Digital Imaging: Front to Back
James L. Fanelli, OD, FAAO
Why Image digitally?
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Advantages
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Available modern technology
Instrumentation provides quality images
Assist in detecting disease
Assist in monitoring disease progression
Ability to enhance and modify images
Patient education
Telemedicine capabilities
Why Image Digitally
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Advantages
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Ancillary advantages
The patient “WOW” factor
 Income generation
 High-tech Eye-tech
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Why Image Digitally
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Disadvantages
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Equipment costs somewhat high
camera
 computer hardware
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Operator must be somewhat familiar with computer technology
Costs actually low in comparison to other comparably priced
instruments (Topography)
Coding and Reimbursement
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Posterior Segment-Medically Necessary
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CPT Code:
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Must be medically necessary for Medicare reimbursement
Medicare reimbursement approximately $63
99250
Coding and Reimbursement
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Posterior Segment-Screening
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CPT Code: NOWAY
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can be offered to patients as an option
typically $20-25 for both eyes
Coding and Reimbursement
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Anterior Segment-Medically Necessary
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CPT Code:
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Must be medically necessary to be Medicare reimbursable
Medicare reimbursement approx. $32
Corneal insults, edema, neovascularization, ptyerigia, pinguecula,
cataracts, heterochromia
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99285
Practice Revenues
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In my office, we charge:
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Fundus Imaging 99250
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Anterior Segment Imaging 92285
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$72/eye
$39/eye
Screening Photography
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$20 both eyes
Practice Revenues
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Office Location #1
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2002
Medically Necessary Photography
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760 photos at approx $72/eye
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If only a 50% reimbursement across the board:
• $46,885 gross billing
• $26,443 net
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Screening Photography
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54 photos at $20
• $1,080
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NET REVENUES:
$27,532
Practice Revenues
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Office Location #2
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2002
Medically necessary anterior segment photography
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464 photos @ $39/eye
• $17,121 Gross
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If only 75% reimbursed across the board
• $12, 841 NET
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NET REVENUE, BOTH OFFICES: $40364
The Nuts and Bolts
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Digital Imaging is a broad term applied to the recording of
images electronically, conversion of those images into a set of
numbers, storage of those numbers in a computer, and
manipulation with computer programs.
Since the images are represented as numeric data, they can be
transmitted over phone lines, satellite, or computer networks.
How does Film Work?
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Black and white photographic film is made up of a thin, light
sensitive emulsion coated on a flexible tri-acetate base. The light
sensitive substance within the emulsion is made up of one or
more of the silver halides:
How does Film Work?
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There are about 86,400,000,000 sliver halide crystals in a 35mm
photographic image.
Silver halide crystal + a photon of light = a tiny spec of solid silver.
More light creates more specs of solid silver, none of which can be seen
by the naked eye.
When the film is exposed in a camera, dark areas in the scene produce
few silver specs, and lighter areas produce more silver specs, creating a
latent image on the film.
How does Film Work?
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Once a latent image has been captured on the film, it is placed in a liquid developer
which reduces the silver halide to metallic silver. Because the development reaction is
strongly catalyzed by the presence of solid silver the areas of the film which were
struck by the greatest amount of light are converted to silver first.
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The development process is halted by a stop bath before unexposed silver halide can
be converted to metallic silver, the remaining silver halide is dissolved away with a
fixing bath, and a black and white photographic negative remains.
How does Film Work?
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The silver in the processed film tends to clump together into small
particles called grain. The grain pattern can be seen when photographs are
projected or enlarged.
Films with finer grain patterns are capable of resolving more detail than
films with coarse grain patterns.
Granularity increases as film speed increases.
How does digital Imaging work?
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Digital imaging is the representation of images as a set of
numbers.
In practice, it encompasses the electronic capture of images, their
conversion to numeric data, the storage and retrieval of those
data, and the manipulation, view and printing of the images.
How does digital Imaging work?
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Assigning numbers to tonal values in a black and white
photograph is a relatively simple concept.
Assume that the brightest white is assigned a value of 255, and
that the darkest black is assigned a value of 0.
The gray tones between white and black are now divided into
255 equal steps.
How does digital Imaging work?
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The numbers are assigned to the average gray tone in a square
area of the image.
These areas of gray tone are called picture elements, or pixels.
To represent an image in very low resolution, a small number of
large pixels would be used, whereas a high resolution image uses
a high number of small pixels.
How does digital Imaging work?
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How many pixels of resolution must a digital image have in
order to offer the same information as a silver image of the same
subject?
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Lots of answers-just ask lots of people!
