Technology of MRI Scanners

Technology of MRI Scanners INTRODUCTION Magnetic Instrumentations are the hardware in the system component of MRI that very significant in the production of Magnetic Resonance (MR) images. It act together with the software program such as pulse sequence and image formation program to complete the process including nuclear alignment, Radio Frequency (RF) excitation, spatial encoding and image formation. The example of hardware in MR imaging are magnet, RF source, magnetic field gradient system, computer system, and image processor. MRI INSTRUMENTATION 1. Define gauss, tesla, and electromagnetic spectrum: 1.1 Gauss Gauss (G) is the older unit of flux density or the unit of low magnetic field strength. 1 Gauss can be define as 1 line or flux per cm2 (Willis, 2009). 1.2 Tesla Tesla unit is the preferred SI unit in larger magnetic field and it can be define as the field strength of 1 Weber per m2. 1 Tesla is equal to 10 000 Gauss (Willis, 2009). 1.3 Electromagnetic spectrum Electromagnetic spectrum is a continuum of all electromagnetic waves or energy arrange according to frequency and wavelength. In MRI, radiofrequency (RF) refers to that portion electromagnetic spectrum which can be generated by alternating current fed to an antenna (Hardiman, 2005). 2. Define paramagnetic, Diamagnetic and Super magnetic: 2.1 Paramagnetic Paramagnetic material such as Ferum, Magnesium and Gadolinium have unpaired electron resulting in positive magnetic susceptibility which induced small magnetic momen. Paramagnetic ion induced large fluctuating magnetic field in external magnetic field. Commonly, Gadolinium (Gd) is used as a MR contrast agent (Ballinger, 1998). 2.2 Diamagnetic Diamagnetic materials have paired electrons such as water, wood, glass, and gold which show no net magnetic moment with the absent of magnetic field. Non magnetic material quickly repels the field when placed in magnetic field, resulting in small negative magnetic susceptibility which contribute to the loss of signal in MRI (Ballinger, 1998). 2.3 Super magnetic Superparamagnetic materials such as iron oxide can be used as t2* as it has magnetic susceptibility slightly higher than paramagnetic (low positive) and lower than ferromagnetic material (high positive). It causes large magnetic moment in the presence of external magnetic field but no remnant magnetic moments when the field is zero (Ballinger, 1998). 3. Describe 3 types of magnet and give advantages and disadvantages of each: 3.1 Superconducting magnet Superconducting magnet have high field strength up to 3.0 T in clinical scanner while 9.4 T in research facility. It is also high in field homogeneity over largest volume. As it provide high field strength, it cause high signal to noise ratio and also fast scanning. It gives low power consumption as it always produce a magnetic field and electric current without primary source (Blink, 2004). Superconducting magnet is high in capital cost and cryogenic cost. It also produces acoustic noise, motion artifact and technical complexity as susceptibility effect is increased when imaging moves to higher field strength (Blink, 2004). 3.2 Resistive magnet The resistive magnets commonly have open designs which make it light weight and overcome claustrophobia among the patient. It been shut off when not in used to conserve the power (Blink, 2004). However, it has limited field strength which below than 0.2 T and low overall volume of homogenous field. It needs high power consumption and has large fringe field (Blink, 2004). Water cooling is required because large amount of heat are generated to produce the magnetic field by an electromagnet (Wang, n.d). 3.3 Permanent magnet Permanent magnets have low power consumption and low operating cost. It also cause small fringe field and does not use cryogen (Wang, n.d). Permanent magnets have limited field strength which is below than 0.3T and give no quench possibility. It is quite heavy and may require reinforced flooring to site the system, particularly if the magnet is not located at ground level (Blink, 2004). 4. Discuss field strength in relation to image contrast: In general, image quality is based on contrast resolution and noise which influence by the field strength of magnet. High field strength provides more signal-to-noise ratio than low field strength. It allows fast imaging that reduces patient motion so that better spatial resolution and image contrast (Thomas Magee, 2003). 5. Discuss purpose of gradient in MRI: Mainly, the gradient is used to either dephase or rephase the magnetic moment of nuclei (Guang Cao, n.d). It also used for slice selection, gradient refocusing, gradient echoes, and gradient moment nulling. It also can spatially locating (encoding) signal along the long axis of the anatomy called Frequency Encoding as well as spatially locating (encoding) signal along the short axis of the anatomy called Phase Encoding (ASRT, 2008). 