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The pre-injection check-list
Once the dye is injected into the arm,
you a short time period of approximately 2 minutes in which most of
the angiographic action takes place. Once that time has passed,
the early and mid phases of the dye transit through the retina are
history. If you don't have any photos, you have missed the
boat. If the angiogram needs to be repeated, the patient will have
to come back another day for another injection. Most patients are
really not amused by that situation.
The above scenario should be motivation
enough for you to have a pre-injection checklist. If you have performed
hundreds of FAs, you
will have a mental checklist. If you are new to angiography, you
should have a written checklist to refer to. There are many, many
things that can go wrong in photography, and almost all of them have
unpleasant consequences.
The check-off ideally takes place just
before the patient is set up for the injection. However, it can take
place at any point up until the dye is actually injected into the
vein. It will be slightly different depending upon your system
being film based, or digitally based. The basic goal of the
checklist is to make sure that your camera is able to record a useful
photograph at the time the injection is made.
Film system check-list:
This checklist assumes that you have already been successful at
taking color fundus photos on your patient. For the basics of
color fundus photography, see Module 10.
- FA camera body mounted. Most
film based FA systems use two separate camera bodies: one for color
slide film and the other for b&w film (usually ISO 400) for the
angiogram. Make sure the body with the black and white film
is mounted.
- Confirm that film is in the camera and
that it is being taken up on the winder reel. Film in the
camera can be confirmed by turning the winder crank. It will
stop turning if there is film in the camera. Watch
the winder crank as you trigger the camera to confirm that the film
is being advanced. The winder crank, or the inner shaft,
should rotate as the film comes out of the cassette.
- Make sure that the flash is
firing. This can only be confirmed by using the trigger.
If you take a name tag photo, the flash confirmation can be done at
the same time.
- Take a name tag photo. This is
always a good idea when using film. This way, the patient name
and other information is on the roll of film, making positive
identification of the photos much easier latter on. Write the
information in a compact manner on a piece of paper. Set the
flash to a low power setting. Set the diopter compensation
knob to a "plus" or "anterior (A)" setting, and
hold the paper in front of the lens. Frame the writing, focus
by moving the paper back and forth, and take a photo.
- If ordered by your physician, take
red-free photos at this time. The flash stays on a low
setting. Focus with the green filter in place. You will
need to turn the illumination light up high to have a good
view. You can leave the focus where it is for the FA.
Some photographers prefer to use the green filter when checking the
focus and alignment during the FA. This way, the illumination
light does not have to be turned down as it does when switching from
the blue light to white light (this does not apply to the newer
Topcon cameras).
- Change the flash power to the FA
setting, which will be at the higher end of the flash power
scale. This setting is pre-determined by previous experience
or the manufacturer's recommendation.
- Be sure that the barrier filter is in
the light path before the FA begins. On some cameras, the
barrier filter is in the camera back (Zeiss FF3 and FF4). With
the Topcon, you have to push a button to insert the filter.
Digital system checklist:
- This procedure will be dependent upon
your capture system. Basically, you want to be sure that the
flash is firing and an image is being captured and is being
displayed on the screen when you trigger the flash.
- Be sure that the computer recognizes
the FA capture device.
- Set the capture device to the
appropriate mode (e.g. black and white vs. color).
- Be sure the gain level is
appropriate. On some systems, gain is expressed as an ISO
rating, similar to the ISO rating of film. ISO 100 would be
low gain and ISO 800 would be a high gain level. Gain has to do with
the sensitivity of the digital sensor to light. A higher gain
setting will capture an image at a lower light level, but at the
expense of increased "noise" in the photo. Noise is
similar to graininess in film. As the grain size
increases, picture detail (resolution) decreases. For image
quality, it is better to increase the flash power instead of the
gain level. The trade-off is that increased flash power
is more uncomfortable for the patient, and higher flash powers
on some cameras will not recycle fast enough for fluorescein
angiography.
The first digital photo above
shows good detail and was taken with an appropriate flash level and gain
level. The second digital photo was taken with a higher than normal
flash level, but the gain had to be maximized because of the poor view
into the eye. The texture is grainier and some of the details have
"blocked up".
-
Instead of a name-tag photo, your
digital system should have a method of digitally identifying each
photo with the patient information. You should have entered
this information into the software database previously, or some
systems use an automatic file naming system that you have to
initiate. You would have entered this information already,
prior to color fundus photography.
-
At this time you would take red-free
(green filter) photos if this is part of your routine. The
flash power will be on a low setting and the illumination will be on
a high setting.
-
Re-set the flash power to the higher
FA setting. If your red-free and exciter filters are on the
same filter wheel, you could leave the green filter in the light
path in order to align and focus just before the injection. If
not, remove the green filter from the light path.
-
Be sure that the barrier filter is in
the light path before the FA begins. On some cameras, the
barrier filter is in the camera back (Zeiss FF3 and FF4). With
the Topcon, you have to push a button to insert the filter.
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