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Questions and Answers
Which Nobel Prize was awarded for the development of X-ray computerized tomography (CT)?
Which Nobel Prize was awarded for the development of X-ray computerized tomography (CT)?
What characteristic is associated with X-ray as a probe in imaging modalities?
What characteristic is associated with X-ray as a probe in imaging modalities?
Which Nobel Prize was awarded in 2003 for contributions to the development of Magnetic Resonance Imaging (MRI)?
Which Nobel Prize was awarded in 2003 for contributions to the development of Magnetic Resonance Imaging (MRI)?
In the context of nuclear medicine, what modality uses gamma rays as a probe?
In the context of nuclear medicine, what modality uses gamma rays as a probe?
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What is the primary focus of nuclear medicine compared to radiology?
What is the primary focus of nuclear medicine compared to radiology?
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Which method uses RF as a probe to assess a specific characteristic?
Which method uses RF as a probe to assess a specific characteristic?
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Who received the Nobel Prize for recognizing isotopes as tracers in chemical process studies?
Who received the Nobel Prize for recognizing isotopes as tracers in chemical process studies?
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Which of these modalities does not primarily focus on electron density?
Which of these modalities does not primarily focus on electron density?
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What is the primary advantage of using SPECT/CT imaging compared to traditional imaging techniques?
What is the primary advantage of using SPECT/CT imaging compared to traditional imaging techniques?
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What determines the ultimate spatial resolution in PET imaging?
What determines the ultimate spatial resolution in PET imaging?
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Why do PET scanners not use collimators?
Why do PET scanners not use collimators?
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Which of the following radionuclides is primarily used in PET imaging?
Which of the following radionuclides is primarily used in PET imaging?
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What factor contributes to image noise in PET images?
What factor contributes to image noise in PET images?
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How is scattered radiation addressed in PET imaging?
How is scattered radiation addressed in PET imaging?
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Which of the following best describes the relationship between the types of coincidences during PET imaging?
Which of the following best describes the relationship between the types of coincidences during PET imaging?
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What factor affects the matrix size in relation to pixel size?
What factor affects the matrix size in relation to pixel size?
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Which configuration is used in SPECT data acquisition for capturing images?
Which configuration is used in SPECT data acquisition for capturing images?
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Which of the following is a known issue for planar NM imaging?
Which of the following is a known issue for planar NM imaging?
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What is the significance of the bar phantom in nuclear medicine imaging?
What is the significance of the bar phantom in nuclear medicine imaging?
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Regarding count rate in data acquisition, which statement is true?
Regarding count rate in data acquisition, which statement is true?
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What is one advantage of SPECT over planar imaging?
What is one advantage of SPECT over planar imaging?
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Which of the following matrices represents a common configuration in nuclear medicine imaging?
Which of the following matrices represents a common configuration in nuclear medicine imaging?
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What is the main purpose of using a collimator in imaging?
What is the main purpose of using a collimator in imaging?
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In SPECT, what is the effect of using a circular versus elliptical rotation orbit?
In SPECT, what is the effect of using a circular versus elliptical rotation orbit?
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What measurement does the pixel depth refer to in matrix imaging?
What measurement does the pixel depth refer to in matrix imaging?
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What is the correct formula to calculate the effective half-life (Te) of a radiopharmaceutical in the body?
What is the correct formula to calculate the effective half-life (Te) of a radiopharmaceutical in the body?
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What is the effect of decreasing the number of angular stops during SPECT image acquisition?
What is the effect of decreasing the number of angular stops during SPECT image acquisition?
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What is the unit of decay constant (𝜆) in radioactivity?
What is the unit of decay constant (𝜆) in radioactivity?
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How does the number of views relate to the matrix size in 360º SPECT?
How does the number of views relate to the matrix size in 360º SPECT?
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Which decay process does NOT change the mass number (A) or atomic number (Z)?
Which decay process does NOT change the mass number (A) or atomic number (Z)?
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In terms of image quality in nuclear medicine, what is a major consequence of scatter?
In terms of image quality in nuclear medicine, what is a major consequence of scatter?
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Which of the following filters is primarily used to suppress blurring in filtered back projection?
Which of the following filters is primarily used to suppress blurring in filtered back projection?
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What is a limitation of filtered back projection in SPECT imaging?
What is a limitation of filtered back projection in SPECT imaging?
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What is the typical effective range of administered activity in nuclear medicine imaging?
What is the typical effective range of administered activity in nuclear medicine imaging?
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What happens to spatial resolution as the distance between the patient and collimator increases?
What happens to spatial resolution as the distance between the patient and collimator increases?
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In iterative reconstruction algorithms like OSEM, how does increasing the number of iterations affect image quality?
In iterative reconstruction algorithms like OSEM, how does increasing the number of iterations affect image quality?
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Which factor does not influence noise in SPECT imaging?
