C.8.19.6 Enhanced XA/XRF Image Functional Group Macros

The following sections contain Functional Group macros specific to the Enhanced XA 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.8.19.6.1 XA/XRF Frame Characteristics Macro

Table C.8.19.6-1 specifies the attributes of the XA/XRF Frame Characteristics Functional Group macro.

Table C.8.19.6-1XA/XRF FRAME CHARACTERISTICS MACRO ATTRIBUTES

Attribute Name Tag Type Attribute Description
XA/XRF Frame Characteristics Sequence (0018,9412) 1 A sequence that describes general characteristics of this frame. Only a single Item shall be included in this sequence.
>Derivation Description (0008,2111) 3 A text description of how this frame was derived. See C.8.7.1.1.5 for further explanation.
>Derivation Code Sequence (0008,9215) 3 A coded description of how this frame was derived. See C.7.6.1.1.3 for further explanation. One or more Items are permitted in this Sequence. More than one Item indicates that successive derivation steps have been applied.
>>Include ‘Code Sequence Macro’ Table 8.8-1 Defined CID 7203.
>Acquisition Device Processing Description (0018,1400) 3 Indicates any visual processing performed on the frame prior to exchange. See Section C.8.7.1.1.3.
>Acquisition Device Processing Code (0018,1401) 3 Code representing the device-specific processing associated with the frame (e.g. Organ Filtering code) Note: This Code is manufacturer specific but provides useful annotation information to the knowledgeable observer.

C.8.19.6.2 X-Ray Field of View Macro

Table C.8.19.6-2 specifies the attributes of the X-Ray Field of View Functional Group macro.

Table C.8.19.6-2X-RAY FIELD OF VIEW MACRO ATTRIBUTES

Attribute Name Tag Type Attribute Description
Field of View Sequence (0018,9432) 1 Sequence containing the field of view for this frame. Only a single item shall be included in this sequence.
>Field of View Shape (0018,1147) 3 Shape of the Field of View, that is the image pixels stored in Pixel Data (7FE0,0010). Enumerated Values: RECTANGLE ROUND HEXAGONAL
>Field of View Dimension(s) in Float (0018,9461) 3 Dimensions in mm of the Field of View, that is the image pixels stored in Pixel Data (7FE0,0010). If Field of View Shape (0018,1147) is: RECTANGLE: row dimension followed by column. ROUND: diameter. HEXAGONAL: diameter of the circle circumscribing the hexagon.
>Field of View Origin (0018,7030) 1C Offset of the TLHC of a rectangle circumscribing the Field of View, i.e., the image pixels stored in Pixel Data (7FE0,0010) before rotation or flipping, from the TLHC of the physical detector area measured in physical detector pixels as a row offset followed by a column offset. See C.8.11.4.1.1 for further explanation. Required if X-Ray Receptor Type (0018,9420) is present and equals DIGITAL_DETECTOR.
>Field of View Rotation (0018,7032) 1 Clockwise rotation in degrees of Field of View, i.e., the image pixels stored in Pixel Data (7FE0,0010), relative to the physical detector. Enumerated Values: 0, 90, 180, 270 See C.8.11.4.1.1 for further explanation.
>Field of View Horizontal Flip (0018,7034) 1 Whether or not a horizontal flip has been applied to the Field of View, i.e., the image pixels stored in Pixel Data (7FE0,0010), after rotation relative to the physical detector as described in Field of View Rotation (0018,7032). Enumerated Values: NO YES See C.8.11.4.1.1 for further explanation.
>Field of View Description (0018,9433) 3 Manufacturer defined description of the field of view selected during acquisition.

C.8.19.6.3 X-Ray Exposure Control Sensing Regions Macro

Table C.8.19.6-3 specifies the attributes that describe the region targeted as area where the x-ray dose value is estimated.