How does digital Imaging work?
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At 512 x 512 pixels:
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most observers would agree that fine detail in the capillaries defining
the avascular zone is lost.
But, sufficient information is captured at this resolution to permit
accurate diagnosis and to formulate an effective course of treatment
with the noted exception of treatment of parafoveal neovascular
membranes.
How does digital Imaging work?
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At 1024 x 1024:
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All but the finest capillary detail is recorded.
This is the resolution employed by most of the companies who make
digital imaging equipment for applications in retinal photography.
How does digital Imaging work?
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At 2048 x 2048 and beyond:
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Possible, but the size of the data files and the cost of the equipment
becomes prohibitive.
A black and white image at 1024 pixels requires about one million
characters of storage space. At 2048, the same image would require
four million characters of space.
Capturing Digital Images
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One common means of capturing image:
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Standard Video Camera
525 horizontal scan lines pass across the subject
as beam passes, voltage is changes, depending on the brightness of the object
 the resultant signal is an analog output, which can be used to put a picture on a
television.
 An analog to digital converter is then used to change the voltages into raw
numbers, thereby creating a digital image.
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Analog to Digital Images
Digital Images from CCD Cameras
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A Charged Couple Device (CCD)
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uses a matrix of capacitors that store electrical charges
often used on digital fundus cameras
Enhancing digital images
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Digital imaging provides a much more extensive collection of
image manipulation possibilities.
Since digital images are nothing more than a set of numbers,
corrections can be made based on pixel statistics and
enhancements can be standardized so that all images are
enhanced in exactly the same way.
Enhancing digital images
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Caveats:
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the original image, obtained before any enhancement is performed, contains the
most accurate information available.
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Alterations to that original image are performed to make characteristics of that
image more apparent to human observers.
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Resolution is never increased through the enhancement process, and care must be
taken not to enhance an image to the extent that features are identified which did
not exist in the original subject.
Enhancing digital images
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With a film image, the original negative always contains more
information than a positive image made from the negative.
With digital imaging, photographs can be changed at will from
negative to positive with no loss of information.
Enhancing digital images
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There are no areas which are pure white or pure black. Of the total
available range of 256 gray values, only values between 40 and 160 are
present. The contrast can be stretched, moving the 160 values up to 255.
The result is an image with higher contrast.
Enhancing digital images
Enhancing digital images
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Image Sharpness:
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Let's say a white book lying on a black desk is photographed. If rendered
perfectly, the edge of the paper would appear as a line of white pixels next
to a line of black pixels. If the image were out of focus, examination of
the edge would reveal a smooth transition from white to black several
pixels wide.
Enhancing digital images
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A computer program can be employed that steepens the
transition between dark and light areas in the image.
The effect is that edge appears to be sharp in the
enhanced photograph.
Enhancing digital images
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Image Sharpness:
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These techniques can be applied to fundus photographs.
The observer must realize that the enhanced image will not exactly match
the one which was precisely in focus at the start.
Enhancing digital images
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Image Sharpness:
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The amount of sharpening can be varied. A program might offer 6 levels of
sharpening, level 1 being minimal and level 6 being maximum.
One difficulty with sharpening and edge detection programs is that they can be applied
to the extent that they identify and display edges which do not exist in the original
image.
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Enhancing digital images
Image Systems:
Synemed Eye Scape Imaging
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Posterior Segment System
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system picks up at back of typical retinal camera
images transfers to computer
Anterior Segment System
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employs beam splitter on microscope
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beam splitter placed in front of oculars
image sent to computer
Synemed Eye Scape Imaging
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Advantages:
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one computer retention/processing system
two image capabilities
cost effective
Disadvantages
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posterior segment image quality affected by media opacities, as in other
imaging systems
Synemed Eye Scape Imaging
sample images: AMD
Synemed Eye Scape Imaging
sample images: AMD
Synemed Eye Scape Imaging
sample images: OAG
Synemed Eye Scape Imaging
sample images: OAG manipulation
Synemed Eye Scape Imaging
sample images: Through cataracts
Synemed Eye Scape Imaging
sample images: Nevus
Synemed Eye Scape Imaging
sample images: Ant Seg
Synemed Eye Scape Imaging
sample images: Educational
The Optomap® Retinal Exam
Opto Map Retinal Exam
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Scanning laser ophthalmoscope (FDA approved)
4 Mega-pixel, high resolution, high contrast digital image, called an
Optomap®
Green and red lasers illuminate different retinal layers
Performed without pupil dilation
Image captured in ¼ of a second per eye
Easily accomplished by technicians