|A typical multimodality PET/CT study|
Let’s first discuss what the “official” guideline as prescribed in the IHE documentation specifies. An order for a multimodality study such as PET/CT, PET/MR or other combination typically has a single requisition based on an order, and is identified by a placer order number issued by a CPOE (Computerized Physician Order Entry) system, and a filler order number, which is typically issued by a scheduling system such as a RIS. This filler order number is often used as the Accession Number, but a RIS can also create a new Accession Number that is unique for a particular department, in this case radiology. The requisition is referred to in the DICOM and IHE specifications as an Image Service Request or ISR.
Upon querying the modality worklist from a worklist provider, which could reside in the PACS, RIS or a separate broker depending on the system architecture, the modality such as the CT/PET machine will display the information of this order in its worklist. Multiple scheduled procedure steps can be included, such as in the case of a CT/PET, one step for the CT and one for the PET. The information in this step includes scheduled date/time, any procedure codes, etc., which is visible to the technologist. Patient demographics and visit information as well as any pertinent details such as weight, allergies, etc, is visible as well, most of which is reused to fill the corresponding data fields in the header of the DICOM images. Invisible to the user is the study identifier that is also provided in the worklist, i.e. the Study Instance UID, which is used to uniquely identify the study. In the CT/PET scenario, each study, i.e. CT and PET gets its own unique Study Instance UID. There could be multiple steps to be performed for each study, for example, a CT might have a set of images acquired without contrast and one set of images with contrast.
When the studies arrive at the PACS, they will be visible to a radiologist on the workstation worklist. Depending on how the worklist is configured, a radiologist might read both studies, but the two studies also can be reported separately as Nuclear Medicine is a specialty that is often served by a dedicated radiologist.
When multiple reports are created, each one is identified with the same Accession Number just as the multimodality study has a single requisition, and therefore single accession number. These results are sent back to the RIS or report storage and distributor.
There are a couple of areas where discrepancies might occur. First of all, not all modality worklist providers can provide multiple scheduled procedure steps as part of a single requisition, or a modality worklist consumer (i.e. modality) might not be able to display multiple items either. If the two modalities are not integrated, but rather, have two separate worklists, e.g. one for the CT and one for the PET, one needs to make sure that the procedure is not completed until both studies are performed, otherwise it might no longer be visible on the second modality’s worklist. At the back-end, the reporting system needs to be able to select either the combined study or individual studies, depending on how it is being reported. When multiple reports are sent back, the receiver needs to be able to recognize that the second report is part of the requisition and not reject it under an assumption that a single requisition always creates one and only one report.
To resolve these issues requires mapping of the multimodality capability of the RIS, modality, PACS and reporting system. At any discrepancy, one might need to spit and/or merge either one automatically or manually. For example, some institutions issue two separate requisitions, one for each study, and are able to merge the results at the backend. Some can create sub-Accession numbers, each having a child associated with its parent relationship. Whatever the capability, one should work with the RIS, modality and reporting experts to come up with the workflow that is the most effective and efficient. Note that these multi-modality studies will become increasingly popular as new modalities are introduced; therefore, it is wise to come up with a permanent solution instead of manual or semi-automated solutions that require repetitious manual labor.