C.8.9 PET Information Module Definitions
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### C.8.9 PET Information Module Definitions

This Section describes Positron Emission Tomography series and image Modules. These Modules contain Attributes that are specific to Positron Emission Tomography images.

#### C.8.9.1 PET Series Module

Table C.8-60 contains IOD Attributes that describe a PET Series.

Table C.8-60. PET Series Module Attributes

Attribute Name | Tag | Type | Attribute Description
--- | --- | --- | ---
Series Date | (0008,0021) | 1 | Date the Series started. See Section C.8.9.1.1.2 for specialization.
Series Time | (0008,0031) | 1 | Time the Series started. See Section C.8.9.1.1.2 for specialization.
Units | (0054,1001) | 1 | Pixel value units. See Section C.8.9.1.1.3 for explanation. Defined Terms: CNTS NONE CM2 CM2ML PCNT CPS BQML MGMINML UMOLMINML MLMING MLG 1CM UMOLML PROPCNTS PROPCPS MLMINML MLML GML STDDEV
SUV Type | (0054,1006) | 3 | Type of Standardized Uptake Value (SUV). Enumerated Values: BSA body surface area BW body weight LBM lean body mass IBW - ideal body weight If absent, and the Units (0054,1001) are GML, then the type of SUV shall be assumed to be BW. ### Note The type of SUV cannot reliably be deduced from the units alone, i.e., SUVbw, SUVibw and SUVlbm all have units of GML.
Counts Source | (0054,1002) | 1 | The primary source of counts. The primary source leads to the underlying image Units (0054,1001), as opposed to secondary sources that are used during reconstruction correction. Enumerated Values: EMISSION TRANSMISSION
Series Type | (0054,1000) | 1 | A multi-valued indicator of the type of Series. See Section C.8.9.1.1.4 for explanation. Value 1 Enumerated Values: STATIC DYNAMIC GATED WHOLE BODY Value 2 Enumerated Values: IMAGE REPROJECTION
Reprojection Method | (0054,1004) | 2C | Method for projecting volumetric data onto planar projection. Required if Series Type (0054,1000), Value 2 is REPROJECTION. Defined Terms: SUM MAX PIXEL
Number of R-R Intervals | (0054,0061) | 1C | The maximum number of R-R Intervals that may exist in this Series. Required if Series Type (0054,1000), Value 1 is GATED.
Number of Time Slots | (0054,0071) | 1C | The maximum number of Time Slots that may exist in this Series. Required if Series Type (0054,1000), Value 1 is GATED.
Number of Time Slices | (0054,0101) | 1C | The maximum number of Time Slices that may exist in this Series. Required if Series Type (0054,1000), Value 1 is DYNAMIC.
Number of Slices | (0054,0081) | 1 | The maximum number of Slices that may exist in this Series.
Corrected Image | (0028,0051) | 2 | One or more values that indicate which, if any, corrections have been applied to the images in this series. Defined Terms: DECY decay corrected ATTN attenuation corrected SCAT scatter corrected DTIM dead time corrected MOTN gantry motion corrected (e.g., wobble, clamshell) PMOT patient motion corrected CLN count loss normalization (correction for count loss in gated Time Slots) RAN randoms corrected RADL non-uniform radial sampling corrected DCAL sensitivity calibrated using dose calibrator NORM detector normalization
Randoms Correction Method | (0054,1100) | 3 | Type of randoms correction processing. Defined Terms: NONE no randoms correction DLYD delayed event subtraction SING singles estimation
Attenuation Correction Method | (0054,1101) | 3 | A textual description of the attenuation correction processing. e.g., measured vs. calculated, transmission source type (ring, line, point), assumed patient geometry (polygon, ellipse, segmented, attenuation coefficient, skull thickness), post-injection transmission, smoothing.
Scatter Correction Method | (0054,1105) | 3 | A textual description of the scatter correction processing. e.g., convolution-subtraction, dual energy window, model-based, use of attenuation data.
Decay Correction | (0054,1102) | 1 | The real-world event to which images in this Series were decay corrected. See Section C.8.9.1.1.5 for explanation. Defined Terms: NONE no decay correction START acquisition start time ADMIN radiopharmaceutical administration time
Reconstruction Diameter | (0018,1100) | 3 | Diameter, in mm, of the region within which the data was used in creating the reconstruction of the image. Data may exist outside this region and portions of the patient may exist outside this region.