Table C.8.19.6-3X-RAY EXPOSURE CONTROL SENSING REGIONS MACRO ATTRIBUTES

Attribute Name Tag Type Attribute Description
Exposure Control Sensing Regions Sequence (0018,9434) 1 Sequence containing the Exposure Control Sensing Region for this frame. One or more items shall be included in this sequence.
>Exposure Control Sensing Region Shape (0018,9435) 1 Shape of the Exposure Control Sensing Region. Enumerated Values: RECTANGULAR CIRCULAR POLYGONAL
>Exposure Control Sensing Region Left Vertical Edge (0018,9436) 1C Required if Exposure Control Sensing Region Shape (0018,9435) is RECTANGULAR. Location of the left edge of the rectangular Exposure Control Sensing Region expressed as effective pixel column. See C.8.19.6.3.1.
>Exposure Control Sensing Region Right Vertical Edge (0018,9437) 1C Required if Exposure Control Sensing Region Shape (0018,9435) is RECTANGULAR. Location of the right edge of the rectangular Exposure Control Sensing Region expressed as effective pixel column. See C.8.19.6.3.1.
>Exposure Control Sensing Region Upper Horizontal Edge (0018,9438) 1C Required if Exposure Control Sensing Region Shape (0018,9435) is RECTANGULAR. Location of the upper edge of the rectangular Exposure Control Sensing Region expressed as effective pixel row. See C.8.19.6.3.1.
>Exposure Control Sensing Region Lower Horizontal Edge (0018,9439) 1C Required if Exposure Control Sensing Region Shape (0018,9435) is RECTANGULAR. Location of the lower edge of the rectangular Exposure Control Sensing Region expressed as effective pixel row. See C.8.19.6.3.1.
>Center of Circular Exposure Control Sensing Region (0018,9440) 1C Required if Exposure Control Sensing Region Shape (0018,9435) is CIRCULAR. Location of the center of the circular Exposure Control Sensing Region expressed as effective pixel row and column. See C.8.19.6.3.1.
>Radius of Circular Exposure Control Sensing Region (0018,9441) 1C Required if Exposure Control Sensing Region Shape (0018,9435) is CIRCULAR. Radius of the circular Exposure Control Sensing Region expressed as effective number of pixels along the row direction. See C.8.19.6.3.1.
>Vertices of the Polygonal Exposure Control Sensing Region (0018,9442) 1C Required if Exposure Control Sensing Region Shape (0018,9435) is POLYGONAL. Multiple Values where the first set of two values are: row of the origin vertex; column of the origin vertex. Two or more pairs of values follow and are the effective pixel row and column coordinates of the other vertices of the polygon Exposure Control Sensing Region. Polygon Exposure Control Sensing Regions are implicitly closed from the last vertex to the origin vertex and all edges shall be non-intersecting except at the vertices. See C.8.19.6.3.1.

C.8.19.6.3.1 X-Ray Exposure Control Sensing Regions attributes

The Exposure Control Sensing Region Left Vertical Edge (0018,9436), Exposure Control Sensing Region Right Vertical Edge (0018,9437), Exposure Control Sensing Region Upper Horizontal Edge (0018,9438), Exposure Control Sensing Region Lower Horizontal Edge (0018,9439) and Center of Circular Exposure Control Sensing Region (0018,9440) may have a negative value when the point defined by the attribute lies outside the left or upper border of the pixel data matrix. The top left pixel of the image has a pixel row and column value of 1.

C.8.19.6.4 XA/XRF Frame Pixel Data Properties Macro

Table C.8.19.6-4 specifies the attributes of the Frame Pixel Data Properties Functional Group macro.

Table C.8.19.6-4XA/XRF FRAME PIXEL DATA PROPERTIES MACRO ATTRIBUTES

Attribute Name Tag Type Attribute Description
Frame Pixel Data Properties Sequence (0028,9443) 1 Sequence containing the pixel data properties for 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 values of the Image Type (0008,0008) attribute. See C.8.19.2.1.1.
>Pixel Intensity Relationship (0028,1040) 1 The relationship between the Pixel and the X-Ray beam intensity. See C.8.19.6.4.1.1.
>Pixel Intensity Relationship Sign (0028,1041) 1 The sign of the relationship between the Pixel sample values stored in Pixel Data (7FE0,0010) and the X-Ray beam intensity. Enumerated Values: 1 = Lower pixel values correspond to less X-Ray beam intensity -1 = Higher pixel values correspond to less X-Ray beam intensity See C.8.11.3.1.2 for further explanation.
>Imager Pixel Spacing (0018,1164) 1C Physical distance measured at the receptor plane of the detector between the centers of each pixel specified by a numeric pair - row spacing value (delimiter) column spacing value in mm. See 10.7.1.3 for further explanation of the value order. The value of this attribute shall never be adjusted to account for calibration against an object of known size; Pixel Spacing (0028,0030) is specified for that purpose. It is only allowed to be adjusted to compensate for the change of the Field of View Dimension(s) in Float (0018,9461) attribute. See C.8.19.6.4.1.2 Required if Image Type (0008,0008) Value 1 equals ORIGINAL. May be present otherwise. Note: These values are the actual pixel spacing distances of the stored pixel values of an image.
>Pixel Data Area Origin Relative To FOV (0018,7036) 3 Offset of the TLHC of the image stored in Pixel Data (7FE0,0010) from the TLHC of the Field Of View Area after FOV rotation and Flip. It is measured in image stored pixels as a row offset followed by a column offset. Note: Due to the differences in image stored pixel and detector element spacing, one may expect this attribute to have non-integer values. See C.8.19.6.4.1.3.
>Pixel Data Area Rotation Angle Relative To FOV (0018,7038) 3 Angle clockwise of the row direction of the image stored in Pixel Data (7FE0,0010) relative to the row direction of the Field Of View Area after FOV rotation and Flip. It is measured in degrees. See C.8.19.6.4.1.3.
>Geometrical Properties (0028,9444) 1 Geometrical characteristics of the pixel data to indicate whether pixel spacing is uniform for all pixels or not. Enumerated Values: UNIFORM NON_UNIFORM
>Geometric Maximum Distortion (0028,9445) 2C The percentage of the maximum deviation of the pixel spacing values of images for which the geometric properties are non-uniform. Note: This attribute may be used to judge the result of measurements, 3D reconstructions, etc. Required if Geometrical Properties (0028,9444) equals NON_UNIFORM.
>Image Processing Applied (0028,9446) 1 The type or a combination of types of image processing applied to the pixel data before being stored. Defined Terms: DIGITAL_SUBTR HIGH_PASS_FILTER LOW_PASS_FILTER MULTI_BAND_FLTR FRAME_AVERAGING NONE

