C.8.15.3 Enhanced CT Image Functional Group Macros

The following sections contain Functional Group macros specific to the Enhanced CT Image IOD.

Note: The attribute descriptions in the Functional Group Macros are written as if they were applicable to a single frame (i.e., the macro is part of the Per-frame Functional Groups Sequence). If an attribute is applicable to all frames (i.e. the macro is part of the Shared Functional Groups Sequence) the phrase "this frame" in the attribute description shall be interpreted to mean " for all frames".

C.8.15.3.1 CT Image Frame Type Macro

Table C.8-117 specifies the attributes of the CT Image Frame Type Functional Group macro.

Table C.8-117CT IMAGE FRAME TYPE MACRO ATTRIBUTES

Attribute Name Tag Type Attribute Description
CT Image Frame Type Sequence (0018,9329) 1 Identifies the characteristics of this frame. Only a single Item shall be included in this sequence.
>Frame Type (0008,9007) 1 Type of Frame. A multi-valued attribute analogous to the Image Type (0008,0008). Enumerated Values and Defined Terms are the same as those for the four values of the Image Type (0008,0008) attribute, except that the value MIXED is not allowed. See sections C.8.16.1 and C.8.15.2.1.1.1.
>Include Common CT/MR Image Description Macro' Table C.8-131

C.8.15.3.2 CT Acquisition Type Macro

Table C.8-118 specifies the attributes of the CT Acquisition Type Functional Group macro.

Table C.8-118CT ACQUISITION TYPE MACRO ATTRIBUTES

Attribute Name Tag Type Attribute Description
CT Acquisition Type Sequence (0018,9301) 1 Contains the attributes defining the CT acquisition mode. Only a single Item shall be included in this sequence.
>Acquisition Type (0018,9302) 1C Description of the method used during acquisition of this frame. See C.8.15.3.2.1 for Defined Terms. Required if Frame Type (0008,9007) Value 1 of this frame is ORIGINAL. May be present otherwise.
>Tube Angle (0018,9303) 1C The constant angle at which the x-ray source is located during acquisition. 0 degrees means that the source is located at the highest point of the gantry orbit. Degrees increase from 0 to positive 360 in a clockwise direction as viewed when facing the gantry where the table enters the gantry. Required if Frame Type (0008,9007) Value 1 of this frame is ORIGINAL and Acquisition Type (0018,9302) is CONSTANT_ANGLE. May be present otherwise if Frame Type (0008,9007) Value 1 of this frame is DERIVED and Acquisition Type (0018,9302) is CONSTANT_ANGLE.
>Constant Volume Flag (0018,9333) 1C Identifies that the acquisition was performed by repetitively acquiring the same volume set over a period of time. Note: The Acquisition Type (0018,9302) value may be SEQUENCED, SPIRAL or STATIONARY depending on whether table movement is necessary to cover the volume. Enumerated Values YES NO Required if Frame Type (0008,9007) Value 1 of this frame is ORIGINAL. May be present otherwise.
>Fluoroscopy Flag (0018,9334) 1C Identifies that near real-time display of a block of continuously acquired data was performed, which may result in a lower than usual image quality. Enumerated Values YES NO Required if Frame Type (0008,9007) Value 1 of this frame is ORIGINAL. May be present otherwise.

C.8.15.3.2.1 Acquisition Type

Acquisition Type (0018,9302) has the following Defined Terms:

SEQUENCED identifies that the acquisition was performed by acquiring single or multi detector data while rotating the source about the gantry while the table is not moving. Additional slices are acquired by incrementing the table position and again rotating the source about the gantry while the table is not moving.

SPIRAL identifies that the acquisition was performed by acquiring data while rotating the source about the gantry while continuously moving the table.

CONSTANT_ANGLE identifies that the acquisition was performed by holding the source at a constant angle and moving the table to obtain a projection image (e.g., a localizer image).

STATIONARY identifies that the acquisition was performed by holding the table at a constant position and acquiring multiple slices over time at the same location.

FREE identifies that the acquisition was performed while rotating the source about the gantry while the table movement is under direct control of a human operator or under the control of an analysis application (e.g., fluoroscopic image).

C.8.15.3.3 CT Acquisition Details Macro

Table C.8-119 specifies the attributes of the CT Acquisition Details Functional Group macro.

