRM) at 7.1 Tesla.

METHODS

High-resolution ex vivo ocular magnetic resonance (MR) images were acquired on an ultrahigh-field MR system (7.1 Tesla, ClinScan, Bruker BioScan, Germany) using a 2-channel coil with 4 coil elements and T2-weighted turbo spin echo (TSE) sequences of human eyes enucleated because of different intraocular lesions. Imaging parameters were: 40×40 mm field of view, 512×512 matrix, and 700 µm slice thickness. The results were correlated with in vivo ultrasound and histology of the enucleated eyes.

RESULTS

Imaging was performed in enucleated eyes with choroidal melanoma, malignant melanoma of iris and ciliary body with scleral perforation, ciliary body melanoma, intraocular metastasis of esophageal cancer, subretinal bleeding in the presence of perforated corneal ulcer, hemorrhagic choroidal detachment, and premature retinopathy with phthisis and ossification of bulbar structures. MR imaging allowed differentiation between solid and cystic tumor components. In case of hemorrhage, fluid-fluid levels were identified. Melanin and calcifications caused significant hypointensity. Microstructural features of eye lesions identified by MRM were confirmed by histology.

CONCLUSION

This study demonstrates the potential of MRM for the visualization and differential diagnosis of intraocular lesions. At present, the narrow bore of the magnet still limits the use of this technology in humans in vivo. Further advances in ultrahigh-field MR imaging will permit visualization of tumor extent and evaluation of nonclassified intraocular structures in the near future.

High-resolution MRI of uveal melanoma using a microcoil phased array at 7 T

High-field MRI is a promising technique for the characterisation of ocular tumours, both in vivo and after enucleation. For in vivo imaging at 7 T, a dedicated three-element microcoil array was constructed as a high-sensitivity receive-only device. Using a dedicated blink/fixation protocol, high-resolution in vivo images could be acquired within 3 min in volunteers and patients with no requirement for post-acquisition image registration. Quantitative measures of axial length, aqueous depth and lens thickness in a healthy volunteer were found to agree well with standard ocular biometric techniques. In a patient with uveal melanoma, in vivo MRI gave excellent tumour/aqueous body contrast. Ex vivo imaging of the enucleated eye showed significant heterogeneity within the tumour.

Accuracy of preoperative MRI with microscopy coil in evaluation of primary tumor thickness of malignant melanoma of the skin with histopathologic correlation

OBJECTIVE

The purpose of this study was to evaluate the accuracy of a preoperative MRI with microscopy coils in determining the primary tumor thickness of malignant melanoma with histopathologic correlation.

MATERIALS AND METHODS

Eleven patients with histopathologically confirmed malignant melanoma were included in this study. MR images of the tumors were obtained with a 47-mm microscopy coil on 1.5T MR scanners and were evaluated by two radiologists, who assessed the thickness of the primary tumor on T2-weighted images (T2WI) and gadolinium-enhanced T1-weighted images with fat suppression (Gd-T1WI) and compared the results with the histopathologic findings as the reference standard. Correlations between tumor thickness on MRI and histopathologic examination were assessed using concordance correlation coefficients (CCCs). Inter- and intraobserver variabilities of tumor measurements were also assessed by intraclass correlation coefficient (ICC).

RESULTS

Among the 11 cases included in the study, 10 cases from the same number of patients were managed with surgical excision and one case was confirmed with punch biopsy. The primary tumor thickness measured on T2WI showed better correlation with histopathologic results, as compared with measurements taken on Gd-T1WI: the CCC of measurements on T2WI ranged from 0.64 to 0.78, indicating a substantial agreement, whereas the CCC of measurements on Gd-T1WI ranged from 0.50 to 0.61, indicating a moderate to substantial agreement. Inter- and intraobserver agreements of readers 1 and 2 were excellent for both T2WI and Gd-T1WI, with ICC ranging from 0.86 to 0.99.

CONCLUSION

MR imaging with microscopy coils may be an accurate technique in the preoperative assessment of tumor thickness in malignant melanoma, especially on T2-weighted images.

Dynamic imaging of paralytic eyelid disorders

PURPOSE

Eyelid dysmotility may result from trauma, tumors, inflammation, infection, and a variety of other conditions. In these cases, a mechanical effect is disrupting a normal neuromuscular apparatus. Dysmotility can also be caused by paralytic eyelid disorders; included in this broad category are neurologic and myogenic disorders of eyelid opening and/or closure. Secondary effects include spastic eyelid closure and synkinesis syndromes. These conditions, by definition, are disorders of movement, and can only be studied adequately using dynamic imaging techniques.

METHODS

A comprehensive literature search was performed on PubMed. Ninety abstracts were reviewed.

RESULTS

Dynamic eyelid imaging has evolved dramatically over the past two decades, at least partially due to the rise of inexpensive digital technology. Magnetic search coil imaging, high- and low-speed videography, electromyography, and high-resolution microscopy coil magnetic resonance imaging each has its advantages and disadvantages, an understanding of which will guide appropriate selection of technology in any given clinical situation.

CONCLUSIONS

Dynamic eyelid imaging is useful to study dysmotility. The optimal technique depends upon the clinical setting and the physiologic or pathologic topic of interest. To our knowledge, a report of this type has not been previously summarized.

MR imaging of papilledema and visual pathways: effects of increased intracranial pressure and pathophysiologic mechanisms

Papilledema, defined as swelling of the optic disc, frequently occurs in the setting of increased ICP and in a variety of medical conditions, including pseudotumor cerebri, sinus thrombosis, intracerebral hemorrhage, frontal lobe neoplasms, and Chiari malformation. Noninvasive imaging of the ON is possible by using MR imaging, with a variety of findings occurring in the setting of papilledema, including flattening of the posterior sclera, protrusion of the optic disc, widening of the ONS, and tortuosity of the ON. Early recognition of papilledema and elevated ICP is of paramount importance for ensuring restoration of vision. Newer advanced MR imaging techniques such as fMRI and DTI may prove useful in the future to assess the potential effects of papilledema on retinal and visual pathway integrity.

A 20-channel coil for improved magnetic resonance imaging of the optic nerve

The purpose of this thesis is to design and construct a radio‐frequency coil for imaging the optic nerve on a 3 Tesla magnetic resonance imaging scanner. The goal of the work is to increase signal‐to‐noise ratio from the orbits to the optic chiasm, compared to the current coil designs used for imaging the optic nerve. The coil utilizes a mask fiberglass former, with the coils designed to obtain the most signal‐to‐noise ratio at the optic nerve. The design uses a 20‐channel radio‐frequency coil array, with coil placement along the optic nerve. The signal‐to‐noise ratio achieved was compared to the clinically available 12‐channel head coil. The improved signal‐to‐noise ratio allowed for higher resolution, diffusion tensor imaging, and parallel imaging superior to the current standard. Patient images showed that the plaques evidenced in the images correspond well to patient histories of bilateral and unilateral disease of the optic nerves. This optic nerve coil has shown improved patient care after increasing the diagnostic power of the magnetic resonance imaging scanner. © 2011 Wiley Periodicals, Inc. Concepts Magn Reson Part B (Magn Reson Engineering) 39B: 26–36, 2011

[Orbita - anatomy, development and deformities]

The development of the structures of the human orbita is very complex, but understanding the development makes it easier to understand normal anatomy and dysplasia. The following article first discusses the embryonic development of the eye structures and then presents the "normal" radiological anatomy using different investigation techniques and the most common deformities.