High resolution MR eye protocol optimization: Comparison between 3D-CISS, 3D-PSIF and 3D-VIBE sequences

MRI and FUNDUS image fusion for improved ocular biometry in Ocular Proton Therapy

INTRODUCTION

Ocular biometry in Ocular Proton Therapy (OPT) currently relies on a generic geometrical eye model built by referencing surgically implanted markers. An alternative approach based on image fusion of volumetric Magnetic Resonance Imaging (MRI) and panoramic fundus photography was investigated.

MATERIALS AND METHODS

Eighteen non-consecutive uveal melanoma (UM) patients, who consented for an MRI and had their tumour base visible on panoramic fundus photography, were included in this comparative analysis. Through generating digitally-reconstructed projections from MRI images using the Lambert azimuthal equal-area projection, 2D-3D image fusion between fundus photography and an eye model delineated on MRI scans was achieved and allowed for a novel definition of the target base (MRI + F_CTV). MRI + F_CTV was compared with MRI-only delineation (MRI_GTV) and the conventional (EyePlan) target definition (EP_CTV).

RESULTS

The combined use of fundus photography and MRI to define tumour volumes reduced the average discrepancies by almost 65% with respect to the MRI only tumour definitions when comparing with the conventionally planned EP_CTV. With the proposed method, shallow sub-retinal tumour infiltration, otherwise invisible on MRI, can be included in the target volume definition. Moreover, a novel definition of the fovea location improves the accuracy and personalisation of the 3D eye model.

CONCLUSION

MRI and fundus image fusion overcomes some of the limitations of ophthalmological MRI for tumour volume definition in OPT. This novel eye tumour modelling method might improve treatment planning personalisation, allowing to better anticipate which patients could benefit from prophylactic treatment protocols for radiation induced maculopathy.

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.

Orbital volume measurements from magnetic resonance images using the techniques of manual planimetry and stereology

Introduction:

Current volume measurement techniques, for the orbit, are time-consuming and involve complex assessments, which prevents their routine clinical use. In this study, we evaluate the applicability and efficacy of stereology and planimetry in orbital volume measurements using magnetic resonance imaging (MRI).

Materials and Methods:

Prospective imaging study using MRI. Sheep craniums and human subjects were evaluated. Water-filling measurements were performed in animal skulls, as the standard validation technique. Planimetry and stereology techniques were used in each dataset. Intraobserver and interobserver reliability testing were applied.

Results:

In stereology customization, 1/6 systematic sampling scheme was determined as optimal with acceptable coefficient of error (3.09%) and low measurement time (1.2 min). In sheep craniums, the mean volume measured by water displacement, planimetry, and stereology was 17.81 ± 0.59 cm³, 18.53 ± 0.24 cm³, and 19.19 ± 0.17 cm³, respectively. Planimetric and stereological methods were highly correlated (r = 0.94; P ≈ 0.001). The mean difference of the orbital volume using planimetry and stereology was 0.316 ± 0.168 cm³. In human subjects, using stereology, the mean orbital volume was found to be 19.62 ± 0.2 cm³ with a CE of 3.91 ± 0.15%.

Conclusions:

The optimized stereological method was found superior to manual planimetry in terms of user effort and time spent. Stereology sampling of 1/6 was successfully applied in human subjects and showed strong correlation with manual planimetry. However, optimized stereological method tended to overestimate the orbital volume by about 1 cc, a considerable limitation to be taken in clinical practice.

Age-related changes in eye morphology and aqueous humor dynamics in DBA/2J mice using contrast-enhanced ocular MRI

PURPOSE

Here, we are testing the hypothesis that dynamic contrast enhanced MRI (DCE-MRI) is a useful approach for non-invasively evaluating age-related changes in aqueous humor outflow and its contribution to elevated intraocular pressure in the DBA/2J model of pigmentary glaucoma.

METHODS

A rodent-specific 7 T MRI was used to assess eye anatomy (anterior chamber (AC) and vitreous body (VB) morphology, eye size, lens size) and aqueous humor dynamics (via intravenous administration of Gd-DTPA and Gd-BOPTA contrast agents) in C57BL/6 and DBA/2J mice at 3 and 9 months of age.

