1,720,998 research outputs found
Developing a portable, high-speed, low-cost desktop photoacoustic tomography imaging system
No full textPhotoacoustic tomography (PAT) is a non-invasive, hybrid biomedical imaging modal- ity. Conventional PAT system uses Nd:YAG-OPO laser as excitation source and a single-element ultrasound transducer (SUT) for detecting the generated photoacoustic (PA) waves from the imaging object. Usually Nd:YAG-OPO laser is bulky, heavy and needs an optical table to deliver non-fluctuating laser beam and it needs external op- tics (reflectors/prisms) to direct the laser beam onto the sample (there are portable OPO lasers from OpoTek, EKSPLA, and various other companies that do not require optical table but they are more expensive than conventional Nd:YAG-OPO lasers). Also, the detecting element of the SUT is placed at orthogonal direction to the laser illumination for deep tissue imaging. Due to this configuration, the length of the transducer body and the connecting cable requires a lot of space inside the water (coupling medium) tank, thereby, increasing the size of the PAT scanner area. All these (laser, additional optics, SUT alignment) make the whole PAT imaging system very large in size and non- portable. Therefore, it is limited to bench-side laboratory imaging purposes. Moreover, this Nd:YAG laser is very expensive and has low pulse repetition rate of (10-100) Hz. So, one SUT takes several minutes to acquire a single cross-sectional PA data. This in turn, inhibits real-time imaging. The acquired PA data using this SUT is reconstructed conventionally using a simple delay-and-sum algorithm to obtain cross-sectional PA images. When this technique is employed for reconstruction, there will be blurring in tangential direction due to the effect of SUT aperture size, thereby, resulting in the degradation in quality (poor tangential resolution) of the PA images, especially when the target is far from the scanning center.
These are some of the limitations in using a conventional PAT system in terms of size, cost, speed and image quality that inhibit the translation of the PAT system into clinics for real-time high-speed imaging applications. Thus, there is a need for a low- cost, portable and high-speed PAT imaging system that can render better quality images.
To minimize the size of the overall PAT system, initially we have reduced the space occupied by the SUT in the PAT scanner. To achieve this, we have placed the transducer vertically instead of conventional horizontal direction and augmented it with an external acoustic reflector to the transducer body. This will reflect/direct the incoming PA waves from the imaging object to the detector element of the vertically placed SUT. We have validated the effectiveness of using the acoustic reflector augmented SUT (SUTR) for PA imaging using phantom and in vivo studies. Further to overcome the space occupied by the bulky Nd:YAG-OPO laser, we have used pulsed laser diode (PLD) as an alternate excitation source.
With advancement in laser technology, pulsed laser diodes have come into existence and been used effectively for PA imaging over the past few years. These PLD lasers are compact in size, light in weight and less expensive compared to the conventional Nd:YAG lasers. Taking these advantages into consideration, we have used a PLD laser directly inside the PAT scanner by mounting it on top of the imaging area (PLD laser is placed directly above the imaging object at the scanning centre). Due to this we saved a humongous amount of space occupied by the previously used Nd:YAG-OPO laser (placed outside the scanning area). In addition, there was no requirement of using any additional optics in this configuration as the laser source directly illuminates the sample. Hence, by employing the PLD excitation source, we have made the PAT system more compact, portable and easy to use for bed-side imaging. Moreover, the pulse repetition rate of this PLD laser is very high (2 kHz) compared to Nd:YAG laser (10 Hz). This is more advantageous for high speed imaging. Therefore, to improve the imaging speed, we have used PLD along with 8 SUTRs rotating in 45 degree (instead of 1 SUTR rotating in 360 degree) and obtained a high scan speed of 0.5 s in vivo.
Experimentally, all these transducers cannot be placed exactly at the same distance from the scanning center manually. Hence the acquired PA data from each transducer needs to be reconstructed with the corresponding radii while using delay-and-sum al- gorithm. This requires the exact location of each transducer from the scanning center. Hence, we proposed a calibration method to find the scanning radius of each transducer. We validated the efficacy of this method using numerical and experimental data.
