Download Chapter 11 Review Question Answers

Chapter 11 Review Question Answers
1. Isomeric transition is the emission of a γ-ray when a nucleus decays from a higher energy
state to a lower energy state. Electron capture occurs when a nucleus combines a proton
with an orbital electron, resulting in a γ-ray and/or a neutrino with or without the production
of secondary x-rays. For each decay process, only electromagnetic radiation (γ-ray or x-ray)
is produced. These photons can penetrate tissue and escape the body without causing tissue
damage. Such photons can be readily detected by external gamma cameras. Nuclear decay
that results in charged particle production can lead to significant tissue damage.
2. For the ventilation scan, either xenon-133 or technetium-99m pentetate DTPA is
administered by the inhalation route to assess distribution within the lung spaces. For the
perfusion scan, technetium 99-m macroaggregated albumin is administered by infusion.
These particles are trapped within the pulmonary microcirculation and aid in assessing
the perfusion of the lungs.
3. In a dual isotope stress test, thallous (thallium-201) chloride is used to obtain the rest
images. Thallium-201 accumulates in the cardiac tissue by Na+/K+ ATPase as well as the
Na+/K+/2Cl- symporter, much like potassium ions. Only viable tissue accumulates the ion.
Thallium-201 decays by electron capture and emits characteristic γ-rays and secondary xrays that are used for imaging. For the stress portion of the dual isotope study, a
technetium-99m product (either sestamibi or tetrofosmin) is injected at the peak of stress
(either exercise or pharmacologic). These lipophilic technetium-99m complexes accumulate
in cardiac tissue by facilitated diffusion. Technetium-99m decays by isomeric transition,
emitting a characteristic γ-ray that is used for imaging.
4. Fluorine-18 (t1/2 = 110 minutes), elapsed time = t = 270 minutes
At  A0 (0.5)t / t1 / 2
A = (50 mCi/mL) (0.5)(270/110)
A = (50 mCi/mL) (0.182)
A = 9.1 mCi/mL
5. Radiographic contrast agents are dense materials that absorb x-ray photons as these
photons penetrate from a source, through a patient, to a film or detector. The absorption
of photons by radiographic contrast agents prevents x-rays from exposing the film or
striking the detector.
MRI contrast agents are substances that can enhance or reduce a localized magnetic
environment once these substances are placed inside a very strong magnetic field. MRI
contrast agents alter the relaxation rate of local precessing nuclei in this strong magnetic
field that recently absorbed energy from a radiofrequency pulse.
Ultrasound contrast agents increase the reflection of sound waves to improve the contrast
between local tissues and the blood vessels that contain the ultrasound agent.
Ch. 11 Review Question Answers
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