Multiview Hilbert transformation in full-ring transducer array-based photoacoustic computed tomography.

Masked cross-domain self-supervised deep learning framework for photoacoustic computed tomography reconstruction

Deep Learning for scaling large-aperture photoacoustic computed tomography : From single fingers to the human hand.

Small animal imaging has recently been focused on basic nuclear medicine. We have designed and built a small animal SPECT imaging system using a semiconductor camera and a newly designed collimator. We assess the performance of this system for small object imaging. We employed an MGC 1500 (Acrorad Co.) camera including a CdTe semiconductor. The pixel size was 1.4 mm/pixel. We designed and produced a parallel-hole collimator with 20-mm hole length. Our SPECT system consisted of a semiconductor camera with the subject holder set on an electric rotating stage controlled by a computer. We compared this system with a conventional small animal SPECT system comprising a SPECT-2000H scanner with four Anger type cameras and pinhole collimators. The count rate linearity for estimation of the scatter was evaluated for a pie-chart phantom containing different concentrations of 99mTc. We measured the FWHM of the 99mTc SPECT line source along with scatter. The system volume sensitivity was examined using a flood source phantom which was 35 mm long with a 32-mm inside diameter. Additionally, an in vivo myocardial perfusion SPECT study was performed with a rat. With regards to energy resolution, the semiconductor camera (5.6%) was superior to the conventional Anger type camera (9.8%). In the count rate linearity evaluation, the regression lines of the SPECT values were y = 0.019x + 0.031 (r2 = 0.999) for our system and y = 0.018x + 0.060 (r2 = 0.997) for the conventional system. Thus, the scatter count using the semiconductor camera was less than that using the conventional camera. FWHMs of our system and the conventional system were 2.9 +/- 0.1 and 2.0 +/- 0.1 mm, respectively. Moreover, the system volume sensitivity of our system [0.51 kcps/(MBq/ ml)/cm] was superior to that of the conventional system [0.44 kcps/(MBq/ml)/cm]. Our system provided clear images of the rat myocardium, sufficient for practical use in small animal imaging. Our SPECT system, utilizing a semiconductor camera, permits high quantitative analysis by virtue of its low scatter radiation and high sensitivity. Therefore, this system may contribute to molecular imaging of small animals and basic medical research.

Progress in understanding the cell biology and diseases depends on advanced imaging and labeling techniques. Here, we address this demand by exploring novel multilayered nanocomposites (MNCs) with plasmonic nanoparticles and absorbing dyes in thin nonabsorbing shells as supercontrast multimodal photoacoustic (PA) and fluorescent agents in the near-infrared range. The proof of concept was performed with gold nanorods (GNRs) and indocyanine green (ICG) dispersed in a matrix of biodegradable polymers. We demonstrated synergetic PA effects in MNCs with the gold-ICG interface that could not be achieved with ICG and GNRs alone. We also observed ultrasharp PA and emission peaks that could be associated with nonlinear PA and spaser effects, respectively. Low-toxicity multimodal MNCs with unique plasmonic, thermal and acoustic properties have the potential to make a breakthrough in PA flow cytometry and near-infrared spasers in vivo by using the synergetic interaction of plasmonic modes with a nearby absorbing medium.

Photoacoustics is a hybrid imaging technique that combines the contrast available to optical imaging with the resolution that is possessed by ultrasound imaging. The technique is based on generating ultrasound from absorbing structures in tissue using pulsed light. In photoacoustic (PA) computerized tomography (CT) imaging, reconstruction of the optical absorption in a subject, is performed for example by filtered backprojection. The backprojection is performed along circular paths in image space instead of along straight lines as in X-ray CT imaging. To achieve this, the speed-of-sound through the subject is usually assumed constant. An unsuitable speed-of-sound can degrade resolution and contrast. We discuss here a method of actually measuring the speedof- sound distribution using ultrasound transmission through the subject under photoacoustic investigation. This is achieved in a simple approach that does not require any additional ultrasound transmitter. The method uses a passive element (carbon fiber) that is placed in the imager in the path of the illumination which generates ultrasound by the photoacoustic effect and behaves as an ultrasound source. Measuring the time-of-flight of this ultrasound transient by the same detector used for conventional photoacoustics, allows a speed-of-sound image to be reconstructed. This concept is validated on phantoms.

