Define Bremsstrahlung radiation .

Bremsstrahlung radiation is produced when fast-moving electrons undergo a steep deceleration on colliding with a metal target, converting some of their kinetic energy into an X-ray photon .

Define characteristic radiation .

Characteristic radiation is produced when an incoming electron knocks an inner-shell electron out of a target atom, and an outer electron fills the vacancy, releasing an X-ray photon with an energy equal to the difference between the two energy levels.

What proportion of an incoming electron's kinetic energy is converted into X-ray photons at the target, and what happens to the rest?

Only about 1% of the kinetic energy is converted into X-rays; the rest is converted into heat energy .

The energy of an X-ray photon produced by Bremsstrahlung can be of any value, up to the .......... of the electron, giving a range of possible X-ray energies.

The energy of an X-ray photon produced by Bremsstrahlung can be of any value, up to the original kinetic energy of the electron, giving a range of possible X-ray energies.

Explain why Bremsstrahlung radiation produces a continuous range of X-ray wavelengths rather than discrete values.

Electrons undergo different amounts of deceleration when they strike the target, so they lose different amounts of kinetic energy as photons, producing a continuous spectrum of wavelengths.

Why does characteristic radiation appear as sharp spikes on an intensity-wavelength graph rather than a continuous spectrum?

Characteristic X-rays are produced by electron transitions between discrete energy levels in the target atom, so only specific, fixed energies (and therefore wavelengths) are produced.

Define thermionic emission .

Thermionic emission is the liberation of electrons from a heated cathode, which then gather in a cloud near its surface.

State the four main components of a rotating-anode X-ray tube.

A heated cathode , an anode , a metal target and a high-voltage power supply .

Why is the anode of an X-ray tube spun at around 3000 rpm, and sometimes water-cooled?

Only about 1% of the electrons' kinetic energy becomes X-rays; the rest becomes heat , so spinning (and cooling) the anode spreads this heat out and prevents overheating .

Why is tungsten used as the metal target in an X-ray tube?

Tungsten is heat-resistant , so it can withstand the high-speed electron collisions that generate X-rays without being damaged.

Why are the anode and cathode of an X-ray tube housed inside a vacuum chamber?

To ensure the electrons do not collide with air particles on their way from the cathode to the metal target.

What is the purpose of the lead shielding and adjustable window on an X-ray tube?

X-rays are produced in all directions , so lead shielding protects operators and patients from stray radiation, while the adjustable window lets a controlled, concentrated beam escape safely.

When electrons arrive at the anode after acceleration through 200 kV, they gain a kinetic energy of 200 keV, but only about .......... of this is converted into X-rays.

When electrons arrive at the anode after acceleration through 200 kV, they gain a kinetic energy of 200 keV, but only about 1% of this is converted into X-rays.

True or False? The cathode is the positive terminal of an X-ray tube.

False. The cathode is the negative terminal, heated to release electrons by thermionic emission; the anode is the positive terminal, connected to the high-voltage supply.

Define contrast (in X-ray imaging).

Contrast is the difference in degree of blackening between structures on an X-ray image.

Define sharpness (in X-ray imaging).

Sharpness is how well-defined the edges of structures are on an X-ray image.

Define contrast medium .

A contrast medium is a substance, such as barium or iodine, that is a good absorber of X-rays, given to a patient so a bigger contrast can be obtained on an X-ray image.

Which control on an X-ray tube determines the intensity of the X-ray beam, and how should it be adjusted to minimise patient exposure?

The cathode current controls the intensity; lowering it reduces the number of ionising photons reaching the patient each second, minimising exposure.

What is the purpose of a beam definer (lead diaphragm plate) in an X-ray machine?

It absorbs scattered photons and only lets a focused, collimated beam through a narrow aperture, so only the area being investigated is exposed to X-rays.

Why is an aluminium filter placed in the path of an X-ray beam between the tube and the patient?

It absorbs a large percentage of low-energy photons, which are not needed to produce an image but would otherwise increase the patient's ionising dose, while allowing high-energy photons through.

Why is iodine used as a contrast medium to observe blood flow, while barium sulphate is used for the digestive system?

Iodine is injected and used as a contrast medium in liquids, such as blood; barium sulphate is ingested (a barium meal) as it is suited to the digestive system.

The large attenuation coefficient of contrast media, such as barium and iodine, is due to their .......... .

The large attenuation coefficient of contrast media, such as barium and iodine, is due to their large atomic number .

True or False? Increasing the anode potential difference increases the number of X-ray photons produced per second.

False. The anode p.d. controls the maximum energy (and so penetration) of the X-ray photons; it is the cathode current that controls the number of photons produced per second.

What is the most common X-ray detection method used in medical facilities today, and where else is it used commercially?

