ZT: 最新医学成像技术透视奇妙人体构造

--鲸鱼按，转自科讯网医疗器械频道，点击标题观看原文。

据美国《探索》杂志报道，医学成像技术在过去几年取得了突飞猛进的发展，如今，这些新技术可以甄别人体任何结构以及许多重要生物过程，比如不同的血流速度。以下这组图片不仅揭示了患病后的人体构造，还在视觉上给人以冲击。

1.弥散张量成像


　　　　　　　　　　　　　　　精神分裂症患者大脑弥散张量成像(DTI)
　　一种描述大脑结构的新方法被称为弥散张量成像(DTI)。这张图便是医疗人员在研究精神分裂症患者时，利用弥散张量成像技术制作出来的。　

　　　　　　　
　　像这样的弥散张量成像图(呈现方式与以前的图像不同)可以揭示脑瘤如何影响神经细胞连接，引导医疗人员进行大脑手术。
　　弥散张量成像其实是核磁共振成像(MRI)的特殊形式。举例来说，如果说核磁共振成像是追踪水分子中的氢原子，那么弥散张量成像便是依据水分子移动方向制图。神经细胞纤维长而薄，分子通常会沿着神经细胞纤维扩散。研究人员可以突出水分子和一组组神经细胞纤维以相同方向运行的部位。像这样的弥散张量成像图(呈现方式与以前的图像不同)可以揭示脑瘤如何影响神经细胞连接，引导医疗人员进行大脑手术。它还可以揭示同中风、多发性硬化症、精神分裂症、阅读障碍有关的细微反常变化。

2. 核磁共振成像


核磁共振成像
　　在核磁共振成像仪器下，患者躺在圆柱形磁体内，暴露于强大的磁场。一旦暴露在磁场中，水分子的质子会排成一行，要是遭到无线电波的攻击，它们会立即乱作一团，不成直线。在质子重新排列过程中，电脑会收集它们的信号，并加工成图像。富含水的组织会发出更强烈的信号，在生成的图像中看上去更亮，而骨骼相对较暗。这项技术用在此处是来描述大脑和颈部动脉的。在注射了用于对比的成像剂以后，放射线专家重复扫描，这时，成像剂在血管中移动，使他们可以看清楚造成中风、脑动脉瘤和各种外伤的堵塞物。

　　　　　　　　
　　　　　　　　　　　　　　　脊椎管和大脑处的明亮区域表示脑脊髓液。
　　核磁共振成像技术还经常用在神经成像方面。脊椎管和大脑处的明亮区域表示脑脊髓液；向下延伸至身体的长条状体则是脊髓。

3.X光血管成像术


　　　　　　　　　　　　　　　　　　　X光血管成像术
　　X光血管成像术让手上如此细小的血管都呈现出来。由这种最新数码探测仪生成的图像质量可以让放射科医师不用使用高剂量辐射物，也能看清楚器官的细微之处。这张照片显示了手外伤的直接影响——没有血液流向第四根手指，而其他手指的小血管却清晰可见。



　　　　　　　　　　　　　　　　X光血管成像术
　　制作有用的医学图像涉及两个主要步骤：一是搜集数据，二是将这些数据转换为可快速、准确解读的图像。这张图像由一种称为X射线断层成像(简称CT)的先进X光技术生成，突出了上述两个方面的进步。体绘制软件(Volume-rendering software)结合CT血管成像技术，可以识别心脏附近主动脉(从图像顶端延伸至身体下部、心脏周围的大片粉色血管)的异常情况。再往下，可以清楚看到肝脏(紫色)和肾脏(鲜红色)。准确测定主动脉直径至关重要，因为外科医生可以借此判断主动脉是否存在破裂的风险。

4.CT血管成像


　　　　　　　　　　　　　　　　CT血管成像
　　对于此处用以显现骨盆的CT血管成像来说，成像剂会注射到静脉，使血管同软组织形成鲜明对比。电脑软件可以进一步凸显骨骼和血管之间的差别，让医生可以做出更明确、更快速地诊断。


　　　　　　　　　　　　　　　　此图中的两只手是尸检扫描的结果
　　通常情况下，CT使用一个X光源，但研究人员可以将两个不同能量的X光源结合起来，更清晰地呈现软组织。根据特定组织(比如图中两只手的腱和韧带)吸收不同能量的事实，仪器可以突出展示它们的图像。为检验这种呈现方式的准确性，研究人员对尸体进行了扫描，将扫描结果同他们的“虚拟”发现相比较。此图中的两只手就是尸检扫描的结果。当然，CT技术的主要目标是改善健康，但也存在用于虚拟尸检的可能性。作为法医检查的一部分，像这样的CT扫描可以揭示小刀等物体的路径。

