Analysis of Optical Imaging Technologies

Analysis of Optical Imaging Technologies PAI is a relatively new imaging modality which displays optical absorption contrast with a high resolution at depths of up to a few centimetres. Tissue is illuminated using short laser pulses and ultrasound waves are generated within the tissue upon optical absorption. An image is formed of the optical absorption contrast based on the arrival times and amplitudes of the acoustic waves (Wang 2009, Lai and Young 1982, Sigrist and Kneubuhl 1978, Jaeger 2007). It began in the late 19th century, when Alexander Graham Bell discovered the extraordinary effect of sound being generated because of absorption of intermittent sunlight (Bell 1880, 1880a). It was not until the 1970s and 1980s that research in this field took off, with the advent of modern pulsed lasers and materials and electronics for acoustic detection and recording. Pulsed laser light, indeed, is used in the majority of PAl techniques in order to illuminate the sample of interest. The succession of phenomena that occur after light exposure is shown in the following list (Wang 2009, Xu and Wang 2006): Light absorption: the molecules that absorb light, start vibrating and this continues until the illumination ceases. Temperature rise: the vibration locally increases the temperature for the period of illumination, after which the temperature decays. Thermoelastic expansion: because of the thermoelastic effect, the heated area tends to expand, with a local increase in pressure for the period of illumination if this happens to quickly for expansion to occur. Acoustic emission: the transient pressure variation propagates away from the transiently heated region. The initial studies were based upon gas-phase analysis, in which gases, depending upon their physical properties would absorb specific wavelengths of pulsed laser radiation, generating acoustic signals recorded by a microphone (Tam 1986, Meyer and Sigrist 1990). It wasn’t until the mid-1990s that biomedical applications of photoacoustics were reported (Kruger 1995, Esenaliev 1997, Hoelen 1998) and from that point, until now, the field has witnessed unprecedented growth to a stage where imaging systems are commercially available. The generation of PA signal can be understood by dividing the phenomenon into two domains: ‘Optical’ and ‘acoustics’ (Kruizinga 2010). In the optical domain, the pulse of light incident on the body surface above the site of interest, penetrates and travels diffusely through the different layers and encounters regions where it is absorbed, causing the generation of heat, which results in volumetric expansion. If this heat is deposited in a short enough time using a nano- or femtosecond laser pulse, then there is no time for dissipation of heat into the surrounding medium nor dissipation of the stress due to the heat-induced increase in pressure, and a transient disequilibrium arises, because of the difference in pressure inside and outside the region of heat deposition. This results in the generation of acoustic emissions, which propagate to be detected at the body surface via the acoustic domain. In the next few sections, these two sub-domains (optical and a coustic) will be explained, followed by a brief outline of the possible imaging applications of PAI. 2.1.1  Optical domain In medical imaging, the wavelength range of 650 nm to 1300 nm is often referred to as the `tissue optical window, wherein the tissue components, primarily haemoglobin, water and melanin absorb minimal light, allowing greater penetration of the photons than at other wavelengths. The two processes that dominate in light interacting with tissue are `scattering and `absorption. The strength of these interactions heavily depend on the wavelength of the light used and the components of the interacting tissue. Before looking into the optical domain, it is necessary to define some common optical parameters and quantities, as listed in Table 2.1. Table 2.1. Definitions of some common optical parameters and quantities With these parameters, it is possible to define the extinction coefficient , as in Equation 1.1[JCB1]. Its reciprocal would be the mean free path between any absorption or scattering events. . (1.1)[JCB2] In order to take into account the anisotropy of light scattering, while evaluating the scattering property of a tissue (as it contains a combination of organelles and cells, ranging in size from nm to ÃŽ ¼m), another scattering coefficient is defined (Cheong et al. 1990). It is called the reduced (or transport) scattering coefficient and it is equal to: , (1.2) where g is the anisotropy factor, which is around 0.9 for tissue in the Vis-to-NIR [JCB3]wavelength range. The approximation of light transport through tissue is given by the diffusion theory. Here the attenuation (a) of light is approximated per unit length d with the use of Beers law , and the effective attenuation coefficient  µeff [JCB4]is given by (Cheong et al. 1990, Oraevsky et al. 1997): , (1.3) Unlike the all-optical imaging modalities, the resolution of PAI does not suffer heavily from the scattering of photons. In fact, scattering within the tissue lead to a more homogenous distribution of photons, which can be useful for effective PA wave generation. The limiting factor that PAI shares with other optical techniques is the low penetration depth of light in tissue. Nevertheless PAI only requires the delivery of light in one direction, and ultrasonic scattering is two to three orders of magnitude weaker than optical scattering in tissue. Therefore PAI allows for high spatial resolution much deeper within tissue than all-optical imaging, and can image to much greater depths than most of the other optical imaging techniques. 2.1.2  Acoustic domain The imaging principle of PAI does not rely on the reflection of an acoustic wave, as in ultrasound imaging, but rather on the detection of an acoustic wave generated from absorption of light. The generation of PA [JCB5]waves occurs only when the incident laser pulse [JCB6]length satisfies the stress confinement condition (Xu and Wang 2006, Jacques 1993). The stress confinement criterion is satisfied when the laser pulse length is shorter than the time ( ) for the stress waves to dissipate from the region of optical absorption: ,(1.4) where, is a representative linear dimension, such as the diameter of the absorbing region or the depth of penetration of the laser beam into the absorbing region, and is the speed of sound in tissue. In general, a pulse width of 3-10 ns is used in PAI. Pulse lengths greater than tens of nanoseconds do not produce a situation that satisfies the stress confinement criterion and generates either a very week or no PA signal. Pulses much shorter than a few nanoseconds lead to the generation of weaker PA signals from tissue. The generated acoustic signals propagate radially from the source, and the amplitude of the PA wave indicates the extent of local optical absorption, while the spatial origin of the acoustic waves, which indicates the location of the absorber, can be determined by the wave shape at the body surface, as given by the time taken for each part of the wave to reach the transducer surface, after laser irradiation. The initial PA pressure generation caused due to thermoelastic expansion can be rewritten as (Oraevsky and Karabutov 2003, Gusev and Karabutov 1993) ,(1.5) where ÃŽ ² is the thermal expansion coefficient, Cp is the specific heat at constant pressure, c is the speed of sound in the absorbing object, F is the light fluence and is the optical absorption coefficient. is referred to as the Grà ¼neisen coefficient ( and H (= is the local energy deposition density. With this equation, it is possible to estimate the intrinsic sensitivity of PAl techniques, which expresses how much the pressure signal amplitude would increase, if the fluence of the laser radiation is increased by a given amount. The acoustic wave that is generated upon light absorption obeys the following wave equation (ignoring thermal diffusion and kinematic viscosity) (Tam 1986, Sigrist 1986, Diebold et al. 1991, Gusev and Karabutov 1993). (1.6) The left side of equation represents the normal wave equation where v[JCB7] is the speed of sound in the medium of propagation, P pressure and t time. The right side describes the PA source, where ÃŽ ² is the thermal expansion coefficient, Cp is the specific heat at constant pressure and H is the amount of heat generated following light absorption. H can be represented as the product of optical absorption coefficient ÃŽ ¼a and the light fluence F (. The PA wave equation (1.6) formalized above can be considered as the key formula used for the construction of PA images, whereby, a linear relation between optical absorption and the measured acoustic amplitude is assumed. [JCB1] Just like figures and talbes, all equations should be referred to in the text. Otherwise, why is the equation there? [JCB2] This is how to centre an equation. Dont use any tabs. Right justify the line, and put spaces between the equation and the equation number until the equation is centred by eye. Why have you used a really tiny font for the equation number? I recommend that you dont do this. Also, even the equations themselves in this thesis are very small. It is boarderline acceptable. Slightly larger would be better. Of course do not make the in-line equations bigger. Finally, rules of grammar also apply to equations. If the finish a sentence or represent a sentence on their own, they should be followed by a full stop. If the are followed by the continuation of a sentence then appropriate punctuation should be used. For example, when they are followed by where variable is given by symbol, then the equation should end in a comma and the word where should begin with a small w. You will find this to be copied from all the good journals and books. [JCB3] Do not use abbreviations that you have not defined. [JCB4] Be careful to make sure that all symbols are correctly italicised and subscripted as appropriate. I wont be able to correct many of these if there are more of these problems. [JCB5] Needs defining. First use is at the beginning of section 1.2.1. [JCB6] Time does not have a width. [JCB7] Do not mix symbols. You said above that c is the speed of sound.

