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List three image qualities which are directly affected by the source-to-image distance (SID).
List three image qualities which are directly affected by the source-to-image distance (SID).
Exposure level, Magnification, Sharpness of recorder detail.
The source-to-image distance (SID) has come to be known by many as the fourth of the '---------- factor of radiography,' along with mA, time and kVp.
The source-to-image distance (SID) has come to be known by many as the fourth of the '---------- factor of radiography,' along with mA, time and kVp.
prime
A red plus-sign or 'X' is engraved in the anode end of the x-ray tube housing to mark the exact location of the ---------- ----------.
A red plus-sign or 'X' is engraved in the anode end of the x-ray tube housing to mark the exact location of the ---------- ----------.
focal spot
When a tape measure is not available on a mobile procedure, one way to estimate the SID is to use the human 'wingspan' from fingertip to fingertip, which for a 6-feet (2 m) tall person measures about ------ inches (cm).
When a tape measure is not available on a mobile procedure, one way to estimate the SID is to use the human 'wingspan' from fingertip to fingertip, which for a 6-feet (2 m) tall person measures about ------ inches (cm).
It is generally desirable to use the ---------- feasible SID.
It is generally desirable to use the ---------- feasible SID.
At 72" (180 cm) distance, magnification of the heart is only about ----- %, which is statistically negligible.
At 72" (180 cm) distance, magnification of the heart is only about ----- %, which is statistically negligible.
Dedicated chest units, however, can have a locked-in SID of ------ inches because chest techniques tend to use very low mAs values.
Dedicated chest units, however, can have a locked-in SID of ------ inches because chest techniques tend to use very low mAs values.
When the x-ray tube is moved farther away from the patient and image receptor, the amount of penumbra produced at the edges of the image -----------.
When the x-ray tube is moved farther away from the patient and image receptor, the amount of penumbra produced at the edges of the image -----------.
The longer the SID, the ---------- the recorded detail in the image.
The longer the SID, the ---------- the recorded detail in the image.
In reality, it is the --------- distance that is directly responsible for these sharpness effects, but changing the SID always changes this too.
In reality, it is the --------- distance that is directly responsible for these sharpness effects, but changing the SID always changes this too.
All other factors equal, increasing the SID ---------- magnification of the image size.
All other factors equal, increasing the SID ---------- magnification of the image size.
Since for most radiographic applications, magnification is undesirable, the goal is generally to use the ----------- feasible SID.
Since for most radiographic applications, magnification is undesirable, the goal is generally to use the ----------- feasible SID.
In cases where there is good separation between the overlying anatomy and the anatomy of interest, intentional use of a ----------- SID can both blur and magnify the obscuring anatomy.
In cases where there is good separation between the overlying anatomy and the anatomy of interest, intentional use of a ----------- SID can both blur and magnify the obscuring anatomy.
When a 30-inch (76-cm) SID is used, technique should be compensated by cutting the mAs to approximately ----------, as compared to a 40-inch technique.
When a 30-inch (76-cm) SID is used, technique should be compensated by cutting the mAs to approximately ----------, as compared to a 40-inch technique.
There is a direct relationship between SID and shape distortion.
There is a direct relationship between SID and shape distortion.
Just like forces such as gravity, magnetism, electrical force and all kinds of radiation, x-rays also follow the ----------- law as they spread out.
Just like forces such as gravity, magnetism, electrical force and all kinds of radiation, x-rays also follow the ----------- law as they spread out.
With digital image processing, this loss of exposure represents a loss of original data that can be fed into the computer, and can quickly lead to visible image noise in the form of ----------- ---------- in the image.
With digital image processing, this loss of exposure represents a loss of original data that can be fed into the computer, and can quickly lead to visible image noise in the form of ----------- ---------- in the image.
For digital imaging systems, it does not take a very great loss of ----------- for mottle to become apparent in the image.
For digital imaging systems, it does not take a very great loss of ----------- for mottle to become apparent in the image.
Any change greater than ------ % in the SID should be compensated for by adjusting the mAs.
