Automatic assessment of time-resolved OCT images for selective retina therapy

Algorithms for optoacoustically controlled selective retina therapy (SRT)

OBJECTIVES

Selective Retina Therapy (SRT) uses microbubble formation (MBF) to target retinal pigment epithelium (RPE) cells selectively while sparing the neural retina and the choroid. Intra- and inter-individual variations of RPE pigmentation makes frequent radiant exposure adaption necessary. Since selective RPE cell disintegration is ophthalmoscopically non-visible, MBF detection techniques are useful to control adequate radiant exposures. It was the purpose of this study to evaluate optoacoustically based MBF detection algorithms.

METHODS

Fifteen patients suffering from central serous chorioretinopathy and diabetic macula edema were treated with a SRT laser using a wavelength of 527 nm, a pulse duration of 1.7 µs and a pulse energy ramp (15 pulses, 100 Hz repetition rate). An ultrasonic transducer for MBF detection was embedded in a contact lens. RPE damage was verified with fluorescence angiography.

RESULTS

An algorithm to detect MBF as an indicator for RPE cell damage was evaluated. Overall, 4646 irradiations were used for algorithm optimization and testing. The tested algorithms were superior to a baseline model. A sensitivity/specificity pair of 0.96/1 was achieved. The few false algorithmic decisions were caused by unevaluable signals.

CONCLUSIONS

The algorithm can be used for guidance or automatization of microbubble related treatments like SRT or selective laser trabeculoplasty (SLT).

Method for controlled tissue theranostics using a single tunable laser source

Tissue diseases and related disorders need to be first recognized using diagnostic methods and then later treated by therapeutic methods-a joint procedure called theranostics. One of the main challenges in the field of retinal therapies remains in the success of the treatment, typically improving the local metabolism, by sparing the surrounding tissue and with the immediate information of the laser effect. In our study, we present a concept for real-time controlled tissue theranostics on a proof-of-concept study capable of using a single tunable ps laser source (in terms of irradiance, fluence, and repetition rate), done on ex-vivo human retinal pigment epithelium. We have found autofluorescence intensity and lifetime imaging diagnostics very promising for the recognition and quantification of laser effects ranging from selective non-destructive molecular tissue modification to complete tissue ablation. The main novelty of our work presents the developed algorithm for optimized theranostics based on the model function used to quantify laser-induced tissue changes through the diagnostics descriptors, fluorescence lifetime and fluorescence intensity parameters. This approach, together with the operation of the single adaptable laser source, can serve as a new theranostics method in personalized medicine in the future not only limited to treat retinal diseases.

Optical dosimeter for selective retinal therapy based on multi-port fiber-optic interferometry

Selective retinal therapy (SRT) employs a micro-second short-pulse lasers to induce localized destruction of the targeted retinal structures with a pulse duration and power aimed at minimal damage to other healthy retinal cells. SRT has demonstrated a great promise in the treatment of retinal diseases, but pulse energy thresholds for effective SRT procedures should be determined precisely and in real time, as the thresholds could vary with disease status and patients. In this study, we present the use of a multi-port fiber-based interferometer (MFI) for highly sensitive real-time SRT monitoring. We exploit distinct phase differences among the fiber ports in the MFI to quantitatively measure localized fluctuations of complex-valued information during the SRT procedure. We evaluate several metrics that can be computed from the full complex-valued information and demonstrate that the complex contour integration is highly sensitive and most correlative to pulse energies, acoustic outputs, and cell deaths. The validity of our method was demonstrated on excised porcine retinas, with a sensitivity and specificity of 0.92 and 0.88, respectively, as compared with the results from a cell viability assay.

Selective retina therapy monitoring by speckle variance optical coherence tomography for dosimetry control

SIGNIFICANCE

Selective retina therapy (SRT) selectively targets the retinal pigment epithelium (RPE) and reduces negative side effects by avoiding thermal damages of the adjacent photoreceptors, the neural retina, and the choroid. However, the selection of proper laser energy for the SRT is challenging because of ophthalmoscopically invisible lesions in the RPE and different melanin concentrations among patients or even regions within an eye.

AIM

We propose and demonstrate SRT monitoring based on speckle variance optical coherence tomography (svOCT) for dosimetry control.

APPROACH

M-scans, time-resolved sequence of A-scans, of ex vivo bovine retina irradiated by 1.7-μs duration laser pulses were obtained by a swept-source OCT. SvOCT images were calculated as interframe intensity variance of the sequence. Spatial and temporal temperature distributions in the retina were numerically calculated in a 2-D retinal model using COMSOL Multiphysics. Microscopic images of treated spots were obtained before and after removing the upper neural retinal layer to assess the damage in both RPE and neural layers.

