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 C.220.127.116.11.2 for specialization.|
|Series Time||(0008,0031)||1||Time the Series started. See C.18.104.22.168.2 for specialization.|
|Units||(0054,1001)||1||Pixel value units. See C.22.214.171.124.3 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 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 and SUVlbm both 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 which are used during reconstruction correction. Enumerated Values: EMISSION TRANSMISSION|
|Series Type||(0054,1000)||1||A multi-valued indicator of the type of Series. See C.126.96.36.199.4 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 C.188.8.131.52.5 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 C.184.108.40.206.6 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 C.220.127.116.11.3 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 C.18.104.22.168.7 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 C.22.214.171.124.8 for explanation.|
|Transverse Mash||(0054,1202)||3||Number of adjacent transverse lines of response mashed together. See C.126.96.36.199.9 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 C.188.8.131.52.10 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|
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.
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, the Image Orientation (0020,0037) attribute 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.
For PET Series, Series Date (0008,0021) and Series Time (0008,0031) are specified to be Type 1. The 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. The 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.
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 MLMINML = milliliter/minute/milliliter MLML = milliliter/milliliter GML = grams/milliliter STDDEV = standard deviations
The Series Type (0054,1000), Value 1 is used to identify the spatial location and temporal nature of the images within a PET Series. The Enumerated Values and their definitions are:
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).
Notes: 1. Using this definition and the comments in C.184.108.40.206.1, 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.
The Series Type (0054,1000), Value 2 is used to identify the volumetric meaning of the images within a PET Series. The Enumerated Values and their definitions are:
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).
The 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. The Defined Terms and definitions are:
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).
Acquisition Start Condition (0018,0073) is the method of starting acquisition data collection. The Defined Terms and definitions are:
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
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.
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 the Axial Mash (0054,1201) is equal to 3\2 .
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.
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.
The following diagram shows the temporal relationships of images within a PET Series.