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Introduction

This section was contributed by Scanwell Health, who provided the Toolkit’s interpretation features.

NOTE

This section assumes that the RDToolkit app is running in portrait mode (display taller than wide) on a phone.

For an app offering landscape orientation, as is common on tablets, see the section for photographing with a Tablet for instructions adapted to landscape orientation.

How to take a good picture

  • Place the RDT on a flat, non-white surface with bright, even lighting. Natural and diffuse light is recommended; avoid putting the RDT in direct sunlight. 
  • The RDT should be oriented vertically. Try and line up the green rectangle on screen with the RDT as closely as possible. 

  • Ensure that the RDT is in sharp focus. It may help to move the phone away from the RDT and slowly move the phone closer in order to get the camera to focus properly (see Section- Blur Error for more tips). 


 

Hold the phone parallel to the RDT, so that the edges of the RDT are as close to the green rectangle on screen as possible.

  • On the next screen, you will see a preview of the picture that was taken. This preview screen shown below is an example - yours may look different. The preview shown represents the outline of the RDT found by the app. 

    • This is the last opportunity to review that the image captured is good quality.

    • Check that the RDT is well lit, in focus, and well oriented.

    • If the preview is satisfactory, proceed on. Otherwise, retake the image.

  • If your app is configured to ask you to provide your interpretation of the RDT, as shown below, select the result and proceed.


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General do’s and don’ts

Do:

  • Only have one RDT in the picture

  • Avoid shadows over the RDT

  • Avoid direct light reflecting off the surface of the RDT

  • Take a clear, sharp picture of the RDT

Do not:

  • Place the RDT on a white or light background 

  • Hold the RDT in your hand

  • Write excessively on the surface of the RDT

  • Photograph multiple RDTs at once

  • Cast shadows over the RDT

  • Try and take a picture in a dark environment

  • Take pictures using a dirty or damaged camera lens

  • Take pictures of the RDT with glare / light reflecting directly off the RDT

  • Read the RDT too early


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Errors

There are several checks built into the app to ensure quality pictures are taken, including orientation, blurry, underexposed, overexposed, RDT not recognized and glare errors. These checks happen sequentially, which means that the user will receive an error message for the first error triggered in the pipeline. Therefore, it is not uncommon to see nonspecific error messaging for an image with quality issues.

For example: in the case of a very dark image, this may be rejected earlier in the pipeline than expected, i.e. the image triggers an orientation error as the app is unable to locate the RDT, rather than the “underexposed” error as expected.

Orientation Error

The app performs several orientation checks to ensure that the RDT is well oriented for analysis. This includes ensuring the RDT is close enough and parallel enough to the camera, without being too close. If the app determines there is an orientation issue with the image, it will display an error. To fix this error, you may:

  • Try and hold the phone as parallel to the RDT as possible. 

  • Try and line up the green rectangle on the screen with the outline of the RDT

  • Make sure that the RDT is placed on a non-white background

  • Make sure that there are no harsh shadows cast over the RDT


One of several orientation errors may be returned, depending on the type of issue detected. These include SHORT_PERIMETER, LONG_PERIMETER, BAD_ASPECT and TOO_OBLIQUE.

Error type

Error code

Commonly caused by

SHORT_PERIMETER

2

Phone is too far from RDT, or shadows or excessive handwriting on the cassette are interfering with the app's ability to detect the outline correctly.

LONG_PERIMETER

3

Phone is too close to RDT.

BAD_ASPECT

4

Phone is too tilted relative to the RDT.

TOO_OBLIQUE

5

Phone is too tilted relative to the RDT.


Below, some examples of images that may cause an orientation error are described.

First, as a reminder, here is an example of proper technique:

A picture containing text

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The RDT is oriented correctly (vertically), and the operator is holding the phone parallel to the RDT, with the edges of the RDT as close to the green rectangle on screen as possible. The RDT is on a non-white background and there are no shadows cast over the RDT.

Here are some more examples of what not to do. 

If the phone Is held too far or close to the RDT, the app may return an orientation error.

A picture containing text

Description automatically generated A picture containing text, indoor

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Left: operator is holding phone too far from RDT. Likely to cause SHORT_PERIMETER error.

Right: operator is holding phone too close to RDT. Likely to cause LONG_PERIMETER error.


The algorithm can handle some tilt, but if the out-of-plane rotation is too extreme, the algorithm will reject the photo.

