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«01/15/05 NHANES DIGITAL GRADING PROTOCOL INTRODUCTION The objective of grading digital retinal images taken of participants in the ancillary eye ...»

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01/15/05

NHANES DIGITAL GRADING PROTOCOL

INTRODUCTION

The objective of grading digital retinal images taken of participants in the ancillary eye

study of the National Health and Nutrition Examination Survey (NHANES) is to estimate

the prevalence and severity of age-related ocular conditions and their relationship to

visual loss in different racial/ethnic groups. Photographs are evaluated in semiquantitative fashion by a grader or reader using a custom written Access database, EyeQ Lite (an image processing database for storage, retrieval and manipulation of digital images), and a dual monitor computer display. Among the features evaluated are diabetic retinopathy severity level, and its supporting lesions, age-related maculopathy (ARM) lesions, glaucomatous changes to the optic nerve and other vascular and retinal changes.

EQUIPMENT AND MATERIALS

CAPTURING DIGITAL IMAGES

Two 45o digital retinal images (Field 1, 2) will be taken of each eye for every NHANES participant using the Canon CR6 nonmydriatic camera with a Canon 10D camera back (6.3 megapixels per image). Field 1 is centered on the optic disc, and Field 2 is centered on the macula, providing photographic documentation of the optic disc, macula, and substantial portions of the superior temporal arcades

REVIEWING DIGITAL IMAGES

The NHANES grader views each retinal image with a high resolution monitor using the EyeQ Lite image processing software and database, and references the written protocol and the digital photographic standards and examples to evaluate retinal abnormalities.

The NHANES grader directly enters his/her evaluations in a microcomputer database.

The following materials are used in the reading process:

(1) Minimum Intel based 900 Mghz PC running Windows 2000 or XP with 256 MB of RAM and a dual monitor capable graphics card (recommended ATI Radeon All-in-Wonder card);

(2) Primary monitor, 21 inch for image viewing, set to a resolution of 1600 X 1200 with 32 bit color, standardized using Verilum calibration software;

(3) Secondary monitor, recommended minimum 15 inch LCD, set to 1024 X 768 resolution (actual value not as critical as this monitor will display the data collection database);

(4) Digital Healthcare EyeQ Lite or Pro image processing software version 4.8 or higher;

(5) NHANES ACCESS database, a direct entry software with a series of data collection screens built in ACCESS available to graders on networked personal computers, and based on the paper data collection form in.

USING THE IMAGE PROCESSING SOFTWARE/DATABASE

LOGGING IN To access the image processing database the grader will double click on the Digital Healthcare EyeQ grading icon on the desktop. The grader will then be asked to log into the database. The login is the same for all workstations with the user name being X and the password XX. Then the grader selects OK from the login screen.

–  –  –

SELECTING A PATIENT VISIT FOR VIEWING

The first screen to appear is the Identify a Patient screen. The grader may type in the Study ID # of the patient to be reviewed and then click on Next. The database will find any patient visits with that study ID and display a list of visits with their corresponding study dates in the Patient Found in Database menu. (For NHANES purposes there should only be one study visit per patient). Double click on the patient visit to be viewed. A final menu called Select Visit/Study will appear. Again double click on the visit to be viewed. A contact strip of 4 or more images will appear. This contact strip should contain fields 1 and 2 of both eyes. (Additional images may be present.) To select an image from the Contact Strip for further viewing or measurements either, right click on that image and the image will enlarge to full size (left clicking on the image (a purple frame will appear around the selected image) and selecting view image from the side bar menu will accomplish the same thing). Note: The title of the sidebar menu is helpful to remember in negotiating through the software.

IMAGE MANIPULATION TOOLS

There are many image manipulations available using the EyeQ software. Change in magnification, various manipulations of contrast, and splitting the image into the separate red, green and blue color channels are among the most commonly used.

Further descriptions of the EyeQ software can be found in the user’s manual.

