舒张期伪门控产生动脉高信号，其TR为1000ms，则心率为（）
A.50次／分
B.60次／分
C.70次／分
D.80次／分
E.90次／分
参考答案：B
解析：动脉血流的速度因心动周期的变化而快慢不等。心脏收缩时，血流速度最快，而在舒张期时，血流速度明显变慢。使用心电门控在舒张期的MR扫描层上，动脉血流信号增高，因为这时血管内信号的形成主要是基于滞缓的血流本身T1、T2时间。同样，即使不用心电门控，若受检者心动周期与重复时间偶然同步，即两者相等时，也可产生类似心电门控的效果。
根据所给10个英语单句的意思，从所给的15个词汇中挑选出10个合适的词或短语分别给每个句子填空。
Many kings and princes wanted to marry Atlanta, but when they heard of her rules they knew it was ________. Anyhow, my ________ is to provide humans with a life of high quality, and I am now truly filled with happiness that I am a devoted friend and helper of the human race. Dinosaurs lived on the earth tens of millions of years ago, long before humans ________ and their future seemed secure at that time. Many young people often dream of playing in front of thousands of people at a concert, and, to be honest, a lot of them ________ great importance to becoming rich and famous. If your friend comes to school very upset, tell him that you are ________ him and you will meet after class and talk then. India has a very large number of ________ English speakers because Britain ruled India from 1765 to 1947, and English became the language for government and education. I am fond of my sister Wang Wei but she has one serious ________ — she can be really stubborn. On July 28, 1976, the city of Tangshan in Hebei Province was hit by a terrible earthquake and the number of people who were killed or seriously ________ reached more than 400,000. It was in 1952 that Elias went to Mandela for legal advice, and Mandela was ________ with his time, for which Elias was very grateful. |