A. Test Protocol for Intraoral Cameras

revised 3/6/2001

Clinical Research Associates

General Science Department

 

I. Product Information.

Record the following:

A. Brand name of camera.

B. Manufacturer’s name, address, phone numbers, & contact names.

C. Items included in system & cost of complete system.

D. Optional items & their cost.

E. Cost of camera alone.

F. Alternate setups, including multi-op, & their costs.

II. Dimensions.

Measure & record the following:

A. Dimensions of camera, system, & portable module if applicable.

B. Weight of camera, system, & portable module if applicable.

C. Length of camera handpiece cord.

D. Length, diameter, & shape of camera handpiece.

E. Size & weight of foot pedal.

III. Controls.

Describe all controls provided, including the following if applicable:

A. Power switches.

B. Capture (freeze) & return to live.

C. Focus.

D. Print.

E. Toggle between live & frozen image.

F. Light source.

G. Toggle between multiple view modes.

H. Selection of specific image in multiple view mode.

I. Camera handpiece cradle switch (or other remote interlocks).

 

IV. Infection Control.

Test & describe the following aspects of infection control:

A. Sterilization & disinfection options for the camera handpiece & cable.

If camera claims ability to withstand immersion disinfection then perform following test:

1. Place camera in Positioning Fixture, focused on Standard Image.

2. Capture & print Standard Image, label as "baseline".

3. Immerse camera in 3.4% glutaraldehyde for 1 hour.

4. Remove camera & rinse well under water. Wipe lenses clean.

5. Capture & print Standard Image, note any differences in performance or image quality.

6. Repeat soaking, rinsing, & capturing of Standard Image as many times as possible to test
    endurance of camera.

7. Label all prints with the camera name, date, & number of soakings completed.

B. Barriers: cost, ease of placement & removal, length, & interference with controls.

C. Disinfection options for all controls & components that must be touched.

V. Clinical Performance.

Describe the performance of the camera in the following areas:

A. Ability to make the following 6 test photos with acceptable quality & minimal handpiece
    manipulation.

1. Intraoral: distal of upper last molar (tooth #2).

2. Intraoral: buccal of upper last molar (tooth #2).

3. Intraoral: lower lingual cuspid to cuspid (teeth #22 - 27).

4. Intraoral: lower full arch, occlusal.

5. Extraoral: full face.

6. Extraoral: bitewing x-ray on viewer.

B. Intraoral access, especially in the posterior regions while taking distal & buccal photos.

C. Ease of focus & ability to achieve sharp focus.

D. Monitor image sharpness & color.

E. Print image sharpness, color, & speed.

F. Ease of manipulating controls while seeing patient.

G. Ergonomics of handpiece, including cable drag & stiffness.

H. Note any problems experienced.

VI. Characteristics.

A. Record all unique features that facilitate ease & speed of use. (For example: built-in freeze frame,
    printer, monitor, pointer, etc.) Also note any features or characteristics that impede ease of use.

VII. Scoring.

For the March, 2001 CRA Newsletter, the following 10 areas were scored. Scoring was done on a 7 point scale (7 = excellent, 5 = good, 3 = fair, 1 = poor). The reasons for a reduced score are listed under each heading & correspond to the comments listed in the Newsletter & on the internet site.

A. Portability:

Small modular unit with single simple connection = 7

  • -1 Heavy or Large Size
  • -1 Heavy or Large w/o handle
  • -1 for each additional connection needed to be made
  • -1 for connection which is not easy or requires alignment
  • -6 for non-portable unit

B. Camera ready when Handpiece picked up:

(Evaluated after power has been turned on and patient file selected)

Camera and lights ready when handpiece lifted from cradle, and turns off when replaced = 7

  • -2 Each additional component that must be operated when picked up or sat down
  • -3 If same control must be operated when picked up and sat down & requires reach

C. Ease of Intraoral Access:

Evaluated while taking 6 test photos, with particular attention on distal and buccal of upper last molar.

Camera easily positioned for all photos = 7

  • -1 if slight difficulty aligning or slight patient discomfort
  • -1 for heavy or stiff cord
  • -2 if significant difficulty aligning or patient discomfort
  • -3 if a photo cannot be aligned correctly
  • -4 If photo cannot be taken

D. Ease of focus and ability to achieve sharp focus:

(Evaluated for all photos within the camera's focal range)

All photos sharp focus with no effort required = 7

  • -1 if manual focus adjustment required
  • -1 if focus adjustment is difficult
  • -1 if focus adjustment has large range of motion (>100 degrees)
  • -1 if focus adjustment not labeled
  • -1 if focus adjustment not provided but photos lack image quality

E. Monitor Image is Sharp and has Natural Color:

(Evaluated for each of the 6 test photos, take best shot if 2 lenses available)

All photos are sharp, acceptable color, and pathology can be resolved = 7

  • -1 Slight blur or pixelization
  • -1 Slightly unnatural color
  • -2 Significant blur or pixelization
  • -2 Severely unnatural color
  • -3 or more poor image quality reduces ability to resolve pathology
  • -6 Non-useable image
  • -1 Slight distortion
  • -2 Severe distortion

