Picture Archiving and Communication System - Querying (C-FIND) and Image Retrieval (C-MOVE)

Querying (C-FIND) and Image Retrieval (C-MOVE)

The communication with the PACS server is done through dicom objects that are similar to dicom images, but with different attributes. A query typically looks as follows:

• The client establishes the network connection to the PACS server.
• The client prepares a query object which is an empty dicom dataset object.
• The client fills in the query object with the keys that should be matched. E.g. to query for a patient ID, the patient ID attribute is filled with the patient's ID.
• The client creates empty attributes (attributes with zero length string values) for all the attributes it wishes to receive from the server. E.g. if the client wishes to receive an ID that it can use to receive images (see image retrieval) it should create the attribute SOPInstanceID with attribute tag (0008,0018) in the query object with an empty value.
• The query object is sent to the server.
• The server sends back to the client a list of response dicom objects.
• The client extracts the attributes that are of interest from the response dicom objects.

Images are retrieved from a PACS server through a C-MOVE request, as defined by the DICOM network protocol. This request specifies where an image instance should be sent through an identifier known as the destination Application Entity Title (AE Title). The server must be configured with mapping of the AE Title to a TCP/IP address and port, and as a consequence the server must know in advance all the AE Titles that it will ever be requested to send images to.

Typically a radiologist is looking for prior studies on a patient to compare the progression of some pathology. In some cases prior studies may be on an off-site archive or a long term storage device. In the example being used, the radiologist or radiology technical must query the off-site or long term archive for the prior exam(s). The archive receives the C-FIND and if the C-FIND is successful the archive invokes a C-MOVE on the study to the called AE Title, in-turn sending the study from the archive to the device requesting the study.