Israel in Egypt is an oil on canvas painting by Sir Edward Poynter. In 1868 the painting was depicted in the Illustrated London News in which there are reports of changes made to the composition of the painting after its first exhibition. Visible and infrared imaging techniques have been used to determine whether additions to the initial composition can be identified from underdrawings. The painting measures 137 cm × 317.5 cm and was not able to be relocated for the study, therefore portable imaging equipment was used throughout. A Canon 700D DSLR camera was modified to allow nearinfrared imaging when combined with a set of longpass filters at 720 nm, 850 nm and 950 nm. An Osiris infrared reflectography camera was also used to look further into the infrared with a sensitivity range of 900 nm – 1700 nm. To obtain high-resolution images with the modified DSLR, a 100 mm lens was used from a distance of 6 metres. In both visible and near-infrared, eight images were taken across the surface of the painting and these images were combined into high-resolution visible and near-infrared panoramas. Images from the Osiris infrared camera were processed in Matlab to create a mosaic from the overview image with high-resolution regions of interest. All processed images were registered in Matlab along with the woodcut engraving of the painting shown in the Illustrated London News. An interactive web-browser viewer was created to enable display and comparison of the registered high-resolution images, allowing users to explore and zoom in to specific areas of interest across the four high-resolution images simultaneously. Conservators and art historians can utilise the resulting images combined with the image viewer to analyse the painting and potentially develop a new interpretation of the composition.
In diffuse optical tomography (DOT), overlapping and multidistance measurements are required to reconstruct depth-resolved images of oxy- (HbO2) and deoxy- (HHb) hemoglobin concentration changes occurring in the brain. These can be considered an indirect measure of brain activity, under the assumption of intact neurovascular coupling. Broadband systems also allow changes in the redox state of cytochrome c oxidase (oxCCO) to be measured, which can be an important biomarker when neurovascular coupling is impaired. We used DOT to reconstruct images of Δ[HbO2], Δ[HHb], and Δ[oxCCO] from data acquired with a broadband system. Four healthy volunteers were measured while performing a visual stimulation task (4-Hz inverting checkerboard). The broadband system was configured to allow multidistance and overlapping measurements of the participants’ visual cortex with 32 channels. A multispectral approach was employed to reconstruct changes in concentration of the three chromophores during the visual stimulation. A clear and focused activation was reconstructed in the left occipital cortex of all participants. The difference between the residuals of the three-chromophore model and of the two-chromophore model (recovering only Δ[HbO2] and Δ[HHb]) exhibits a spectrum similar to that of oxCCO. These results form a basis for further studies aimed to further optimize image reconstruction of Δ[oxCCO].
We present a method for acquiring whole-head images of changes in blood volume and oxygenation from the infant brain at cot-side using time-resolved diffuse optical tomography (TR-DOT). At UCL, we have built a portable TR-DOT device, known as MONSTIR II, which is capable of obtaining a whole-head (1024 channels) image sequence in 75 seconds. Datatypes extracted from the temporal point spread functions acquired by the system allow us to determine changes in absorption and reduced scattering coefficients within the interrogated tissue. This information can then be used to define clinically relevant measures, such as oxygen saturation, as well as to reconstruct images of relative changes in tissue chromophore concentration, notably those of oxy- and deoxyhaemoglobin. Additionally, the effective temporal resolution of our system is improved with spatio-temporal regularisation implemented through a Kalman filtering approach, allowing us to image transient haemodynamic changes. By using this filtering technique with intensity and mean time-of-flight datatypes, we have reconstructed images of changes in absorption and reduced scattering coefficients in a dynamic 2D phantom. These results demonstrate that MONSTIR II is capable of resolving slow changes in tissue optical properties within volumes that are comparable to the preterm head. Following this verification study, we are progressing to imaging a 3D dynamic phantom as well as the neonatal brain at cot-side. Our current study involves scanning healthy babies to demonstrate the quality of recordings we are able to achieve in this challenging patient population, with the eventual goal of imaging functional activation and seizures.
The production of accurate and independent images of the changes in concentration of oxyhemoglobin and deoxyhemoglobin by diffuse optical imaging is heavily dependent on which wavelengths of near-infrared light are chosen to interrogate the target tissue. Although wavelengths can be selected by theoretical methods, in practice the accuracy of reconstructed images will be affected by wavelength-specific and system-specific factors such as laser source power and detector sensitivity. We describe the application of a data-driven approach to optimum wavelength selection for the second generation of University College London’s multichannel, time-domain optical tomography system (MONSTIR II). By performing a functional activation experiment using 12 different wavelengths between 690 and 870 nm, we were able to identify the combinations of 2, 3, and 4 wavelengths which most accurately reproduced the results obtained using all 12 wavelengths via an imaging approach. Our results show that the set of 2, 3, and 4 wavelengths which produce the most accurate images of functional activation are [770, 810], [770, 790, 850], and [730, 770, 810, 850] respectively, but also that the system is relatively robust to wavelength selection within certain limits. Although these results are specific to MONSTIR II, the approach we developed can be applied to other multispectral near-infrared spectroscopy and optical imaging systems.