C.8.19.6.4.1 XA/XRF Frame Pixel Data Properties Attributes

C.8.19.6.4.1.1 Pixel Intensity Relationship

Pixel Intensity Relationship (0028,1040) shall identify the relationship of the pixel values to the X-Ray beam intensity. Defined terms are:

LIN Approximately proportional to X-Ray beam intensity.
LOG Non-linear “ Log Function”; A Pixel Intensity Relationship LUT shall be included with the image to allow it to be mapped back to its proportional value to X-Ray beam intensity.
OTHER Not proportional to X-Ray beam intensity. If a TO_LINEAR Pixel Intensity Relationship LUT item is supplied, scaling back to X-Ray beam intensity is possible. Notes: 1. When the relationship can be better defined (e.g., square root data) a more precise Defined Term can be used than OTHER. 2. Providing a TO_LINEAR Pixel Intensity Relationship LUT is encouraged.

C.8.19.6.4.1.2 Imager Pixel Spacing

The two values of the Imager Pixel Spacing (0018,1164) attribute are related to the value(s) of the Field of View Dimension(s) in Float (0018,9461) attribute in the X-Ray Field of View Functional Group of this frame and the values of the Rows (0028,0010) and Columns (0028,0011) attributes.

The value(s) of Field of View Dimension(s) in Float (0018,9461) may change on a frame by frame base. The values of the Rows and Columns attributes are equal for all frames. The relationship between the attributes depends on the Field of View Shape (0018,1147) attribute:

If the Field of View Shape (0018,1147) attribute equals RECTANGLE:

Imager Pixel Spacing row spacing = FOV Dimension row dimension / Rows

Imager Pixel Spacing column spacing = FOV Dimension column dimension / Columns

If the Field of View Shape (0018,1147) attribute equals ROUND or HEXAGONAL:

Imager Pixel Spacing row spacing = FOV Dimension diameter / Rows

Imager Pixel Spacing column spacing = FOV Dimension diameter / Columns

C.8.19.6.4.1.3 Pixel Data Area Relative to FOV

In the case where the Field of View does not have the same size as the stored Pixel Data (7FE0,0010), the stored Pixel Data (7FE0,0010) may be the result of cropping, rotation, resizing and/or padding of the Field of View. The following Attributes specify the relationship of the Pixel Data area to the Field Of View Area:

- Pixel Data Area Origin Relative to FOV (0018,7036)

- Pixel Data Area Rotation Angle Relative to FOV (0018,7038)

Note: In order to make use of the Pixel Data Area Origin Relative to FOV (0018,7036), the Imager Pixel Spacing (0018,1164) is needed.

[pic]

Figure C.8.19.6.4-1 Explanation of Pixel Data Area Attributes

C.8.19.6.5 X-Ray Frame Detector Parameters Macro

Table C.8.19.6-5 specifies the attributes containing the X-Ray Frame Detector Parameters Functional Group macro.

Table C.8.19.6-5X-RAY FRAME DETECTOR PARAMETERS MACRO ATTRIBUTES

Attribute Name Tag Type Attribute Description
Frame Detector Parameters Sequence (0018,9451) 1 Sequence containing the detector properties for this frame. Only a single Item shall be included in this sequence.
>Detector Active Time (0018,7014) 3 Time in mSec that the detector is active during acquisition of this image. Note: This activation window overlaps the time of the X-Ray exposure as defined by Exposure Time in ms (0018,9328) and Detector Activation Offset From Exposure (0018,7016).
>Detector Activation Offset From Exposure (0018,7016) 3 Offset time in mSec that the detector becomes active after the X-Ray beam is turned on during acquisition of this image. May be negative.

C.8.19.6.6 X-Ray Calibration Device Usage Macro

Table C.8.19.6-6 specifies the attributes containing the X-Ray Calibration Device Usage Functional Group macro.

