C.7.6.16.2.11 Real World Value Mapping Macro

Table C.7.6.16-12 specifies the attributes of the Real World Value Mapping Functional Group macro.

Table C.7.6.16-12REAL WORLD VALUE MAPPING MACRO ATTRIBUTES

Attribute Name Tag Type Attribute Description
Real World Value Mapping Sequence (0040,9096) 1 The mapping of stored values to associated real world values. One or more Items shall be included in this sequence.
>Real World Value First Value Mapped (0040,9216) 1 Specifies the first stored value mapped for the Real Word Value Intercept (0040,9224) and Real World Value Slope (0040,9225) or Real World Value LUT (0040,9212) of this Item. See C.7.6.16.2.11.1 for further explanation.
>Real World Value Last Value Mapped (0040,9211) 1 Specifies the last stored value mapped for the Real Word Value Intercept (0040,9224) and Real World Value Slope (0040,9225) or Real World Value LUT (0040,9212) of this Item. See C.7.6.16.2.11.1 for further explanation.
>Real World Value Intercept (0040,9224) 1C The Intercept value in relationship between stored values (SV) and the real world values. See section C.7.6.16.2.11.2 for further explanation. Required if Real World Value LUT Data (0040,9212) is not present.
>Real World Value Slope (0040,9225) 1C The Slope value in relationship between stored values (SV) and the real world values. See section C.7.6.16.2.11.2 for further explanation. Required if Real World Value LUT Data (0040,9212) is not present.
>Real World Value LUT Data (0040,9212) 1C LUT Data in this Sequence. Required if Real World Value Intercept (0040,9224) is not present.
>LUT Explanation (0028,3003) 1 Free form text explanation of the meaning of the transformation in this Item.
>LUT Label (0040,9210) 1 Label that is used to identify the transformation of this Item.
>Measurement Units Code Sequence (0040,08EA) 1 Units of measurement. Only a single Item shall be included in this sequence. See C.7.6.16.2.11.1 for further explanation.
>>Include Code Sequence Macro Table 8.8-1 Defined CID 82, or as specified in the macro invocation.

C.7.6.16.2.11.1 Real World Value representation

C.7.6.16.2.11.1.1 Real World Value Mapping Sequence

The items in the Real World Value Mapping Sequence (0040,9096) may be used to translate stored values into real world values when there is such a relationship. The Real World Value Mapping Sequence (0040,9096) is independent of the Modality LUT (or Pixel Value Transformation Macro), as illustrated in Figure C.7.6.16-6.

Each item specifies the range of stored values as well as the associated mapping function. Each item can specify either a linear mapping, using Real World Value Slope (0040,9225) and Real World Value Intercept (0040,9224), or a non-linear mapping using Real World Value LUT Data (0040,9212). More than one Real World Value Mapping Item is allowed.

The range of stored pixel values specified by different Real Value World Mapping Sequence (0040,9096) Items can overlap (as illustrated in the example in Figure C.7.6.16-7).

[pic]

Figure C.7.6.16-6The Real World Value LUT and the Image Viewing pipeline

Note: For example, MR images may contain data that is not only the result of the physical/chemical properties of the scanned anatomy, but may also contain information that is representing real world values, such as, temperature [in degrees C], flow [in l/min], speed [in m/sec], relative activity [in %], relative contrast enhancement [in %], diffusion [in sec/mm2], etc.

In some cases the conversion from Stored Values to Real World Values can be linear (through "slope" and "intercept") or non-linear (through look-up tables).

Both transformation methods can be applied to one range of stored values. Overlapped ranges might be used for different representations such as log versus linear scales or for different representations in units such as cm/sec versus mm/sec. Alternative methods can be identified by the labels assigned to the transformations.

C.7.6.16.2.11.1.2 Real World Values Mapping Sequence Attributes

The Real World Value First Value Mapped (0040,9216) and Real World Value Last Value Mapped (0040,9211) Attributes describe the range of stored pixel values that are mapped by the Sequence Item. Stored pixel values less than the first value mapped, or greater than the last value mapped have no real value attached.

When the Real World Value Intercept (0040,9224) and Real World Value Slope (0040,9225) attributes are supplied, the stored value (SV) is converted to a real world value (RV) using the equation:

RV = (Real World Value Slope) * SV + Real World Value Intercept

When the Real World Value LUT Data (0040,9212) attribute is supplied, Real World Values are obtained via a lookup operation. The stored pixel value of the first value mapped is mapped to the first entry in the LUT Data. Subsequent stored pixel values are mapped to the subsequent entries in the LUT Data up to a stored pixel value equal to the last value mapped.

The number of entries in the LUT data is given by:

Number of entries = Real World Value Last Value Mapped- Real World Value First Value Mapped + 1

The physical units for the real world values obtained from the sequence item are given by the Measurement Units Code Sequence (0040,08EA).

[pic]

Figure C.7.6.16-7Example of mapping stored values to real world values