90°射频脉冲激发后,组织中将产生宏观横向磁化矢量,射频脉冲关闭后,由于主磁场的不均

题型:单项选择题 A3/A4型题

问题:

90°射频脉冲激发后,组织中将产生宏观横向磁化矢量,射频脉冲关闭后,由于主磁场的不均匀造成了质子群失相位,组织中的宏观横向磁化矢量逐渐衰减。到TE/2时刻,施加一个180°聚相脉冲,质子群逐渐聚相位,组织中宏观横向磁化矢量逐渐增大;到了TE时刻,质子群得以最大程度聚相位,组织中宏观横向磁化矢量达到最大值,从此时刻开始,质子群又逐渐失相位,组织中的横向宏观磁化矢量又逐渐衰减。

该序列中90°脉冲的作用是()

A.产生失相位

B.产生横向磁化

C.产生回波

D.相位重聚

E.翻转磁化矢量

考点:放射医学技术(主管技师)MR成像理论MR成像理论题库
题型:单项选择题 A3/A4型题

Do you know Weibo? Do you write a Weibo? If you don't, you are "out"! Weibo means microblog. People may spend muchtime writing a blog, but it takes a little time to write a microblog.Why? Because every message on a microblog is less than 140 words.

Microblog started in the USA. It came to China in 2009 andit has developed very fast. In 2011, the number of Chinesemicro-bloggers grew to 300 million. Now, more and more people are interested in writing microblogs. For manymicroblog users, it is a great way of learning the freshest news,talking with friends and sharing different kinds of information, including news, daily life, pictures,music and so on. Many stars and famous people also write microblogs and share good things with theirfans.

It is easy and fast to send a message on a microblog. However, this can also lead to problems and even cause panic . For example, when thebig earthquake and tsunami hit Japan in March, 2011, messages like " Salt can protectpeople from radiation" were hot on microblogs. It soon caused a crazy buying of salt. Later people realized it was just arumor (谣言).

In a word, microblog plays a new role in the life of Chinese people.

小题1:People spend _____ time and _____ words writing microblog.

A.little, a few

B.a little, few

C.a little, a few

D.a few, a little小题2:There were 300 million Chinesemicro-bloggersin _____.

A.2008

B.2009

C.2011

D.2013小题3:Which of the following is TRUE?

A. Writing a microblog needs a special training.

B. Microblog appeared in China only one year ago but it has developed rapidly.

C. As a popular thing, microblog has its advantages and disadvantages.

D. More and more Chinese show great interest in microblog because it started in the USA.

题型:单项选择题 A3/A4型题

下列关于早期胃癌的描述,错误的是()

A.病变局限于黏膜层

B.病变局限于黏膜层或黏膜下层

C.病变的大小与早期胃癌的定义无关

D.有无周围淋巴结转移与早期胃癌的定义无关

E.病变仅累及黏膜肌层

题型:单项选择题 A3/A4型题

My father is very busy these days. He has to do        .[ ]

A. many work

B. many works

C .a lot of work

D. a lot of works

题型:单项选择题 A3/A4型题

原发性肝癌与活动性肝病如何鉴别?

题型:单项选择题 A3/A4型题

与海藻相反的药物是()

A.藜芦

B.昆布

C.大枣

D.甘草

E.细辛

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