Homework 3 Flashcards
What do you understand by the term ‘Half Value Thickness’ (HVT)?
It is a half value layer.
HVT is the thickness of a specific material which reduces the radiation intensity to one half of the original intensity.
It is a reference value used to determine the thickness of material required for radiation shielding; e.g. for construction of a work bay in a fabrication shop.
When the intensity of the X-ray equipment is increased, the half value thickness will:
Remain the same
Which of the following effects the half value thickness?
Intensity x
wavelength ✓
exposure time x
If a radiographer doubles the kV will the half value thickness of the material also double?
No, the hvt is not proportional to the energy provided
Is the HVT at 200 kilovolts the same as 300 kilovolts in the same material
No because the wavelength is different
How does kilovolts affect contrast?
Less kV equals higher contrast
(lower penetration = more silver halides affected by x-rays and therefore turn black)
A radiographic film is, usually, made up of seven layers. Which of the following is true regarding this construction?
It contains a ‘base layer which is of a suitable substrate such as Polyester or Cellulose Triacetate.
A subbing layer which adheres the layer of emulsion consisting of millions of ‘silver halide crystals’ which are suspended in a ‘gelatine binding medium on either side of the ‘base layer’.
A ‘supercoat’ layer on either side acting as a finish coat protecting the emulsion layer from possible mechanical and chemical damage.
All of the above are correct.
A radiographic film is, usually, made up of seven layers. Which of the following is true regarding this construction?
It contains a ‘base layer which is of a suitable substrate such as Polyester or Cellulose Triacetate.
A subbing layer which adheres the layer of emulsion consisting of millions of ‘silver halide crystals’ which are suspended in a ‘gelatine binding medium on either side of the ‘base layer’.
A ‘supercoat’ layer on either side acting as a finish coat protecting the emulsion layer from possible mechanical and chemical damage.
All of the above are correct.
Which of the following is true regarding large grain size in the emulsion layer of photographic film?
Faster film speed AND poorer definition.
What is a direct type film?
A direct-type film in radiography is a type of film that is directly sensitive to X-rays or gamma rays without the need for an intermediate step, such as the use of a scintillator.
What is a fluoro metallic screen?
A fluorescent metallic screen (or sometimes called a fluorometallic screen) is a type of intensifying screen used in radiographic imaging. It is designed to enhance the effects of X-ray exposure by converting X-rays into visible light, which in turn exposes the radiographic film. These screens are commonly used in conjunction with indirect-type films, which are sensitive to light.
What is film factor?
The film factor is a comparative measure of the exposure requirements of a radiographic film relative to a reference film. It helps in adjusting exposure settings when switching between different films to maintain consistent image quality and desired contrast levels.
It is a number which relates to the speed of a particular film and is obtained from the ‘Characteristic Curve’ of the film.
Film factors are used on the SCRATA gamma exposure calculator to establish exposure times.
The lower film factor number, the faster the film speed.
Is a film factor 2 twice as fast as film factor 4?
Yes
What is a characteristic curve
The characteristic curve (also known as the H&D curve, Hurter and Driffield curve, or density curve) is a graphical representation of the relationship between the exposure of a photographic or radiographic film and its resulting optical density (the darkness of the image).
The x-axis (horizontal) represents the logarithm of the exposure (log E), where “E” refers to the amount of radiation or light exposure received by the film.
The y-axis (vertical) represents the optical density (D) of the film, which is a measure of the darkness or blackness of the film after development.
Which of the following information is true regarding the ‘Characteristic Curve?
A new exposure time can be determined for a change of film type in order to achieve the same radiographic density.
The position of the straight line portion of the curve against the density axis will show the density range within which the film contrast will be highest.
The steepness of the slope on the curve gives information about film contrast.