5.正电子放射层扫描术(PET)


　　　　　　　　　　　　　　　　　　正电子放射层扫描术(PET)
　　很多医学成像技术主要集中在解剖构造方面，正电子放射层扫描术(PET)有所不同：这种技术生成的图像突出了细胞活动。医生先给患者注射放射性示踪剂，接着，吸收示踪剂最多的细胞会发出亮光。此图中的示踪剂是葡萄糖。癌细胞会快速生长并分裂，因此会消耗大量能量，吸收葡萄糖。红色表示患者肝脏和肩部有问题。大脑和心脏(C形红块是心脏肌肉壁，即心肌层)同样会大量消耗能量，所以也会呈现出来。PET扫描和CT扫描二者结合，能够突出图中的人体构造。图一是PET扫描，图二是CT扫描，图三是PET扫描和CT扫描的结合，这使得医生可以更准确地看清楚问题所在。同核磁共振成像仪一样，正电子放射层扫描仪可以采集多个平面的数据。在这三张图中，分别只有一个“切片”显示出来，只要结合所有这些切片，就能生成三维图。


　　　　　　　　　　　　　　　　在这张图中，PET扫描确认的癌组织是蔚蓝色圆团状物体，而CT扫描锁定了它在结肠的位置。
　　根据CT扫描，肾脏(红色)、骨骼和血管的结构也都清晰可见。PET技术最常用于肿瘤学检查，也应用于心脏病学和神经病学领域。生成此图的仪器制造商“GE Healthcare”日前引进了两种系统，帮助研究人员探索新的临床应用。据美国放射学学院的布鲁斯·希尔曼(Bruce Hillman)介绍，由于可以监测细胞功能，PET就是一系列用以监控人体细胞和亚细胞新工具的典型代表。

Ig Nobel awards: the power of panda poo

The Biology prize of Ig Nobel awards (the 2nd best Nobel prize) this year, was shared by Fumiaki Taguchi, Song Guofu and Zhang Guanglei of Kitasato University graduate school of medical sciences in Japan for demonstrating that kitchen waste can be reduced by more than 90% by using bacteria extracted from giant panda excrement. Taguchi suspected panda faeces must contain bacteria capable of breaking down even the hardiest of foods because of the bear's vast consumption of bamboo.

What a easy logic!

How many colors are there in this picutre?

The answer is in my other blog.

Werner Forssmann

-- I found this Doctor's story very interesting. The courage he showed as a young physician during the course he performed the first Cardiac catheterization on himself is extraordinary. If there is some bold people who are born and awarded to be the pioneers of human-being, he is one of them. BTW, he was given a Nobel prize in 1956 for his reckless attempt which is one of the milestones of modern medicine.

Werner Theodor Otto Forßmann, (August 29, 1904 – June 1, 1979) was a physician from Germany who won the Nobel Prize in Medicine for developing a procedure that allowed for the catheterization of the heart.

Forßmann was born in Berlin on August 29, 1904. Upon graduating from Askanische Gymnasium, he entered the University of Berlin to study medicine, passing the State Examination in 1929.^[1]

He hypothesized that a catheter could be inserted directly into the heart, for such applications as directly delivering drugs, injecting radiopaque dyes, or measuring blood pressure. The fear at the time was that such an intrusion into the heart would be fatal.^[2] In order to prove his point, he decided to try the experiment on himself.

In 1929, while working in Eberswalde, he performed the first human cardiac catheterization. He ignored his department chief and tied his assistant to an operating table. ^[3]Then, he anesthetized his own lower arm and inserted a cannula into his antecubital vein, threading it 65cm all the way to his heart. ^[1] Afterwards, he walked some distance to the X-ray department to photograph the catheter which was now lying in his right auricle.

The head clinician at Eberswalde, recognizing Werner's discovery, created an unpaid position for him at the Berliner Charité Hospital, working under Ferdinand Sauerbruch. Though, once Sauerbruch saw his paper, he was thrown out of the hospital. Sauerbruch commented, "You certainly can't begin surgery in that manner".^[4] Facing such disciplinary action for self-experimentation, he was forced to quit cardiology and take up urology.^[2]

He left to work at City Hospital at Mainz. And then, went to study urology under Karl Heusch at the Rudolf Virchow Hospital in Berlin. Later, he was appointed Chief of the Surgical Clinic at both the City Hospital at Dresden-Friedrichstadt and the Robert Koch Hospital in Berlin.^[1]

In 1933, he married Dr. Elsbet Engel, a specialist in urology.