To improve the image quality in terms of tangential resolution, we have used a mod- ified delay-and-sum algorithm, an improved version of conventional simple delay-and- sum algorithm for reconstructing the PA images and observed three-fold improvement in tangential resolution. In addition to it, this algorithm also preserved the shape of the target object which is very useful for diagnosis and treatment purposes.
Overall, by combining all the innovations described earlier, we have developed an affordable, portable, high-speed desktop PLD based PAT imaging system. Using this system we achieved a high spatial resolution of 165 μm and an in vitro imaging depth of 3 cm. We also demonstrated its dynamic imaging ability at a high scan speed of 2 frames/s by monitoring the fast uptake and clearance process of indocyanine green (ICG) dye in rat cortical vasculature.Doctor of Philosoph
Experimental validation of tangential resolution improvement in photoacoustic tomography using modified delay-and-sum reconstruction algorithm
No full textFor a circular scanning geometry in photoacoustic tomography, the axial/radial resolution is spatially invariant and is not affected by the ultrasound transducer (UST, detector) aperture. However, the tangential resolution is dependent on the detector aperture size and it varies spatially. Many techniques were proposed to improve the tangential resolution, such as attaching a concave lens in front of the nonfocused transducer or using a virtual point detector. Both of these methods have difficulties. Therefore, a modified delay-and-sum reconstruction algorithm has been proposed which can be used together with a standard ultrasound detector (nonfocused) to improve the tangential resolution. In this work, we validate the modified delay-and-sum algorithm experimentally for both flat and cylindrically focused USTs. More than threefold improvement in tangential resolution is observed. It is also shown that the object shape is recovered with this modified algorithm, which is very helpful for diagnosis and treatment purposes.MOE (Min. of Education, S’pore)Published versio
Going Beyond Counting First Authors in Author Co-citation Analysis
Get PDFThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Variations on the Author
Get PDF“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
Appropriate Similarity Measures for Author Cocitation Analysis
Get PDFWe provide a number of new insights into the methodological discussion about author cocitation analysis. We first argue that the use of the Pearson correlation for measuring the similarity between authors’ cocitation profiles is not very satisfactory. We then discuss what kind of similarity measures may be used as an alternative to the Pearson correlation. We consider three similarity measures in particular. One is the well-known cosine. The other two similarity measures have not been used before in the bibliometric literature. Finally, we show by means of an example that our findings have a high practical relevance.information science;Pearson correlation;cosine;similarity measure;author cocitation analysis
Dispelling the Myths Behind First-author Citation Counts
Get PDFWe conducted a full-scale evaluative citation analysis study of scholars in the XML research field to explore just how different from each other author rankings resulting from different citation counting methods actually are, and to demonstrate the capability of emerging data and tools on the Web in supporting more realistic citation counting methods. Our results contest some common arguments for the continued
use of first-author citation counts in the evaluation of scholars, such as high correlations between author rankings by first-author citation counts and other citation
counting methods, and high costs of using more realistic citation counting methods that are not well-supported by the ISI databases. It is argued that increasingly available digital full text research papers make it possible for citation analysis studies to go beyond what the ISI databases have directly supported and to employ more
sophisticated methods
koamabayili/VECTRON-author-checklist: VECTRON author checklist
No full textWe have done our best to complete the author checklist relating to the use of animals in the hut study. Note that the objective for the hut study was to evaluate the IRS treatment applications for residual efficacy against Anopheles mosquitoes, including the local An. coluzzii mosquito population. Cows were only used to attract mosquitoes into the huts and no tests were carried out directly on the cows. The author checklist is intended for use with studies where experiments are carried out on animals, which is why we have had such difficulty in completing this for the hut study, as many of the questions do not relate to how the cows were used
Author-wise bibliometric analysis based on entropy.
No full textAuthor-wise bibliometric analysis based on entropy.</p
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