King arthur Essay Example | Topics and Well Written Essays - 1000 words

King arthur - Essay Example According to legend, he was the son of Uther Pendragon, king of Britain, and Ygraine of Cornwall. During his childhood, Arthur's identity was kept anonymous. Upon his maturity, he was abruptly presented to the people as their king and became a prudent and brave ruler ("Microsoft Encarta"). On the other hand, in the early Latin chronicles, Arthur is characterized as a "dux bellorum," i.e. a military leader rather than a king or emperor ("Camelot Project"). Despite the varying depiction, Arthur consistently appears as the epitome of ideal kingship ("Wikipedia"). Based on the Arthurian romances that gained popularity in the 12th century, Arthur gained the throne as he was the only one who had successfully withdrawn the Excalibur, a magical sword, from a stone. Many others attempted but failed since this act could not be accomplished apart from the "true king." This implied that Arthur was indeed the divinely appointed king and the true heir of Uther Pendragon ("Wikipedia"). He then established a court at Camelot, which is believed to be the modern Caerleon on the southern border of Wales or the great hill fort at South Cadbury in Somerset ("The New Dictionary of Cultural Literacy"). At Camelot, Arthur gathered the Knights of the Round Table, which were comprised of Sir Aglova... ne; Sir Ector de Maris, son of King Ban of Benwick; Sir Florence, son of Sir Gawain; Sir Gaheris; Sir Galahad, Sir Lancelot's son and the hero of the quest for the Holy Grail; Sir Gareth; Sir Gawain, Arthur's nephew, who at some points appeared as the embodiment of knightly courtesy and bitter opponent of Lancelot; Sir Geraint; Sir Kay, Arthur's villainous foster brother; Sir Lamorak; Sir Lancelot; Sir Lucan; Sir Palamedes the Saracen; Sir Percival; Sir Tristan; and Sir Yvain, son of King Uriens of Gore (Lacy). These knights were awarded the highest order of chivalry at the court of King Arthur as narrated in the literary cycle, the Matter of Britain. According to Sir Thomas Malory, the knights abided by a set of rules called the Code of Chivalry. Provisions of this code include not committing outrage or murder; fleeing treason; not succumbing to cruelty but instead giving mercy to those who ask; helping and never forcing ladies, gentlewomen or widows; and not taking up wicked battles for love or worldly goods. Aside from Arthur and his knights, the Arthurian legend also featured notable characters such as Merlin, a powerful wizard possessing the gifts of prophesy and metamorphosis who partook in the court at Camelot and revealed the existence of the Holy Grail to Arthur, and Queen Guinevere, the wife of Arthur. Moreover, it gives an account of the knights' numerous quests, perhaps the most famous of which is the search for the Holy Grail ("Wikipedia"), and Arthur's wars and victories, which extended to the European continent where he triumphantly fought the Roman Empire forces ("Microsoft Encarta"). One of the main themes in the Arthurian legend is the downfall of Arthur's kingdom, which is primarily attributed to two reasons. In the chronicle tradition, the

BLIP Echo Planar Imaging Method Essay Example | Topics and Well Written Essays - 2500 words

BLIP Echo Planar Imaging Method - Essay Example Sampling of k-space is different in EPI that enables high quality of images acquired. EPI uses quickly switching gradients to produce its echo train as against use of RF pulses in FSE. EPI frequency encoding gradient oscillates from positive to negative to create odd and even echoes. Each read gradient echo corresponds to one k-space with the positive and negative gradients changing the direction of the line that is read. The changing of direction of the line read results in a phase ‘blip’ causing a shift in Ky and this method of phase encoding is referred to as blip EPI. Characteristics of EPI: EPI has three distinct characteristics in terms of speed, the variety of contrast and the flexibility in terms of available resolution for imaging small structures like the pituitary gland. EPI offers higher speeds (6 to 10 times) of imaging of short temporal events under motion. It provides with high image quality by collecting more averages with increased slice frequency per TR . The signal to noise ratio of the images is high and the resolution is also high. Its usefulness depends on the MR system used and the efficiency is determined by the ability to perform 1282 or 2562 in a very short time to avoid large off resonance artifacts. It means that high quality images of moving patients can be obtained by using the speed of EPI. A variety of tissue contrasts (T1, T2 and T2*) are allowed by EPI for image acquisition and small structures are imaged using the flexibility in resolution where the field view can be reduced, the echo train length can be increased or geometric distortions can be reduced to increase the resolution. Also, just half of the data of the image can be gathered that can be further synthesized through conjugation to obtain the remaining data. Flexibility in contrast can be used to produce an image similar in standards to that of an SE image with the same TE and TR by using an excitation pulse in the front part followed by a 1800 pulse (T2* dephasing) to create the first echo. EPI compared to conventional fast imaging methods: EPI uses the Blip EP method of phase encoding where each phase blip between echoes causes a shift in k-space line. Each k-space line is contributed by the gradient refocused echo and is either read positively or negatively through the gradient change. The quickly switching gradients that produce the echo train are responsible for the odd and even echoes. When the lines are read, the reversed read lines are reordered before constructing the image. Also, the rf pulse is not used to create multiple echoes as in conventional FSE. Figure 1: (a) Pulse diagram of FSE, 4 echoes and (b) pulse diagram of EPI. Source: (McMahan, 2012). Benefits in EPI: Acquiring single snap shot images is much faster (20-100 ms) using EPI when compared to conventional FSE as gradient echoes take less time as all the encoding steps are obtained after one single excitation pulse is applied. This is in contrast to the train of rf pulses applied that increases TR. Also, EPI allows flexibility in contrast that enables even small structures to be imaged very fast. Further, slice coverage is increased with EPI when compared to FSE. EPI has fewer rf pulses that result in low specific absorption rate (SAR). As SAR is low, TR is also low, resulting in more slices to be covered in the same TR as in FSE. Sensitivity to resonance effects: A disadvantage in EPI is that it is sensitive to off resonance effects of the echo gradients