G485 Medical Physics - Nuclear Medicine
Medical Physics is split into two sections:
1. X-rays & Ultrasound
2. Nuclear Medicine
This mind map is for Nuclear Medicine
PLEASE ZOOM IN WHEN USING AS THERE IS A LOT OF INFORMATION AND IT IS VERY CRAMPED WHEN ZOOMED OUT :)
- Created by: abbiemca
- Created on: 20-04-16 22:11
View mindmap
- Medical Physics (II) Nuclear Medicine
- The Gamma Camera
- The gamma camera is a system which detects gamma-rays and converts them into an image!
- Four main components: lead collimator tubes, the scintillator (crystal), the photomultipliertubes and the computer
- Scintillator
- As relatively few gamma rays pass through the collimator tubes, the scintillator converts each gamma ray photon into many visible light photons
- Increases the signal with which to work with
- As relatively few gamma rays pass through the collimator tubes, the scintillator converts each gamma ray photon into many visible light photons
- Photomultiplier Tubes
- Each visible light photon is converted into one electron
- Each electron is accelerated towards a dynode and 2-3 electrons are produced
- Continuouslyfired towards dynodes until there are lots of electrons present
- Each electron is accelerated towards a dynode and 2-3 electrons are produced
- Each visible light photon is converted into one electron
- Computer
- Detects the electrical signal from photomultiplier tubes and converts the signal into an image
- Each photomultiplier tube corresponds to one pixel
- Detects the electrical signal from photomultiplier tubes and converts the signal into an image
- Scintillator
- The quality of the image can be improved by using narrower or longer collimators, or a longer scanning time
- Medical Tracers
- A medical tracer is a way of determining the structure of the body using a radioactive source
- Patient is then placed inside a gamma camera
- Most commonly used tracer is Technetium-99m (metastable)
- Metastable means the isotope remains in an excited state for some time after its production
- Decays into its ground state by gamma emission
- Other commonly used tracers are iodine-131 and fluorine-18
- Metastable means the isotope remains in an excited state for some time after its production
- Explain what is meant by a medical tracer
- A radioactive substance is ingested or injected into the patient
- and the resulting radiation is detected (by gamma cameras) to reveal the structure of the body
- A radioactive substance is ingested or injected into the patient
- A medical tracer is a way of determining the structure of the body using a radioactive source
- Positron Emission Tomography (PET)
- tomography is the product of 3D images of the internal structure of a body by observing how waves react at boundaries in the body
- A positron is the antiparticle of the electron
- Fluorine-18 is commonly used in medical imaging. It decays by beta+ decay and emits a positron
- The positron and electron annihilate each other to form 2 identical gamma rays at 180 degrees to each other
- Magnetic Resonance Imagine (MRI)
- Main components of an MRI scanner: large superconducting magnet, RF coils, gradient coils and a computer
- Superconducting Magnet
- Needed to produce external magnetic field to align protons
- RF Coils
- One coil to transmit RF pulses into body. Another to detect RF signal emitted from relaxing protons
- Gradient coils
- Produce an additional magnetic field that varies across patient's body. Results in Larmor frequency of nuclei will be slightly different for reach part of the body
- Only a small volume of the body is the right field value for resonance and the computer can locate the source of the RF signal
- Produce an additional magnetic field that varies across patient's body. Results in Larmor frequency of nuclei will be slightly different for reach part of the body
- Computer
- Controls gradient coils and RF pulses, which stores and analyses the received date producing and displaying an image
- Superconducting Magnet
- Advantages:non-ionising and non invasive. Better contrast between soft tissues
- Disadvantages: patients with metallic objects cannot be scanned. Patent has to remain still for a long time. Unsuitable for claustrophobic patents due to confined space
- Operation of MRI scanner
- MRI vs. PET
- Positron Emission Tomography (PET)
- tomography is the product of 3D images of the internal structure of a body by observing how waves react at boundaries in the body
- A positron is the antiparticle of the electron
- Fluorine-18 is commonly used in medical imaging. It decays by beta+ decay and emits a positron
- The positron and electron annihilate each other to form 2 identical gamma rays at 180 degrees to each other
- PET uses radioactive substances, MRI does not
- PET reveals brain function so can diagnoses diseases such as Alzheimer's
- MRI shows tissue variation
- Positron Emission Tomography (PET)
- Main components of an MRI scanner: large superconducting magnet, RF coils, gradient coils and a computer
- The Gamma Camera
- Make sure that the gamma rays are all travelling in the same direction!