The manipulations that will be performed on all NHANES images before measurements are performed are listed below in order. After each manipulation the image should be returned to its normal state before starting the any measurements. If at any time the grader notes a suspicious area in the image the grader may zoom in/out and/or lighten/darken to enhance the area of concern Zoom In (or Zoom Out): This will magnify the entire image for viewing.

Magnifying the image two times at most is usually adequate (available on the View Image Menu). To magnify a localized area of the retina (to closely examine retinal vessels or specific lesions or color changes) the grader can left click on mouse when the magnifying glass is displayed. This can be done at any time during image manipulation even after a complete zoom has been performed.





Another method for zooming in is to use the scrolling wheel on the mouse. This can be done at any time.

Lighten (or darken): (This option is available in the contrast menu only.) When an image is particularly light or dark this function is very helpful. One or two clicks is adequate to allow better viewing of poorly illuminated areas of the retina (similarly for overly exposed retinal images and darkening).

Image Manipulation Steps for all images:

1. Zoom in (lighten/darken/stretch as needed)

2. Red-Free (or 3 RGB components) (stretch lighten/darken as needed)

–  –  –

View Image Menu 1. Red-free or RGB color option: This provides the grader with a full screen view of the green channel. The grader should select Zoom In (or Zoom Out) and left click on the mouse to magnify a given area, and scan the entire photo. After magnification the grader should select the Contrast submenu, and Lighten (or darken), and/or Stretch the image for another view. (Again, suggest manipulating the image two times at most). To return the image to its normal state, click Undo to negate the lightening (or darkening) of the image and return grader to the original image. (Instead of choosing the Red-free option, the grader can view all of the color channels (red, green and blue) by selecting RGB. This will display a montage of the color image and each of its color components. The 3 color channels can be split and saved back to the contact strip for additional manipulations or measurements (lighten/darken, zoom in/out, stretch, etc) or the entire montage can be save as one image to the contact strip. It should be noted that saving these images is only temporary, remaining intact only while the grader has that patient file open. This montage is helpful in gauging areas of overexposure in the red channel, among other things.)

Contrast Menu

This menu takes the grader to a submenu of options for increasing contrast of an image. All manipulations are temporary and will never overwrite the study images. If the grader wishes to restore the image to its original state they should select Undo. If the grader wishes to perform additional manipulations or measurements on the image that are not available in the Contrast Menu then the grader should select Quit and Store. This will return the manipulated image to the contact strip. When the grader quits this patient visit, the contact strip will return to the original study images only.

2. Equalize histogram: This function examines the distribution of levels and redistributes them as evenly as possible across the range from 0 to 255 in all three channels. Values of pixels are changed so that an equal number of pixels have each of the possible levels. Thus, details in areas that are particularly bright, where there are many pixels at a similar brightness, are seen clearer.

While this function dramatically shifts the colors of the image when combined with Lighten/Darken, it is often quite helpful in detecting small color changes, drusen or microaneurysms.

3. Invert image: This function alters every pixel so that its grey-level, initially G, becomes 255 - G. This reverses the grey scale or in the case of a color image, reverses each color channel. The operation works over the window selected in the processing menu. If the range option is in the menu and the limits shown by it are not 0 and 255, the contrast is inverted linearly within the narrower range.

Pixels with grey levels less than the minimum range limit are all set to 255. Pixels with grey levels greater than the maximum range limit are all set to zero.

4. Median -128: This option determines the median grey level, then scales the grey levels so that pixels at median value get a level of 128 (halfway between 0 and 255).

Contact Strip MenuGrading Tools and Grids After all standard manipulations are performed on the study images for the eye the grader is ready to perform measurements using the Macular Grid, Neovascular or Optic Nerve Grid and Measure Lesions found in the View Image Menu under Grading Tools.

Any measurement performed can only be done on the original color or the red free image. Stretching, Lightening/Darkening and Zoom In/Out are the only acceptable manipulations during the measurement session. Measurements may not be performed on any other type of manipulated image.

