The new meaning of Quality Essay Example | Topics and Well Written Essays - 1250 words

The new meaning of Quality - Essay Example If we see the size of operations at Sainsbury's meting these attributes consistently is a big challenge . Over the years the business and organizational environment has increasingly become more and more complex. There has been an explosion in choices, options, opportunities and threats, requirements, data and information through IT systems. Organizations have understood the hidden cost of quality, errors, inventories associated with inefficient supply chain. These factors have led to the emergence of a new discipline of supply chain management. A supply chain is essentially managing the journey of inputs to the outputs along with all the associated activities having impact on cost, speed and quality of the output through the journey. Ganeshan & Harrison in their paper explains how traditionally there has been organizations within organizations, silos of functions / departments, each one having their own characteristic goals, many a time at conflict with the organizational goal, resulting in an inefficient supply chain marked by interface problems. The result of these factors is that there is not a single, integrated plan for the organization. Supply chain addresses these issues effectively. Coordination between the various players in the chain is key in its effective management. Cooper and Ellram [1993] compare supply chain management to a well-balanced and well-practiced relay team. Quality begins and ends with customers For any Quality Management System, customer requirement is the input and customer satisfaction is the desired output. The entire quality movement is based on simple but elegant Deming's PDCA cycle. First step in the quality journey is capturing customer requirement followed by design / modification of functions/systems for deployment and continuous improvement of the same through repetitive cycles of feedbacks. The customer experience is captured at Sainsbury's through well-placed mechanisms. Customer Insights group carries out the work of obtaining the true customer requirement by interacting with more than 4000 customers every month which includes obtaining the performance of competitors also in the area of customer satisfaction. Besides the regular channels of obtaining customer perception there is another mechanism to find out customer requirement, which involves trained auditors capturing the customer experiences in the store itself. The practice of interviewing customers in their homes is yet another valuable source of customer expectation determination. The information captured through these mechanisms form the inputs for the Quality Management systems and other operational instruments for delivering the quality products and services to the customers. Supply Chain Transformation at Sainsbury's for improving delivery of quality Sainsbury's had witnessed more than 100 years of successful operations and established itself as market

BUSINESS D M Essay Example | Topics and Well Written Essays - 500 words

BUSINESS D M - Essay Example All members of the team also agreed on most fundamental point that selected site should have maximum business potential otherwise no sensible promoter will ever risk their funds in a private venture. While doing strength and weakness analysis of each sites by group members following points emerged for each sites. Strengths Weaknesses Site A Site B Site C Plenty of land available Politically quite suitable site Semi-skilled and unskilled workers are available plenty. Most profitable site for business Professionals will love to live here Skilled professionals are available Plenty of the land available for the project A ‘mid cost’ site Not enough housing facilities Professional staff would not like to move here A lot of amount required to be spent on clean up and sterilization Not having enough business potential Protected wild life site Media is against in selection of this site Political activists oppose this site Road conditions are dismal Parking is an issue at this sit e Transport link would take huge budget The group members agreed after deliberations on the following main criteria/objectives of the hospital project that must be fulfilled while selecting the site and they are listed as per the following. 1.