- Lead Collimator Tubes
- Four main components: lead collimator tubes, the scintillator (crystal), the photomultipliertubes and the computer
- Scintillator
- As relatively few gamma rays pass through the collimator tubes, the scintillator converts each gamma ray photon into many visible light photons
- Increases the signal with which to work with
- As relatively few gamma rays pass through the collimator tubes, the scintillator converts each gamma ray photon into many visible light photons
- Photomultiplier Tubes
- Each visible light photon is converted into one electron
- Each electron is accelerated towards a dynode and 2-3 electrons are produced
- Continuouslyfired towards dynodes until there are lots of electrons present
- Each electron is accelerated towards a dynode and 2-3 electrons are produced
- Each visible light photon is converted into one electron
- Computer
- Detects the electrical signal from photomultiplier tubes and converts the signal into an image
- Each photomultiplier tube corresponds to one pixel
- Detects the electrical signal from photomultiplier tubes and converts the signal into an image
- Scintillator
- Four main components: lead collimator tubes, the scintillator (crystal), the photomultipliertubes and the computer
- This ensures a clear image
- Lead Collimator Tubes
- Alpha and beta are unsuitable as they are very damaging to cells (a lot of energy absorbed by only a few cells
- gamma mostly leaves the body with much less interaction
- Must be a gamma emitting source
- Medical Tracers
- A medical tracer is a way of determining the structure of the body using a radioactive source
- Patient is then placed inside a gamma camera
- Most commonly used tracer is Technetium-99m (metastable)
- Metastable means the isotope remains in an excited state for some time after its production
- Decays into its ground state by gamma emission
- Other commonly used tracers are iodine-131 and fluorine-18
- Metastable means the isotope remains in an excited state for some time after its production
- Explain what is meant by a medical tracer
- A radioactive substance is ingested or injected into the patient
- and the resulting radiation is detected (by gamma cameras) to reveal the structure of the body
- A radioactive substance is ingested or injected into the patient
- A medical tracer is a way of determining the structure of the body using a radioactive source
- Medical Tracers
- The half life of a medical tracer is a few hours
- Any longer is unsuitable because there would be a low decay constant and so the activity would be small and hard to detect
- Any shorter means the source would have decayed between ingesting and detecting
- Basic principles of a PET scan
- Brain/body is surrounded by gamma cameras
- Positrons from F-18 nuclei annihilate electrons
- This annihilation produces 2 identical gamma ray photons traveling in opposite directions
- Decay time between the 2 photons is used to determine location of annihilation (which are areas of increased activity)
- Computer is connected to gamma cameras and an image is formed using the electrical signals from the cameras
- Decay time between the 2 photons is used to determine location of annihilation (which are areas of increased activity)
- This annihilation produces 2 identical gamma ray photons traveling in opposite directions
- Positrons from F-18 nuclei annihilate electrons
- Brain/body is surrounded by gamma cameras
- Positrons from F-18 nuclei annihilate electrons
- This annihilation produces 2 identical gamma ray photons traveling in opposite directions
- Decay time between the 2 photons is used to determine location of annihilation (which are areas of increased activity)
- Computer is connected to gamma cameras and an image is formed using the electrical signals from the cameras
- Decay time between the 2 photons is used to determine location of annihilation (which are areas of increased activity)
- This annihilation produces 2 identical gamma ray photons traveling in opposite directions
- Superconducting Magnet
- Needed to produce external magnetic field to align protons
- Protons precess around the magnetic field which is provided with the strong electromagnet
- The frequency of precession is the Larmor frequency
- Transmitting coils provide pulses of radio waves f frequency that is equal to Larmor frequency
- Protons absorb energy from the radio waves, resonate and enter into a higher energy state (they become excited)
- When the protons return back to their original energy state (relaxation), they emit photons of radio frequency
- The relaxation time is the average time taken for the protons to return back to their original energy state
- relaxation time spends on tissue type
- a computer processes all of the signals from receiving coils, and suing computer software, produces a 3D image
- relaxation time spends on tissue type
- The relaxation time is the average time taken for the protons to return back to their original energy state
- When the protons return back to their original energy state (relaxation), they emit photons of radio frequency
- Protons absorb energy from the radio waves, resonate and enter into a higher energy state (they become excited)
- Transmitting coils provide pulses of radio waves f frequency that is equal to Larmor frequency
- Protons have spin and so they behave like tiny magnets
- Operation of MRI scanner
- The frequency of precession is the Larmor frequency
- Protons absorb energy from the radio waves, resonate and enter into a higher energy state (they become excited)
- When the protons return back to their original energy state (relaxation), they emit photons of radio frequency
- The relaxation time is the average time taken for the protons to return back to their original energy state
- relaxation time spends on tissue type
- a computer processes all of the signals from receiving coils, and suing computer software, produces a 3D image
- relaxation time spends on tissue type
- The relaxation time is the average time taken for the protons to return back to their original energy state
- When the protons return back to their original energy state (relaxation), they emit photons of radio frequency
Comments
No comments have yet been made