Which factor does not influence noise in SPECT imaging?
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What does the term 'counted' refer to in the context of image degradation due to scatter?
What does the term 'counted' refer to in the context of image degradation due to scatter?
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What can be said about the selection of filters in SPECT imaging?
What can be said about the selection of filters in SPECT imaging?
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Which equation accurately describes the relationship between the initial amount of radioactive atoms (N0) and the amount at time t (Nt)?
Which equation accurately describes the relationship between the initial amount of radioactive atoms (N0) and the amount at time t (Nt)?
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What is the traditional unit of radioactivity represented by 3.7 × 10^10 disintegrations per second?
What is the traditional unit of radioactivity represented by 3.7 × 10^10 disintegrations per second?
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What is the primary purpose of attenuation correction in radionuclide imaging?
What is the primary purpose of attenuation correction in radionuclide imaging?
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How does the typical effectiveness of a LEHR collimator compare to its theoretical capabilities?
How does the typical effectiveness of a LEHR collimator compare to its theoretical capabilities?
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How long does a typical projection take during SPECT image acquisition?
How long does a typical projection take during SPECT image acquisition?
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What can be concluded about the step and shoot acquisition method in SPECT?
What can be concluded about the step and shoot acquisition method in SPECT?
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Study Notes
Medical Physics - Introduction to Nuclear Medicine
- The presentation covers medical imaging techniques, including X-rays, radiopharmaceuticals, CT, and MRI.
- Wilhelm Roentgen received the Nobel Prize in 1901 for discovering X-rays.
- George de Hevesy received the Nobel Prize in 1943 for employing isotopes as tracers in chemical processes.
- Godfrey Hounsfield and Allan Cormack were awarded the Nobel Prize in 1979 for developing X-ray computed tomography (CT).
- Peter Mansfield and Paul Lauterbur received the Nobel Prize in 2003 for their contributions to the development of magnetic resonance imaging (MRI).
- Nuclear Medicine studies physiology, while Radiology studies anatomy.
Medical Imaging Techniques
- X-rays: Discovered in 1901 by Wilhelm Roentgen. These are high-energy electromagnetic radiation able to pass through soft tissues but get absorbed by denser structures, creating images of the internal structure.
- Radiopharmaceuticals: Radioactive materials are chemical compounds that concentrate in specific organs or tissues to allow visualization of the organ's or tissue's function.
- CT (Computed Tomography): Developed in 1979, CT scans use X-rays to create detailed cross-sectional images of the body.
- MRI (Magnetic Resonance Imaging): Discovered in 2003, MRI uses strong magnetic fields and radio waves to create detailed images of the body's soft tissues.
Radioisotopes and Radiopharmaceuticals
- Radioisotope: A radioactive form of an element that emits radiation.
- Radiopharmaceutical: A drug containing a radioisotope that targets specific organs or tissues, allowing assessment of their function in relation to the radioisotope's activity.
- A radiopharmaceutical is made by combining a radioisotope with a pharmaceutical.
- Example: Fluorine-18 + Glucose = 18F-FDG, a commonly used radiopharmaceutical in PET scans.
Radiation Detectors in Nuclear Medicine
- Survey meters (ionization chambers, Geiger-Müller): Used for detecting radiation levels.
- Dose calibrator (ionization chambers): Measures the activity of radioactive sources.
- Well counter (scintillation detector): Measures the activity in liquid samples.
- Thyroid probe (scintillation detector): Used to measure thyroid function.
Nuclear Decay Rules
- Beta-minus (β−) decay: A neutron converts to a proton, emitting an electron and an antineutrino.
- Beta-plus (β+) decay: A proton converts to a neutron, releasing a positron and a neutrino.
- Electron capture: A proton absorbs an electron, turning into a neutron and emitting a neutrino.
- Gamma decay (γ-decay): Changes in nuclear energy levels without alteration in A or Z (atomic number).
Radioactivity
- Becquerel (Bq): The SI unit of radioactivity, representing one disintegration per second.
- Curie (Ci): A traditional unit of radioactivity, equaling 3.7 × 10¹⁰ Bq.
- 1 mCi = 37 MBq
- Nuclear medicine imaging generally uses 1 to 30 mCi (30 - 1100 MBq).
Physical Half-life (Tp)
- The time required for the number of radioactive atoms to reduce by half, following exponential decay.
- Basic equations, incorporating decay constant λ: N₁ = Noe-λt or A₁ = Aoe-λt and T₁/₂ = 0.693/ λ.
Effective Half-life (Te)
- The time needed for the concentration of a radiopharmaceutical to decrease by half in a biological system due to radioactive decay and physiological clearance.
- Te = [Tp × Tb] / [Tp + Tb] and if Tp >> Tb, then Te ≈ Tb and if Tp << Tb, then Te ≈ Tp. where Tp = physical half life. Tb is biological half life.
