| DICOM PS3.16 2024e - Content Mapping Resource |
|---|
This Template conveys the dose and equipment parameters of a single irradiation event.
A CT irradiation event is the loading of X-Ray equipment caused by a single continuous actuation of the equipment's irradiation switch, from the start of the loading time of the first pulse until the loading time trailing edge of the final pulse. Any on-off switching of the radiation source during the event shall not be treated as separate events; rather the event includes the time between start and stop of radiation as triggered by the user, e.g., a single sequence of scanning comprised of multiple slices acquired with successive tube rotations and table increments shall be treated as a single irradiation event. Depending on the examination workflow and the anatomical target region the CT irradiation event data may split into multiple instances of this Template for better dose estimation. The irradiation event is the "smallest" information entity to be recorded in the realm of Radiation Dose reporting. Individual Irradiation Events are described by a set of accompanying physical parameters that are sufficient to understand the "quality" of irradiation that is being applied. This set of parameters may be different for the various types of equipment that are able to create irradiation events.
Table TID 10013. CT Irradiation Event Data
|
User-defined type of clinical acquisition protocol for creating images or image-derived measurements. May be taken from Protocol Name (0018,1030) or from Performed Procedure Step Description (0040,0254). |
|
|
Description of the method used during acquisition of this CT irradiation event, may be derived from Acquisition Type (0018,9302). |
|
|
Though not a characteristic of the acquisition per se, the type of reconstruction intended has a bearing on the technique used. If multiple types of reconstruction are performed, multiple values can be listed. These values should correspond to the values of Reconstruction Algorithm (0018,9315) in the reconstructed images. |
|
|
The acquisition was performed with or without contrast medium application. |
|
|
If an acquisition is a repeat because an earlier acquisition was unsatisfactory, this may be recorded along with a coded reason and the earlier acquisition's irradiation event UID. This is intended to help with subsequent analysis by providing a priori information about why the study might be flagged as an outlier with higher dose exposure values than usual for the type of study. |
|
|
If an acquisition is a rejected because it was unsatisfactory, this may be recorded along with a coded reason. This is intended to help with subsequent analysis by providing a priori information about why the study might be flagged as an outlier with higher dose exposure values than usual for the type of study. |
|
|
The DateTime that the application of X-Rays started for this irradiation event. This shall correspond to the start of the first irradiation in the Irradiation Event, which defines the starting point for the calculation of the contents of the Row 21 "CT Dose" CONTAINER. |
|
|
Total time the patient has received X-Ray exposure during the irradiation event. |
|
|
The value of the nominal width (referenced to the location of the isocenter along the z axis) of a single collimated slice in mm. |
|
|
The value of the nominal width (referenced to the location of the isocenter along the z axis) of the nominal total collimation in mm over the area of active X-Ray detection (z-coverage). |
|
|
Pitch Factor: For Spiral Acquisition, the Pitch Factor is the ratio of the Table Feed per Rotation to the Nominal Total Collimation Width. For Sequenced Acquisition, the Pitch Factor is the ratio of the Table Feed per single sequenced scan to the Nominal Total Collimation Width. |
|
|
CT X-Ray source parameters related to the acquisition. For each X-Ray source an item must be present. For multi-energy acquisitions, multiple items may be present for each X-Ray source, each item describing one energy level. |
|
|
Identification of the X-Ray source. Identifies the particular X-Ray source (in a multi-source CT system) for which the set of X-Ray source parameter values is reported. |
|
|
Exposure time as measured/recorded by the system per rotation. |
|
|
Thickness of an equivalent filter constructed from aluminum, in case of multi-source CT systems AND if Row 4 is not present |
|
|
"Mean CTDIvol" refers to the average value of the CTDIvol applied within this acquisition. CTDIvol is the volume CTDIw, where CTDIw is the weighted computed tomography dose index 100 as defined in [IEC 60601-2-44]. For Sequenced and Spiral scanning, CTDIvol = CTDIw / Pitch Factor. For Stationary and Free scanning, CTDIvol = CTDIw ✕ Number of Rotations. For Shuttle Mode scanning, CTDIvol = CTDIw ✕ Number of Rotations for Entire Scan Series ✕ Nominal Total Collimation Width / (Nominal Total Collimation Width + Distance Between the Two Scan Positions). According to [IEC 60601-2-44] Ed 3 for Constant Angle Acquisition may be calculated as CTDIvol = (CTDIw / Current Time Product (mAs)) ✕ X-Ray Tube Current (mA) x (Nominal Total Collimation Width (mm) / Table Speed (mm/s)). NoteThe ratio CTDIw / Current Time Product is evaluated independently of the Constant Angle Acquisition but with the same settings of tube voltage and Total Collimation Width as those of the Constant Angle Acquisition. See also CTDIvol (0018,9345) and Spiral Pitch Factor (0018,9311) in the “Enhanced CT Image IODs” in PS3.3 . |
|
|
