What is a bone scan?
A bone scan, also known as bone scintigraphy, is a medical examination by doctors using radiological technology to show the image of the bones of the skeleton inside the body. It mainly detects bone disorders, including fractures, arthritis, bone tumors, and bone cancer.
The history of the bone scan
In 1895, the X-ray was first discovered, which means the beginning of radiology. In about 1900, Thomas Edison developed a TV-like technique called fluoroscopy that could show the inner body parts as the patient moved. In 1918, film became an alternative way to capture x-ray images. In the 1940s, the early study of skeletal metabolism was carried out by Charles Pecher, using Phosphorus-32. After that, positrons and Gamma emitters such as Fluorine-18 and strontium isotopes were proved more effective in imaging. The use of Technetium-99m labeled phosphate agents, as in the modern technique, was first proposed in 1971. Nowadays, AI technology is even introduced in analysis of the bone scan images.
The Physics behind Bone Scan- Gamma radiation
In the Marvel movie Hulk, scientist Dr. Bruce Banner was exposed to heavy Gamma radiation. Then he gets the superpower that can transform himself into Hulk when he gets angry. However, this will not happen in real life. People often tend to exaggerate the effect of Gamma radiation in science fiction movies or comic books, imagining that exposure to Gamma rays could grant superpowers. This imagination can be amusing since Gamma radiation is high-energy radiation, not something special that grants superpowers.
Gamma radiation is a radiological ray used in bone scans. It is in the form of electromagnetic radiation. In the electromagnetic spectrum, the Gamma ray has the shortest wavelength and therefore the greatest energy. By the process of Gamma decay, Gamma radiation is emitted. Gamma decay is a process in which an excited-state nucleus transits to a low-energy state by emitting a high-energy Gamma photon which is also a Gamma ray. The equation of the Gamma decay process is (A/Z)X→(A/Z)Y+γ.
How does the procedure work?
The technician may administer the patient with a small amount of radioactive materials called radiotracers. Then, the materials will be injected into the patient’s bloodstream. Also, the patient would be asked to drink a large amount of water to make sure there are no other unnecessary radiotracers left in the body. The most commonly used radiotracer is Technetium-99m (Tc99m) for radiolabeling because of its low price and good quality for imaging. It has a 6-hour half-life that will not perform excessive radiation to patients, which is relatively safe to process. Then, the radiotracers gather in the region under testing, emitting gamma rays at that location. Before the examination, the patient should urinate to avoid any substance in the urine obstructing the visibility of the pelvic bones when scanning.
During the scan, the camera will detect the energy released, creating a series of images. It is resulting from the interactions between the accumulated gamma photons of the radioactive decay and the sodium iodide crystals in front of the Gamma camera. After striking the crystal, the photons are converted into electrical signals. The computer will process the signals and display them on the screen, generating pictures of the bones that can clearly show the location of infection.
Similar principles applied in PET
PET is called positron emission tomography, a nuclear medical technology that also uses radiotracers and nuclear radiation to create images of organs. Similar with the bone scan, PET usually uses radiotracers like Fluorine-18(F18), Oxygen-15(O15), Carbon-11(C11), or Nitrogen-13(N13). After the radiotracers have accumulated, the PET camera which also contains crystals detects the emitted photons. The absorbed photons are then converted into electrical signals that can be displayed on the computer. Therefore, a series of pictures of blood flow, metabolism, neurotransmitters, or radiolabeled drugs are generated.
Benefits and risks of bone scan
The bone scan plays a significant role in the examination of bone disorders by giving doctors accurate, useful, and clear information about the details of the bone structures and functions. It can greatly improve the efficiency of disease diagnosis and treatments. What's more, its affordable price has contributed to its widespread use in the evaluation of bone diseases.
During the bone scan, the patient's body is exposed to the radiation, so there is a little risk of damage to the organs. Some people are not recommended to do the bone scan. For example, pregnant and breastfeeding women are not allowed to do a bone scan since radiation exposure can lead to fetal or developmental abnormalities.
Therefore, it is important to be aware of the risks of bone scan. Patients should inform doctors of their health conditions and follow the safety instructions of the procedure.
References
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