Before any measurements the grader should confirm that the disc diameter calibration measurements are correct. To do this the grader selects the Grading Tools option, and confirms that Measure disc diameter is 346.7 (the number of pixels in a standard disc diameter) for a Canon 10D (as well as the D60), the camera used in NHANES. For a Canon D30 Camera the measurement should be 243.8 pixels for a standard disc diameter. If 0 or an incorrect measurement is shown, then grader selects Enter disc diameter pixels, and inserts the correct measurement, then selects OK.

There are two grids available to the grader for use in areas of measurement. The grids, were developed for use with Canon 45o retinal photographs, are based on the diameter of an average optic disc as calculated by comparing Zeiss 30o and Canon 45o photographs of the same eye from several individuals and appropriately scaling down from the standard disc diameter (DD) for Zeiss 30o photographs.

Neovascular or Optic Nerve Grid: The first grid is the optic nerve grid. The optic nerve grid will be used for grading both new vessels on the disc and for defining the 4 quadrants evaluated for arterial narrowing and A/V nicking. The grid consists of three concentric circles centered on the optic disc and four spokes at 12:00, 3:00, 6:00 and 9:00. The inner circle approximates the disc margin assuming an average size disc (diameter = 1 DD or one disc diameter, radius = 1/2 DD); the second circle demarcates a zone extending to 1/2 DD from an average disc margin (radius of circle = 1 DD), hereafter referred to as Zone A;

and the outer circle demarcates a zone extending from 1/2 DD to 1 DD from the disc margin (radius of circle = 1 1/2 DD), hereafter referred to as Zone B. The four spokes extend outward from the edge of Zone A and demarcate the four quadrants named for their relationship to the posterior pole (the most posterior retinal region which contains the optic disc and the macula, or center of acute vision). Beginning at the upper left and moving clockwise, the four quadrants in the right eye are the superior temporal, superior nasal, inferior nasal and inferior temporal; in the left eye, the superior nasal, superior temporal, inferior temporal and inferior nasal.

Macular Grid: The second grid to be used is the macula grid. This grid will be placed over the center of the macula to define the macular area for grading of Age-Related Maculopathy (ARM) and for Clinically Significant Macular Edema (CSME). It consists of 3 concentric circles with diameters of 1000 microns (.6666 DD), 2 DD and 4 DD and has 4 radiating lines from the central circle radiating out at 1/4 hours (1:30, 4:30, 7:30 and 10:30). The grader will left click on the mouse to position the grid in the center of the fovea, then release the mouse button to “drop” the grid onto the image. Once centered, the X and Y coordinates of the center point, or the fovea, should be recorded for future grid placements. Once placed on the image, the grid can be tilted or adjusted by using Meridian angle 0 degrees.

Meridian angle 0 degrees. This option adjusts the tilt of the macular grid. Left click, and select the location on the image where the horizontal line will cross the optic nerve (Right eye at about 7:30, Left eye about 4:30 on the disc margin).

This X and Y coordinates of the first point will need to be recorded for future grid placement. For the second point, plug in the X and Y coordinates saved from the macular grid placement earlier (center of the macula). The grid should rotate into the correct position.

Measure lesions. This measurement tool is used primarily for measuring drusen size and area. The grader can size lesions using the circle sizes ranging from Co (comparable to 63 microns diameter) to 1 DA/DD (a circle of 1500 microns in diameter). Right click on the mouse for ascending order in size; left click for descending order. By using the center scroll wheel the image can be zoomed in and out during measurement.

GRADING PROCEDURES AND RULES

All sets of participant images are assigned a sequential reading list (five participants per list) as the images are received at the Reading Center. The grader selects a reading list from the NHANES coordinator’s tracking binder at the beginning of a grading session.

Upon completion, the grader initials and dates the tracking sheet and forwards the list to the appropriate basket provided for completed lists.

Photograph graders at the Reading Center use the following conventions in evaluating

the presence and severity of abnormalities:



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