The Money Game Book Report Essay Example | Topics and Well Written Essays - 2500 words

The Money Game Book Report - Essay Example I began considering to have a â€Å"budget† and decided to put off some planned but unnecessary purchases. I just opened a savings account with a passbook dedicated for future investment. The course affected me and I would like to answer the questions below with how I understood the subject except on some occasions that it will be best for understanding to lift something from the book. I believe it will best serve the purpose of this course to use my own words as much as possible and also for my better understanding, to conceptualize my answers as I understood it. B. Questions for Book Report 1. Why is the book called â€Å"The Money Game?† The book is called â€Å"The Money Game† because it teaches us to understand the dynamics of how to secure our future from a pragmatist perspective. When I said, pragmatist, it tackles the subject not merely from academic point view, but on its real life application. Moreso, when it also presented the perspective of the both s ides of the coin, the Wall Street view and the Main Street with the author being partial on us the consumers on how we could avoid the financial pitfalls and better secure our future by giving us a hindsight about the other side of the fence. The author has no pretension about the reality on how we should go about in handling our finances, especially in dealing with financial institutions inorder to be financially secured. In fact, a game plan was introduced called Big Dog Playbook II which details the play on we can better our financial position and get rid of debts. 2. Why do many Americans die before they ever have a chance to live? Many Americans die before they ever have a chance to live because they work all their lives and never had the chance to enjoy it. This is because of wrong mindset and priorities and being unprepared for the financial uncertainties and old age. During the most productive part of their lives, they worked so hard to acquire the â€Å"bling-blings† or facade of success and thus raising the standard of their lives but not the actual quality of their lives. They are so mired with work that they did not notice how good the â€Å"rose smell†. As they acquire, they fall to the trap of indulgence, living for today (and more often than not, beyond their means) and not preparing for tomorrow. Such that when financial uncertainty and/or retirement come upon them, many of them are caught unprepared and had to continue working despite retirement age. 3. Who are the three main characters in the book and what impact do they have on your finances? The Invisible Man- The Invisible Man represents the unaccounted expenses that we don’t usually notice because they are just small. But when they are totally accounted for, we will be surprise to learn how much they add up so quickly. The real danger about the Invisible Man is that we do not know that he is already taking toll on our resources. The Money Monster – The Money Mo nster represents our tendency to consume; our endless wants that could never be satisfied. This Money Monster is insatiable and will continue to eat our resources no matter how we much feed it. If we do not tame or put the Money on a diet, we will always be on spending binge without any savings with a mounting debt to surmount. The Precreditor- â€Å"The Precreditor has a growing appetite for our money and will influence law to keep the gravy train going. His hunger has manifested into hundreds of billions of dollars in opportunity cost for consumers

Globalization, as the world has experienced it since the 1970s, has Assignment

Globalization, as the world has experienced it since the 1970s, has been rooted in neoliberal policy. Discuss alternative frame - Assignment Example As Jessop notes, neoliberal doctrine emerged as a dominant ideological force due to the convergence of progressive trends of economic internationalization, the apparent failure of Keynesian welfare state, East Asian developmentalism and Soviet model of central planning; and the emergence of new social forces brought about by the former developments (Jessop 105). The neoliberal theorists seem to proceed from the same assumptions that social liberals take for granted; they proclaim their commitment to a basic right of individual autonomy and assert that the basis of modern society should consist of wide variety of voluntary associations independent from the state control. Nevertheless, neoliberals take the common idea of all liberal thinkers about the necessity of expansion of market economy (Jessop 106) to its extreme limits, arguing that all social relations should be evaluated from the point of their compatibility with the freedom of market transactions. This includes an emphasis on deregulation of the financial markets both in domestic and international spheres; the ideological commitment to the curtailment of state intervention in the capitalist market economy; the introduction of the principle of market efficiency into the sphere of public welfare; and the commitment for the privatization of public enterprises and services (Jessop 107). The cities and city regions are especially affected by the neoliberal project of globalization. The dramatic restructuring of urban communities that began in the 1970s to 1980s led to the increasing marginalization of the relatively numerous swathes of the urban population caused by the drastic rise in unemployment (Swyngedouw, Moulaert, and Rodriguez