Table C.8.19.6-6X-RAY CALIBRATION DEVICE USAGE MACRO ATTRIBUTES

Attribute Name Tag Type Attribute Description
Calibration Sequence (0018,9455) 1 Sequence containing the calibration flag for this frame. Only a single Item shall be included in this sequence.
>Calibration Image (0050,0004) 1 Indicates whether a reference object (phantom) of known size is present in the frame and was used for calibration. Enumerated Values: YES NO Note: Device is identified using the Device module. See C.7.6.12.

C.8.19.6.7 X-Ray Object Thickness Macro

Table C.8.19.6-7 specifies the attributes containing the X-Ray Object Thickness Group macro.

Table C.8.19.6-7X-RAY OBJECT THICKNESS MACRO ATTRIBUTES

Attribute Name Tag Type Attribute Description
Object Thickness Sequence (0018,9456) 1 Sequence containing object thickness for this frame. Only a single Item shall be included in this sequence.
>Calculated Anatomy Thickness (0018,9452) 1 The physical thickness in mm of the anatomic region of interest as specified in the Anatomic Region Sequence (0008,2218) in the direction of the center of the beam. Note: The value takes in account the position relative to object and the X-Ray source - detector axis.

C.8.19.6.8 X-Ray Frame Acquisition Macro

Table C.8.19.6-8 specifies the attributes containing the X-Ray Frame Acquisition Functional Group macro.

Table C.8.19.6-8X-RAY FRAME ACQUISITION MACRO ATTRIBUTES

Attribute Name Tag Type Attribute Description
Frame Acquisition Sequence (0018,9417) 1 Sequence containing the acquisition parameters for this frame. Only a single Item shall be included in this sequence.
>KVP (0018,0060) 1 Exact peak kilo voltage output of the X-Ray generator used for this frame.
>X-Ray Tube Current in mA (0018,9330) 1 Exact Nominal X-Ray tube current in milliamperes applied during the Acquisition Duration (0018,9220) for this frame.

C.8.19.6.8.1 X-Ray Frame Acquisition Sequence Attributes

These attribute may only be used if the information is available on a frame-by-frame base. The average values for these attributes of all frames shall be stored in the same attribute in the XA/XRF Acquisition Module (Section C.8.19.3).

C.8.19.6.9 X-Ray Projection Pixel Calibration Macro

Table C.8.19.6-9 specifies the attributes of the X-Ray Projection Pixel Calibration Functional Group macro.

Table C.8.19.6-9 X-RAY PROJECTION PIXEL CALIBRATION MACRO ATTRIBUTES

Attribute Name Tag Type Attribute Description
Projection Pixel Calibration Sequence (0018,9401) 1 A sequence that describes the geometrical position of the patient relative to the equipment. Only a single Item shall be included in this sequence.
>Distance Object to Table Top (0018,9403) 2 Distance between the anatomic region of interest of observation and table top in mm. Notes: 1.This value is always positive, the object is assumed to be above the table. 2.The value of this attribute is depending on the patient position on the tabletop (supine, left or right decubitus, etc.)
>Object Pixel Spacing in Center of Beam (0018,9404) 1C Physical distance within the anatomic region of interest in the center of the beam and perpendicular to the beam between the center of each pixel, specified by a numeric pair adjacent row spacing (delimiter) adjacent column spacing in mm. See C.8.19.6.9.2. See 10.7.1.3 for further explanation of the value order. Required if Distance Object to Table Top (0018,9403) is not empty. Note: This value is provided besides the values that are the input parameters of the calibration algorithm.
>Table Height (0018,1130) 1C The distance of the top of the patient table to the center of rotation of the source (i.e. the isocenter) in mm. A positive value indicates that the tabletop is below the isocenter. Note: All the distances are measured perpendicular to the Table Top plane. Required if Image Type (0008,0008) Value 1 is ORIGINAL, may be present otherwise.
>Beam Angle (0018,9449) 1C The equipment related angle in degrees of the X-Ray beam relative to the perpendicular to the tabletop plane. An angle from 0 to +90 degrees indicates that the X-Ray source is below the table. The valid range is 0 to +180 degrees. Required if Image Type (0008,0008) Value 1 is ORIGINAL, may be present otherwise.

C.8.19.6.9.1 Projection Calibration Method

The X-Ray Projection Pixel Calibration Macro defines the attributes needed to completely describe the specific inputs and results from projection image pixel calibration based on isocenter reference. The attributes are provided to allow usage of calibration result as well as recalibration. The below included figures illustrate the relationship of the attributes.

In these figures, the object of interest of size D (in mm) is projected on the stored image over a distance of #Px (in pixels). The pixel spacing on the stored image is called (Px . The “Source to Isocenter Distance” is called ISO . The “Source Image Receptor Distance” is called SID . The shortest distance from the tabletop plane to the Isocenter and to the object of interest are called respectively TH and TO . The angle between the X-Ray beam and the axis perpendicular to the tabletop plane is called Beam Angle . Finally, the distance from the X-Ray source to the object of interest in the direction of the X-Ray beam is called SOD and is calculated from the other distances.