Table C.8-119CT ACQUISITION DETAILS MACRO ATTRIBUTES

Attribute Name Tag Type Attribute Description
CT Acquisition Details Sequence (0018,9304) 1 Contains the attributes defining the details of the acquisition. Only a single Item shall be included in this sequence.
>Rotation Direction (0018,1140) 1C Direction of rotation of the source about the gantry, as viewed while facing the gantry where the table enters the gantry. Enumerated Values: CW = clockwise CC = counter clockwise Required if Frame Type (0008,9007) Value 1 of this frame is ORIGINAL and Acquisition Type (0018,9302) is other than CONSTANT_ANGLE. Otherwise may be present if Frame Type (0008,9007) Value 1 of this frame is DERIVED and Acquisition Type (0018,9302) is other than CONSTANT_ANGLE.
>Revolution Time (0018,9305) 1C The time in seconds of a complete revolution of the source around the gantry orbit. This value is independent of the Reconstruction Angle (0018,9319) of the frame. Required if Frame Type (0008,9007) Value 1 of this frame is ORIGINAL and Acquisition Type (0018,9302) is other than CONSTANT_ANGLE. Otherwise may be present if Frame Type (0008,9007) Value 1 of this frame is DERIVED and Acquisition Type (0018,9302) is other than CONSTANT_ANGLE.
>Single Collimation Width (0018,9306) 1C The width of a single row of acquired data (in mm). Note: Adjacent physical detector rows may have been combined to form a single effective acquisition row. Required if Frame Type (0008,9007) Value 1 of this frame is ORIGINAL. May be present otherwise.
>Total Collimation Width (0018,9307) 1C The width of the total collimation (in mm) over the area of active x-ray detection. Note: This will be equal to the number of effective detector rows multiplied by single collimation width. Required if Frame Type (0008,9007) Value 1 of this frame is ORIGINAL. May be present otherwise.
>Table Height (0018,1130) 1C The distance in mm from the top of the patient table to the center of rotation of the source (i.e. the data collection center or isocenter). The distance is positive when the table is below the data collection center. Required if Frame Type (0008,9007) Value 1 of this frame is ORIGINAL. May be present otherwise.
>Gantry/Detector Tilt (0018,1120) 1C Nominal angle of tilt in degrees of the scanning gantry. Not intended for mathematical computations. Zero degrees means the gantry is not tilted, negative degrees are when the top of the gantry is tilted away from where the table enters the gantry. Required if Frame Type (0008,9007) Value 1 of this frame is ORIGINAL. May be present otherwise.
>Data Collection Diameter (0018,0090) 1C The diameter in mm of the region over which data were collected. See C.8.15.3.6.1. Note: In the case of an Acquisition Type (0018,9302) of CONSTANT_ANGLE, the diameter is that in a plane normal to the central ray of the diverging X-Ray beam as it passes through the data collection center. Required if Frame Type (0008,9007) Value 1 of this frame is ORIGINAL. May be present otherwise.

C.8.15.3.4 CT Table Dynamics Macro

Table C.8-120 specifies the attributes of the CT Table Dynamics Functional Group macro.

Table C.8-120CT TABLE DYNAMICS MACRO ATTRIBUTES

Attribute Name Tag Type Attribute Description
CT Table Dynamics Sequence (0018,9308) 1 Contains the attributes defining the movement of the CT table. Only a single Item shall be included in this sequence.
>Table Speed (0018,9309) 1C The distance in mm that the table moves in one second during the gathering of data that resulted in this frame. Required if Frame Type (0008,9007) Value 1 of this frame is ORIGINAL and Acquisition Type (0018,9302) is SPIRAL or CONSTANT_ANGLE. May be present otherwise if Frame Type (0008,9007) Value 1 of this frame is DERIVED and Acquisition Type (0018,9302) is SPIRAL or CONSTANT_ANGLE.
>Table Feed per Rotation (0018,9310) 1C Motion of the table (in mm) during a complete revolution of the source around the gantry orbit. Required if Frame Type (0008,9007) Value 1 of this frame is ORIGINAL and Acquisition Type (0018,9302) is SPIRAL. May be present otherwise if Frame Type (0008,9007) Value 1 of this frame is DERIVED and Acquisition Type (0018,9302) is SPIRAL.
>Spiral Pitch Factor (0018,9311) 1C Ratio of the Table Feed per Rotation (0018,9310) to the Total Collimation Width (0018,9307). See C.8.15.3.4.1 for further explanation and some examples. Required if Frame Type (0008,9007) Value 1 of this frame is ORIGINAL and Acquisition Type (0018,9302) is SPIRAL. May be present otherwise if Frame Type (0008,9007) Value 1 of this frame is DERIVED and Acquisition Type (0018,9302) is SPIRAL.

