Podcast
Questions and Answers
The rapid shape changes, or vibrations, of the crystals in a transducer produce ______ that travel outward.
The rapid shape changes, or vibrations, of the crystals in a transducer produce ______ that travel outward.
ultrasound
To determine the depth of a medium using ultrasound, we need to measure the ______ between emitted and received reflected pulses.
To determine the depth of a medium using ultrasound, we need to measure the ______ between emitted and received reflected pulses.
time delay
[Blank] is defined as the product of the density of a medium and the speed of a wave in that medium.
[Blank] is defined as the product of the density of a medium and the speed of a wave in that medium.
Specific acoustic impedance
Ultrasound gel is used during scans to minimize the intensity of ______ of the pulse at the skin's surface.
Ultrasound gel is used during scans to minimize the intensity of ______ of the pulse at the skin's surface.
To enhance sharpness in an X-ray image, one can reduce the aperture size, which decreases the beam _________.
To enhance sharpness in an X-ray image, one can reduce the aperture size, which decreases the beam _________.
[Blank] refers to the reduction in intensity of a wave as it passes through a medium.
[Blank] refers to the reduction in intensity of a wave as it passes through a medium.
The ______ gives information about the nature of tissues in ultrasound imaging, as the degree of reflection depends on the impedances of two media at a boundary.
The ______ gives information about the nature of tissues in ultrasound imaging, as the degree of reflection depends on the impedances of two media at a boundary.
To improve the contrast of an X-ray image, a fluorescent '______ medium' can be used during the procedure.
To improve the contrast of an X-ray image, a fluorescent '______ medium' can be used during the procedure.
The kinetic energy of electrons is converted into thermal energy in the metal target, which is then cooled by ______.
The kinetic energy of electrons is converted into thermal energy in the metal target, which is then cooled by ______.
A key advantage of X-rays is their ability to create images where ______ is trapped, such as within the lungs.
A key advantage of X-rays is their ability to create images where ______ is trapped, such as within the lungs.
The sharp cutoff at the short wavelength end of the X-ray spectrum occurs because an electron gives all its energy to ______ in a single collision.
The sharp cutoff at the short wavelength end of the X-ray spectrum occurs because an electron gives all its energy to ______ in a single collision.
Unlike an A-scan, a ______ repeats A-scans from multiple angles to form a 2-dimensional image.
Unlike an A-scan, a ______ repeats A-scans from multiple angles to form a 2-dimensional image.
A continuous distribution of wavelengths in X-ray production occurs because electrons are decelerated when hitting the target, leading to a continuous range of ______ and therefore wavelengths.
A continuous distribution of wavelengths in X-ray production occurs because electrons are decelerated when hitting the target, leading to a continuous range of ______ and therefore wavelengths.
A filter in X-ray equipment functions to absorb low energy wavelengths, which serves to reduce the X-ray ______ to the patient.
A filter in X-ray equipment functions to absorb low energy wavelengths, which serves to reduce the X-ray ______ to the patient.
In PET scanning, a ______ is a substance containing radioactive nuclei that is absorbed by the tissue being studied.
In PET scanning, a ______ is a substance containing radioactive nuclei that is absorbed by the tissue being studied.
Narrow peaks of increased intensity at specific wavelengths in the X-ray spectrum are caused by the de-excitation of orbital electrons in the inner shell of the target atom, which then emits ______.
Narrow peaks of increased intensity at specific wavelengths in the X-ray spectrum are caused by the de-excitation of orbital electrons in the inner shell of the target atom, which then emits ______.
A ______ is used to ensure a parallel X-ray beam, improving image quality and reducing unnecessary exposure.
A ______ is used to ensure a parallel X-ray beam, improving image quality and reducing unnecessary exposure.
One significant advantage of CT scans over traditional X-rays is that the final image can be viewed from ______ angle.
One significant advantage of CT scans over traditional X-rays is that the final image can be viewed from ______ angle.
The term '______' of an X-ray beam refers to its penetration ability, where greater ______ indicates higher photon energy.
The term '______' of an X-ray beam refers to its penetration ability, where greater ______ indicates higher photon energy.
A primary disadvantage of CT scans, compared to X-rays, is the greater ______ to radiation for the patient.
A primary disadvantage of CT scans, compared to X-rays, is the greater ______ to radiation for the patient.
