C.8.27 Intravascular Optical Coherence Tomography Modules

C.8.27.1 Intravascular OCT Series Module

Table C.8.27.1-1 specifies the Attributes that identify and describe general information about the Intravascular Optical Coherence Tomography Series.

Table C.8.27.1-1INTRAVASCULAR OCT SERIES MODULE ATTRIBUTES

Attribute Name Tag Type Attribute Description
Modality (0008,0060) 1 Type of equipment that originally acquired the data used to create the images in this Series. Enumerated Values: IVOCT See section C.7.3.1.1.1 for further explanation.
Series Number (0020,0011) 1 A number that identifies this Series.
Referenced Performed Procedure Step Sequence (0008,1111) 1C Uniquely identifies the Performed Procedure Step SOP Instance to which the Series is related (e.g. a Modality or General-Purpose Performed Procedure Step SOP Instance). Only a single Item shall be included in this sequence. Required if the Modality Performed Procedure Step SOP Class or General Purpose Performed Procedure Step SOP Class is supported.
>Referenced SOP Class UID (0008,1150) 1 Uniquely identifies the referenced SOP Class.
>Referenced SOP Instance UID (0008,1155) 1 Uniquely identifies the referenced SOP Instance.
Presentation Intent Type (0008,0068) 1 Identifies the intent of the images that are contained within this Series. Enumerated Values: FOR PRESENTATION FOR PROCESSING

C.8.27.1.1 Intravascular OCT Series Attribute Descriptions

C.8.27.1.1.1 Presentation Intent Type

Presentation Intent Type (0008,0068) identifies the intent for the purposes of display or other presentation of all Images within this Series.

Notes: 1. Since this is a Series level attribute, all Images within a Series have the same value for this Attribute.

2. The intent of this restriction is to ensure that FOR PRESENTATION and FOR PROCESSING images are placed in separate Series, so that no confusion can arise as to which images are suitable for diagnostic reading as determined by local policy.

A Series of Images intended for viewing by an observer shall have an Enumerated Value of FOR PRESENTATION. The value shall not be set to FOR PRESENTATION unless Z Offset correction, refractive index correction and polar to rectangular conversion have been applied

Images or individual frames of a FOR PRESENTATION image shall reference their associated source FOR PROCESSING frames, if any exist, using the Derivation Image Functional Group Macro, with the Derivation Code (113093, DCM, “Polar to Rectangular Scan Conversion”) and the Purpose of Reference Code (121358, DCM, “For Processing Image”).

Notes: 1. FOR PRESENTATION images are still be of Image Type (0008,0008) and Frame Type (0008,9007) ORIGINAL rather than DERIVED despite having undergone processing, such as corrections for Z Offset, Refractive index and Polar to Rectangular conversion. In this case a DERIVED image would have undergone yet further processing to make it substantially different from the original. See Figure C.8-X. The Derivation Image Functional Group Macro may be used even if Image Type (0008,0008) and Frame Type (0008,9007) is ORIGINAL.

2. FOR PRESENTATION images may still be subjected to processing or further processing, if appropriate, depending on the application.

3. FOR PRESENTATION images are intended for display on a device, without (further) processing, since that device may not be capable of image processing. The quality of the displayed image or its suitability for any purpose is beyond the scope of the DICOM Standard.

4. If all of the frames of a FOR PRESENTATION image are created by processing all of the frames of a FOR PROCESSING image, then a reference to the FOR PROCESSING SOP Instance only, without reference to specific frame numbers, in the Shared Functional Group Sequence avoids the need for a frame-by-frame reference in each Per-Frame Functional Group, though there is no requirement that the order of the frames or the number of frames in the FOR PROCESSING and FOR PRESENTATION instances correspond.

FOR PROCESSING images may have Z Offset correction applied to the A-line data and/or Refractive Index applied to A-line Pixel Spacing (0052,0014). However, due to irreversible loss of information, images that have had Polar to Rectangular scan conversion applied shall not be stored as FOR PROCESSING images.