6. Discuss the purpose of cryogen: Cryogen is used in MRI to supercool the electrical conductor in superconductive magnet. It is because a quench cause a rapid loss of static magnetic field in MRI (Blink, 2004). So, the cryogen usually liquid helium and some liquid nitrogen is used to ensure the temperature as low as -269ËÅ ¡c (-452ËÅ ¡c) are achieve (C.L. Dennis, 2009). 7. Discuss the type and purpose of shielding and shimming: In MRI, RF shielding use copper shielding or Faraday cage to reduce the transmission of electric or magnetic fields from one space to another. Meanwhile, magnetic shielding used to reduce the level of RF radiation that enter or leaves the shielded room (Hipskind, 2009). Passive magnetic shielding use a steel plate while active magnetic shielding employ additional solenoid electromagnet to reduce the area affected by the fringe field (ETS.LINDGREN, 2009). Shimming is used to remove small inhomogeneities which present in the magnetic field (Z. Ren, 2009). It uses metal discs or plates in passive shimming to get magnetic field to a particular level of homogeneity and additional solenoid magnet in active shimming to optimize for each patient examination (D. Tomasi, 2009). 8. Discuss construction, use and selection of linear, quadrature, phase array, multichannel, transmits or receive coil and receive coil only: Linear or surface coil consist of single or double loop of copper wire that use to improve SNR when examine the structure near the skin surface such as temporo-mandibular joint, orbit or shoulder (Blink, 2004). Quadrature or circularly polarized coils contain at least two loops of wire which commonly used today that produce √2 more signal than single loop coil (Zhou, n.d). Phased array coils consist of multiple surface coils which have the highest SNR but limited sensitive area (Zhou, n.d). Multichannel or Helmholtz coil have pair of circular coil that widely used in MRI because of its fairly uniform magnetic field (Zhou, n.d). Transmit/receive coil transmit RF then change to a receive mode to receive the MR signal. It allows acquisition of more slices and reduce artifact. It has complex design and decrease uniformity over volume of interest (Spring, 2005). Receive only coil design only receive MR signal using body coil as a transmitter and they include surface and phased array coil. It has simple design which used together with the transmit body coil to provide uniform excitation over the entire volume of interest (Spring, 2005). 9. Explain the principle of magnetism, the specific of MR instrumentation, and hardware required for MR imaging: 9.1 Principle of magnetism Magnetism not just occurs in ferromagnetic substances like iron. In an external magnetic field, magnetization can occur in tissue but it disappears when the field is removes (Michael N.Hoff, n.d). 9.2 Specific of MR instrumentation Ancillary equipment needs an additional instrumentation for scanning such as ECG leads and respiratory bellows as well as the power injector. It also supplies patient monitoring like ECG, pulse oximetry and fiber optic while patient transportation provide a wheelchairs, stretchers, patient table and step stool (ASRT, 2008). 9.3 Hardware required for MR imaging Other than magnet, gradient and radio frequency system, the hardware required for MR imaging is the computer. It controls all the system and has the pulse control unit as well as array processor for fourier transform and 2D and 3D imaging. Computer also stored the data in the hard drive as well as processing and handling it (ASRT, 2008). 10. Explain MRI imaging chain: Diagram1: Schematic diagram of MRI imaging chain (Anonymos, n.d). Mainly, the central computer controls the scanning operation. It specifies the shape of gradient and RF waveform as well as the timing to be used. Then, the information is passes to the waveform generator before the signal is passes to be amplified and sent to the coils. Once NMR signal has been phase, it is sensitively detected and turned to a digital signal by analogue to digital converter. The image is displayed on a monitor after digital signal sent to image processor for Fourier transformation (Anonymos, n.d). The signal before Fourier transformation called raw data is stored to enable the application of corrections in the post processing. Matrix sizes of 2n are usually used to allow the use of fast Fourier transformation (Anonymos, n.d). 