快猫短视频

WHEN my grandmother found a lump in her breast at the age of sixty-four, her
doctor told her it was nothing to worry about. By the time he realised his
mistake, it was too late. 鈥淵ou鈥檝e killed me,鈥� she told him on his final visit
before her death.

She had already lost her mother and grandmother to breast cancer. Today, the
hereditary nature of some breast cancers is better understood, and cancer
researchers are seeking reliable ways to screen women with this genetic
predisposition. The available techniques are not perfect: they can still miss a
developing cancer, and with it the opportunity for lifesaving intervention. But
a recent discovery involving the weird quantum laws that govern the microscopic
world of atoms could provide a better solution.

Researchers are now testing a magnetic scanner that creates a strange quantum
link between atomic nuclei in different parts of the body. The two linked nuclei
act as one, synchronising their movements even if they are centimetres apart.
But this strange behaviour only occurs when the tissue under scrutiny does not
contain any abnormalities. This means that the quantum link can deliver vital
information about any developing health problems. Clinical trials of the
technique are already under way, promising to detect tumours earlier than ever
before, and to tell malignant and benign tumours apart at a very early stage.
Quantum effects used to be an odd abstraction, with little relevance to our
daily existence. But one day soon, the weird nature of quantum physics might
just save your life.

The potential of this quantum imaging technique first came to light nearly a
decade ago when a group of Princeton University researchers, led by chemist
Warren Warren, uncovered a flaw in the 50-year-old theory of magnetic resonance
imaging (MRI). This technology is currently considered the most sensitive way to
screen for breast cancers, and is used as a follow-up when suspiciously dark
areas of breast tissue show up on mammograms (see 鈥淪creen test鈥�).

Warren and his collaborators were investigating the structure of proteins by
hitting small samples of protein molecules in water with complicated sequences
of radio pulses. They hoped that the response of the molecules to this radiation
would cast light on the structure. But they didn鈥檛 understand the results they
were getting.

The nuclei of certain atoms behave like tiny magnetic spinning tops. In the
strong magnetic field of an MRI machine the spinning nuclei all line up with
their axes aligned with the magnetic field. When a radio-wave pulse hits the
aligned nuclei, it knocks them out of alignment. They carry on spinning, but at
an angle鈥攋ust as a knocked top will continue to spin even when it is
leaning over. Having all these spins at an angle to the main field creates a
measurable magnetic signal, which fades as the nuclei gradually return to their
aligned, equilibrium position.

Warren and his colleagues thought they would be able to learn about the
protein鈥檚 structure from the different ways in which this magnetic signal faded
when they varied the characteristics of the radio-wave pulse. But the signal in
Warren鈥檚 samples didn鈥檛 fade in the way that MRI theory suggested it should. 鈥淚t
was even happening in control samples containing pure water,鈥� says Warren. 鈥淲e
thought something must be wrong with the instruments.鈥�

When the instruments checked out, he thought he might have made a mistake in
designing his pulse sequences. So he pared down the experiment until he was
using the simplest possible sequence of just two pulses: a radio-wave pulse
followed by a short-lived magnetic field pulse called a crusher. The crusher
kicks each of the spins by a different amount, and so should leave them in
disarray, destroying any measurable magnetic signal in the sample.

But there was a signal. It was only about a tenth as strong as the usual
magnetic resonance signals, but it was still more than a thousand times stronger
than the background noise. Warren performed the experiment time and again. There
was no doubt that the signal was there.

The researchers found the results of these simple sequences so bizarre that
they called the sequences 鈥淐RAZED鈥�. The term has stuck: it is now the accepted
name for the pulses that produce these unexpected weak signals. Warren suspects
that he wasn鈥檛 the first researcher to see signals from CRAZED pulse sequences.
鈥淲hen it happened before, people probably thought 鈥業 made a mistake on my
sequence鈥�,鈥� he says. But Warren was sure of what he was doing and what he was
seeing. All he needed now was an explanation.

Having traced the way the unexpected magnetisation gradually faded, Warren
used the mathematical technique known as Fourier transform to reveal the
different frequency components of the signal. This provided him with the
mysterious signal鈥檚 鈥渇ingerprint鈥濃�攁nd it looked strangely familiar.

Strange connection

When a pulse of radio waves is produced under certain conditions, its photons
acquire a quantum mechanical connection, called 鈥渃oherence鈥�, which keeps them in
step with each other. When two coherent photons hit a pair of spinning nuclei
they transfer their quantum coherence to the two nuclei. This link binds the
nuclei together into one quantum state. One result of this is that the spins
will return to equilibrium at exactly the same time, and this simultaneous
response gives rise to the characteristic frequency spectrum that Warren
recognised.

Warren had only ever seen this link occur between nuclei within the same
molecule. But when he examined the quantum coherence created by the CRAZED pulse
he was surprised to find that the linked nuclei were micrometres apart, far more
than the width of a molecule. Instead of wreaking its normal havoc and
destroying all correlation between the spins as it was expected to, the crusher
had left the delicate quantum link between two hugely distant spins intact.

Warren eventually worked out what was happening. Although the crusher rotates
the axis of each of the spinning nuclei by a different amount, that rotation
doesn鈥檛 destroy every one of the quantum coherences. If it rotated one spin by
10 degrees, say, and another by 370 degrees鈥攁 full circle plus 10
degrees鈥攖heir original relationship would remain the same. Far from
knocking all the spins out of alignment, the crusher pulse would allow certain
nuclei to remain in step and so maintain their ghostly link.