To increase the hardness of an X-ray beam, one should increase the ______ of the accelerating electrons.
To increase the hardness of an X-ray beam, one should increase the ______ of the accelerating electrons.
In the context of X-ray intensity calculation, the equation I = I0e^______x is used, where μ represents the attenuation coefficient.
In the context of X-ray intensity calculation, the equation I = I0e^______x is used, where μ represents the attenuation coefficient.
An aluminium filter is used to absorb low energy wavelengths, cutting off 'soft' X-rays, in order to reduce ______.
An aluminium filter is used to absorb low energy wavelengths, cutting off 'soft' X-rays, in order to reduce ______.
In X-ray imaging, different tissues attenuate the X-ray beam by different amounts, which produces a '______' image of structures on the photographic plate.
In X-ray imaging, different tissues attenuate the X-ray beam by different amounts, which produces a '______' image of structures on the photographic plate.
Flashcards
Filament Voltage Function
Filament Voltage Function
Heated filament releases high-speed electrons via thermionic emission.
Cathode-Anode Voltage Function
Cathode-Anode Voltage Function
Accelerates electrons from cathode to anode.
Target Rotation Purpose
Target Rotation Purpose
Rotating target cools it by spreading thermal energy.
Sharp Cut-off Cause
Sharp Cut-off Cause
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Continuous Wavelengths Cause
Continuous Wavelengths Cause
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Narrow Peaks Origin
Narrow Peaks Origin
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X-ray Hardness
X-ray Hardness
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Aluminum Filter Function
Aluminum Filter Function
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Contrast (X-ray)
Contrast (X-ray)
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Increase Sharpness (X-ray)
Increase Sharpness (X-ray)
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Increase Contrast (X-ray)
Increase Contrast (X-ray)
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Advantage of X-ray
Advantage of X-ray
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Disadvantage of X-ray
Disadvantage of X-ray
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Ultrasound definition
Ultrasound definition
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Piezo-electric crystal function
Piezo-electric crystal function
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Piezoelectric effect principle
Piezoelectric effect principle
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Ultrasound Transducer
Ultrasound Transducer
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Specific Acoustic Impedance
Specific Acoustic Impedance
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Attenuation
Attenuation
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Intensity Reflection Coefficient
Intensity Reflection Coefficient
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A-scan vs. B-scan
A-scan vs. B-scan
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Radiotracer
Radiotracer
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Annihilation
Annihilation
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Positron Annihilation Result
Positron Annihilation Result
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Study Notes
X-Ray Production
- Voltage across the filament heats it, causing thermionic emission and releasing high-speed electrons.
- Voltage across the cathode and anode accelerates the electrons.
- Kinetic energy from electrons transfers to the metal target as thermal energy which is cooled by the target's rotation.
X-Ray Spectrum
- A sharp cutoff at short wavelengths occurs when an electron gives all its energy to one photon and stops after a single collision.
- A continuous distribution of wavelengths is produced by decelerating electrons hitting the target.
- Electrons are attracted by the nucleus of the anode's atom and lose energy which depends on the magnitude of deceleration, resulting in a continuous spectrum of wavelengths.
- Narrow peaks of high intensity appear at specific wavelengths.
- A high-speed electron excites an orbital electron in the inner shell of a target atom.
- De-excitation of the electron will emit a photon, giving rise to spectrum lines due to discrete energy levels and photon wavelengths.
Properties and Control of X-Rays
- Hardness refers to the penetration of the X-ray beam; a harder X-ray has higher photon energy and more penetrating power.
- Increase the voltage of accelerating electrons to increase hardness.
- Increase the voltage across the filament to increase intensity.
- More intense X-rays produce images more quickly.
X-Ray Imaging
- Aluminum filters are used to absorb low-energy (soft) X-rays to reduce radiation dose.
- X-ray beams are directed through the body onto a detector plate; tissues attenuate the beam differently based on absorption properties.
- The varying attenuation leads to a shadow image on a photographic plate
- Sharpness refers to the clarity of image edges.
- Contrast is the difference in the degree of blackening in different regions of the image.
Improving Image Quality
- Reduce the target anode area
- Reduce aperture size (window) to reduce beam width.
- Place a lead grid in front of the photographic film to absorb scattered X-rays and reduce partial images.