F. All component power switches are obvious and easy to use:

(Consider power switch(es) for camera only)

Obvious, easy switch = 7

  • -1 Non-obvious switch (small, unlabeled, camouflaged)
  • -2 Hidden switch
  • -1 Each additional switch

G. Simple, Fast, Easy Controls:

(Evaluation of commonly used controls except power switches and focus controls)

All controls are clearly labeled, obvious, simple, and easily operated = 7

  • -1 Unlabeled control
  • -1 Control is difficult to operate
  • -1 Easy to cause accidental prints
  • -1 Control required reaching to activate (i.e. printer)
  • -1 Unstable capture
  • -1 If Footpedal not stable
  • -2 Complicated or easily misplaced controls (i.e. remotes)

H. Ease of Infection Control:

Simple, easy, thorough infection control = 7

  • -1 Camera and cable cannot tolerate soak disinfection
  • -1 Each additional component that must be touched (keyboard, printer, mouse)
  • -1 Sheath doesn’t cover up whole handpiece
  • -1 For non-disposable sheath

I. Minimal Handpiece manipulation needed for 6 test photos:

All photos are acceptable and require no manipulation = 7

  • -1 All photos acceptable, but require focusing
  • -1 for each photos that lacks ability to resolve pathology
  • -6 Camera cannot get all photos acceptable with a single lens

J. Sheath ease of use:

(1) Sheath slides on easily, (2) Slides off easily, (3) Fits wells, (4) Does not hamper controls,
(5) Does not slip around handpiece = 7

  • -1 Any of the five criteria with a slight problem
  • -2 Any of the five criteria with a significant problem
  • -3 Any of the five criteria with a critical problem that makes camera use with
        sheath impossible

 

VIII. Comparison of Multiple Cameras.

If comparing multiple cameras, perform the following 2 steps to facilitate scoring.

A. Comparison of monitor image quality.

    1. Capture the same test photo on each camera & display it on all the monitors simultaneously
    2. Group similar cameras & score according to image sharpness & natural color.
    3. Print out each image as a record of picture (if possible).
    4. Repeat for each of the 6 test photos.
B. Comparison of print image quality (optional, since many cameras don't include printers).
  1. Print the same 6 test photos on each camera (done at the same time as the monitor
    image comparison).
  2. Lay out prints & examine for sharpness & natural color.
  3. Group cameras with similar print quality & score.

 

IX. Technical Measurements.

A. Angle of View & Field of View.

1. Prepare a grid of 1 mm squares approximately 5 cm X 5 cm. Bold the vertical &
    horizontal center lines of the grid.

2. Place the grid on a spacer block about 5 cm high.

3. Drop a plumb line down to the horizontal center line of the grid, just to one side of the
    vertical center line. Tie the plumb line to a support (such as a lab stand).

4. Position the camera lens above the center of the grid using a lab stand & clamp. The
    lens should be parallel to the grid below, & the plumb line should pass by the center
    of the lens (see figure 1).

Figure 1: Setup for measuring angle of view, field of view, & magnification.

5. Examine the camera monitor to determine if the angle of view differs from 90 degrees.
    If the horizontal center line of the grid does not pass through the center of the screen,
    then the angle of view is greater than or less than 90 degrees & must be calculated
    (see figure 2).

Figure 2: Screen display during measurement of angle of view.

6. Calculate the angle of view as follows:

q = tan-1(d/h) + 90

q = angle of view from the horizontal (degrees)

d = difference between center of grid & center of screen (in mm, as shown by grid)

h = height of camera lens above grid (mm)

[Note: if the center of the grid is below the center of the screen then q = 90 - tan-1(d/h).]

 

7. Calculate field of view from the same screen image as follows (see figure 3):

a hor = 2 X tan-1(w/2h)

a ver = 2 X tan-1(H/2h)

a hor = horizontal field of view (degrees)

a ver = vertical field of view (degrees)

w = width of screen (in mm, as shown by grid)

h = height of camera lens above grid (mm)

H = height of screen (in mm, as shown by grid)

Figure 3: Screen display during measurement of field of view.

B. Magnification.

Note: Magnification should always be measured for an object in sharp focus, but since many cameras have a variable focus &/or a large depth of field, the magnification can vary over a range of values. Therefore, it is necessary to decide beforehand how to standardize the magnification measurement. Examples: 1) Measure maximum magnification at the closest focus; 2) Measure the range of magnification across the depth of field at a fixed focal setting; etc. In any case, the focal setting (if applicable) & distance between the camera & object should be specified along with the magnification.

1. Measure magnification at the same time & using the same setup as the Angle of View test
   (see figure 1).

2. Lay a ruler on the monitor screen & measure the apparent width (in mm) of one square in
    the middle of the screen (see figure 4).

Figure 4: Taking the magnification measurement right from the monitor.

 

3. Calculate the magnification as follows:

Mag = L/m

where

Mag = magnification (no units) for the specified focus setting & distance to the grid.

