Dr. Thomas J. Allen Profile

Dr. Thomas J. Allen

Senior Research Associate at Univ College London

SPIE Involvement:

Author

Publications (21)

Proceedings Article | 13 March 2024 Presentation

Parallelized interrogation of a Fabry-Perot ultrasound sensor using compressed sensing for fast photoacoustic tomography

Thomas Allen, Edward Zhang, Paul Beard

Proceedings Volume PC12842, PC128420A (2024) https://doi.org/10.1117/12.3008990

KEYWORDS: Ultrasonography, Sensors, Photoacoustic tomography, Fabry–Perot interferometers, Compressed sensing

Read Abstract +

Proceedings Article | 9 March 2023 Presentation

Clinical 3D microvascular imaging using the Fabry Perot photoacoustic scanner

Nam Trung Huynh, Edward Zhang, Jiaqi Zhu, Thomas Allen, Rehman Ansari, Madhura Castelino, Katerina Soteriou, Ahshin Mosahebi, Muholan Kanapathy, Ahmed Yassin, Filip Kuklis, Jiri Jaros, Ben Cox, Olivia Francies, Andrew Plumb, Paul Beard

Proceedings Volume PC12379, PC123790D (2023) https://doi.org/10.1117/12.2655765

KEYWORDS: 3D scanning, 3D image processing, Laser scanners, Stereoscopy, Photoacoustic spectroscopy, Imaging systems, 3D acquisition, Visualization, Optical scanning systems, Video

Read Abstract +

Proceedings Article | 9 March 2023 Presentation

High-density ultrasound array based on the fully parallelised read-out of a Fabry-Perot sensor for fast photoacoustic tomography

Thomas Allen, Edward Zhang, Paul Beard

Proceedings Volume PC12379, PC123791S (2023) https://doi.org/10.1117/12.2656065

KEYWORDS: Ultrasonography, Sensors, Photoacoustic tomography, Fabry–Perot interferometers

Read Abstract +

Proceedings Article | 9 March 2023 Paper

Photoacoustic wavefront shaping with a long coherence length laser

Maxim Cherkashin, Benjamin Keenlyside, Thomas Allen, Paul Beard, James Guggenheim

Proceedings Volume 12379, 1237913 (2023) https://doi.org/10.1117/12.2652242

KEYWORDS: Photoacoustic imaging, Photoacoustic microscopy, Adaptive optics, Tissues, Scattering media, Spatial light modulators, Light scattering, Wavefronts, Diffusers, Tissue optics, Speckle pattern, Speckle, Photoacoustic spectroscopy

Read Abstract +

Proceedings Article | 20 April 2020 Presentation

Fully parallelised read-out of a Fabry-Perot ultrasound sensor using an InGaAs camera for fast photoacoustic imaging (Conference Presentation)

Thomas Allen, Edward Zhang, Paul Beard

Proceedings Volume 11240, 112400U (2020) https://doi.org/10.1117/12.2550127

KEYWORDS: Fabry–Perot interferometers, Ultrasonography, Sensors, Indium gallium arsenide, Cameras, Photoacoustic imaging

Read Abstract +

Proceedings Article | 20 April 2020 Presentation

High resolution 3D photoacoustic scanner for clinical vascular imaging applications (Conference Presentation)

Nam Trung Huynh, Olivia Francies, Katerina Soteriou, Thomas Allen, Khoa Pham, Sacha Noimark, Semyon bodian, Adrien Desjardins, Jiaqi Zhu, Oshaani Abeyakoon, Filip Kuklis, Edward Zhang, Ben Cox, Andrew Plumb, Paul Beard

Proceedings Volume 11240, 1124003 (2020) https://doi.org/10.1117/12.2549559

KEYWORDS: 3D scanning, Photoacoustic spectroscopy, Laser scanners

Read Abstract +

SPIE Journal Paper | 6 December 2018 Open Access

Ultrafast laser-scanning optical resolution photoacoustic microscopy at up to 2 million A-lines per second

Thomas John Allen, Josh Spurrell, Martin Berendt, Olumide Ogunlade, Shaif Alam, Edward Zhang, David Richardson, Paul Beard

JBO, Vol. 23, Issue 12, 126502, (December 2018) https://doi.org/10.1117/12.10.1117/1.JBO.23.12.126502

KEYWORDS: Video, Fiber lasers, Ear, Optical resolution, Photoacoustic microscopy, Imaging systems, Photoacoustic spectroscopy, Fiber optics sensors, Sensors, Laser optics

Read Abstract +

DOWNLOAD PAPER

Proceedings Article | 15 March 2018 Presentation

Compact fibre laser system with 15mJ pulse energy for photoacoustic tomography (Conference Presentation)

