Factors Affecting Contrast In An Xray Image Health Essay

Factors Affecting Contrast In An Xray Image Health Essay To test resolution, a line pair guage is used. To measure MTF in an x-ray system, the sine wave equivalent of a line pair gauge is used. The closest distinguishable pair of cycles determines the best MTF, it is quoted in cycles per mm [2]. A common way to express the system resolution is to quote the frequency where the MTF is reduced to either 3%, 5% or 10% of the original height [3]. MTF and spatial frequency are related by MTF curves. Examples of MTF curves are given below; Mammography System: Fig 2: MTF curve for a mammography system [4]. Chest Radiography System: Fig 3: MTF curve for a typical chest X-ray. Three different detector types are indicated on the plot [5]. Fluoroscopy System: Fig 4: MTF curve for a Fluoroscopy system with plots shown for individual components of the imaging process. The film and the optics have excellent resolution. The MTF of the imge intensifier is shown to have a limiting resolution of approximately 4.8 cycles/mm. The TV camera is the worst in the series, it limits the MTF of the overall image during live fluoroscopy and videotaped imaging. [6] Question 2: Contrast is the variation in brightness or optical density across an image. Factors affecting contrast in an x-ray image include the tube output, or the kVp. This is a measure of the energy of the x-ray beam leaving the x-ray tube and passing through the patient to form an image. X-rays with higher kVp can penetrate deeper into materials. In an image with the correct kVp bone is white and soft tissues and air are gray/black. If the kVp is too high, the x-rays will pass through even dense bone, creating an image that is mostly black with indistinguishable features [7]. The opposite occurs when a kVp which is too low is used. The most suitable kVp depends on the feature under investigation. Also among the factors affecting the image contrast is the patient. The density, the atomic number Z and the thickness of the part of the patient being imaged. Denser tissue, tissue with higher Z or tissue of a greater thickness results in lighter areas on the image because they have blocked the x-r ay from exposing the image receptor. Variation in contrast occurs because tissues in the body attenuate x-rays differently. The human eye can percieve a difference of approximately 2% in contrast between adjacent areas [8]. The final influence on image contrast to be discussed here is the image receptor. In film imaging, the contrast of the resultant image depends on the sensitivity of the film used. To produce an image with the correct contrast, a film with corrresponding sensitivity must be chosen before imaging. In digital imaging, there is no fixed sensitivity. It has the advantage of being able to record the full range of exposures and digital processing after imaging can be used to improve the contrast in the image. Image contrast can be evaluated using a densiometer. This device emits light of a known energy. The light is reflected back from the image and detected by the densitometer. The difference in energy between emitted and detected light is used to compute the optical density (blackness) in that area. Since contrast is the variation in optical density, this method can be used to survey the contrast in the image. Question 3: The following description is based on an article from the NDT database [9]. Spatial resolution of an x-ray system is limitied by the size of the focal spot. Fourier analysis can be used to calculate the focal spot size. X-rays are passed through a test object with a known pattern. This test object is placed between the x-ray source and detector, the arrangement is shown in the figure below. The focal spot of the x-ray is not assumed to be point-like, as the detector is moved away from the source, the detected focal spot appears larger. Blurring of the image by the detector is included, this blurring is related to the point spread funtion (psf) of the detector. Otherwise, an ideal detector is assumed. Image deterioration due to noise is also factored into the description. Fig 5: Setup for determing the focal spot size. The X-ray source, the flat object, and the intensity distribution measured at the detector system lie in different planes for which different coordinate systems with the variables (x, y), (x, y) and (x, y) respectively, are used. This is done in order to include magnification effects in the calculations. The measurement of the x-ray transmission, t, is derived mathematically. This is done by convolving the intensity distribution of the focal spot f with the transmission profile of the flat object g and the detector point spread function d. Also, t is deteriorated by noise, which is taken into consideration by addition of a noise term n to the result of the convolution. In order to take into account the geometrical magnification, V, of the setup, these functions are represented in one of these planes (here the plane of the detector), whereby the physical magnification effects of the setup were observed before the convolution is accomplished, this is shown in the second part of the equation below. The magnification is the distance between the source and the detector system divided by the distance between the source and the object. The Convolution Theorem states that the Fourier transform of a convolution is the product of the Fourier transforms. Conversely, the Fourier transform of a product is the convolution of the Fourier transforms. Using the above equation, a deconvolution of t with gâ‚ ¬Ã‚  (â‚ ¬Ã‚  d yields an estimate of f. In a technique like this, a suitable test object is measured. The resulting image corresponds to a convolution of the test object with the intensity distribution of the focal spot and other factors. Information on the focal spot is derived from this measurement using knowledge on the test object and other influencing values which means that the convolution