USA and Vietcong forces in the 1960s. Essay Example for Free

USA and Vietcong forces in the 1960s. Essay The tactics used by the Vietcong and US military forces were very different and changed during the course of the war. At the beginning of the war the Vietcong (NLF) army was aggressive whilst the US army was defensive. The Gulf of Tonkin incident became Americas excuse to become aggressive towards the Vietcong. In 1965 General W. Westmoreland developed the strategy of search and destroy. Its objective was to find and kill any members of the NLF. US soldiers found this difficult however as the Vietcong always dressed in civilian clothing, and killing peasants by mistake was not uncommon; if hes dead and Vietnamese, hes a V. C. was the view of the troops carrying out the search and destroy missions. It was clear from the outset of war that the US had far more technologically advanced weapons than the Vietcong, which they used throughout the conflict. B-52 bombers altogether dropped 8,000,000 tons of bombs between 1965 and 1973which equated to 300 tons of bombs per person living in Vietnam. This was over three times the amount dropped during the whole of World War Two. Aside from bombs the US also dropped a considerable amount of napalm, a mixture of petrol, phosphorous and a chemical thickener which attaches itself to the skin causing horrific fifth-degree burns to the victim, which could quite often be an unlucky US soldier. Agent Orange, a complex biological weapon was dropped over a lot of the thick vegetation of Vietnam, causing all plant life to die, potentially to expose any hiding Vietcong. The US pioneered the development of anti-personnel bombs, smaller than those dropped from the B-52s, such as the pineapple, which shot shards and needles of metal in all directions. With the many different developments of anti-personnel bombs it was the USs aim not to kill the North Vietnamese but to injure them badly. It cost the Vietcong worse in time and resources to help the injured, whilst dead simply needed burying. Ironically, the Vietcongs supply of explosives for mines and suchlike mostly came from the 800 tons of US bombs that were dropped every month which failed to explode. In order to counter the powerful and technologically-advanced US army, the  Vietcong employed guerrilla tactics which had been used to great effect in Mao Zedongs victory in winning China for communism. The Vietcong were split into small groups of between three and ten soldiers, known as a cell. Cells worked together but knowledge between them was kept to a minimum so that if the cell or part of it was captured and tortured, any confessions made would not damage the Vietcong side very much. The cells, who dressed in civilian clothing, would move between South Vietnamese villages winning the support of the NLF from the villagers. They would help the peasants, not do anything against their wishes and educate them on poverty and other issues, in exchange for food, political and sometimes even military support. To defeat the more powerful enemy, a guerrilla has to dictate the terms of warfare to its advantage. The Vietcong chose the setting of the borders of the thick dense forests of South Vietnam as ambush was very easy. Another of the technical advances on Americas side was the realisation that the helicopter could directly bring the troops straight into the heart of the battle and get them out again quickly. However there was a massive risk related to this. Once the US had decided on a landing area for the helicopter it was not difficult for it to be shot and destroyed by the Vietcong even in the few seconds it was touching the ground. After the troops had been dispatched they would be surrounded on most sides by an invisible enemy hidden in the forest, making the USs task a nightmare. It was not that the Vietcong and NLF leaders did not care that thousands of their soldiers were being sent into battle and being killed. It is that they had the will to continue doing so until the US gave up. Physical losses to the US were not as great as those losses from the American persons view of the war. This I will explain in the next and final question; Why was there such different reactions in the USA to the countrys involvement in the conflict in Vietnam in the 1960s.

Parkinson Disease Essay Example for Free