At the start of World War II, he became a medical officer. In the course of his service, he rose to the rank of Sergeant-Major, until he was captured and put into a POW camp. Upon his release, in 1945, he worked as a lumberjack and then as a country doctor in Schwarzwald with his wife. In 1950, he began practicing as urologist in Bad Kreuznach^[1][2]

During the time of his imprisonment, his paper was read by André Frédéric Cournand and Dickinson W. Richards. They developed ways of applying his technique to heart disease diagnosis and research. And, in 1956, the Nobel Prize in Physiology or Medicine was awarded to Cournand, Richards, and Forssmann.^[1]

After winning the Nobel Prize, he was given the position of Honorary Professor of Surgery and Urology at the University of Mainz.^[1]

Later, in 1954, he was given the Leibniz Medal of the German Academy of Sciences. And, in 1961, he became an Honorary Professor at the National University of Cordoba.^[1]. In 1962, he became a member of the Executive Board of the German Surgical Society. He also became a member of the American College of Chest Physicians, honorary member of the Swedish Society of Cardiology, the German Society of Urology, and the German Child Welfare Association.^[1]

He and Elsbet had six children: Klaus Forssmann in 1934, Knut Forssmann in 1936, Jörg Forssmann in 1938, Wolf Forssmann in 1939 (who was first to isolate the atrial natriuretic peptide), Bernd Forssmann in 1940 (who helped develop the first clinical lithotriptor), and Renate Forssmann in 1943.^[1][2]

He died in Schopfheim, Germany of heart failure on June 1, 1979.^[2]

Digital camera tutorials and digital photography course - DCVIEWS

Digital camera tutorials and digital photography course - DCVIEWS: "Blooming effect
Image distortion - Blooming effect - Digital cameras, digital camera reviews, photography views and news tutorials

Photo by Andreas BusseWhen light passes the lens of a digital camera and is captured by the CCD it is converted into an electrical charge.
There is a limit to how much charge each pixel or photosite can store. If there is too much charge for one photosite it will overflow to its neighbouring pixel causing an effect which is called blooming or streaking. Manufacturers try to eliminate this effect by “anti-blooming gates” which can be compared to vertical drainage channels running beside each row of photosites. These allow the overflowing charge to flow away without affecting surrounding pixels.

Though these anti-blooming gates are fairly successful at avoiding the problem, very extreme exposure situations can still lead to blooming. Especially where a very bright edge is next to a very dark edge, as seen with leaves or branches of a tree shot against a bright sky. It will be visible as a white halo or vertical streak which extends for several pixels. The effects of blooming often make chromatic aberrations more visible. These are the purple lines along dark edges in an image, caused by the effect of blue light bending more than red light."

铱星计划-Story of Iridium satellite phone

I found this story very interesting. The idea of Iridium satellite constellation is fascinating even now when I already know it was a commercial failure. The story is thought-provoking and a good lesson for all high-tech product companies. However, in a technical term, the dream of connecting people over any obstacles on the ground using a satellite network is amazing. I would be very interesting to see where ISC phone will go and if it can turn out to be a commercial success in the future.

