5.5 Medical Applications Using Radioactivity (a) A scanner is used to detect radiation from a radioisotope that has accumulated in an organ. (b) A scan of the thyroid shows the accumulation of radioactive iodine-131 in the thyroid. Learning Goal Describe the use of radioisotopes in medicine.

Medical Applications Radioisotopes with short half-lives are used in nuclear medicine because the cells in the body do not differentiate between non-radioactive atoms and radioactive atoms. once incorporated into cells, the radioactive atoms are detected because they emit radiation, giving an image of an organ.

Radioisotopes, Medical Applications

Scans with Radioisotopes After a radioisotope is ingested by the patient, the scanner moves slowly over the organ where the radioisotope is absorbed. the radiologist determines the level and location of the radioactivity emitted by the radioisotope. the gamma rays emitted from the radioisotope can be used to expose a photographic plate, producing a scan of the organ.

Scans with Radioisotopes A scan shows the radioactive isotope I-131 in the thyroid.

Positron Emission Tomography (PET) Positron emitters with short half-lives can be used to study brain function, metabolism, and blood flow. might be carbon-11, oxygen-15, nitrogen-13, or fluorine-18. combine with electrons after emission to produce gamma rays, which are then detected by computers, creating a 3-D image of the organ.

Positron Emission Tomography (PET) These PET scans of the brain show a normal brain on the left and a brain affected by Alzheimer’s disease on the right.

Computed Tomography (CT) Another imaging method used to scan organs such as the brain, lungs, and heart is called computed tomography (CT). A computer monitors the absorption of 30 000 X-ray beams directed at the brain in successive layers. Differences in absorption based on tissue densities and fluids provide images of the brain. A CT scan shows a tumor (yellow) in the brain.

Magnetic Resonance Imaging (MRI) is an imaging technique that does not involve X-ray radiation. is the least invasive imaging method available. is based on the absorption of energy when protons in hydrogen atoms are excited by a strong magnetic field. works because the energy absorbed is converted to color images of the body.

Magnetic Resonance Imaging (MRI) An MRI scan provides images of the heart and lungs.

Study Check Which of the following radioisotopes are most likely to be used in nuclear medicine? A. 40K half-life 1.3 × 109 years B. 42K half-life 12 hours C. 131I half-life 8 days

Solution Which of the following radioisotopes are most likely to be used in nuclear medicine? Radioisotopes with short half-lives are used in nuclear medicine. A. 40K half-life 1.3  109 years Not likely; half-life is too long. B. 42K half-life 12 hours Short half-life; likely used. C. 131I half-life 8 days Short half-life; likely used.

Chemistry Link to Health: Brachytherapy The process of brachytherapy, or seed implantation, is an internal from of radiation therapy. Permanent brachytherapy is a treatment option for prostate cancer in males. involves the implantation of 40 or more titanium capsules or “seeds” in the malignant area. utilizes radioactive iodine-125, palladium-103, or cesium-131 in the seeds, which decay by gamma emission. The radiation from the seeds destroys the cancer by interfering with the reproduction of cancer cells with minimal damage to adjacent normal cells.

Chemistry Link to Health: Brachytherapy Temporary brachytherapy is also a treatment option for prostate cancer in males. involves the implantation of long needles containing iridium-192 in the tumor. can be used to deliver a higher dose of radiation over a shorter time and may be repeated in a few days. The needles are removed after 5 to 10 minutes depending on the activity of the iridium isotope.