As reported by Advanced Imaging, September 26, 2005.

Biomedical Imaging Put to Work

Imaging Is the Interface to View the Human Machine

By Mike May

Modern biomedical images are often attention grabbers. They can appear as art when various fluorescent markers create a pattern of color inside cells. Scientists today, however, demand more than pretty pictures. Images must work. A biomedical image should diagnose a disease, describe a biochemical pathway, monitor the impact of a treatment, or guide a procedure.

Roderic Pettigrew, director of the National Institute of Biomedical Imaging and Bioengineering (Bethesda, MD), says that imaging has value on several levels. Perhaps the most obvious value is the ability to diagnose a disease without invading the body. "There is a tremendous shift in the whole healthcare paradigm," Pettigrew says, "from hunting down disease and treating it to forecasting disease and preventing it."

To predict the future, imaging must surpass simple observation. Biomedical scientists now use imaging to understand structure and function and how the two interact. "We are biological machines," says Pettigrew, "and imaging provides a way to see how these machines work."

From the Heart

David Piwnica-Worms, director of the Molecular Imaging Center at Washington University School of Medicine (St. Louis), does imaging research on molecular functions. His work uses Tc-99m-Sestamibi (Cardiolite), a radioactive compound from Bristol-Myers Squibb (New York) that is used to image blood flow in the heart. This fat-loving compound diffuses across cell membranes and accumulates in the mitochondria in heart cells. At the whole-tissue level, the retained radiopharmaceutical generates a snapshot of blood flow to different regions of the heart.

Cancer cells also have lots of mitochondria, and Cardiolite, an imaging agent, gets in them, too. In some cancer cells, though, a membrane transporter known as P-glycoprotein pumps chemotherapy agents out of the cell. In cells with this protein, entire families of chemotherapy agents fail. P-glycoprotein also recognizes Cardiolite, and pumps it out of the cancerous cell. With Cardiolite, Piwnica-Worms can noninvasively examine cancer cells in patients using gamma cameras and see if they resist chemotherapy by way of the P-glycoprotein. "This shows if a certain cancer is multi-drug resistant," says Piwnica-Worms. "If it is, then a different agent is needed to fight it."

Harmonic Visualization

In some cases, getting the best view demands new techniques. For example, scientists demonstrated second harmonic imaging microscopy (SHIM) more than 25 years ago, but it is just now being demonstrated as a practical technique for high-resolution imaging of cell and tissue structure and physiology. In essence, this technique relies on intense laser illumination that interacts with a highly ordered material, such as biomolecular arrays. The light comes out with half the wavelength of the laser light, but with twice the energy.

Leslie Loew, director of the Center for Biomedical Imaging Technology (CBIT) at the University of Connecticut Health Center (Farmington, CT) says that SHIM can use dye molecules that label parts of the cell. "This provides physiological output with 3-D, high-resolution accuracy," says Loew. In addition, SHIM may need no dye at all, because some biological structures — including actomyosin complexes — produce second harmonic signals. "That way, a native specimen can be used without dyes that might interfere with natural processes," he adds. His colleagues at CBIT use this approach to study muscle-related diseases.

Many other diseases may also be diagnosed with advanced imaging. At UCLA's Laboratory of Neuro Imaging, Arthur Toga and Rico Magsipoc combine optics and computers to explore brain development and disease. Toga says, "We create multi-modal representations for relationships between observations. We want to know the relationship between changes in a particular area of the brain relative to functional activity." Combining data from various imaging modalities and watching changes over time creates data sets that are 4 gigabytes (GB) on average and can reach 100 GB.

To handle the data, Toga and Magsipoc turned to Silicon Graphics' (Mountain View, CA) Onyx systems. "We need a combination of a broad infrastructure and tailored hardware that enables rapid interactions with complex visualization," says Toga. "The Silicon Graphics platform was the only solution for us to achieve that."

The large data sets demand powerful ways to move and archive data. Magsipoc says, "We can move 400 to 500 megabytes per second." With so much computing power, these scientists can follow brain changes associated with years of Alzheimer's disease or watch a child's brain develop. Toga adds, "We knew that disease processes impacted specific areas of the brain, but now we have specific maps of this and can see it in a way that we never could in the past."

Out With The Eyepiece

Despite revolutionary advances in optical imaging, some scientists still see the traditional microscope as nothing more than a complicated magnifying glass. Nikon Instruments (Melville, NY) is changing this perception with the COOLSCOPE that allows users to load a slide and display an image on a monitor or projector.

Stan Schwartz, Nikon's vice president, microscopy, says, "COOLSCOPE is tailored to scientific applications that rely on using stained slides for imaging. Scientific disciplines such as pathology, histology, anatomy and drug discovery have already benefited from simplified image capture and analysis benefits." With a click of a mouse, it focuses automatically on an image and adjusts the aperture and brightness. Nikon is teaming with Bacus Laboratories (Lombard, IL) so that images from the COOLSCOPE hop on the Internet where the pieces can be reassembled with Bacus' WebSlide software.

Loew and his colleagues also marry images and computing with their Virtual Cell, which is available online (www.nrcam.uchc.edu). "We take quantitative data from microscopy and build mathematical models of cellular processes and functions," says Loew. This lets scientists do virtual experiments. "You can dig into fundamental cellular mechanisms," he adds. "We can ask questions such as: 'What happens if a particular part of a system is broken or if we intervene with a particular drug?'"

In many cases, biomedical scientists want the closest possible look at living cells. In the past, the closest look came from electron microscopy, but that required using dead samples. Today, though, live cells can be imaged with some forms of scanning electron microscopy, such as the extended-pressure EVO Series of Scanning Electron Microscopes from Carl Zeiss (Oberkochen, Germany). Watching live cells up close could be the future of biomedical imaging.

Taking Aim At Cancer

As a doctoral student at Stanford University, Joshua Jones wanted a better way to measure the timing of cell division. With conventional methods, it takes weeks or even months to get enough data to see if cells are dividing faster, slower or about normally. During cell division, or mitosis, the nuclear membrane breaks down. So, Jones took a fluorescent protein and attached it to a peptide that grabs membrane. When a cell is not dividing, Jones' fluorescent protein is located in the nucleus deep in the cell. During mitosis, the nuclear membrane breaks down and releases the fluorescent protein to the cellular membrane, where it can fluoresce. "It's like a light switch," Jones says, "that turns on during mitosis and is off at all other times."

With this technique, Jones and his colleagues can track the mitotic rate of up to 100 cells in about five hours. Because cancerous cells divide rapidly, Jones can use this technique to see which drugs might slow down division in cancerous cells. "This technique will now, for the first time, enable one to screen libraries of compounds for their effects on mitotic timing," Jones says.

Mitotic changes could be associated with cancer, and other imaging techniques target this disease. In the June 2005 issue of Nature Medicine, Mark Stroh and his colleagues at the E.L. Steele Laboratory for Tumor Biology at the Massachusetts General Hospital and Harvard Medical School, reported using quantum dots — fluorescent nanocrystals — to distinguish cancerous from healthy cells in a solid tumor. These investigators also used the quantum dots to see what size particles could get inside the tumor. This work could help the scientists better understand the basic biology of a tumor and what kind of therapeutics could be delivered to a tumor's inner region.

Today's scientists see more than a pretty picture in biomedical images. Instead, they see how diseases develop and how they can battle them.