C.8.16 Common CT and MR Descriptions

This section contains descriptions of Macros and Attributes used in Modules and Functional Group Macros that are common to the Enhanced CT Image, Enhanced MR Images and MR Spectroscopy IODs.

C.8.16.1 Image Type and Frame Type

The Image Type (0008,0008) and associated Image Type related attributes provide a high level description of a multi-frame SOP Instance. These attributes describe properties that provide key summary information to users of the SOP Instance. Image Type (0008,0008) contains the highest level summary of what is in the SOP Instance.

The Frame Type (0008,9007) attribute mirrors the corresponding Image Type attribute and applies to the frame level rather than to the image level.

If more than one value is used by the set of frames for a given Frame Type (0008,9007) attribute value or associated attribute value then the corresponding value of the Image Type (0008,0008) or associated attribute shall contain a value of MIXED. This indicates that a mixed set of values exists within the multi-frame SOP Instance.

The value MIXED shall only be used in the Image Type (0008,0008) when the corresponding values for the individual frames are not equal. When a value of an attribute is equal for all frames, the same value shall be used for the corresponding value of the Image Type (0008,0008). Values 2 and 3 of Image Type (0008,0008) are an exception to the rule for MIXED: Values 2 and 3 may never have the value of MIXED as described in sections C.8.16.1.2 and C.8.16.1.3.

Image Type (0008,0008) and Frame Type (0008,9007) shall consist of four non-zero length values.

C.8.16.1.1 Pixel Data Characteristics

Value 1 of Image Type (0008,0008) and Frame Type (0008,9007) shall use one of the following Enumerated Values from Table C.8-127.

Value 1 of Image Type (0008,0008) and Value 1 of Frame Type (0008,9007) shall not be zero length.

Table C.8-127IMAGE TYPE AND FRAME TYPE VALUE 1

Enumerated Value Name Enumerated Value Description
ORIGINAL An image or frame is original if its pixel data was directly reconstructed from the original data that is obtained from the sensors of the imaging equipment, Image Type (0008,0008) Value 4 is NONE, and Volume Based Calculation Technique (0008,9207) is NONE. Notes: (1) For MR, original data is data directly reconstructed from k-space data. (2) For CT, original frames are those directly reconstructed from projection data.
DERIVED An image or frame is derived if its pixel data was calculated from original or other derived pixel data (i.e. it is not original).
MIXED Used only as a value in Image Type (0008,0008) if frames within the SOP Instance contain different values for Value 1 in their Frame Type (0008,9007).

C.8.16.1.2 Patient Examination Characteristics

Value 2 for Image Type (0008,0008) and Frame Type (0008,9007) follows the standard definition and shall have the following Enumerated Value from Table C.8-128.

Value 2 of Image Type (0008,0008) and Value 2 of Frame Type (0008,9007) shall not be zero length.

Table C.8-128IMAGE TYPE AND FRAME TYPE VALUE 2

Enumerated Value Name Enumerated Value Description
PRIMARY See C.7.6.1.1.2

C.8.16.1.3 Image Flavor

Value 3 is an overall representation of the image type. This value may be a summary of several other attributes or a duplication of one of the other attributes to indicate the most important aspect of this image. Value 3 Image Flavor is to be used with Value 4 Derived Pixel Contrast to indicate the nature of the image set.

Note: For example Value 3 = DIFFUSION together with Value 4 = NONE indicates that the image set was originally collected for DIFFUSION.

If Value 3 = DIFFUSION together with Value 4 = DIFFUSION this indicates that the object contains DIFFUSION weighted post processed images.

Value 3 of Image Type (0008,0008) shall not be zero length.

Value 3 of Frame Type (0008,9007) may have the same value as found in Value 3 of Image Type (0008,0008), or may have a different value or may be of zero length.

The attribute value may not be MIXED as this value needs to be a summary of the primary purpose of the images, whether the frames have the same value or not.

Table C.8-129 specifies the Defined Terms for Value 3 for Image Type (0008,0008) and Frame Type (0008,9007) that are common to CT and MR. Additional defined terms are defined in the modality-specific Module and Macro definitions.