Convolution Kernel | (0018,1210) | 3 | Textual description of the convolution kernel(s) used to reconstruct the data (e.g., name, cutoff, radial/axial/angular, mathematical form, DC handling)
Reconstruction Method | (0054,1103) | 3 | Textual description of reconstruction processing, e.g., 2D filtered backprojection, 2D iterative, 3D PROMIS, 3D FAVOR, 3D iterative.
Detector Lines of Response Used | (0054,1104) | 3 | Textual description of which detector lines of response were used, mashed, or otherwise processed during tomographic reconstruction.
Acquisition Start Condition | (0018,0073) | 3 | Description of how the data collection was started. Defined Terms: DENS density (counts/sec) RDD relative density difference (change in counts/sec) MANU manual TIME time AUTO automatic, when ready TRIG physiological trigger See Section C.8.9.1.1.6 for explanation.
Acquisition Start Condition Data | (0018,0074) | 3 | Count density, change in count density, or physiological triggers causing data collection to start.
Acquisition Termination Condition | (0018,0071) | 3 | Description of how the data collection for the series was stopped. Defined Terms: CNTS counts DENS density (counts/sec) RDD relative density difference (change in counts/sec) MANU manual OVFL data overflow TIME time TRIG physiological trigger See Section C.8.4.9.1.3 for explanation.
Acquisition Termination Condition Data | (0018,0075) | 3 | Number of counts, count density, change in count density, or physiological triggers causing the termination.
Field of View Shape | (0018,1147) | 3 | Shape of the field of view of the PET camera. Defined Terms: CYLINDRICAL RING HEXAGONAL MULTIPLE PLANAR
Field of View Dimensions | (0018,1149) | 3 | Dimensions of the field of view, in mm. Transverse detector diameter followed by axial width.
Gantry/Detector Tilt | (0018,1120) | 3 | Angle of tilt in degrees of the gantry. See Section C.8.9.1.1.7 for explanation.
Gantry/Detector Slew | (0018,1121) | 3 | Angle of slew in degrees of the gantry. Positive slew is moving the gantry on the patient's left toward the patient's superior, when the patient is supine.
Type of Detector Motion | (0054,0202) | 3 | Describes the detector motion during acquisition. Defined Terms: NONE stationary gantry STEP AND SHOOT Interrupted motion, acquire only while stationary CONTINUOUS Gantry motion and acquisition are simultaneous and continuous WOBBLE wobble motion CLAMSHELL clamshell motion
Collimator Type | (0018,1181) | 2 | Collimator Type. Defined Terms: NONE no collimator RING transverse septa
Collimator/Grid Name | (0018,1180) | 3 | Label describing the collimator used.
Axial Acceptance | (0054,1200) | 3 | Maximum axial angle accepted, in degrees.
Axial Mash | (0054,1201) | 3 | Number of adjacent axial lines of response mashed together. See Section C.8.9.1.1.8 for explanation.
Transverse Mash | (0054,1202) | 3 | Number of adjacent transverse lines of response mashed together. See Section C.8.9.1.1.9 for explanation.
Detector Element Size | (0054,1203) | 3 | Size of an individual detector element, in mm. Transverse dimension followed by axial dimension. For a discrete crystal, this is the crystal size. For a continuous detector, this is the pixel bin size.
Coincidence Window Width | (0054,1210) | 3 | The width of the coincidence timing window, in nsec. The maximum time difference accepted between two single events.
Energy Window Range Sequence | (0054,0013) | 3 | Sequence of Items that describes the energy windows used for this Series. One or more Items are permitted in this sequence. See Section C.8.9.1.1.10 for explanation.
>Energy Window Lower Limit | (0054,0014) | 3 | The lower limit of the energy window, in KeV.
>Energy Window Upper Limit | (0054,0015) | 3 | The upper limit of the energy window, in KeV.
Secondary Counts Type | (0054,1220) | 3 | Array defining the type of additional counts accumulated during acquisition. Defined Terms: DLYD delayed events SCAT scattered events in secondary window SING singles DTIM events lost due to deadtime
Scan Progression Direction | (0054,0501) | 3 | The anatomical order in which the slices were acquired. Enumerated Values: FEET_TO_HEAD Slices closest to the patient's feet were acquired first. HEAD_TO_FEET Slices closest to the patient's head were acquired first.