铱星计划是一个让许多摩托罗拉人兴奋不已的想法。
　　　　　　革命性的想法从何而来？对于摩托罗拉的工程师巴里•伯蒂格来说，它来自于妻子在加勒 比海度假时的抱怨，说她无法用手机联系到她的客户。回到家以后，巴里和摩托罗拉在亚利桑那州工作的卫星通信小组的另外两名工程师想到了一种铱星解决方案 ——由77颗近地卫星组成的星群，让用户从世界上任何地方都可以打电话。由于金属元素铱有 77 个电子，这项计划就被称为了铱星计划，虽然后来卫星的总数降到了 66 个。
　　　　
　　　　　　这是个好的创意吗？尽管遭到伯蒂格顶头 上司的否决，这一计划却得到了摩托罗拉总裁罗伯特•高尔文的青睐并给予了支持。对于罗伯特，以及他的儿子克里斯 •高尔文（后来成为他的继任人）来说，铱星计划是摩托罗拉技术高超的显示，具有巨大潜力，令人振奋，决不可放弃。对于摩托罗拉的工程师们来说，建立铱星群 的挑战是一次经典的“技术拉锯战”——50多亿美元的代价终于让他们在1998年将铱星首次投入使用。
　　　　这是一个非常宏伟而超前的计划，它 最大的技术特点是通过卫星与卫星之间的传输来实现全球通信，相当于把地面蜂窝移动系统搬到了天上。从技术讲，铱星系统是相当了不起的，它采用星际链路。在 极地，66 颗卫星要汇成一个点，又要避免碰撞，难度很高。从管理上讲，它又是一个完整的独立网，呼叫、计费等管理是独立于各个国家通信网的。（这种独立计费再后来给 它的运营带来很大麻烦。）低轨道卫星与目前使用的同步轨道卫星通信系统比较有两大优势：首先，因为轨道低，只有几百公里，信息损耗小，这样才可能实现手机 到卫星的直接通信。我们现在的任何手机都不可能和三万公里以外的同步卫星直接通信；第二，由于不需要专门的地面基站，可以在地球上任何地点进行通信。 1991 年摩托罗拉公司联合了好几家投资公司，正式启动了“铱星计划”。1996 年 ，第一颗铱星上天；
　　　　　　1998年11月1日， 在进行了耗资1.8亿美元的广告宣传之后铱星公司展开了它的通信卫星电话服务。开幕式上，副总统阿尔•戈尔用铱星打了第一通电话。电话机的价格是每部 3，000美元，每分钟话费3-8美元。结果却令人不无沮丧。到1999年4月，公司还只有1万个用户。面对着微乎其微的收入和每月四千万美元的贷款利 息，公司陷入了巨大的压力之中。4月里，就在公司宣布其季度财务报告的前两天，首席执行官斯坦阿诺辞职，宣称他与董事会在战略问题上发生了分歧。公司内部 一位资深人员约翰•理查德森迅速接替斯坦阿诺成为临时首席执行官，但毁灭的阴影却已经笼罩了上来。
　　　　
　　　　　　1999年6月，铱星解雇了15％的员工，甚至包括几位参与了公司营销战略规划的经理。8月，它的用户只上升到2万个，离贷款合同要求的5万2千个相去甚远。1999年8月13日，星期五，在拖欠了15亿美元贷款的两天之后，铱星提出了破产保护的申请。
　　　　半年后的 2000 年 3 月 18 日，铱星公司正式破产。铱星成了美丽的流星。66 颗卫星在天上自己飞了几年，终于于 2001 年被一家私募基金公司（Private Equity）以两千五百万美元的低价买下。
　 　　　铱星计划是通信史上一个流星，一个美丽的故事（A Beautiful Story）。摩托罗拉公司很聪明地利用其技术优势吸引了全世界的眼球。该计划一出炉就引起世人的广泛注目，也赢得了风险投资家的青睐。摩托罗拉为此自己 拿出了十亿美元，同时钓鱼似的从投资公司有拿到近五十亿美元，从而大大降低了自己的风险。但是，在商业运作上，摩托罗拉做得很不成功。首先，市场分析现在 看来就有问题，成本过高导致用户数量不可能达到预计的盈利所必需的规模。而成本过高的原因又是技术选择的失误造成的。摩托罗拉长期以来都是一个了不起的技 术公司，它长于技术，但是过分相信技术的作用。铱星计划在技术上是无与伦比的，但是，过于超前市场的技术不仅导致成本过高，而且维护费用也是巨大的。另 外，引入风投本身的弊端在项目的后期凸显出来，那就是投资者为了收回投资，过早将铱星系统投入商用，当时这个系统通话的可靠性和清晰度很差，数据传输速率 也仅有 2.4Kps ，因此除了打电话没法做任何事，这使得潜在的用户大失所望。概况来讲，就是铱星计划太超前了，它开业的前两个季度，在全球只有一万个用户，而当初市场的分 析去乐观地预计，仅在中国就能有这个数的十倍。在后期商业运作上。铱星公司问题很多，最终导致银行停止贷款、部分股东撤回投资，并导致公司在股市上停盘的 致命打击。
　　　　现在，仍然可以买到铱星手机。在淘宝搜索“铱星”，能找到不少卖家价钱在1万到1万6之间。据说，这类手机在国内也还比较畅销，针对于特定野外探险的人群进行销售。这种几乎成了奢侈品，像我们这等普通大众，是无福消受了。

What is the temperature in space?

If you are too lazy to read this post, I will give you a quick answer. It is 3 kelvin or -270 degree if you prefer calcius. If you want to know more, come to read this.

