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在自旋回波序列中如何实现T1WI
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所谓加权即重点突出某方面的特性。之所以要加权是因为在一般的成像过程中，组织的各方面特性(如：质子密度、T1值、T2值)均对MR信号有贡献，几乎不可能得到仅纯粹反映组织一种特性的MR图像，通过利用成像参数的调整，使图像主要反映组织某方面的特性，而尽量抑制组织其他特性对MR信号的影响，这就是“加权”。T1加权成像是指这种成像方法重点突出组织纵向弛豫差别，而尽量减少组织其他特性如横向弛豫等对图像的影响；T2加权成像重点突出组织的横向弛豫差别；质子密度加权像则主要反映组织的质子含量差别。 关于T1wI下列叙述错误的是
Usually one and a half hours before departure, the check-in counters open and passengers begin to check in for their flight.A passenger service agent checks the passenger’s ticket and his reservations status. The ticket must be the right one and the status should be OK. If the passenger has any baggage to check in, the agent weighs it and takes care of it. Each first-class passenger has a free baggage allowance of thirty kilograms, and for economy-class passengers the allowance is twenty kilograms. Airlines can charge for overweight baggage.The agent attaches a tag to each piece of checked baggage, and gives the identification tag, i.e. the baggage claim check to the passenger. The passenger claims his baggage with this identification tag upon arrival.Besides, passengers must pay an airport tax. The charge varies from country to country. In the United States it is US $3 for each passenger. In Japan it is Japanese￥2,000, and it’s RMB ￥50 in China.Then the passenger receives a boarding pass. The pass shows the flight number, the class, and the seat assignment. Next he goes to the passport control and the departure gate. How can the passenger claim his baggageWith（）
Silence is unnatural to man. He be gins life with a cry and ends it in stillness. In the (B1) he does all he can to make a noise in the world, and there are few things of which he stands in more fear than of the (B2) of noise. Even his conversation is in great (B3) a desperate attempt to prevent a dreadful silence. If he is introduced to a fellow mortal and a number of (B4) occur in the conversation, he regards himself as a (B5) , a worthless person, and is full of (B6) of the emptiest-headed chatterbox (唠叨多言的人). He knows that ninety-nine percent of human conversation means no more than the buzzing of a fly, (B7) he longs to join in the buzz and to prove that he is a man and not a wax-work (B8) . The object of conversation is not, for the (B9) part, to communicate ideas: it is to keep up the buzzing sound. Most buzzing, (B10) , is agreeable to the ear. and some of it is agreeable even to the (B11) He would be a foolish man, (B12) , who waited until he had a wise (B13) to take part in the buzzing with his neighbors. Those who (B14) the weather as a conversational opening seem to be (B15) of the reason why human beings wish to talk. Very few human beings join in a conversation (B16) the hope of learning anything new. Some of them are (B17) if they are merely allowed to go on making a noise into other people’’ s ears, (B18) they have nothing to tell them except that they have seen a new play. At the end of an evening during which they have said nothing at immense (B19) , they justly pride themselves (B20) their success as conversationalists.
In 1971 the Royal College of Physicians decided to take action on the problem of smoking and health. They formed an organization called Action on Smoking and Health -- ASH. Its aims are to make people aware of the dangers of smoking and to help those people who do smoke to give up. As part of its campaign to make people see how smoking damages us all, both as individuals and as members of society, ASH has gathered together some every convincing facts and figures. For in stance, smoking is very harmful to industry. Nearly 50 million working days are lost in Britain every year due to smoking -- at least four times the number of days lost in strikes. And the cost of treating people suffering from smoking related disease is around ￡ 100 million each year.But the human suffering which smoking causes is far more serious than the economic price which society has to pay. 95% of those who suffer from bronchitis are smokers. It has been estimated that 20% of all cigarette smokers become disabled by chronic bronchitis and may eventually die of the disease. Over 20,000 people die of bronchitis every year.Lung cancers kill more people than any other types; of cancers; 90% of them are caused by smoking. With coronary heart disease the risk of death is 2 to 3 times as great in smokers as in non - smokers and this disease is now the major cause of death in Britain.Bronchitis, lung cancer and coronary heart disease arc the three most serious reasons for not smoking but there are other masons which are also important. The message from ASH is clear -- if you do smoke you should give up now and if you don’t smoke then you should not start -- ever. Due to smoking, which of the following statements is NOT true（）
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