| DICOM PS3.3 2024e - Information Object Definitions |
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The table in this section contains Attributes that describe a time-based waveform. A waveform consists of one or more multiplex groups, each encoded into an Item in the Waveform Sequence. All channels within a multiplex group are synchronously digitized at a common sampling frequency.
Table C.10-9. Waveform Module Attributes
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Sequence of Items, each representing one waveform multiplex group. One or more Items shall be included in this Sequence. Ordering of Items in this Sequence is significant for external reference to specific multiplex groups. |
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Offset time in milliseconds from a reference time (see Section C.10.9.1.1). Required if Acquisition Time Synchronized (0018,1800) value is Y; may be present otherwise. |
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Offset time in milliseconds from a synchronization trigger to the first sample of a waveform multiplex group. May be positive or negative. Required if waveform acquisition is synchronized to a trigger. |
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Sample number whose time corresponds to a synchronization trigger (see Section C.10.9.1.2). |
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See Section C.10.9.1.3. |
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Unique Identifier for the multiplex group. Required if the same Multiplex Group is used in more than one SOP Instance. May be present otherwise. |
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Sequence of Items, with one Item per channel (see Section C.10.9.1.4). One or more Items shall be included in this Sequence. Ordering of Items in this Sequence is significant for reference to specific channels. |
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Text label for channel, which may be used for display purposes. |
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One or more values for the status of this channel within this SOP Instance. Precise location of a change in status may be noted in an Annotation. |
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A coded descriptor of the waveform channel source (metric, anatomical position, function, and technique). Only a single Item shall be included in this Sequence. (see Section C.10.9.1.4.1). |
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>>>Include Table 8.8-1 “Code Sequence Macro Attributes”. |
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Sequence of Items that further qualify the Waveform Source. One or more Items shall be included in this Sequence. Ordering of Items in this Sequence may be semantically significant. Required if Channel Source Sequence (003A,0208) does not fully specify the semantics of the source. |
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>>>Include Table 8.8-1 “Code Sequence Macro Attributes”. |
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A Sequence that provides reference to a DICOM waveform from which this channel was derived. |
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>>>Include Table 10-11 “SOP Instance Reference Macro Attributes” |
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Identifies the waveform multiplex group and channel within the referenced SOP Instance. Pair of values (M,C). |
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Nominal numeric value of unit quantity of sample. Required if samples represent defined (not arbitrary) units. |
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A coded descriptor of the Units of measure for the Channel Sensitivity. Only a single Item shall be included in this Sequence. (see Section C.10.9.1.4.2). |
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>>>Include Table 8.8-1 “Code Sequence Macro Attributes” |
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Multiplier to be applied to encoded sample values to match units specified in Channel Sensitivity (003A,0210) (e.g., based on calibration data) (see Section C.10.9.1.4.2). |
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Offset of encoded sample value 0 from actual 0 using the units defined in the Channel Sensitivity Units Sequence (003A,0211). |
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Offset of first sample of channel from waveform multiplex group start time, in seconds (see Section C.10.9.1.4.3) |
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Offset of first sample of channel from waveform multiplex group start time, in samples (see Section C.10.9.1.4.3) |
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Additional offset of first sample of channel to be used in aligning multiple channels for presentation or analysis, in seconds (see Section C.10.9.1.4.3). |
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Number of significant bits within the waveform samples (see Section C.10.9.1.4.4). |
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Nominal 3dB point of lower frequency of pass band; in Hz. Required if Waveform Amplifier Type (003A,0317) is AC and Filter Low Frequency Characteristics Sequence (003A,0318) is not present. Shall not be present if Waveform Amplifier Type (003A,0317) is DC. May be present otherwise. |
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The properties of low frequency (high-pass) filters used for the waveform acquisition. Required if Waveform Amplifier Type (003A,0317) is AC and Filter Low Frequency (003A,0220) is not present. May be present otherwise unless Waveform Amplifier Type (003A,0317) is DC. |
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>>>Include Table C.10.12-1 “Waveform Filter Characteristics Macro Attributes” |
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Nominal 3dB point of upper frequency of pass band; in Hz. Required if Waveform Amplifier Type (003A,0317) is present and Filter High Frequency Characteristics Sequence (003A,0319) is not present. May be present otherwise. |