11. Describe MRI quality assurance program: The evaluation of all MRI system should be done prior to and following installation. It must be monitor at least annually to ensure proper functioning and high-quality diagnostic images are produced (ASRT, 2008). For the performance evaluation, it should include the tests phase stability, magnetic field homogeneity, calibration of all RF coils, image signal-to-noise ratio and uniformity for all coils, inter-slice RF interference, artifact evaluation, hardcopy and softcopy fidelity, spatial resolution and low contrast object detectability, magnetic field gradient calibration, intensity for all volume coil, film processor quality control, physical and mechanical inspection, and evaluation of MRI safety (Geoffrey D. Clarke, 2002). In quality control program, the physicist/MR scientist should assist annually on the RF calibration and image SNR and uniformity for the head coil, film processor QC, physical and mechanical inspection, magnetic field gradient calibration, and hardcopy and softcopy fidelity. The corrective action is taken if the parameter falls outside control limit (Geoffrey D. Clarke, 2002). The protocol of acceptance testing include the evaluation of the coil and follow-up procedure or written survey report from the physicist/ MR scientist to the physicians and to the responsible professional (ASRT, 2008). CONCLUSION In MRI system, a magnet is required for nuclear alignment, radio frequency source for excitation, magnetic field gradient system for spatial encoding, computer system for image formation process as well as the user interface, and image processor to convert signal into images. This hardware plays important role along the software program like pulse sequence and image formation program to produce the MR images. However, to ensure proper functioning and high-quality diagnostic images produce, the MRI system should be evaluated through Quality Assurance (QA) program because if there are parameter falls outside control limit, immediate corrective action is taken.

Existing television channels Essay

Distinctiveness and originality are always key in any aspect of the media, as it allows anything to be set apart from the rest, drawing the audiences attention towards it. However distinctiveness and originality are becoming a thing of the past as ideas are running thin. Constantly we are able to see similar or replicas of past programming on our screens, whether it be in reality television, soap storylines or big dramas. The BBC have always been known for is popular programming. In the early days of the BBC, they strived to follow a common trend of having an educational programme, follow an entertainment programme. However, as such programming scheduling has been scrapped, both educational programmes do appear in the scheduling. But the question is how original and distinctive are these programmes that the BBC are producing? Well firstly the BBC have publicly admitted that they will be reducing their amounts of repeats to below 10% in their programming schedule within the next 10 years. But will this help the BBC become more original and distinctive? In one sense it will, as the BBC have become well known for having constant repeats they will now have to think ip exciting ideas to fill the slots of the original repeats. However will the BBC crumble under the pressure and resort to common concepts and genres, such as reality and soaps? Well it seems not as the BBC have made a vow to bring the best original ideas to the screen, Saying that the channel will invent, refresh and discover new passions and interests. New educational programmes such as The Blue Planet and Son of God are among the line up. With The Blue Planet exploring the earths final frontier, from the deep to the shore, from pole to pole. It revealed new and extraordinary life and behaviour that had never before been captured on film. While Son on God used breakthroughs in archaeology, astronomy, forensic science and history to help viewers make up their own minds about the man who changed the world. There is said to be no crisis of orginality in British television – though there may be for ITV. Why is this? Well for one ITV has a very important and unique posistion as the only UK channel expected to deliver a mass audience to advertisers, day in day out. With this kind of pressure on their backs ITV have the most to prove with originality and distinctiveness in their programming. Numerous programmes have catered to these needs in recent years. For example the television revival of John Galsworty’s Forsyte novels The Forsyte Saga, and also The Jury, an innovative six parter starring Derek Jacobi and Antony Sher. However ITV is not required to cater specifically for non-mainstream tastes and interests, or to meet particular requirements for innovation, experimentation or distinctiveness. That is not to say that these characteristics will not appear in ITV’s programming. Channel 4 has always stood out, as in the beginning it was designed for minority groups. But today, Channel 