Quantifying changes in retinal circulation: the generation of parametric images from fluorescein angiograms

Hipwell, John H.; Manivannan, A.; Vieira, Pedro; Sharp, P.; Forrester, John V.

doi:10.1088/0967-3334/19/2/004

Cited by 21 publications

(20 citation statements)

References 21 publications

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“…These local contrast enhancement methods, however, are not appropriate because these methods improve the visibility of local details in images. To eliminate non-uniform illumination from angiogram images, Hipwell et al [18] used a 'flood' image, which is the illumination mask of each digitized angiogram image. This image records the illumination when no negative is present, and it generally consists of a central 'white' (value 255) region which fades towards the periphery of the image due to the reduced light level.…”

Section: Discussionmentioning

confidence: 99%

New Parametric Imaging Method with Fluorescein Angiograms for Detecting Areas of Capillary Nonperfusion

et al. 2014

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ObjectivesFluorescein angiography (FAG) is currently the most useful diagnostic modality for examining retinal circulation, and it is frequently used for the evaluation of patients with diabetic retinopathy, occlusive diseases, such as retinal venous and arterial occlusions, and wet macular degeneration. This paper presents a method for objectively evaluating retinal circulation by quantifying circulation-related parameters.MethodsThis method allows the semiautomatic preprocessing and registering of FAG images. The arterial input function is estimated from the registered set of FAG images using gamma-variate fitting. Then, the parameters can be computed by deconvolution on the basis of truncated singular value decomposition, and they can finally be presented as parametric color images in a combination of three colors, red, green, and blue.ResultsAfter the estimation of arterial input function, the parameters of relative blood flow and mean transit time were computed using deconvolution analysis based on truncated singular value decomposition.ConclusionsThe parametric color image is helpful to interpret the status of retinal blood circulation and provides quantitative data on retina ischemia without interobserver variability. This system easily provides the status of retinal blood circulation both qualitatively and quantitatively. It also helps to standardize FAG interpretation and may contribute to network-based telemedicine systems in the future.

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Section: Discussionmentioning

confidence: 99%

New Parametric Imaging Method with Fluorescein Angiograms for Detecting Areas of Capillary Nonperfusion

et al. 2014

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“…Hipwell and colleagues6 have demonstrated the potential value of a digital SLO in quantifying the state of the retinal circulation. They measured the curves showing fluorescence as a function of time after injection at every point in the image.…”

Section: Quantitative Imagingmentioning

confidence: 99%

“…In general, shorter wavelengths such as argon (488 nm) are useful for fluorescein angiography studies6 15 observing patterns of herpes simplex keratitis16 and leucocyte velocity 717Green (514 nm) has been used for densitometry study 18…”

Section: Multispectral Imagingmentioning

confidence: 99%

Laser imaging of the retina

Sharp

Manivannan

Vieira

et al. 1999

British Journal of Ophthalmology

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The development of the scanning laser ophthalmoscope (SLO), first conceived by Webb et al in 1980 1 heralded the first widespread application of lasers for retinal imaging. A highly collimated beam from a laser is swept over the retina delivering all its energy to a very small spot for a very short time, typically of the order of some tens of nanoseconds. Light reflected from the spot is detected and synchronously decoded to form an image on a monitor.The use of a laser in this way oVers a number of fundamental advantages for retinal imaging: + as the input laser beam occupies only a small part of the pupil most of the pupil is available for light collection permitting non-mydriatic imaging and levels of illumination that are a factor of 200 lower than with the fundus camera + there is no need to employ high intensity flash so rapid imaging can be carried out oVering the potential for serial imaging + since imaging is carried out point by point, data are readily acquired as digital images allowing quantitative measurements and image processing + since the detected light is focused at a single point confocal imaging can be employed to give three dimensional images + the scattered light can be imaged separately from the reflected component, Tyndall imaging, to enhance pathological structures that have a high scattering component + the wavelength of the illuminating light can be selected by choice of laser so oVering the potential for multispectral imaging + changes in polarisation of the reflected light can be used to measure retinal nerve fibre layer (RNFL) thickness. While a number of these factors make imaging simpler there are three major advances that the SLO oVers to retinal imaging-the ability to do quantitative imaging, multispectral imaging, and three dimensional imaging. Quantitative imagingThe SLO is inherently a digital imaging technique; the image is produced by taking a series of samples of the light reflected from the retina as the beam is scanned in a raster fashion whereas with the fundus camera the whole of the retina is imaged simultaneously. However, the advantage of digital acquisition of data is now available with the digital fundus camera, so what advantages does laser imaging offer?One of the hopes of digital imaging is the automated analysis of retinal images both to identify abnormal pathology and to quantify the degree of pathology present.2 The precursor to image analysis is the need to correct for any non-uniformities in the illumination of the retina.3 In theory the SLO provides a uniform illumination of the retina so minimising the need for correction. In practice, however, there is still some non-uniformity in illumination.A second advantage is the ability to select the laser wavelength to improve the contrast of the features under analysis. This will be discussed later, although relatively little work has been done on it.But perhaps the main contribution is the ability of the SLO to image rapidly. Since there is no need to utilise flash, images can be taken rapidly, as one avoids t...

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“…Whilst this is useful, it does not provide insight to the degree and extent to which the vasculature in any given location may be altered. A method was developed by Hipwell et al [23], to analyze the entire image in human fluorescein angiograms. Although the analysis was limited to identifying the time to reach maximal fluorescence, it demonstrated the potential that analysis of the whole image has in assessing retinal vascular disease.…”

Section: Introductionmentioning

confidence: 99%

Quantitative Spatial and Temporal Analysis of Fluorescein Angiography Dynamics in the Eye

et al. 2014

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PurposeWe describe a novel approach to analyze fluorescein angiography to investigate fluorescein flow dynamics in the rat posterior retina as well as identify abnormal areas following laser photocoagulation.MethodsExperiments were undertaken in adult Long Evans rats. Using a rodent retinal camera, videos were acquired at 30 frames per second for 30 seconds following intravenous introduction of sodium fluorescein in a group of control animals (n = 14). Videos were image registered and analyzed using principle components analysis across all pixels in the field. This returns fluorescence intensity profiles from which, the half-rise (time to 50% brightness), half-fall (time for 50% decay) back to an offset (plateau level of fluorescence). We applied this analysis to video fluorescein angiography data collected 30 minutes following laser photocoagulation in a separate group of rats (n = 7).ResultsPixel-by-pixel analysis of video angiography clearly delineates differences in the temporal profiles of arteries, veins and capillaries in the posterior retina. We find no difference in half-rise, half-fall or offset amongst the four quadrants (inferior, nasal, superior, temporal). We also found little difference with eccentricity. By expressing the parameters at each pixel as a function of the number of standard deviation from the average of the entire field, we could clearly identify the spatial extent of the laser injury.ConclusionsThis simple registration and analysis provides a way to monitor the size of vascular injury, to highlight areas of subtle vascular leakage and to quantify vascular dynamics not possible using current fluorescein angiography approaches. This can be applied in both laboratory and clinical settings for in vivo dynamic fluorescent imaging of vasculature.

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Quantifying changes in retinal circulation: the generation of parametric images from fluorescein angiograms

Cited by 21 publications

References 21 publications

New Parametric Imaging Method with Fluorescein Angiograms for Detecting Areas of Capillary Nonperfusion

New Parametric Imaging Method with Fluorescein Angiograms for Detecting Areas of Capillary Nonperfusion

Laser imaging of the retina

Quantitative Spatial and Temporal Analysis of Fluorescein Angiography Dynamics in the Eye

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