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Figure C.8.27-1 - Explanation of Presentation Intent Type

C.8.27.2 Intravascular OCT Image Module

Table C.8.27.2-1 specifies the Attributes that describe an Image produced by Intravascular OCT imaging modalities.

Table C.8.27.2-1INTRAVASCULAR OCT IMAGE MODULE ATTRIBUTES

Attribute Name Tag Type Attribute Description
Image Type (0008,0008) 1 Image identification characteristics. See C.8.27.2.1 for specialization.
Volumetric Properties (0008,9206) 1 Indication if geometric manipulations are possible with frames in the SOP Instance. See C.8.27.2.2.
Pixel Presentation (0008,9205) 1 Indication of the presence or absence of color information that may be used during rendering. See C.8.27.2.3 for a description and Enumerated Values.
Samples Per Pixel (0028,0002) 1 Number of samples (planes) in this image. Enumerated value shall be 1.
Acquisition Datetime (0008,002A) 1 The date and time that the acquisition of data started. Note: The synchronization of this time with an external clock is specified in the synchronization Module in Acquisition Time synchronized (0018,1800) .
Acquisition Duration (0018,9073) 1C The scan time in seconds used to create all frames of an Intravascular Optical Coherence Tomography image. Required if Image Type (0008,0008) Value 1 is ORIGINAL. May be present otherwise.
Acquisition Number (0020,0012) 1 A number identifying the single continuous gathering of data over a period of time which resulted in this image.
Photometric Interpretation (0028,0004) 1 Specifies the intended interpretation of the pixel data. Enumerated Value shall be MONOCHROME2.
Pixel Representation (0028,0103) 1 Data representation of pixel samples. Enumerated Value shall be 0.
Bits Allocated (0028,0100) 1 Number of bits allocated for each pixel sample. See C.8.27.2.4 for specialization.
Bits Stored (0028,0101) 1 Number of bits stored for each pixel sample. See C.8.27.2.4 for specialization.
High Bit (0028,0102) 1 Most significant bit for pixel sample data. High Bit (0028,0102) shall be one less than Bits Stored (0028,0101).
Presentation LUT Shape (2050,0020) 1C Specifies an identity transformation for the Presentation LUT, such that the output of all grayscale transformations defined in the IOD containing this Module are defined to be P-Values. Enumerated Value: IDENTITY = output is in P-Values. Required if Presentation Intent Type (0008,0068) equals FOR PRESENTATION.
Lossy Image Compression (0028,2110) 1C Specifies whether an Image has undergone lossy compression (at a point in its lifetime). Enumerated Values: 00 = Image has NOT been subjected to lossy compression. 01 = Image has been subjected to lossy compression. Once this tag has been set to 01 it shall not be reset. See C.7.6.1.1.5 Required if Lossy Compression has been performed on the Image.
Lossy Image Compression Ratio (0028,2112) 1C Describes the approximate lossy compression ratio(s) that have been applied to this image. Required if Lossy Image Compression (0028,2110) has a value of “01”. See C.7.6.1.1.5 for further explanation. May be multi-valued if successive lossy compression steps have been applied. Notes: 1. For example, a compression ratio of 30:1 would be described in this Attribute with a single value of 30. 2. For historical reasons, the lossy compression ratio should also be described in Derivation Description (0008,2111).
Lossy Image Compression Method (0028,2144) 1C A label for the lossy compression method(s) that have been applied to this image. See C.7.6.1.1.5 for further explanation. May be multi-valued if successive lossy compression steps have been applied; the value order shall correspond to the values of Lossy Image Compression Ratio (0028,2112). Required if Lossy Image Compression (0028,2110) has a value of “01”. Note: For historical reasons, the lossy compression method should also be described in Derivation Description (0008,2111).
Burned In Annotation (0028,0301) 1 Indicates whether or not image contains sufficient burned in annotation to identify the patient and date the image was acquired. Enumerated Value: NO
Recognizable Visual Features (0028,0302) 1 Indicates whether or not the image contains sufficiently recognizable visual features to allow the image or a reconstruction from a set of images to identify the patient. Enumerated Values: NO
Referenced Instance Sequence (0008,114A) 3 A sequence which provides reference to a set of non-image SOP Class/Instance pairs significantly related to this Image, including waveforms that may or may not be temporally synchronized with this image. One or more Items are permitted in this sequence.
>Include ‘SOP Instance Reference Macro' Table 10-11
>Purpose of Reference Code Sequence (0040,A170) 1 Code describing the purpose of the reference to the SOP Instances. Only a single Item shall be included in this sequence.
>>Include 'Code Sequence Macro' Table 8.8-1 Defined Context ID is CID 7004 for referenced waveforms.
Image Comments (0020,4000) 3 User-defined comments about the image.
Recommended Display Frame Rate (0008,2144) 3 Recommended rate at which the frames of an Intravascular OCT image should be displayed in frames/second.
Interpolation Type (0052,0039) 1C The type of interpolation used for the Polar to Cartesian scan-conversion. Defined Terms: REPLICATE BILINEAR CUBIC Required if Presentation Intent Type (0008,0068) equals FOR PRESENTATION.
Referenced Color Palette Instance UID (0028,0304) 1C The identifier of a color palette (i.e., an instance of the Color Palette Storage SOP Class “1.2.840.10008.5.1.4.39.1”) that may be used during rendering. See PS 3.4 Color Palette Storage Service Class and PS 3.6 Well-Known Color Palettes. Required if Pixel Presentation (0008,9205) is COLOR_REF.