Thomas Allen, Martin Berendt, Shaif-ul Alam, Nam Huynh, David Richardson, Paul Beard

Proceedings Volume 10494, 104941Z (2018) https://doi.org/10.1117/12.2288820

KEYWORDS: Fiber lasers, Photoacoustic tomography, Tomography, Photoacoustic spectroscopy, Acquisition tracking and pointing, Acoustics, Laser scanners, 3D scanning, Laser tissue interaction, Pulsed laser operation

Read Abstract +

Photoacoustic signals are typically generated using Q-switched Nd:YAG pumped OPO systems, as they can provide the necessary nanosecond pulse durations with mJ pulse energies required for photoacoustic tomography. However, these sources are often bulky, require external water cooling and regular maintenance and provide low pulse repetition frequencies (PRF<100Hz) thus limiting image frame rate. Fibre lasers can overcome these limitations and additionally offer much greater flexibility in their temporal output characteristics (e.g. pulse shaping and duration). Although fibre lasers have been used in optical-resolution photoacoustic microscopy, they have found limited application in widefield photoacoustic tomography (PAT) due to the relatively low pulse energy (<1mJ) provided by commercial systems. These low pulse energies are a consequence of small core diameter (<25m) fibres required to achieve a high beam quality. However, for widefield PAT, high beam quality is not a requirement and therefore fibre lasers with larger core diameters (>100m) can be used, enabling significantly higher pulse energies (>10mJ) to be achieved. A novel compact fibre laser which uses a custom drawn large core diameter fibre (100m) to provide high pulse energies (15mJ) and variable PRFs (100Hz-1kHz) and pulse durations (10-400ns) has been developed and evaluated. The fibre laser was combined with a fast Fabry Perot (FP) scanner in order to evaluate its suitability for PAT of biological tissue. The high PRF (>400Hz) of the laser has allowed tomographic images of the microvasculature of the palm of a hand to be obtained in less than one second, significantly quicker than previously achieved with a FP scanner. In addition, the ability to arbitrarily vary the temporal shape of the laser pulse offers new opportunities for controlling the acoustic frequency content of the photoacoustic signal in order to optimise penetration depth and image resolution. For example, the laser pulse duration can be increased in order to shift the acoustic frequency components to lower frequencies which are less attenuated by tissue acoustic absorption and thus improve SNR. To investigate these concepts, a tissue mimicking phantom was imaged for a range of tailored excitation pulses (e.g. different pulse durations, trains of pulses) and their effect on the contrast to noise ratio (CNR) and image resolution observed. A novel compact fibre laser, able to provide higher pulse energies (>10mJ) than previously reported and with enhanced functionality is presented. It is demonstrated that fibre lasers are a viable alternative to standard Q-switched lasers for photoacoustic tomographic applications in medicine and biology.

Proceedings Article | 17 March 2016 Presentation + Paper

Novel fibre lasers as excitation sources for photoacoustic tomography and microscopy

T. Allen, M. Berendt, J. Spurrell, S. Alam, E. Zhang, D. Richardson, P. Beard

Proceedings Volume 9708, 97080W (2016) https://doi.org/10.1117/12.2211733

KEYWORDS: Fiber lasers, Photoacoustic tomography, Photoacoustic spectroscopy, Imaging systems, Laser development, Acquisition tracking and pointing, Image acquisition, Photoacoustic imaging, Microscopy, Optical resolution

Read Abstract +

SPIE Journal Paper | 26 May 2015 Open Access

Photoacoustic imaging of human lymph nodes with endogenous lipid and hemoglobin contrast

James Guggenheim, Thomas Allen, Andrew Plumb, Edward Zhang, Manuel Rodriguez-Justo, Shonit Punwani, Paul Beard

JBO, Vol. 20, Issue 05, 050504, (May 2015) https://doi.org/10.1117/12.10.1117/1.JBO.20.5.050504

KEYWORDS: Lymphatic system, Photoacoustic imaging, Cancer, Photoacoustic spectroscopy, Absorption, Visualization, Sensors, 3D image processing, Magnetic resonance imaging, Signal to noise ratio

Read Abstract +

DOWNLOAD PAPER

Proceedings Article | 11 March 2015 Paper

Large-field-of-view laser-scanning OR-PAM using a fibre optic sensor

T. Allen, E. Zhang, P. Beard

Proceedings Volume 9323, 93230Z (2015) https://doi.org/10.1117/12.2082815

KEYWORDS: Sensors, Photoacoustic microscopy, Fiber optics sensors, Ultrasonography, Fiber optics, Photoacoustic spectroscopy, Signal detection, Acoustics, Absorption, Signal to noise ratio

