DICOM PS3.3 2018b - Information Object Definitions

C.8.9.4 PET Image Module
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#### C.8.9.4 PET Image Module

Table C.8-63 contains IOD Attributes that describe PET images.

Table C.8-63. PET Image Module Attributes

Attribute Name | Tag | Type | Attribute Description
--- | --- | --- | ---
Image Type | (0008,0008) | 1 | Image identification characteristics. See Section C.8.9.4.1.1 for specialization.
Samples per Pixel | (0028,0002) | 1 | Number of samples (planes) in this image. Enumerated Values: 1
Photometric Interpretation | (0028,0004) | 1 | Specifies the intended interpretation of the pixel data. See Section C.8.9.4.1.2 for specialization.
Bits Allocated | (0028,0100) | 1 | Number of bits allocated for each pixel sample. Each sample shall have the same number of bits allocated. Enumerated Values: 16
Bits Stored | (0028,0101) | 1 | Number of bits stored for each pixel sample. Each sample shall have the same number of bits stored. The value shall be the same as the value in Bits Allocated (0028,0100).
High Bit | (0028,0102) | 1 | Most significant bit for pixel sample data. Each sample shall have the same high bit. Shall be one less than the value in Bits Stored (0028,0101).
Rescale Intercept | (0028,1052) | 1 | The value b in relationship between stored values (SV) and pixel value units (U) defined in Units (0054,1001): U = m*SV+b. The Rescale Intercept is always zero for PET images.
Rescale Slope | (0028,1053) | 1 | m in the equation specified in Rescale Intercept (0028,1052).
Frame Reference Time | (0054,1300) | 1 | The time that the pixel values in the image occurred. Frame Reference Time is the offset, in msec, from the Series reference time. See explanation in Section C.8.9.4.1.5.
Trigger Time | (0018,1060) | 1C | Time interval, in msec, from the start of the trigger to the beginning of data acquisition for this image. Required if Series Type (0054,1000), Value 1 is GATED.
Frame Time | (0018,1063) | 1C | Nominal duration per individual frame, in msec. Required if Series Type (0054,1000), Value 1 is GATED. See Section C.8.9.4.1.3 for explanation.
Low R-R Value | (0018,1081) | 1C | R-R interval lower limit for beat rejection, in msec. Required if Series Type (0054,1000), Value 1 is GATED and Beat Rejection Flag (0018,1080) is Y.
High R-R Value | (0018,1082) | 1C | R-R interval upper limit for beat rejection, in msec. Required if Series Type (0054,1000), Value 1 is GATED and Beat Rejection Flag (0018,1080) is Y.
Lossy Image Compression | (0028,2110) | 1C | Specifies whether an Image has undergone lossy compression (at a point in its lifetime). Enumerated Values: 00 Image has NOT been subjected to lossy compression. 01 Image has been subjected to lossy compression. Once this value has been set to 01 it shall not be reset. See Section C.7.6.1.1.5. Required if Lossy Compression has been performed on the image. May be present otherwise.
Image Index | (0054,1330) | 1 | An index identifying the position of this image within a PET Series. See Section C.8.9.4.1.9 for explanation.
Acquisition Date | (0008,0022) | 2 | The date the acquisition of data that resulted in this image started. See Section C.8.9.4.1.4 for specialization.
Acquisition Time | (0008,0032) | 2 | The time the acquisition of data that resulted in this image started. See Section C.8.9.4.1.4 for specialization.
Actual Frame Duration | (0018,1242) | 2 | Elapsed time of the data acquisition for this image, in msec. See Section C.8.9.4.1.6 for explanation.
Nominal Interval | (0018,1062) | 3 | Average duration of accepted beats, in msec, of the R-R interval.
Intervals Acquired | (0018,1083) | 3 | Number of heartbeats that fall within Low R-R Value (0018,1081) and High R-R Value (0018,1082), and were therefore accepted and contribute coincidence events to this R-R Interval.
Intervals Rejected | (0018,1084) | 3 | Number of heartbeats that fall outside Low R-R Value (0018,1081) and High R-R Value (0018,1082), and do not contribute coincidence events to this R-R Interval. However, they may contribute coincidence events to other R-R Intervals.
Primary (Prompts) Counts Accumulated | (0054,1310) | 3 | The sum of events that occur in the primary event channel. The counts include Trues +Scatter+ Randoms if Randoms Correction Method (0054,1100) is NONE; otherwise the counts are Trues +Scatter.
Secondary Counts Accumulated | (0054,1311) | 3 | Sum of counts accumulated in secondary channels. See Section C.8.9.4.1.7 for explanation.
Slice Sensitivity Factor | (0054,1320) | 3 | The slice-to-slice sensitivity correction factor that was used to correct this image. The value shall be one if no slice sensitivity correction was applied.
Decay Factor | (0054,1321) | 1C | The decay factor that was used to scale this image. Required if Decay Correction (0054,1102) is other than NONE. If decay correction is applied, all images in the Series shall be decay corrected to the same time.
Dose Calibration Factor | (0054,1322) | 3 | Factor that was used to scale this image from counts/sec to Bq/ml using a dose calibrator. The value shall be one if no dose calibration was applied. See Section C.8.9.4.1.8 for explanation.
Scatter Fraction Factor | (0054,1323) | 3 | An estimate of the fraction of acquired counts that were due to scatter and were corrected in this image. The value shall be zero if no scatter correction was applied.
Dead Time Factor | (0054,1324) | 3 | The average dead time correction factor that was applied to this image. The value shall be one if no dead time correction was applied.
Include Table 10-7 “General Anatomy Optional Macro Attributes” | No Context ID for the Anatomic Region Sequence is defined.
Include Table 10-25 “Optional View and Slice Progression Direction Macro Attributes” |
Isocenter Position | (300A,012C) | 3 | Isocenter coordinates (x,y,z), in mm. Specifies the location of the machine isocenter in the Patient-Based Coordinate System associated with the Frame of Reference. It allows transformation from the Equipment-Based Coordinate System to the Patient-Based Coordinate System.