Optical mammography is a functional imaging technique that uses near-infrared light to produce three-dimensional breast images of tissue oxygen saturation and hemoglobin concentration. It has been used to monitor the response to neoadjuvant chemotherapy in breast cancer patients. We present the first results on monitoring tumor response to hormone therapy using optical mammography. We present three case studies from postmenopausal women treated with neoadjuvant hormone therapy for locally advanced breast cancer. The women were scanned before starting treatment, once during treatment, and then before surgery. Changes in physiological and optical properties within the tumor and in the rest of the breast were evaluated. At the time of surgery, two patients partially responded to treatment and one did not respond. The patients that partially responded on ultrasound revealed a corresponding recovery to normal in the hemoglobin concentration images, whereas the nonresponder indicated an increase in hemoglobin concentration in the tumor compared to her pretreatment images. These case studies suggest that optical imaging of the breast during neoadjuvant hormone treatment can provide potentially valuable information, and that physiological changes within the tumor can be seen in response to treatment.
An optical imaging system has been developed which uses measurements of diffusely reflected near-infrared light to
produce maps of changes in blood flow and oxygenation occurring within the cerebral cortex. Optical sources and
detectors are coupled to the head via an array of optical fibers, on a probe held in contact with the scalp, and data is
collected at a rate of 10 Hz. A clinical electroencephalography (EEG) system has been integrated with the optical system
to enable simultaneous observation of electrical and hemodynamic activity in the cortex of neurologically compromised
newborn infants diagnosed with seizures. Studies have made a potentially critically important discovery of previously
unknown transient hemodynamic events in infants treated with anticonvulsant medication. We observed repeated
episodes of small increases in cortical oxyhemoglobin concentration followed by a profound decrease in 3 of 4 infants
studied, each with cerebral injury who presented with neonatal seizures. This was not accompanied by clinical or EEG
seizure activity and was not present in nineteen matched controls. The underlying cause of these changes is currently
unknown. We tentatively suggest that our results may be associated with a phenomenon known as cortical spreading
depolarization, not previously observed in the infant brain.
A method is presented to select the optimal wavelengths for multispectral optical topography, which not only gives good separation between chromophores, absorption, and scattering, but also minimizes the differences between interrogated volumes. This method uses the sum of squared differences to compare photon measurement density functions, which were generated for wavelengths in the near-infrared (NIR) range for a suitable model of tissue optical properties. It is found that including this condition significantly influences the range of optimal wavelengths. However, for the adult human head, the differences between interrogated volumes at NIR wavelengths are very small and image reconstruction is only slightly improved when measurements with overlapping sensitivities are used.
Medical imaging equipment is routinely characterised and tested using tissue equivalent phantoms. Combined x-ray and
optical mammography could provide increased screening specificity over either system alone. The ongoing evaluation of
this approach depends upon the development of phantoms with simultaneously breast tissue equivalent optical and x-ray
properties. Furthermore deformation models used in the registration of optical and x-ray images, which are acquired at
differing levels of breast compression, require validation through phantoms which are also mechanically tissue
equivalent. As well as static imaging, dynamic optical imaging of blood flow whilst breast compression is applied has
been proposed as a method of enhancing screening specificity. The effect of changes in blood flow and volume on
optical tomography still need to be established. A novel phantom material created by freezing and thawing a solution of
polyvinyl alcohol (PVAL) in ethanol to create a solid yet elastically compressible gel is described. These gels have x-ray
attenuation coefficients equivalent to those of breast tissues whilst their optical and mechanical properties are readily
modified. Titanium dioxide is added to the optically non-scattering and colourless gels to obtain the transport scattering
coefficient required. Cancerous tissues are often many times stiffer than healthy. Similar differences in stiffness are
achieved between gels by varying PVAL concentration. The first x-ray and optical images of an anthropomorphically
shaped breast phantom made from this gel are presented. This contains a lesion filled with blood equivalent dye whose
volume changes upon compression of the phantom.
The choice of the regularization parameter has a profound effect on the solution of ill-posed inverse problems such as optical topography. We review 11 different methods for selecting the Tikhonov regularization parameter that have been described previously in the literature. We test them on two trial problems, deblurring and optical topography, and conclude that the L-curve method is the method of choice, though in particularly ill-posed problems, generalized cross-validation may provide an alternative.