C.8.15.3.4.1 Spiral Pitch Factor

The formula for Spiral Pitch Factor (0018,9311) in terms of Table Feed per Rotation (0018,9310) and Total Collimation Width (0018,9307) is:

Spiral Pitch Factor = (Table Feed per Rotation (mm))/(Total Collimation Width (mm))

An example calculation of Spiral Pitch Factor (0018,9311) for a single slice spiral acquisition of an image with a Total Collimation Width of 2.5mm and a Table Feed per Rotation of 10mm is:

Spiral Pitch Factor = (10 mm)/(2.5 mm) = 4.0

An example calculation of Spiral Pitch Factor (0018,9311) for a multiple slice spiral acquisition having a Total Collimation Width of 20mm and a Table Feed per Rotation of 10mm is:

Spiral Pitch Factor = (10 mm)/(20 mm) = 0.5

C.8.15.3.5 CT Position Macro

Table C.8-121 specifies the attributes of the CT Position Functional Group macro.

Table C.8-121CT POSITION MACRO ATTRIBUTES

Attribute Name Tag Type Attribute Description
CT Position Sequence (0018,9326) 1 Contains the attributes defining the CT geometry. Only a single Item shall be included in this sequence.
>Table Position (0018,9327) 1C Relative longitudinal position of acquisition location of this frame in mm from an implementation specific reference point. Shall be relative to the same reference point for all frames in this SOP Instance, but may be different from the reference point in other SOP Instances. Positions as the table moves into the gantry viewed from the front are more negative. Notes: 1. For contiguous slices reconstructed from multiple detectors one would expect different values for adjacent slices. 2. Lateral positioning or tilting or swiveling are not described. Required if Frame Type (0008,9007) Value 1 of this frame is ORIGINAL. May be present otherwise.
>Data Collection Center (Patient) (0018,9313) 1C The x, y, and z coordinates (in the patient coordinate system) in mm of the center of the region in which data were collected. See C.8.15.3.6.1. Required if Frame Type (0008,9007) Value 1 of this frame is ORIGINAL. May be present otherwise.
>Reconstruction Target Center (Patient) (0018,9318) 1C The x, y, and z coordinates (in the patient coordinate system) of the reconstruction center target point as used for reconstruction in mm. See C.8.15.3.6.1. Note: If the reconstructed image is not magnified or panned the value corresponds with the Data Collection Center (0018,9313) attribute. Required if Frame Type (0008,9007) Value 1 of this frame is ORIGINAL. May be present otherwise.

C.8.15.3.6 CT Geometry Macro

Table C.8-122 specifies the attributes of the CT Geometry Functional Group macro.

Table C.8-122CT GEOMETRY MACRO ATTRIBUTES

Attribute Name Tag Type Attribute Description
CT Geometry Sequence (0018,9312) 1 Contains the attributes defining the CT geometry. Only a single Item shall be included in this sequence.
>Distance Source to Detector (0018,1110) 1C Distance in mm from source to detector center. See C.8.15.3.6.1. Note: This value is traditionally referred to as Source Image Receptor Distance (SID). Required if Frame Type (0008,9007) Value 1 of this frame is ORIGINAL. May be present otherwise.
>Distance Source to Data Collection Center (0018,9335) 1C Distance in mm from source to data collection center. See C.8.15.3.6.1. Required if Frame Type (0008,9007) Value 1 of this frame is ORIGINAL. May be present otherwise.

C.8.15.3.6.1 Relationships Between CT Geometric Attributes (Informative)

In Figure C.8-19 the relationship of the Geometric Attributes within the CT Geometry and CT Reconstruction functional groups is shown. The figure, viewed from the front of the gantry (where the table enters the gantry), is informative only and is not meant to represent a standardization of an equipment-based frame of reference.

[pic] Figure C.8-19: Geometry of CT Acquisition System

C.8.15.3.7 CT Reconstruction Macro

Table C.8-123 specifies the attributes of the CT Reconstruction Functional Group macro.

