What makes the film sensitive to light?
The sensitive elements in the film are crystals of, most often, silver halide which can change their structure when excited by light (photons). When a photon of light strikes a grain it dissipates its energy in the crystal (grain). This energy may or may not be enough to flip the crystal into a latent state.
What kind of film which is sensitive to UV rays blue and green colors but not in red color?
Almost all modern photographic film is panchromatic. Some older types of film were orthochromatic and were not sensitive to certain wavelengths of light. As naturally prepared, silver halide photographic emulsion are much more sensitive to blue and UV light than to green and red wavelengths.
What is sensitivity in radiography?
The sensitivity is taken as the smallest diameter wire that can be seen divided by the component thickness, expressed as a percentage. Most application codes specify a sensitivity of between 2-4% ; this is a maximum, the smaller the figure the greater the sensitivity of the radiograph.
What is SFD in radiography?
SFD – Source-to-Film Distance – is the distance between the radiation source and the film in radiographic testing, as measured in the direction of the beam.
What is the difference between density and contrast in radiography?
Contrast is the difference in density or difference in the degree of grayness between areas of the radiographic image. It is the most important factor contributing to subject contrast. A higher density material will attenuate more x-rays than a lower density material.
What are the 5 radiographic densities?
The five basic radiographic densities: air, fat, water (soft tissue), bone, and metal. Air is the most radiolucent (blackest) and metal is the most radiopaque (whitest).
What affects film density and contrast?
H and D Curve. As the curve increases, the density increases. The sharper the angulation of the curve, the less the latitude of the film and the greater the contrast. The flatter the angulation, the greater / wider the latitude of the film and the less the contrast.
What happens when kVp is increased?
The higher the kVp, the more likely the x-ray beam will be able to penetrate through thicker or more dense material. Low kVp photons are weak and easily absorbed by body tissues or filters that have been placed.
Is kV the same as kVp?
One standard way to measure pulsating DC is its peak amplitude, hence kVp. Most modern X-ray generators apply a constant potential across the x-ray tube; in such systems, the kVp and the steady-state kV are identical.
How is kVp calculated?
(measured thickness in centimetres x 2) + 40 = initial kVp For example, if your dog measures 14cm thickness at the 12th rib, the initial kVp should be 68.
What is the 15 kVp rule?
The 15% rule states that changing the kVp by 15% has the same effect as doubling the mAs, or reducing the mAs by 50%; for example, increasing the kVp from 82 to 94 (15%) produces the same exposure to the IR as increasing the mAs from 10 to 20. A 15% decrease in kVp has the same effect as decreasing the mAs by half.
What is a kVp?
Kilovoltage peak (kVp) is the peak potential applied to the x-ray tube, which accelerates electrons from the cathode to the anode in radiography or computed tomography. Tube voltage, in turn, determines the quantity and quality of the photons generated.
How does kVp affect quantity?
An increase in kVp increases the efficiency of x-ray production and the quantity and quality of the x-ray beam. The relationship between the mA and the number of photons produced directly affects the amplitude of the x-ray emission spectrum.
What is the density maintenance formula?
The Inverse square law formula maintains the “Intensity of the beam” while the then Direct square law/Density maintenance formula maintains the mAs (technique) needed to maintain optimal density at varying SID’s. Optimal density is achieved at an SID of 40 inches using 25 mAs.
What is the exposure maintenance formula?
AKA the exposure maintenance formula: as SID increases, intensity decreases, causing a decrease in film exposure and density. You maintain density by increasing mAs as distance also increases.
What is the inverse square law in radiology?
Inverse Square law: The radiation Intensity is inversely proportional to the square of the distance. Notice in the diagram that as the distance doubles, the area quadruples and thus, the initial radiation amount is spread over that entire area and is therefore reduced, proportionately.
What is the difference between the inverse square law and the exposure maintenance formula?
How do the inverse square law and the exposure maintenance formula differ? The exposure maintenance formula is based on the inverse square law, but reversed, because mAs must be increased as distance is increased and vice versa, in order to maintain IR exposure.
What is IR exposure?
in radiology, a measure of the amount of ionizing radiation at the surface of the irradiated object, such as a person’s body; calculated by multiplying milliamperage times exposure time in seconds, expressed in units of milliampere seconds (mAs). See also x-rays.
How do high contrast images differ from low contrast images?
How do high contrast images differ from low contrast images? High contrast images have few shades of gray, where low contrast images produce more discernible shades of gray. Therefore low contrast images provide better diagnostic images.
What is the effect of a grid on contrast?
As radiographers, we know that the whole purpose of using grids in radiography is to reduce scatter radiation, thereby increasing radiographic contrast. Thus, using grids with higher ratios and higher frequencies cleans up more scatter radiation, which increases contrast more than low-ratio and low-frequency grids.
What is Bucky factor?
The Bucky factor is the ratio of radiation on the anti-scatter grid to the transmitted radiation. Hence, the Bucky factor reflects the increased radiation dose required from anti-scatter grid use, as any increase in mAs proportionally increases dose.
What is air gap technique?
The air gap technique is a radiographic technique that improves image contrast resolution through reducing the amount of scattered radiation that reaches the image detector. The air gap technique is utilized in both plain radiography and mammography.
How is contrast resolution improved?
The contrast resolution of CT can be optimized by increasing the attenuation of administered intravenous contrast (for CT angiography [CTA]) and by decreasing image noise. Intravascular contrast attenuation can be optimized with proper timing, high iodine flux, and adequate contrast volume.
What improves temporal resolution?
A high frame rate and hence enhanced temporal resolution may be improved by: reduced depth of penetration, since pulses have to travel a short distance; reduced number of focal points, since scan lines do not have to be duplicated; reduced scan lines per frame, using narrow frames rather than wide frames.
What is the difference between resolution and contrast?
Higher resolutions or larger screens do little to make images more convincing. Put simply, contrast ratio is the difference between the brightest part and the darkest part of an image. The difference is quantified as ratio, hence the term ‘contrast ratio’.
What is high contrast resolution?
High Contrast (Spatial) Resolution Typically, those reconstruction filters that enhance or preserve the higher spatial frequencies (smaller objects) do so at the cost of increased noise in the image. For high signal to noise objects, this tradeoff is usually acceptable.
What is the best spatial resolution?
The finest resolution as of now is 30cm provided by very high-resolution commercial satellites. We generally stick to the following subdivision of satellite images: – Low resolution: over 60m/pixel. – Medium resolution: 10 ‒ 30m/pixel.
What are the different types of resolution that affects radiographic imaging?
Spatial resolution is expressed in line pairs per mm (lp mm)….See also
- spatial resolution (CT)
- spatial resolution (MRI)
- axial resolution (ultrasound)
- lateral resolution (ultrasound)
- contrast resolution.
What is the resolution of an MRI?
Nowadays, most MRI scanners used for medical purposes have B0 values of 1.5 or 3 T and can reach typical resolutions of around 1.5×1.5×4 mm3.