FFF.2.1.5.3 Encoding details

This section provides detailed recommendations of the key attributes to address this particular scenario.

Table FFF.2. 1-40 ENHANCED X-RAY ANGIOGRAPHIC IMAGE IOD MODULES

IE Module PS 3.3 Reference Usage
Image XA/XRF Acquisition C.8.19.3 Specifies the type of detector.
X-Ray Image Intensifier C.8.19.4 Conditional to type of detector. Applicable in case of IMG_INTENSIFIER.
X-Ray Detector C.8.19.5 Conditional to type of detector. Applicable in case of DIGITAL_DETECTOR.

Table FFF.2. 1-41 ENHANCED XA IMAGE FUNCTIONAL GROUP MACROS

Functional Group Macro PS 3.3 Reference Usage
X-Ray Field of View C.8.19.6.2 Specifies the field of view.
XA/XRF Frame Pixel Data Properties C.8.19.6.4 Specifies the Imager Pixel Spacing.

FFF.2.1.5.3.1 XA/XRF Acquisition Module Recommendations

The usage of this module is recommended to specify the type and details of the receptor.

Table FFF.2.1-42 XA/XRF ACQUISITION MODULE Recommendations

Attribute Name Tag Comment
X-Ray Receptor Type (0018,9420) Two values are applicable to this scenario: IMG_INTENSIFIER or DIGITAL_DETECTOR
Distance Receptor Plane to Detector Housing (0018,9426) Applicable to this scenario, regardless the type of receptor.

Distance Receptor Plane to Detector Housing (0018,9426) is a positive value except in the case of an image intensifier where the receptor plane is a virtual plane located outside the detector housing, which depends on the magnification factor of the intensifier.

The Distance Receptor Plane to Detector Housing (0018,9426) may be used to calculate the pixel size of the plane in the patient when markers are placed on the detector housing.

FFF.2.1.5.3.2 X-Ray Image Intensifier Module Recommendations

When the X-Ray Receptor Type (0018,9420) equals “IMG_INTENSIFIER” this module specifies the type and characteristics of the image intensifier.

[pic]

Figure FFF.2.1-23Schema of the Image Intensifier

The Intensifier Size (0018,1162) is defined as the physical diameter of the maximum active area of the image intensifier. The active area is the region of the input phosphor screen that is projected on the output phosphor screen. The image intensifier device may be configured for several predefined active areas to allow different levels of magnification.

The active area is described by the Intensifier Active Shape (0018,9427) and the Intensifier Active Dimension(s) (0018,9428).

The field of view area is a region equal to or smaller than the active area, and is defined as the region that is effectively irradiated by the X-Ray beam when there is no collimation. The stored image is the image resulting from digitizing the field of view area.

There is no attribute that relates the FOV origin to the intensifier. It is commonly assumed that the FOV area is centered in the intensifier.

The position of the projection of the isocenter on the active area is undefined. It is commonly understood that the X-Ray positioner is calibrated so that the isocenter is projected in the approximate center of the active area, and the field of view area is centered in the active area.

FFF.2.1.5.3.3 X-Ray Detector Module Recommendations

When the X-Ray Receptor Type (0018,9420) equals “DIGITAL_DETECTOR” this module specifies the type and characteristics of the image detector.

The size and pixel spacing of the digital image generated at the output of the digital detector are not necessarily equal to the size and element spacing of the detector matrix. The detector binning is defined as the ratio between the pixel spacing of the detector matrix and the pixel spacing of the digital image.

If the detector binning is higher than 1.0 several elements of the detector matrix contribute to the generation of one single digital pixel.

The digital image may be processed, cropped and resized in order to generate the stored image. The schema below shows these two steps of the modification of the pixel spacing between the detector physical elements and the stored image:

[pic]

Figure FFF.2.1-24Generation of the Stored Image from the Detector Matrix

Table FFF.2.1-43 X-RAY DETECTOR MODULE Recommendations

Attribute Name Tag Comment
Detector Binning (0018,701A) The ratio between the pixel spacing of the detector matrix and the pixel spacing of the digital image. It does not describe any further post-processing to resize the pixels to generate the stored image.
Detector Element Spacing (0018,7022) Pixel spacing of the detector matrix.
Position of Isocenter Projection (0018,9430) Relates the position of the detector elements to the isocenter reference system. It is independent from the detector binning and from the field of view origin. This attribute is defined if the Isocenter Reference System Sequence (0018,9462) is present.

FFF.2.1.5.3.4 X-Ray Field of View Macro Recommendations

The usage of this macro is recommended to specify the characteristics of the field of view.

When the field of view characteristics change across the multi-frame image, this macro is encoded on a per-frame basis.

The field of view region is defined by a shape, origin and dimension. The region of irradiated pixels corresponds to the interior of the field of view region.

When the X-Ray Receptor Type (0018,9420) equals “IMG_INTENSIFIER”, the intensifier TLHC is undefined. Therefore the field of view origin cannot be related to the physical area of the receptor. It is commonly understood that the field of view area corresponds to the intensifier active area, but there is no definition in the DICOM standard that forces a manufacturer to do so. As a consequence, it is impossible to relate the position of the pixels of the stored area to the isocenter reference system.

Table FFF.2.1-44 X-RAY FIELD OF VIEW MACRO Recommendations

Attribute Name Tag Comment
Field of View Sequence (0018,9432)
>Field of View Shape (0018,1147) Applicable in this scenario.
>Field of View Dimension(s) in Float (0018,9461) Applicable in this scenario.
>Field of View Origin (0018,7030) Applicable only in the case of digital detector.
>Field of View Rotation (0018,7032) Applicable regardless the type of receptor.
>Field of View Horizontal Flip (0018,7034) Applicable regardless the type of receptor.
>Field of View Description (0018,9433) Free text defining the type of field of view as displayed by the manufacturer on the acquisition system. For display purposes.

FFF.2.1.5.3.5 XA/XRF Frame Pixel Data Properties Macro Recommendations

The usage of this macro is recommended to specify the Imager Pixel Spacing.

When the field of view characteristics change across the multi-frame image, this macro is encoded on a per-frame basis.

Table FFF.2.1-45 XA/XRF FRAME PIXEL DATA PROPERTIES MACRO Recommendations

Attribute Name Tag Comment
Frame Pixel Data Properties Sequence (0028,9443)
>Imager Pixel Spacing (0018,1164) Applicable regardless the type of receptor.

In case of image intensifier, the Imager Pixel Spacing (0018,1164) may be non-uniform due to the pincushion distortion, and this attribute corresponds to a manufacturer-defined value (e.g., average, or value at the center of the image).