Read Abstract +

Proceedings Article | 3 March 2014 Paper

Characterization of the thermalisation efficiency and photostability of photoacoustic contrast agents

T. Stahl, T. Allen, P. Beard

Proceedings Volume 8943, 89435H (2014) https://doi.org/10.1117/12.2039694

KEYWORDS: Photoacoustic spectroscopy, Absorption, Gold, Carbon nanotubes, Rhodamine B, Nanoparticles, Ultrasonography, Transducers, Signal detection, Nanorods

Read Abstract +

Proceedings Article | 4 March 2013 Paper

Light emitting diodes as an excitation source for biomedical photoacoustics

T. Allen, P. Beard

Proceedings Volume 8581, 85811F (2013) https://doi.org/10.1117/12.2004471

KEYWORDS: Photoacoustic spectroscopy, Light emitting diodes, Signal generators, Signal to noise ratio, Biomedical optics, Semiconductor lasers, Signal detection, Blood, Absorption, Electronic filtering

Read Abstract +

SPIE Journal Paper | 7 May 2012 Open Access

Spectroscopic photoacoustic imaging of lipid-rich plaques in the human aorta in the 740 to 1400 nm wavelength range

Thomas Allen, Paul Beard, Andrew Hall, Amar Dhillon, James Owen

JBO, Vol. 17, Issue 6, 061209, (May 2012) https://doi.org/10.1117/12.10.1117/1.JBO.17.6.061209

KEYWORDS: Photoacoustic spectroscopy, Absorption, Tissue optics, Tissues, Blood, Spectroscopy, Photoacoustic imaging, Imaging spectroscopy, Image segmentation, Photography

Read Abstract +

DOWNLOAD PAPER

Proceedings Article | 23 February 2012 Paper

Optimising the detection parameters for deep-tissue photoacoustic imaging

T. Allen, P. Beard

Proceedings Volume 8223, 82230P (2012) https://doi.org/10.1117/12.908813

KEYWORDS: Sensors, Acoustics, Photoacoustic spectroscopy, Signal to noise ratio, Signal attenuation, Tissue optics, Chemical elements, Signal detection, Photoacoustic imaging, Breast

Read Abstract +

Proceedings Article | 1 March 2011 Paper

Use of a pulsed fibre laser as an excitation source for photoacoustic tomography

Thomas Allen, Shaiful Alam, Edward Zhang, Jan Laufer, David Richardson, Paul Beard

Proceedings Volume 7899, 78991V (2011) https://doi.org/10.1117/12.875291

KEYWORDS: Fiber lasers, Photoacoustic spectroscopy, Photoacoustic tomography, Signal detection, Pulsed fiber lasers, Tissue optics, Laser tissue interaction, Photoacoustic imaging, Imaging systems, Tissues

Read Abstract +

Proceedings Article | 24 February 2010 Paper

Photoacoustic imaging of lipid rich plaques in human aorta

T. Allen, A. Hall, A. Dhillon, J. Owen, P. Beard

Proceedings Volume 7564, 75640C (2010) https://doi.org/10.1117/12.842205

KEYWORDS: Photoacoustic spectroscopy, Blood, Tissue optics, Tissues, Absorption, Signal detection, Photoacoustic imaging, Near infrared, Visible radiation, Spectroscopy

Read Abstract +

Proceedings Article | 25 February 2009 Paper

Photoacoustic characterisation of vascular tissue at NIR wavelengths

Thomas Allen, Paul Beard

Proceedings Volume 7177, 71770A (2009) https://doi.org/10.1117/12.808777

KEYWORDS: Photoacoustic spectroscopy, Absorption, Tissues, Tissue optics, Blood, Near infrared, Signal detection, Spectroscopy, Ultrasonography, Visible radiation

Read Abstract +

Proceedings Article | 27 February 2007 Paper

Dual wavelength laser diode excitation source for 2D photoacoustic imaging

Thomas Allen, Paul Beard

Proceedings Volume 6437, 64371U (2007) https://doi.org/10.1117/12.698651

KEYWORDS: Semiconductor lasers, Photoacoustic spectroscopy, Signal detection, Blood, Tissues, Signal generators, Laser systems engineering, Photoacoustic imaging, Imaging systems, Signal to noise ratio

Read Abstract +

Proceedings Article | 8 March 2006 Paper

Development of a pulsed NIR multiwavelength laser diode excitation system for biomedical photoacoustic applications

