Retina Today - Innovation in Diagnostic Retinal Imaging: Multispectral Imaging (October 2014)

摘要

Multispectral imaging (MSI) technology is used in various applications from airborne mapping to astronomical imaging to extract detailed information from distant views.1 The term refers to imaging systems that use a number of nonoverlapping discrete spectral bands, or slices, to highlight certain features within the field of view. MSI has been used in a variety of medical applications including dentistry, dermatology, and histopathology.2 An emerging and advanced application of MSI is its use in visualizing the entire span of the posterior pole of the eye from the internal limiting membrane (ILM) through to the choroid, highlighting the retinal pigment epithelium (RPE).3 MSI TECHNOLOGY The RHA digital imaging ophthalmoscope (Annidis) combines advanced MSI technology with intuitive software, providing a 45° noninvasive en face view of the retina and choroid for early detection and diagnosis of a variety of ocular pathologies such as age-related macular degeneration (AMD), diabetic retinopathy, and glaucoma. The image output is the result of collecting and combining spectral information that highlights specific anatomic and metabolic signatures to assist in disease detection and management. Examples of these signatures include melanin stacking in geographic atrophy (GA) and hemoglobin oxygenation in choroidal neovascular membranes (CNVM). The instrument utilizes safe, discrete, light emitting diodes (LEDs) across a wavelength range from 520 nm (green) to 940 nm (infrared) to progressively examine the layers of the retina and choroid; the longer wavelengths penetrate deeper into the structures of the eye.4 Automated spatial and spectral filters further combine wavelengths to enhance the system’s flexibility and specificity for better visualization and differential diagnosis, accentuating small details that might not otherwise be visible. Each narrow band spectral slice represents successive images of the fundus as the targeted and deliberately selected LED light sources differentially reflect, scatter, and absorb deeper into the posterior pole, enhancing differential visibility of the retinal and choroidal features. MSI has a role in aiding the clinician with the identification, interpretation, diagnosis, and management of ocular pathology via spectral dissection. The RHA is designed as a platform to support ongoing improvements as medical innovations emerge. LIMITATIONS OF WHITE LIGHT IMAGING Traditional fundus imaging provides a visual representation of a clinical observation with minimal diagnostic value.5 Diagnostic fundus imaging technologies, such as optical coherence tomography (OCT) and MSI, are vital in aiding clinicians in the diagnosis, management, and understanding of retinal and choroidal diseases. Early and subtle ocular pathologies are often difficult to isolate, identify, and interpret, and this is even more evident when pathologies overlap within the retina, as in the case of comorbidity. In addition, macular pigment, rod and cone pigments, the lens, and blood all restrict the ability to see and image deeper retinal structures when white light digital photography is used, ultimately limiting the clinician’s ability to detect, differentiate, and further investigate pathologies as they develop. Figure 1 shows a diagram of the visible and near infrared portions of the spectrum relative to the response of the human eye, which is illustrated by the bell-shaped curve peaking at 555 nm and falling rapidly to either side, versus the spectral range of MSI. Conventional fundus photography uses white light and broad color filters in a limited range from 480 nm to 600 nm to match the sensitivity of the human eye. This restricts the discrimination of the reflected light to the blue, green, and red channels within the curve and provides a replica of what is seen with the human eye. Structures that fall outside of the sensitivity curve cannot be readily observed. WAVELENGTH-STRUCTURE CORRELA