The use cases fall into five broad groups:
A referring physician receives radiological diagnostic reports on CT or MRI examinations. These reports contain references to specific images. He chooses to review these specific images himself and/or show the patient. The references in the report point to particular slices. If the slices are individual images, then they may be obtained individually. If the slices are part of an enhanced multi-frame CT/MR object, then retrieval of the whole multi-frame object might take too long. The Composite Instance Root Retrieve Service allows retrieval of only the selected frames.
The source of the image and frame references in the report could be KOS, CDA, SR, presentation states or other sources.
Selective retrieval can also be used to retrieve 2 or more arbitrary frames, as may be used for digital subtraction (masking), and may be used with any multi-frame objects, including multi-frame ultrasound, XR etc.
Features of interest in many long “video” examinations (e.g. endoscopy) are commonly referenced as times from the start of the examination. The same benefits of reduced WAN bandwidth use could be obtained by shortening the MPEG-2 or JPEG 2000 Part 2 Multi-component based stream prior to transmission.
Retrieval using the Composite Instance Retrieve Without Bulk Data Retrieve Service allows determination and retrieval of a suitable subset of frames. This could for instance be used to retrieve only the slices with particular imaging characteristics (e.g. T2 weighting from an enhanced MR object).
A multi-frame CT or MR may cover a larger area of anatomy than is required for use as a relevant prior. How the SCU determines which frames are relevant is outside the scope of the standard.
Relevant priors may be specified by instance and frame references in a worklist and benefit from the same facilities.
There are times when it would be useful to retrieve from a multi-frame image only those frames satisfying certain dimensionality criteria, such as those CT slices fitting within a chosen volume. Initial retrieval of the image using the Composite Instance Retrieve Without Bulk Data Retrieve Service allows determination and retrieval of a suitable sub-set of frames.
Given the massively enhanced amount of dimensional information in the new CT/MR objects, applications could be developed that would use this for statistical purposes without needing to fetch the whole (correspondingly large) pixel data set. The Composite Instance Retrieve Without Bulk Data Retrieve Service permits this.
A hospital has a large PACS (that supports multi-frame objects) that does not support WADO. The hospital installs a separate WADO server that obtains images from the PACS using DICOM. WADO has the means to request individual frames, supporting many of the above use cases.