The X-ray flat panel (FTP) detector is the most common detection method in medical facilities; it is also used commercially, such as in airport security .

State the three layers of an X-ray flat panel (FTP) detector, in order, and the function of the first layer.

The scintillator layer , the photodiode pixel layer , and the electronic scanner layer . The scintillator layer absorbs X-rays and emits visible photons .

What is the purpose of the two fluorescent screens in an intensifying cassette used with photographic film?

They emit light when they absorb X-rays, which exposes the film faster than X-rays alone (about 20 times faster), shortening the exposure time.

Why is the final image on a fluoroscopic image intensifier's output screen about 5000 times brighter than the image on the first fluorescent screen?

The electrons are focused onto a smaller area , increasing intensity, and are accelerated through a large potential difference (about 25 kV), so each electron produces several photons at the exit screen.

Which X-ray detection method is best for imaging a dynamic process such as blood flow, and why does it involve a higher radiation dose?

The fluoroscopic image intensifier , as it produces real-time images; it requires a continuous beam of X-rays for the duration of the procedure, giving a higher dose than a single exposure.

In a fluoroscopic image intensifier, electrons emitted from the .......... are accelerated through a potential difference of about 25 kV towards the anodes.

In a fluoroscopic image intensifier, electrons emitted from the photocathode are accelerated through a potential difference of about 25 kV towards the anodes.

State three advantages of flat panel (FTP) detectors over photographic film.

Faster (no processing or developing needed, so images can be produced in real time), more sensitive (a lower radiation dose gives an image of the same quality), and produces digital images (easily processed, stored and transferred).

True or False? Flat panel detectors require a higher radiation dose than photographic film to produce an image of the same quality.

False. FTP detectors are more sensitive than film, so a lower radiation dose produces an image of the same quality.

Define half-value thickness .

The half-value thickness is the thickness of a material which reduces the intensity of X-rays to half its original level, for a specified energy of X-rays.

Why is the energy range 30 keV to 100 keV used to distinguish bone from soft tissue in X-ray imaging?

In this range, bone (higher-Z elements) absorbs photons much more readily than soft tissue , giving good contrast; below 30 keV both absorb similarly, and above 100 keV all tissues absorb similarly.

Elements with .......... atomic numbers tend to absorb a greater proportion of X-rays.

Elements with higher atomic numbers tend to absorb a greater proportion of X-rays.

True or False? X-ray photons with energies above 100 keV are ideal for producing high-contrast diagnostic images.

False. Above 100 keV, photons are absorbed equally by all types of tissue, including bone, so they produce no distinction between tissues and are not used diagnostically.

Define computed tomography (CT) scanning .

CT scanning is an imaging technique which uses X-rays to produce high-resolution 2D images of thin slices of the body and detailed 3D images of sections of the body.

Describe the main components of a CT scanner.

A ring-shaped structure allowing rotation, an X-ray tube mounted on one side, an array of detectors on the opposite side, and a computer which processes the images.

Describe how a CT scanner builds up a 2D image of one slice of the body.

The X-ray tube and detector array rotate in opposite directions around the stationary patient, sending a narrow beam through the same slice from many directions; the detector signals are combined by a computer into a 2D image.

In a CT scanner, the X-ray tube produces a narrow, .......... beam of X-rays as short pulses.

In a CT scanner, the X-ray tube produces a narrow, monochromatic beam of X-rays as short pulses.

State two advantages of CT scanning compared with a simple X-ray image.

Produces high- resolution , high- contrast images with no overlapping structures, can distinguish tissues with similar attenuation coefficients, images bone and soft tissue in a single process, and produces a 3D image .

State two disadvantages of CT scanning compared with a simple X-ray image.

A much higher radiation dose to the patient, more time-consuming and expensive, and possible side effects from the contrast media .

True or False? A CT scan exposes a patient to a lower radiation dose than a single simple X-ray image.

False. A CT scan involves many exposures from different directions to build up a 3D image, giving a much higher radiation dose than a single simple X-ray.

A LevelPhysicsAQAFlashcardsMedical PhysicsX-ray Imaging

X-ray Imaging (AQA A Level Physics): Flashcards

Exam code: 7408

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Define Bremsstrahlung radiation.

