Exam 3 S2 Flashcards
STUDY the CHART with cause & effects! (Big time bro)
Study the math!
Take a look at the images regarding the elongation + foreshortening from previous lessons
What is a primary result for increased SID? (1)
What is also affected? (2)
Decreased size distortion
Also:
decreased IR exposure (beam divergence)
Increased sharpness (less penumbra)
What is a primary result of increased OID? (1)
What else does it affect? (4)
Decreased sharpness
Also:
Decreased IR exposure (air gap)
Increased subject contrast (air gap)
Decreased noise (scatter)
Increased size distortion (magnification)
What is a primary factor of increased SOD? (2)
Increased sharpness & decrease size distortion (lower penumbra)
What is the result of increased motion? (3)
Decreased subject contrast
Increased noise (blur)
Decreased sharpness
What is a primary result of increased alignment?
Decreased shape distortion
Increased SID without adjustment. How does it affect?
IR exposure?
Detail?
Magnification?
IR exposure goes down (beam divergence)
Detail increases (lower penumbra)
Magnification decreases (increase SID decreases magnification)
Increased SID and adjusted technique to compensate. How does this affect:
IR exposure?
Detail?
Magnification?
IR exposure stays the same (technique has been adjusted)
Detail increases due to increase SID (technique plays no role in this)
Magnification decreases due to increased SID (technique plays no role)
(Only factor affected here is IR exposure & that has been compensated for)
Increased OID without any adjustments. How does this affect:
Contrast?
Noise?
Shape distortion?
What is the primary factor with increased OID?
Increased contrast (air gap technique)
Noise decreased (less scatter)
Shape distortion stays the same (shape distortion= elongation + foreshortening)
Decreased sharpness
What affects spatial resolution?
SID affected (more SID less OID)
Time not affected
KVP not affected
What is the SID measured from?
From the source (x-ray tube/anode focal spot) to the image receptor (distance)
Why is the measuring tape on the collimator cut?
To account for the distance within the x-ray tube (focal spot to the collimator)
What are the relationships between OID/SOD/SID?
OID + SOD = SID
SID - OID = SOD
SID- SOD =OID
What is the square law?
What is the formula?
Used to maintain IR exposure
Old/new ***
What is the inverse square law?
What is the formula?
Used to determine intensity of (new) exposure
(new over old)**
In regards to formulas of the square & inverse square law what does these sign represent?
E=
D=
n=
O=
E= exposure (mGy or mSv)
D = Distance (SID)
N= new
O= old
A satisfactory L-spine x-ray is performed using 40 mAs at a distance of 48”. If the SID is increased to 72” what mAs should be used?
(40/x) (48/72) ^2=
48 x 48 = 2304
72 x 72 = 5184
40 x 5184 = 207,360
2304 x X= 2304x
207,360 / 2304x= 90
90 mAs is the new technique
Square law*
An exposure is made at 72 inches and results in an exposure of 25 mGy. If the distance is adjusted to 60 inches, what is the new exposure?
Inverse square law
Determine the missing factor:
400 mA ____ mA
.17 sec .33 sec
70 kVp 80 kVp
8:1 grid 5:1 grid
60 SID 50 SID
What is the air gap technique?
What does it do?
Getting separation between the object and image receptor**
Increases OID
improves increases magnification
decreases detail (increases penumbra)
how does determine the actual size of the image? (with magnification)
projected size / mag factor (MF)
how do we determine the size of an object on the image? (with magnification)
Mag factor (MF) x size
What is magnification?
How to we calculate this factor?
size distortion
SID/SOD
How does shape distortion take place?
caused by misalignment
(either part, IR, tube)
what is it referred to when the image is longer than normal?
how does this happen?
elongation
tube or IR is angled ***
what is it called when the image is shorter than usual?
how does this happen?
foreshortened
part is angled (misaligned)
off-centering is the same as?
angling *
What is ceiszynski’s law?
angle 1/2 the angle of the part to IR angle
(if anatomy is angled 40 degrees, angle tube 20)**
How many minimum views should be obtained/used?
2 views
Motion is usually caused by:
patients
Low Ma techniques can lead to:
possible increased motion
(due to the longer the time the more chance for the patient to move)
what are technique charts for?
when given a technique chart:
consistency
find the factors
What is the modulation transfer function?
what can happen?
a way of physicists can measure contrast resolution
when line pairs become too small their penumbrae merge and reduce contrast
Why are calipers used?
to set manual techniques
What is the ONLY thing AEC controls?
TIME
AEC contains 3:
ionization chambers
Density settings require?
+2 to see a visible change
How much should back-up time be set too?
150% of anticipated time
if we have .6 sec anticipated time, what would be the backup time?
0.9 secs
Positioning is?
why?
very important when it comes to AEC
improper positioning could lead to anatomy receiving under/over exposure
If AEC were to encounter unsuspected metal?
time increases
motion increases (because of time)
patient exposure increases (overall because more exposure to that cell)
IR exposure increases (because everything else is seeing more than normal exposure)
what happens if mA increases?
IR exposure increases (primary)
noise decreases (QM)
what happens if time increases?
IR exposure increases (primary)
noise decreases (QM)
If kVp increases what happens?
IR exposure increases (primary)
Subject contrast increases (primary)
noise increase (more scatter)
What happens if filtration increases?
patient dose decreases
what does increased collimation do?
decreases IR exposure
increases subject contrast (primary)
decreases noise (scatter (primary)
what does increased part thickness do?
decreases IR exposure (primary)
decreases subject contrast (primary)
increases noise (primary)
decreased sharpness (OID)
increased size distortion (OID)
if scatter increases?
increased IR exposure
decreased subject contrast (bc of the negative output from scatter)
increase noise (bc of scatter)
if focal spot size increases?
sharpness goes down (only thing)
What is the anode heel effect?
x-ray beam is weaker on the anode side (bc of attenuation)
sharpness is higher of the anode side