Table C.8-123CT RECONSTRUCTION MACRO ATTRIBUTES

Attribute Name Tag Type Attribute Description
CT Reconstruction Sequence (0018,9314) 1 Contains the attributes holding information about the reconstruction techniques used. Only a single Item shall be included in this sequence.
>Reconstruction Algorithm (0018,9315) 1C Description of the algorithm used when reconstructing the image from the data acquired during the acquisition process. Defined Terms: FILTER_BACK_PROJ ITERATIVE Required if Frame Type (0008,9007) Value 1 of this frame is ORIGINAL. May be present otherwise.
>Convolution Kernel (0018,1210) 1C A label describing the convolution kernel or algorithm used to reconstruct the data. A single value shall be present. Required if Frame Type (0008,9007) Value 1 of this frame is ORIGINAL. May be present otherwise.
>Convolution Kernel Group (0018,9316) 1C A label describing the group that the Convolution Kernel (0018,1210) belongs. Defined Terms: BRAIN SOFT_TISSUE LUNG BONE CONSTANT_ANGLE Required if Convolution Kernel (0018,1210) is present. May be present otherwise.
>Reconstruction Diameter (0018,1100) 1C The diameter in mm of the region from which data were used in creating the reconstruction of the image. Data may exist outside this region and portions of the patient may exist outside this region. See C.8.15.3.6.1. Required if Frame Type (0008,9007) Value 1 of this frame is ORIGINAL and Reconstruction Field of View (0018,9317) is not present. Otherwise may be present if Frame Type (0008,9007) Value 1 of this frame is DERIVED and Reconstruction Field of View (0018,9317) is not present.
>Reconstruction Field of View (0018,9317) 1C The field of view width (x-dimension) followed by height (y-dimension) as used for reconstruction in mm. Required if Frame Type (0008,9007) Value 1 of this frame is ORIGINAL and Reconstruction Diameter (0018,1100) is not present. Otherwise may be present if Frame Type (0008,9007) Value 1 of this frame is DERIVED and Reconstruction Diameter (0018,1100) is not present.
>Reconstruction Pixel Spacing (0018,9322) 1C Physical distance in the patient between the center of each reconstructed pixel, specified by a numeric pair - adjacent row spacing (delimiter) adjacent column spacing in mm. See 10.7.1.3 for further explanation of the value order. Required if Frame Type (0008,9007) Value 1 of this frame is ORIGINAL. May be present otherwise.
>Reconstruction Angle (0018,9319) 1C Angle (in degrees) over which the data from which the frame was reconstructed was collected, where 360 degrees signifies a complete revolution of the source around the gantry orbit. It is possible, in the case of over-scanning that the Reconstruction Angle is greater than 360 degrees. Shall be 0 if Acquisition Type (0018,9302) is CONSTANT_ANGLE. Required if Frame Type (0008,9007) Value 1 of this frame is ORIGINAL. May be present otherwise.
>Image Filter (0018,9320) 1C A label describing the filter applied to the reconstructed image after the original reconstruction has been completed. Note: When Frame Type (0008,9007) Value 1 of this frame is DERIVED and Frame Type (0008,9007) Value 4 is FILTERED the type of filtration is described in Derivation Image Macro. Required if Frame Type (0008,9007) Value 1 of this frame is ORIGINAL.

C.8.15.3.8 CT Exposure Macro

Table C.8-124 specifies the attributes of the CT Exposure Functional Group macro.