### Note

The formulas for the determination of SUVbw, SUVbsa, SUVlbm and SUVibw are defined in Sugawara et al. Reevaluation of the Standardized Uptake Value for FDG: Variations with Body Weight and Methods for Correction. Radiology, 1999 at http://radiology.rsna.org/content/213/2/521. See also CID 84 “PET Units” in PS3.16 .

##### C.8.9.1.1 PET Series Attribute Descriptions

### Note

The meaning of a General Series in DICOM is determined by the attributes in the General Series Module and by the Source Entities (Patient, Study, Frame of Reference, Equipment) that originate the Series. The Source Entities are the single-valued entities of the 1->n relationship, where the Series is the multi-valued entity. Therefore, a Series is a group of images that: are from the same patient and study; are from the same Equipment; and, are from the same spatial Frame of Reference.

The PET Image IOD further refines a PET Series IE by the attributes in the PET Series Module, the PET Isotope Module, the PET Multi-gated Acquisition Module and the Acquisition Context Module. These are the attributes that shall not change from Image to Image. Therefore, in addition to the criteria above for a General Series (same patient, study, frame of reference, equipment), the attributes in the PET Series IE define a PET series as a group of images that: are from the same temporal frame of reference; have the same fundamental meaning (e.g., same units: either activity density, metabolism, or attenuation); are derived from the same activity source (emission or transmission); are from the same isotope and radiopharmaceutical; were derived from the same reconstruction processing; and, originated from the same acquisition setup and parameters, including the patient conditions (cardiac stress or rest) if applicable.

###### C.8.9.1.1.1 Specialization of Image Plane Module and Image Pixel Module Attributes

For PET Series, the following Image Pixel Module attributes shall not vary from Image to Image:

- Photometric Interpretation (0028,0004)

- Rows (0028,0010)

- Columns (0028,0011)

- Bits Allocated (0028,0100)

- Bits Stored (0028,0101)

- Pixel Representation (0028,0103)

For PET Series, the following Image Plane Module attributes shall not vary from Image to Image:

- Pixel Spacing (0028,0030)

For PET Series where Series Type (0054,1000), Value 2 is IMAGE, the following Image Plane Module attributes shall not vary from Image to Image:

- Image Orientation (Patient) (0020,0037)

### Note

This means that for a Series Type (0054,1000) Value 2 of IMAGE, all images in the PET Series lie on parallel planes. The images, however, may have non-uniform spacing along the normals to the planes.

For PET Series where Series Type (0054,1000), Value 2 is REPROJECTION, Image Orientation (0020,0037) shall vary such that the images rotate about a single axis. Geometrically, the normal to each image plane is defined by the cross product of its row and column vectors. Each reprojection image has one Center Normal that passes through the center of the image. Reprojection images within a PET Series shall have their Center Normals be co-planar and pass through a single point.

