Материал: part03

Figure C.8-7. Pixel Component Calibration​

An example of Component Calibration for an ultrasound image is shown in Figure C.8-8.​

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Figure C.8-8. Pixel Component Calibration Example​

In this example, some pixels lie within two Regions. One Region specifies pixel component calibration for Doppler velocity values.​ The second Region specifies pixel component calibration for Doppler magnitude. A particular Pixel Data (7FE0,0010) value will thus​ map to a displayed value, a Doppler velocity and magnitude value.​

The example has a Palette Color Photometric Interpretation with 16 Bits Allocated and Bits Stored per sample. The Palette Color​ Lookup Tables also have 16 bits for each entry. The fact that the example has just one sample per pixel means that each composite​ pixel value is identical to the single Pixel Data value. An example Pixel Data value is shown in brackets along with the output values​ resulting from each step where it is processed.​

The Pixel Data value is mapped to red, green, and blue values from the supplied Palette Color Lookup Tables before being displayed.​ The display device supports 8 bits per sample and thus requires the scaling of the output values from the 16 bit per entry LUTs.​

The Doppler Velocity Region maps each pixel value in the Region to the Doppler velocity. The Pixel Component Organization​ (0018,6044) has a value of zero, indicating bit aligned positions with a bit mask. The Pixel Component Mask (0018,6046) specifies​ that the least significant 4 bits of the most significant byte convey the Doppler velocity of each pixel. The Pixel Component Physical​ Units (0018,604C) are cm/sec, and the Pixel Component Data Type (0018,604E) indicates color flow velocity. The Table of X Break​ Points (0018,6052) and Table of Y Break Points (0018,6054) map each masked composite pixel value to a Doppler velocity value in​ cm/sec.​

The Doppler Magnitude Region maps each pixel value in the Region to the Doppler magnitude. The Pixel Component Organization​ (0018,6044) has a value of zero, indicating bit aligned positions with a bit mask. The Pixel Component Mask (0018,6046) specifies​ that the most significant 4 bits of the most significant byte convey the Doppler magnitude of each pixel. The Pixel Component Phys-​ ical Units (0018,604C) is set to dB, and the Pixel Component Data Type (0018,604E) indicates color flow magnitude. The Table of X​ Break Points (0018,6052) and Table of Y Break Points (0018,6054) map each masked composite pixel value to a Doppler magnitude​ value in dB.​

C.8.5.5.1.5 Pixel Component Mask​

PixelComponentMask(0018,6046)isANDedwiththeCompositePixelCode(seeSectionC.7.6.3.1.1)foreachpixelwithintheregion,​ then shifted right by the number of contiguous least significant zeros in the mask to obtain what will be referred to as the "Shifted​ Masked Composite Pixel Code".​

The mask will most likely (but not necessarily) contain a block of contiguous ones, surrounded by leading and trailing zeros. The​ purpose of this mask is to keep only those bits within the composite pixel code that pertain to the region. It is to be used only when​ Pixel Organization is bit aligned positions.​

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C.8.5.5.1.6 Pixel Component Physical Units​

Enumerated Values:​

0000H​None or not applicable​ 0001H​Percent​

0002H​dB​ 0003H​cm​

0004H​seconds​ 0005H​hertz(seconds-1)​ 0006H​dB/seconds​

0007H​cm/sec​

0008H​cm2​

0009H​cm2/sec​

000AH​cm3​

000BH​cm3/sec​ 000CH​degrees​

C.8.5.5.1.7 Pixel Component Data Type​

Enumerated Values:​

0000H​None or not applicable​ 0001H​Tissue​ 0002H​Spectral Doppler​ 0003H​Color Flow Velocity​ 0004H​Color Flow Variance​ 0005H​Color Flow Intensity​ 0006H​Gray bar​ 0007H​Color bar​ 0008H​Integrated Backscatter​ 0009H​Computed Border​ 000AH​Tissue Classification​

