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A numerical model of Gaussian beam propagation in planar Fabry-Perot (FP) etalons is presented. The model is based on the ABCD transfer matrix method. This method is easy to use and interpret, and readily connects models of lenses, mirrors, fibres and other optics to aid simulating complex multi-component etalon systems. To validate the etalon model, its predictions were verified using a previously validated model based on Fourier optics. To demonstrate its utility, three different etalon systems were simulated. The results suggest the model is valid and versatile and could aid in designing and understanding a range of systems containing planar FP etalons. The method could be extended to model higher order beams, other FP type devices such as plano-concave resonators, and more complex etalon systems such as those involving tilted components.

We present a model that calculates optical fields reflected and transmitted by a Fabry-Perot (FP) etalon composed of interfaces with non-planar surface topography. The model uses the Rayleigh-Rice theory, which predicts the fields reflected and transmitted by a single interface, to account for the non-planar surface topography of each interface. The Rayleigh-Rice theory is evaluated iteratively to account for all round trips that light can take within the FP etalon. The model predictions can then be used to compute Interferometer transfer function (ITF)s, by performing wavelength or angle resolved simulations enabling predictions of the bandwidth, peak transmissivity, and sensitivity of FP etalons. The model was validated against the Pseudospectral time-domain (PSTD) method, which resulted in good agreement. Since the model accuracy is expected to reduce as the Root mean square (RMS) of the topographic map increases, the error in the model’s predictions was studied as a function of topographic map RMS. Finally, application of the model was exemplified by predicting the impact of roughness on ITFs and computing the changes in FP etalon transmissivity as cavity thickness is modulated by an ultrasonic wave.

Fabry-Perot (FP) etalons are used as filters and sensors in a range of optical systems. The reflected and transmitted fields associated with an FP etalon have traditionally been predicted by the Airy function, which assumes a plane wave illumination. FP etalons are, however, often illuminated by non-collimated beams, rendering the Airy function invalid. To address this limitation, we describe the angular Airy function which calculates the reflected and transmitted fields for arbitrary illumination beams, using angular spectrum decomposition. Combined with realistic models of the experimental illumination beams and detection optics, we show that the angular Airy function can accurately predict experimental wavelength resolved intensity measurements. Based on the angular Airy function, we show that the fundamental operating principle of an FP etalon is as an angular-spectral filter. Based on this interpretation we explain the asymmetry, broadening and visibility reduction seen on wavelength resolved intensity measurements from high Q-factor FP etalons illuminated with focused Gaussian beams.

Simulating coherent light propagation through mm or cm scale biological tissues would aid in studying phenomena such as optical memory effects, optical focussing via wavefront shaping, and image formation in techniques such as optical coherence tomography. This is challenging however, because existing simulation methods are either not complete enough to model the underlying deterministic scattering and interference processes accurately, or are too computationally intensive to model large enough volumes of tissue. To address this challenge, we use the “T-matrix” method to simulate coherent light propagation through a discrete particle model of tissue. Using this method, we find that the speckle pattern produced by a plane wave incident on a 100 μm thick tissue-like medium can be simulated in about a tenth of the time needed for a pseudospectral time-domain simulation. Moreover, by varying the plane wave's incident angle, the angular memory effect can be observed and the the angular memory correlation range measured. By demonstrating the method's efficiency and its applicability to studying a coherent phenomenon in a tissue like medium, this work could pave the way to modelling a range of coherent optical phenomena in deep tissue using this technique.

Performing high-resolution photoacoustic (PA) imaging through an endoscope could unlock a range of new biomedical and clinical applications. However, producing sub-mm scale ultrasonic sensors at the distal tip as required to detect PA signals is challenging using traditional piezoelectric technology. In the present study, an alternative approach involving using an all-optical Fabry-Perot (FP) ultrasound sensor positioned at the distal end of a multi-mode fibre (MMF) is investigated. In a prototype benchtop system, it is shown that by using optical wavefront shaping to overcome the scrambling of light, a focussed interrogation laser beam can be delivered through an MMF and scanned to multiple pre-defined locations on a FP sensor to enable the spatially localised detection of ultrasound. This could pave the way to the development of sub-mm MMF based PA endoscopes for surgical guidance and other applications.