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The properties of high frequency (low-pass) filters used for the waveform acquisition. Required if Waveform Amplifier Type (003A,0317) is present and Filter High Frequency (003A,0221) is not present. May be present otherwise. |
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>>>Include Table C.10.12-1 “Waveform Filter Characteristics Macro Attributes” |
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The properties of notch filters used for the waveform acquisition. |
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>>>Include Table C.10.12-1 “Waveform Filter Characteristics Macro Attributes” |
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Filter Lookup Table providing the total effect of all filters applied. |
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>>>Include Table C.10.13-1 “Waveform Filter Lookup Table Macro Attributes” |
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Sequence of items with impedance values for the given channel (see Section C.10.9.1.11). |
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Minimum valid sample value as limited by the acquisition equipment (see Section C.10.9.1.4.5). |
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Maximum valid sample value as limited by the acquisition equipment (see Section C.10.9.1.4.5). |
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Size of each waveform data sample within the Waveform Data; see Section C.10.9.1.5 |
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Data representation of the waveform data points. See Section C.10.9.1.5. |
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Value of waveform samples inserted in channels when input is absent or invalid. Required if acquisition equipment inserts padding. See Section C.10.9.1.6. |
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Encoded data samples - channel multiplexed. See Section C.10.9.1.7 |
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The recommended time-based waveform data display scale in units of mm/s (see Section C.10.9.1.8). |
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A color triplet value recommended for rendering the waveform display background on a color display. The units are specified in PCS-Values, and the value is encoded as CIELab. See Section C.10.7.1.1. |
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Sequence of Items, each Item describing a Presentation Group of one or more waveform channels to be displayed together. |
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Sequence of Items, each Item describing a channel to be displayed in the Presentation Group. |
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Identifier of the displayed channel, specified as a pair of values (M,C) where the first value is the ordinal of the Item of Waveform Sequence (5400,0100) (i.e., the Multiplex Group Number), and the second value is the ordinal of the Item of the Channel Definition Sequence (003A,0200) Attribute (i.e., the Waveform Channel Number) within the multiplex group. |
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The offset in seconds from the beginning of the channel waveform data to the first sample to be used for presentation. Value may be negative. |
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A color triplet value recommended for rendering the channel on a color display. The units are specified in PCS-Values, and the value is encoded as CIELab. See Section C.10.7.1.1. |
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Position of the Channel within the Presentation Group display area (see Section C.10.9.1.9). |
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Specifies display area shading between the displayed waveform channel and another line. The nature of the shading (e.g., solid, or cross-hatching) is implementation dependent. Enumerated Values:
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Fraction of the Presentation Group vertical display dimension assigned to the unit quantity (least significant bit) of the Channel samples (see Section C.10.9.1.10). Required if Absolute Channel Display Scale (003A,0248) is not present, may be present otherwise. |
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Nominal vertical display height in mm assigned to the unit quantity (least significant bit) of the Channel samples (see Section C.10.9.1.10). Required if Fractional Channel Display Scale (003A,0247) is not present, may be present otherwise. |
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Multiplex Group Time Offset (0018,1068) specifies the offset time in milliseconds from a reference time to the first sample of the multiplex group. The reference time is Acquisition DateTime (0008,002A), if present in the SOP Instance.
In all other cases, the offset is from an arbitrary reference time that is the same for all Multiplex Groups in the SOP Instance; i.e., the Multiplex Group Time Offset allows only relative time synchronization between Multiplex Groups in the SOP Instance. The arbitrary reference time may nominally be assumed to be Content Time (0008,0033).
The Trigger Sample Position (0018,106E) specifies the sample that was digitized at the same time as a synchronization trigger. Sample positions are enumerated by channel, with the first sample enumerated 1. This provides a single trigger sample location for all channels of the multiplex group. Although channels may not have been sampled synchronously (as specified by Channel Time Skew or Channel Sample Skew), for the purpose of determining the location of the trigger with an integer value position, all channels are considered to be synchronous.
Waveform Originality (003A,0004) shall have the value ORIGINAL if the Waveform Data samples are the original or source data, and shall have the value DERIVED if the Waveform Data samples have been derived in some manner from the sample data of other waveforms.
Waveform Originality (003A,0004) is comparable to Image Type (0008,0008) Value 1 (see Section C.7.6.1.1.2). Within a single Multiplex Group, all channels shall have the same Originality value.
Waveform data that has been transcoded from a non-DICOM format may have Waveform Originality value ORIGINAL if the samples are unchanged from the originally acquired waveform samples.
