Using Radiographs with Metron-PX
Introduction
EponaTech’s
Metron software can be used with any radiographs, but if
the radiographs are taken following these guidelines, they will
be particularly well-suited for use with the software.The most important radiograph for use with Metron is the
lateral radiograph of the hoof and the last three phalanges.This document will focus on how to take the lateral radiograph,
and how to import radiographs in general.
Four
Things to Consider when Taking Radiographs
1)
Measure the Film-Focal Distance (FFD) and Object-Film Distance (OFD)
When
you take the radiograph, make sure to measure and record the distance
from the
X-ray machine to the film. This
is called the film-focal distance (FFD) and is generally
a value between 20” and 40”.
Metron software will ask you for this value
when you import the image.
You
should also measure the distance between the film and the center-of-the-leg.
Generally,
this distance is pretty small, perhaps 2” to 3.5”.
This is called the object-film
distance (OFD). Metron will also ask for this value.
Both
these measurements are shown schematically below:
2)
Stand the foot on a block which has a metal marker.
If the horse is shod when you take the
radiograph, you don’t have to worry about this, as the metal
of the shoe itself will show up in the radiograph and will define
the ground reference. However, if the horse is barefoot, prepare
a wood block as follows.
Ideally, the horse should stand on a block which has a wire or other
piece of metal
running down the center of it’s top plane. You want this metal to show up in the
radiograph and be right on the surface the horse is
standing on, and running from toe back to heel at the approximate
centerline of the hoof (from side to side).
Instead of a wire it also works to use a block with two BBs
set about 4 inches apart on the centerline of the block.
In Metron you will be prompted to pick two points on the
wire, or to pick the two BBs to establish the ground reference.
Here’s
an image we obtained using our BB method (here we had a couple
other
BBs in the image for another purpose, so just ignore them).
If
the horse is shod, then in Metron we’ll use the top
of the shoe as a reference
plane, as in the image below:
3)
Place a metal marker on the front hoof wall, up to the hairline
In
order to make sure that the front (dorsal surface) of the hoof
wall is visible in the
radiograph, place a metal marker on it.
A piece of flexible wire, taped to the hoof,
works pretty well – its flexibility lets it adapt to the
shape of the hoof wall, which
is sometimes not straight.
We are also interested in knowing where the top
of the hoof wall is (at the coronary band) so we suggest placing
the metal marker with its top end at the transition from hoof
wall to hairline. Metron will prompt you to pick four points on
the front hoof wall --- the 4th point, at the top of
the wall will be easy to pick if you’ve marked the top of
the wall.
4)
Standard “Good Technique” for taking quality radiographs
Finally, the standard elements of taking good radiographs
are, of course,important. It
is beyond the scope of this document to go into all the details,
but the main items of importance are:
A)
Getting
a good exposure. This
is done by adjusting time or power settings of the X-ray machine.
Veterinarians or vet-techs who do radiographs, will be
familiar with which settings are appropriate for which
radiographic views.
B)
Lining
up the shot. For a lateral
radiograph of the foot, generally the center of the beam is aimed at a point near the top of P3 (pedal
bone) or perhaps at P2 (short pastern). Also
it is very important to have the pointing direction of the X-ray
machine lined up at a right-angle to the centerline of the foot.
C)
It’s
a good idea to have both feet up on a block of similar height
when taking the radiograph so the horse’s weight distribution
is approximately equal.
How to get Radiographs into Metron
1)
Two Choices: Photograph it on a Lightbox, or use a Transparency Scanner
There
are basically two ways: either photograph the radiograph directly
off
a lightbox, or use a scanner that is capable of scanning transparencies.
Probably,
the simplest and best way for most people will be to take a photo
of the radiograph while its on a light box.
We do this all the time, and it If you are photographing
off a lightbox: You can use either a conventional (film) camera,
or a digital camera. If
you use a digital camera, things are very fast and simple. If you use a conventional film camera, then
you either have to use a scanner to scan in the resulting photo,
or you have to use a developer that can return your pictures in
digital form – on a floppy disk or CD.
Almost all film developers now offer this (even the one
at your local grocery store)!
2)
Adding a Scale Marker
If you are taking a photo with the radiograph on a
lightbox, place an object of known size on the radiograph. Later in Metron, you will be prompted to pick
two points in the image which are a known distance
apart, and you will be able to use this object.
This will set a scale for the image.
In a pinch, something simple like a business card can be placed on the radiograph
while on the lightbox – most business cards are 2” across on the short end,
so you’ll be able to use that to set the scale later.
If
you’re using a scanner, then just record how many “DPI”
(Dots Per Inch) you use to
scan with. You will be able to type this value into Metron later to scale the
image.
3)
Getting a Digital Image with the Correct Size and Format.
In
order to end up with a file that is suitable for use with Metron,
you need to
create a file with a "good" number of pixels (not too
many, not too few) and
it must be either a "JPEG" file or a "Bitmap"
file. It is best to try
to end
up with a "JPEG" file which will have the extension
".jpg". For example, the
filename might be "my_hoof.jpg".
The second choice is to use a "Bitmap" file which
will have the extension ".bmp", for example "a_hoof.bmp".
Now,
getting a convenient size in terms of the number of "pixels"
is the other concern. A reasonable size for use with Metron is an image that is about
640x480
or perhaps 800x600 or maybe even 1024x770.
The number of pixels you
end up with depends on the resolution setting on your digital
camera, or the
resolution the developer used when returning your images on a
disk, or the "DPI"
(dots per inch) setting you choose on your scanner (with your
scanner's software). The total number of pixels also depends on the size of the image.
If
you use images with lots of pixels (like 1600 X 1200 pixels or
greater) things will
work (Metron can handle any size) but things will
be slower to deal with and
will take more disk space, and there really won’t be an advantage
to keeping all
those extra pixels. You may find that you’ll need to use a
magnification setting in Metron
(like 50%) in order to avoid having to use the scroll-bars all
the time to scroll around
your image. All in all, it’s best to try to get your
image of an appropriate size from
the start. Again, this would be somewhere from 640X480
up to 1024X770.
If
you’re using a scanner: A lot of scanners you see advertise
that they can scan at 600
DPI or even 1200 DPI, but these settings will generate a file
that is way too big to be
practical for our purposes. All scanners can be configured to scan at lower
resolutions,
like 72 DPI, 100 DPI, or 150 DPI.
4)
Image Orientation
All images in Metron need to be oriented with the “ground”
towards the bottom ofyour computer screen (for lateral and frontal views)
and with the “toe” towards the bottom of your computer screen for the view of the
sole. If your images are
oriented another way, Metron has image rotation abilities, which
you should be sure to use first, before going thru the “guided markup” procedure
in Metron.
For radiographs, in case you put the radiograph upside
down on the lightbox or scanner, Metron has a lateral flip
capability to fix up such an image.
Of course, it’s always simplest just to get the image
scanned or photographed properly to start with!
5)
Importing Images into Metron
When an image is imported into Metron,
a copy of the original is made and placed into a set of folders
where Metron maintains its image database.
Your original file will not be altered or deleted.
This means that after an import into Metron, you will actually
have two copies of your file on your disk (the original, and the
copy in the
Metron database).
If you wish, you could then delete your original and rely
on Metron for storage of your images.
There is an “Export Image” feature in Metron
that would allow you to create a copy from the Metron database
back out to any location you choose, should you need the image
file for another application.
If you are building a large, valuable database of images
in Metron, we suggest backing up the entire image database
from time to time. This
means saving a copy of the folder called “Databases”
which is in the folder that you installed Metron into.
The default location for this would be C:/Epona/Databases
.