Fabry-Perot (FP) etalons, composed of two parallel mirrors, are used widely as optical filters and sensors. In certain applications, however, such as when FP etalons with polymer cavities are used to detect ultrasound, the mirrors may not be perfectly parallel due to manufacturing limitations. As little is known about how the mirrors being non-parallel impacts upon FP etalon performance, it is challenging to optimize the design of such devices. To address this challenge, we developed a model of light propagation in non-parallel FP etalons. The model is valid for arbitrary monochromatic beams and calculates both the reflected and transmitted beams, assuming full-wave description of light. Wavelength resolved transmissivity simulations were computed to predict the effect that non-parallel mirrors have on the sensitivity, spectral bandwidth and peak transmissivity of FP etalons. Theoretical predictions show that the impact of the non-parallel mirrors increases with both mirror reflectivity and incident Gaussian beam waist. Guidelines regarding the maximum angle allowed between FP mirrors whilst maintaining the sensitivity and peak transmissivity of a parallel mirror FP etalon are provided as a function of mirror reflectivity, cavity thickness and Gaussian beam waist. This information, and the model, could be useful for guiding the design of FP etalons suffering a known degree of non-parallelism, for example, to optimize the sensitivity of polymer based FP ultrasound sensors.

The impact of optical absorption in the spacer layer of Fabry-Perot (FP) ultrasound sensors is discussed. It is shown that absorption significantly limits the sensitivity of planoconcave microresonators (PCMRs; FP type sensors with a planoconcave geometry). Using materials of lower absorption or selecting sensor interrogation wavelengths to avoid absorption peaks in existing spacer materials could provide at least an order of magnitude higher sensitivity, paving the way to multi-cm deep-tissue PA imaging applications.

There has been considerable interest in extending photoacoustic imaging techniques to endoscopic devices, which would enable a diverse range of applications, e.g. assessment of coronary artery disease or surgical guidance. However, the difficulty of miniaturising traditional piezoelectric sensors has mostly prevented tomography-mode endoscopic imaging, where an array of sensors is used to reconstruct the full ultrasound field to centimeter-scale depths. In this work we demonstrate how wavefront shaping through multimode fibres onto a Fabry-Perot optical ultrasound sensor can overcome this limitation, producing an endoscopic imaging system with a footprint an order of magnitude smaller than the state of the art.

Deep tissue applications (>1 cm) for photoacoustic imaging are currently limited for traditional Fabry-Perot ultrasound transducers interrogated by tightly focused Gaussian beams due to beam walk-off. We investigate the optical confinement of the beam using plano-concave microresonators with a model based on the ABCD formalism and the use of high-sensitive and high-density multi-element arrays. The results show an improvement in the sensitivity enabling an increase of the penetration depth in tomographic photoacoustic imaging.

We present Jolab: an open source package for performing full-wave simulation of light propagation in optical systems. Jolab enables a very broad range or researchers, engineers and practitioners to simulate light propagation through complex optical systems. Jolab takes a relatively simple script as its input in which the optical system is defined and light is propagated by each optical components sequentially using built-in functions. Jolab scripts are simple and readable and their structure is designed to mimic the design of optical systems making it easy to learn. We will present a range of examples including time-domain simulations and wavefront-shaping experiments.

Fabry-Perot (FP) polymer film sensors are used as ultrasound sensors for Photoacoustic (PA) imaging. Optical models predict that FP sensors should have higher sensitivity than observed experimentally. The models assume FP sensors to be optically flat whereas in practice the polymer film spacer exhibits a degree of surface roughness. To understand the impact of the roughness, an optical model of rough FP sensors was developed. Theoretical results show that roughness can reduce the optical sensitivity by a factor of two. The model will help to guide the design of FP sensors to optimize their sensitivity and, therefore, the imaging depth.

An open source package for performing full-wave simulation of light propagation in optical systems is presented. The package includes pre-defined functions to model specific optical components. Optical systems are modelled simply by combining these functions. We outline its implementation and show examples of possible applications.

The manufacturing process of high sensitivity planar Fabry-Perot (FP) sensors for Photoacoustic (PA) imaging is very challenging and typically results in non-uniformities of the cavity thickness. The non-uniformities leads to an angular tilt between the two mirrors forming the FP sensor. Based on a full wave model, we study the impact of this tilt which reveals a strong dependence between optical sensitivity and degree of tilt. As an example, an angular tilt as small as 0.1 mrad can reduce the sensitivity by 75%. To achieve high sensitivity FP sensors, high mirror reflectivities are required which in turn increases the impact of the non-uniformities in the cavity thickness. Therefore, the optimal design of the sensors is dependent on the manufacturing precision.

