Custom Metadata Provider

In this how-to guide we will show you how to create a custom metadata provider.

Introduction

Cornerstone DOES NOT deal with fetching of the metadata. It uses the registered metadata providers (in the order of priority) to call each providers passing the imageId and type of the metadata to be fetched. Usually, the metadata provider has a method to add parsed metadata to its cache.

One question you might ask is:

How

How can I build a custom metadata provider?

Implementation

Through the following steps, we implement a custom metadata provider that stores the metadata for scaling factors of PT images.

Step 1: Create an add method

We need to store the metadata in a cache, and we need a method to add the metadata.

const scalingPerImageId = {};

function add(imageId, scalingMetaData) {
  const imageURI = csUtils.imageIdToImageURI(imageId);
  scalingPerImageId[imageURI] = scalingMetaData;
}

imageId vs imageURI

With the addition of Volumes in Cornerstone3D, and the caching optimizations that happen internally between Volumes and Images (imageLoader) we should store the imageURI (instead of the imageId) inside the provider's cache, since the imageURI is unique for each image but can be retrieved with different loading schemes.

Step 2: Create a provider

Next, a provider function is needed, to get the metadata for a specific imageId given the type of metadata. In this case, the provider only cares about the scalingModule type, and it will return the metadata for the imageId if it exists in the cache.

function get(type, imageId) {
  if (type === 'scalingModule') {
    const imageURI = csUtils.imageIdToImageURI(imageId);
    return scalingPerImageId[imageURI];
  }
}

Step 3: Register the provider

Finally, we need to register the provider with cornerstone.

/src/myCustomProvider.js

const scalingPerImageId = {};

function add(imageId, scalingMetaData) {
  const imageURI = csUtils.imageIdToImageURI(imageId);
  scalingPerImageId[imageURI] = scalingMetaData;
}

function get(type, imageId) {
  if (type === 'scalingModule') {
    const imageURI = csUtils.imageIdToImageURI(imageId);
    return scalingPerImageId[imageURI];
  }
}

export { add, get };

src/registerProvider.js

import myCustomProvider from './myCustomProvider';

const priority = 100;
cornerstone.metaData.addProvider(
  myCustomProvider.get.bind(myCustomProvider),
  priority
);

Usage Example

Now that the provider is registered, we can use it to fetch the metadata for an image. But first, let's assume during the image loading we fetch the metadata for the imageId and store it in the cache of the provider. Later, we can use the provider to fetch the metadata for the imageId and use it (e.g., to properly show SUV values for tools).

// Retrieve this metaData
const imagePlaneModule = cornerstone.metaData.get(
  'scalingModule',
  'scheme://imageId'
);