This is an interesting question, because if there is no molecules, there is no indicate to termperature. However, the truth is there is still particles in the space though very few. The temperture in space should be better refered as the temperture of an object if we place it in an empty space. I found an interesting article about it. I am sure you will feel you are very lucky to be the citizen of the earth. Update your knowledge:
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Empty space itself cannot have a temperature, unless you mean some abstruse question about quantum vacuums.

However, if you put a physical object into space, it will reach a temperature that depends on how efficiently it absorbs and emits radiation and on what heating sources are nearby. For example, an object that both absorbs and emits perfectly, put at the Earth's distance from the Sun, will reach a temperature of about 280 K or 7 C. If it is shielded from the Sun but exposed to interplanetary and interstellar radiation, it reaches about 5 K. If it were far from all stars and galaxies, it would come into equilibrium with the microwave background at about 2.7 K. Spacecraft (and spacewalking astronauts) often run a bit hotter than 280 K because they generate internal energy. Arranging for them to run at the desired temperature is an important aspect of design. Some people also consider the "temperature" of high energy particles like the solar wind or cosmic rays or the outer parts of the Earth's
atmosphere. These particles are not in thermal equilibrium, so it's not correct to speak of a single temperature for them, but their energies correspond to temperatures of thousands of kelvins or higher. Generally speaking, these particles are too tenuous to affect the temperature of macroscopic objects. There simply aren't enough particles around to transfer much energy. (It's the same on the
ground. There are cosmic rays going through your body all the time, but there aren't enough to keep you warm if the air is cold. The air at the Earth's surface is dense enough to transfer plenty of heat to or from your body.)

30米望远镜花落夏威夷

Thirty Meter Telescope Selects Mauna Kea

July 21 , 2009

PASADENA, Calif. — After careful evaluation and comparison between two outstanding candidate sites—Mauna Kea in Hawai‘i and Cerro Armazones in Chile—the board of directors of the TMT Observatory Corporation has selected Mauna Kea as the preferred site for the Thirty Meter Telescope. The TMT will be the most capable and advanced telescope ever constructed.

When completed in 2018, the TMT will enable astronomers to detect and study light from the earliest stars and galaxies, analyze the formation of planets around nearby stars, and test many of the fundamental laws of physics.

To achieve these outstanding results, the TMT will integrate the latest innovations in precision control, segmented mirror design, and adaptive optics to correct for the blurring effect of Earth’s atmosphere, enabling the TMT to study the Universe as clearly as if the telescope were in space. Building on the success of the twin Keck telescopes, the core technology of TMT will be a 30-meter primary mirror composed of 492 segments. This will give TMT nine times the collecting area of today’s largest optical telescopes.

To ensure that the site chosen for TMT would enable the telescope to achieve its full potential, a global satellite survey was conducted, from which five outstanding candidate sites were chosen for further ground-based studies of atmospheric stability, wind patterns, temperature variation, and other meteorological characteristics that would affect the performance of the telescope.

Based on these results and extensive studies, Mauna Kea and Cerro Armazones were selected in May 2008 for further evaluation and environmental, financial, and cultural impact studies. The TMT board used the results from these meticulous research campaigns to help guide the final site-selection process.

"It was clear from all the information we received that both sites were among the best in the world for astronomical research,” said Edward Stone, Caltech's Morrisroe Professor of Physics and vice chairman of the TMT board. “Each has superb observing conditions and would enable TMT to achieve its full potential of unlocking the mysteries of the Universe.”

“In the final analysis, the board selected Mauna Kea as the site for TMT. The atmospheric conditions, low average temperatures, and very low humidity will open an exciting new discovery space using adaptive optics and infrared observations. Working in concert with the partners’ existing facilities on Mauna Kea will further expand the opportunities for discoveries,” said Stone.

Henry Yang, TMT board chair and chancellor of the University of California at Santa Barbara, expressed excitement at this decision. "Our scientists and engineers have been designing and building the key components that will go into the telescope. By deciding to build on Mauna Kea, the TMT board has given a clear signal that we are ready to move forward and begin building in earnest as soon as all the necessary approvals are in place. I want to thank the Moore Foundation for its visionary support. I also want to thank our scientific colleagues and the coalition of community members, educators, businesses, unions, political leaders, and stakeholders in Hawai‘i who have brought us to the point of this site selection. The board expresses a strong commitment to respect the long history and cultural significance of Mauna Kea to the Hawaiian people, and has committed annual funding for local community benefits and education in Hawai‘i.”

Before construction can begin on Mauna Kea, the TMT must submit and have approved an application for a Conservation District Use Permit (CDUP) to the Hawaiian Department of Land and Natural Resources. This will be done through the community-based Office of Mauna Kea Management, which oversees the Mauna Kea summit as part of the University of Hawai'i at Hilo.