(Px: Imager Pixel Spacing (0018,1164)

ISO : Source Isocenter Distance (0018,9402)

SID : Distance Source to Detector (0018,1110)

TH : Table Height (0018,1130)

TO : Distance Object to Table Top (0018,9403)

Beam Angle: Beam Angle (0018,9449)

Note: The equipment related Beam Angle attribute (0018,9449) shall be consistent with the patient oriented Positioner Primary Angle (0018,1510) and Positioner Secondary Angle (0018,1511) together with the patient orientation on the table specified in Patient Orientation Code Sequence (0054,0410) attributes.

The Figures C.8.19.6-1 and C.8.19.6-2 illustrate the usage of the attributes under the conditions laid out above.

[pic]

Figure C.8.19.6-1Project Calibration without angulation of the X-Ray beam (Beam Angle = 0)

[pic]

Figure C.8.19.6-2Project Calibration with angulation of the X-Ray beam (Beam Angle not equal 0)

C.8.19.6.9.2 Object Pixel Spacing in Center of Beam

The value provided for the Beam Angle (0018,9449) attribute shall correspond to the other attribute values within this module and according to the mathematic terms listed in section C.8.19.6.9.1.

The terms listed will result in infinite result when used with 90-degree beam angles.

It is outside the scope of this Standard to define reasonable limits for single input values in the above-mentioned terms, or to define the mathematical accuracy of applications using those terms.

Note: It may be reasonable to limit automatic calculations to a narrow range of +/- 60 degrees for Beam Angle and inform users about possible deviations in the calibration result when exceeding such range limits.

C.8.19.6.10 X-Ray Positioner Macro

Table C.8.19.6-10 specifies the attributes of the X-Ray Positioner Functional Group macro. If included into the Shared Functional Groups Sequence (5200,9229) no DYNAMIC motion was performed during acquisition. If included in the Per-frame Functional Groups Sequence (5200,9230) the indication of a DYNAMIC motion is given.

Table C.8.19.6-10 X-RAY POSITIONER MACRO ATTRIBUTES

Attribute Name Tag Type Attribute Description
Positioner Position Sequence (0018,9405) 1 A sequence that describes the geometrical position of the positioner. Only a single Item shall be included in this sequence.
>Positioner Primary Angle (0018,1510) 1C Position of the X-Ray Image Intensifier about the patient from the RAO to LAO direction where movement from RAO to vertical is positive. See C.8.7.5.1.2. Required if Positioner Type (0018,1508) equals CARM.
>Positioner Secondary Angle (0018,1511) 1C Position of the X-Ray Image Intensifier about the patient from the CAU to CRA direction where movement from CAU to vertical is positive. See C.8.7.5.1.2 Required if Positioner Type (0018,1508) equals CARM.
>Column Angulation (Patient) (0018,9447) 1C Angle of the X-Ray beam in degree relative to an orthogonal axis to the detector plane. Positive values indicate that the tilt is towards the head of the patient. Notes: 1. The detector plane is assumed to be parallel to the table plane 2. This attribute differentiates form the attribute Column Angulation (0018,1450) by using the patient based coordinate system instead of the equipment based coordinate system. Required if Positioner Type (0018,1508) equals COLUMN.

C.8.19.6.11 X-Ray Table Position Macro

Table C.8.19.6-11 specifies the attributes of the X-Ray Table Position Functional Group macro.

Table C.8.19.6-11X-RAY TABLE POSITION MACRO ATTRIBUTES

Attribute Name Tag Type Attribute Description
Table Position Sequence (0018,9406) 1 A sequence that describes the geometrical position of the table top. Only a single Item shall be included in this sequence.
>Table Top Vertical Position (300A,0128) 1 Table Top Vertical position with respect to an arbitrary chosen reference by the equipment in (mm). Table motion downwards is positive
>Table Top Longitudinal Position (300A,0129) 1 Table Top Longitudinal position with respect to an arbitrary chosen reference by the equipment in (mm). Table motion towards LAO is positive assuming that the patient is positioned supine and its head is in normal position.
>Table Top Lateral Position (300A,012A) 1 Table Top Lateral position with respect to an arbitrary chosen reference by the equipment in (mm). Table motion towards CRA is positive assuming that the patient is positioned supine and its head is in normal position.
>Table Horizontal Rotation Angle (0018,9469) 1 Rotation of the table in the horizontal plane (clockwise when looking from above the table).
>Table Head Tilt Angle (0018,9470) 1 Angle of the head-feet axis of the table in degrees relative to the horizontal plane. Positive values indicate that the head of the table is upwards.
>Table Cradle Tilt Angle (0018,9471) 1 Angle of the left-right axis of the table in degrees relative to the horizontal plane. Positive values indicate that the left of the table is upwards.