Any change greater than ------ % in the SID should be compensated for by adjusting the mAs.
Distance changes are normally compensated for by using ---------, although the kVp can be adapted to make the correction by applying the 15% rule.
Distance changes are normally compensated for by using ---------, although the kVp can be adapted to make the correction by applying the 15% rule.
From a 40" technique, since the 80" distance would require two doublings in technique, 60 inches SID will require --------- doubling of the mAs.
From a 40" technique, since the 80" distance would require two doublings in technique, 60 inches SID will require --------- doubling of the mAs.
From a 40" technique, a 30" distance would require ----------- the mAs.
From a 40" technique, a 30" distance would require ----------- the mAs.
The relationship between a 40-inch (100 cm) technique and a 72-inch (180 cm) technique is a factor of ---------.
The relationship between a 40-inch (100 cm) technique and a 72-inch (180 cm) technique is a factor of ---------.
When a 72-inch (180 cm) chest technique must be adapted for a supine trauma patient on a stretcher- with the x-ray tube 40 inches above the gurney, use -------- the mAs from a 72-inch technique.
When a 72-inch (180 cm) chest technique must be adapted for a supine trauma patient on a stretcher- with the x-ray tube 40 inches above the gurney, use -------- the mAs from a 72-inch technique.
SID is a factor impacting subject contrast in the image.
SID is a factor impacting subject contrast in the image.
Decreasing the SID ---------- penumbra.
Decreasing the SID ---------- penumbra.
Image sharpness is directly proportional to which radiographic distance?
Image sharpness is directly proportional to which radiographic distance?
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Study Notes
Source-to-Image Distance (SID) Impact on Radiography
- SID directly affects image quality through exposure level, magnification, and sharpness of recorded detail.
- Known as the "fourth prime factor" in radiography alongside mA, time, and kVp.
- A red plus sign or "X" on the x-ray tube housing indicates the location of the focal spot.
Estimating SID
- In the absence of a tape measure, the "wingspan" of a 6-foot tall person (approximately 72 inches or 180 cm) can be used to estimate SID.
- Maximum feasible SID is generally preferred for improved image quality.
Magnification and Sharpness
- At 72 inches (180 cm), heart magnification is about 3%, which is statistically negligible.
- Dedicated chest units often use a fixed SID of 96 inches for low mAs techniques.
- Moving the x-ray tube further from the patient decreases penumbra at the image edges, enhancing detail.
Relationship Between SID and Image Characteristics
- Longer SID results in sharper recorded detail.
- SOD (Source-to-Object Distance) is the primary determinant of sharpness, and changes in SID affect it as a result.
- Increasing SID reduces image size magnification, while maximum SID usage is the objective due to undesirable magnification.
Shorter SID Usage
- In situations requiring separation of overlying anatomy, using a shorter SID can intentionally blur and magnify obscuring anatomy.
Technique Adjustments for SID Changes
- Adjusting mAs is vital when changing SID; a 30-inch (76 cm) SID requires halving the mAs compared to a 40-inch SID.
- No direct relationship exists between SID and shape distortion.
- X-rays adhere to the inverse square law as they disperse, similar to other forces.
Digital Imaging Considerations
- Loss of exposure in digital systems can lead to image noise manifested as quantum mottle.
- Mottle is noticeable even with minor exposure losses.
- Adjustments to mAs should be made for any over 10% change in SID.
Doubling mAs for Distance Variations
- Transitioning from a 40-inch technique to an 80-inch distance necessitates doubling the mAs; similarly, a 60-inch SID requires 2x mAs.
- Conversely, transitioning to a 30-inch distance from a 40-inch technique warrants halving the mAs.
Comparison of Techniques
- The relationship between 40-inch (100 cm) and 72-inch (180 cm) techniques is a factor of 3x, indicating the required increase in mAs.
- When adapting a 72-inch technique for a supine trauma patient, use one-third of the original mAs.
SID and Subject Contrast
- SID is not a determining factor affecting subject contrast in images.
- Decreasing SID increases penumbra, which can degrade image sharpness.
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