L = apparent length of 1 mm (mm)

m = actual length of 1 mm (mm)

C. Depth of field ("In focus" method).

Note: Cameras with a variable focus may have a unique depth of field at any given focus setting, thus the focus setting must be specified along with the depth of field.

1. Set up the camera & grid as for the Angle of View measurement, omitting the plumb line
    (see figure 5).

2. If the camera has a variable focus then set it to the desired value & record it.

3. Lower the camera towards the grid until the grid is noticeably out of focus.

4. Slowly raise the camera until the grid is just perceived to be in focus.

5. Record the distance (d, in mm) between the camera lens & the grid.

6. Raise the camera away from the grid until the grid is noticeably out of focus.

7. Slowly lower the camera until the grid is just perceived to be in focus.

8. Record the distance (D, in mm) between the camera lens & the grid.

Figure 5: Setup for measuring depth of field.

9. Calculate the depth of field as follows:

depth = D - d

where

depth = depth of field (mm)

D = maximum distance in focus (mm)

d = minimum distance in focus (mm)

Note: This method tends to exaggerate the actual depth of field defined by the distance in "sharp focus". This is due to human perception. The same is true clinically, where the eye & brain indicate that an image is acceptable because detail can be resolved, even though it is slightly out of focus. Another approach is to standardize the desired resolution (as explained in the next test), but this also has serious clinical drawbacks. Consequently, measuring depth of field is always subjective, depending on the observer’s perception of what is in focus & acceptable & what is not.

 

D. Depth of field ("Line pairs" method).

Note: Cameras with a variable focus may have a unique depth of field at any given focus setting, thus the focus setting must be specified along with the depth of field.

1. Clamp the camera into an adjustable lab stand.

2. Place a line pair target (USAF 1951 target, or Edmund’s Scientific Depth of Field target,
    or Welch Allyn starburst target, or equivalent) on the spacer block under the camera.

3. Using the data from the Angle of View test, position the camera to look straight down
    at the target.

4. Select the desired number of line pairs per millimeter that you want to resolve at all times.
    This decision is somewhat arbitrary since any given line pair may not represent the clinically
    useful range of the camera. For example: At the distance required to focus on a single tooth
    surface the camera may resolve 10 line pairs / mm, but at the distance required to look at
    the lower arch at the same focus setting it may only be able to resolve 6 line pairs / mm, even
    though the lower arch still appears to be in sharp focus to the human eye.

5. If the camera has a variable focus then set it to the desired value & record it.

6. Lower the camera towards the target until the selected line pairs can no longer
    be resolved.

7. Slowly raise the camera until the line pairs are just able to be resolved.

8. Record the distance (d, in mm) between the camera lens & the target.

9. Raise the camera away from the target until the line pairs can no longer be resolved.

10. Slowly lower the camera until the line pairs are just able to be resolved.

11. Record the distance (D, in mm) between the camera lens & the target.

12. Calculate the depth of field as follows:

depth = D - d

where

depth = depth of field (mm) for the specified line pair resolution

D = maximum distance where line pairs could be resolved (mm)

depth = minimum distance where line pairs could be resolved (mm)

E.Distortion.

1. Place the 1mm grid on the countertop.

2. Position the camera above the center of the grid using a lab stand & clamp.

3. Using the data from the Angle of View test, position the camera so it is looking straight
    down at the grid.

4. Adjust the distance between the camera & the grid, & the focus of the camera if possible,
    to bring the grid into focus.

5. Capture and print the image of the grid.

6. Examine the prints to determine what level of distortion is apparent.

 

F. Resolution.

Note: Because the resolution will depend on the focal setting & the distance between the camera & the target, these parameters should be controlled & recorded. It is possible to achieve high resolution by moving closer to the target even though the line pairs are out of focus; it should be decided beforehand if such readings will be counted. Furthermore, the meaning of resolution measurements is not certain because clinically useful photos may have low resolution. For example: A photo of a patient’s full face may be well lighted & in sharp focus, but only have a resolution of 0.5 line pairs per millimeter since the camera is so far away. The same camera may have a resolution of 30 line pairs per millimeter when at a distance corresponding to viewing the margin of a restoration. One possible way to standardize the measurement for comparing cameras is to have a predefined area completely filling the field of view. For example: Completely fill the screen with the occlusal view of a lower first molar, then lay the target on top of it & measure the maximum resolution.

1. Place the USAF 1951 resolution target (black lines on transparent glass) in an
    adjustable lab stand.

2. Position the target over an x-ray viewbox to provide backlighting through the glass.

3. Clamp the camera in a lab stand & position it over the target. Adjust the angle as necessary
    using the data from the Angle of View test to ensure that the camera is looking straight down
    at the target (see figure 6).

4. Deactivate the camera’s built-in light source to reduce glare on the target.

5. Adjust the camera &/or target up & down to get the maximum resolution (i.e. to resolve
    the three distinct lines of the highest group & number possible on the target).

6. Record the group & number resolved & the equivalent line pairs per millimeter as indicated
    by the conversion chart provided with the target.

7. Record the focal setting of the camera, if applicable, & the distance between the lens &
    the target.

Figure 6: Setup for measuring resolution.

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