This section will discuss how scientists have harnessed what goes on in the atomic orbitals for various applications like medical imaging and therapy. We'll connecting how physicists utilize the basic properties of chemistry (atomic orbitals) for medical applications.
We've all heard of X-rays. In fact, many of us have even had the privilege of getting images of our own body parts. Maybe you broke a bone or needed a chest X-ray to look at your lungs during a bad cold.
Wilhelm Röntgen discovered X-rays back in 1895. He called them "X-rays" because he used the mathematical designation "x" for something unknown. He was obviously steeped in algebra wisdom. He suspected they were a new kind of ray or type of electromagnetic radiation.
The first X-ray picture was taken only two weeks after Wilhelm's discovery. He decided to take a picture of his wife's hand. Apparently, when she saw her skeleton she exclaimed, "I have seen my death." Creepy, right?
This is a projection X-ray image; a bunch of X-rays were shot over her hand and the resulting image was collected on a photographic plate below her hand. The photographic plate is like film—it's sensitive to light, so when light hits the plate it is exposed.
X-rays are just a form of energetic light. They're super hopped up on Pixi Stix. They are energetic enough to penetrate the body. When a hand is placed over the plate, the X-rays become blocked at different rates based on the composition of the hand. Bone blocks the rays more than skin, fat, or muscle, which is why we tend to see the outline of her bones in the picture above.
Notice the ring on one of her fingers; it shows up darker than the rest of her hand. That's because metal really blocks the X-rays. It's a metal, like the lead vest they put on you at the dentist's office. The metal keeps the X-rays from reaching the plate even more than bone does, so they are often used as X-ray shields. Makes you feel a little better about those cavities now, doesn't it?
Scientists have been able to harness these highly energetic X-rays for all sorts of medical imaging devices.
Projection Radiographs: These are your typical Grade-A X-rays. They're the kind you get to see if you've broken any bones.
Mammography: These use low energy X-rays to look for abnormalities in breast tissue. It's used as a screening device for breast cancer.
Computed Tomography (CT): These use X-rays to get a three-dimensional image of the body. This allows doctors to look at various slices of the body in different orientations.
Fluoroscopy: These use X-rays to get a continuous real-time view of the body. Surgeons often use this imaging system to help guide them during surgery including: metal implants during orthopedic surgery, angiography for placement of stents in blood vessels, and implanting pacemakers.
How does all this relate to what we've been studying? X-rays are produced by interactions of random high-energy electrons with the electrons found in atoms.
There are two ways X-rays are produced:
1) Bremsstrahlung X-rays
2) Characteristic X-rays
Check out the image below. The incident high-energy electron (we'll call him George) runs into an orbital electron (we'll call him Buster). Buster was perfectly happy hanging out in his orbital and he wants to hold on, but George has pushed him too far. Buster gets flung out of his orbital and loses some of his energy to boot. He goes one way and his lost energy goes the other (in the form of an X-ray). Buster get's his revenge, though. He knocks other electrons out of their orbitals, too. They lose energy to X-rays, and Buster gets the last laugh.
This one gets a little more complicated, but stay with us.
This time, the electron (we'll call him Karl) is chilling in an inner orbital. In the diagram below, he's in the K orbital. He's safe, secure, and bound tightly to his atom. Or is he? George, the high-energy electron, comes plowing into the inner orbital and runs into Karl, sumo-style.
Once again, George overpowers the electron. Karl is ejected from his atom. To make matters worse, a new electron, Lucy, from a higher energy orbital takes his place. (Poor Karl.) This is due to the Aufbau Principle. Lucy drops down from the L orbital in the diagram below. Things aren't all roses for Lucy, though. She loses some energy in the form of an X-ray, just like Buster. We're sure Buster is happy he isn't the only one getting picked on.
Depending on the element (such as Cu, Mo, ect.), Lucy's lost X-ray wavelength will change. This is called a characteristic X-ray.
Note: K and L are just placeholders—don't confuse them with the s, p, d, and f subshells.
Scientists have also used high-energy electrons and high-energy photons (X-rays are a type of "photon") to treat cancerous tumors. This type of therapy is known as Radiation Therapy, and uses linear accelerators to produce these therapeutic electron beams or X-ray beams.
Radiation therapy works by damaging the DNA of cancer cells either directly by electron beam therapy or indirectly by electron displacement within cancer cells with X-rays. Indirect ionization happens as a result of the ionization of water, which forms free radicals (hydroxyl radicals), which then damage the DNA.
One of the first patients treated with a linear accelerator was back in 1957 for a retinoblastoma (cancer of the retina in the eye). They used an electron beam in this case to treat a localized tumor in the child's left eye.
Since then the field has grown immensely, and very sophisticated linear accelerator devices exist today which do a great job at damaging cancerous tissue while sparing surrounding healthy tissue. See this video for more information.