Greek Sports :: Ancient Greece Greek History

Greek Sports Ancient boxing had fewer rules than the modern sport. Boxers fought without rounds until one man was knocked out, or admitted he had been beaten. Unlike the modern sport, there was no rule against hitting an opponent when he was down. There were no weight classes within the mens' and boys' divisions opponents for a match were chosen randomly. There were both 2-horse chariot and 4-horse chariot races, with separate races for chariots drawn by foals. Another race was between carts drawn by a team of 2 mules. The course was 12 laps around the stadium track (9 miles). The course was 6 laps around the track (4.5 miles), and there were separate races for full-grown horses and foals. Jockeys rode without stirrups. The ancient Greeks considered the rhythm and precision of an athlete throwing the discus as important as his strength.Only wealthy people could afford to pay for the training, equipment, and feed of both the driver (or jockey) and the horses. As a result, the owner received the olive wreath of victory instead of the driver or jockey. This event was a grueling combination of boxing and wrestling. Punches were allowed, although the fighters did not wrap their hands with the boxing himantes. Rules outlawed only biting and gouging an opponent's eyes, nose, or mouth with fingernails. Attacks such as kicking an opponent in the belly, which are against the rules in modern sports, were perfectly legal. The ancient Greeks considered the rhythm and precision of an athlete throwing the discus as important as his strength. The discus was made of stone, iron, bronze, or lead, and was shaped like a flying saucer. Sizes varied, since the boys' division was not expected to throw the same weight as the mens'. The javelin was a man-high length of wood, with either a sharpened end or an attached metal point. It had a thong for a hurler's fingers attached to its center of gravity, which increased the precision and distance of a javelin's flight. Athletes used lead or stone jump weights (halteres) shaped like telephone receivers to increase the length of their jump. The halteres were held in front of the athlete during his ascent, and forcibly thrust behind his back and dropped during his descent to help propel his body further. There were 4 types of races at Olympia. The stadion was the oldest event of the Games.