Parkinson Disease Essay Parkinson disease is a gradually progressive degenerative disorder of the central nervous system. Parkinson disease belongs to a group of conditions called movement disorders. There are four characteristic problems caused by Parkinson disease, including tremor at rest, balance problems, stiffness, and slowness of movement. Parkinson disease occurs when areas of the brain, including an area called the substantia nigra, is slowly destroyed. The exact reason for this destruction is not completely known. In some patients, it may be due to genetic, environmental, or a combination of both causes. The end result is a deprivation in the brain of an important neurochemical, called dopamine. Dopamine helps regulate movement, and its loss leads to increased tone, rigidity, and slowness of movement. Lack of dopamine results in the symptoms associated with Parkinson disease . Approximately 50,000 Americans are diagnosed with Parkinson disease every year. 95% of those diagnosed are over 50 years old. At any given time, about 500,000 people, or 1% of those over age 50 in the US are struggling with this condition. Diagnosis of Parkinson disease is a clinical one, based on history and physical examination. There are no lab tests to definitively diagnose the condition. Your doctor will ask about your medical history and perform a thorough physical exam. A systematic neurological exam will include testing your reflexes and observing things like muscle strength throughout your body, coordination, balance, and other details of movement, including: * Muscle tone Rapid alternating movements * Gait, posture * Postural stability * Quickness and precision of movement * Observation of a tremor (during rest or activity) A mini mental status exam will be performed; questions pertaining to mood, thoughts, and behavior will be asked. Activities of daily living will be evaluated, such as dressing, cutting and eating food, swallowing, hygiene, walking, and falls. The exact cause of PD is unknown. It may have both genetic and environmental components. Some scientists think that viruses can trigger PD as well. Low levels of dopamine and norepinephrine, a substance that regulates dopamine, have been linked with PD. Abnormal proteins called Lewy bodies have also been found in the brains of people with PD. Scientists do not know what role, if any, Lewy bodies play a role in the development of PD. Certain groups of people have an increased risk of PD. Men are one and a half times more likely to get PD than women. Whites are more likely to get PD than African-Americans or Asians. PD usually appears between the ages of 50 and 60. It only occurs before the age of 40 in five to 10 percent of cases. People with a family history are more likely to develop this disorder. The four major motor problems seen in PD are: * tremor—shaking that occurs at rest * slow movements * stiffness of arms, legs, and trunk * problems with balance and tendency to fall Secondary symptoms of PD include: * blank facial expression * a tendency to get stuck when walking * small, cramped handwriting * muffled, low-volume speech * decreased blinking and swallowing * tendency to fall backwards * reduced arm swinging when walking Other, more extreme, symptoms of PD are: flaky white or yellow scales on oily parts of the skin, known as seborrheic dermatitis * sleep disturbances—including vivid dreams, talking, and movement during sleep * depression * anxiety * hallucinations * psychosis * problems with attention and memory * difficulty with visual-spatial relationships There is no specific test for PD. Diagnosis is made based on health history and a physical and neurological exam. Tests such as C AT scan or MRI may be used to rule out other conditions. Adequate rest, exercise, and a balanced diet are important. Speech therapy, occupational therapy, and physical therapy can also help to improve communication and self care. Surgical interventions are reserved for people who don’t respond to medication, therapy, and lifestyle changes. So are procedures such as deep brain stimulation (DBS). In almost all cases of PD, medication will be required to help control the various physical and mental health symptoms associated with the disease. Drugs and Medication Used to Treat Parkinson’s Disease | Medication A number of different drugs can be used to treat PD. Levodopa Levodopa is the most common treatment for PD. It helps to replenish dopamine. About 75 percent of cases respond to levodopa, but not all symptoms are improved. Levodopa is generally given with cardiodopa. This delays the conversion of levodopa to carbidopa until it gets into the brain. Dopamine Agonists Dopamine agonistscan imitate the action of dopamine in the brain. Dopamine agonists are less effective than levodopa. However, they can be useful as bridge medications when levodopa is less effective. Drugs in this class include bromocriptine, pramipexole, and ropinirole.