Since this discovery, Warren and his collaborators have published a string of
papers in the journal Science, explaining their data and its
implications. The most far-reaching of these, Warren has realised, is that it is
possible to change the characteristics of the crusher pulse and alter the
distance over which the link occurs. The researchers have since established a
quantum link between two nuclei that are centimetres apart. 鈥淲e鈥檝e even done
this between molecules in different test tubes,鈥� Warren says.

Although these long-distance correlations are impressive and strange, it is
the possibility of going down the scale, and producing quantum coherences
between nuclei just one-tenth of a millimetre apart that has got imaging
researchers excited. Warren鈥檚 quantum coherences only form between pairs of
nuclei that are in exactly the same environment鈥攚hich means they must be
in tissue that鈥檚 in the same state of health. So by imaging neighbouring
molecules, and finding where the coherences don鈥檛 form, Warren can pinpoint
exactly where the health of the tissue changes. This should allow him to trace
out, say, the border of a tumour. The technique will provide a resolution about
50 times finer than the limit of conventional MRI.

And this is just the start. Because Warren鈥檚 technique provides an accurate
measure of the oxygen concentration in body tissues, it can also diagnose the
exact state of a tumour. Tumours use oxygen in a very particular way. The
outside of a malignant tumour co-opts its own blood supply from the body to
provide a stream of oxygen for growth. But the inside of the tumour has stopped
growing and is largely dead and deoxygenated. Most normal tissue has an
oxygenation level somewhere between these two extremes.

The oxygenation level of the tissue determines the rate at which its spinning
nuclei, disturbed by the radio-wave pulse, will return to their original
orientation. Only two spins that return at the same rate will form a quantum
coherence and give out the fingerprint signal. At the borders of a tumour, where
there is a sharp change in the level of oxygenation, the quantum coherence can鈥檛
form, and thus there is no signal.

With Mitch Schnall at the Hospital of the University of Pennsylvania, in
Philadelphia, Warren has now begun clinical trials of breast tissue imaging
using the new quantum states. They have two aims: to pick up breast tumours too
small to see with current techniques, and to use the better resolution to pick
out more detail in the blood supply. If they can see exactly how the tumour is
growing they should be able to determine the level of malignancy without the
need to remove a sample of tissue for biopsy鈥攁 painful and distressing
procedure. The clinical trials will run for a year, and until they are over,
Schnall doesn鈥檛 want to make any concrete claims. 鈥淲e鈥檙e not yet in a position
to say it鈥檚 better, but it has the potential for substantial impact,鈥� he
says.

Researchers at the Institute of Cancer Research at the Royal Marsden NHS
Trust hospital in Surrey are also generating images using the new technique.
Angelo Bifone and Martin Leach have produced the first quantum coherence images
of the human brain and of brain tumours, although they are still learning how to
interpret the pictures. 鈥淲e know there鈥檚 a lot of new information in there,鈥�
says Leach, 鈥渂ut we don鈥檛 know how to use it yet.鈥� Nevertheless the team can see
attractive possibilities ahead. 鈥淚f you want to study smaller blood vessels you
can just use a pulse that鈥檚 twice as long or twice as strong鈥攖here鈥檚
nothing like that in conventional MRI,鈥� says Bifone.

In his latest study, Bifone has used the new method on the bone of people
suspected of having osteoporosis, where the bone becomes porous, or
鈥渢rabecular鈥�. 鈥淵ou can look at holes on different length scales in the
trabecular bone to see if and how they鈥檙e thinning,鈥� he says.

It鈥檚 still too soon to tell exactly how good the technique will prove in all
these situations, but Warren believes that quantum imaging could eventually
save lives. His own mother died of breast cancer the same year he discovered the
quantum links. She was diagnosed in 1986, and fought the tumour through surgery
and chemotherapy. But nine years later, the cancer recurred and killed her. At
the time Warren was some way from his first images. 鈥淭oday,鈥� he says, 鈥渟he would
have been a prime candidate for what we hope we can achieve: aggressive, very
early detection.鈥�

I can鈥檛 help wondering whether this quantum imaging would also have saved my
grandmother鈥檚 life. Or whether, one day, the strange nature of quantum physics
will come between me and my genetic fate.

THE techniques currently used to screen women for breast cancer are good, but
not good enough. X-ray mammography, the basic screening tool, looks for
variations in the density of breast tissue. In theory, X-rays can distinguish
the higher density of a tumour from that of normal tissue, just as they
distinguish bone from muscle. The technique is routinely used to screen women
over 50 in Britain. In the US, where missed diagnoses have resulted in lawsuits,
mammography screening clinics are not so common.

However, the technique does not work well in younger women, whose breast
tissue can have the same density as a developing tumour. This is a problem
because many women with a genetic predisposition to breast cancer are young when
their tumours begin to form.

Clinicians in Britain and the US are testing the routine screening potential
of magnetic resonance imaging (MRI), which is already used to investigate
suspicious lumps found through mammography. MRI is superior to mammography
because it doesn鈥檛 rely on density measurements, doesn鈥檛 give a radiation dose,
and it can provide images in 鈥渟lices鈥� rather than the single view through the
breast that you get from X-rays.

But MRI has its own shortcomings: the contrast between healthy and cancerous
tissue is slight, so seeing tumours is difficult until they become large and
dangerous. Clinicians can inject compounds that increase the contrast, but it
doesn鈥檛 always help. It is still not clear whether MRI screening will improve
early cancer detection and provide an alternative to voluntary mastectomies,
often used to protect women in high risk groups.