4 still stands out with its range of programmes, and it is often said that distinctiveness, diversity and innovation are key requirements to Channel 4’s programming. Shows such as Green Wing, Touching the Void, Spitfire Ace, My Foetus and Supernanny demonstrate that these have been achieved in every part of the schedule and with significant public impact. Channel 4 proved its distinctiveness with programmes ranging from Shameless to Hamburg Cell to Sex Traffic. Channel for has continued and progressed in supplying original and quality programmes that challenge the veiwers opinions and personal veiws. Channel 4 continued to find new formats and reach new audiences with Musicality, Cheating At Athens – Is It Worth It? , Bollywood Star, The Great British Asian Invasion and Time Team’s Big Dig. Overall i feel that originality and distinctiveness has great importance of the ever changing television market, as it sets each channel apart form one another. Also it allows us all to see the potential that these channels have and what they could do when they enter the digital age after the analogue switch off. With this originality and distinctiveness, will the Big 5 be able to compete in the digital age with numerous other channels pinning for the maximum audience share? Yes, i feel they will as they will have a step up on the other channels with their programming. However i feel that this will only happen if the Big 5 continue and improve their originality and distinctiveness in programming, instead of settling for a common concept.

The Foolproof Cheap Term Paper Writing Service Strategy

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The Roman Relationship Between Patron and Client

The people of ancient Rome were divided into two classes: wealthy, aristocratic patricians and poorer commoners called plebians. Patricians, or upper-class Romans, were patrons to plebian clients. The patrons provided many types of support to their clients who, in turn, rendered services and loyalty to their patrons. The number of clients and sometimes the status of clients conferred prestige on the patron. The client owed his vote to the patron. The patron protected the client and his family, gave legal advice, and helped the clients financially or in other ways. This system was, according to the historian Livy, created by Romes (possibly mythical) founder, Romulus. Rules of Patronage Patronage was not just a matter of picking out an individual and giving him money to support himself. Instead, there were formal rules pertaining to patronage. While the rules did change over the years, the following examples provide an idea of how the system worked: A patron could have a patron of his own; therefore, a client, could have his own clients, but when two high-status Romans had a relationship of mutual benefit, they were likely to choose the label amicus (friend) to describe the relationship since amicus did not imply stratification.Some clients were members of the plebian class but had never been slaves. Others were freed slaves. While freeborn plebes could choose or change their patron, freed slaves called liberti or freedmen automatically became clients of their former owners and were obligated to work for them in some capacity.Each morning at dawn, clients were required to greet their patrons with a greeting called the salutatio. This greeting could also be accompanied by requests for help or favors. As a result, clients were sometimes called salutatores.Clients were expected to support their patrons in all matters, personal and political. As a result, it was possible for a wealthier patron to count on the votes of his many clien ts. Meanwhile, however, patrons were expected to provide a range of goods and services including food (which was often traded for cash) and legal counsel.There was also patronage in the arts where a patron provided the wherewithal to allow the artist to create in comfort. The work of art or book would be dedicated to the patron. Outcomes of the Patronage System The idea of client/patron relationships had significant implications for the later Roman Empire and even medieval society. As Rome expanded throughout the Republic and Empire, it took over smaller states which had its own customs and rules of law. Rather than attempting to remove the states leaders and governments and replace them with Roman rulers, Rome created client states. Leaders of these states were less powerful than Roman leaders and were required to turn to Rome as their patron state. The concept of clients and patrons lived on in the Middle Ages. Rulers of small city/states acted as patrons to poorer serfs. The serfs claimed protection and support from the upper classes who, in turn, required their serfs to produce food, provide services, and act as loyal supporters.