Medical imaging continues to grow with the future

I‘m an old “Star Trek” fan – the one with Captain Kirk and Mr. Spock and the Tribbles. And the doctor – Bones they called him – could fix anything, even whip up an antidote to some interstellar virus that was attacking the crew in alarming numbers. And he had this gizmo any doctor would die for – the tricorder. It was a handheld wonder that could diagnose any ailment and formulate any cure. All he had to do was wave it over the patient.

I thought about Bones and his toy as I stood with my husband while he waited to get wheeled in for a CT scan. (He’s fine.) Medical imaging has come a long way since Roentgen got his Nobel Prize for the discovery of X-rays and since I graduated from medical school and residency.

The simple X-ray provides us with a two-dimensional picture and gives us great views of bones and what’s going on in the lungs. The plain old X-ray has not outlived its usefulness. It’s the easiest way to tell if that stupid head-over-heels fall on the ski hill left you with a broken leg or if that horrendous cough and fever mean pneumonia.

But plain X-rays can’t tell us much else about what’s going on inside the body. For that, most often, we turn to the CT (computed tomography) scan. Like so many breakthroughs in imaging, it is the rapid advance in computer technology that makes the CT scan possible, because the CT scan uses X-rays just like a chest X-ray.

The person being scanned is moved inside a donut-shaped enclosure that houses the X-ray apparatus. It spins around rapidly, taking pictures from all angles. The computer takes the information, collates it, and produces an image or “slice,” a cross-section of the body at that point. Numerous slices are recorded, giving the radiologist an opportunity to study not only the bones that X-rays are so good at imaging, but our soft insides as well – the intestines, the liver, the spleen, the kidneys and on and on. And so we could tell that Jeffry’s bout of severe abdominal pain wasn’t anything serious.

Because the CT scan uses X-rays, patients are exposed to a bit of radiation, although these sophisticated machines have learned to do more with less. Magnetic resonance imaging, or MRI, uses powerful magnets to jiggle hydrogen atoms in the tissues, causing them to send energy signals to the collecting camera and on to the computer to produce, as with the CT scan, elegant pictures of slices through the body.

MRIs provide a somewhat more sophisticated and detailed image of our insides, because unlike X-rays or CT scans, which are essentially pictures of shadows, MRIs can identify different types of tissues based on their hydrogen content.

MRIs are really good at imaging the brain and spinal column, as well as joints like the knee damaged in the above-mentioned skiing accident. MRIs are particularly good at distinguishing cancer from noncancerous tissue. (They are also considerably more expensive than CT scans.)

Unlike the CT and MRI, which look at anatomy, the PET (positron emission tomography) gives us a functional picture of the body. The patient gets a dose of a mildly radioactive compound that travels to the tissues the doctor wants to study.

The radioactive compound decays by emitting a positron. The positron meets up with its negative equivalent, the electron, and they annihilate each other. Two photons emerge (remember E=mc2?), heading off in opposite directions. The computer recognizes only photons arriving in opposite directions at the same time; no stray photons are acknowledged.

The computer can identify where the radioactive tracer is concentrated, generally in areas of increased metabolic activity. Cancer cells are highly active, and so PET scans are used routinely to look for the spread of cancer.

Yes, medical imaging has nearly reached sci-fi status. But I’m still waiting for my tricorder.

Beam me up, Scottie!