读economist---tracing the blood stream

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粉红-我认为的好词句

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Medical imaging

Tracing the bloodstream

Mar 11th 2009
From Economist.com

Magnetic-particle imaging shows how blood flows

OVER the past three decades it has become possible to peer inside the human body and discern ever finer details of its functions. The technology for this relies on magnetism, namely, magnetic-resonance imaging (MRI). Now a new type of scanner is being developed to work alongside MRI that will also use magnetism to allow doctors to watch how blood flows through organs. This will yield even more informed pictures and help improve medical diagnosis and treatment. (说明性文章，先点明主题:MRI)

MRI works in an ingenious way, winning Nobel prizes for its architects. It relies on the fact that the human body is mostly water, and that different organs contain different arrangements of the wet stuff. Placing a person in a strong magnetic field causes the hydrogen nuclei of water to align with the magnetic field. The person is then zapped with a carefully chosen pulse of electromagnetic radiation—specifically, radio waves. This causes the hydrogen nuclei to flip over. As they subsequently realign themselves with the magnetic field, they emit radio signals that have the same frequency as the radiation they had just absorbed. These signals are detected and interpreted by the scanner, which uses them to build up a picture of the person’s insides.(MRI工作原理)

The new technology, called magnetic-particle imaging, is being developed by Jürgen Weizenecker of Philips Research in Hamburg, Germany, and his colleagues. It measures the magnetic properties of tiny particles of iron oxide that are injected into the bloodstream. Iron oxide, or rust, to give its common name, is already used in medical imaging to enhance the contrast between damaged and undamaged parts of the liver, for example, in an MRI scan. The new technique creates a three-dimensional image of the flow of the magnetic particles injected into the bloodstream. This can then be overlaid on an anatomical map of the body provided by an MRI scan.

As the iron-oxide particles move through the body, their magnetisations are aligned to the static magnetic field of the scanner. This field is shaped such that it is strong in most places, but its strength falls to zero at a particular point. At this point, the iron-oxide particles lose their magnetism. The researchers then introduce a second, oscillating field generated by small coils. This second magnetic field is strong enough to magnetise the particles nearby, flipping their magnetisations to-and-fro and getting them to emit characteristic radio signals as they do so. Those iron-oxide particles at the point where the static magnetic field is zero can be distinguished from the particles elsewhere because their magnetic flipping is unaffected by the static magnetic field. The strength of the signal reveals the concentration of iron-oxide particles at that point. Adding two more sets of coils placed at right angles to the first enables the researchers to create a three-dimensional picture.（以上两段是在说明MRI中的核心技术：magnetic-particle的）

Dr Weizenecker and his colleagues recently used a mouse to show that the technique works. They placed the creature in a tiny scanner and traced the flow of magnetic particles through the four chambers of its beating heart. The chambers showed up as bright signals in the image, with a new image captured 50 times a second. By calculating the concentrations and flow of the particles, the researchers reckon（to regard or think of as） that it would be possible to carry out a range of cardiovascular measurements. They reported the results in a recent issue of Physics in Medicine and Biology. （magnetic-particle的可能应用）

Scaling up the technology from the murine to the human scale calls for a considerable feat of engineering. But Philips, which makes MRI scanners, is confident it can be done. Besides working with MRI, such a machine could also complement the results from other scanners, including computerised-tomography (CT) machines, which use X-rays. Both MRI and CT can produce three-dimensional pictures out of lots of two-dimensional slices through the body. When it becomes possible to view the blood flowing within them, these images will also spring to life.（前景预测）

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编辑又有问题，疯了。。。。不改了