By Greg Clark
Radiation helps doctors reveal hidden illnesses
The images were the results of a bone scan done by radiologist Dennis Patton and medical resident Mike Rosellini in the Arizona Health Sciences Center's Division of Nuclear Medicine.
Images of a man's skeleton were clipped to a light table. They looked like full skeletal X-rays, with several bright white spots appearing on three ribs.
Doctors had injected the patient with a radioactive isotope that builds up in bone and then recorded images of the radiation it emitted.
"I see it as the bone shining with its own light," said Patton, a professor of radiology at optical sciences at the UA's College of Medicine.
An X-ray shows the shadow of bone but with a scan the bone itself emits detectable radiation, Patton explained.
The radioactive tracer builds up most in areas where new bone material is being generated as part of the healing process. This happens in areas where cancer is active, Patton said.
These areas appear as bright white spots on the scan image.
"This patient was recently diagnosed with prostate cancer, and we can see by the hot spots on the ribs that it has spread to the bone," Rosellini said.
The doctors at Nuclear Medicine perform radio isotope scans on 70 to 80 patients per week, said radiologist Walter Williams, an associate professor of radiology at the UA College of Medicine.
They run heart, brain, blood and bone scans using different tracer isotopes, he said.
Though the radioactive isotopes are injected directly into the patients, Patton and Williams said, the procedure is safe.
"There is very little radiation involved, about as much as a chest X-ray," Williams said.
The half-life of the isotopes used is about six hours, Patton said. The isotope, therefore, loses half its energy every six hours, so it quickly decays and becomes harmless, he said.
Williams said bone scans are most often used to determine the stage of breast and prostate cancers, which spread primarily to bone.
They can also be used to see stress fractures, which do not appear in X-rays, Patton said.
Heart scans are done using a tracer that builds up in the heart muscle.
Doctors remove about 10 milliliters of the patient's blood, mark the red blood cells with the tracer and then inject the blood back into the patient.
By taking a series of pictures of the heart, doctors can develop a three dimensional image of the blood supply to the tissues of the whole heart, Patton said.
"These are images of a process," Patton said as he looked at a dozen color-coded computer images of a cross sectioned heart. "We can see how the heart is functioning at different times during the cardiac cycle."
Heart scans are routinely done on prospective heart transplant patients to see how well their hearts are working and to evaluate heart function in people experiencing chest pains, Williams said.
Brain scans are performed with a different isotope to analyze blood supply to the brain. This can be useful to doctors to determine the effects of stroke, Alzheimer's disease and to diagnose brain death, Williams said.
By labeling white blood cells and seeing where they concentrate, physicians can find infections that they could not otherwise locate, Patton said.
Scans can also be run on the lungs, liver or thyroid gland, Patton said. Other organs and glands can also be targeted, provided a known tracer builds up in that tissue, he said.
"That's the art in all this: to design a tracer that just goes to the tissues you want to see."