Table C.8-124CT EXPOSURE MACRO ATTRIBUTES

Attribute Name Tag Type Attribute Description
CT Exposure Sequence (0018,9321) 1 Contains the attributes defining exposure information. Only a single Item shall be included in this sequence.
>Exposure Time in ms (0018,9328) 1C Duration of exposure for this frame in milliseconds. If Acquisition Type (0018,9302) equals SPIRAL the duration of the exposure time for this frame shall be the Revolution Time (0018,9305) divided by the Spiral Pitch Factor (0018,9311). See C.8.15.3.8.1. Required if Frame Type (0008,9007) Value 1 of this frame is ORIGINAL. May be present otherwise.
>X-Ray Tube Current in mA (0018,9330) 1C Nominal X-Ray tube current in milliamperes. Required if Frame Type (0008,9007) Value 1 of this frame is ORIGINAL. May be present otherwise.
>Exposure in mAs (0018,9332) 1C The exposure expressed in milliampere seconds, for example calculated from exposure time and X-Ray tube current. Required if Frame Type (0008,9007) Value 1 of this frame is ORIGINAL. May be present otherwise.
>Exposure Modulation Type (0018,9323) 1C A label describing the type of exposure modulation used for the purpose of limiting the dose. Defined Terms: NONE Required if Frame Type (0008,9007) Value 1 of this frame is ORIGINAL. May be present otherwise.
>Estimated Dose Saving (0018,9324) 2C A percent value of dose saving due to the use of Exposure Modulation Type (0018,9323). A negative percent value of dose savings reflects an increase of exposure. Required if Frame Type (0008,9007) Value 1 of this frame is ORIGINAL and Exposure Modulation Type (0018,9323) is not equal to NONE. Otherwise may be present if Frame Type (0008,9007) Value 1 of this frame is DERIVED and Exposure Modulation Type (0018,9323) is not equal to NONE.
>CTDIvol (0018,9345) 2C Computed Tomography Dose Index (CTDIvol), in mGy according to IEC 60601-2-44, Ed.2.1 (Clause 29.1.103.4), The Volume CTDIvol. It describes the average dose for this frame for the selected CT conditions of operation. Required if Frame Type (0008,9007) Value 1 of this frame is ORIGINAL. May be present otherwise.
>CTDI Phantom Type Code Sequence (0018,9346) 3 The type of phantom used for CTDI measurement according to IEC 60601-2-44. Only a single Item is permitted in this Sequence.
>>Include Code Sequence Macro Table 8.8-1 Defined CID 4052

Note: The dose that a patient receives in a given procedure may be reported in one or more instances of the Radiation Dose Report SOP Class using the CT Radiation Dose Template TID 10011.

C.8.15.3.8.1 Exposure Time in ms Attribute (Informative)

An example of how the value of Exposure Time in ms (0018,9328) can be calculated:

The Exposure Time T exposuretime of a volume shall be the time of the X-Ray radiation in position with this volume. It depends on the travel speed and the total collimation width.

T exposuretime of the volume represented by a distinguished frame of a Spiral Scan can be calculated as follows:

T exposuretime = N x S / V travelspeed

CT pitchfactor = DD / N x S

V travelspeed = DD / T revolutiontime

From this the exposure time can be derived:

T exposuretime = N x S x T revolutiontime / DD = T revolutiontime / CT pitchfactor

Legend:

DD = Table Feed per Rotation (0018,9310) in mm distance moved by the patient support in the z direction per 360 o revolution in Spiral scanning

S = collimation of a single slice in mm

N = number slices

N x S = Total Collimation Width (0018,9307) in mm

V travelspeed = Table Speed (0018,9309) in mm/second, travel speed of the patient table

T revolutiontime = Revolution time (0018,9305) in seconds

CT pitchfactor = Spiral Pitch Factor (0018,9311)

C.8.15.3.9 CT X-Ray Details Macro

Table C.8-125 specifies the attributes of the CT X-Ray Details Functional Group macro.

