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rdt_configuration.md

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Configuration for New RDTs

Please follow the instruction to add new RDTs to the app.

1. Getting a suitable template

RDTScan requires a clear, upright, and tightly cropped image of an unused RDT. Below are some examples of good and bad images:

Good Example Bad Example 1 Bad Example 2 Bad Example 3 Bad Example 4
An example of a good RDT photo that is tightly cropped and perspective-corrected An example of a bad RDT photo because it is taken from too far away and includes the background An example of a bad RDT photo because only part of the RDT is shown An example of a bad RDT photo because only part of the RDT is shown An example of a bad RDT photo because the RDT is skewed
Cropped and perspective-corrected. Too far away. Background included. Only a part of RDT is shown. Only a part of RDT is shown. RDT is skewed.

There are two ways to get such an image:

  1. Use a document scanning app like OfficeLens. As long as the RDT is on a clean and distinct background, the app will perform perspective correction and crop the image tightly around the RDT.
  2. Take a photo yourself using a camera. The camera should be as parallel to the RDT as possible (i.e., each corner of the RDT should be 90°). Open up the photo using an image-editing program (e.g., PhotoShop, GIMP) and crop the image as close to the RDT's edges as possible.

Once you have the template image, add it to the following folder in your Android code: app/src/main/res/drawable/nodpi/.

2. Identifying regions of interest

When trained clinicians look at an RDT design, they can usually quickly infer where test results should appear on the RDT and what they should mean. Currently, you will need to provide RDTScan with information to bootstrap the algorithm.

Location of result window (required)

This information will tell RDTScan where the image should be cropped so the user can see a zoomed version of their results.

Top-Left Corner (x, y) Bottom-Right Corner (x, y)
An RDT with the location of its result window annotated An image explaining where you should point your cursor to locate the top-left corner of the result window in an image-editing program An image explaining where you should point your cursor to locate the bottom-right corner of the result window in an image-editing program

Location of control/test lines (required)

This information will tell RDTScan where the different lines should be located. This is used to help RDTScan assign meaning to each of the lines and to prevent RDTScan from picking up on marks that are not actual lines.

Top line (x, y) Middle line (x, y) Bottom line (x, y)
An RDT with the location of its result lines annotated An image explaining where you should point your cursor to locate the top line within the result window in an image-editing program An image explaining where you should point your cursor to locate the middle line within the result window in an image-editing program An image explaining where you should point your cursor to locate the bottom line within the result window in an image-editing program

Location of fiducials (optional)

Some RDTs may have the samge general design, but vary in exact appearance from test to test because they include a visual feature that encodes a unique identifier (e.g., barcode, QR code). Similarly, some designs vary because they are cut from a sheet at an interval that is different from their underlying pattern (e.g., Quidel's QuickVue Influenza A+B Test. These designs can produce features that are inconsistent across RDTs from the same brand, thus complicating RDTScan's feature-based template-matching approach. To accommodate such designs, you can specify the location of visual features that are consistently in the same location but vary in appearance across RDTs. RDTScan considers these features to be fiducials and use their location as additional information for locating the RDT's result window.

Fiducial corners [(x, y), (x, y)]
An RDT with the location of its fidicials annotated An image explaining where you should point your cursor to locate the corner of the fiducials in an image-editing program

3. Modifying the configuration file

If you are working directly on our repository, open app/src/main/assets/config.json. If you are starting from scratch, copy that file over to the corresponding location in your code. The key value of each entry, corresponding to the RDT's name , will be used throughout the code as a lookup identifier. The values that follow the key are listed below:

Data Field Required? Data Types Range Description
REF_IMG ✔️ String Filename of the template image for the RDT
VIEW_FINDER_SCALE ✔️ double min = 0.0, max = 1.0 Relative height of the viewfinder compared to screen's height
RESULT_WINDOW_RECT_TOP_LEFT ✔️ [double, double] (x, y) coordinates of result window's top-left corner
RESULT_WINDOW_RECT_BOTTOM_RIGHT ✔️ [double, double] (x, y) coordinates of result window's bottom-right corner
TOP_LINE_POSITION ✔️ [double, double] (x, y) coordinates of the top line's center point
MIDDLE_LINE_POSITION ✔️ [double, double] (x, y) coordinates of the middle line's center point
BOTTOM_LINE_POSITION ✔️ [double, double] (x, y) coordinates of the bottom line's center point
TOP_LINE_NAME ✔️ String Meaning of the top line (e.g., "Control", "Influenza A"). (Note) One of the line names must be Control.
MIDDLE_LINE_NAME ✔️ String Meaning of the middle line (e.g., "Control", "Influenza A"). (Note) One of the line names must be Control.
BOTTOM_LINE_NAME ✔️ String Meaning of the bottom line (e.g., "Control", "Malaria P.f"). (Note) One of the line names must be Control.
LINE_INTENSITY ➖ int min = 0, max= 255 The minimum trough depth of an expected line in the result window (default: 60)
CHECK_GLARE ➖ boolean true, false Indicate whether the RDT requires to check glare in the result window. If the result window has reflective material, we recommend CHECK_GLARE to be assigned to 'true'
FIDUCIALS ➖ List of pairs of [double, double] (x, y) coordinates of the top-left and bottom-right corners for each fiducial (Note: RDTScan currently only supports either no fiducials or two fiducials; this will be addressed in a later update)

Note that the LINE_INTENSITY parameter gives you direct control over the interpretation accuracy of RDTScan for the target RDT. If RDTScan is under-reporting positive cases because it is missing faint lines, LINE_INTENSITY can be decreased to lower the threshold needed for a postivie test result. Conversely, LINE_INTENSITY can be increased if RDTScan is over-reporting positive cases. The default value is based on deployments and studies with a handful of RDT brands, so it should serve as a reasonable baseline in most cases.