Radionuclides used in Nuclear Medicine
- The presentation lists various radionuclides and their uses in nuclear medicine (imaging and therapy).
Structural & Functional Imaging
- Images are used to show either structure or function of body parts and organs.
- CT & MRI are anatomical imaging techniques.
- Radioactive tracer methods (e.g., PET, SPECT) are functional imaging techniques.
NM and PET Process
- The presentation explains the steps in nuclear medicine and positron emission tomography (PET) processes, including how radiopharmaceuticals are used and how images are created.
Why is Nuclear Medicine Different?
- Nuclear medicine uses the patient's own body as the source of radiation.
- It is used for functional imaging and not anatomical imaging.
NM Activity Poles
- Three main roles/groups:
- Radiopharmacy
- Physicians (for procedure applications and interpretative analysis)
- Instrumentation / manufacture (equipment).
Methods for Obtaining a NM Image
- Administer the radiopharmaceutical (tracer).
- The radiopharmaceutical concentrates in the desired location(s).
- The nucleus of the radiopharmaceutical decays and emits gamma rays.
- Detect the gamma photons using a gamma camera.
Major Components of a Gamma Camera
- A scintillation crystal (e.g., NaI(Tl)) converts gamma radiation to light.
- Photomultiplier tubes detect light photons and convert them into electronic signals.
- Collimators direct detected photons into useful areas of detection.
- Electronics process the signals from PMTs to form an image.
Major Components of a PET Scanner
- Multiple rings of detectors to detect photons from positron-electron annihilation.
- Electronics process the signals from the detector array for reconstructing images.
- A computer with software to process data and display the image.
- A system to hold the patient and perform necessary movements for the scan.
Gamma Camera, Scintillation Camera
- These are two names for the same system.
- They detect and convert gamma rays into light and then to electronic signals to create an image.
Basic Principle of Scintillation Detectors
- Gamma rays hit the scintillator and produce light flashes.
- Photomultiplier tubes detect the light flashes and convert them into electric pulses.
Basic Principle of Gamma Camera
- Gamma rays hit a crystal causing light flashes.
- The light flashes are converted to electrical pulses.
- The pulses determine the energy & position of the incident photons.
- The system forms an image of the radionuclide distribution in the body.
Nuclear medicine is emission imaging
- Gamma photons are emitted from inside the patient's body.
- Relatively poor image quality due to limited photon numbers, image noise, and poor spatial resolution.
- CT uses transmission imaging.
Nuclear Medicine is Molecular Imaging
- Interaction of radiopharmaceutical with cells or molecules.
- Radiopharmaceutical molecules bind to a target molecule.
- Accumulation by molecular or cellular activities (e.g., 18F-FDG, 99mTc-sestamibi, 131|¯).
- Molecular or cellular studies (perfusion of heart, brain; metabolism of cancers) lead to earlier diagnosis.
Different Parallel-Hole Collimators
- Low-energy (LEAP), medium-energy (MEAP), and high-energy (HEAP)
- Used for different radionuclides and photon energies.
- Collimators are used in different orientations (e.g., parallel-hole, pin-hole, converging).
Collimators
- Determine geometric relationships between source and image.
- Affect count rate and spatial resolution of the result.
Scintillation Process in Detector
- Detector material converts photons to photons of a different color.
- The photon numbers are proportional to the energy deposited by the original incident photon.
- A PMT counts the number of electrons from photons to characterize the energy of the source radiation.
- The electrical pulse height is proportional to the energy deposited by the original photon in the crystal.
Desirable Scintillator Properties
- High density (p), atomic number (Z) → high absorption efficiency.
- High light output → high conversion efficiency and improved energy discrimination.
- Transparent to emitted light → improved light output linearity, sensitive detector.
Photomultiplier Tube (PMT)
- Photocathode converts light into electrons.
- Dynodes amplify the electron signal.
- Anode collects the amplified electron signal.
- High efficiency in converting and amplifying incoming light flashes.
Time-of-Flight PET Scan
- Measures delay between photon detection
- Improves signal to noise ratio & quality
- Necessary for wider scan areas/longer scans.
Patient Studies and their Advantages/Disadvantages
- No overlap of structural images.
- 3-dimensional lesion locations are measurable.
- Fusion with high resolution images (CT or MRI) is possible.
- Time consuming.
- Images are noisy.
PET Image Formation
- A positron is emitted from the radioisotope inside the patient.
- The positron and an electron annihilate, producing 2 gamma photons.
- The detector determines the direction of the photons, which is directly related to the location of the radioisotope-emitting area in the body.
- The detectors analyze the time interval between the emissions and assign a location of origin to each image point.
Positron Emission
- The process in which a proton transforms into a neutron, releasing a positron and neutrino.
- Fluorine-18 isotope is typically used.