"We are very grateful for the support that TMT has received from both the people and governments of Hawai‘i and Chile during the site-selection process," said Professor Ray Carlberg, the Canadian Large Optical Telescope project director and a TMT board member. “We are excited about the prospect of being the first of the next generation of extremely large telescopes.”

The TMT project is an international partnership among the California Institute of Technology, the University of California, and ACURA, an organization of Canadian universities. The National Astronomical Observatory of Japan (NAOJ) joined TMT as a Collaborating Institution in 2008.

“The selection of Hawai‘i as the site for the Thirty Meter Telescope will greatly strengthen international cooperation in astronomy. The synergy between TMT and the highly successful Subaru Telescope already on Mauna Kea will lead to many further research breakthroughs,” said Professor Masanori Iye, the Extremely Large Telescope Project Director of the NAOJ.

The TMT project has completed its $77 million design development phase with primary financial support of $50 million from the Gordon and Betty Moore Foundation and $22 million from Canada. The project has now entered the early construction phase thanks to an additional $200 million pledge from the Gordon and Betty Moore Foundation. Caltech and the University of California have agreed to raise matching funds of $50 million to bring the construction total to $300 million, and the Canadian partners propose to supply the enclosure, the telescope structure, and the first light adaptive optics.

TMT gratefully acknowledges support for design and development from the following: Gordon and Betty Moore Foundation, Canada Foundation for Innovation, Ontario Ministry of Research and Innovation, National Research Council of Canada, Natural Sciences and Engineering Research Council of Canada, British Columbia Knowledge Development Fund, Association of Universities for Research in Astronomy, and the National Science Foundation (USA).

Spectral-domain OCT wows interventional cardiologists

(From Bio Optics)

A live demonstration of a next-generation optical coherence tomography (OCT) system from LightLab Imaging (Westford, MA) drew rave reviews from a crowd of more than 1000 interventional cardiologists attending the Transcatheter Cardiovascular Therapeutics (TFT) conference in Washington D.C. last October. Performed in Germany by Prof. Dr. Eberhard Grube of the Helios Heart Center (Siegburg, Germany) and beamed live to the main hall of the Washington Convention Center, the procedure provided real-time OCT images of a recently implanted stent and the tissues covering the stent struts with a resolution of 15 to 20 µm—more than 10 times the resolution of intravascular ultrasound (IVUS), the dominant intracoronary imaging technology these days (see figure). The images were provided by LightLab’s next-generation spectral-domain scanning-laser OCT system (SL-OCT).

According to Gregg Stone, M.D., professor of medicine at Columbia University and chairman of the Cardiovascular Research Foundation (CRF), which sponsors the TFT meeting, many in the crowd were “amazed” at the OCT images. Gary Mintz, chief medical officer of the CRF, said it was the most excitement he’d seen at the meeting in recent years.

“The difference in resolution between OCT and IVUS is extraordinary,” Dr. Stone says. “This should significantly improve our ability to make accurate decisions for patients.”

The SL-OCT system from LightLab Imaging provides in vivo images of intravascular stents at much faster rates and higher resolution than competing technologies such as intravascular ultrasound. (Courtesy of LightLab Imaging)

The 1300 nm LightLab SL-OCT device is based on the fundamental Fourier-domain modelocking technology developed at the Massachusetts Institute of Technology (Cambridge, MA) by James Fujimoto (see related story, p. 20). LightLab’s first-generation system, the M2 OCT, is a time-domain OCT system. Compared to the M2 system, the SL-OCT system is much faster and provides higher-resolution, higher-quality images, according to Joe Schmitt, chief technology officer at LightLab. The SL-OCT system collects about 45,000 lines/s at 100 frames/s, compared to the M2, which collects about 4800 lines/s at 15 frames/s. In addition, the SL-OCT system takes a different approach to resolving a fundamental issue in cardiovascular applications: OCT cannot image in blood because the components of red blood cells cause diffuse reflection of near-infrared light.

“Our earlier generation of this product (the M2) uses an occlusion balloon to briefly stop the blood flow while doing OCT imaging in the arteries,” Schmitt says. “With the new system we are using a rapid-flush method that is auto-triggered. When you press the syringe (to deliver the saline), image acquisition begins. The catheter begins to spin, the sheath moves back, and you end up with a full spiral scan. Because you can pull back about 20 mm/s, you only need two to three seconds to cover the entire image area.”