- Contrast can be increased by increasing exposure time, using harder X-rays, reducing X-ray beam scattering, and using fluorescent contrast medium
Advantages and Disadvantages of X-Rays
- Sharp images can be formed, contrast improved, and images are possible where air is trapped.
- Equipment is heavy, not portable and can cause ionization and tissue damage.
Components of X-Ray Equipment
- Filters absorb low-energy wavelengths to reduce radiation dose.
- Collimators produce parallel X-ray beams.
Computed Tomography (CT)
- CT images are 3D and can be viewed from any angle.
- CT scans can distinguish between tissues that have similar attenuation coefficients.
Disadvantages of CT Scans
- Greater radiation exposure.
- Increased health risks
- It's more expensive
- The person must remain stationary during imaging
CT Principle
- Series of X-ray images for one section/slice are taken from different angles to give image of the section/slice
- Images are processed and combined in two dimensions.
- Process repeated for successive slices to build up three-dimensional image.
- Computers are needed to store and process large amount of data
X-Ray Intensity Equation
- The equation to calculate the intensity of an X-ray: I = Ioe^-μx
Ultrasound
- Ultrasound is a sound wave with a frequency above 20kHz.
- Piezo-electric transducers are used to record and produce ultrasonic waves; a.c. across vibrates the crystal, generating ultrasound.
- Detection of reflected ultrasound generates induced potential difference.
Piezoelectric Effect
- Piezoelectric crystals are coated with silver on two sides to serve as electrodes.
- Alternating potential difference is applied to the crystals which alter their shape which causes vibrations.
- Crystal's natural frequency is in the ultrasound range.
- Crystals resonate at ultrasound frequencies, producing vibrations that generate ultrasound.
Pulse Ultrasound
- The ultrasound from the transducer is pulsed.
- Transducers act as receivers and transmitters.
- Time delay between received reflected pulses and emitted pulses determines depth of medium.
Specific Acoustic Impedance
- Specific acoustic impedance defined as the product of density of a medium and the speed of a wave passing through it.
Gel Use in Ultrasound
- Reduce reflection at air-skin boundary
- Without gel, most ultrasound is reflected at air-skin boundary.
- With gel present, most ultrasound energy enters the body
Attenuation
- Describes the reduction in intensity of a wave and it passes through a medium.
- I = Ioe^-kx
Intensity Reflection Coefficient
- It's the ratio of intensity of reflected to incident wave.
- α = (IR/I) = ((Z2-Z1)/(Z2 + Z1))^2
Ultrasound Scanning
- Pulses emitted from generator, gel use minimizes reflection at skin.
- Pulses reflected at boundaries detected by ultrasound generator.
- The signal is then processed and displayed on a computer.
- Time delay gives boundary depth.
- Reflected intensity gives information about tissue, and the degree of reflection depends on impedances of two media at boundary.
A-scan vs B-scan
- A-scan: measures distance from transducer in one position graphically.
- B-scan: repeats A-scan from multiple angles to 2D image
Advantages of Ultrasound Imaging
- Portable equipment.
- Less harmful than X-rays.
Disadvantages of Ultrasound Imaging
- Images are not sharp due to refraction
- Cannot be used to image where air is trapped like lungs
Positron Emission Tomography (PET)
- Radiotracers are substances with radioactive nuclei that are absorbed by tissue being studied.
- Annihilation is when a particle interacts with its antiparticle, converting mass into energy.
- Electron + positron yields two gamma photons
Energy and Momentum in PET
- Total energy = 2 x mass of electron x C²
- P = energy of one photon / c = h / wavelength of one photon
Principle of PET Imaging
- Positrons interact with electrons which travels in opposite directions outside the body and detected.
- Determining where gamma photons arrive defines tracer concentration in the tissue
Key aspects of detectors utilized in PET imaging
- A crystal receives a gamma-photon.
- An electron becomes excited via the photoelectric effect.
- One electron will stimulate more electrons.
- As electrons return to ground state, visible light photons are released.
- A photomultiplier transforms photons into electrical reading for the computer.
Advantages & Disadvantages of PET Imaging
- Can be used to detect cancer
- Can show metabolic activity of cells
- Equipment is heavy and not portable
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Description
This covers the principles of ultrasound and X-ray imaging. Key concepts include wave propagation, depth measurement using ultrasound, acoustic impedance, and attenuation. It also touches on image enhancement techniques in X-ray imaging.