A miniaturized photoacoustic device with laptop readout for point-of-care testing of blood glucose

NIR absorbing thiophene derivatives with photoacoustic and photothermal effect used in drug release

Combined Photoacoustic (PA) and Ultrasound (US) imaging systems are finding more preclinical and clinical applications. However, majority of the commercial systems use expensive pulsed lasers. In most small animal studies and clinical applications like arthritis screening of finger joints, there is a need for tomographic imaging. In this work, we present PA and US tomographic imaging using a commercial imaging system with LED arrays as illumination source. We employ multiangle spatial compounding of PA and US images using a probe with a linear array transducer and four LED arrays, to form dual-mode tomographic images. Using phantom experiments, the proposed approach is validated and thoroughly tested. Further, the potential of the system is demonstrated by imaging knee joint and abdominal region of a mouse. This proposed approach has several advantages. First, the resolution and signal to noise ratio (SNR) are improved with the compounding of images from multiple angles. The resolution improvement owes to better axial resolution compared to lateral and high SNR with averaging. Secondly, the limited view artifacts and loss of information from the use of a linear array US probe is tackled. The US tomographic images of the mouse-knee RA model show structural details of the joint and blood vessels were visible in the tomographic PA images. The whole animal images enabled improved functional and structural information. An affordable PA/US tomographic imaging system with potential in clinical arthritis-screening and small animal imaging is presented.

In this paper, we suggest a multi-wavelength source for photoacoustic (PA) imaging using stimulated Raman scattering (SRS) effect. In order to demonstrate the feasibility of high-speed functional in-vivo PA imaging, we performed the spectroscopic PA imaging with 300 kHz of acquisition rate.

High intensity focused ultrasound (HIFU) is a non-invasive technique for treating soft tissue tumors. A feasibility study for using the photoacoustic (PA) effect to monitor in-situ temperature changes during HIFU exposures is presented. A PA wave is generated from the thermoelastic expansion of a light-absorbing medium with its amplitude related to the Grüneisen parameter of the medium, which, for water, depends linearly on temperature. A 2-MHz HIFU transducer heated a cylindrical graphite inclusion in which a wire thermocouple was embedded. A 532-nm pulsed laser illuminated the inclusion at a rate of 10 Hz, and a 15-MHz passive transducer monitored the PA response throughout the 30-s exposure. Singular-value-decomposition analysis of the PA response was performed to extract the contribution from temperature change. Thermocouple measurements indicated a temperature increase from 22–60 °C, depending on the HIFU intensity employed, with a concomitant 20%–30% increase in PA amplitude. PA-based temperature curves correlated with the thermocouple measurements (rms deviation <5 °C). This technique tracked both the heating and cooling phases of the HIFU exposure and potentially could be used to noninvasively monitor in-situ temperature in real-time during HIFU. [Work supported by a Boston University Dean’s Catalyst Award and the RRI’s Biomedical Engineering Research Fund.]

This chapter presents details of the design and characterization of an improved photoacoustic system optimized for tomographic small animal imaging. The system uses a 128-element transducer array and features a higher operating frequency for resolution of fine features, such as brain vasculature, while retaining high sensitivity for deeper imaging. The chapter provides a discussion of the system architecture and design with special consideration of electronics and transducer parameters. It also presents simulations and characterization measurements of system performance, including resolution, field-of-view, and sensitivity. The chapter describes the effects of target geometry, orientation, and size on tomographic imaging quality. It demonstrates the impact of both system design and target characteristics through ex vivo imaging of mouse brain vasculature. The chapter explains a brief discussion of system design implications for photoacoustic imaging fidelity with the complex and varied features typical of in vivo tissues.

In this work the performance of a compact multiresolution and multicontrast x-ray phase system based on edge illumination is investigated. It has been designed for small animal imaging and with a limited footprint for ease of deployment in laboratories. The presented edge illumination system is based on a compact microfocus tungsten x-ray source combined with a flat panel detector. The source has a maximum output of 10W when the minimum spot size of about 15μm is used. The system has an overall length of 70cm. A new double sample mask design, obtained by arranging both skipped and nonskipped configurations on the same structure, provides dual resolution capability. To test the system, we carried out computed tomography (CT) scans of a plastic phantom with different source settings using both single-image and multi-image acquisition schemes at different spatial resolutions. In addition, CT scans of an ex-vivo mouse specimen were acquired at the best identified working conditions to demonstrate the application of the presented system to small animal imaging. We found this system delivers good image quality, allowing for an efficient material separation and improving detail visibility in small animals thanks to the higher signal-to-noise ratio (SNR) of phase contrast with respect to conventional attenuation contrast. The system offers high versatility in terms of spatial resolution thanks to the double sample mask design integrated into a single scanner. The availability of both multi- and single-image acquisition schemes coupled with their dedicated retrieval algorithms, allows different working modes which can be selected based on user preference. Multi-image acquisition provides quantitative separation of the real and imaginary part of the refractive index, however, it requires a long scanning time. On the other hand, the single image approach delivers the best material separation and image quality at all the investigated source settings with a shorter scanning time but at the cost of quantitativeness. Finally, we also observed that the single image approach combined with a high-power x-ray source may result in a fast acquisition protocol compatible with in-vivo imaging.