###### C.8.9.1.1.2 Series Date, Series Time

For PET Series, Series Date (0008,0021) and Series Time (0008,0031) are specified to be Type 1. Series Date (0008,0021) and Series Time (0008,0031) are used as the reference time for all PET Image attributes that are temporally related, including activity measurements. Series Date (0008,0021) and Series Time (0008,0031) are not tied to any real-world event (e.g., acquisition start, radiopharmaceutical administration) and their real-world meaning are implementation dependent.

###### C.8.9.1.1.3 Units

The units of the pixel values obtained after conversion from the stored pixel values (SV) (Pixel Data (7FE0,0010)) to pixel value units (U), as defined by Rescale Intercept (0028,1052) and Rescale Slope (0028,1053).

Defined Terms:

CNTS

  counts

NONE

  unitless

CM2

  centimeter**2

PCNT

  percent

CPS

  counts/second

BQML

  Becquerels/milliliter

MGMINML

  milligram/minute/milliliter

UMOLMINML

  micromole/minute/milliliter

MLMING

  milliliter/minute/gram

MLG

  milliliter/gram

1CM

  1/centimeter

UMOLML

  micromole/milliliter

PROPCNTS

  proportional to counts

PROPCPS

  proportional to counts/sec

MLMINM

  milliliter/minute/milliliter

MLML

  milliliter/milliliter

GML

  grams/milliliter

STDDEV

  standard deviations

###### C.8.9.1.1.4 Series Type

Series Type (0054,1000) Value 1 is used to identify the spatial location and temporal nature of the images within a PET Series.

Enumerated Values for Value 1:

STATIC

  a group of images at varying spatial locations at the same time

DYNAMIC

  a group of images at a set of spatial locations (e.g., slices) at varying time slices, with all spatial locations acquired at all time slices

GATED

  a group of images at the same spatial location, same starting and ending time, but acquired in different time slots of (possibly) different R-R intervals

WHOLE BODY

  same as STATIC, except covering multiple transverse fields of view (and therefore acquired at a different time)

### Note

1. Using this definition and the comments in Section C.8.9.1.1.1, here are some examples of PET series and the encoding of Series Type (0054,1000) Value 1.

   - Static acquisition: a group of n transverse images at varying superior<->inferior locations, all acquired between the same starting and ending time. Series Type = STATIC.

   - Dynamic acquisition: a group of n*m transverse images at n superior<->inferior locations, acquired with m different starting and ending times. Series Type = DYNAMIC.

   - Gated acquisition: a group of n*m*p transverse images at n superior<->inferior locations, all acquired between the same starting and ending time, acquired in m different R-R Intervals (as determined by Low R-R Value (0018,1081) and High R-R Value (0018,1082)),and acquired in p time slots of a given R-R Interval (as determined by Trigger Time (0054,1000)). Series Type = GATED.

   - Whole body acquisition: a group of n transverse images at varying superior<->inferior locations covering a significant fraction of the entire body. Series Type = WHOLE BODY.

   - Multiple transverse fields of view: a group of n transverse images at varying superior<->inferior locations. Series Type = WHOLE BODY.

   - Interleaved: group of 2*n transverse images acquired at overlapped AFOVs to increase transverse sampling. Series Type = WHOLE BODY.

   - Sagittal (Coronal, Oblique): sagittal (coronal, oblique) re-sliced images derived by reformatting transverse images. The Series Type is STATIC, DYNAMIC, GATED, or WHOLE BODY depending on source Series Type.

   - Arithmetic: images derived by an arithmetic operation on operand images. The Series Type is STATIC, DYNAMIC, GATED, or WHOLE BODY depending on source Series Type.

   - Metabolic: images derived by a metabolic model. The Series Type is STATIC, DYNAMIC, GATED, or WHOLE BODY depending on source Series Type.

2. Using this definition, here are some images that are not stored in the same PET Series:

   - Two images from the same scan that were reconstructed differently.

   - Emission and transmission images for the same Patient and Study, even if acquired simultaneously (because emission and transmission images have different reconstruction processing).