C.8.27.2.1 Image Type and Frame Type

In addition to the requirements specified in C.8.16.1 Image Type, the following additional requirements and Defined Terms are specified.

Value 1 of Image Type (0008,0008) and Frame Type (0008,9007) is discussed in C.8.16.1.1. No additional requirements or Defined Terms.

Value 2 of Image Type (0008,0008) and Frame Type (0008,9007) is discussed in C.8.16.1.2. No additional requirements or Defined Terms.

Value 3 of Image Type (0008,0008) and Frame Type (0008,9007) is discussed in C.8.16.1.3. .

Table C.8.27.2-2 specifies the Defined Terms for IVOCT for Value 3 for Image Type (0008,0008) and Frame Type (0008,9007).

Table C.8.27.2-2 IVOCT IMAGE TYPE AND FRAME TYPE VALUE 3

Defined Term Name Defined Term Description
AXIAL An image that has an orientation that is perpendicular to the long axis of the vessel. (I.e. cross-sectional).
LONGITUDINAL An image that has an orientation that is parallel to the long axis of the vessel.

Value 4 of Image Type (0008,0008) and Frame Type (0008,9007) is discussed in C.8.16.1.4. No additional requirements or Defined Terms.

C.8.27.2.2 Volumetric Properties

The value of the Volumetric Properties attribute (0008,9206) allows applications doing geometric manipulations 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.8.27.2-3 specifies the Enumerated Values for the Volumetric Properties (0008,9206) attribute.

Table C.8.27.2-3VOLUMETRIC PROPERTIES ATTRIBUTE VALUES

Enumerated Value Name Enumerated Value Description
DISTORTED Frames do not represent the true geometry of the vessel.

C.8.27.2.3 Pixel Presentation

Pixel Presentation (0008,9205) is used to indicate whether a color tint is intended to be applied to the IVOCT image. See Table C.8.27.2-4.

Table C.8.27.2-4PIXEL PRESENTATION ATTRIBUTE VALUES

Enumerated Value Name Enumerated Value Description
COLOR Image is intended to be displayed in color using Supplemental Palette Color LUTs, but can be displayed in grayscale if current display does not support color or with a user selected LUT. See section C.8.13.3.1.2.1.
COLOR_REF Image is intended to be displayed in color using an externally defined Palette Color LUTs, but can be displayed in grayscale if current display does not support color, or with a user selected LUT. I.e., the encoded pixel values are still continuous grayscale values (and not arbitrarily order indices into a lookup table).
MONOCHROME Image is intended to be displayed in grayscale only.

