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Chapter 10: Problem 18

Why is a PET scan more accurate than a SPECT scan?

Short Answer

Expert verified
In summary, PET scans are more accurate than SPECT scans mainly due to their higher resolution and sensitivity. PET scans use positron-emitting radionuclides and coincidence detection, resulting in reduced background noise and more precise imaging of tissue function and metabolism. However, factors such as availability, cost, and radiation dose may limit the widespread use of PET scans compared to SPECT scans.

Step by step solution

01

Understanding PET and SPECT scans

PET and SPECT scans are imaging techniques used for diagnosis and monitoring of various diseases. Both methods involve injecting a small amount of radioactive material (tracer) into the patient's bloodstream. These tracers emit radiation and are detected by the scanners, which create images of the tracer distribution in the body, providing information on the function and metabolism of tissues and organs.
02

The working principle of PET scans

PET scans use tracer molecules marked with a positron-emitting radionuclide. When a positron encounters an electron, it results in annihilation, producing two gamma photons (with 511 keV energy) traveling in opposite directions (180 degrees apart). These two photons are detected by the PET scanner, which forms a line of response (LOR) between the two detected points. The image is then constructed by calculating the tracer distribution along these lines.
03

The working principle of SPECT scans

SPECT scans use tracer molecules marked with a gamma-emitting radionuclide. The tracer emits a single gamma photon, which is detected by a gamma camera that rotates around the patient. This rotation allows the system to capture images from different angles and create a 3D image of the tracer distribution. The SPECT scan does not need annihilation, and the emitted photon's energy varies depending on the radionuclide used.
04

Resolution and sensitivity

PET scans generally have a better resolution and sensitivity compared to SPECT scans. The spatial resolution of PET scans ranges from 2-5 mm, while SPECT scans have a spatial resolution of 7-15 mm. This means that PET scans can detect smaller structures and changes in tissue function with greater precision. The increased sensitivity of PET scans is attributed to the coincidence detection system, which significantly reduces background noise and increases the signal-to-noise ratio.
05

Clinical applications and limitations

Both PET and SPECT scans have various clinical applications, including oncology, cardiology, and neurology. PET scans are more commonly used for oncology (tumor imaging) due to their higher resolution and sensitivity. SPECT scans are more frequently used for cardiac perfusion imaging and brain perfusion imaging. However, PET scans have some limitations, such as higher costs, a shorter half-life of tracers, and a higher radiation dose compared to SPECT scans. Additionally, PET scanners are less widely available than SPECT scanners.
06

Conclusion: Why PET scans are more accurate

In summary, PET scans are considered more accurate than SPECT scans mainly due to their better resolution and sensitivity. The use of positron-emitting radionuclides and coincidence detection in PET scans reduces background noise and allows for more precise imaging of tissue function and metabolism. However, availability, cost, and radiation dose are factors that may limit the widespread use of PET scans relative to SPECT scans.

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Most popular questions from this chapter

Define and make clear distinctions between the terms neutron, nucleon, nucleus, and nuclide.

Armor-piercing shells with depleted uranium cores are fired by aircraft at tanks. (The high density of the uranium makes them effective.) The uranium is called depleted because it has had its \(^{235} \mathrm{U}\) removed for reactor use and is nearly pure \(^{238} \mathrm{U}\). Depleted uranium has been erroneously called nonradioactive. To demonstrate that this is wrong: (a) Calculate the activity of \(60.0 \mathrm{g}\) of pure \(^{238} \mathrm{U} .\) (b) Calculate the activity of \(60.0 \mathrm{g}\) of natural uranium, neglecting the \(^{234} \mathrm{U}\) and all daughter nuclides.

(a) Calculate the energy released in the neutron-induced fission \(n+^{238} \mathrm{U} \rightarrow^{96} \mathrm{Sr}+^{140} \mathrm{Xe}+3 n,\) given \(m\left(^{96} \mathrm{Sr}\right)=95.921750 \mathrm{u}\) and \(m\left(^{140} \mathrm{Xe}\right)=139.92164\). (b) This result is about \(6 \mathrm{MeV}\) greater than the result for spontaneous fission. Why? (c) Confirm that the total number of nucleons and total charge are conserved in this reaction.

The Galileo space probe was launched on its long journey past Venus and Earth in \(1989,\) with an ultimate goal of Jupiter. Its power source is \(11.0 \mathrm{kg}\) of \(^{238} \mathrm{Pu}\) a by-product of nuclear weapons plutonium production. Electrical energy is generated thermoelectrically from the heat produced when the \(5.59-\mathrm{MeV} \quad \alpha\) particles emitted in each decay crash to a halt inside the plutonium and its shielding. The half-life of \(^{238} \mathrm{Pu}\) is 87.7 years. (a) What was the original activity of the \(^{238} \mathrm{Pu}\) in becquerels? (b) What power was emitted in kilowatts? (c) What power was emitted 12.0 y after launch? You may neglect any extra energy from daughter nuclides and any losses from escaping \(\gamma\) rays.

(a) Calculate the energy released in the \(\alpha\) decay of \(^{238} \mathrm{U} .\) (b) What fraction of the mass of a single \(^{238} \mathrm{U}\) is destroyed in the decay? The mass of \(^{234} \mathrm{Th}\) is 234.043593 u. (c) Although the fractional mass loss is large for a single nucleus, it is difficult to observe for an entire macroscopic sample of uranium. Why is this?
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