Channel Source Sequence (003A,0208) identifies the metric (quality being measured, e.g., voltage or pressure), the anatomical position of the sensor or probe, the function of the channel (e.g., measurement or stimulus), and any particulars of technique that affect those parameters (e.g., pull-back across multiple anatomic sites, or differential input from two distinct sites). If the full semantics of the source is not carried in a single coded entry (e.g., if it specifies the location but not the metric), additional qualifiers are identified in Channel Source Modifiers Sequence (003A,0209) coded entries.
When a single sensor channel is used to collect a waveform from two (or more) anatomic sites, e.g., in hemodynamic pull-back procedures, multiple Channel Source Modifier Items will identify the sequence of sites, if not encoded in the semantics of the Channel Source Coded Entry. Transition times from one site to another may be indicated with an Annotation, or pull-back rate may be indicated with an Acquisition Context Sequence (0040,0555) Item (see Section C.7.6.14).
The Baseline CIDs are defined by IOD in accordance with Section A.34. Restrictions in the IOD may also determine the pattern of specification of the waveform source, i.e., which Item is to be encoded in the Channel Source Sequence, and the order in which Channel Source Modifier Items are to be encoded. Unless otherwise specified, pattern of specification of the waveform source shall be:
If the function of the channel is not measurement, the function (and optionally additional parameters of the channel source) shall be encoded in the Channel Source Item.
If the function of the channel is measurement of a waveform originating in the patient (the implicit default function), the metric (and optionally additional parameters of the channel source) shall be encoded in the Channel Source Item.
If not encoded in the Channel Source Item, and a particular technique needs to be encoded, that technique shall be encoded in the first Channel Source Modifier Item.
Channel Sensitivity (003A,0210) is the nominal value of one unit (i.e., the least significant bit) of each waveform sample in Waveform Data (5400,1010). It includes both the amplifier gain and the analog-digital converter resolution. It does not relate the vertical scaling of a waveform on a particular display.
A previous release specified Channel Sensitivity Units Sequence (003A,0211) DCID 3082 “Cardiology Measurement Unit (Retired)”. CID 3082 “Cardiology Measurement Unit (Retired)” was a subset of CID 82 “Measurement Unit”, and has been retired in favor of the more general CID 82 “Measurement Unit”. See PS3.3-2011.
Channel Sensitivity Correction Factor (003A,0212) is the ratio of the actual (calibrated) value to the nominal channel sensitivity specified in Channel Sensitivity (003A,0210). Thus a waveform sample value multiplied by the Channel Sensitivity value provides the nominal measured value in Channel Sensitivity Units, and that nominal value multiplied by the Channel Sensitivity Correction Factor provides the calibrated measured value.
Skew is also known as a sub-sample time delay, typically caused by using a multiplexed analog to digital converter that switches from channel to channel. For analysis it may be important to know if the analog channels were all latched simultaneously or sequentially and then digitized. Skew may be represented as time offset in seconds, or a fractional number of samples.
Separate and additional to skew is an offset time adjustment (sometimes called latency) by which one waveform channel is displaced significantly relative to others before sampling.
As an example, a hemodynamic pressure is measured at the external end of a catheter, and thus its measurement is delayed by the time for the pressure wave to propagate down the catheter. With a dual catheter measurement, two signals may be acquired at the same time, but one arrives by a longer distance (e.g., a pulmonary capillary wedge pressure, compared to a left ventricular pressure). To obtain an accurate comparison of the waveforms (e.g., the gradient across the mitral valve), one waveform has to be offset (perhaps as much as 30 ms) to synchronize them.
Waveform Bits Stored (003A,021A) specifies the number of significant bits within the Waveform Bits Allocated of each sample, for signed or unsigned integers.
If Waveform Sample Value Representation is MB or AB, Waveform Bits Stored shall be 8.
Waveform Bits Allocated (5400,1004) specifies the number of bits allocated for each sample, and Waveform Sample Interpretation (5400,1006) specifies the data representation of each waveform sample. Waveform Bits Allocated shall be a multiple of 8. These Attributes are related, and their Defined Terms are specified in Table C.10-10.
Table C.10-10. Waveform Bits Allocated and Waveform Sample Interpretation
The set of valid values from within this table may be constrained by definition of the IOD (see Section A.34).
mu-law and A-law encoding is without the alternate bit inversion used for PCM transmission through the telephone network.
This representation also applies to the Channel Minimum and Maximum Data Values, and Waveform Padding Value.
Equipment that produces digitized waveform curves may encode a specific value when the source is disconnected or otherwise invalid. This value is encoded like the Waveform Data (5400,1010) Attribute with one sample only.