C.8.27.2.4 Bits Allocated, Bits Stored and Samples Per Pixel

For IVOCT images, Bits Allocated (0028,0100), Bits Stored (0028,0101) Samples Per Pixel (0028,0002) are specified to use the following values for Presentation Intent Type (0008,0068) attribute:

Table C.8.27.2-5BITS ALLOCATED/STORED

Presentation Intent Type Bits Allocated / Bits Stored Samples Per Pixel
FOR PRESENTATION 8/8, 16/12 or 16/16 1
FOR PROCESSING 8/8, 16/12 or 16/16 1

C.8.27.3 Intravascular OCT Acquisition Parameters Module

Table C.8.27.3-1 describes the parameters used to acquire an Intravascular Optical Coherence Tomography image.

Table C.8.27.3-1INTRAVASCULAR OCT ACQUISITION PARAMETERS MODULE ATTRIBUTES

Attribute Name Tag Type Attribute Description
OCT Focal Distance (0052,0002) 2 Distance from focal point to center of catheter, in mm (measured in air).
Beam Spot Size (0052,0003) 2 The full width at half maximum (FWHM) of the point spread function (PSF) or line spread function (LSF), in µm (measured in air). Also known as Transverse Resolution.
Effective Refractive Index (0052,0004) 2C Index of refraction of the tissue and flush medias used during the Intravascular OCT acquisition. Required if Presentation Intent Type (0008,0068) is FOR PROCESSING. May be present otherwise.
OCT Acquisition Domain (0052,0006) 1 The type of OCT acquisition domain. Defined Terms: TIME FREQUENCY SPECTRAL
OCT Optical Center Wavelength (0052,0007) 2 Center optical wavelength of the OCT light source, in µm.
Axial Resolution (0052,0008) 2 The full width at half maximum (FWHM) of the axial plane response function, in µm (measured in air)
Ranging Depth (0052,0009) 1 Maximum detectable sample-to-reference path displacement, in mm (measured in air). This is the radius of the FOR PRESENTATION image in air. Note: Ranging Depth is distinct from Penetration Depth, which is the depth to which one can obtain an OCT signal in tissue.
A-line Rate (0052,0011) 1 The number of IVOCT A-lines acquired per second in Hz.
A-lines Per Frame (0052,0012) 1 Number of A-lines acquired in an IVOCT frame, including unused (padded) A-lines. Note: Will be the same as Rows (0028,0010) for a FOR PROCESSING image.

C.8.27.4 Intravascular OCT Processing Parameters Module

Table C.8.27.4-1 describes the parameters used for processing an Intravascular Optical Coherence Tomography polar data image.

Table C.8.27.4-1INTRAVASCULAR OCT PROCESSING PARAMETERS MODULE ATTRIBUTES

Attribute Name Tag Type Attribute Description
OCT Z Offset Applied (0052,0026) 1 Indicates whether or not Z offset correction was applied to the OCT image frames. Enumerated Values: YES NO
Refractive Index Applied (0052,003A) 1 Indicates whether or not Refractive Index correction was applied. Enumerated Values: YES NO See section C.8.27.4.1 for further explanation.
A-line Pixel Spacing (0052,0014) 1 Spacing of pixels in the A-line (X-axis), in mm.
Pixel Intensity Relationship (0028,1040) 1 The relationship between the pixel sample values and the IVOCT A-line intensity. See Section C.8.27.4.2.
First A-line Location (0052,0034) 1 Orientation in degrees at which the 1st A-line in the frame should be displayed. Value shall be between 0 and 360, with zero representing vertical.

C.8.27.4.1 Refractive Index Applied

For Refractive Index Applied (0052,003A) a value of YES indicates that Effective Refractive Index (0052,0004) correction has been applied to the reported A-line Pixel Spacing (0052,0014) attribute. A value of NO indicates that Effective Refractive Index (0052,0004) correction has not been applied (i.e. A-line Pixel Spacing corresponds to the pixel spacing in air).

