Magnetic resonance imaging and spectroscopy of intraocular tumors

MRI and dual-energy CT fusion anatomic imaging in Ru-106 ophthalmic brachytherapy

PURPOSE

Brachytherapy with Ru-106 is widely used for the treatment of intraocular tumors, and its efficacy depends on the accuracy of radioactive plaque placement. Ru-106 plaques are MRI incompatible and create severe metal artifacts on conventional CT scans. Dual-energy CT scans (DECT) may be used to suppress such artifacts. This study examines the possibility of creating fusion images from MRI scans (preoperatively) and DECT scans (with the plaque in place) as a tool for confirming the anatomic accuracy of plaque placement.

METHODS AND MATERIALS

Six patients with intraocular lesions (5 with choroidal melanoma and 1 with a retinal vasoproliferative lesion) were included. Fusion images of preoperative MRI scans and DECT scans with the plaque in place were created with the Demo version of the ImFusion suite (ImFusion GmbH, Munchen Germany). Clearance margins between the tumor and plaque edge in axial, transverse, and coronal planes as well as the elevation of the posterior plaque edge from the sclera were recorded and associated with the location of the lesion.

RESULTS

Plaque-tumor clearance margins for transverse, sagittal, and coronal planes were higher for anteriorly located lesions (5.13 mm ± 0.11 [5.0-5.2], 5.10 mm ± 0.26 [4.9-5.4], and 5.33 mm ± 0.45 [4.9-5.8] respectively) than for posteriorly located lesions (4.16 mm ± 1.44 [2.5-5.1], 4.13 mm ± 1.42 [2.5-5.1], and 4.2 mm ± 1.21 [2.8-5.0], respectively). The elevation of the posterior plaque edge from the sclera was 0.33 mm ± 0.28 [0-0.5] and 0.63 mm ± 0.60 [0.7-1.2] for posterior and anterior lesions, respectively.

CONCLUSIONS

Fusion images between DECT and MRI scans may be used as a tool to confirm the accuracy of Ru-106 plaque placement in relation with the intraocular tumors in ophthalmic brachytherapy.

Choroidal melanoma

Choroidal melanoma is the most common primary intra-ocular malignant tumor and second most common site of ten malignant melanoma sites in the body. Current diagnosis of choroidal melanoma is based on both the clinical experience of the specialist and modern diagnostic techniques such as indirect ophthalmoscopy, A- and B-ultrasonography scans, fundus fluorescein angiography, and transillumination. Invasive studies such as fine needle aspiration cytology can have significant morbidity and should only be considered if therapeutic intervention is indicated and diagnosis cannot be established by any other means. Several modes of treatment are available for choroidal melanoma. Multiple factors are taken into account when deciding one approach over other approaches, such as visual acuity of the affected eye, visual acuity of the contralateral eye, tumor size, location, ocular structures involved and presence of metastases. A comprehensive review of literature available in books and indexed journals was done. This article discusses in detail epidemiology, diagnosis, current available treatment options, and prognosis and survival of choroidal melanoma.

Nuclear magnetic resonance spectroscopy. Principles and applications in neuroophthalmology

Magnetic resonance spectroscopy is a valuable method for the non-invasive investigation of metabolic processes and can now be combined with conventional magnetic resonance imaging in patients. This article gives a brief introduction into the principles and physiological and clinical applications of in vivo proton magnetic resonance spectroscopy, surveys experiences in healthy volunteers and presents exemplary results in patients suffering from cortical blindness or visual field defects. The causes of visual loss include brain trauma, cerebral ischemia, and brain tumors. In traumatic, ischemic and neoplastic lesions, an important spectral finding is an elevated lactate resonance which has been explained by increased anaerobic glycolysis of ischemic brain tissue and macrophages invading necrotic tissue. In our investigations using a clinical spectroscopy protocol on a 1.5 T MR system, a significant lactate signal was absent in spectra obtained from the visual cortex of normal volunteers, even during photic stimulation with a stroboscope. Other spectral changes in the patients include a decreased N-acetyl-aspartate resonance which indicates a decreased number of viable neurons in the examined brain region.

Management of posterior uveal melanoma

In recent years, there have been a number of advances in the diagnosis and management of patients with malignant melanoma of the posterior uvea (ciliary body and choroid). This review provides a brief update on the current status of diagnostic modalities, such as fluorescein angiography, ultrasonography, computed tomography, magnetic resonance imaging, fine needle aspiration biopsy, and the radioactive phosphorus uptake test. Following that is a more detailed review of the current controversy regarding the natural course of uveal melanomas and the available therapeutic modalities. Current indications, techniques, complications, and results are provided for various forms of management, such as observation, laser photocoagulation, plaque radiotherapy, charged particle radiotherapy, local tumor resection, enucleation, and orbital exenteration.

In vivo phosphorus 31 magnetic resonance spectroscopy of human uveal melanomas and other intraocular tumors

We studied the feasibility of using the surface coil probe technique for the noninvasive in vivo study of ocular tumors by phosphorus 31 magnetic resonance spectroscopy. The characteristic organophosphate metabolites of suspected uveal melanomas before proton beam irradiation were determined qualitatively by phosphorus 31 magnetic resonance spectroscopy in vivo using a three-turn surface coil. Spectra of choroidal hemangioma, osteoma, and metastasis were also obtained in vivo and compared with those of uveal melanomas. Analysis of spectra performed at 1.5 T showed significant peaks of phosphomonoesters, inorganic phosphate, phosphodiesters, phosphocreatine, and adenosine 5'-triphosphates. The unusually high concentration of phosphodiesters may be considered as a marker for uveal melanomas and other choroidal tumors. By analyzing the ratio of phosphocreatine to phosphodiesters spectral area values, we interpreted qualitatively spectra of intraocular tumors to differentiate malignant tumors from benign lesions. Nevertheless, the main limitation of interpreting the spectra was their contamination by signals from surrounding tissues.

Magnetic resonance imaging: an emerging technique for the diagnosis of ocular disorders

With developments in proton and sodium imaging on eyes and ocular lesions, MRI has been rapidly advancing into the field of ophthalmology. Although many intraocular lesions have been T1 and T2 characterized, and MRI may aid in their diagnosis, there remain a few problems with the technique. One is the presence of motion artifacts which sometimes occur with lengthy scanning times. A patient must be imaged on the order of minutes with MRI. In addition ambiguities exist even with the T1 and T2 characterizations, although the specificity surpasses that of CT. Eventually these problems may be solved, but even now proton coupled with sodium imaging and other diagnostic techniques appear promising in the evaluation of ocular disorders.