- Positrons are the antimatter equivalent of electrons.
Detector Materials
- Various materials are used in different PET imaging systems.
- Materials considered include BGO, LSO, LYSO, and GSO.
Advantages of PET Imaging
- Higher spatial resolution.
- Higher detection efficiency.
Attenuation Correction in PET/CT
- Used to account for the fact that some gamma photons are lost due to absorption by tissues located between the source of emission and the detector.
- Attenuation maps and related calculations/models correct the issue and enhance clarity of the image.
Semiquantitative PET
- Standard Uptake Value (SUV) is commonly used to assess the uptake of radiotracers, primarily in biological samples measured for cancer and other diagnostic purposes
- Calculated as the ratio of activity in a region of interest (e.g., a tumor) divided by the activity per unit mass of the organ.
- Used in clinical studies to evaluate diseases
Normalization
- Correction for individual detector varying performance is called normalization.
Limitation of Functional Imaging
- Limited spatial resolution.
- Poor signal-to-noise ratio.
- Poor uptake in diseased areas.
- Registration with anatomical images is useful when combining functional and anatomical data.
Typical Oncology Protocol: FDG Scan
- Administer 10-20 mCi/ml of FDG.
- In a quiet space, wait 60 minutes to allow for uptake and clearance from blood.
- Scan from eyes-to-thighs, taking 6-7 scans/positions 15cm.
- Total scan time ~ 30 minutes.
Patient Dose for FDG Scan
- Effective dose to patient = ~7 mSv for ~10 mCi of FDG.
- CT dose for attenuation correction is ~ 5 -18 mSv.
- Organ of max. dose is typically bladder.
SPECT vs. PET
- SPECT uses single photons; PET uses coincident photons from the annihilation of positron-electron pairs in the body.
- PET is better for resolution; SPECT is better for quick acquisition.
- SPECT resolution is highly dependent on the collimator. Collimator resolution drops with scan distance.
- SPECT images use one camera at a time, acquiring a single projection at a time.
Advantages of PET Over SPECT
- Superior spatial resolution, usually less than 2mm.
- Greater sensitivity for identifying areas of interest with high metabolic activity.
- Easy attenuation correction.
Limitations of Functional Imaging
- Limited spatial resolution
- Poor signal to noise ratio
- Poor radiotracer uptake in diseased conditions.
- Combining with anatomical images for more comprehensive diagnosis.
Fusing Anatomy and Function
- Hand-drawn, visual, software, and hardware fusion methods are used to combine anatomical (e.g., CT) and functional (e.g., PET) imaging data.
History of Dual-Modality Imaging (SPECT/CT and PET/CT)
- Early prototypes (1990s and 1998) for combining SPECT/CT and PET/CT
- Full commercial systems installed by approximately 1999 and 2000
- Combining anatomical and functional imaging information.
Gamma Camera Components
- Stationary gantry
- Rotating gantry
- Detectors
- Patient table
- Acquisition station
- Processing station
- Transmission acquisition system
PET Scanner Components
- Gantry
- Detector ring
- Patient table
- Acquisition and processing station
PET/CT Scanner
- Gantry
- PET detector module
- CT detector module
- Acquisition and processing station
- Patient table
The PET/CT Power!
- CT is used for determining if there are anatomical lesions
- Combining anatomical and functional imaging data for a stronger diagnosis
Anatomic and Functional Imaging
- Anatomic imaging (CT)
- Functional imaging (NM)
- Complementation of modalities (e.g., CT/NM & PET/CT)
Effective Dose of NM Procedures
- Comprehensive list of effective dose values for different nuclear medicine procedures.
- Ranges vary based on radionuclide, organ(s) undergoing the procedure, dosage, and other variables.
- Effective doses are expressed in mSv.
- Specific activity parameters and other factors must be taken into account when performing effective dose calculations.
Dose Limits
- Occupational exposure limits, based on recommendations such as NCRP (1993)/ICRP (2007), vary based on type of exposure (e.g., occupational vs. public exposure)
- Limits are specific for certain regions/parts of the body (e.g., lens of eye, skin, hands/feet) and cumulative exposures (annual/5-year).
- Occupational exposure and cumulative limits and public exposure limits are expressed in mSv and are usually specific to specific bodies and/or parts of the body.
Other Topics
- Further information/details on various topics are presented, such as attenuation correction, iterative reconstruction, different detectors (e.g., scintillators and PMTs), time-of-flight (ToF) imaging, and others. Additional details/images explaining the operation, results, and other processes are provided. The details and specific data relate to particular devices and are quite intricate.
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Description
Test your knowledge on the various Nobel Prizes related to medical imaging technologies such as CT and MRI. Explore the fundamental principles of nuclear medicine and the characteristics of different imaging modalities. This quiz will challenge your understanding of the applications and differences within medical imaging fields.
