FFF.1.2.5 Field of View Transformations

FFF.1.2.5.1 Detector

The following concepts illustrate the model of the X-Ray detector:

Physical detector array (or physical detector matrix) is the matrix composed of physical detector elements .

Note: Not all the detector elements are activated during an X-Ray exposure. The active detector elements are in the detector active area, which can be equal to or smaller than the physical detector area.

Physical detector element coordinates represented as (i det, j det ) are columns and rows of the physical detector element in the physical detector array.

Detector TLHC element is the detector element in the Top Left Hand Corner of the physical detector array and corresponds to (i det, j det ) = (0,0).

The attribute Detector Element Physical Size (0018,7020) represents the physical dimensions in mm of a detector element in the row and column directions.

The attribute Detector Element Spacing (0018,7022) contains the two values Δ jdet and Δ idet , which represent the physical distance in mm between the centers of each physical detector element:

The attribute Detector Element Physical Size (0018,7020) may be different from the Detector Element Spacing (0018,7022) due to the presence of spacing material between detector elements.

The attribute Position of Isocenter Projection (0018,9430) contains the point (ISO_P idet, ISO_P jdet ), which represents the projection of the Isocenter on the detector plane, measured as the offset from the center of the detector TLHC element. It is measured in physical detector elements.

The attribute Imager Pixel Spacing (0018,1164) contains the two values Δ j and Δ i , which represent the physical distance measured at the receptor plane between the centers of each pixel of the FOV image:

The zoom factor represents the ratio between Imager Pixel Spacing (0018,1164) and Detector Element Spacing (0018,7022). It may be different from the detector binning (e.g., when a digital zoom has been applied to the pixel data).

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Figure FFF.1.2-9Physical Detector and Field of View Areas

FFF.1.2.5.2 Field of View

The following concepts illustrate the model of the field of view:

The field of view (FOV) corresponds to a region of the physical detector array that has been irradiated.

The field of view image is the matrix of pixels of a rectangle circumscribing the field of view. Each pixel of the field of view image may be generated by multiple physical detector elements.

The attribute FOV Origin (0018,7030) contains the two values (FOV idet, FOV jdet ), which represent the offset of the center of the detector element at the TLHC of the field of view image, before rotation or flipping, from the center of the detector TLHC element. It is measured in physical detector elements. FOV Origin = (0,0) means that the detector TLHC element is at the TLHC of a rectangle circumscribing the field of view.

The attribute FOV Dimension (0018,9461) contains the two values FOV row dimension and FOV column dimension, which represent the dimension of the FOV in mm:

FOV pixel coordinates represented as (i , j) are columns and rows of the pixels in the field of view image.

FOV TLHC pixel is the pixel in the Top Left Hand Corner of the field of view image and corresponds to (i , j) = (0,0).

As an example, the point (ISO_P i, ISO_P j ) representing the projection of the Isocenter on the field of view image, and measured in FOV pixels as the offset from the center of the FOV TLHC pixel, can be calculated as follows:

ISO_P i = (ISO_P idet - FOV idet ) . Δ idet / Δ i - (1 - Δ idet / Δ i ) / 2

ISO_P j = (ISO_P jdet - FOV jdet ) . Δ jdet / Δ j - (1 - Δ jdet / Δ j ) / 2

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Figure FFF.1.2-10Field of View Image

FFF.1.2.5.3 Field of View Rotation and Flip

The attribute FOV Rotation (0018,7032) represents the clockwise rotation in degrees of field of view relative to the physical detector.

The attribute FOV Horizontal Flip (0018,7034) defines whether or not a horizontal flip has been applied to the field of view after rotation relative to the physical detector.

The attribute Pixel Data (7FE0,0010) contains the FOV image after rotation and/or flipping.

Pixel data coordinates is the couple (c,r) where c is the column number and r is the row number.

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Figure FFF.1.2-11Examples of Field of View Rotation and Horizontal Flip