   - Two images of same patient, one after NH3 injection and one after FDG injection.

   - Two images: an original image created from reconstructed scan data and its derived image based on a metabolic model.

Series Type (0054,1000) Value 2 is used to identify the volumetric meaning of the images within a PET Series.

Enumerated Values for Value 2:

IMAGE

  a tomographic image slice

REPROJECTION

  a projection image derived from forward projection through slices of tomographic images, using the algorithm defined in Reprojection Method (0054,1004)

###### C.8.9.1.1.5 Decay Correction

Decay Correction (0054,1102) is the real-world event to which images in this Series were decay corrected. If decay correction is applied, all images in the Series shall be decay corrected to the same time.

Defined Terms:

NONE

  no decay correction

START

  acquisition start time, Acquisition Time (0008,0032)

ADMIN

  radiopharmaceutical administration time, Radiopharmaceutical Start Time (0018,1072)

The time to which images have been decay corrected can be derived from Decay Factor (0054,1321), Frame Reference Time (0054,1300), Radionuclide Half Life (0018,1075), Series Date (0008,0021) and Series Time (0008,0031).

###### C.8.9.1.1.6 Acquisition Start Condition

Acquisition Start Condition (0018,0073) is the method of starting acquisition data collection.

Defined Terms:

DENS

  preset count density (counts/sec) was reached

RDD

  preset relative count density difference (change in counts/sec) was reached

MANU

  acquisition was started manually

TIME

  preset time limit was reached

AUTO

  start automatically, when ready

TRIG

  preset number of physiological triggers was reached

###### C.8.9.1.1.7 Gantry/Detector Tilt

Gantry/Detector Tilt (0018,1120) for PET Image data is the angle in degrees of the gantry relative to the patient's major (Head to Feet) axis (or the table supporting the patient). Positive tilt is moving the top of the gantry towards the patient's feet.

###### C.8.9.1.1.8 Axial Mash

Axial Mash (0054,1201) is multi-valued and is defined as the number of unique axial Lines of Response (LOR) that were mashed together (center of the axial field of view only). Value 1 is the number of LORs mashed for an odd slice. Value 2 is the number of LORs mashed for an even slice. For discrete crystal scanners, each unique LOR corresponds to a pair of crystals. For continuous detectors whose bin size is variable, the number of LORs mashed is determined by the actual bin size divided by the Detector Element Size (0054,1203), Value 2. The value of Axial Mash (0054,1201) is the same regardless of whether the mashing was done during acquisition or reconstruction.

### Note

As an example on a discrete crystal scanner, if a ring difference of -2,0,+2 are binned as an odd slice and a ring difference of -1,+1 are binned as an even slice, then Axial Mash (0054,1201) is equal to 3\2.

###### C.8.9.1.1.9 Transverse Mash

Transverse Mash (0054,1202) is defined as the number of unique transverse Lines of Response (LOR) that were mashed together. For discrete crystal scanners, each unique LOR corresponds to a pair of crystals. For continuous detectors whose bin size is variable, the number of LORs mashed is determined by the actual bin size divided by the Detector Element Size (0054,1203), Value 1. The value of Transverse Mash (0054,1202) is the same regardless of whether the mashing was done during acquisition or reconstruction.

###### C.8.9.1.1.10 Energy Window Range Sequence

Multiple energy windows are allowed in order to allow coincidence events based on additional Energy Windows (e.g., Compton events scattered in the detector). All energy windows are assumed to contribute to all images in the PET Series.

###### C.8.9.1.1.11 Temporal Relationships of Images in PET Series

Figure C.8.9.1.1.11-1a and Figure C.8.9.1.1.11-1b show the temporal relationships of images within a PET Series.

Figure C.8.9.1.1.11-1a. Example DYNAMIC PET Series

Figure C.8.9.1.1.11-1b. Example GATED PET Series

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