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DICOM PS3.17 2020a - Explanatory Information |
•Measurement Units Code Sequence (0040,08EA) = (mm2/s, UCUM, "mm2/s")
•Quantity Definition Sequence (0040,9220):
•CODE (246205007, SCT, "Quantity") = (113041, DCM, "Apparent Diffusion Coefficient")
•CODE (370129005, SCT, "Measurement Method") = (113250, DCM, "Mono-exponential ADC model")
•CODE (113241, DCM, "Model fitting method") = (113260, DCM, "Log of ratio of two samples")
•NUMERIC (113240, DCM, "Source image diffusion b-value") = 0 (s/mm2, UCUM, "s/mm2")
•NUMERIC (113240, DCM, "Source image diffusion b-value") = 1000 (s/mm2, UCUM, "s/mm2")
•TEXT (121050, DCM, "Equivalent Meaning of Concept Name") = "ADC mono-exponential log ratio B0 and B1000"
In this usage, the text of the (121050, DCM, "Equivalent Meaning of Concept Name") is redundant with the value of LUT Explanation (0028,3003); either or both could be omitted.
The parameter describing a b-value of 0 is expected to be sent, and one should not assume that a b-value of 0 is used if it is absent, since some methods may use a low b-value (e.g., 50), which is not 0.
There is no consensus in the MR community or scientific literature as to the appropriate units to use to report diffusion coefficient values to the user, nor amongst the MR vendors as to how to encode them. In this example, the units are specified as "s/mm2". If the diffusion coefficient pixel values were encoded as integers with such a unit, they could then be encoded with a Rescale Slope of 1E- 06, given the typical range of values encountered. Alternatively, the pixel values could be encoded as floating point pixel data values with identity rescaling. Or, if the units were specified "um2/s" (or "10-6.mm2/s", which is the same thing), then integer pixels could be used with a Rescale Slope of 1. Application software can of course rescale the values for display and convert the units as appropriate to the user's preference, as long as they are unambiguously encoded.
EEEE.2 Encoding Diffusion Model Parameters for ROIs in Measurement Report SR Documents
This example shows how to describe the mean ADC value of a region of interest on a volume of ADC values obtained from a pair of B0 and B1000 images fitting the log ratio ot two samples to a mono-exponential function (single compartment model). In this case the template used is TID 1419 “ROI Measurements”.
•NUM (113041, DCM, "Apparent Diffusion Coefficient") = 0.75E-3 (mm2/s, UCUM, "mm2/s")
•HAS CONCEPT MOD CODE (370129005, SCT, "Measurement Method") = (113250, DCM, "Mono-exponential ADC model")
•HAS CONCEPT MOD CODE (113241, DCM, "Model fitting method") = (113260, DCM, "Log of ratio of two samples")
•HAS CONCEPT MOD CODE (121401, DCM, "Derivation") = (373098007, SCT, "Mean")
•INFERRED FROM NUM (113240, DCM, "Source image diffusion b-value") = 0 (s/mm2, UCUM, "s/mm2")
•INFERRED FROM NUM (113240, DCM, "Source image diffusion b-value") = 1000 (s/mm2, UCUM, "s/mm2")
•HAS CONCEPT MOD TEXT (121050, DCM, "Equivalent Meaning of Concept Name") = "Mean ADC mono-exponential log ratio B0 and B1000"
EEEE.3 Relationship of Derived Diffusion Model Parametric Maps to Diffusion Weighted Source Images
ThisexampleillustrateshowtodescribethemannerinwhichanADCParametricMapimagewasderivedfromB0andB1000images.
Theintentistoprovidelinkstotheimages,nottoreplicatealltheinformationthatcanbeprovidedintheQuantityDefinitionSequence.
ThisparticularexampleillustratesthereferencefromanADCParametricMaptoapairofEnhancedMRimages,oneforeachb-value (or a pair of subsets of frames of a single Enhanced MR image), but the same principle is applicable when single frame IODs are used as source or derived image.