### Note

Referenced Overlay Sequence (0008,1130) and Referenced Curve Sequence (0008,1145) were previously included in this Module as optional Attributes but have been retired. See PS3.3-2004.

##### C.8.9.4.1 PET Image Module Attribute Descriptions

###### C.8.9.4.1.1 Image Type

For PET Images, Image Type (0008,0008) is specified to be Type 1.

### Note

For PET images, Image Type (0008,0008) Value 1 will be ORIGINAL for reconstructed images. DERIVED may be appropriate for some other results images. For PET images, Image Type (0008,0008) Value 2 will be PRIMARY.

###### C.8.9.4.1.2 Photometric Interpretation

Enumerated Values:

MONOCHROME2

See Section C.7.6.3.1.2 for definition of this term.

###### C.8.9.4.1.3 Frame Time

Frame Time (0018,1063) is the explicit duration of the gated frame when Cardiac Framing Type (0018,1064) is equal to FORW or BACK. Frame Time (0018,1063) is the nominal duration of the gated frame when Cardiac Framing Type (0018,1064) is equal to PCNT.

###### C.8.9.4.1.4 Acquisition Date, Acquisition Time

For PET Images, Acquisition Date (0008,0022) and Acquisition Time (0008,0032) are specified to be Type 2. Acquisition Date (0008,0022) and Acquisition Time (0008,0032) use the same time base as Series Time (0008,0031).

For Series Type (0054,1000) Value 1 equal to STATIC, WHOLE BODY, or DYNAMIC, Acquisition Time (0008,0032) is the real-world beginning of the accumulation of events into this Image. For STATIC, WHOLE BODY, or DYNAMIC Series, Acquisition Time (0008,0032) may vary from Image to Image within a PET Series.

For Series Type (0054,1000) Value 1 equal to GATED, Acquisition Time (0008,0032) is the real-world beginning of the capability of accumulating events into this Image. (The actual accumulation of events has only occurred during an R-R Interval.) For GATED Series, Acquisition Time (0008,0032) shall not vary from Image to Image within a PET Series.

###### C.8.9.4.1.5 Frame Reference Time

Frame Reference Time (0054,1300) is the time that the pixel values in the Image occurred. Frame Reference Time is defined as the time offset, in msec, from the Series Reference Time, where the Series Reference Time is defined by the combination of Series Date (0008,0021) and Series Time (0008,0031).

### Note

Frame Reference Time (0054,1300) is implementation dependent and may or may not be tied to any real-world event. To illustrate the meaning of Frame Reference Time (0054,1300), the following are some examples of possible implementations:

- Example 1: For a long-lived radionuclide and a non-time-varying radiopharmaceutical distribution, an implementation sets the Frame Reference Time (0054,1300) to the midpoint of the Actual Frame Duration (0018,1242).