A picture containing text, indoor

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the operator has tilted the phone and as a result, the bottom side of the RDT appears longer than the top side.
Likely to return a SHORT_PERIMETER, BAD_ASPECT, or TOO_OBLIQUE error.

  A picture containing text

Description automatically generated

The operator has tilted the phone and as a result, the left side of the RDT appears longer than the right side.
Likely to return a BAD_ASPECT or TOO_OBLIQUE error.

Blurry Error

The app requires a sharp picture, without blur from focus problems or shakiness, to accurately analyze the RDT. If the app determines that the picture taken is too blurry for analysis, it will display a blur error. To fix this error, you may:

  • Move to a location where more light is available (this improves the camera’s ability to take sharp pictures)

  • Move the phone up and down a few centimeters to trigger a new focus cycle

  • Make sure that nothing is covering or blocking the camera lens

  • Clean the camera lens

  • Stabilize yourself by placing your elbows on the table (this helps reduce shakiness)


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Sometimes, even though the lighting is good and the RDT is aligned correctly, the image can appear blurry if the lens is out of focus. If this occurs, lower and raise the phone as shown below to retrigger the camera’s autofocus cycle. You may need to do this a few times. Then, press the “Take Picture” button when the RDT is aligned with the green rectangle and the picture is sharp.

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Explanation on Images above from left to right: 

  1. RDT appears blurry, even though the edges of the RDT are lined up well with the green rectangle on screen.
  2. The operator slowly moves the phone farther away from the RDT, allowing the camera to focus.
  3. The operator slowly moves the phone back into position, with all four sides of the RDT lined up with the green rectangle on screen. The picture is now sharp.

Certain phones simply cannot focus close enough to take a satisfactory picture. If you repeatedly see the blur error, even when all other photographic factors are good, you may need a different phone. 

Underexposed Error

The app requires bright and even lighting across the RDT. If the app determines that the picture taken is too dim to accurately analyze the test, it will display an underexposed error.

To fix this error, you may:

  • Move to a brighter location where more light is available, and/or

  • Reposition the RDT and/or yourself to avoid casting shadows over the RDT.


Note: Take care that the phone itself does not cast shadows over the RDT.

Note: Intense light sources can create darker shadows that prevent accurate analysis. Natural and diffuse light is recommended.


A picture containing text

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The image captured is too dark. Move to a brighter location.


Overexposed Error


The app requires bright and even lighting across the RDT. If the app determines that the picture taken is too overexposed to accurately analyze the test, it will display the overexposed error.

To fix this error, you may:

  • Avoid very intense light sources,

  • Move the RDT from a dark or black background to a medium background, and/or

  • Allow the camera more time to adjust to the lighting

  • Tap inside the green rectangle to focus and expose on the RDT instead of the background


 

The RDT is overexposed.

RDT Not Recognized Error

The app will return an error if it cannot confirm that the RDT in the picture matches the type of RDT it was expecting.

To fix this, you may:

  • Confirm that you are using one of the RDTs listed below:

    • SD Bioline Ag Pf/Pv Malaria RDT

    • CareStart Malaria Pf/Pv (HRP2/pLDH) Ag Combo RDT and 

    • First Response Malaria Ag P. falciparum (HRP2) Card Test

  • Ensure that the RDT being imaged is the one that was selected in the app.

  • Ensure the RDT is being imaged on a non-white background.

  • Try other general troubleshooting techniques to provide a better picture of the RDT.

Glare Error

Light reflecting off of the surface of the RDT can interfere with the app’s ability to correctly analyze the assay window. If the app determines that there is too much glare on the surface of the RDT, it will return the glare error. Light reflection is particularly common when working with RDTs that have a clear plastic layer on top of the test strip.

To fix this error, you may:

  • Move to a location with more even lighting. 

  • Avoid intense light sources. Natural and diffuse light is recommended.

  • Move the phone slightly to avoid reflections, which may be caused by the phone itself.


A picture containing text

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Light is reflecting off the assay window and obscures the app’s ability to detect control and/or test lines.


Support

For questions, or to report a problem, contact the Scanwell team at hello@scanwellhealth.com with a description of the problem. 

Additional training materials will be made available at www.scanwellhealth.com/partners/malariaprograms.

Developer Information

The Scanwell RDT Reader App is developed by:

Scanwell Health

800 Wilshire Blvd, Suite 200

Los Angeles, CA 90017

U.S.A



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