C.8.19.6.11.1 X-Ray Table Position Macro Attribute Description

The Table Top Position attributes of the Table Position Sequence (0018,9406) specify the geometrical position of the Table in the three spatial directions (i.e. Vertical, Longitudinal and Lateral) relative to the Table Top plane (see Figure C.8.19.6-3). The absolute reference point to which the Table positions are related is arbitrarily defined by the manufacturer.

The Table Angle attributes of the Table Position Sequence (0018,9406) specify the rotation and tilt of the Table Top Plane with respect to a plane arbitrarily defined by the manufacturer (usually the horizontal plane).

The Table Top Position attributes allow to describe the incremental translation of the Table top between frames of the same Multi-frame image, and between frames of different images, provided that the Table Angles are not modified between these frames.

When the table angles are modified between two frames, the Table Position Sequence (0018,9406) does not allow to characterize the relationship between the two table positions in an absolute reference coordinate system. For this purpose, the X-Ray Isocenter Reference System Macro has to be used.

Note: The incremental table translation may be used, in conjunction with the Positioner Position Sequence attributes (0018,9405), for simple 2D-2D registration applications (object tracking, pixel shift…), assuming that the patient position is fixed on the table. For more complex registration applications, and in order to properly handle the changes in the table angles, it is recommended to use the X-Ray Isocenter Reference System Macro attributes.

[pic]

Figure C.8.19.6-3Table Position Vectors

C.8.19.6.12 X-Ray Collimator Macro

Table C.8.19.6-12 specifies the attributes of the X-Ray Collimator Functional Group macro.

Table C.8.19.6-12X-RAY COLLIMATOR MACRO ATTRIBUTES

Attribute Name Tag Type Attribute Description
Collimator Shape Sequence (0018,9407) 1 A sequence that describes the collimator shape. Only a single Item shall be included in this sequence.
>Collimator Shape (0018,1700) 1 Shape(s) of the collimator. Enumerated Values: RECTANGULAR CIRCULAR POLYGONAL This multi-valued Attribute shall contain at most one of each Enumerated Value.
>Collimator Left Vertical Edge (0018,1702) 1C Required if Collimator Shape (0018,1700) is RECTANGULAR. Location of the left edge of the rectangular collimator expressed as effective pixel column. See C.8.7.3.1.1 and C.8.19.6.12.1.
>Collimator Right Vertical Edge (0018,1704) 1C Required if Collimator Shape (0018,1700) is RECTANGULAR. Location of the right edge of the rectangular collimator expressed as effective pixel column. See C.8.7.3.1.1 and C.8.19.6.12.1.
>Collimator Upper Horizontal Edge (0018,1706) 1C Required if Collimator Shape (0018,1700) is RECTANGULAR. Location of the upper edge of the rectangular collimator expressed as effective pixel row. See C.8.7.3.1.1 and C.8.19.6.12.1.
>Collimator Lower Horizontal Edge (0018,1708) 1C Required if Collimator Shape (0018,1700) is RECTANGULAR. Location of the lower edge of the rectangular collimator expressed as effective pixel row. See C.8.7.3.1.1 and C.8.19.6.12.1.
>Center of Circular Collimator (0018,1710) 1C Required if Collimator Shape (0018,1700) is CIRCULAR. Location of the center of the circular collimator expressed as effective pixel row and column. See C.8.7.3.1.1 and C.8.19.6.12.1.
>Radius of Circular Collimator (0018,1712) 1C Required if Collimator Shape (0018,1700) is CIRCULAR. Radius of the circular collimator expressed as effective number of pixels along the row direction. See C.8.7.3.1.1 and C.8.19.6.12.1.
>Vertices of the Polygonal Collimator (0018,1720) 1C Required if Collimator Shape (0018,1700) is POLYGONAL. Multiple Values where the first set of two values are: row of the origin vertex; column of the origin vertex. Two or more pairs of values follow and are the effective pixel row and column coordinates of the other vertices of the polygon collimator. Polygon collimators are implicitly closed from the last vertex to the origin vertex and all edges shall be non-intersecting except at the vertices. See C.8.19.6.12.1.

C.8.19.6.12.1 X-Ray Collimator attributes

The top left pixel of the image has a pixel row and column value of 1.

C.8.19.6.13 X-Ray Isocenter Reference System Macro

Table C.8.19.6-13 specifies the attributes of the X-Ray Isocenter Reference System Functional Group macro.