RESULTS

Gd-MRI was used to demonstrate an anterior solute pathway into the mouse AC. Topical latanoprost treatment in C57BL/6J mice reduced Gd-BOPTA accumulation in the AC. Age-related increases in AC area, AC depth and eye size were observed in DBA/2J mice compared to C57BL/6J mice. The rate of Gd-DTPA accumulation and peak Gd-DTPA intensity was lowest in 9-month old DBA/2J mice compared to 3-month old DBA/2J mice and C57BL/6J mice at both ages. Leakage of Gd-DTPA posteriorly into the VB was also observed in 9-month old DBA/2J mice.

CONCLUSIONS

These studies support the idea that age-related changes in aqueous humor outflow contribute to elevated intraocular pressure (IOP) in the DBA/2J model of pigmentary glaucoma. Gd-MRI is a valuable tool for better understanding of mechanisms and dynamics of aqueous humor circulation in normal and glaucomatous mouse eyes or following topical administration of medicines to reduce IOP.

Surface-Coil MRI for Small Peripheral Choroidal Melanoma: Imaging in a Rabbit Eye Model

Introduction

Imaging of small peripheral choroidal melanomas remains challenging in clinical and experimental settings, requiring wide-field ophthalmoscopy modalities. In this study, we applied surface-coil MRI to assess imaging feasibility for small peripherally located choroidal melanoma in a rabbit eye model.

Methods

A female albino rabbit with a body weight of 2.8 kg was immunosuppressed with intramuscular cyclosporine 15 mg/kg daily for 3 days prior to inoculation of 14 million 92.1 line melanoma cells into the peripheral suprachoroidal space of the right eye. The experimental animal continued to receive the same dosage of cyclosporine daily for 26 days postinoculation until the day of sacrifice. On that interval, it underwent surface-coil MRI scanning using various protocols and models subsequently sacrificed to allow histological evaluation. A comparative examination of various MRI sequences for optimal lesion imaging was performed, based on semiquantitative criteria.

Results

Imaging quality and superimposed artifacts varied across different sequences and the optimal tumor delineation from adjacent tissues was achieved in T1-weighted sequences.

Conclusions

MRI of small peripheral choroidal melanomas is feasible in a rabbit model using surface coils, particularly in T1-weighted sequences. Findings may be used as a basis for further development of this technique for experimental and clinical applications.

Automated segmentation of ophthalmological images by an optical based approach for early detection of eye tumor growing

PURPOSE

Iris neoplasm is a non-symptom cancer that causes a gradual loss of sight. The first purpose of this study was to present a novel and automatic method for segmenting the iris tumors and detecting the corresponding areas changing along time. The second aim of this work was to investigate several recently published methods after being applied for the iris tumors segmentation.

METHODS

Our approach consists firstly in segmenting the iris region by using the Vander Lugt correlator based active contour method. Secondly, by treating only the iris region, a K-means clustering model was used to assign the tumorous tissue to one pixel-cluster. This model is quite sensitive to the center initialization and to the choice of the distance measure. To solve these problems, a proportional probability based approach was introduced for the cluster center initialization, and the impact of several distance measure was investigated. The proposed method and the different comparative methods were evaluated on two databases: the Eye Cancer and the Miles Research.

RESULTS

Results reported using several performance metrics reveal that the first step assures the detection of all iris tumors with an accuracy of 100%. Additionally, the proposed method yields better performance compared to the recently published methods.

Medical Physics: Forming and testing solutions to clinical problems

According to the European Federation of Organizations for Medical Physics (EFOMP) policy statement No. 13, "The rapid advance in the use of highly sophisticated equipment and procedures in the medical field increasingly depends on information and communication technology. In spite of the fact that the safety and quality of such technology is vigorously tested before it is placed on the market, it often turns out that the safety and quality is not sufficient when used under hospital working conditions. To improve safety and quality for patient and users, additional safeguards and related monitoring, as well as measures to enhance quality, are required. Furthermore a large number of accidents and incidents happen every year in hospitals and as a consequence a number of patients die or are injured. Medical Physicists are well positioned to contribute towards preventing these kinds of events". The newest developments related to this increasingly important medical speciality were presented during the 8th European Conference of Medical Physics 2014 which was held in Athens, 11-13 September 2014 and hosted by the Hellenic Association of Medical Physicists (HAMP) in collaboration with the EFOMP and are summarized in this issue.