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Cards in this collection (48)

Define Bremsstrahlung radiation.
Bremsstrahlung radiation is produced when fast-moving electrons undergo a steep deceleration on colliding with a metal target, converting some of their kinetic energy into an X-ray photon.
Define characteristic radiation.
Characteristic radiation is produced when an incoming electron knocks an inner-shell electron out of a target atom, and an outer electron fills the vacancy, releasing an X-ray photon with an energy equal to the difference between the two energy levels.
What proportion of an incoming electron's kinetic energy is converted into X-ray photons at the target, and what happens to the rest?
Only about 1% of the kinetic energy is converted into X-rays; the rest is converted into heat energy.
State the equation for the maximum possible energy, $E_{m a x}$ , of an X-ray photon produced in an X-ray tube with accelerating potential difference V.
$E_{m a x} = e V$
The energy of an X-ray photon produced by Bremsstrahlung can be of any value, up to the .......... of the electron, giving a range of possible X-ray energies.
The energy of an X-ray photon produced by Bremsstrahlung can be of any value, up to the original kinetic energy of the electron, giving a range of possible X-ray energies.
True or False?
The continuous Bremsstrahlung spectrum has no minimum-wavelength limit.
False.
The accelerating potential difference sets a maximum energy ( $E_{m a x} = e V$ ) for the electrons, which corresponds to a minimum wavelength cut-off below which no X-ray photons can be produced.
Explain why Bremsstrahlung radiation produces a continuous range of X-ray wavelengths rather than discrete values.
Electrons undergo different amounts of deceleration when they strike the target, so they lose different amounts of kinetic energy as photons, producing a continuous spectrum of wavelengths.
Why does characteristic radiation appear as sharp spikes on an intensity-wavelength graph rather than a continuous spectrum?
Characteristic X-rays are produced by electron transitions between discrete energy levels in the target atom, so only specific, fixed energies (and therefore wavelengths) are produced.
Define thermionic emission.
Thermionic emission is the liberation of electrons from a heated cathode, which then gather in a cloud near its surface.
State the four main components of a rotating-anode X-ray tube.
A heated cathode, an anode, a metal target and a high-voltage power supply.
Why is the anode of an X-ray tube spun at around 3000 rpm, and sometimes water-cooled?
Only about 1% of the electrons' kinetic energy becomes X-rays; the rest becomes heat, so spinning (and cooling) the anode spreads this heat out and prevents overheating.
Why is tungsten used as the metal target in an X-ray tube?
Tungsten is heat-resistant, so it can withstand the high-speed electron collisions that generate X-rays without being damaged.
Why are the anode and cathode of an X-ray tube housed inside a vacuum chamber?
To ensure the electrons do not collide with air particles on their way from the cathode to the metal target.
What is the purpose of the lead shielding and adjustable window on an X-ray tube?
X-rays are produced in all directions, so lead shielding protects operators and patients from stray radiation, while the adjustable window lets a controlled, concentrated beam escape safely.
When electrons arrive at the anode after acceleration through 200 kV, they gain a kinetic energy of 200 keV, but only about .......... of this is converted into X-rays.
When electrons arrive at the anode after acceleration through 200 kV, they gain a kinetic energy of 200 keV, but only about 1% of this is converted into X-rays.
True or False?
The cathode is the positive terminal of an X-ray tube.
False.
The cathode is the negative terminal, heated to release electrons by thermionic emission; the anode is the positive terminal, connected to the high-voltage supply.
Define contrast (in X-ray imaging).
Contrast is the difference in degree of blackening between structures on an X-ray image.
Define sharpness (in X-ray imaging).
Sharpness is how well-defined the edges of structures are on an X-ray image.
Define contrast medium.
A contrast medium is a substance, such as barium or iodine, that is a good absorber of X-rays, given to a patient so a bigger contrast can be obtained on an X-ray image.
Which control on an X-ray tube determines the intensity of the X-ray beam, and how should it be adjusted to minimise patient exposure?
The cathode current controls the intensity; lowering it reduces the number of ionising photons reaching the patient each second, minimising exposure.
What is the purpose of a beam definer (lead diaphragm plate) in an X-ray machine?
It absorbs scattered photons and only lets a focused, collimated beam through a narrow aperture, so only the area being investigated is exposed to X-rays.
Why is an aluminium filter placed in the path of an X-ray beam between the tube and the patient?
It absorbs a large percentage of low-energy photons, which are not needed to produce an image but would otherwise increase the patient's ionising dose, while allowing high-energy photons through.
Why is iodine used as a contrast medium to observe blood flow, while barium sulphate is used for the digestive system?
Iodine is injected and used as a contrast medium in liquids, such as blood; barium sulphate is ingested (a barium meal) as it is suited to the digestive system.
The large attenuation coefficient of contrast media, such as barium and iodine, is due to their ...........
The large attenuation coefficient of contrast media, such as barium and iodine, is due to their large atomic number.
True or False?
Increasing the anode potential difference increases the number of X-ray photons produced per second.