process is undone to a certain extent. Also, with the presented method an arbitrary two dimensional intensity distribution can be measured, regardless of shape. According to the convolution theorem, a convolution in the spatial domain corresponds to a point-by-point multiplication in the corresponding Fourier domain. Furthermore, according to the addition theorem, an addition in the spatial domain corresponds to an addition in the corresponding Fourier domain. (Note: lower case letters represent functions and upper case letters represent the Fourier transforms of the equivalent functions.) The initial equation now becomes; At certain spatial frequencies | N | can be significantly higher than| F Æ’-â‚ ¬Ã‚  P |. At these spatial frequencies division of T by P mainly increases noise and deteriorates the image quality. This is due to the fact, that information on F is lost at these spatial frequencies. For that reason, independently of the deconvolution method applied, all spatial frequencies which are contained with high intensity in | F | should be contained with high intensity in |P| in order that | FÆ’- P | is significantly larger than | N |. This means that the test object (in combination with the detector imaging properties) should contain the major spatial frequencies which are required to describe the focal spot with sufficient intensity. In this case F can be restored well at these spatial frequencies, which yields a good estimate of f. Question 4: Using a bar phantom similar to that used for determining resolution can lead to an error determining the focal spot size. This is because the line pairs are aligned in one direction only. For accurate measurement of the focal spot size, many images with the bar phantom at different angles would be necessary [10]. To overcome this problem, a star phantom is used. This is a disc of alternating Lead spokes and x-ray transparent material. At a particular diameter of the focal spot the image of the spokes blurs, i.e., adjacent spokes cannot be distinguished from each other. The diameter of the blur is an indication of the focal spot size [11]. Fig 6: Star pattern for testing focal spot size [12] Question 5: 5a. The most obvious parts of a CT scanner are the moving patient table and the gantry or tube. Conventional projection radiography is limited because it collapses 3D objects onto 2D images. CT has a rotating system of emission and detection and so it can give accurate 3D diagnostic information about the distribution of structures inside the body. Inside the gantry there is the X-ray tube, x-ray detectors and slip-rings. The X-ray beam is collimated and radiates in a fan-beam shape. The x-ray emitter and detectors rotate in the gantry to measure projections that form an image that is a slice though the body. There are brushes around the rotating slip-rings to transmit signals. In CT, the linear attenuation coefficient, ÃŽÂ ¼ is measured. This tells how much intensity is lost as the beam travels through the medium. This distribution of ÃŽÂ ¼ is the basis of image formation. There are two distinct motions of the x-ray beam relative to the patients body during CT imaging. One motion i s the scanning of the beam around the body. The other motion is the movement of the beam along the length of the body.   This is achieved by moving the body through the beam as it is rotating around Fig 7: External appearance of a CT scanner. [13] Fig 8: Basic schematic of the construction of a CT scanner. Fig 9: CT image quality and electromechanical acceptance tests. The Priority column indicates which of the tests are the most important. [14] 5b. CT images are formed by multiple intersecting projections. This is illustrated in the figure on the left. In the bottom right section, it is seen that the combination of the projections causes blurring in the final image. The blurring goes as 1/r, i.e., it is proportional to the distance from the centre point. The 2D Fourier transform of 1/r is 1/à Ã‚ . Since the inverse of 1/à Ã‚  is |à Ã‚ |, it is possible to compute the 2D Fourier Transform of the blurred image, multiply the Fourier transform of the resultant image by |à Ã‚ | and the calculate the inverse Fourier transform to obtain a sharper image [15]. Fig 10: On the left, unfiltered back projections and on the right, filtered back projections. The conversion is done in the spatial domain by convolving the projection with the IFT of |à Ã‚ |. Fig 11: The mathematics of the image reconstruction process, can be expressed compactly in the above equation, where the terms have been grouped to reflect the filtered-back-projection approach [15]. 5c. The fundamental system performance indicators are CT number, resolution, noise, and patient dose.26 The accuracy of CT numbers is measured by scanning a water-filled phantom at least monthly. The CT number for water should be zero over a 20-cm-diameter phantom, with a variation of less than 1 CT number. Deviation from the expected CT number of 0 for water at any energy is adjusted by applying a correction factor for the pixel value. Constancy of the value should be monitored with a daily scan. An overall check of system performance is obtained from semiannual measurements of CT image noise, defined as the standard deviation of CT numbers in a region of interest. Constancy of performance is checked by evaluation of the standard deviation in the daily water scan mentioned previously. Resolution is measured by scanning phantoms on a monthly basis. Of particular importance is low contrast resolution, which is a sensitive indicator of changes in component performance as they affect noise. Patient dose is evaluated semiannually. Specially designed ionization chambers provide measurements from which the dose may be calculated for the exposure conditions (narrow beam, variable slice thickness) used in CT. The values should agree with manufacturers specifications to within 20%. [hendee]

Did the Nazis solve Germany’s economic problems from 1933 to 1939?