Fabry-Perot etalon-based ultrasound detectors are typically interrogated with a focused Gaussian beam in order to achieve a desired acoustic element size. However, tightly focused Gaussian beams lead to beam ‘walk-off’ within the etalon cavity which reduces sensitivity. In previous work, the planar geometry of the Fabry-Perot etalon has been replaced by a curved geometry matched to the interrogation beam geometry, thus preventing walk-off. In this work we instead propose using propagation invariant Bessel beams, thus matching the beam geometry to that of the planar etalon geometry, to reduce beam walk-off and increase sensitivity. Increased sensitivity may extend the imaging depth of Fabry-Perot ultrasound detection systems and may thus enable photoacoustic imaging to access a range of deep tissue imaging applications.

Parylene C (PPXC) is a polymer deposited from the gas phase to form optically clear thin films used in devices including waveguides and sensors. The performance of these devices depends on the visible and near infrared absorption coefficient of PPXC. However, the absorption coefficient is difficult to measure. This is because PPXC films are typically too thin to exhibit detectable absorption in conventional transmittance measurements. To address this challenge, a method involving measuring the transmittance of multiple films immersed together in a liquid filled cuvette was devised. This increased the sensitivity to absorption by increasing the path length in PPXC, while also minimizing reflections and surface losses. Using 200-500 µm thick films, this method was applied to measure the absorption coefficient of PPXC at wavelengths in the range 330-3300 nm. The coefficient was found to vary spectrally by more than two orders of magnitude from 0.025 mm-1 at 1562 nm to 7.7 mm-1 at 3262 nm. These absorption measurements could aid the design of PPXC based sensors and waveguides. The method could be useful for measuring the absorption coefficient of other thin, low-loss materials, particularly those for which it is challenging to obtain thick samples such as other polymers deposited from the gas phase in a similar manner to PPXC.

Highly sensitive broadband ultrasound detectors are needed to expand the capabilities of biomedical ultrasound, photoacoustic imaging and industrial ultrasonic non-destructive testing techniques. Here, a generic optical ultrasound sensing concept based on a novel plano-concave polymer microresonator is described. This achieves strong optical confinement (Q-factors > 105) resulting in very high sensitivity with excellent broadband acoustic frequency response and wide directivity. The concept is highly scalable in terms of bandwidth and sensitivity. To illustrate this, a family of microresonator sensors with broadband acoustic responses up to 40 MHz and noise-equivalent pressures as low as 1.6 mPa per √Hz have been fabricated and comprehensively characterized in terms of their acoustic performance. In addition, their practical application to high-resolution photoacoustic and ultrasound imaging is demonstrated. The favourable acoustic performance and design flexibility of the technology offers new opportunities to advance biomedical and industrial ultrasound-based techniques.

The Fabry-Perot interferometer (FPI) is widely used in photoacoustic imaging (PAI) as an ultrasound (US) sensor due to its high sensitivity to weak US waves. Such high sensitivity is important as it allows for increasing the depth in tissue at which PAI can access, thus strongly influencing its clinical applicability. FPI sensitivity is impacted by many factors including the FPI mirror reflectivity, focussed beam spot size, FPI cavity thickness and aberrations introduced by the optical readout system. Improving FPI sensitivity requires a mathematical model of its optical response which takes all of these factors into account. Previous attempts to construct such a model have been critically limited by unrealistic assumptions. In this work we have developed a general model of FPI optical readout which based upon electromagnetic theory. By making very few assumptions, the model is able to replicate experimental results and allows insight to be gained into the operating principles of the sensor.

Fabry-Pérot (FP) etalons are used as filters and sensors in a range of optical systems. Often FP etalons are illuminated by collimated laser beams, in which case the transmitted and reflected light fields can be calculated analytically using well established models. However, FP etalons are sometimes illuminated by more complex beams such as focussed Gaussian beams, which may also be aberrated. Modelling the response of FP etalons to these beams requires a more sophisticated model. To address this need, we present a model that can describe the response of an FP etalon that is illuminated by an arbitrary beam. The model uses an electromagnetic wave description of light and can therefore compute the amplitude, phase and polarization of the optical field at any position in the system. It can also account for common light delivery and detection components such as lenses, optical fibres and photo-detectors, allowing practical systems to be simulated. The model was validated against wavelength resolved measurements of transmittance and reflectance obtained using a system consisting of an FP etalon illuminated by a focussed Gaussian beam. Experiments with focal spot sizes ranging from 30 µm to 250 µm and FP etalon mirror reflectivities in the range 97.2 % to 99.2 % yielded excellent visual agreement between simulated and experimental data and an average error below 10% for a range of quantitative comparative metrics. We expect the model to be a useful tool for designing, understanding and optimising systems that use FP etalons.