Table C.8.19.6-13 X-RAY ISOCENTER REFERENCE SYSTEM MACRO ATTRIBUTES

Attribute Name Tag Type Attribute Description
Isocenter Reference System Sequence (0018,9462) 1 A sequence that describes the Isocenter Reference Coordinate System (O, X, Y, Z). Only a single Item shall be included in this sequence.
>Positioner Isocenter Primary Angle (0018,9463) 1 Position of the X-Ray center beam in the isocenter reference system in the X direction (deg). See C.8.19.6.13.1.2 for further explanation.
>Positioner Isocenter Secondary Angle (0018,9464) 1 Position of the X-Ray center beam in the isocenter reference system in the Z direction (deg). See C.8.19.6.13.1.2 for further explanation.
>Positioner Isocenter Detector Rotation Angle (0018,9465) 1 Rotation of the X-Ray detector plane (deg). See C.8.19.6.13.1.2 for further explanation.
>Table X Position to Isocenter (0018,9466) 1 X position of the Table Reference Point with respect to the Isocenter (mm). See C.8.19.6.13.1.3 for further explanation.
>Table Y Position to Isocenter (0018,9467) 1 Y position of the Table Reference Point with respect to the Isocenter (mm). See C.8.19.6.13.1.3 for further explanation.
>Table Z Position to Isocenter (0018,9468) 1 Z position of the Table Reference Point with respect to the Isocenter (mm). See C.8.19.6.13.1.3 for further explanation.
>Table Horizontal Rotation Angle (0018,9469) 1 Rotation of the table in the horizontal plane. See C.8.19.6.13.1.3 for further explanation.
>Table Head Tilt Angle (0018,9470) 1 Angle of the head-feet axis of the table in degrees relative to the horizontal plane. See C.8.19.6.13.1.3 for further explanation.
>Table Cradle Tilt Angle (0018,9471) 1 Angle of the left-right axis of the table in degrees relative to the horizontal plane. See C.8.19.6.13.1.3 for further explanation.

C.8.19.6.13.1 Isocenter Reference System Attribute Description

The Isocenter Reference System Attributes describe the 3D geometry of the X-Ray equipment composed by the X-Ray positioner and the X-Ray table.

These attributes define three coordinate systems in the 3D space:

The Isocenter Reference System attributes describe the relationship between the 3D coordinates of a point in the table coordinate system and the 3D coordinates of such point in the positioner coordinate system (both systems moving in the equipment), by using the Isocenter coordinate system that is fixed in the equipment.

Note: PS 3.17 Annex Enhanced XA/XRF Encoding Examplesdescribes the transformations necessary to transpose between coordinate systems.

C.8.19.6.13.1.1 Isocenter Coordinate System

The Isocenter coordinate system (O,X,Y,Z) of the equipment is defined as follows:

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Figure C.8.19.6-4Isocenter Coordinate System

C.8.19.6.13.1.2 Positioner Coordinate System

The positioner coordinate system (O p , X p , Y p , Z p ) is defined as follows:

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Figure C.8.19.6-5 Positioner Coordinate System

Note: The quantities SID and ISO are specified by the attributes Distance Source to Detector (0018,1110) and Distance Source to Isocenter (0018,9402) respectively.

The Positioner coordinate system (O p , X p , Y p , Z p ) is characterized, with respect to the Isocenter coordinate system (O, X, Y, Z), by two angles describing the X-Ray center beam, and a third angle describing the rotation of the X-Ray detector plane. These angles are relative to the Isocenter reference system, and independent from the patient position on the equipment.

Positioner Isocenter Primary Angle (0018,9463) (so-called Ap 1 in Figure C.8.19.6-6) is defined in the plane XY, as the angle between the plane YZ and the plane Y p Z. The axis of rotation of this angle is the Z axis. Angle from -Y to +X is positive. The valid range of this angle is -180 to +180 degrees.

Positioner Isocenter Secondary Angle (0018,9464) (so-called Ap 2 in Figure C.8.19.6-6) is defined in the plane Y p Z, as the angle of the X-Ray Center Beam (i.e. Y p ) relative to the XY plane. The axis of rotation of this angle is perpendicular to the plane Y p Z. Angle from the plane XY to +Z is positive. The valid range of this angle is -180 to +180 degrees.

Positioner Isocenter Detector Rotation Angle (0018,9465) (so-called Ap 3 in Figure C.8.19.6-6 and in Figure C.8.19.6-7) is defined in the detector plane, as the angle of the vertical scan-lines of the detector (i.e. Z p ) relative to the intersection between the detector plane and the plane Y p Z. The sign of this angle is positive clockwise when facing on to the detector plane (see Figure C.8.19.6-7). The valid range of this angle is -180 to +180 degrees.

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Figure C.8.19.6-6Positioner Isocenter Angles

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Figure C.8.19.6-7Positioner Isocenter Detector Rotation Angle when Ap 1 =0 and Ap 2 =0

C.8.19.6.13.1.3 Table Coordinate System

The table coordinate system (O t , X t , Y t , Z t ) is defined as follows:

The table coordinate system (O t , X t , Y t , Z t ) is characterized, with respect to the Isocenter coordinate system (O, X, Y, Z), by a 3D translation and 3 angles describing the tilting and rotation:

Table X Position to Isocenter (0018,9466) (so-called T X in Figure C.8.19.6-8) is defined as the translation of the Table Reference Point O t with respect to the Isocenter coordinate system in the X direction. Table motion toward +X is positive.