Thomas Allen, Paul Beard

Proceedings Volume 6086, 60861P (2006) https://doi.org/10.1117/12.655537

KEYWORDS: Semiconductor lasers, Photoacoustic spectroscopy, Signal to noise ratio, Signal detection, Signal generators, Signal attenuation, Acoustics, Biomedical optics, Capillaries, Laser systems engineering

Read Abstract +

An important capability of photoacoustic methods is the ability to make spatially resolved spectroscopic measurements of blood oxygenation by imaging at multiple NIR excitation wavelengths, usually sourced from Q-switched Nd:YAG pumped OPO based systems. These excitation sources are usually bulky, expensive and with limited scope for varying the pulse repetition rate and pulse width. An alternative would be to use pulsed laser diodes as excitation sources. To evaluate the possibility of developing a multiwavelength excitation system composed of three wavelengths 810, 850 and 905nm, a single wavelength (905nm) system was built. To achieve a sufficient SNR, four high peak power pulsed laser diodes were combined. The design of the laser drivers provided variable pulse duration (65-500ns) and repetition rates of up to 2.5KHz. This allowed the pulse duration to be optimised in order to (a) maximise the energy in the generated photoacoustic signal and (b) reduce the effects of frequency dependent acoustic attenuation of tissue on the propagating acoustic wave by avoiding the generation of excessively high frequency components. It also enabled the high repetition rate of laser diodes to be exploited in order to average a large number of acquisitions over a short time period to increase SNR. Preliminary measurements of SNR were made in phantoms using the single wavelength excitation system, to demonstrate the practical biomedical utility of the system. A tissue phantom consisting of two capillaries (null set 460μm)filled with an absorbing dye of similar optical properties to blood (μa ≈ 1mm-1), immersed at different depths in a 1% solution of intralipid (μs ≈ 1mm-1) was used. To further demonstrate the capability of the system it was combined with a cylindrical scanning system to image a strongly absorbing cylinder immersed to a depth of 1cm in 1% solution of intralipid (μs ≈ 1mm-1). This study demonstrated the potential for using laser diodes as excitation sources for pulsed photoacoustic spectroscopic biomedical applications.

Proceedings Article | 25 April 2005 Paper

Generating photoacoustic signals using high-peak power pulsed laser diodes

Thomas Allen, B. Cox, Paul Beard

Proceedings Volume 5697, (2005) https://doi.org/10.1117/12.597321

KEYWORDS: Semiconductor lasers, Photoacoustic spectroscopy, Signal attenuation, Acoustics, Signal to noise ratio, Signal generators, Signal detection, Q switched lasers, Pulsed laser operation, Absorption

Read Abstract +

Photoacoustic signals are usually generated using bulky and expensive Q-switched Nd:YAG lasers, with limited scope for varying the pulse repetition frequency, wavelength and pulse width. An alternative would be to use laser diodes as excitation sources; these devices are compact, relatively inexpensive, and available in a wide variety of NIR wavelengths. Their pulse duration and repetition rates can also be varied arbitrarily enabling a wide range of time and frequency domain excitation methods to be employed. The main difficulty to overcome when using laser diodes for pulsed photoacoustic excitation is their low peak power compared to Q-switched lasers. However, the much higher repetition rate of laser diodes (~ kHz) compared to many Q-switched laser systems (~ tens of Hz) enables a correspondingly greater number of events to be acquired and signal averaged over a fixed time period. This offers the prospect of significantly increasing the signal-to-noise ratio (SNR) of the detected photoacoustic signal. Choosing the wavelength of the laser diode to be lower than that of the water absorption peak at 940nm, may also provide a significant advantage over a system lasing at 1064nm for measurements in tissue. If the output of a number of laser diodes is combined it then becomes possible, in principle, to obtain a SNR approaching that achievable with a Q-switched laser. It is also suggested that optimising the pulse duration of the laser diode may reduce the effects of frequency-dependent acoustic attenuation in tissue on the photoacoustic signal. To investigate this, a numerical model based on the Poisson solution to the wave equation was developed. To validate the model, a high peak power pulsed laser diode system was built. It was composed of a 905nm stacked array laser diode coupled to an optical fibre and driven by a high current laser diode driver. Measurements of the SNR of photoacoustic signals generated in a purely absorbing medium (ink) were made as a function of pulse duration. This preliminary study shows the potential for using laser diodes as excitation sources for photoacoustic applications in the biomedical field.

Showing 5 of 21 publications

View contact details

UPDATE YOUR PROFILE

Is this your profile? Update it now.

Sign into your SPIE.org account

Don’t have a profile and want one?

Create an account on SPIE.org

Keywords/Phrases

Search In:

Publication Years