The Waveform Padding Value need not be within the range specified by the Channel Minimum and Maximum Data Values.
Each sample shall be encoded using the defined Waveform Sample Interpretation (5400,1006), using the defined number of Waveform Bits Stored (003A,021A) right justified in the sample. If the number of Waveform Bits Stored is less than the number of bits in Waveform Bits Allocated, the sign bit shall be extended to the highest order bit of the data sample.
Data values are encoded interleaved, incrementing by channel and then by sample (i.e., C1S1, C2S1,C3S1, … CnS1, C1S2, C2S2, C3S2, … CnSm), with no padding or explicit delimitation between successive samples. Cx denotes the channel defined in the Channel Definition Sequence (003A,0200) Item in Item number x.
With 8-bit Waveform Data, there may be an odd number of channels and an odd number of samples; see PS3.5 for rules on encoding.
The sign bit extension rule differs from the rules for pixel data, which do not require sign extension.
Waveform Data Display Scale (003A,0230) specifies the recommended display scale in the time dimension for the waveform data in units of mm/s. The display application needs to know the horizontal pixel scaling of the display device to effectively apply this Attribute. Waveform Data Display Scale (003A,0230), divided by Sampling Frequency (003A,001A), times the display scaling in pixels/mm gives the number of horizontal pixels between subsequent samples.
This presumes a conventional waveform display with time in the horizontal dimension, and waveform measured quantity in the vertical dimension.
This Attribute is useful for size consistency between softcopy display and classical hardcopy ECG printouts. E.g., for the channels of a multiplex group whose Sampling Frequency is 400 Hz, and whose Waveform Data Display Scale (003A,0230) is 25 mm/s, and that is being displayed on a monitor at 4.1 pixels/mm, the horizontal interval between samples is
How the display application renders samples at fractional pixel spacing is implementation dependent.
Channel Position (003A,0245) specifies the position of the channel display baseline in the Presentation Group vertical display dimension. The channel position is relative to the top of the display area. Each Presentation Group display area is defined with vertical dimension positions of 0.0 (top of display area) to 1.0 (bottom of display area).
This presumes a conventional waveform display with time in the horizontal dimension, and waveform measured quantity in the vertical dimension.
Compare Bounding Box Annotation Units (0070,0003) value DISPLAY in Section C.10.5.
Channel sample value 0 maps to the Channel Position (003A,0245) display baseline. The Real World Value associated with the baseline is specified in Channel Baseline (003A,0213).
Multiple channels may overlap, and may share the same Channel Position (003A,0245).
Fractional Channel Display Scale (003A,0247) or Absolute Channel Display Scale (003A,0248) specifies the vertical scaling of the channel display. If both Attributes are provided, the selection of which to use for display control is implementation dependent.
Fractional Channel Display Scale (003A,0247) specifies the fraction of the Presentation Group vertical display dimension used to offset each unit of the waveform sample value from the baseline Channel Position (003A,0245). Positive offset values are towards the top of the display area.
E.g., for a channel whose Fractional Channel Display Scale (003A,0247) value is 0.004, and whose Channel Position (003A,0245) value is 0.5, a sample whose value is -37 would be displayed at a position
of the total vertical display dimension below the top of the Presentation Group display area.
Absolute Channel Display Scale (003A,0248) specifies the nominal physical distance on a display device (monitor) used to offset each unit of the waveform sample value from the baseline Channel Position (003A,0245). The display application needs to know the vertical pixel scaling of the display device to effectively apply this Attribute. The Channel Sensitivity (003A,0210) value in Channel Sensitivity Units (003A,0211), divided by Absolute Channel Display Scale (003A,0248) value, gives the real-world scaling of the intended display.
This Attribute is useful for size consistency between softcopy display and classical hardcopy waveform printed charts. E.g., a channel whose Channel Sensitivity (003A,0210) value is 44 uV (per least significant bit), and whose Absolute Channel Display Scale (003A,0248) value is 0.44 mm, has a real-world display scale of 0.1 mV/mm.
E.g., for a channel whose Absolute Channel Display Scale (003A,0248) value is 0.44 mm, and that is being displayed on a monitor at 4.1 pixels/mm, a sample whose value is 107 would be displayed at a position
Display for waveform samples that would lie outside the Presentation Group display area is unspecified.
Negative values of Fractional Channel Display Scale (003A,0247) and Absolute Channel Display Scale (003A,0248) are allowed.
| DICOM PS3.3 2024e - Information Object Definitions |
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