C.8.5.5.1.8 Number of Table Break Points​

The Number of Table Break Points (0018,6050) gives the number of entries in each of two tables: the Table of X Break Points​ (0018,6052) and Table of Y Break Points (0018,6054). These tables are used to designate a curve mapping the value of a pixel​ component to its actual physical value, as described in Section C.8.5.5.1.9.​

C.8.5.5.1.9 Table of X Break Points and Table of Y Break Points​

Table of X Break Points (0018,6052) and Table of Y Break Points (0018,6054) are individual arrays of coordinates that interpreted​ togetherareusedtocreateapiecewiselinearcurve.EachXvaluefromtheTableofXBreakPointsismatchedwiththecorresponding​ Y value from the Table of Y Break Points yielding an (X,Y) coordinate. The set of (X,Y) coordinates describes a piecewise linear curve​ mapping the value of a pixel component to its actual physical value (in units defined in Pixel Component Physical Units (0018,604C)).​

The X direction on the curve has no units, and represents actual pixel component values. If the Pixel Component Organization​ (0018,6044) is "Bit aligned positions", and the width of the Pixel Component Mask is n bits then the X coordinates are in the range 0​ through 2n-1. If the Pixel Component Organization is Ranges, then the X coordinates are in the range 0 through 2 number of bits in​ the composite pixel- 1.​

Note​

The X value is NOT relative to the Pixel Component Range Start (0018,6048). Not all possible X values in the range need​ be covered by the curve.​

For any pixel component value in the range of the curve described by this table, the corresponding Y value is the actual physical​ value for that pixel, in units specified in Pixel Component Physical Units (0018,604C). If the pixel component value is NOT within the​ range of specified X values for the curve, then no pixel calibration is defined by this region. It may be possible for pixel calibration to​ be defined by other spatial regions intersecting this one.​

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C.8.5.5.1.10 TM-line Position X0, Y0, X1 and Y1​

The TM-Line Position X0 (0018,603D) and TM-Line Position Y0 (0018,603F) are the coordinates of the starting point and TM-Line​ Position X1 (0018,6041), TM-Line Position Y1 (0018,6043) are the coordinates of the end point of the TM-line. The coordinate is​ defined as the displacement, in pixels, from the Reference pixel. Typically used for M-mode line and CW Doppler.​

C.8.5.5.1.11 Number of Table Entries​

The Number of Table Entries (0018,6056) gives the number of entries in the Table of Pixel Values, the number of entries in the Table​ of Parameter Values (0018,605A), if present, and the number of Items in the Pixel Value Mapping Code Sequence (0040,9098), if​ present.​

C.8.5.5.1.12 Table of Pixel Values​

The Table of Pixel Values (0018,6058) specifies the pixel values that are mapped to real world parameter values or coded concepts​ (tissue characterizations). The number of entries in the table is given by Number of Table Entries (0018,6056).​

A pixel is calibrated (mapped to a real-world value) by finding an entry in the Table of Pixel Values that matches its Composite Pixel​ Code (see Section C.7.6.3.1.1). The offset index of this entry is used as an index into the Parameter Value Table (0018,605A) or as​ a Sequence Item number in the Pixel Value Mapping Code Sequence (0040,9098) to select the real world value. The first Table of​ Pixel Values entry corresponds to Sequence Item 1.​

Note​

If a Composite Pixel Code has no matching value in the Pixel Value Table then there is no unambiguous way to determine​ the corresponding Parameter Value. A method may exist to determine a valid Parameter Value but the specification of such​ a method is outside the scope of the DICOM Standard. No assumption should be made that linear interpolation will produce​ a valid result.​

C.8.5.5.1.13 Table of Parameter Values​

The Table of Parameter Values (0018,605A) provides the real world values for pixel values identified in the Table of Pixel Values​ (0018,6058). The number of table entries is given by Number of Table Entries (0018,6056) and the physical units are given by Pixel​ Component Physical Units (0018,604C). Values may repeat when a parameter value is associated with more than one Composite​ Pixel Code value.​