The SL-OCT system possesses a higher sensitivity than the M2 system and its resolution is approximately three times higher, he adds, allowing for even more detailed intravascular observation and paving the way to 3-D intravascular imaging. Potential applications in clinical diagnostics include improved diagnosis of vulnerable plaques, identification of the presence of thrombus following coronary stent treatment and image diagnosis that helps to decide endpoints for the treatment of incomplete stent apposition, and auxiliary diagnosis for determining the period to discontinue antiplatelet therapy in drug-eluting stent patients.

The market potential for OCT imaging in cardiology is significant; currently, IVUS is a $400 million market with only 14% market penetration, according to Volcano (San Diego, CA), a leading provider of IVUS technologies. Given that OCT offers 10 times the resolution of IVUS, the future looks quite bright indeed for companies like LightLab Imaging and even Volcano. In mid-December Volcano announced that it will pay $25 million to acquire CardioSpectra (San Antonio, TX), a small company founded to commercialize OCT technology developed at the University of Texas (see related story, p. 14).

The LightLab SL-OCT system is in preclinical trials. The company is preparing to begin U.S. clinical trials and hopes to launch the system commercially by the end of 2008.

“Five years ago, intravascular imaging was a $150 million to $200 million market,” Schmitt says. “Now it is double that because of stents. But ultrasound doesn’t have enough resolution to image the thrombosis that can occur with stents. So our OCT product is quite timely.” —KK

A commercial available profuct could be seen from here.

The sound of light

Jun 4th 2009
From The Economist print edition

Biomedical technology: A novel scanning technique that combines optics with ultrasound could provide detailed images at greater depths

Mary Evans Picture Library

IF LIGHT passed through objects, rather than bouncing off them, people might now talk to each other on “photophones”. Alexander Graham Bell demonstrated such a device in 1880, transmitting a conversation on a beam of light. Bell’s invention stemmed from his discovery that exposing certain materials to focused, flickering beams of light caused them to emit sound—a phenomenon now known as the photoacoustic effect.

It was the world’s first wireless audio transmission, and Bell regarded the photophone as his most important invention. Sadly its use was impractical before the development of optical fibres, so Bell concentrated instead on his more successful idea, the telephone. But more than a century later the photoacoustic effect is making a comeback, this time transforming the field of biomedical imaging.

new technique called photoacoustic (or optoacoustic) tomography, which marries optics with ultrasonic imaging, should in theory be able to provide detailed scans comparable to those produced by magnetic-resonance imaging (MRI) or X-ray computerised tomography (CT), but with the cost and convenience of a hand-held scanner. Since the technology can operate at depths of several centimetres, its champions hope that within a few years it will be able to help guide biopsy needles deep within tissue, assist with gastrointestinal endoscopies and measure oxygen levels in vascular and lymph nodes, thereby helping to determine whether tumours are malignant or not. There is even scope to use photoacoustic imaging to monitor brain activity and gene expression within cells.

To create a photoacoustic image, pulses of laser light are shone onto the tissue being scanned. This heats the tissue by a tiny amount—just a few thousandths of a degree—that is perfectly safe, but is enough to cause the cells to expand and contract in response. As they do so, they emit sound waves in the ultrasonic range. An array of sensors placed on the skin picks up these waves, and a computer then uses a process of triangulation to turn the ultrasonic signals into a two- or three-dimensional image of what lies beneath.

The technique works at far greater depths (up to seven centimetres) than other optical-imaging techniques such as confocal microscopy or optical-coherence tomography, which penetrate to depths of only about a millimetre. And because the degree to which a particular wavelength of light is absorbed depends on the type of tissue and, in the case of blood, on whether it is oxygenated or deoxygenated, there is, in effect, a natural contrast agent. This makes the technique superior to ultrasound alone when it comes to picking out detailed features such as veins.

MRI and CT scans are also capable of delivering this kind of detail. But they usually require contrast dyes to be injected into the bloodstream, says Lihong Wang, a photoacoustic researcher at Washington University in St Louis, Missouri. CT scans also involve potentially harmful ionising radiation. And MRI and CT scans are very expensive, using machines that cost millions of dollars and require dedicated staff to operate them. Photoacoustic tomography, by contrast, could eventually be performed using portable hand-held devices, similar to those used for ultrasound scanning. This would allow doctors to diagnose and monitor patients in clinics, and reduce the need to refer them to consultants. “Photoacoustics provides greater access at a much lower cost than these other technologies,” claims Michael Thornton of Endra, a medical-imaging company based in Ann Arbor, Michigan.