C.8.27.4.2 Pixel Intensity Relationship

Pixel Intensity Relationship (0028,1040) shall identify the relationship of the pixel values to the IVOCT A-line intensity. Defined terms are:

LIN Approximately proportional to A-line intensity.
LOG Non-linear “Log Function”; A Pixel Intensity Relationship LUT shall be included with the image to allow it to be scaled back to its proportional A-line intensity value.

C.8.27.5 Intravascular Image Acquisition Parameters Module

Table C.8.27.5-1 describes the parameters and characteristics of an intravascular image acquisition. These parameters are common to both IVUS and IVOCT.

Table C.8.27.5-1INTRAVASCULAR IMAGE ACQUISITION PARAMETERS MODULE ATTRIBUTES

Attribute Name Tag Type Attribute Description
IVUS Acquisition (0018,3100) 1 Type of Intravascular Image Acquisition. Enumerated Values are: MOTORIZED MANUAL SELECTIVE MEASURED See section C.8.27.5.1.
IVUS Pullback Rate (0018,3101) 1C Intravascular imaging catheter pullback rate. Specified in units of mm/sec. Required if IVUS Acquisition (0018,3100) value is MOTORIZED. See section C.8.27.5.2.
IVUS Pullback Start Frame Number (0018,3103) 1C Frame number at which the motorized portion of the acquisition begins. Required if IVUS Acquisition (0018,3100) value is MOTORIZED. See section C.8.27.5.1.
IVUS Pullback Stop Frame Number (0018,3104) 1C Frame number at which the motorized portion of the acquisition is complete. Required if IVUS Acquisition (0018,3100) value is MOTORIZED. See section C.8.27.5.1.
Catheter Direction of Rotation (0052,0031) 1C Direction of rotation of the Intravascular rotating catheter during acquisition, from the perspective of the motor, proximal to distal. Enumerated Values: CW = clockwise CC = counter-clockwise Required if rotational catheter is used.
Catheter Rotational Rate (0052,0013) 1C Rate of rotation of the Intravascular rotating catheter during acquisition, in Hz. Required if rotational catheter is used.
Mode of Percutaneous Access Sequence (0052,0016) 2 Mode of access of the Intravascular Imaging Catheter. Zero or one Item shall be included in this sequence.
>Include ‘Code Sequence Macro’ (Table 8.8-1). Defined Context ID is 3746 Percutaneous Entry.

C.8.27.5.1 IVUS Acquisition

The attribute IVUS Acquisition (0018,3100) denotes the method used to acquire the Intravascular Images.

MOTORIZED: The Intravascular imaging catheter is positioned in the blood vessel proximal or distal to the anatomical structures to be examined. The catheter is attached to a motorized mechanism capable of either pushing forward or pulling back the catheter through the vessel at a constant velocity, as specified by the IVUS Pullback Rate (0018,3101). The motorized acquisition takes place during the time between acquisition of the IVUS Pullback Start Frame Number (0018,3103), and acquisition of the IVUS Pullback Stop Frame Number (0018,3104).

MANUAL: The Intravascular imaging catheter is positioned in the blood vessel proximal or distal to the anatomical structures to be examined. The catheter is then manually pulled back or pushed forward through the vessel segment of interest.

SELECTIVE: The Intravascular imaging catheter is positioned in the blood vessel. The catheter is then manually pushed forward and/or pulled back to examine the anatomical structures in the vessel.

MEASURED: The Intravascular imaging catheter is positioned in the blood vessel near the anatomical structures to be examined. The catheter is then pulled back or pushed forward through the vessel segment of interest. The longitudinal movement between each acquired frame is measured and recorded. See C.8.27.6.2 for more information.

