During the procedure, the equipment typically changes the position of the X-Ray Source.
The Radiation Output is the accumulated dose over the defined time period of the encoding, which can include several X-Ray exposures.
This section provides guidance for RDSR encoding of the time periods related to the Radiation Output and the X-Ray Source Position.
The start and end times of the encoding of positions do not necessarily align with the start and end times of the encoding of the Radiation Output values.
At any given X-Ray Source position there is typically one Radiation Output value, but multiple values are permitted. For positions where no radiation occurs, the Radiation Output value may be omitted or may be encoded with a value of zero. The specification does not permit one Radiation Output value to span a period during which the position of a given X-Ray source changes.
Radiation Output is described at a particular point, the Output Measurement Point Position. The Radiation Output value encoding may not span time periods with updates to the Output Measurement Point Position, similar to the requirements to the X-Ray Source position (described by the Transformation Matrix).
Consider the following real-world scenario of a given time period between TA and TH that includes a single X-Ray Source, four different positions, and four X-Ray exposures. The first graphic represents the different X-Ray Source positions as abstracted positions P1 to P4 representing the X-Ray Source Transformation Matrix. The second graphic represents the different X-Ray exposures as periods of X-Ray "On," the Radiation Output is represented inside each period as an accumulated air kerma value.
The time of the exposures is not aligned with the time of the positions.
The different values of the X-Ray Source position are encoded as several inclusions of the TID 10050. The Radiation Output is encoded either as several inclusions of the TID 10048 or as table of entries within one single inclusion of TID 10048. There are several options for encoding the time periods.
Each X-Ray Source position is encoded as a separate inclusion of TID 10050. The time period of each inclusion is aligned with the timing of the X-Ray exposures at that position. Values of the X-Ray Source position are encoded only when there is an X-Ray exposure (thus TID 10050 is not included for P4).
Each Radiation Output value is encoded as a separate inclusion of TID 10048. The start and end time of each inclusion is aligned with the start or end of an X-Ray exposure. One inclusion may group multiple X-Ray exposures at the same position (e.g., between T1and T4). Changes to other parameters, such as collimated area, may preclude such grouping.
Table UUUU.4.5.4.3-1 illustrates the encoding of TID 10050 (P1 to P3 representing the X-Ray Source Transformation Matrix), and Table UUUU.4.5.4.3-2 illustrates the encoding of TID 10048.
Table UUUU.4.5.4.3-1. Encoding Option 1 of TID 10050 X-Ray Source Reference Coordinate System
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TID 10050 “X-Ray Source Reference Coordinate System” CONTAINER inclusion #1 |
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TID 10050 “X-Ray Source Reference Coordinate System” CONTAINER inclusion #2 |
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TID 10050 “X-Ray Source Reference Coordinate System” CONTAINER inclusion #3 |
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Table UUUU.4.5.4.3-2. Encoding Option 1 of Several Inclusions of TID 10048 Radiation Output
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TID 10048 “Radiation Output” CONTAINER inclusion #1 |
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TID 10048 “Radiation Output” CONTAINER inclusion #2 |
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TID 10048 “Radiation Output” CONTAINER inclusion #3 |
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Each X-Ray Source position is encoded as a separate inclusion of TID 10050. The time period of each inclusion is aligned with the timing of the position changes. This option choses to encode the start and end time of each period for which the position is constant. It is not necessary to encode the positions when they are changing because there is no X-Ray exposure during this time.
Each Radiation Output value is encoded as a separate inclusion of TID 10048. The start and end time of each inclusion is aligned with the start or end of an X-Ray exposure. One inclusion may group multiple X-Ray exposures at the same position (e.g., between T1and T4). Changes to other parameters, such as collimated area, may preclude such grouping.
Table UUUU.4.5.4.3-3 illustrates the encoding of TID 10050 (P1 to P4 representing the X-Ray Source Transformation Matrix), and Table UUUU.4.5.4.3-4 illustrates the encoding of TID 10048.
Table UUUU.4.5.4.3-3. Encoding Option 2 of TID 10050 X-Ray Source Reference Coordinate System
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TID 10050 “X-Ray Source Reference Coordinate System” CONTAINER inclusion #1 |
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TID 10050 “X-Ray Source Reference Coordinate System” CONTAINER inclusion #2 |
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TID 10050 “X-Ray Source Reference Coordinate System” CONTAINER inclusion #3 |
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TID 10050 “X-Ray Source Reference Coordinate System” CONTAINER inclusion #4 |
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Table UUUU.4.5.4.3-4. Encoding Option 2 of Several Inclusions of TID 10048 Radiation Output
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TID 10048 “Radiation Output” CONTAINER inclusion #1 |
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TID 10048 “Radiation Output” CONTAINER inclusion #2 |
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TID 10048 “Radiation Output” CONTAINER inclusion #3 |
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Each X-Ray Source position is encoded as a separate inclusion of TID 10050. The time period of each inclusion is aligned with the timing of the position changes. This option choses to encode the start and end time of each period for which the position is constant. It is not necessary to encode the positions when they are changing because there is no X-Ray exposure during this time.
The Radiation Output values are encoded as table entries in a single inclusion of the TID 10048, the table entries are encoded based on the timing of the X-Ray Source positions.
This implementation should make sure to encode several table entries with zero-dose value when the X-Ray Source Position changes between exposures and also when the X-Ray Source position is undefined, because one Radiation Output value different than zero cannot span a period during which this position change. For this reason, the recommended implementation is to align the time periods of the table entries of the Radiation Output value with the time periods of the X-Ray Source Position.
This encoding of Radiation Output as table entries is well suited for a rotating source (e.g., Cone Beam CT acquisitions). Refer to examples of chapter 5.2 that illustrate the encoding of a rotating source where the Radiation Output values are encoded as table entries of one inclusion of the TID 10048.
Table UUUU.4.5.4.3-5 illustrates the encoding of TID 10050 (P1 to P4 representing the X-Ray Source Transformation Matrix), and Table UUUU.4.5.4.3-6 illustrates the encoding of TID 10048.
Table UUUU.4.5.4.3-5. Encoding Option 3 of TID 10050 X-Ray Source Reference Coordinate System
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TID 10050 “X-Ray Source Reference Coordinate System” CONTAINER inclusion #1 |
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TID 10050 “X-Ray Source Reference Coordinate System” CONTAINER inclusion #2 |
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TID 10050 “X-Ray Source Reference Coordinate System” CONTAINER inclusion #3 |
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TID 10050 “X-Ray Source Reference Coordinate System” CONTAINER inclusion #4 |
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Table UUUU.4.5.4.3-6. Encoding Option 3 of One Inclusion of TID 10048 Radiation Output
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TID 10048 “Radiation Output” CONTAINER inclusion #1 |
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