Bioluminescence imaging (BLI) is a non-contact, optical imaging technique based on measurement of emitted light due to an internal source, which is then often directly related to cellular activity. It is widely used in pre-clinical small animal imaging studies to assess the progression of diseases such as cancer, aiding in the development of new treatments and therapies. For many applications, the quantitative assessment of accurate cellular activity and spatial distribution is desirable as it would enable direct monitoring for prognostic evaluation. This requires quantitative spatially-resolved measurements of bioluminescence source strength inside the animal to be obtained from BLI images. This is the goal of bioluminescence tomography (BLT) in which a model of light propagation through tissue is combined with an optimization algorithm to reconstruct a map of the underlying source distribution. As most models consider only the propagation of light from internal sources to the animal skin surface, an additional challenge is accounting for the light propagation from the skin to the optical detector (e.g. camera). Existing approaches typically use a model of the imaging system optics (e.g. ray-tracing, analytical optical models) or approximate corrections derived from calibration measurements. However, these approaches are typically computationally intensive or of limited accuracy. In this work, a new approach is presented in which, rather than directly using BLI images acquired at several wavelengths, the spectral derivative of that data (difference of BLI images at adjacent wavelengths) is used in BLT. As light at similar wavelengths encounters a near-identical system response (path through the optics etc.) this eliminates the need for additional corrections or system models. This approach is applied to BLT with simulated and experimental phantom data and shown that the error in reconstructed source intensity is reduced from 49% to 4%. Qualitatively, the accuracy of source localization is improved in both simulated and experimental data, as compared to reconstruction using the standard approach. The outlined algorithm can widely be adapted to all commercial systems without any further technological modifications.

A simple method for measuring the directivity of an ultrasound receiver is described. The method makes use of a custom-designed laser ultrasound source which generates a large diameter (1 cm) broadband monopolar plane wave with a continuous frequency content extending from to . The plane wave is highly uniform in amplitude (±5% over8 mm) and phase (equivalent to at 80 MHz over ). To measure directivity, the source is rotated around the receiver under test in a compact centimeter-scale setup. To demonstrate the method, it was used to measure the directivity of two broadband small aperture Fabry-Perot ultrasound sensors over an angular range of ±50° at frequencies up to 80 MHz. Measurements were found to be highly repeatable with an estimated typical repeatability4% in the range of 0.5-25 MHz. Due to the broad bandwidth, large size, and adjustable nature of the source, the method is widely applicable and could aid the characterization of receivers used in medical ultrasound, ultrasonic nondestructive testing. and ultrasound metrology.

Measurement of high acoustic pressures is necessary in order to fully characterize clinical high-intensity focused ultrasound (HIFU) fields, and for accurate validation of computational models of ultrasound propagation. However, many existing measurement devices are unable to withstand the extreme pressures generated in these fields, and those that can often exhibit low sensitivity. Here, a planar Fabry-Pérot interferometer with hard dielectric mirrors and spacer was designed, fabricated, and characterized, and its suitability for measurement of nonlinear focused ultrasound fields was investigated. The noise equivalent pressure (NEP) of the scanning system scaled with the adjustable pressure detection range between 49 kPa for pressures up to 8 MPa and 152 kPa for measurements up to 25 MPa, over a 125 MHz measurement bandwidth. Measurements of the frequency response of the sensor showed that it varied by less than 3 dB in the range 1-62 MHz. The effective element size of the sensor was 65 and waveforms were acquired at a rate of 200 Hz. The device was used to measure the acoustic pressure in the field of a 1.1 MHz single-element spherically focused bowl transducer. Measurements of the acoustic field at low pressures compared well with measurements made using a Polyvinylidene difluoride needle hydrophone. At high pressures, the measured peak focal pressures agreed well with the focal pressure modeled using the Khokhlov-Zabolotskaya-Kuznetsov equation. Maximum peak positive pressures of 25 MPa and peak negative pressures of 12 MPa were measured, and planar field scans were acquired in scan times on the order of 1 min. The properties of the sensor and scanning system are well suited to measurement of nonlinear focused ultrasound fields, in both the focal region and the low-pressure peripheral regions. The fast acquisition speed of the system and its low NEP are advantageous, and with further development of the sensor, it has potential in application to HIFU metrology.