Table C.8-125CT X-RAY DETAILS SEQUENCE MACRO ATTRIBUTES

Attribute Name Tag Type Attribute Description
CT X-Ray Details Sequence (0018,9325) 1 Contains the attributes defining the x-ray information. Only a single Item shall be included in this sequence.
>KVP (0018,0060) 1C Peak kilo voltage output of the x-ray generator used. Required if Frame Type (0008,9007) Value 1 of this frame is ORIGINAL. May be present otherwise.
>Focal Spot(s) (0018,1190) 1C Used nominal size of the focal spot in mm. The attribute may only have one or two values, for devices with variable focal spot, small dimension followed by large dimension Required if Frame Type (0008,9007) Value 1 of this frame is ORIGINAL. May be present otherwise.
>Filter Type (0018,1160) 1C Type of filter(s) inserted into the X-Ray beam. Defined Terms: WEDGE BUTTERFLY MULTIPLE FLAT SHAPED NONE Note: Multiple type of filters can be expressed by a combination, e.g., BUTTERFLY+WEDGE. Required if Frame Type (0008,9007) Value 1 of this frame is ORIGINAL. May be present otherwise.
>Filter Material (0018,7050) 1C The X-Ray absorbing material used in the filter. May be multi-valued. Defined Terms: MOLYBDENUM ALUMINUM COPPER RHODIUM NIOBIUM EUROPIUM LEAD MIXED Note: MIXED may be used to indicate a filter type of complex composition for which listing the individual materials would be excessive or undesirable; it is not intended to mean “unknown”. Required if Frame Type (0008,9007) Value 1 of this frame is ORIGINAL and the value of Filter Type (0018,1160) is other than NONE. May be present otherwise.
>Calcium Scoring Mass Factor Patient (0018,9351) 3 The calibration factor for the calcium mass score. These factors incorporate the effects of KV value of the CT image the patient size. machine specific corrections See C.8.2.1.1.7.
>Calcium Scoring Mass Factor Device (0018,9352) 3 The calibration factors for the calcium mass score of the device. These factors incorporate the effects of KV value of the CT image machine specific corrections This a multi-value attribute, the first value specifies the mass factor for a small patient size, the second value for a medium patient size and the third value for a large patient size. See C.8.2.1.1.7.
>Energy Weighting Factor (0018,9353) 1C The weighting factor of the data from the primary source in a multiple energy composition image. This factor incorporates the effects of the specific X-Ray source and kV value examination specific characteristics. Required if Required if Frame Type (0008,9007) Value 4 of this frame is ENERGY_PROP_WT. May be present otherwise.

C.8.15.3.10 CT Pixel Value Transformation Macro

Table C.8-126 specifies the attributes of the CT Pixel Value Transformation Functional Group macro.

Notes: 1. This Macro is equivalent to the Modality LUT transformation in non Multi-frame IODs.

2. This in effect specializes the C.7.6.16.2.9 Pixel Value Transformation Macro.

Table C.8-126CT PIXEL VALUE TRANSFORMATION MACRO ATTRIBUTES

Attribute Name Tag Type Attribute Description
Pixel Value Transformation Sequence (0028,9145) 1 Contains the attributes involved in the transformation of stored pixel values. Only a single Item shall be included in this sequence.
>Rescale Intercept (0028,1052) 1 The value b in relationship between stored values (SV) and the output units. Output units = m*SV + b.
>Rescale Slope (0028,1053) 1 m in the equation specified by Rescale Intercept (0028,1052).
>Rescale Type (0028,1054) 1 Specifies the output units of Rescale Slope (0028,1053) and Rescale Intercept (0028,1052). See C.11.1.1.2 for further explanation. If Frame Type (0008,9007) Value 1 of this frame is ORIGINAL and Frame Type (0008,9007) Value 3 is not LOCALIZER, the value shall be HU (Hounsfield Units).

C.8.15.3.11 CT Additional X-Ray Source Macro

Table C.8-126b specifies the attributes of the CT Additional X-Ray Source Macro. This sequence may be multi-valued, depending on the number of additional active X-Ray sources. It defines the X-Ray source parameters beyond the basic system.

Table C.8-126bCT ADDITIONAL X-RAY SOURCE MACRO ATTRIBUTES

Attribute Name Tag Type Attribute Description
CT Additional X-Ray Source Sequence (0018,9360) 1 Contains the attributes defining the data acquisition in a multiple X-Ray source system beyond the primary source. The primary X-Ray source is specified in the CT X-Ray Details Sequence. One or more Items shall be included in this sequence.
>kVP (0018,0060) 1 Peak kilo voltage output of the X-Ray generator used.
>X-Ray Tube Current in mA (0018,9330) 1 Nominal X-Ray tube current in milliamperes.
>Data Collection Diameter (0018,0090) 1 The diameter in mm of the region over which data were collected.
>Focal Spot(s) (0018,1190) 1 Used nominal size of the focal spot in mm.
>Filter Type (0018,1160) 1 Type of filter(s) inserted into the X-Ray beam. See Section C.8.15.3.9.
>Filter Material (0018,7050) 1 The X-Ray absorbing material used in the filter.
>Exposure in mAs (0018,9332) 1 The exposure expressed in milliampere seconds, for example calculated from exposure time and X-Ray tube current.
>Energy Weighting Factor (0018,9353) 1C The weighting factor of the data from this additional source in a multiple energy composition image. This factor incorporates the effects of the specific X-Ray source and kV value examination specific characteristics. Required if Required if Frame Type (0008,9007) Value 4 of this frame is ENERGY_PROP_WT. May be present otherwise.