C.8.27.5.2 IVUS Pullback Rate

The attribute IVUS Pullback Rate (0018,3101) specifies the constant velocity of longitudinal movement of the Intravascular imaging catheter. Positive values indicate movement from Distal to Proximal (pulling back). Negative values indicate movement from Proximal to Distal (pushing forward).

C.8.27.6 Intravascular OCT Functional Group Macros

The following sections contain Functional Group macros specific to the Intravascular OCT IOD.

C.8.27.6.1 Intravascular OCT Frame Type Macro

Table C.8.27.6.1-1 specifies the attributes of the Intravascular OCT Frame Type Functional Group.

Table C.8.27.6.1-1INTRAVASCULAR OCT FRAME TYPE MACRO ATTRIBUTES

Attribute Name Tag Type Attribute Description
Intravascular OCT Frame Type Sequence (0052,0025) 1 Identifies characteristics of this frame. Only a single Item shall be included in this sequence.
>Frame Type (0008,9007) 1 Type of Frame. A multi-valued attribute analogous to the Image Type (0008,0008). Enumerated Values and Defined Terms are the same as those for the four values of the Image Type (0008,0008) attribute, except that the value MIXED is not allowed. See section C.8.27.2.1.

C.8.27.6.2 Intravascular Frame Content Macro

Table C.8.27.6.2-1 specifies the attributes of the Intravascular Frame Content Functional Group.

Table C.8.27.6.2-1INTRAVASCULAR FRAME CONTENT MACRO ATTRIBUTES

Attribute Name Tag Type Attribute Description
Intravascular Frame Content Sequence (0052,0027) 1 A sequence that describes a general description of this image or frame. Only a single Item shall be included in this sequence.
>Intravascular Longitudinal Distance (0052,0028) 1C Longitudinal distance in millimeters between this frame and the previous acquired frame. Positive values indicate movement is from Distal to Proximal (pull back). Negative values indicate movement is from Proximal to Distal (push forward). Required if Intravascular Acquisition (0018,3100) equals MEASURED.
>Seam Line Location (0052,0033) 2C Clockwise rotational orientation (in degrees) at which the seam line in the frame is displayed, relative to vertical (zero degrees). Required if Presentation Intent Type (0008,0068) equals FOR PRESENTATION.

C.8.27.6.3 Intravascular OCT Frame Content Macro

Table C.8.27.6.3-1 specifies the attributes of the Intravascular OCT Frame Content Functional Group.

Table C.8.27.6.3-1INTRAVASCULAR OCT FRAME CONTENT MACRO ATTRIBUTES

Attribute Name Tag Type Attribute Description
Intravascular OCT Frame Content Sequence (0052,0029) 1 A sequence that describes a general description of this image or frame. Only a single Item shall be included in this sequence.
>OCT Z Offset Correction (0052,0030) 1 The amount to shift the frame along the axial direction, in pixels, to correct for interferometer path-length mismatch. See section C.8.27.6.3.1 for further explanation.
>Seam Line Index (0052,0036) 1 The A-line number (zero index) that coincides with the seam line as indicated with the First A-line Location (0052,0034) attribute.
>Number of Padded A-lines (0052,0038) 1C The number of padded A-lines contained in the FOR PROCESSING image frame. Required if the FOR PROCESSING image contains padded A-lines. See section C.8.27.6.3.2 for further explanation.

C.8.27.6.3.1 OCT Z Offset Correction

OCT Z Offset Correction (0052,0030) specifies the number of pixels to shift the A-lines of the frame to correct for the path length difference between the OCT Sample arm and Reference arm (in air). A positive value of Z Offset correction means pixels are shifted further away from the catheter optics. A negative value of Z Offset correction means pixels are shifted closer to the catheter optics. See Figure C.8.27-2

[pic]

Figure C.8.27-2 OCT Z Offset Correction Example

C.8.27.6.3.2 A-line Padding

Padded A-lines shall not be used in FOR PRESENTATION frames. Padded A-lines shall only be encoded in the high order rows of the FOR PROCESSING frame and shall be contiguous. Padded A-lines may contain arbitrary pixel values.