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image quality, was A LNT Experience
My perspective on this is possibly analogous but may
be a bit irrelevant, as I am using light photography
as an analogy to radiography. I am not a radiologist,
but I have very much enjoyed forays into ordinary 35mm
photography. One of my fave courses back at UC
Riverside during the 1980's was Photo 101 with Kenda
North, who is now at the University of Texas.
Since the course was taught a number of years ago, we
students were fortunate enough to use manual-set 35 mm
cameras. Thus, we gained a clear understanding of the
relationship between film speed, exposure time, and
f-stop (amount of light). I still vastly prefer a
manual 35 mm camera opposed to an automatic.
Unfortunately, because film and developing are
expensive, I have acquired an auto-focus digital
camera. I am 'OK' with the results, but not as happy
as when I can choose my film speed, f-stop, and
exposure time.
In photography (I believe that this applies to both x-
and light), the 'slower' the film, the finer the grain
will be. Contrast and subtle shading will show up in
more detail on, for example, ASA (ISO) 100 rather than
ASA (ISO) 400. The tradeoff is that 'slow' film
requires a large amount of light - either bright sun
or a longer exposure.
Although I am not a radiologist, from my background in
photography, I have a tendency to doubt that the best
diagnostic images are not often also the best esthetic
images, from the standpoint of the esthetics of a
'technical' photographer (think Ansel Adams or even
Robert Mapplethorpe's flower images). This type of
image is somewhat 'old hat' in today's art scene, but
I am a partisan of exquisite demonstrations of natural
beauty.
Esthetics are a very individual thing.
With social images (such as portraits and prom
pictures), a slightly grainy image may be appreciated
more than a fine-toned high-contrast image. 200 or
400-speed film is often used for portraits, where one
may not want to demonstrate variabilities in
complexion. ;-) A 400-speed film will somewhat
obscure things like freckles or those doohickies many
of us had/have as teenagers ;-)].
News and sports photographers usually use 200-400
(600?) speed film so that they can capture action in a
hurry.
However, when one is demonstrating the stark beauty of
a Western landscape, or the perfection of a flower,
50-speed or even 25-speed film is often used.
Professional outdoor photographers often aim for
landscapes (or even closeups using a tripod so that a
30-second or perhaps a 2 minute exposure may be made)
that demonstrate sharp contrast and fine detail. For
this purpose, a slower film that depends on a
relatively large quantity of photons is used. The
photographer either shoots in bright sunlight using
f/16 or f/11 or uses a tripod with f/16 or f/11 and a
long exposure time in order to 'snarf up' the large
number of photons he needs to create a delicately
detailed image.
My very rough guesstimate in diagnostics is that the
film speed necessary would be variable depending on
the tissue or organ that is imaged. There is
inherently much more contrast in an image of a bone
fracture than in a mammogram. It's my guess that a
faster speed film could be used on a busted tibia than
on an image of organs.
Some improvement in image quality may be had by
choosing the appropriate developer.
However, I would think that there would be many cases
where a relatively slow speed film would yield a
higher resolution of the image and would show subtle
contrasts between tissues better (e.g. an infection)
than a high-speed film would. I suspect that very
high-speed film would have problems with 'graininess.'
I'll leave folks with links to a couple of
unfortunately advertising-infested (popup windows) pix
of mine from a few years ago:
http://www.angelfire.com/ms/hwy61/hard.html
http://www.angelfire.com/ms/hwy61/soft.html
~Ruth 2 the 'creative'
> We must remember that for both dental radiography
> and mammography
> image quality is judged on the basis of diagnostic
> information, not
> esthetic quality.
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