C.8.5.5.1.14 Region Location Min X0, Min Y0, Max X1 and Max Y1​

TheseAttributesspecifythelocationoftheregion,RegionLocationMinX0(0018,6018),RegionLocationMinY0(0018,601A),Region​ Location Max X1 (0018,601C), Region Location Max Y1 (0018,601E) expressed as offsets to the pixel coordinates. The upper left​ corner of the entire image is x=0,y=0 and the lower right corner is x=image width - 1, and y=image length - 1. Thus, a region will be​ specified as within these bounds. Where x0,y0 is the coordinate of the upper left corner of the region and x1,y1 is the coordinate of​ the lower right corner of the region.​

C.8.5.5.1.15 Physical Units X Direction and Physical Units Y Direction​

Physical Units X Direction (0018,6024) and Physical Units Y Direction (0018,6026) indicate the physical units of the dimensions of​ the region.​

Enumerated Values:​

0000H​None or not applicable​ 0001H​Percent​

0002H​dB​ 0003H​cm​

0004H​seconds​ 0005H​hertz(seconds-1)​ 0006H​dB/seconds​

0007H​cm/sec​

0008H​cm2​

0009H​cm2/sec​

000AH​cm3​

000BH​cm3/sec​

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000CH​degrees​

C.8.5.5.1.16 Reference Pixel X0 and Reference Pixel Y0​

This coordinate pair, Reference Pixel X0 (0018,6020), Reference Pixel Y0 (0018,6022) defines the location of a virtual "reference"​ pixel. This reference pixel location is used to tie the image's pixel coordinate system to the physical coordinate system. For example,​ the reference pixel could be defined where a depth of zero centimeters occurs in the 2D image, or it could define where the baseline​ (i.e., zero frequency) resides in a spectral display. The reference pixel location is the relative offset from the Region Location Min X0​ (0018,6018) and Region Location Min Y0 (0018,601A), not the image origin. The location is not required to be within the region or​ even within the image boundary. For this reason, the Reference Pixel X0 and Reference Pixel Y0 values can be positive or negative.​

The reference pixel location varies depending on the type and spatial organization of the data within the region.​

C.8.5.5.1.16.1 2D - Tissue or Color Flow​

Tissue data is tissue echo intensity displayed as grayscale. The Region Data Type (0018,6014) value is 0001H (Tissue). Color flow​ is Doppler signal displayed as color and encoded as some function of Doppler magnitude and velocity of blood flow or tissue motion.​ The Region Data Type value is 0002H (Color flow). For 2D, the Region Spatial Format (0018,6012) is 0001H (2D), meaning that the​ region is a tomographic image. For such 2D regions the reference pixel location is typically at the center of the transducer face on​ the tissue-transducer interface (skin line).​

Figure C.8-1 shows 2D Attribute values of reference pixel location along with Region Location Min and Region Location Max. for 2D-​ Tissue and 2D-Color Flow Regions:​

Transducer

Figure C.8-1. 2D Regions with Reference Pixel​

Both the 2D regions-Tissue and Color Flow-share the same physical location at the skin line but the reference pixel location values​ (Reference Pixel X0 and Reference Pixel Y0) are relative to their respective region origins at the skin line.​

C.8.5.5.1.16.2 Spectral - CW or PW Doppler or Doppler Trace​

Spectral Doppler is the time varying magnitude of Doppler signal as function of frequency. Region Data Type (0018,6014) value is​ 0003H(pulsedwaveDoppler)or0004H(continuouswaveDoppler).SpectralDopplerregionsdisplaythemagnitudeofDopplersignal​ with frequency or velocity as the vertical dimension and time as the horizontal dimension. Spectral Doppler regions have a Region​

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