Table C.8-129IMAGE TYPE AND FRAME TYPE VALUE 3 COMMON

Defined Term Name Defined Term Description
ANGIO Collected for the purpose of angiography
CARDIAC Images of the heart
CARDIAC_GATED Cardiac gated images, other than of the heart
CARDRESP_GATED Cardiac and respiratory gated images
DYNAMIC An image in which the same anatomical volume is imaged at multiple times in order to capture images of a non-cyclic, time varying event. For example, imaging of the uptake of a tracer or contrast in a specific organ over time. Note: This is different from gating techniques, in which the same anatomical volume is imaged during some portion of a cyclic event , e.g. inspiration or R-R Interval.
FLUOROSCOPY Real-time collection of single slices (e.g. CT or MR Fluoroscopy)
LOCALIZER Collected for the purpose of planning other images.
MOTION Collected for looking at body motion
PERFUSION Collected for the purposes of perfusion calculations.
PRE_CONTRAST Collected before contrast was administered
POST_CONTRAST Collected during or after contrast was administered
RESP_GATED Respiratory gated images
REST Cardiac rest image set
STATIC A group of frames at varying spatial locations acquired at the same time.
STRESS Cardiac stress image set
VOLUME Set of frames that define a regularly sampled volume
NON_PARALLEL Set of frames that are not parallel
PARALLEL Set of frames that are parallel but do not constitute a regularly sampled volume
WHOLE_BODY A group of frames of the whole body; the frames may be acquired at various times (as distinct from STATIC).

C.8.16.1.4 Derived Pixel Contrast

Value 4 shall be used to indicate derived pixel contrast - generally, contrast created by combining or processing images with the same geometry. Value 4 shall have a value of NONE when Value 1 is ORIGINAL.

Note: If more than one of the following derived types is applicable, then it is up to the generating application to specify the value that best characterizes the derived image.

Value 4 of Image Type (0008,0008) and Value 4 of Frame Type (0008,9007) shall not be zero length.

Table C.8-130 specifies the Defined Terms for Value 4 for Image Type (0008,0008) and Frame Type (0008,9007) that are common to CT and MR. Additional defined terms are defined in the modality-specific Module and Macro definitions.

Table C.8-130IMAGE TYPE AND FRAME TYPE VALUE 4 COMMON

Defined Term Name Defined Term Description
ADDITION Created through Pixel by pixel addition operation
DIVISION Created through Pixel by pixel division operation
MASKED Created through Pixel by pixel masking operation
MAXIMUM Created through Pixel by Pixel Maximum operation
MEAN Created through Pixel by pixel mean operation
MINIMUM Created through Pixel by Pixel Minimum operation
MTT Mean Transit Time
MULTIPLICATION Created through Pixel by pixel multiplication operation
RCBF Regional Cerebral Blood Flow (rCBF)
RCBV Regional Cerebral Blood Volume (rCBV)
RESAMPLED Pixels have been spatially re-sampled, e.g., MPR
STD_DEVIATION Standard Deviation
SUBTRACTION Created through Pixel by pixel subtraction operation
T_TEST Student’s T-Test
TTP Time To Peak map
Z_SCORE Z-Score Map
NONE Not a calculated image
MIXED Used only as value in Image Type (0008,0008) if frames within the image SOP Instance contain different values for value 4 in their Frame Type (0008,9007) attribute.

C.8.16.2 Common CT/MR Image Description Macro

This section describes the Common CT/MR Image Description Macro.

Table C.8-131 specifies the attributes of the Common CT/MR Image Description Macro.

Table C.8-131COMMON CT/MR IMAGE DESCRIPTION MACRO ATTRIBUTES

Attribute Name Tag Type Attribute Description
Pixel Presentation (0008,9205) 1 Indication of the presence or absence of color information that may be used during rendering. See C.8.16.2.1.1 for a description and Enumerated Values.
Volumetric Properties (0008,9206) 1 Indication if geometric manipulations are possible with frames in the SOP Instance. See C.8.16.2.1.2 for a description and Enumerated Values.
Volume Based Calculation Technique (0008,9207) 1 Method used for volume calculations with frames in the SOP Instance. See C.8.16.2.1.3 for a description and Defined Terms.

C.8.16.2.1 Common CT/MR Image Description Attribute Description

C.8.16.2.1.1 Pixel Presentation

Table C.8-132PIXEL PRESENTATION ATTRIBUTE VALUES

Enumerated Value Name Enumerated Value Description
COLOR Image is best displayed in color using Supplemental Palette Color LUTs, but can be displayed in grayscale if current display does not support color. See section C.8.16.2.1.1.1.
MONOCHROME Image is intended to be displayed in grayscale only. No Supplemental Palette Color LUTs are supplied.
MIXED Used only as a value in Pixel Presentation (0008,9205) in the Enhanced MR Image Module or Enhanced CT Image Module if frames within the image SOP Instance contain different values for the Pixel Presentation attribute in the MR Image Frame Type Functional Group or CT Image Frame Type Functional Group.
TRUE_COLOR Image can be displayed in color only

C.8.16.2.1.1.1 Supplemental Palette Color LUTs

Figure C.8-20 presents two separate image visualization pipelines that can be used for interpreting the stored pixel values.

