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可是磁体和声音是两个完全不搭界的概念8 f! H+ O" }, }" A" H3 j% d% s4 F
唯一相同的是他们都是波的形势传递,但是无论从波形,频率还是传播媒介来说都是没有共同点的 ! j3 o/ P# l# r. }) q 5 C. o! J- X( ]再说了,无论磁场强度多少,产生磁场并不需要,也不会伴随机械振动,怎么会有声音呢,希望哪个专家来解释一下。作者: hefei01 时间: 21.7.2009 14:50
The body is largely composed of water molecules which each contain two hydrogen nuclei or protons. When a person goes inside the powerful magnetic field of the scanner, these protons align with the direction of the field. + a9 m. ?% [1 \ i' r1 Y# Y2 v. v2 QA radio frequency electromagnetic field is then briefly turned on, causing the protons to alter their alignment relative to the field. When this field is turned off the protons return to the original magnetization alignment. These alignment changes create a signal which can be detected by the scanner. The frequency of the emitted signal depends on the strength of the magnetic field. The position of protons in the body can be determined by applying additional magnetic fields during the scan which allows an image of the body to be built up. These are created by turning gradients coils on and off which creates the knocking sounds heard during an MR scan. 7 ^) K; ^* e; N/ B0 a--- from Wikipedia http://en.wikipedia.org/wiki/Magnetic_resonance_imaging作者: collboy 时间: 21.7.2009 14:57
明白了,谢谢作者: collboy 时间: 21.7.2009 15:27
支持,挣外快的好机会# s* r, w# }; J2 c6 |7 T
可惜我视力太差了,不然我也去了作者: mafial 时间: 22.7.2009 10:38
感谢楼上啊,已经有3~4个童鞋了作者: slstone 时间: 22.7.2009 10:46
羡慕视力好的同学们作者: mafial 时间: 22.7.2009 12:03
zb,可以, 8 H6 A ? K3 R/ I4 i我这次换了试验的模式了,欢迎来啊~,哈哈,$ \' z& Z7 e. P