A planar hard-dielectric Fabry-Perot (FP) optical ultrasound sensor was modelled analytically to study how different wave modes affect the directionality. The sensor was modelled as a multilayered structure using the global matrix method. Modal dispersion curves were extracted from the model to enable features of the directional response to be linked to specific wave phenomena. The analytical model showed good agreement with the measured directional response. The key features of the directional response are linked to wave effects such as the water-substrate and water-spacer compressional and shear critical angles. A region of high sensitivity immediately after the shear critical angle is associated with a leaky-Rayleigh wave which has a frequency-dependent phase speed. At higher frequencies, this region is diminished by a minimum which occurs when the mirrors have the same vertical displacement, resulting in a lack of sensitivity.

The Fabry-Perot (FP) polymer film sensor can detect ultrasound over a broadband frequency range (tens of MHz), with small element sizes (tens of microns), and high sensitivity. It has been used extensively in photoacoustic imaging as well as general ultrasound field characterisation. Although it will clearly affect the ultrasound field measurements, the directional response of the sensor has not been widely studied. The objective of this work was to develop an analytical model to study how the various wave types propagating in the multilayer FP sensor affect the directionality. This is critical to optimise the design of the FP sensor, and to reduce sensor-related image artefacts.

The planar Fabry-Perot (FP) sensor provides high quality photoacoustic (PA) images but beam walk-off limits sensitivity and thus penetration depth to ≈1 cm. Planoconcave microresonator sensors eliminate beam walk-off enabling sensitivity to be increased by an order-of-magnitude whilst retaining the highly favourable frequency response and directional characteristics of the FP sensor. The first tomographic PA images obtained in a tissue-realistic phantom using the new sensors are described. These show that the microresonator sensors provide near identical image quality as the planar FP sensor but with significantly greater penetration depth (e.g. 2-3cm) due to their higher sensitivity. This offers the prospect of whole body small animal imaging and clinical imaging to depths previously unattainable using the FP planar sensor.

Most photoacoustic scanners use piezoelectric detectors but these have two key limitations. Firstly, they are optically opaque, inhibiting backward mode operation. Secondly, it is difficult to achieve adequate detection sensitivity with the small element sizes needed to provide near-omnidirectional response as required for tomographic imaging. Planar Fabry-Perot (FP) ultrasound sensing etalons can overcome both of these limitations and have proved extremely effective for superficial ( 1cm) photoacoustic imaging in vivo. Imaging results for second generation microresonator sensors (with R = 99.5% and thickness up to ~800um) are compared to the best achievable with the planar FP sensors and piezoelectric receivers.

Bioluminescence Tomography attempts to quantify 3-dimensional luminophore distributions from surface measurements of the light distribution. The reconstruction problem is typically severely under-determined due to the number and location of measurements, but in certain cases the molecules or cells of interest form localised clusters, resulting in a distribution of luminophores that is spatially sparse. A Conjugate Gradient-based reconstruction algorithm using Compressive Sensing was designed to take advantage of this sparsity, using a multistage sparsity reduction approach to remove the need to choose sparsity weighting a priori. Numerical simulations were used to examine the effect of noise on reconstruction accuracy. Tomographic bioluminescence measurements of a Caliper XPM-2 Phantom Mouse were acquired and reconstructions from simulation and this experimental data show that Compressive Sensing-based reconstruction is superior to standard reconstruction techniques, particularly in the presence of noise.

A novel straightforward, accessible and efficient approach is presented for performing hyperspectral time-domain diffuse optical spectroscopy to determine the optical properties of samples accurately using geometry specific models. To allow bulk parameter recovery from measured spectra, a set of libraries based on a numerical model of the domain being investigated is developed as opposed to the conventional approach of using an analytical semi-infinite slab approximation, which is known and shown to introduce boundary effects. Results demonstrate that the method improves the accuracy of derived spectrally varying optical properties over the use of the semi-infinite approximation.