- Example 2: For a short-lived radionuclide and a non-time-varying radiopharmaceutical distribution, an implementation sets the Frame Reference Time (0054,1300) to the time at which the average activity occurs for a decaying radionuclide, Tave. If image acquisition started at the Series Reference Time and the image has not been decay corrected, then Tave will be:

  where:

  - lambda = decay constant = (ln 2) / T1/2

  - T1/2 = Radionuclide Half Life (0018,1075)

  - T = Actual Frame Duration (0018,1242)

  Note that Tave will be sooner than the midpoint of the Actual Frame Duration (0018,1242).

- Example 3: For a short-lived radionuclide and a time-varying radiopharmaceutical distribution, an implementation with supplementary data (e.g., scanner count rates or blood sample data) sets the Frame Reference Time (0054,1300) to a derived time determined to be its best estimate of the time that the pixel values occurred.

###### C.8.9.4.1.6 Actual Frame Duration

The accumulation of counts for a PET Image shall occur entirely between:

1. the acquisition starting time (as specified by Acquisition Date (0008,0022) and Acquisition Time (0008,0032)), and

2. the acquisition ending time, which is equal to the acquisition starting time in (1) plus the Actual Frame Duration (0018,1242).

If Series Type (0054,1000) Value 1 is GATED, then the actual accumulation of counts has only occurred during an R-R Interval.

###### C.8.9.4.1.7 Secondary Counts Accumulated

Secondary Counts Accumulated (0054,1311) is multi-valued and, if supplied, has Values corresponding to the Secondary Counts Type (0054,1220). The number and order of the Values in Secondary Counts Accumulated (0054,1311) shall be the same as Secondary Counts Type (0054,1220).

###### C.8.9.4.1.8 Dose Calibration Factor

The Dose Calibration Factor (0054,1322) is the factor that was used to scale this image from counts/sec to Bq/ml using an external dose calibrator. The value shall be one if no dose calibration was applied. The application of a dose calibration correction is specified by Corrected Image (0028,0051) equal to DCAL.

### Note

Dose Calibration Factor (0054,1322) is not equal to the inverse of the sensitivity (kcps/Bq/ml) of the scanner, which is usually measured for a given radiopharmaceutical distribution and excluding the effects of attenuation.

###### C.8.9.4.1.9 Image Index

Image Index (0054,1330) is an index identifying the position of this image within a PET Series.

### Note

The scheme for encoding Image Index (0054,1330) is as follows. Images within a PET Series can be viewed as a multi-dimensional array whose possible dimensions include R-R Intervals, Time Slots, Time Slices, and Slices. The dimensions of the array are defined by Series Type (0054,1000) Value 1. Each dimension of the array has an index that identifies the position of this image in the array. The indices are: R-R Interval Index, Time Slot Index, Time Slice Index, Slice Index. The indices are calculated as follows:

Index | Range of Index | Order of Images along that Dimension
--- | --- | ---
R-R Interval Index | 1 to Number of R-R Intervals (0054,0061) | Increasing Low R-R Value (0018,1081)
Time Slot Index | 1 to Number of Time Slots (0054,0071) | Increasing Trigger Time (0018,1060)
Time Slice Index | 1 to Number of Time Slices (0054,0101) | Increasing Frame Reference Time (0054,1300)
Slice Index | 1 to Number of Slices (0054,0081) | If Series Type (0054,1000) Value 2 is IMAGE:Order is in increasing position along the normal, where the normal is determined by the cross product of the direction cosines of the row and column of the image. See Image Orientation (0020,0037) in the Image Plane Module. If Series Type (0054,1000) Value 2 is REPROJECTION:Order is in increasing or decreasing angle of the normal, where the normal is determined by the cross product of the direction cosines of the row and column of the image. See Image Orientation (0020,0037) in the Image Plane Module. (Note that reprojection images rotate about only a single axis as described in Section C.8.9.1.1.1. Therefore, all normals are co-planar and make a single angle with respect to each other.)

Using these index values the position of this image within the multi-dimensional array (Image Index (0054,1330)) is calculated as follows:

Series Type (0054,1000), Value 1 | Dimensions of Array (Last dimension is most rapidly changing) | Encoding of Image Index (0054,1330)
--- | --- | ---
STATIC | Slice | Slice Index
WHOLE BODY | Slice | Slice Index
DYNAMIC | Time Slice \Slice | ((Time Slice Index - 1) * (Number of Slices (0054,0081))) + Slice Index
GATED | R-R Interval \Time Slot \Slice | ((R-R Interval Index - 1) * (Number of Time Slots (0054,0071)) * (Number of Slices (0054,0081))) + ((Time Slot Index - 1) * (Number of Slices (0054,0081))) + Slice Index

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DICOM PS3.3 2018b - Information Object Definitions