Physics - Recall for Chapter 27; Medical Imaging
Flashcards
When are X-rays produced?
When high-energy X-rays are slowed down.
What are the typical wavelengths of X-rays in meters?
What process causes the creation of X-rays in an X-ray machine?
Thermionic emission.
Roughly what percentage of electron energy is converted to X-rays in an X-ray machine?
How can the intensity of X-rays be increased in an X-ray machine?
Increase the current in the cathode.
How can the maximum energy of X-rays be increased in an X-ray machine?
Increase the accelerating potential difference.
What are the four ways X-rays can interact with matter?
- Simple scattering
- Photoelectric effect
- Compton scattering
- Pair production
For what energies does simple scattering of X-ray photons occur?
For what energies does the photoelectric effect occur for X-ray photons?
For what energies does Compton scattering of X-rays occur?
For what energies does pair production occur for X-ray photons?
How does the intensity of a parallel beam of X-rays change as it passes through a material?
It decreases exponentially.
What are the units of the attenuation coefficient of a material?
How can bone and soft tissue be differentiated in simple X-ray images?
Bone has a higher attenuation coefficient and so absorbs more X-rays.
Why is it difficult to identify soft tissue and muscle in simple X-ray images?
They have similar attenuation coefficients.
How can the contrast between tissues with similar attenuation coefficients be increased?
Use a contrast medium.
What is true about the proton numbers of contrast mediums?
They have high proton numbers.
What does CAT stand for?
Computerised axial tomography.
What are two advantages of CAT scans?
- Can better differentiate between soft tissues
- Can produce a 3D image
What is a disadvantage of CAT scans?
- Patients are exposed to more radiation
- More expensive
What does the X-ray beam used in CAT scans look like?
Thin and fan-shaped.
How is a 3D scan built in a CAT scanner?
Many thin 2D X-ray images are compiled together by a computer.
What energy photons does Technetium-99m emit?
How can Technetium-99m be used in medical imaging?
It can be combined with a medical tracer to target a specific organ and investigate its function.
What piece of equipment is used to detect gamma rays from a radiopharmaceutical?
A gamma camera.
What are the three main parts of a gamma camera?
- Collimator
- Scintillator
- Photomultiplier tube
What is the function of the collimator component of a gamma camera?
Only allows photons travelling along the axis of the detector to reach the scintillator.
What is the function of the scintillator component of a gamma camera?
To absorb gamma photons and convert them into thousands of visible light photons.
What is the function of the photomultiplier tube in a gamma camera?
Convert visible light photons into an electrical pulse.
What does PET stand for?
Positron emission tomography.
What is the half life of fluorodeoxyglucose?
Roughly 2 hours.
Where does fluorodeoxyglucose (FDG) gather inside a patient?
In organs or tissues with high rates of respiration.
Why are PET scans expensive?
As medical tracers need to produced on-site.
What is the limit of human hearing?
What is ultrasound?
Sound waves with a frequency above $20\text{kHz}$.
How can ultrasound be produced and detected?
Using an ultrasound transducer.
What is the piezoelectric effect?
The production of an EMF when certain materials are compressed or extended, and vice versa.
How does an ultrasound transducer work?
A high-frequency AC PD is applied across a piezoelectric crystal, causing it to produce an ultrasound wave of that frequency.
What is true about the frequency of the alternating current produced by a piezoelectric crystal detecting a sound wave?
It is equal to the frequency of the sound wave.
What are three advantages of ultrasound images?
- Non-ionising
- Can provide contrast between soft tissues
- Real-time images
What is the acoustic impedance of a material in words?
The product of the density of the material and the speed of ultrasound in the material.
What is true when there are large reflected intensities of ultrasound waves between tissues?
There is a large difference in acoustic impedance.
How can ultrasound reflections between air and a patient’s skin be reduced?
Using a coupling gel.
How can the speed and direction of a patient’s blood flow be determined using ultrasound?
Measuring the frequency change of the reflected wave due to the Doppler effect.