Patient and procedure information is provided to the equipment by the DICOM Modality Worklist or manually entered by the operator.

Equipment settings like protocols, patient position relative to the table, etc., are then provided to the equipment by the operator.

CT has two broad types of acquisition modes: one where the X-Ray source is stationary and the patient moves in a linear direction (e.g., during a localizer acquisition) and another where the X-Ray tube is rotating relative to the patient. In the case of the rotating X-Ray source, the patient may move in a linear direction either during (e.g., helical/spiral acquisition), between (e.g., axial acquisition), or not at all (e.g., stationary acquisition) with relation to the X-Ray exposures during an acquisition.

CT acquisitions are typically controlled from a remote location outside the CT scanner room. A CT operator actuates the beginning of the first CT acquisition, which may have delays or other timing associated with patient instructions, contrast agent injections, cardiac monitors, etc., The CT acquisition does not typically require continuous actuation of a switch or pedal, unlike other modalities.

For each CT acquisition, the dose and other related information is collected and recorded in an Irradiation Event.

Subsequent acquisitions with new Irradiation Event UIDs may take place automatically following the scan parameters set up by the CT operator. This is often required due to the precise timing requirements associated with multiple CT acquisitions, especially when trying to capture dynamic information (e.g., cardiac motion, respiratory motion, contrast agent enhancement, etc.).Subsequent acquisitions may also take place via manual actuation of the irradiation switch by the CT operator. In such a case, the acquisitions are associated with new Irradiation Event UIDs. A CT Study may contain a combination of automatic and manually started CT acquisitions, depending on the specific protocol.

Some CT scanners may include multiple X-Ray sources that are simultaneously irradiating during an acquisition. An acquisition with multiple sources still produces a single Irradiation Event UID, regardless of the number of sources.

For acquisitions when the X-Ray tube is rotating, the data collected during an acquisition may be reconstructed into one or more CT images. The same acquisition data may be reconstructed into CT images using different reconstruction filters, slice thicknesses, fields-of-view, axial ranges, cardiac gating, etc., Data from certain acquisitions, e.g., bolus-tracking series, may not be saved. Several acquisitions may be combined to create a single CT image set, e.g., dual energy images. Any CT images created from one or more acquisitions should include the Irradiation Event UID(s) that was/were used for reconstruction. If multiple reconstructions come from the same acquisition, all would include the same Irradiation Event UID.

Additional reconstructions, e.g., multiplanar reformats or maximum intensity projections (MIPs), may be generated from the CT images generated in the previous step. If the Irradiation Event UID is present in the additional reconstructions, it should be copied from the original image.

The RDSR contains information for long-term storage and distribution to dose information management systems and cross-institutional systems such as dose registries, in order to perform relevant dose QA analysis, produce related reports, and support medical regulations.

The RDSR Instance defines its scope of accumulation which indicates the period of irradiation reported in that RDSR Instance (the Study, the Series, the Performed Procedure Step). Each RDSR Instance includes information of all the Irradiation Events within its scope of accumulation, as well as Accumulated Dose Data within that same scope.

For almost all procedures, there will be an RDSR with the scope that covers all of the Irradiation Events during that procedure.

The RDSRs are stored in a new DICOM Series different from the one where the CT images are stored.

Dose analysis based on the information of the Irradiation Events contained in the created RDSRs.

Irradiation Events and images are often one to one, but there may be Irradiation Events with no stored images (e.g., aborted acquisitions), and there may be also one Irradiation Event that results in multiple images (e.g., multiple reconstruction filters, etc.). For this reason, dose analysis is driven by the Irradiation Events, not by images. See Section UUUU.4.1.4 for the importance to use the Irradiation Event UIDs in the RDSRs.