If Pixel Presentation (0008,9205) equals COLOR, the stored values are split into two ranges. The stored values up to one less than the second value of the Red, Green and Blue Palette Color Lookup Table Descriptor (0028,1101-1103) are passed through the gray scale visualization pipeline. The values equal to or greater than the second value of the Red, Green and Blue Palette Color Lookup Table Descriptor (0028,1101-1103) are mapped by the Palette Color LUTs.

Notes: 1. Some images may be purely color, and there will be no grayscale range of stored pixel values “below” those that are passed through the color lookup tables.

2. Images containing Supplemental Palette Color LUTs cannot be irreversibly (lossy) compressed, since that would potentially change the index values and result in different colors being rendered.

The complete range of stored pixel values can also be displayed via the grayscale visualization pipeline only, but the information content may be less useful because the color information is not available.

[pic] Figure C.8-20 MONOCHROME2 Photometric Interpretation with Supplemental Palette Color mapping

C.8.16.2.1.2 Volumetric Properties

The value of the Volumetric Properties attribute (0008,9206) allows applications doing geometric manipulations (e.g., MAX_IP or MPR or planning) to determine if the image is an appropriate candidate for an operation without having to know all the details of the generating application.

Table C.8-133 specifies the Enumerated Values for the Volumetric Properties (0008,9206) attribute.

Table C.8-133VOLUMETRIC PROPERTIES ATTRIBUTE VALUES

Enumerated Value Name Enumerated Value Description
VOLUME Image contains pixels that represent the volume specified for the image (Examples: Volume Based Calculation Technique (0008,9207) is NONE or MPR).
SAMPLED The specified frame or each frame within the image will not contain a representation of the average information in the slice direction because the frame was calculated by the non-linear re-sampling of a volume where each pixels of the resulting frame does not contain an average representation of the voxel represented by the frame's pixel. For example a projection (MAX_IP) frame uses the maximum value along a ray for each pixel rather than the average value of the represented voxel.
DISTORTED Image contains significantly distorted information from what is specified by the image volume attributes. For example this image should not be used in planning or for 3D volume. An example of this image type is a curved reformatted image (CURVED_MPR).
MIXED Used only as a value in the Volumetric Properties (0008,9206) attribute in the Enhanced MR Image Type Module or Enhanced CT Image Type Module if frames within the image SOP Instance contain different values for the Volumetric Properties (0008,9206) attributes in the MR Image Frame Type Functional Group or CT Frame Type Functional Group.

C.8.16.2.1.3 Volume Based Calculation Technique Attribute

The value of the Volume Based Calculation Technique attribute (0008,9207) shall be used to indicate the method used for calculating pixels based on geometry.

Shall have a value of NONE when Value 1 of Image Type (0008,0008) or Value 1 of Frame Type (0008,9007) is ORIGINAL.

Table C.8-134 specifies the Defined Terms for the Volume Based Calculation Technique (0008,9207) attribute.

Table C.8-134VOLUME BASED CALCULATION TECHNIQUE ATTRIBUTE VALUES

Defined Term Name Defined Term Description
MAX_IP Maximum Intensity Projection
MIN_IP Minimum Intensity Projection
VOLUME_RENDER Volume Rendering Projection Volume Rendering Image represents 3D voluminar information constructed from measured voxel intensities covering a 3D volume.
SURFACE_RENDER Surface Rendering Projection Surface Rendering Image represents 3D surface information constructed from measured voxel intensities covering a 3D volume.
MPR Multi-Planar Reformat
CURVED_MPR Curved Multi-Planar Reformat
NONE Pixels not derived geometrically
MIXED Used only as a value in Volume Based Calculation Technique (0008,9207) attribute in the Enhanced MR Image Module or MR Spectroscopy Module if frames within the image SOP Instance contain different terms for the Volume Based Calculation Technique attribute in MR Frame Type Functional Group or MR Spectroscopy Frame Type Functional Group.