Table Y Position to Isocenter (0018,9467) (so-called T Y in Figure C.8.19.6-8) is defined as the translation of the Table Reference Point O t with respect to the Isocenter coordinate system in the Y direction. Table motion toward +Y is positive.

Table Z Position to Isocenter (0018,9468) (so-called T Z in Figure C.8.19.6-8) is defined as the translation of the Table Reference Point O t with respect to the Isocenter coordinate system in the Z direction. Table motion toward +Z is positive.

Note: A translation of ( T X, T Y, T Z ) = (0, 0, 0) means that the Table Reference Point O t is at the System Isocenter.

Table Horizontal Rotation Angle (so-called At 1 in Figure C.8.19.6-9) is defined in the horizontal plane XZ, as the angle of the projection of the +Zt axis in the XZ plane relative to the +Z axis. The axis of rotation of this angle is the vertical axis crossing the Table Reference Point Ot. Zero value is defined when the projection of +Zt in the XZ plane is equal to +Z. Angle from +Z to +X is positive. The valid range of this angle is -180 to +180 degrees.

Table Head Tilt Angle (so-called At 2 in Figure C.8.19.6-9) is defined in the vertical plane containing Z t (i.e. YZ t ), as the angle of the +Z t axis relative to the horizontal plane XZ. The axis of rotation of this angle is defined as the intersection between the horizontal plane XZ and the plane X t Y t . Zero value is defined when +Z t is contained in the horizontal plane XZ. Angle from horizontal (plane XZ) to -Y direction (upwards) is positive, indicating that the head of the table is above the horizontal plane. The valid range of this angle is -45 to +45 degrees.

Table Cradle Tilt Angle (so-called At 3 in Figure C.8.19.6-9) is defined in the X t Y t plane, as the angle of the +X t axis relative to the intersection between the X t Y t plane and the horizontal plane XZ. The axis of rotation of this angle is the axis Z t . Zero value is defined when +X t is contained in the horizontal plane XZ. Angle from horizontal (plane XZ) to -Y direction (upwards) is positive, indicating that the left of the table is above the horizontal plane. The valid range of this angle is -45 to +45 degrees.

Note: The angles At 1 , At 2 and At 3 are independent from any specific mechanical design of the table rotation axis defined by a manufacturer. In particular, they don’t require the three rotation axis to cross on a single point. If a mechanical rotation axis does not cross the Table Reference Point O t , a mechanical rotation around this axis will generate a change in one or more table angles as well as a translation of the Table Reference Point.

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Figure C.8.19.6-8 Table Translation with respect to the Isocenter Reference System

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Figure C.8.19.6-9 Table Angulations with respect to the Isocenter Reference System

C.8.19.6.13.2 Relationship Patient Coordinate System

The Isocenter Reference System attributes allow expressing the positioner angulations (i.e. X-Ray Center Beam direction) as a vector in the table coordinate system. If the relationship between the X-Ray table and the patient is known, it is possible to express any vector of the table coordinate system as a direction in the patient.

Therefore, the Isocenter Reference System attributes allow calculating the positioner angulations in the patient-based coordinate system if the following attributes are present:

Further, the Isocenter Reference System attributes allow calculating the patient anatomical directions (i.e. left, right, head, feet, anterior, posterior) of the rows and columns of the stored image, if the following attributes are present:

For registration purposes, a given point fixed in the patient (object of interest) that is defined in the table coordinate system can be expressed as row and column coordinates of the stored image if the relationship between the positioner coordinate system and the stored image is fully characterized. Therefore, the Isocenter Reference System attributes allow calculating the projection of a point of the patient as row and column coordinates of the stored image, if the following attributes are present:

In addition for a system equipped with a digit al detector the following attributes need to be present:

C.8.19.6.14 X-Ray Geometry Macro

Table C.8.19.6-14 specifies the attributes containing the X-Ray Geometry Functional Group macro.

Table C.8.19.6-14X-RAY GEOMETRY MACRO ATTRIBUTES

Attribute Name Tag Type Attribute Description
X-Ray Geometry Sequence (0018,9476) 1 Sequence containing the geometric properties for this frame. Only a single Item shall be included in this sequence.
>Distance Source to Isocenter (0018,9402) 1 Distance from source to isocenter in mm.
>Distance Source to Detector (0018,1110) 1 Distance from source to receptor plane perpendicular to the receptor plane in mm. Note: This value is traditionally referred to as Source Image Receptor Distance (SID).