Plano-convex optical microresonator detectors have been developed as an alternative to planar Fabry-Perot (FP) sensors used in all-optical photoacoustic imaging systems with the potential to provide two or more orders-of-magnitude higher detection sensitivity. This study further characterises the performance of these detectors by investigating their normal incidence frequency response and frequency-dependent directivity. It is shown that sensors with thicknesses in the range ~50-320μm provide broadband, smooth frequency response characteristics and low directional sensitivity. This suggests that a photoacoustic imaging system based on microresonator detectors may be capable of imaging with similar performance to the FP system but with significantly higher sensitivity, paving the way to deep tissue imaging applications such as the clinical assessment of breast cancer and preclinical whole body small animal imaging.

Lymph nodes play a central role in metastatic cancer spread and are a key clinical assessment target. Abnormal node vascularization, morphology, and size may be indicative of disease but can be difficult to visualize with sufficient accuracy using existing clinical imaging modalities. To explore the potential utility of photoacoustic imaging for the assessment of lymph nodes, images of ex vivo samples were obtained at multiple wavelengths using a high-resolution three-dimensional photoacoustic scanner. These images showed that hemoglobin based contrast reveals nodal vasculature and lipid-based contrast reveals the exterior node size, shape, and boundary integrity. These two sources of complementary contrast may allow indirect observation of cancer, suggesting a future role for photoacoustic imaging as a tool for the clinical assessment of lymph nodes.

A Fabry-Perot ultrasound sensor with nonhygroscopic dielectric mirrors made out of Ta2O5 and SiO2 for use in photoacoustic tomography is described. The sensor offers flat frequency response up to 36 MHz, low noise-equivalent pressure (70 Pa), and near-omnidirectional response up to 20 MHz as well as optical transparency for near-infrared illumination. A numerical model was developed to predict its frequency response, and the results were validated experimentally. An image of the human palm was acquired to demonstrate in vivo imaging capabilities.

A multi-modal optical imaging system for quantitative 3D bioluminescence and functional diffuse imaging is presented, which has no moving parts and uses mirrors to provide multi-view tomographic data for image reconstruction. It is demonstrated that through the use of trans-illuminated spectral near-infrared measurements and spectrally constrained tomographic reconstruction, recovered concentrations of absorbing agents can be used as prior knowledge for bioluminescence imaging within the visible spectrum. Additionally, the first use of a recently developed multi-view optical surface capture technique is shown and its application to model-based image reconstruction and free-space light modelling is demonstrated. The benefits of model-based tomographic image recovery as compared to two-dimensional (2D) planar imaging are highlighted in a number of scenarios where the internal luminescence source is not visible or is confounding in 2D images. The results presented show that the luminescence tomographic imaging method produces 3D reconstructions of individual light sources within a mouse-sized solid phantom that are accurately localized to within 1.5 mm for a range of target locations and depths, indicating sensitivity and accurate imaging throughout the phantom volume. Additionally the total reconstructed luminescence source intensity is consistent to within 15%, which is a dramatic improvement upon standard bioluminescence imaging. Finally, results from a heterogeneous phantom with an absorbing anomaly are presented, demonstrating the use and benefits of a multi-view, spectrally constrained coupled imaging system that provides accurate 3D luminescence images.

Spectral bioluminescence imaging and prior knowledge of bioluminescence shape were used to accurately localise, and reconstruct two luminescent sources in a phantom mouse via Markov Chain Monte Carlo sampling, and estimate reconstruction reliability.

Free-space modelling is important for quantitative bioluminescence imaging. Data using a new imaging system and a commercial system are compared to highlight this important phenomena showing inaccuracies of ~50% when free-space models are ignored.

A novel method is presented for accurately reconstructing a spatially resolved map of diffuse light flux on a surface using images of the surface and a model of the imaging system. This is achieved by applying a model-based reconstruction algorithm with an existing forward model of light propagation through free space that accounts for the effects of perspective, focus, and imaging geometry. It is shown that flux can be mapped reliably and quantitatively accurately with very low error

We show how a random matrix can be used to reduce the dimensionality of the bioluminescence tomography reconstruction problem. A randomised low-rank approximation for the sensitivity matrix is computed, and we show how this can be used to reconstruct the bioluminescence source distribution on a randomised basis for the mesh nodes. The distribution on the original mesh can be found easily via a simple matrix multiplication. The majority of the computation required can be performed in advance of the reconstruction, and the reconstruction time itself is of the order milliseconds. This could allow for high frame rate real-time reconstructions to be performed.