Between 1933 and 1939 Germany suffered economic problems. The main economic problems were Germany was dependent on the foreign market and the imports, the industrial production, unemployment, the cost of living and wages. Hitler and the Nazis tried to solve the problems, they were successful but there were hidden factors to each solution. Firstly unemployment was a problem because it had risen to over six million by 1933 and that was 25. 9% of the country. With people out of work the standards of living dropped. By 1939 Hitler had reduced the number of unemployed, it was now just above three hundred thousand, which was 0. 5% of the country and thanks to one of Hitler's schemes to reduce unemployment, new roads had been built. Hitler reduced unemployment by introducing the autobahn scheme, which created many jobs for men as the Nazis were aiming to build over 7000 km of road. Hitler also continued with the national labour service, which became compulsory for German men between 18-25 years old. The men had to work on public works schemes such as land reclamation, tree planting, construction and road building. The schemes seemed to work, removing thousands of young men from the unemployment figures. The schemes appeared to be working but the results were that the unemployment figures hid a lot, such as the impact on women and Jews. The loss of rights for workers because trade unions were banned. There was no negotiation of wages and there was no right to strike. The national labour service was temporary and there was low wages for those who joined. The autobahn was actually part of war plans. The next problem was that Germany was too dependent on the foreign market and its imports. Hitler felt that Germany was too reliant on the foreign imports, which he felt made Germany to venerable and Hitler wanted to stop the need for the foreign market. Hitler's solution to this problem was â€Å"Autarky†. Autarky was the creation of artificial substitutes (using ersatz) for products such as oil, textiles, food and rubber. The effect of Autarky was ersatz materials. These were developed, produced and ordered. The increase of ersatz made Germany more self reliant but it was still not totally reliant, as Germany continued to import 33% of its raw materials and 17% of its food. The result of Autarky was ersatz was a complete failure because they were inferior products. Ersatz contributed to the decrease in living standards for German people. The third problem was the industrial production of Germany. Due to high unemployment, many factories were closed down. This meant that production was at a low level and by 1933 the production of goods ad fallen by a third since 1929. Between 1933 and 1939 the production in heavy industry increased largely. Coal and chemical production doubled, oil, iron and steel production trebled and iron ore extract production increased by five fold. Consumer goods were not as important so they were produced at a slower rate. Hitler managed to increase production by firstly introducing autarky. By doing this it enabled the country to become more self sufficient for wartime production. Hitler began rearmament, which opened up job opportunities both in the factories and the army. Rearmament helped to reduce unemployment levels. Hitler's other solution was to increase working hours. In 1933 on average, per week, working hours were 42. 9 but had increased to 47. 0 in 1939. This meant that production increased. The result of Hitler's solutions was Germany became more likely to start war. The next problem was the issue with wages. The problem was that because of the high unemployment, employers had lots of people wanting jobs, so they could offer low wages and people would have to accept them. This lead to the working class not having a very high standard of life. Hitler's solution was to get rid of local and national wage rates and introduce performance principle. This scheme meant that the more work a person did the more money they earned. The effect was that the real value of take home pay increased and longer working days let people gain more money. The positive result of Hitler's solutions was that the quality of life got a little bit better for a majority of the working class. The negative results of Hitler's solution were it didn't suit older people and less fit people, as they could not work as long as others. Sickness and absenteeism increased meaning people didn't earn money. Longer working days and hours meant people do not have much energy to work and trade unions were taken away, which gave the people little rights. The last problem was the cost of living. The problem was that everyday items were too expensive because of the average pay; there was not enough money. Hitler did nothing about this problem because he wanted to keep the support from the farmers. The effect from this problem was the cost of living in 1939 had increased since 1933. All basic groceries, except fish had risen in price. This was because food items were in short supply and it was the Nazis policy to discourage agricultural production because it had to keep up prices for the benefit of farmers. The result was the standard of living was very low for most Germans, mainly the working class. Hitler did manage to solve most of Germanys economical problems but it was not entirely down to Hitler and the Nazis. Before Hitler can chancellor in the early 30's, the Weimar government was in power and this was during the 1920's depression. After the 1920's depression, the German economy was starting to recover, the worst of the depression was over, unemployment was decreasing and inflation was going back to a suitable amount. With the economy going back to normal the Weimar government started to set up new schemes to help solve all the problems. The Weimar government set up the national labour service, but Hitler improved it by making it compulsory to join in 1935 and the Weimar government also came up with the autobahn idea but lack of money in the 20's meant it could not go ahead but in 1934 Hitler had enough money to start the construction of the autobahn. So although it may have seemed that Hitler came up with these ideas and solved the economical problems he didn't, he made the Weimar governments ideas better because he had the money to do so. When Hitler was came into power there was a worldwide recovery happening after the depression and in Germany. This factor led to an increase in production, which helped solve one of the economical problems in the early 30's in Germany. Hitler's solution did bring about some improvements such as the fall in unemployment, new roads and German citizens having a slightly better quality of life, but there were a lot of hidden and negative factors to these improvements. Women could not work nor the Jewish, so there standard of living dropped, a lot of the improvements were for the war effort, not the country, the autobahn, rearming and conscription were part of the war effort and trade unions were abolished meaning workers had no or very little rights. This was all part of Hitler's plan for dictatorship. Another factor was most of these solutions were not long term and Hitler hadn't really thought about the consequences because the standard of living was still going down, there was still food being imported and the working hours were getting longer.