Uniformity of gamma camera images

Uniformity of gamma camera images Introduction In 1958, Hal Anger developed the first ?- camera and forever changed the area of nuclear medical imaging. Angers camera (also known as scintillation camera or gamma camera) used a 6 mm thick scintillation crystal (NaI) coupled to seven photomultiplier tubes (PMTs), each 3.5 cm diameter, arranged in a hexagonal shape. The crystal was used to convert the gamma rays into scintillation photos which would then be converted into electrical signals by the PMTs. The output of the PMTs in Angers camera was analogue and represented continuous values of gamma ray energy and the position of the event. The camera had a collimator mounted in front of the sodium iodine crystal, which was used to stop scattered gamma rays and essentially form the image. In the initial design of the gamma camera all the circuits were analogue and the camera is still known as an analogue camera. The images were displayed in cathode ray tubes (CRTs) or they were imprinted onto photographic films which were used as hard copies.   Ã‚  Ã‚  Ã‚  Ã‚  Ã‚  Ã‚  Ã‚  Later on, with the development of electronics and computer technology, the analogue output of the photomultiplier tubes would be fed into a digital computer which would process the signals to form the clinical image. In order to achieve that, analogue to digital converters (ADCs) were incorporated into Angers design which would digitize the signals before feeding it to the processing unit. Gradually all the major electrical components of the gamma camera were replaced by digital electronics and in modern cameras the signals are digitized by ADCs installed individually in every PMT. The complete digitization of the gamma camera allowed for significant improvements of the prototype gamma camera. With the increased processing power available, modern gamma cameras can nowadays image at high count rates, can store digital images and display them directly onto computer screens. Furthermore, they can implement a range of corrections which have drastically imp roved the quality of the modern clinical images. Our objective in this essay is to describe the factors that affect the uniformity of gamma camera images, the technological advancements that have improved the cameras imaging quality and capability as well as the methods that are currently used to assess and correct a ? cameras uniformity. The basic components of a gamma camera and their function The general principles behind the function of a gamma camera are rather simple to understand. So, before we proceed onto discussing the uniformity of a ?-camera, we ought to mention its basic components and their function since they can affect image uniformity. The main components of a gamma camera are described below. The gantry of the gamma camera provides mechanical support to the detector head. The scintillation crystal [usually NaI (TI)], is maybe the most important component of gamma camera. Its function is to convert the incident gamma rays, originating from the patient, into scintillation photons. Between the crystal and the photomultiplier tubes, a transparent light guide is put in place to maximize the optical transmission of light from the crystal to the PMTs. Once the scintillation photons reach the photocathodes of the PMTs, they get converted into photoelectrons. The photoelectrons then, go through an amplification stage where their number is multiplied by a series of dynodes. Finally the electrons hit the PMTs anode and we get the output voltage that represents our signal. The photomultiplier tubes are connected to the pulse arithmetic circuits where the position and the energy of each event are determined. In addition, at the PMT output, gamma cameras incorporate a pulse height analyzer that determines which events get accepted based on their energy. This mechanism is put in place in an effort to reject signals arising from scattered photons that have managed to penetrate the collimator. The pulse height analyzer is also known as the energy window. The energy window is usually set to accept events with energies ranging from -10% to +10% of the peak energy. For example, when imaging with 99mTc (? emitter, 140 KeV, T1/2 = 6 h) the energ y window is set between 126 KeV and 154 KeV. The final component of the detector head of the gamma camera is the collimator. It is a lead plate with a large number of holes which is placed in front of the scintillation crystal. The main function of this component is to control which of the gamma rays pass through to the crystal and which ones are stopped. Gamma rays that travel parallel to the collimators holes (perpendicular to the crystal) are allowed through while oblique rays are attenuated. The role of the collimator is essential because it provides the PMTs with the ability to identify the location of each event and it stops scattered x-rays which spoil the contrast of the images. In addition, the collimator provides physical protection to the extremely sensitive and fragile scintillation crystal that lies beneath it. Camera Uniformity The term uniformity refers to the variations of intensity present in an image acquired using a uniform radioactive source. Factors that affect ? camera uniformity In the previous section of this essay we described briefly the function of the gamma camera. In reality however, things do not work perfectly. In fact there are numerous sources that can cause