Practical imaging constraints restrict the number of wavelengths that can be measured in a single Biolumines- cence Tomography imaging session, but it is unclear which set of measurement wavelengths is optimal, in the sense of providing the most information about the bioluminescent source. Mutual Information was used to integrate knowledge of the type of bioluminescent source likely to be present, the optical properties of tissue and physics of light propagation, and the noise characteristics of the imaging system, in order to quantify the information contained in measurements at different sets of wavelengths. The approach was applied to a two-dimensional simulation of Bioluminescence Tomography imaging of a mouse, and the results indicate that different wavelengths and sets of wavelengths contain different amounts of information. When imaging at a single wavelength, 580nm was found to be optimal, and when imaging at two wavelengths, 570nm and 580nm were found to be optimal. Examination of the dispersion of the posterior distributions for single wavelengths suggests that information regarding the location of the centre of the bioluminescence distribution is relatively independent of wavelength, whilst information regarding the width of the bioluminescence distribution is relatively wavelength specific.

Knowledge of the surface geometry of an imaging subject is important in many applications. This information can be obtained via a number of different techniques, including time of flight imaging, photogrammetry, and fringe projection profilometry. Existing systems may have restrictions on instrument geometry, require expensive optics, or require moving parts in order to image the full surface of the subject. An inexpensive generalised fringe projection profilometry system is proposed that can account for arbitrarily placed components and use mirrors to expand the field of view. It simultaneously acquires multiple views of an imaging subject, producing a cloud of points that lie on its surface, which can then be processed to form a three dimensional model. A prototype of this system was integrated into an existing Diffuse Optical Tomography and Bioluminescence Tomography small animal imaging system and used to image objects including a mouse-shaped plastic phantom, a mouse cadaver, and a coin. A surface mesh generated from surface capture data of the mouse-shaped plastic phantom was compared with ideal surface points provided by the phantom manufacturer, and 50% of points were found to lie within 0.1mm of the surface mesh, 82% of points were found to lie within 0.2mm of the surface mesh, and 96% of points were found to lie within 0.4mm of the surface mesh.

Bioluminescence Tomography characteristics suggest its suitability to Compressive Sensing-based reconstruction. Numerical simulations examining reconstruction quality in the presence of noise demonstrate improved robustness and compactness.

An automated, multi-view, spectral bioluminescence tomography system that utilises structured-light-based surface capture techniques along with a model-based approach to image reconstruction is presented.

Steps are presented towards the development of a new bioluminescence tomography (BLT) imaging system for in vivo small animal studies. A 2-mirror-based multi-view data collection scheme is investigated in conjunction with multi-spectral imaging, leading to the production of 3D volumetric maps of molecular source distributions in simulation and in physical phantom studies by way of a finite element model (FEM) based reconstruction method. A proof of concept is subsequently demonstrated showing a full work flow from data acquisition to 3D reconstruction. Results suggest that the multi-view mirror-based approach represents a strong improvement over standard single-view methods, with improvements of up to 58% in source localisation accuracy being observed for deep sources.

Planar glass-etalon Fabry-Pérot (FP) optical ultrasound sensors offer an alternative to piezoelectric sensors for the measurements of high-intensity focused ultrasound (HIFU) fields and other metrological applications. In this work, a model of the frequency-dependent directional response of the FP sensor was developed using the global matrix method, treating the sensor as a multilayered elastic structure. The model was validated against the experimentally measured directional response of an air-backed cover-slip FP sensor with well-known material properties. In addition, the model was compared with the measurements of an all-hard-dielectric sensor suitable for HIFU measurements. The model was then used to calculate modal dispersion curves for both glass-etalon sensors, allowing the features of the directional response to be linked to specific wave phenomena. The features in the directivity of the air-backed cover-slip sensor are due to guided Lamb waves. Symmetric Lamb modes give rise to regions of high sensitivity, whereas anti-symmetric modes cause regions of low sensitivity. For the all-hard-dielectric sensor, two features correspond to the water-substrate and water-spacer compressional and shear critical angles. A region of high sensitivity close to the shear critical angle is associated with a leaky-Rayleigh wave, which has a frequency-dependent phase speed. At higher frequencies, this feature is counteracted by a region of low sensitivity, which occurs when there is no difference in the vertical displacement of the mirrors forming the FP cavity. The model may be used to improve and optimize the design of FP sensors or could be used to assist with the accurate deconvolution of the directional response from array measurements in metrological and imaging applications.