On the Sidewalk Bleeding Monuloge Essay

All I feel is the excruciating pain entering my aching body. The irritation and agony makes me feel defenceless. I have a multitude of varied thoughts racing through my confused mind. As I am helplessly laying on the cold, wet concrete, with the rain drilling down on me, I am thinking if this is how I am going to die, my life over at the age of just 16. I can think back and faintly remember someone saying, â€Å"that’s for you royal!† and just thinking to myself, if I was not wearing this stupid jacket that I once thought was so important, I perchance wouldn’t have even been in this discomforting situation. All I can do at this point is helplessly lay here praying for someone to find me. Then finally I take a great effort and look over to the end of the street though the rain blurring my vision and see the bright neon lights of a vehicle binding me. I feel a massive relief, I see two figures coming toward me I try to yell again but they seem to just be talking to each other. I want to get their attention but all the sound I can make is the bubbling of blood filing my mouth, as if I am drowning in my own vital fluid. It sounds like the grunt of an animal and that’s the only sound I am capable of making in this state. I start to panic because the people aren’t recognising that I am there, after I tak e all my energy and frustration to get their attention they look at me for a little then they mutter to each other, I can’t understand much they are mumbling about. I just feel powerless hoping he will make the right decision and just get a cop or hep me. He looks at me, my cut body and the rain soaking my purple royals jacket. He sympathetically says, â€Å"Sorry royal,† and walks away. At this very moment I feel frustrated, overwhelmingly confused with anger and abundance. Is it that big of a deal that I am a royal? I am not just a royal, I am Andy. I feel drastically judged and labelled. Right now I will do anything and everything I am physically capable of just to take this jacket off, the only thing that jacket ever did to me was rob me of my life.

Ethical Codes Across Cultures Ethics - 774 Words

Ethical Codes Across Cultures According to Abiodun and Oyeniyi (2010), ethics addresses issues of good and bad and with moral issues and duties. Ethics sets rules of conduct in place in the hopes of providing guidelines for human behaviors focused on the preservation of a society. In the United States, National Conference of State Legislatures (NCSL) has put instruction or guides specific to restriction for legislators in relation to restrictions on gifts from lobbyists to legislators. Some states are more specific and prohibit gift giving with exceptions. This writer is of the opinion, the exceptions are where the â€Å"S† is taken out of stretch. I will use the example of Washington, DC council member Michael Brown, who pled guilty to bribery that totaled $55,000. According to NCLS, money and or gifts in excess of $100 value should not be given and or solicited by/to any registrant or anyone acting on behalf of a registrant should give any unauthorized contribution. In essence, if the money is to influence and or gain an advantage of the legislator it is in violation. The lack of adequate disclosure for a public campaign solidifies the act as unethical and unlawful. In the case of Mr. Brown, he disguised money given to him from businessmen who wanted to be guaranteed federal contracts, a direct violation of DC campaign finance law (Press Release, 2013). 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