image imperfections and ruin the uniformity of our images. The most common sources and factors that affect image uniformity are: Collimator defects variations in hole size and angulation variations in septal thickness Crystal and light guide non uniformities in the crystals stopping power non uniformities in the number of scintillation photons emitted by the crystal non uniformities in the transmission of light through the light guide and the optical grease Photomultiplier Tubes variations in light collection efficiency with the events position in the crystal due to geometry variations in light collection efficiency with the depth of interaction in the crystal due to geometry variations in the quantum efficiency of the photocathode across the face of the photomultiplier tubes variations in PMT tuning gain differences between PMTs Count rate Energy of incident gamma rays To begin with, it is fairly obvious that a poorly constructed or damaged collimator will affect primarily the sensitivity of the gamma camera. The sensitivity variations arise from the fact that a defective collimator will attenuate gamma rays in a non uniform manner. That is to say, that the number of gamma rays which pass through the collimators holes will vary either due to differences in the septal thickness or due to differences in the angulation of the holes. So, the image will appear either hot or cold depending on the number of counts, thus ruining the uniformity of the image. The collimator, however, is not the only cause of imperfections. In an ideal world, the scintillation crystal would exhibit properties such as homogeneous stopping power, interaction with gamma rays only through photoelectric absorption, transparency towards scintillation photons and high conversion efficiency (gamma to scintillation photons). However, in reality, the crystal presents with variations in its stopping power which ultimately lead to sensitivity imperfections and the appearance of hot and cold spots on our images. As we mentioned above, this variation in counts is a manifestation of non uniformity. Furthermore, the scintillation crystals exhibit incongruities in their light output. This is attributed to variations in the doping of the crystal with the chemical which serves as the activation centre for the luminescence phenomenon. (In the NaI crystal the doping is performed using thallium). In addition real crystals exhibit non uniform transmission of light, in cases where the optical grease used to couple Crystal-PMTs is dried out, or if the crystal has been exposed to moisture in which case opacities (yellowing) are developed. Finally, non uniformities in the images also originate from variations in the fraction of light that the photomultipliers collect. Light is lost between the gaps of the PMTs array but also near the edges of each individual PMT due to reflection. The majority of scintillation photons are collected near the center of the PMT, where the collection efficiency is best. This causes the counts to appear as if they were pulled towards the centre of the PMT and results to non- linearities. Even, the smallest non linearities will result in large non uniformities in the images. Last but not least, we ought to mention non uniformities arising from variations in the function of the photomultiplier tubes. The photocathode of a PMT, in reality, does not convert photons into electrons uniformly. Its quantum efficiency is better near its center and deteriorates as we move toward the edges. In addition, different PMTs tend to exhibit slightly different gains which ultimately lead to non uniformities. For example, a PMT with a gain above/below the correct gain will result in fewer counts falling within the energy window, creating a cold area over the dysfunctional PMT. Drift in PMT gain is usually caused over time, due to ageing, exposure to magnetic fields (Earth, MRIs), temperature fluctuations or power supply instabilities. So far we have discussed how the function of the gamma camera components can affect uniformity in practice. For completeness, we ought to mention that gamma camera uniformity (specifically the intrinsic uniformity) can also be affected by other factors such as: the activity of the radionuclide used to image, the number of acquired counts, the source-camera distance and the source volume. According to Elkamhawy, Rothenbach, Damaraju and Badruddin the intrinsic uniformity of the gamma camera increases with the increase of the source activity. However the increase in activity must not exceed the count rate capabilities of the camera otherwise non uniformities may be caused. In addition, according to Elkamhawy et al., the intrinsic uniformity increases as the counts go up. This is something to be expected, considering the probabilistic nature of the phenomenon of radioactive decay. Poisson statistics teach us that as the counts become higher the relative standard deviation decreases. That is to say that the coefficient of variation is reduced as the number of counts goes up and the statistical noise decreases. Finally, there are reports of an inverse correlation between the source to camera distance and the intrinsic uniformity. As the distance increases the intrinsic uniformity is increased due to a more uniform attenuation of the gamma rays travelling towards the crystal. That is to say, when the source is close to the crystal the gamma rays have to travel longer to reach the edges of the crystal