Leadership and Tech Final Exam

In my business there are 3 types of Leadership levels there is the lead man that's a technical expert and guides the team through it day to day operations. The there is the first level manager that gives the daily drill down of operations notes and ensures the deliverables are made.. Then the senior manager who's task is the developing the budget, travel keeping the organization fresh with the latest each, and constantly keeping a fresh vision of the organization. 64. Describe a data visualization tool and how it is used. Prize is a great data visualization tool it gives you the ability to, 1.Use visual aids to help communicate your point. 2. It helps you compartmentalize your pitch to segmented parts to build upon the chain of information you trying to convey. 3. Prize gives you the ability to use video, pictures , AR etc to help get your point across. 65. Explain the value to leaders, in using dashboards and data visualization tools. Using a dashboard is value added when compiling any type of metrics and project status. It gives the ability to have a home base of the latest data that everyone can have access to from Eng I/E, MR. , Quality, Operations.Many decisions are based on the database daily such as overtime, manpower distribution, and Eng resources. 66. In the book Progress Makers, the author uses platforms to describe a methodology for incremental transformation. Give one example of leadership transformation using this concept. Use your own thoughts and ideas to express your answer. 67. How do you become Mayor of a location? If a user has checked-in to a venue on more days than anyone else in the past 60 days, and the check-ins re valid under foursquare time and distance protocols, they will be crowned mayor.The user must have a profile picture in order to be crowned â€Å"Mayor† of that venue. Someone else may earn the title by checking in more times than the previous mayor. 68. What is the purpose of a â€Å"special† on foursquare? To g ive the users of foursquare incentives to update data and give them a perks such as coupons for restaurants or apparel shops. Essay 69. (1 0 pits) Describe the difference between leadership in the classic sense and leadership as it relates to the field of technology? Why is it different? The rotational leadership model may include a top down method, which may be antiquated but functional, and gets the job done.The manager will ask the team for certain deliverables and really have no idea of how the deliverable is made and what it takes to get it done. And as long as you have a good team making the deliverables a leader might be able to survive, depending on the strength of his or her team. Technology has changed the nature of classic leadership in some ways, providing some additional challenges. For instance, working in the technology field, a leader must stay current with the latest and greatest technology or his r her group will lose vision and be behind the curve of technology ve ry quickly, rendering them out of date.

Privacy Ethics - 1207 Words

Privacy and ethics have become somewhat of a lost art. Two things we as Americans used to hold as part of our highest core values. However, now it appears as though privacy has become a thing of the past and ethical behavior is just something you hear about once in a while. It seems as though little by little pieces of ourselves are being chipped away, and we are standing by allowing it to happen. We continually allow our privacy to be invaded on a daily basis by our smartphones, social media, and many other outlets that we try to connect ourselves to just to attempt to feel as though we are alive? That is just a small piece on a colossal scale of privacy and ethical issues we face. Look at the Edward Snowden case and how he put the†¦show more content†¦A Congressional Research Service report, for example, notes the worry that drones â€Å"will be used to spy on American citizens,† and asserts that, â€Å"[Undoubtedly, the government’s use of drones for domestic surveillance operations implicates the Fourth Amendment and other applicable laws† (Blitz, 2015, p.65). Once again, this is always going to be up for debate due to the ethics of it all. If you consider the capabilities of the technology out there a lot of lives could be saved if we used the technology in place of human lives to go into dangerous situations. â€Å"A number of newer technologies enable sense-enhancement or super- human-like powers. Infrared sensors, heat sensors, and new powerful radar systems all allow people (mainly police) to â€Å"see† through walls. Facial recognition and automated license plate readers enable the large- scale capture of information, tracking of individuals and their vehicles, and correlation of that information with information housed in massive databases.† (Kaminski,2015, p.1119). Allowing law enforcement the tools to conduct thorough searches without having to places themselves in the line of fire is an excellent idea. I am all for giving them the capabilities to do so. The biggest issue now is making sure all of the drone use is covered legally, therefore, â€Å"state governments are scrambling to address the regulatory issues that these drones raise. Issues of privacy and government overreach areShow MoreRelatedThe Ethics Of Commercial Privacy1654 Words   |  7 PagesThe Ethics of Commercial Privacy In â€Å"The Right of Privacy,† Richard Posner argues that, â€Å"the law should in general accord private business information greater protection than it accords personal information. 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