It is significant to precisely control the size and spacing of gold nanoparticles for enhancing the effect of localized surface plasmon resonance (LSPR) in photothermal (PT) therapy and photoacoustic (PA) imaging. A multi-layer array of gold nanoparticles in the optic-thermal-acoustic field was modeled in this study using numerical simulation methods as a means of quantitatively analyzing the microscale heat transfer parameters and nonlinear enhanced PA/PT effects. High special resolution was achieved by taking isolated gold nanoparticles with radii of 20 nm, 40 nm, and 50 nm as examples by finite element analysis (FEA). The peak value of acoustic pressure was 74 Pa under the excitation of 5 ns pulse laser with a wavelength of 532 nm. Gold nanoarray was packed by nanoparticle with separation spacings of 6 nm,7 nm,8 nm, 15 nm, 20 nm, and 40 nm. The optical and thermoacoustic properties of the nanoarray varied as the assembled density of the gold nanoarray increased. The model also verified that mixing the polydimethylsiloxane (PDMS) with gold nanoparticles improved the efficiency of the thermal transformation of nanoarrays by at least 43.52% and amplified PA pressure by 3 grades. The results showed that high PA generation efficiency could be achieved by rationally constructing the composites of PDMS and gold nanoarray. INDEX TERMS Photoacoustic effect, gold nanocomposites, optic-thermal-acoustic field, FEA.

We have designed a three dimensional (3D) fluorescence optical tomography system for small animal imaging based on an innovative system geometry that uses a truncated conical mirror which permits the entire surface of the animal to be viewed simultaneously by a single CCD camera. Compared with traditional approaches that employ a flat mirror, the conical mirror system has approximately 3 times better measurement sensitivity. By utilizing a fast switching filter wheel (switching time < 100 milliseconds), emission data at multiple wavelengths can be efficiently collected. An array of appropriately shaped neutral density filters, mounted on a linear stage, can be used to increase the system measurement dynamic range by 3 orders of magnitude. An x-y galvo mirror scanning system makes it possible to scan a collimated laser beam to any location on the mouse surface. A pattern of structured light incident on the animal surface is used to extract the surface geometry. A finite element based algorithm is applied to model photon propagation in the turbid media and a preconditioned conjugate gradient (PCG) method is used to solve the large linear system matrix. The reconstruction algorithm and the system performance are evaluated by phantom experiments.

The photoacoustic (PA) effect is an effective method fer obtaining information on the thermal and optical properties of materials [1-10]. The success of this JeW spectroscopic technique is mainly due to the &ct that only the absorbed light contributes to the ~gnal, giving a large signal to noise ratio. According !O the Rosencwaig-Gersho theory [3], the primary ~urce of the acoustic signal in the cell arises from Ihe periodic beat flow from the solid to the coupling mediwn, as the solid is cyclically heated by the ~rption of chopped light. The periodic flow of !his heat into the coupling medium produces pressure fluctuations, which are detected as an acoustic signal by microphone at the modulation frequency, f in this energy conversion (optical to acoustic), the thermal properties of the sample play a significant role. This suggests the possibility of using Ihc PA effect for the study of thermal properties of solids such as the thermal diffusivity and specific heat capacity. A search through the literature reveals that very few PA studies have been carried out on metal complexes and that no work has been reported on benzimidazole complexes. Complexes of benzimidazoles have attracted considerable attention in recent years. Benzimidazole derivatives have been reported to have antibacterial, antifungal, antiviral, antitumour, anticancer, antifiammatory. analgesic, antipyretic, antineoplastic, antihelmentic, germicidal and immW1o-chemical agent activities. Complex compounds of transition metal ions with imidazole, benzimidazole and their substituted ligands have been studied extensively [11-15]. Recently, many low molecular weight complexes of Cu(u) containing imidazole ligand ha~e been proposed as models of active sites of Cu proteins [16-18]. Incorporation of nitro groups in the azole compounds gives them anti-amoebic activity as well [19]. Some of the Co(lI) and CU(II) complexes reported have shown better catalytic activity, particularly in the synthetically ·important reaction of oxidation of substituted phenols, in which Co(u) and Cu(n) play a major role in catalysing these types of reactions. The structure of the ligand is shown in Fig. 1. Tn this letter, we report thermal studies of 1nitrobenzyl-2-nitrophenyl benzimidazole (NBPBI) complexes of CoCH), CU(II) and Cu(J) by laser induced photoacoustic techniques. Figure 1 Structure of the ligand (NBPBI).