than the centre. (See figure 2). Therefore the gamma rays travelling towards B will suffer greater attenuation that gamma rays travelling to point A. This dif ference in attenuation will result in count differences thus increasing the intrinsic non uniformity. However, if we increase the source to crystal distance, the gamma rays will undergo more or less the same attenuation due to the inverse square law and the counts will be more uniform throughout the crystal. Developments in gamma camera technology that have contributed in uniformity improvements. In older, analogue gamma cameras, the only correction that could be performed was a sensitivity correction that dealt with sensitivity variations on the images. Following the technological developments, the high processing capabilities of modern microprocessors and the implementation of analog to digital converters into their design, modern gamma cameras have been equipped to deal with non uniformities through a series of corrections.   Ã‚  Ã‚  Ã‚  Ã‚  Ã‚  Ã‚  Ã‚  Differences in photomultiplier gain used to be dealt with using the cosmetic approach which entailed the individual tuning of each PMT to match the other. Advances in microprocessors now allow for more advanced approaches. Maps containing the regional differences in pulse heights, as acquired from uniform flood sources, can be used to correct on an event to event basis (on the fly). As we mentioned earlier PMTs are affected by various external factors and they are caused to drift. Novel technologies have been introduced into gamma cameras which enables them to keep the gains stable in real time. For example, manufactures such as Toshiba, Elscint and IGE have implemented auto stabilization techniques where LEDs are used to tune the PMTs. The LEDs emit light which is detected by the tubes and the output voltage is then compared with a reference voltage and the gain is adjusted accordingly. With the increased processing power other corrections are current ly being used too. Linearity and energy corrections are common ways to improve the degree of uniformity in modern cameras. In the energy correction the most common practice is to expose the camera to a monochromatic gamma ray source (usually 99mTc) and acquire reading for the energy in various positions. Theoretically, the energy signal should remain constant independent of location on the crystal. However, as we have mentioned earlier there is always a small fraction of light which is lost. So, the readings are compared to the mean expected energy and a map of correction factors is stored in the gamma cameras memory which is used to rectify any errors in the energy signals. The linearity correction has a similar function. We would expect every events position coordinates to appear as a linear combination of the PMTs output voltages. , Y. But again due to light losses that is never true in practice. Fortunately, this is easily corrected through the linearity correction maps similar to those that we acquire for the energy correction. First of all, we remove the collimator and we introduce a lead plate with parallel holes throughout its extent. Then the system is exposed to a uniform point source. The image is processed and the positional errors are determined and stored as a separate correction map. The final correction to be applied on an image is the sensitivity correction, which has been used in the past as the only uniformity correction of analogue cameras. In modern cameras the technicians first stabilize the gains of the PMTs and then they proceed to apply the energy and linearity correction which have the greatest impact in the cameras uniformity. Then, and only then, they proceed with the sensitivity correction. The correction maps for the sensitivity are acquired by exposing the gamma camera (with the collimator mounted) to a uniform radioactive source. The counts are scaled up or down to eliminate any remaining cold or hot spots on the image. We should note that the individual correction maps should be acquired for each collimator since the sensitivity variations are primarily caused by collimator defects and other factors that we have already discussed. The scientific community has not stopped at the abovementioned corrections. Manufacturers and researchers have shifted their focus to new technologies hoping to replace components that contribute to bad uniformity but also to improve other gamma camera properties (resolution, count rate capability e.t.ch). For example, position sensitive photomultiplier tubes have been introduced (Hamamatsu, Photonis et. al.), which are capable of detecting the location of the event more accurately and efficiently that conventional PMTs. In addition to that, silicon photodiode arrays are being used coupled to the scintillation crystals for improved light sensitivity and quantum efficiency. Finally, there is a shift of interest towards replacing scintillation crystals with semiconducting materials. The combination of cadmium telluride with zinc makes for a great x ray and gamma ray detector. The main advantage of semiconductors over scintillation crystals is that the first converts photons directly in to electrical current. Contrary to the scintillation crystal that needs to use the photomultiplier tubes which are a significant source of non uniformities as we have mentioned. Quality Control: Measurement of non uniformity in gamma cameras Maintaining good uniformity in clinical