Download 5 Medical Applications GOB Structures

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.
General, Organic, and Biological Chemistry: Structures of Life, 5/e
Karen C. Timberlake
© 2016 Pearson Education, Inc.
Medical Applications
Radioisotopes with short half-lives are used in nuclear
medicine because
• the cells in the body do not differentiate between nonradioactive atoms and radioactive atoms.
• once incorporated into cells, the radioactive atoms are
detected because they emit radiation, giving an image
of an organ.
General, Organic, and Biological Chemistry: Structures of Life, 5/e
Karen C. Timberlake
© 2016 Pearson Education, Inc.
Radioisotopes, Medical Applications
General, Organic, and Biological Chemistry: Structures of Life, 5/e
Karen C. Timberlake
© 2016 Pearson Education, Inc.
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.
General, Organic, and Biological Chemistry: Structures of Life, 5/e
Karen C. Timberlake
© 2016 Pearson Education, Inc.
Scans with Radioisotopes
• A scan shows the radioactive isotope I-131 in the thyroid.
General, Organic, and Biological Chemistry: Structures of Life, 5/e
Karen C. Timberlake
© 2016 Pearson Education, Inc.
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.
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• combine with electrons after emission to produce gamma
rays, which are then detected by computers, creating a 3-D
image of the organ.
General, Organic, and Biological Chemistry: Structures of Life, 5/e
Karen C. Timberlake
© 2016 Pearson Education, Inc.
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.
General, Organic, and Biological Chemistry: Structures of Life, 5/e
Karen C. Timberlake
© 2016 Pearson Education, Inc.
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.
General, Organic, and Biological Chemistry: Structures of Life, 5/e
Karen C. Timberlake
© 2016 Pearson Education, Inc.
Magnetic Resonance Imaging (MRI)
Magnetic resonance imaging
• 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.
General, Organic, and Biological Chemistry: Structures of Life, 5/e
Karen C. Timberlake
© 2016 Pearson Education, Inc.
Magnetic Resonance Imaging (MRI)
An MRI scan provides images of the heart and lungs.
General, Organic, and Biological Chemistry: Structures of Life, 5/e
Karen C. Timberlake
© 2016 Pearson Education, Inc.
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
General, Organic, and Biological Chemistry: Structures of Life, 5/e
Karen C. Timberlake
© 2016 Pearson Education, Inc.
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.
General, Organic, and Biological Chemistry: Structures of Life, 5/e
Karen C. Timberlake
© 2016 Pearson Education, Inc.
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.
General, Organic, and Biological Chemistry: Structures of Life, 5/e
Karen C. Timberlake
© 2016 Pearson Education, Inc.
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.
General, Organic, and Biological Chemistry: Structures of Life, 5/e
Karen C. Timberlake
© 2016 Pearson Education, Inc.