False.
The anode p.d. controls the maximum energy (and so penetration) of the X-ray photons; it is the cathode current that controls the number of photons produced per second.
What is the most common X-ray detection method used in medical facilities today, and where else is it used commercially?
The X-ray flat panel (FTP) detector is the most common detection method in medical facilities; it is also used commercially, such as in airport security.
State the three layers of an X-ray flat panel (FTP) detector, in order, and the function of the first layer.
The scintillator layer, the photodiode pixel layer, and the electronic scanner layer. The scintillator layer absorbs X-rays and emits visible photons.
What is the purpose of the two fluorescent screens in an intensifying cassette used with photographic film?
They emit light when they absorb X-rays, which exposes the film faster than X-rays alone (about 20 times faster), shortening the exposure time.
Why is the final image on a fluoroscopic image intensifier's output screen about 5000 times brighter than the image on the first fluorescent screen?
The electrons are focused onto a smaller area, increasing intensity, and are accelerated through a large potential difference (about 25 kV), so each electron produces several photons at the exit screen.
Which X-ray detection method is best for imaging a dynamic process such as blood flow, and why does it involve a higher radiation dose?
The fluoroscopic image intensifier, as it produces real-time images; it requires a continuous beam of X-rays for the duration of the procedure, giving a higher dose than a single exposure.
In a fluoroscopic image intensifier, electrons emitted from the .......... are accelerated through a potential difference of about 25 kV towards the anodes.
In a fluoroscopic image intensifier, electrons emitted from the photocathode are accelerated through a potential difference of about 25 kV towards the anodes.
State three advantages of flat panel (FTP) detectors over photographic film.
Faster (no processing or developing needed, so images can be produced in real time), more sensitive (a lower radiation dose gives an image of the same quality), and produces digital images (easily processed, stored and transferred).
True or False?
Flat panel detectors require a higher radiation dose than photographic film to produce an image of the same quality.
False.
FTP detectors are more sensitive than film, so a lower radiation dose produces an image of the same quality.
Define linear attenuation coefficient, $μ$ .
The linear attenuation coefficient is the fraction of X-rays removed per unit thickness of a material, for a specified energy of X-rays.
Define half-value thickness.
The half-value thickness is the thickness of a material which reduces the intensity of X-rays to half its original level, for a specified energy of X-rays.
State the equation linking half-value thickness $x_{1 / 2}$ to the linear attenuation coefficient $μ$ .
$x_{1 / 2} = \frac{\ln 2}{μ}$
State the equation for the attenuation of X-ray intensity $I$ with distance $x$ travelled through a material.
$I = I_{0} e^{- μ x}$
Define mass attenuation coefficient.
The mass attenuation coefficient is the linear attenuation coefficient divided by the density of the absorbing material, $μ_{m} = μ / ρ$ ; it is a constant value for a given substance.
Why is the energy range 30 keV to 100 keV used to distinguish bone from soft tissue in X-ray imaging?
In this range, bone (higher-Z elements) absorbs photons much more readily than soft tissue, giving good contrast; below 30 keV both absorb similarly, and above 100 keV all tissues absorb similarly.
Elements with .......... atomic numbers tend to absorb a greater proportion of X-rays.
Elements with higher atomic numbers tend to absorb a greater proportion of X-rays.
True or False?
X-ray photons with energies above 100 keV are ideal for producing high-contrast diagnostic images.
False.
Above 100 keV, photons are absorbed equally by all types of tissue, including bone, so they produce no distinction between tissues and are not used diagnostically.
Define computed tomography (CT) scanning.
CT scanning is an imaging technique which uses X-rays to produce high-resolution 2D images of thin slices of the body and detailed 3D images of sections of the body.
Describe the main components of a CT scanner.
A ring-shaped structure allowing rotation, an X-ray tube mounted on one side, an array of detectors on the opposite side, and a computer which processes the images.
Describe how a CT scanner builds up a 2D image of one slice of the body.
The X-ray tube and detector array rotate in opposite directions around the stationary patient, sending a narrow beam through the same slice from many directions; the detector signals are combined by a computer into a 2D image.
In a CT scanner, the X-ray tube produces a narrow, .......... beam of X-rays as short pulses.
In a CT scanner, the X-ray tube produces a narrow, monochromatic beam of X-rays as short pulses.
State two advantages of CT scanning compared with a simple X-ray image.
Produces high-resolution, high-contrast images with no overlapping structures, can distinguish tissues with similar attenuation coefficients, images bone and soft tissue in a single process, and produces a 3D image.
State two disadvantages of CT scanning compared with a simple X-ray image.
A much higher radiation dose to the patient, more time-consuming and expensive, and possible side effects from the contrast media.
True or False?
A CT scan exposes a patient to a lower radiation dose than a single simple X-ray image.
False.
A CT scan involves many exposures from different directions to build up a 3D image, giving a much higher radiation dose than a single simple X-ray.

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