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Autofluorescence imaging with near-infrared excitation:normalization by reflectance to reduce signal from choroidal fluorophores.

ABSTRACT: We previously developed reduced-illuminance autofluorescence imaging (RAFI) methods involving near-infrared (NIR) excitation to image melanin-based fluorophores and short-wavelength (SW) excitation to image lipofuscin-based flurophores. Here, we propose to normalize NIR-RAFI in order to increase the relative contribution of retinal pigment epithelium (RPE) fluorophores.Retinal imaging was performed with a standard protocol holding system parameters invariant in healthy subjects and in patients. Normalized NIR-RAFI was derived by dividing NIR-RAFI signal by NIR reflectance point-by-point after image registration.Regions of RPE atrophy in Stargardt disease, AMD, retinitis pigmentosa, choroideremia, and Leber congenital amaurosis as defined by low signal on SW-RAFI could correspond to a wide range of signal on NIR-RAFI depending on the contribution from the choroidal component. Retinal pigment epithelium atrophy tended to always correspond to high signal on NIR reflectance. Normalizing NIR-RAFI reduced the choroidal component of the signal in regions of atrophy. Quantitative evaluation of RPE atrophy area showed no significant differences between SW-RAFI and normalized NIR-RAFI.Imaging of RPE atrophy using lipofuscin-based AF imaging has become the gold standard. However, this technique involves bright SW lights that are uncomfortable and may accelerate the rate of disease progression in vulnerable retinas. The NIR-RAFI method developed here is a melanin-based alternative that is not absorbed by opsins and bisretinoid moieties, and is comfortable to view. Further development of this method may result in a nonmydriatic and comfortable imaging method to quantify RPE atrophy extent and its expansion rate.

SUBMITTER: Cideciyan AV

PROVIDER: S-EPMC4455314 | biostudies-literature | 2015 May

REPOSITORIES: biostudies-literature

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Autofluorescence imaging with near-infrared excitation:normalization by reflectance to reduce signal from choroidal fluorophores.

Cideciyan Artur V AV Swider Malgorzata M Jacobson Samuel G SG

Investigative ophthalmology & visual science 20150501 5

<h4>Purpose</h4>We previously developed reduced-illuminance autofluorescence imaging (RAFI) methods involving near-infrared (NIR) excitation to image melanin-based fluorophores and short-wavelength (SW) excitation to image lipofuscin-based flurophores. Here, we propose to normalize NIR-RAFI in order to increase the relative contribution of retinal pigment epithelium (RPE) fluorophores.<h4>Methods</h4>Retinal imaging was performed with a standard protocol holding system parameters invariant in he ...[more]

PMID: 26024124

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Project description:Contrast-free autofluorescence (AF) of the parathyroid glands (PTGs) and thyroid tissue occurs in the near-infrared (NIR) spectrum on excitation by light in the upper range of the visible spectrum or lower NIR spectrum. In vivo, PTGs autofluoresce more brightly than thyroid (by a factor of 2-20 times) and appear as a bright spot against surrounding thyroid, muscle or fat on a processed image which is generated in real-time. NIR-AF of PTGs was first described in 2009 although NIR-AF had previously been used in several other clinical applications. Since then there has been a great amount of interest in the use of NIR-AF in thyroid and parathyroid surgery with over 25 published reports of the utilisation of both self-built and proprietary NIR-AF devices in neck endocrine surgery. All of these reports have confirmed the feasibility of NIR-AF intraoperatively and its ability to detect PTGs, although the reported accuracy varies from 90-100%. Reports of the effect of NIR-AF on relevant clinical endpoints i.e., post-operative hypoparathyroidism in thyroidectomy and persistent disease in parathyroidectomy are however scant. There has been one multicentre clinical trial of NIR-AF in thyroidectomy but this did not report clinical outcomes and two single-centre, non-randomised studies which did report post-operative hypoparathyroidism but with differing results: one showing no benefit in 106 NIR-AF vs. 163 controls and one, a reduction of early hypocalcaemia from 20% to 5% in 93 NIR-AF patients vs. 420 controls. There were only 2 cases of permanent hypoparathyroidism across both studies and therefore no significant observable difference in this key outcome variable. In parathyroidectomy, possible variability of the AF signal due to composition of a PTG adenoma, secondary/tertiary disease and MEN1 as well as depth-penetration preventing detection of sub-surface PTGs would imply that NIR-AF in its current form is not well-placed to improve cure-rates in hyperparathyroidism, which may already be as high as 98%. Thus far, no study has addressed this. Despite the promising results of NIR-AF, the absence of data demonstrating an improvement in outcomes and the cost of its use currently limit its use in routine clinical practice, especially in a publicly funded healthcare system with budgetary constraints. However, it can be utilised in research settings and this should be undertaken within the context of well-designed and conducted randomised, multi-centre, appropriately powered studies, which will assist in establishing its role in neck endocrine surgery.

Dataset Information

Autofluorescence imaging with near-infrared excitation:normalization by reflectance to reduce signal from choroidal fluorophores.

Publications

Autofluorescence imaging with near-infrared excitation:normalization by reflectance to reduce signal from choroidal fluorophores.

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