Just like I talked about in my digital c-map detail is the sharpness of the edges on the film. Detail
can also be referred to as spatial resolution. There are many things that are the same on the film c-map
as the digital c-map but there are a few things that have changed. On film spatial resolution is affected
by the SID, OID, motion, focal spot size, part angle, tube angle, film screen contact, and the film speed.
As you can see many are the same as digital with the same concept. Just like digital, detail is increased if
you use a longer SID and a small OID (zero being optimal). The same with motion, any motion on the
film will cause a decrease in sharpness. This is why no matter if you’re using film or digital you always
want to decrease motion as much as possible. This is done by using good communication skills,
providing clear instructions for the patient, and by using a faster film speed. The faster your speed is the
less detail you will get but, motion will decrease your detail more.
It is very important to have very close film screen contact. The closer the film is to the screen the
better your detail is. The casing of the cassette is purposely made with a slight curve in order to push out
all our and hold the film closer to the screen. Focal spot size is the same as for digital as well. The smaller
the focal spot size the more detail there will be. Using a small focal spot size every time though is not
always a good idea because the heat is concentrated to a smaller filament and it will eventually burn the
tube out. Angling the body part is not a good idea because it will cause foreshortening of the part. This is
when the image looks smaller and squashed when it really is not like that. When you angle the tube to
the part this will cause elongation which is when the part appears thinner and longer then it really is.
This has the same affect on a digital or CR systems.
Contrast is the difference between adjacent densities. There is high contrast short scale and low
contrast long scale. There are two categories of contrast Film contrast and Subject contrast. Subject
contrast is anything that has to do with the patient. This involves patient thickness, tissue mass density,
contrast media, atomic number, and KVp. The thicker the patient is the less contrast the image will
have. This is because the thickness causes more scatter to reach the film which in return will decrease
your contrast. The KVp is the penetrating power of the x-ray beam. KVp has the most direct effect on
controlling the amount of contrast on the radiograph. If you increase your KVp this will result in a lower
absorption which means more scatter on the film and less contrast. Anytime you decrease your scatter
you will be increasing the contrast. There are many things that can be used to decrease your scatter
such as a grid, collimation, OID, and filtration. The higher the grid ratio on the grid the more scatter will
be removed this will give you a high contrast with a short scale. By increasing your collimation you will
be decreasing the amount of scatter on the film which will increase your contrast. Same with OID, if you
increase your OID you will increase your contrast because you decrease the amount of scatter on the
film. By increasing your tube filtration you will be decreasing scatter and increasing the contrast on the
film. Anytime scatter reaches the film it creates noise on the image which decreases the contrast. This is
why it is very important to make sure to decrease scatter as much as possible.
The generator being used may also have an effect on the amount of contrast on the image. A
high frequency generator will decrease the amount of contrast because it is the highest quality with high
energy and provides the most x-rays. A single phase generator will increase the amount of contrast on
the film because it is a low quality with low energy and provides the least amount of x-rays. The
processing of the film may also affect the contrast. If the temperature is not correct then fog can be put
on the film which will decrease the contrast.
Density is the amount of blackness on the film. In order to visualize the anatomy you must have
a sufficient amount of density. Density is controlled by milliamperage and exposure time. If mAs is
increased then density will increase as well because by increasing your mAs the quantity of radiation
increases. There are many factors that influence density including kVp, SID, OID, the central ray angle,
the patient thickness, the grid ratio, the collimation, the amount of fog, the film screen speed, filters,
the anode heel affect, the reciprocity law, and the type of generator being used. When you increase
your kVp the penetration of the beam increases there for more photons are reaching the film and this
increases density. This goes hand in hand with the patient thickness. The thicker the anatomical part the
less photons will reach the film which means the density on the film decreases. This leads to the reason
why angling the tube results in a decrease in density. When you angle the tube this increase the
thickness of the patient that needs to be penetrated. It is also important to think about SID and OID
when taking an x-ray. Increasing the SID or OID increases the divergence of the beam which means not
as much radiation is striking the film. This causes a decrease in density. When a grid is used it absorbs
some of the radiation exiting the patient which means not as much radiation is reaching the film. This
decreases density unless compensated by increasing or changing the mAs. Film screen speed also affects
the density on an image. Increasing your film screen speed means more radiation is used on the film
which will increase the density. If you increase film screen speed you should decrease your mAs to
maintain density on the film. By increasing collimation the radiation reaching the film is decreased and
so is the density on the film. Compensating filters decrease the intensity of the x-ray beam which also
leads to a decrease in density. The generator being used to take the radiograph makes a difference as
well. If you use a high frequency generator the density will be increased because it increased the
quantity and quality of the x-ray beam. If a single phase generator is used this will decrease your density
because it uses the least amount of x-ray and the lowest quality of x-ray. Also take into account the
anode heel affect. The anode side of the tube decreases the intensity of the primary x-ray beam because
the radiation has to travel through the heel of the anode. This causes an increase in the intensity on the
cathode side; this is way the thickest part of what is x-rays should always be under the cathode side. For
the processing of the film it is important to check the temp of the chemicals, this could have an affect on
the density by causing fog on the image. Fog can also be caused by scatter or the safelights. Fog will
cause an increase of density on the film.