Nuclear medicine Flashcards

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1
Q

What is β- decay and what happens to the atomic number and mass number of the nucleus undergoing this decay?

A

β- decay is a type of radioactive decay where an unstable, neutron-rich nucleus transforms a neutron into a proton, emitting an electron (beta particle) and an electron antineutrino. The atomic number increases by one while the mass number remains unchanged.

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2
Q

Explain β+ decay and its impact on the atomic number and mass number of the nucleus.

A

β+ decay is a radioactive decay where a proton-rich nucleus transforms a proton into a neutron, emitting a positron (antimatter counterpart of an electron) and an electron neutrino. The atomic number decreases by one while the mass number remains unchanged.

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3
Q

Electron Capture

A

This process reduces the atomic number by one while the mass number remains unchanged.

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4
Q

Excess energy release from β decay:

A

Excess energy from β decay can be released through either Isomeric Transition or Gamma Emission.
Isomeric Transition involves decay to an excited metastable state followed by emission of a gamma photon, while Gamma Emission directly transitions the nucleus from an excited state to a lower energy state.

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5
Q

Mathematical relationship for decay rate

A

The decay rate of an isotope is described by the exponential decay equation: A = A0 * e^(-λt).
This equation is related to the half-life, given by T1/2 = ln(2) / λ, which is the time required to reduce the activity by one-half.

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6
Q

Appropriate half-life

A

The radioisotope’s half-life should match the intended application. Shorter half-lives are preferred for medical imaging to minimize patient exposure, while longer half-lives are necessary for radiometric dating of ancient events.

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7
Q

Type of emitted radiation

A

The emitted radiation type (alpha, beta, or gamma) determines the radioisotope’s suitability for specific applications. Gamma emitters are ideal for imaging and non-destructive testing due to their high penetrating power, while alpha or beta emitters are used in targeted radiation therapy for cancer treatment.

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8
Q

Chemical properties

A

The radioisotope should possess chemical properties that enable it to react, bond, or accumulate in the desired target or system. This is crucial for tracer studies or targeted medical treatments.

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9
Q

Availability

A

A useful radioisotope should be readily available or producible in sufficient quantities for the intended application. Production often occurs in nuclear reactors or particle accelerators.

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10
Q

Detection

A

The emitted radiation should be easily detectable and measurable with standard equipment, enabling accurate quantification or visualization of the radioisotope’s behavior.

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11
Q

What is gamma imaging, and what is its primary purpose in medical diagnostics?

A

non-invasive diagnostic technique in nuclear medicine.
It aims to obtain detailed images of the body’s internal structures and functions using radioisotopes emitting gamma radiation, which can be detected by specialized equipment.

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12
Q

Describe the process involved in gamma imaging, including the role of radiopharmaceuticals.

A

A patient receives a small amount of a radiopharmaceutical, a decaying isotope chemically bound to target nuclides.
The radiopharmaceutical targets specific tissues or organs, accumulates there, and emits gamma photons.
A gamma camera detects these emitted gamma photons, processing the signals to create a two-dimensional image (scintigram) depicting the distribution and concentration of the radiopharmaceutical within the body.

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13
Q

What components make up a gamma camera, and what are their functions?

A

A gamma camera consists of a collimator, a scintillation crystal, and photomultiplier tubes.
The collimator shields and guides gamma photons emitted from the patient’s body to ensure only linearly traveling photons reach the scintillation crystal, enhancing image precision.
The scintillation crystal converts incoming gamma photon energy into visible light, enabling detection and measurement of the radiation.

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14
Q

how to improve the gamma camera signal?

A

centroiding
energy scatter rejection

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15
Q

What role do photomultiplier tubes (PMTs) play in gamma imaging, and what are their main components?

A

PMTs are highly sensitive light detectors that convert light photons emitted by the scintillation crystal into electrical signals for image creation.
A PMT comprises three main components: the photocathode, the electron multiplier, and the anode.

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16
Q

Describe the function of each component within a photomultiplier tube (PMT).

A

Photocathode: The first component, the photocathode, is a light-sensitive material coating the inner surface of the PMT. It ejects electrons when struck by visible photons through the photoelectric effect.
Electron multiplier: Following ejection, electrons move into the electron multiplier, a series of dynodes at increasingly higher voltages. Collisions with these dynodes result in secondary emission, amplifying the signal.
Anode: Multiplied electrons then reach the anode, where they are collected and generate an electrical current proportional to the initial light photons, facilitating image creation.

17
Q

How does a photomultiplier tube (PMT) amplify weak light signals in gamma imaging?

A

PMTs amplify weak light signals by utilizing the photoelectric effect in the photocathode to eject electrons, which then undergo multiple collisions in the electron multiplier, resulting in an electron avalanche and significant signal amplification.
The multiplied electrons produce an electrical current at the anode proportional to the initial light photons, enabling the creation of diagnostic images.

18
Q

What is Single Photon Emission Computed Tomography (SPECT), and how does it function?

A

SPECT is a 3-dimensional imaging technique utilizing Gamma cameras to create images of radiopharmaceutical distribution within the body.
It involves compensating for tissue attenuation, a process that corrects for the reduction in gamma photon intensity due to absorption and scattering within the patient’s body.

19
Q

What is the significance of tissue attenuation correction in SPECT imaging?

A

Tissue attenuation correction compensates for the reduction in gamma photon intensity caused by absorption and scattering within the patient’s body.
Without proper attenuation correction, SPECT images may underestimate radiopharmaceutical concentrations, leading to inaccurate functional data interpretation.

20
Q

What are the limitations of SPECT-CT for quantitative imaging?

A

Tissue attenuation: Absorption and scattering of gamma photons within the patient’s body can lead to signal intensity reduction from deeper locations, causing underestimation of tracer concentration.
Scatter correction: Scattered gamma photons can distort images, requiring accurate correction methods for minimization.
Collimator line of response: Collimator geometry and material can affect image resolution and sensitivity, influencing quantitative accuracy.
Radiopharmaceutical diffusion: Distribution and diffusion of radioisotopes within the body may vary, introducing quantification uncertainty.
Image reconstruction: Reconstruction algorithm imperfections can lead to limitations and errors in quantitative measurements.
Count statistics: Low count rates may increase noise and reduce image quality, necessitating longer acquisitions that could blur images due to patient motion.

21
Q

What is Positron Emission Tomography (PET), and how does it differ from SPECT?

A

PET is a nuclear medicine imaging technique providing functional and metabolic information about organs and tissues, similar to SPECT.
The main difference is that PET exclusively uses radioisotopes with positive beta decay, emitting positrons that undergo annihilation, producing two gamma photons detected by PET scanners.

22
Q

What is coincidence detection in PET, and how does it contribute to image reconstruction?

A

Coincidence detection in PET involves identifying and recording simultaneous detection of gamma photon pairs from the same annihilation event.
These pairs form lines of response (LORs), collected to reconstruct a three-dimensional image of radiopharmaceutical distribution within the body.

23
Q

What are the limitations of SPECT-CT for quantitative imaging?

A

tissue attenuation
scatter correction
collimator line of response
radiopharmaceutical diffusion
image reconstruction
count statistic

24
Q

What are the limitations of nuclear imaging?

A

physiological uptake
inflammation and infection
post-treatment changes
pathways of excretion

25
Q
A