Shining a light

A pioneer of the technique in the late 1980s was Alexander Oraevsky, who was based at the Soviet Academy of Sciences in Moscow at the time. He had been evaluating lasers as a means of removing tissue, but in the course of his experiments he realised that his samples were producing ultrasound, and began exploring the potential of this effect for imaging. Since then the technology has come a long way, not least because of the development of nanosecond pulsing lasers. Being able to deliver such brief pulses of energy to the sample being imaged—a nanosecond is a thousand-millionth of a second—has helped improve the resolution of the resulting images. Dr Oraevsky and other researchers have shown that it is possible to image the entire blood-supply system of a mouse, for example, down to a resolution of about half a millimetre.

One of the most promising applications for photoacoustics is in the treatment of cancer. Since blood cells are natural absorbers of light, photoacoustics is particularly good at providing high-contrast images of the formation of blood vessels (angiogenesis) and detecting increased metabolic activity (hypermetabolism), both of which are hallmarks of cancer, notes Dr Wang. Preliminary clinical research is now under way to look at how the technology can be used to monitor the development of breast cancer and identify how far it has progressed.

Even with mammography and ultrasound, the current gold standards for breast-cancer screening, doctors cannot tell if a tumour is malignant or benign without performing an invasive and expensive biopsy. “About eight out of ten patients who undergo a biopsy come back negative,” says Dr Oraevsky, who now works for Fairway Medical Technologies, a company based in Houston, Texas. Photoacoustic tomography could potentially be used to diagnose women in the doctor’s surgery.

One approach being explored by Michael Pashley, head of ultrasound imaging and therapy at Philips Research in Briarcliff Manor, New York, is to develop a hybrid ultrasound scanner that can produce ordinary ultrasound scans as well as photoacoustic images. In theory the two images could even be superimposed, he says. At the moment the work, which is being carried out in collaboration with Dr Wang, is geared towards monitoring the development of breast cancers that have already been diagnosed, says Dr Pashley. But if the technology proves successful, he hopes to move on to using it for the initial diagnosis.

Lihong V. WangGetting the picture

Although the different absorption characteristics of oxygenated and deoxygenated blood provide an extremely good natural contrast agent, this approach has its limits. So some companies are exploring the use of photoacoustics in conjunction with artificial contrast-agents introduced to the bloodstream. VisualSonics, an ultrasound-imaging company based in Toronto, has been evaluating contrast agents made up of gold nanorods attached to antibodies that bind to specific targets found in cancer cells. Ultrasound is already used to detect such agents but its resolution is sufficient to show only the structure of blood vessels. Dr Wang reckons that if contrast agents that are too small to be picked up by ordinary ultrasound were introduced into a patient’s bloodstream, they could be detected using photoacoustic imaging. Furthermore, it would be possible to see where the contrast agents built up, and hence determine the extent of a tumour. And by creating contrast agents that bind to specific genetic targets, the same technique could be used to monitor gene expression, he suggests.

Room for improvement

Despite its potential and its many advantages over other methods, there are some difficulties with photoacoustic imaging that have not yet been resolved. As light penetrates deeper into tissue, the resulting ultrasonic signal diminishes. This is partly because some of the light has been absorbed by the preceding tissue, but it is also because the laser light is dispersed, diffused and back-scattered. This places limits on just how deeply photoacoustic imaging can delve. In the future it might be possible to go a little deeper, says Dr Wang, but probably not by much. “If light is delivered from both sides of the tissue, ten-centimetre-thick tissue can potentially be imaged,” he says.

Bone tissue represents another obstacle to the technology, but not for the reason you might think. Laser light usually passes easily through bone, but sound does not. The speed at which sound travels through bone is different from the speed at which it travels through soft tissue, and as the ultrasound passes from one medium to the next it is distorted. Air cavities, many of which are found inside the human body, pose a similar problem, says Dr Wang.

Even so, VisualSonics and other companies are keen to explore the use of photoacoustics for neuroimaging. It is not an insurmountable problem, says Dr Wang, who is working on a technique to model the skull so that its effects on the ultrasonic waves can be predicted and eliminated in software, restoring clarity to the signals. If he can get this approach to work, it would further extend the revolutionary potential of photoacoustic imaging in the coming years. Doctors would not merely be able to diagnose cancer in the comfort of their own surgeries—they would be able to perform brain scans, too. A technology that traces its roots to a stillborn 19th-century communications device would have taken another step towards the futuristic dream of the all-purpose hand-held medical tricorder seen in “Star Trek”.