Multispectral retinal image analysis: a novel non-invasive tool for retinal imaging.

PURPOSE: To develop a non-invasive method for quantification of blood and pigment distributions across the posterior pole of the fundus from multispectral images using a computer-generated reflectance model of the fundus. METHODS: A computer model was developed to simulate light interaction with the fundus at different wavelengths. The distribution of macular pigment (MP) and retinal haemoglobins in the fundus was obtained by comparing the model predictions with multispectral image data at each pixel. Fundus images were acquired from 16 healthy subjects from various ethnic backgrounds and parametric maps showing the distribution of MP and of retinal haemoglobins throughout the posterior pole were computed. RESULTS: The relative distributions of MP and retinal haemoglobins in the subjects were successfully derived from multispectral images acquired at wavelengths 507, 525, 552, 585, 596, and 611 nm, providing certain conditions were met and eye movement between exposures was minimal. Recovery of other fundus pigments was not feasible and further development of the imaging technique and refinement of the software are necessary to understand the full potential of multispectral retinal image analysis. CONCLUSION: The distributions of MP and retinal haemoglobins obtained in this preliminary investigation are in good agreement with published data on normal subjects. The ongoing development of the imaging system should allow for absolute parameter values to be computed. A further study will investigate subjects with known pathologies to determine the effectiveness of the method as a screening and diagnostic tool.

Value of orientation training in laparoscopic cholecystectomy.

BACKGROUND: It is well established that disorientation during laparoscopic operations such as cholecystectomy is associated with increased morbidity and mortality. The aim of the present study was to evaluate whether high-performance orientation strategies could be taught to a cohort without relevant experience of laparoscopic cholecystectomy, resulting in improved performance and spatial awareness, thereby reducing the need for operative experience to command this skill. METHODS: Thirty medical students participated in a randomized controlled trial, with half randomized to a tutorial teaching orientation strategies at specific stages of laparoscopic cholecystectomy and half to a control group without any teaching. Attention as represented by gaze was captured using eye tracking as subjects were presented with 12 images of various stages of the operation, with the task of interpreting the orientation of the image. The primary outcome measure was subject performance in orientation. Secondary outcome measures were gaze dwell time on relevant anatomical structures within the images and comparison of individual behaviour using a visual behaviour profiling algorithm. RESULTS: The intervention group was significantly more likely to orientate correctly than the control group (mean 75·6 versus 56·1 per cent; P = 0·019). A difference in visual attention behaviour between the two groups was apparent for the majority of images when examining the output of the visual profiling algorithm, in the form of increased homogeneity of visual behaviour and/or an overall difference in orientation strategy. The mean orientation rate of all surgeons under identical conditions in a previously published study was 78·6 per cent. CONCLUSION: Training novices in orientation strategies improved their performance significantly and it could reach the level of a surgeon with several years of experience in laparoscopic surgery.

Quality control and assurance in functional near infrared spectroscopy (fNIRS) experimentation.

Functional near infrared spectroscopy (fNIRS) is a rapidly developing neuroimaging modality for exploring cortical brain behaviour. Despite recent advances, the quality of fNIRS experimentation may be compromised in several ways: firstly, by altering the optical properties of the tissues encountered in the path of light; secondly, through adulteration of the recovered biological signals (noise) and finally, by modulating neural activity. Currently, there is no systematic way to guide the researcher regarding these factors when planning fNIRS studies. Conclusions extracted from fNIRS data will only be robust if appropriate methodology and analysis in accordance with the research question under investigation are employed. In order to address these issues and facilitate the quality control process, a taxonomy of factors influencing fNIRS data have been established. For each factor, a detailed description is provided and previous solutions are reviewed. Finally, a series of evidence-based recommendations are made with the aim of improving consistency and quality of fNIRS research.

Quantitative analysis of multi-spectral fundus images.

We have developed a new technique for extracting histological parameters from multi-spectral images of the ocular fundus. The new method uses a Monte Carlo simulation of the reflectance of the fundus to model how the spectral reflectance of the tissue varies with differing tissue histology. The model is parameterised by the concentrations of the five main absorbers found in the fundus: retinal haemoglobins, choroidal haemoglobins, choroidal melanin, RPE melanin and macular pigment. These parameters are shown to give rise to distinct variations in the tissue colouration. We use the results of the Monte Carlo simulations to construct an inverse model which maps tissue colouration onto the model parameters. This allows the concentration and distribution of the five main absorbers to be determined from suitable multi-spectral images. We propose the use of "image quotients" to allow this information to be extracted from uncalibrated image data. The filters used to acquire the images are selected to ensure a one-to-one mapping between model parameters and image quotients. To recover five model parameters uniquely, images must be acquired in six distinct spectral bands. Theoretical investigations suggest that retinal haemoglobins and macular pigment can be recovered with RMS errors of less than 10%. We present parametric maps showing the variation of these parameters across the posterior pole of the fundus. The results are in agreement with known tissue histology for normal healthy subjects. We also present an early result which suggests that, with further development, the technique could be used to successfully detect retinal haemorrhages.