images is extremely important. Even the smallest degree of non uniformity can cause artifacts which can prevent doctors from diagnosing the patient or lead them to the wrong diagnosis. The assessment of a gamma cameras uniformity is an integral part of its quality control and it is carried out in regular intervals (daily or weekly basis). These kind of investigations are carried out to ensure that there are no, non-uniform areas in the cameras field of view. The uniformity of a gamma camera can be measured either intrinsically or extrinsically. In the intrinsic setup, the collimator is removed and the naked crystal is exposed to a low activity uniform flood source. This setup has the advantage that the measurements are not affected by collimator induced non uniformities. In the extrinsic setup the system uniformity is assesses and the collimator is mounted onto the crystal. The advantage in this case is that the conditions of measurement are closer clinical parameters since in clinical acquisition the collimator is always in place. As far as the flood sources are concerned, 99mTc and 57Co are the most common choices. The technetium has the advantage of being readily available in hospitals and can be used as a mixture of radioactive material and water to create a uniform flood source. Also technetium is the most common radionuclide used in daily medical practices. Moreover, the presence of water presents a more realistic scatter source re sembling scattering conditions in patients. The main drawback of the technetium flood source is that it has a short half life and must be used soon after its creation. In addition, the construction method presents with the danger of spilling and contamination. An alternative to 99mTc is a 57Co source which has a convenient half life of 271 days. The peak energy of cobalt is close to that of technetium which is convenient in cases where the cameras performance is energy dependent. On the other hand, cobalt flood sources are quite costly and are usable only for about a year. Furthermore, cobalt sources often contain amounts of other cobalt isotopes Co60 and Co58 which emit higher energy gammas and may affect our measurements. A common testing protocol is the following. The radioactive source is placed at a distance approximately 4 times the field of view to ensure that the variation between the counts in the centre and the edge of the crystal is sufficiently small (as we have explained in figure 2) and can be ignored. The crystal is irradiated uniformly and a few million counts are acquired (approximately 1- 5 million counts). We need to acquire a statistically sufficient number of counts to ensure that the Poisson noise is minimal. We make sure that all the right corrections have been applied before we assess the images. A visual inspection of the images usually reveals gross deviations in performance. However, once the images have been acquired they are processed, using the cameras software, to yield values for common parameters such as the mean uniformity and the corrected uniformity which are used to quantify the quality of the camera. The mean uniformity informs us for the overall uniformity of the c amera throughout the FOV. The corrected uniformity is acquired by removing the Poisson noise from the mean uniformity. Those are not the only parameters that we can examine and other such as the integral uniformity and the differential uniformity are often assessed. Conclusion The uniformity of a gamma camera is maybe the most important parameter that expresses the quality of the cameras performance. Non uniform areas in the field of view can result in misdiagnosed patients and low quality of clinical services. Thus it is essential to perform regular checks to ensure optimal performance of the ? camera. Assessing the uniformity of a camera is not easy. As a parameter, uniformity is dependent on many factors and there are many things that can go wrong. Gamma cameras require regular testing, responsible operation and expert knowledge of its governing principles to make sure that its performance stays within clinically acceptable levels. References Professor Richard Lawson, The Gamma Camera , Lecture notes for the Nuclear Medicine Module of the University of Manchester MSc in Medical Physics, 2010. Peter F. Sharp, Howard G. Gemmell , Alison D. Murray, Practical Nuclear Medicine , 1-19, 65-90 Springer Publications, Third Edition. http://en.wikipedia.org/wiki/Gamma_camera EMITEL, http://www.emitel2.eu/emitwwwsql/encyclopedia.aspx, Scintillation Camera http://upload.wikimedia.org/wikipedia/commons/0/0c/ Gamma_camera_cross_section.PNG Abdelhamid A. Elkamhawy, Joseph R. Rothenbach, Srikanth Damaraju and Shamim M. Badruddin, Intrinsic Uniformity and Relative Sensitivity Quality Control Tests for Single Head Gamma Cameras, Nuclear Medicine Department, Cuero Community Hospital, Cuero; and Nuclear Medicine Department, Spohn Shoreline Hospital, Journal of Nuclear Medicine Technology 2000; 28: 252-256 A. Hughes and P.F Sharp, Factors affecting gamma camera non-uniformity, Department of Bio-Medical Physics and Bio-Engineering, university of Aberdeen, Forester hill, Aberdeen, AB92ZD, UK, Phys. Med. Bio., 1988, Vol 33, No.2, 259-269, IOP Publishing Ltd, 1988 A. 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Uniformity measurement, Isotrak C-ThruTM Flood Source, High Technology Sourced Ltd, www.hightechsource.co.uk Length : 3.300 excl references and title.