Investigators have previously attempted to determine the optimal wavelengths to employ for Near-Infrared
Spectroscopy (NIRS) which yield the best separation between absorption and scatter and the least influence
of noise. Although these are important criteria it is also important that the volume of tissue sampled at each of
the wavelengths is the same. In our study we have generated spatial sensitivity profiles at multiple wavelengths for
a suitable model of tissue optical properties, and studied the spatial sensitivity overlap for different combinations
of wavelengths. It is found that including this condition significantly influences the range of optimal wavelengths.
The quality of phase and amplitude data from two medical optical tomography systems were compared. The two systems are a 32-channel time-domain system developed at University College London (UCL) and a 16-channel frequency-domain system developed at Helsinki University of Technology (HUT). Difference data measured from an inhomogeneous and a homogeneous phantom were compared with a finite-element method (diffusion equation) and images of scattering and absorption were reconstructed based on it. The measurements were performed at measurement times between 1 and 30 s per source. The mean rms errors in the data measured by the HUT system were 3.4% for amplitude and 0.51 deg for phase, while the corresponding values for the UCL data were 6.0% and 0.46 deg, respectively. The reproducibility of the data measured with the two systems was tested with a measurement time of 5 s per source. It was 0.4% in amplitude for the HUT system and 4% for the UCL system, and 0.08 deg in phase for both systems. The image quality of the reconstructions from the data measured with the two systems were compared with several quantitative criteria. In general a higher contrast was observed in the images calculated from the HUT data.
Optical tomography is a medical imaging technique which can provide images of haemodynamic parameters and oxygenation at the bedside. Here, we examine two approaches to optical tomography which are intended to provide information about perinatal brain injury. First, we reconstruct static 3D images showing the increase in blood volume and decrease in oxygenation associated with intra-ventricular haemorrhage. Second, we present the first 3D optical tomography images of the whole head during motor evoked responses and show that the peak of activation can be localised to within 11 mm of the estimated position of the motor cortex.
A method has been devised for generating three-dimensional optical images of the breast using a 32-channel time-resolved system and a liquid-coupled interface. The breast is placed in a hemispherical cup surrounded by sources and detectors, and the remaining space is filled with a fluid with tissue-like optical properties. This approach has three significant benefits. First, cups can accommodate a large range of breast sizes, enabling the entire volume of the breast to be sampled. Second, the coupling of the source and detector optics at the surface is constant and independent of the subject, enabling intensity measurements to be employed in the image reconstruction. Third, the external geometry of the reconstructed volume is known exactly. Images of isolated targets with contrasting absorbing and scattering properties have been acquired, and the performance of the system has been evaluated in terms of the contrast, spatial resolution, and localization accuracy. These parameters were strongly dependent on the location of the targets within the imaged volume. Preliminary images of a healthy human subject are also presented, which reveal subtle heterogeneity, particularly in the distribution of scatter. The ability to detect an absorbing target adjacent to the breast is also demonstrated.
We present a multi-dimensional TCSPC technique that combines multi-detector and multiplexing capability, and records fast and virtually unlimited sequences of time-of-flight distributions. The system consists of four fully parallel TCSPC channels. Each channel records simultaneously in up to eight detection channels. Up to four lasers and 32 source positions can be multiplexed. The total count rate is up to 4 x 107 photons per second. Time-of-flight sequences can be recorded with a resolution of 50 to 100 ms per curve. The system is operated within a single personal computer.
Optical tomography is being developed at UCL as a tool for understanding the mechanisms of haemorrhagic and hypoxic-ischaemic brain injury and assessing the effectiveness of novel neural rescue therapies in the newborn infant. Our 32-channel time-resolved optical imaging system measures photon flight times between multiple pairs of points on the surface of the head, and images sensitive to local variation in tissue absorption and scattering properties are reconstructed using non-linear algorithms. Several studies have been performed on premature infants using custom-built helmets, which hold up to 32 sources and detectors in contact with the head. Simulations have revealed that combining data with reference measurements acquired on a homogeneous object using the same fibre locations can significantly reduce errors in reconstructions due to uncertainty in the location of the sources and detectors. To provide the reference data, a homogeneous phantom based on a balloon filled with a scattering fluid of precisely known optical properties was made and inserted into the helmet immediately following each infant scan. In this paper, we evaluate the effectiveness of this approach by acquiring data on a realistically head-shaped phantom containing a small perturbation, and reconstructing it using the homogeneous head-shaped phantom and the fluid-filled balloon.
Access to the requested content is limited to institutions that have purchased or subscribe to SPIE eBooks.
You are receiving this notice because your organization may not have SPIE eBooks access.*
*Shibboleth/Open Athens users─please
sign in
to access your institution's subscriptions.
To obtain this item, you may purchase the complete book in print or electronic format on
SPIE.org.
INSTITUTIONAL Select your institution to access the SPIE Digital Library.
PERSONAL Sign in with your SPIE account to access your personal subscriptions or to use specific features such as save to my library, sign up for alerts, save searches, etc.