Volume Loaders

Similar to the Image Loaders, a volume loader takes a volumeId and other information that is required to load a volume and returns a Promise that resolves into a Volume. This Volume can be a constructed from a set of 2D images (e.g., imageIds) or can be from one 3D array object (such as NIFTI format).

We have added cornerstoneStreamingImageVolumeLoader library to support streaming of the 2D images (imageIds) into a 3D volume and it is the default volume loader for streaming volumes.

Register Volume Loaders

You can use registerVolumeLoader to define a volume loader which should be called on a particular scheme. Below you can see a simplified code for our cornerstoneStreamingImageVolumeLoader in which:

1. Based on a set of imageIds, we compute volume metadata such as: spacing, origin, direction, etc.

2. Instantiate a new StreamingImageVolume

   • StreamingImageVolume implements methods for loading (.load)
   • It implements load via using imageLoadPoolManager
   • Each loaded frame (imageId) is put at the correct slice in the 3D volume

3. Return a Volume Load Object which has a promise that resolves to the Volume.

function cornerstoneStreamingImageVolumeLoader(
  volumeId: string,
  options: {
    imageIds: Array<string>,
  }
) {
  // Compute Volume metadata based on imageIds
  const volumeMetadata = makeVolumeMetadata(imageIds);
  const streamingImageVolume = new StreamingImageVolume(
    // ImageVolume properties
    {
      volumeId,
      metadata: volumeMetadata,
      dimensions,
      spacing,
      origin,
      direction,
      scalarData,
      sizeInBytes,
    },
    // Streaming properties
    {
      imageIds: sortedImageIds,
      loadStatus: {
        loaded: false,
        loading: false,
        cachedFrames: [],
        callbacks: [],
      },
    }
  );

  return {
    promise: Promise.resolve(streamingImageVolume),
    cancel: () => {
      streamingImageVolume.cancelLoading();
    },
  };
}

registerVolumeLoader(
  'cornerstoneStreamingImageVolume',
  cornerstoneStreamingImageVolumeLoader
);

// Used for any volume that its scheme is not provided
registerUnknownVolumeLoader(cornerstoneStreamingImageVolumeLoader);

As seen above, since the cornerstoneStreamingImageVolumeLoader is registered with the scheme cornerstoneStreamingImageVolume, we can load a volume with the scheme cornerstoneStreamingImageVolume by passing the volumeId as shown below:

const volumeId = 'cornerstoneStreamingImageVolume:myVolumeId';

const volume = await volumeLoader.createAndCacheVolume(volumeId, {
  imageIds: imageIds,
});

Default unknown volume loader

By default if no volumeLoader is found for the scheme, the unknownVolumeLoader is used. cornerstoneStreamingImageVolumeLoader is the default unknown volume loader.

info

Even if you don't provide the scheme, the cornerstoneStreamingImageVolumeLoader will be used by default.

So the following code will work as well:

const volumeId = 'myVolumeId';
const volume = await volumeLoader.createAndCacheVolume(volumeId, {
  imageIds: imageIds,
});