问题 单项选择题 A3/A4型题

通过控制层面选择梯度场和射频脉冲来完成MR图像层面和层厚的选择。在完成了层面选择后还必须进行层面内的空间定位编码。层面内的空间定位编码包括频率编码和相位编码。频率编码让来自不同位置的MR信号包含有不同的频率,采集到混杂有不同频率的MR信号后,通过傅里叶变换才能解码出不同频率的MR信号,而不同的频率代表不同的位置。在前后方向上施加了频率编码梯度场后,经傅里叶转换的MR信号仅完成了前后方向的空间信息编码,必须对左右方向的空间信息进行相位编码,才能完成层面内的二维定位。

磁共振利用____梯度进行层面选择时,可以减小层厚()

A.梯度场不变,加宽射频脉冲带宽

B.梯度场减小斜率,加宽射频脉冲带宽

C.射频脉冲带宽不变,梯度场加大斜率

D.射频脉冲带宽不变,梯度场减小斜率

E.梯度场不变,增高射频脉冲频率

答案

参考答案:C

填空题
阅读理解

Although there are no state controlled survival courses in Britain or the United States,there are various independent organizations offering similar activities.Students can participate(take part)in outdoor training courses through university clubs and societies.Anyone can register with such groups,which then organize courses,training and trips for all members.

One of the most popular outdoor training programmes in both the US and Britain is Outward Bound(户外训练).It was founded in 1941 in Wales and attracts hundreds of thousands of adventurous types every year. The courses are intended to broaden minds through experiences that build confidence, self-esteem(自尊)and character.As well as specialist courses such as canoeing,leadership skills and sailing,participants can take part in week long adventure training camps which include a host of sports and survival training education skills.

Michael Williams,an American student,took part in an Outward Bound course last year.He said:“We learned lots of first aid skills,lots of natural history ,lots of environmental facts, and participated in a wildlife preservation programme.Beyond that,my favorite skills learned were sailing and rock climbing.”Courses can last up to 40 days and are open to anyone over the age of 14.Students must be in general good health,but do not need to be experienced in outdoor-sports.There is no selection process;everyone is welcome,although new participants are advised to pick a course matching their physical capacity.Most of the British courses take place in the Brecon Beacons in Wales.Another similar organization is the UK Survival School,which includes courses on learning to 1ive with the environment, sailing and  winter survival.On a basic survival weekend students will learn how to get water and food, how to make fire and cook with it,to find and build a shelter,control survival life support,how to cross rivers.Send off a distress signal,and to use compasses(指南针)by day and night.

According to the leaders,such adventures are “an awakening, an exploration into the unknown.”Outward Bound believes that participants will “use mind and body traveling some of the Earth’s roughest wilderness areas.”   

小题1:In Britain and the United States,survival courses are popular with    

A.old people

B.young people

C.dangerous people

D.weak people小题2:The advantage of the training courses is that   .

A.participants can make friends with others

B.participants can visit some places of interest

C.participants can experience different adventures

D.participants can learn how wonderful nature is小题3:In an Outward Bound course last year,the most exciting experience Michael Williams had was   .

A.learning first aid skills

B.collecting facts of environment

C.rock climbing and sailing

D.preserving wildlife