Image Acquisition - Spatial Resolution and Distortion
examples where distortion is used advantageously: 1. sigmoid colon 2. clavicle 3. oblique lumbar spine
all of the above
spatial resolution is influenced by which of the following: 1. OID 2. SOD 3. SID
all of the above
The area on the anode where the high speed electrons hit is called the
actual focal spot
refers to the size of the area on the anode target that is exposed to electrons from the filament
actual focal spot
which focal spot is larger
actual focal spot
what type of shape distortion would be caused by angling the xray tube along the long axis of the part being examined
elongation
two types of shape distortion
elongation and foreshortening
how does increasing SID affects spatial resolution
increase spatial resolution
which one of these maneuvers would cause the least magnification of the thoracic spine on a radiographic image
placing the patient on the xray table face up (supine)
true or false: the effective focal spot is always smaller than the actual focal spot
true
what is the average anode angle range of a diagnostic xray tube
15-17 degrees
spatial resolution is directly related to: 1. mAs 2. Focal-spot size 3. SID
3 only
images of objects that appear longer than the true object
elongation
types of shape distortion include: 1. foreshortening 2. magnification 3. elgonation
1 and 3
which of the following will contribute to the production of longer (low) scale of contrast: 1. an increase in kVp 2. an increase in grid ratio 3. an increase in photon energy
1 and 3
how many focal spots are generally found in an xray tube
2
which of the following will produce the greatest distortion
37 degree PA axial projection of the skull
magnification factor
M= SID/SOD
single most important factor controlling size distortion
OID
If the radiographer is unable to achieve a short OID because of the structure of the body part or patient condition, which of the following adjustments can be made to minimize magnification distortion?
a longer SID should be used
how does OID affect size distortion
as OID increases, the size increases and spatial resolution decreases
at which portion of the xray beam is the effective focal spot the largest (least spatial resolution)
at the cathode end
how does a large focal spot compare to a small focal spot as it relates to anode heat capacity
can handle heat produced by large exposures
where is focal spot blue the greatest
cathode side
how does increase OID affect spatial resolution
causes magnification
how does SID affect size distortion
decreasing SID will cause more distortion
focal spots are represented in mm's. Example 0.3, 0.6, 1.0, or 1.2. Which focal spot doe these numbers represent: actual or effective focal spot
effective focal spot
refers to focal spot size as measured directly under the anode target
effective focal spot
the radiographic misrepresentation of either the size or the shape of the anatomic part
distortion
what determines focal spot size
filament size
as focal spot size increases, distortion would
focal spot does not affect magnification
a condition caused by angling the xray tube against the main axis of the part is
foreshortening
images that appear shorter than the true objects
foreshortening
what type of shape distortion would be caused by angling the xray tube against the main axis of the part being examined
foreshortening
to get a magnification factor of 2, where should the object be placed
half way between the image receptor and xray tube
A table top radiograph of the knee is made using 6 mAs, 70 kVp and a 40 inch SID. If a repeat image of the same knee needs to be done in the Bucky, with compensation of exposure factors to maintain receptor exposure, magnification/distortion will
increase
how to best reduce size distortion if there is a large OID
increase SID
states that by angling the target on the anode, one makes the effective focal spot smaller than the actual focal spot
line focus principle
which of the following terms/units is used to express the spatial resolution of a diagnostic image
line pairs per millimeter (lp/mm)
another name for size distortion
magnification
indications how much size distortion or magnification is demonstrated on the IR
magnification factor
what is considered the greatest enemy of spatial resolution
motion
an undistorted radiographic image will result when the object plane and the image place are
parallel
unsharpness/blur produced by xray tube focal spots
penumbra
two types of distortion
size and shape
misrepresentation of the shape of the structure recorded as compared to the actual shape of the structure
shape distortion
an increase in the image size of an object compared with its true or actual size
size distortion
does a small or large focal spot create a higher spatial resolution
small
the sharpness of the structural edges recorded in the image
spatial resolution
OID is related to spatial resolution in which of the following ways?
spatial resolution is inversely related to OID
the Line-Focus Principle expresses the relationship between
the actual and the effective focal spot
how does part thickness and body part location affects spatial resolution
the larger the OID, the less spatial resolution
how do part/object thickness affect distortion
thick objects have more distortion
ow does distortion affect spatial resolution
when an image is distorted, spatial resolution is reduced