The type of phantom used for CTDI measurement according to [IEC 60601-2-44] (e.g., Head 16 cm diameter PMMA, Body 32 cm diameter PMMA). |
|
|
The CTDIfree air Calculation Factor is the CTDIfree air per mAs, expressed in units of mGy/mAs. The CTDIfree air Calculation Factor may be used in one method calculating Dose. For example, for this acquisition, Effective Dose = Mean X-Ray Tube Current ✕ Cumulative Exposure Time ✕ CTDIfree air Calculation Factor ✕ (Effective Dose/ CTDIfree air). |
|
|
MeanCTDIfree air is the mean CTDI for this acquisition, evaluated free-in-air according to [IEC 60601-2-44]. MeanCTDIfree air = Mean X-Ray Tube Current ✕ Cumulative Exposure Time ✕ CTDIfree air Calculation Factor. The CTDIfree air may be used in one method of calculating Effective Dose. |
|
|
For Spiral scanning, DLP = CTDIvol ✕ Scanning Length. For Sequenced scanning, DLP = CTDIvol ✕ Table Travel Between Consecutive Scans ✕ Number of Scans. For Stationary and Free scanning, DLP = CTDIvol ✕ Nominal Total Collimation Width. For Shuttle Mode scanning, DLP = CTDIvol ✕ (Nominal Total Collimation Width + Distance Between the Two Scan Positions) (according to [IEC 60601-2-44]). |
|
|
Effective Dose in mSv of the single continuous time-frame of the irradiation computed as described in TID 10012 “CT Accumulated Dose Data”. |
|
|
The Effective Dose Conversion Factor is the ratio of the Effective Dose to the DLP, expressed in units of mSv/mGy.cm, and it is used as a factor in one method of estimating Effective Dose. Monte Carlo Simulations (or dosimetric measurements in an anthropomorphic phantom, e.g., the Alderson-Rando phantom) may be used as a basis for the evaluation of Effective Dose Conversion Factors. This is different from the Conversion Factor to compute a Size Specific Dose Estimate from a Water Equivalent Diameter. |
|
|
This value represents a Size Specific Dose Estimate (SSDE) for this irradiation event as a whole. More than one Size Specific Dose Estimate may be included, for example if different computation methods are used. If SSDE is estimated for multiple Z positions within a single irradiation event, that is found in Row 34f. |
|
|
Methods including [AAPM Report 204] and [IEC 62985] are listed in CID 10023 “Size Specific Dose Estimation Method for CT”; other methods may be used. The phantom size (16cm or 32cm) used for the calculation is available from the phantom type defined in Row 23. |
|
|
The condition specifies inclusion of the Measured Lateral Dimension if it was used in the calculation. |
|
|
The condition specifies inclusion of the Measured AP Dimension if it was used in the calculation. |
|
|
The Derived Effective Diameter is conditionally included, whether it was derived from measurements or estimated from age, but may not be used for other (non-AAPM Report 204) methods. |
|
|
The conversion factor described by the coefficients is used both for the SSDE(z) values in Row 34f and, if Row 31 is (113988, DCM, "Estimated from Water Equivalent Diameter"), for the SSDE value in Row 30. |
|
|
If the Water Equivalent Diameter was computed from raw views rather than reconstructed images, then the Raw Data may be referenced. |
|
|
A single value for Water Equivalent Diameter is encoded. If Row 31 is (113988, DCM, "Estimated from Water Equivalent Diameter"), this value is used to generate Row 30. If Row 31 is (113989, DCM, "Arithmetic Average of SSDE(z)"), this value is not used directly to generate Row 30, but is still present and represents Dw, the Arithmetic Average of the Dw(z) values in Row 34h as described in [IEC 62985]. |
|
|
This z position is patient (not table or gantry) relative, to allow it to be defined in the Patient Coordinate System and hence related to the Image Position (Patient) in the reconstructed images (see TID 10014 “Scanning Length”, included at Row 9). It is required if the method uses a representative slice, but may also be present if the method used a Localizer or Raw Data at a single location rather than the entire scan range. |
|
|
A set of Size Specific Dose Estimates at particular z positions along the scan axis. These values correspond to the SSDE(z) values identified in [IEC 62985]. |
|
|
The z position at which the SSDE in Row 34f was calculated. As with Row 34e, the value is patient relative. |
|
|
The Water Equivalent Diameter used to calculate the SSDE in Row 34f using the conversion factor described in Row 34a. This value, along with the Row 34h values for the other SSDEs in Row 34f, corresponds to the set of Dw(z) values identified in [IEC 62985]. |
|
|
Record of details associated with using the NEMA Dose Check Standard [NEMA XR 25-2019]. |
|
|
The type of exposure modulation. May use the value of Exposure Modulation Type (0018,9323) from the CT Exposure Macro or from the CT Image Module. |
|
|
People responsible for the administration of the radiation reported in the irradiation event. May include values that would appear in Performing Physicians' Name (0008,1050), Performing Physician Identification Sequence (0008,1052), Operators' Name (0008,1070) and/or Operator Identification Sequence (0008,1072). |
|
|
The device that produced the irradiation in this Irradiation Event. I.e., the CT scanner. This is not required to be present if the information is the same as that already recorded in the TID 1004 “Device Observer Identifying Attributes” encoded via the inclusion of TID 1002 “Observer Context” in TID 10011 “CT Radiation Dose” Row 4, which in turn may be absent if identical to the content in the Enhanced General Equipment Module. |
| DICOM PS3.16 2024e - Content Mapping Resource |
|---|