Imaging Videos – 10/18/07
Video 1
Lesson #1 -- A change of 1 or 2 kVp does not significantly darken or lighten the film.
Lesson #1A – If the kVp you desire does not line up perfectly with a time line – interpolate.
Lesson 2 – An increase of 15% in KvP makes the film a lot darker.
Lesson 3 – A decrease of 15% in kvP makes the film a lot lighter
Lesson 4 – Large changes in kVp will have to be offset by changing mAs to maintain film
density
Video 2
Body parts less than 12 cm do not require a grid. Grids help block scatter. Smaller than 12 cm
and you have minimal scatter radiation to begin with.
Decreasing the kVp by 15% will lighten the film, so mAs needs to be doubled to balance the
density.
Increasing the kVp by 15%, you’ll need to ½ the mAs to balance the density
Lesson 1 – Using 15% less kVp and double the maws results in a noticeable increase in
image contrast
Lesson 2 – Using 15% more kVp and ½ the mAs results in a noticeable decrease in image
contrast
Lesson 3 --Smaller body parts (creating less Compton scatter) do not create as noticeable
change
Video 3
Exposure Time check by using Spin Top. Try to put X-ray photons through spin top to check
exposure time.
Lesson 1 -- The rate of rotation of a manual spin top is variable
Lesson 2 – The length of the arc (with manual top) is NOT proportional to the exposure
time.
Lesson 3 – With single phase generators the number of dots ARE proportional to exposure
time.
Video 4
Is there a difference in darkness between anode part of beam and cathode part of beam?
What effect by anode-heel effect occurs with a longer focal film distance?
40” film Note how the OD varies from anode end to cathode end. The focal distance of 40 cm
vs. 72 cm will present with 40 having greater density. The anode-heel effect is lessened with
distance.
Also, the optical density is highest in the middle, but lower on the ends.
Lesson 1 –At 40”, the OD varies considerable from anode end to cathode end and is evident
to your eye.
Lesson 2 – At 72”it varies little from anode end to cathode end and appears isodense to
your eye.
Lesson 3 – The anode heel effect is real, is exacerbated at 40” and minimized at 72”
Video 5
Inverse Square Law – Increasing the distance by 100%, you’ll have to almost quadruple the
exposure
Lesson 1 – A 40” radiographic technique used at 72” results in a remarkable underexposed
film. Increasing the distance, you’ll need to increase intensity of dose. If you don’t, films
will be severely underexposed
Lesson 2 – To obtain an isodense film at 72”, it requires 3.24 times the mAs
Lesson 3 – With appropriate mAs correction for FFD changes (resulting in isodense films)
predict the dose difference to a patient for both films (It is better for patients to do it closer
with lower dose than further with higher dose).
Lesson 4 – There are measurable differences in the same object X-rayed at 40” and 72”
(Closer the shot, the bigger the anatomical area/segment is).
Video 6
Scatter Radiation
Lesson 1 – Scatter radiation is created with each exposure
Lesson 2 – You must remain behind the protective barrier to protect yourself from scatter
radiation
Lesson 3 – Scatter can cause plus density (fog) on film
Lesson 4 – Exposed (sensitized) films are more susceptible to fog sources than unsensitized
films.
Lesson 5 – fog from any source decreases contrast and destroys anatomic detail.
Video 7
Lesson 1 – The appropriate total correction factor (TCF) is essential for delivering the
proper amount of radiation for a diagnostic film.
You can cut the mAs by using faster (higher #) film speed.
Lesson 2 – Predict what would happen if you used a TCR of -4 (correct for 600 speed) but
chose a 100 speed (extremity gray border) cassette.
Lesson 3 – There is reasonable linearity between different film screen combinations from
the same manufacturer