RESULTS

SvOCT images show abrupt speckle variance changes when the retina is irradiated by laser pulses. The svOCT intensities averaged in RPE and photoreceptor layers along the axial direction show sharp peaks corresponding to each laser pulse, and the peak values were proportional to the laser pulse energy. The calculated temperatures in the neural retina layer and RPE were linearly fitted to the svOCT peak values, and the temperature of each lesion was estimated based on the fitting. The estimated temperatures matched well with previously reported results.

CONCLUSION

We found a reliable correlation between the svOCT peak values and the degree of retinal lesion formation, which can be used for selecting proper laser energy during SRT.

Towards Automatically Controlled Dosing for Selective Laser Trabeculoplasty

Purpose

Selective laser trabeculoplasty (SLT) is a treatment option for open-angle glaucoma; however, it lacks an instant evidence for successful irradiation. So far ophthalmologists use the visible appearance of permanent champagnelike bubbles (macro bubbles) as an indicator for appropriate pulse energy. We hypothesize that micro bubbles, which start energetically far below the appearance of macro bubbles, already trigger the therapeutic benefit. Here we present two methods to capture the onset of these micro bubbles.

Methods

The trabecular meshwork of freshly enucleated porcine eye globes was irradiated with a series of 15 pulses with a pulse duration of 1.7 μs and with increasing energy at a repetition rate of 100 Hz per each spot of 200 μm in diameter. An optical and an optoacoustic method have been developed and appropriate algorithms investigated towards the real-time detection of the onset of micro bubbles.

Results

Both observation methods are capable of detecting micro bubble nucleation. Threshold radiant exposures were found at 310 ± 137 mJ/cm². By combination of both methods a sensitivity and specificity of 0.96 was reached.

Conclusions

In case that the therapeutically demanded pressure reduction is already achieved with these micro bubbles, which needs to be proven clinically, then the methods presented here can be used in an automatic feedback loop controlling the laser irradiation. This will unburden the clinicians from any dosing during SLT.

Translational Relevance

Automatic real-time pulse energy dosing based on the formation of micro bubbles in SLT significantly improves and facilitates the treatment for the physician.

Selective retina therapy: toward an optically controlled automatic dosing

Selective retina therapy (SRT) targets the retinal pigment epithelium (RPE) with pulsed laser irradiation by inducing microbubble formation (MBF) at the intracellular melanin granula, which leads to selective cell disruption. The following wound healing process rejuvenates the chorio-retinal junction. Pulse energy thresholds for selective RPE effects vary intra- and interindividually. We present the evaluation of an algorithm that processes backscattered treatment light to detect MBF as an indicator of RPE cell damage since these RPE lesions are invisible during treatment. Eleven patients with central serous chorioretinopathy and four with diabetic macula edema were treated with a SRT system, which uses a wavelength of 527 nm, a repetition rate of 100 Hz, and a pulse duration of 1.7 μs. Fifteen laser pulses with stepwise increasing pulse energy were applied per treatment spot. Overall, 4626 pulses were used for algorithm parameter optimization and testing. Sensitivity and specificity were the metrics maximized through an automatic optimization process. Data were verified by fluorescein angiography. A sensitivity of 1 and a specificity of 0.93 were achieved. The method introduced in this paper can be used for guidance or automatization of microbubble-related treatments like SRT or selective laser trabeculoplasty.

Motion-invariant SRT treatment detection from direct M-scan OCT imaging

PURPOSE

Selective retina therapy (SRT) is a laser treatment targeting specific posterior retinal layers. It is focused on inducing damage to the retinal pigment epithelium (RPE), while sparing other retinal tissue compared to traditional photocoagulation. However, the targeted RPE layer is invisible with most imaging modalities and induced SRT lesions cannot be monitored. In this work, imaging scans acquired from an experimental setup that couples the SRT laser beam with an optical coherence tomography (OCT) beam are analyzed in order to evaluate the treatment as they occur.

METHODS

We isolated a small part of the time-resolved scan corresponding to the end of the treatment, for which we have microscopic evidence of the SRT outcome. We then use a convolutional neural network to correspond each scan to the treatment result. We explore which aspects of the scan convey more valuable information for a robust therapy evaluation. By only using this adequately small part, we can achieve an online estimation, while being resilient to eye movement.

RESULTS

The available dataset consists of time- resolved OCT scans of 98 ex vivo porcine eyes, treated with different energy levels. The proposed method yields high performance in the task of predicting whether the applied energy was adequate for SRT treatment, by focusing on the immediate OCT signal acquired during treatment time.

CONCLUSIONS

We propose a strategy toward online noninvasive SRT treatment assessment, able to provide a satisfying evaluation of a treatment status, that therefore could be used for the planning of the treatment continuation.