The Better to 
See You With

By Emory Professor of Physics Emeritus Sidney Perkowitz

The first time I had my heart checked by ultrasound at the Emory Clinic, I didn’t know what to expect. The technologist pressed a small device against my chest and moved it around, using a gel-type substance as a conductor, until an image appeared on a computer screen off to the side. Craning my neck, I could just make out a moving shape. It took me a second to realize what I was seeing. It was my own heart, beating even as I watched it—the closest I’ve ever come to an out-of-body moment.

As a physicist, I understand the mechanics of medical imaging. Put simply, images from inside your own body are gathered using sound waves, X-rays, gamma rays, or radio waves and a magnetic field.

These physical probes enable ultrasound, X-ray computed tomography (CT), positron emission tomography (PET), and magnetic resonance imaging (MRI)—medical tools developed by physicists, engineers, and physicians that are now essential to patient care.

Jon Lewin, executive vice president for health affairs at Emory and CEO of Emory Healthcare, is a professor of radiology and imaging sciences and biomedical engineering, and an innovator in the field. What drew Lewin to medical imaging was its trifecta of tech, biomedical science, and patient impact. “When I got involved in the mid-1980s,” he says, “imaging was going from being very static—looking at X-rays, shadows on a screen—to interrogating and visualizing the human body as never before, even during surgery.”

And the level of detail just keeps accelerating, he says. “The kind of information it is possible to learn through current imaging is transforming how medical care is provided across almost every specialty.”

Take, for example, functional brain imaging—“how thoughts are translated into electrical impulses and blood flow,” says Lewin.

Or the advances made possible by interventional radiology. “Minimally invasive, image-guided therapies have changed what used to be major surgery and a week in the hospital into outpatient surgery through a needle hole,” Lewin says. “I had to tell one patient to at least take the weekend to recuperate.”

THE DARK AGES

Long before these techniques existed, physicians had to try to heal patients without knowing much about what was inside their bodies.

Anatomists and physicians eventually learned more through invasive surgery, by dissecting dead animals and people, and by using tools like the microscope. But it took an accidental observation in 1895 to allow doctors to finally peer inside the living human body without cutting into it.

German physicist Wilhelm Röntgen was working with a novel lab device, a glass tube pumped free of most of its air, with a metal electrode at each end. When high voltage was applied to the electrodes, a glow appeared between them. That was not new, but something else was.

Though the tube had an opaque covering, Röntgen noticed that whenever it was turned on, a fluorescent screen three meters away would light up. Röntgen had discovered an unknown kind of penetrating radiation he dubbed “X-rays.” They generated universal wonderment.

Only later did physicists learn that X-rays are energetic electromagnetic waves emitted by electrons streaming within the tube. The medical value of these new rays became immediately clear when Röntgen displayed an X-ray photo of the bones in his wife’s hand [FIG 1]. In less than a year, American physician William Morton published The X-Ray: or, Photography of the Invisible and Its Value in Surgery as a guide to medical use of the technique [FIG 2].

MUTUAL ANNIHILATION

Like CT, positron emission tomography (PET) also assembles 2D images into 3D, in this case to locate normal and abnormal metabolic processes in the body.

Positrons are elementary particles first suggested in 1928 when French physicist Paul Dirac predicted that an electron has a kind of fraternal twin, exactly the same but with the opposite (positive) electrical charge. This was confirmed when positrons were found in cosmic rays. Now, of course, we know that every kind of elementary particle has an antiparticle and that antimatter exists along with ordinary matter.

Antimatter is a staple of science fiction because of a dramatic fact: when antimatter meets matter, they annihilate each other in a burst of energy. That burst makes PET the only practical application of antimatter so far.

In PET, the patient is injected with a biologically active and weakly radioactive compound, frequently a special formulation of the sugar glucose. As this is taken up by bodily tissues, it emits positrons, each traveling a millimeter or less before meeting an electron resident in the body. The particles mutually annihilate and generate two gamma rays, powerful electromagnetic waves that, like X-rays, must be carefully monitored. The gamma rays travel in opposite directions until they are detected outside the body, at which point a computer tracks their paths back to their internal point of origin. Adding up many such calculations produces images of regions with strong metabolic activity, as shown by their glucose uptake.

A high metabolic rate typically shows the presence of a tumor, so a main use of PET is to identify and monitor cancers. Brain activity also involves glucose metabolism so PET can diagnose brain tumors, guide brain surgery, and confirm diagnosis of brain deterioration, as in Alzheimer’s disease.

Carolyn Meltzer, chair of radiology at Emory, specializes in PET, and has shown that the best results come when a patient is evaluated by a combined PET/CT scanner—the resulting near-perfect alignment of the two sets of images outperforms separate scans.

For instance, when squamous cell carcinoma, the second-most prevalent type of skin cancer, is suspected in the head and neck, a PET/CT scan facilitates the ability to differentiate between cancer and other abnormalities.

Radiology has medical applications far beyond what people normally think of, says Meltzer. “We are interested in expanding work with imaging agents that have both diagnostic and therapeutic functions, as well as further innovation in image-guided interventional treatments for such wide-ranging conditions as obesity, pain, and tumor ablation.”

ALTERNATIVE TO OPIOIDS

Interventional radiology (IR) is, indeed, a field to watch. Image-guided ablation is an effective treatment for early kidney cancer. Interventional radiologist Sherif Nour also has performed many successful ablations of liver and prostate cancers at Emory. Last year, he traveled to Egypt to teach the technique.

And David Prologo, associate professor of radiology and imaging sciences and an interventional radiologist at Emory Johns Creek Hospital, is helping to develop an IR program in Tanzania. Prologo is also investigating the use of IR in reducing obesity by freezing a portion of the vagus nerve that sends hunger signals to the brain.

But much of his and other interventional radiologists’ work is pain related. “We are using our skill set to solve new, long-standing problems, like chronic pain, phantom limb pain, cancer pain. We are able to make dramatic changes in patients’ quality of life,” he says.

One of Prologo’s patients had metastatic lung cancer in her spine and intractable nerve-related pain for more than a year. She underwent CT guided cryoablation of the cancer and the nerve, to block the pain signals. “I ran into her at Publix and she was crying because she was so relieved,” he says.

IR is being used more and more as a drug-free alternative to opioids for pain relief.

“We do our procedure while viewing the CT on a screen, in real time,” Prologo says. “It allows us to guide a needle in safely. We inject the nerve with the anesthetic bupivacaine, a temporary block, and if it works on the patient, we feel justified in doing something more permanent, such as ablation.”

Interventional radiologists work with doctors from all subspecialties— surgeons, ob/gyns, generalists, orthopedists, and bariatric, pain, and palliative care physicians. “We can do more for the patient,” says Prologo, “when we all work together.”