Материал: part03

C.10.9.1 Waveform Attribute Descriptions​

C.10.9.1.1 Multiplex Group Time Offset​

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).​

C.10.9.1.2 Trigger Sample Position​

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.​

C.10.9.1.3 Waveform Originality​

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.​

Note​

1.​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.​

2.​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.​

C.10.9.1.4 Channel Definition Sequence​

C.10.9.1.4.1 Channel Source and Modifiers​

Channel Source Sequence (003A,0208) identifies the metric (quality being measured, e.g., voltage or pressure), the anatomical pos-​ ition 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 pro-​ cedures, multiple Channel Source Modifier Items will identify the sequence of sites, if not encoded in the semantics of the Channel​ SourceCodedEntry.TransitiontimesfromonesitetoanothermaybeindicatedwithanAnnotation,orpull-backratemaybeindicated​ 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​

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Channel Source Modifier Items are to be encoded. Unless otherwise specified, pattern of specification of the waveform source shall​ be:​

1.​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.​

2.​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.​

3.​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.​

Note​

For example, an intracardiac measurement of a pressure waveform across the mitral valve by means of a catheter pullback​ maybeencodedinoneofthefollowingthreeways(usingpseudo-codedterminology),dependingontheavailabilityofcoded​ terms with sufficient expressive power:​

C.10.9.1.4.2 Channel Sensitivity and Channel Sensitivity Units​

Channel Sensitivity 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.​

Note​

A prior edition specified CID 3082 “Cardiology Units of Measurement (Retired)” as the Defined Context Group for Channel​ Sensitivity Units Sequence. CID 3082 “Cardiology Units of Measurement (Retired)” was a subset of CID 82 “Units of Meas-​ urement”, and has been retired in favor of the more general CID 82 “Units of Measurement”. See PS3.3-2011.​

ChannelSensitivityCorrectionFactor(003A,0212)istheratiooftheactual(calibrated)valuetothenominalchannelsensitivityspecified​ 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.​

C.10.9.1.4.3 Channel Skew and Channel Offset​

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.​

Note​

Asanexample,ahemodynamicpressureismeasuredattheexternalendofacatheter,andthusitsmeasurementisdelayed​ 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.​

C.10.9.1.4.4 Waveform Bits Stored​

Waveform Bits Stored (003A,021A) specifies the number of significant bits within the Waveform Bits Allocated of each sample, for​ signed or unsigned integers.​

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If Waveform Sample Value Representation is MB or AB, Waveform Bits Stored shall be 8.​

C.10.9.1.4.5 Channel Minimum and Maximum Value​

Channel Minimum Value (5400,0110) and Channel Maximum Value (5400,0112) Attributes may be used to send the analog-to-digital​ converter limits (i.e., the clipping levels).​

Note​

These values do not represent the maximum and minimum values in the encoded data, but rather the valid range of values.​

C.10.9.1.5 Waveform Bits Allocated and Waveform Sample Interpretation​

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 At-​ tributes are related, and their Defined Terms are specified in Table C.10-10.​

Table C.10-10. Waveform Bits Allocated and Waveform Sample Interpretation​

Note​

1.​The set of valid values from within this table may be constrained by definition of the IOD (see Section A.34).​

2.​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.​

C.10.9.1.6 Waveform Padding Value​

Equipmentthatproducesdigitizedwaveformcurvesmayencodeaspecificvaluewhenthesourceisdisconnectedorotherwiseinvalid.​ 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.​

C.10.9.1.7 Waveform Data​

EachsampleshallbeencodedusingthedefinedWaveformSampleInterpretation(5400,1006),usingthedefinednumberofWaveform​ BitsStored(003A,021A)rightjustifiedinthesample.IfthenumberofWaveformBitsStoredislessthanthenumberofbitsinWaveform​ 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.​

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Note​

1.​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.​

2.​The sign bit extension rule differs from the rules for pixel data, which do not require sign extension.​

C.10.9.1.8 Waveform Data Display Scale​

Waveform Data Display Scale (003A,0230) specifies the recommended display scale in the time dimension for the waveform data in​ unitsofmm/s.ThedisplayapplicationneedstoknowthehorizontalpixelscalingofthedisplaydevicetoeffectivelyapplythisAttribute.​ 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.​

Note​

1.​Thispresumesaconventionalwaveformdisplaywithtimeinthehorizontaldimension,andwaveformmeasuredquantity​ in the vertical dimension.​

2.​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​

25 / 400 * 4.1 = 0.25625 pixels​

How the display application renders samples at fractional pixel spacing is implementation dependent.​

C.10.9.1.9 Channel Position​

ChannelPosition(003A,0245)specifiesthepositionofthechanneldisplaybaselineinthePresentationGroupverticaldisplaydimension.​ 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).​

Note​

1.​Thispresumesaconventionalwaveformdisplaywithtimeinthehorizontaldimension,andwaveformmeasuredquantity​ in the vertical dimension.​

2.​Compare Bounding Box Annotation Units (0070,0003) value DISPLAY in Section C.10.5.​

Channelsamplevalue0mapstotheChannelPosition(003A,0245)displaybaseline.Therealworldvalueassociatedwiththebaseline​ is specified in Channel Baseline (003A,0213).​

Multiple channels may overlap, and may share the same Channel Position (003A,0245).​

C.10.9.1.10 Channel Display Scale​

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.​

Note​

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​

0.5 - (-37 * 0.004) = 0.648​

of the total vertical display dimension below the top of the Presentation Group display area.​

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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​ SensitivityUnits(003A,0211),dividedbyAbsoluteChannelDisplayScale(003A,0248)value,givesthereal-worldscalingoftheintended​ display.​

Note​

1.​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.​

2.​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​

107 * 0.44 * 4 = 193.028​

pixels above the Channel Position (003A,0245) baseline.​

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.​

C.10.10 Waveform Annotation Module​

The table in this section contains Attributes that identify annotations to the waveform of the current SOP Instance. Each annotation​ conceptually forms the equivalent of a overlay on a presentation display of the annotated entity. Annotations may represent a meas-​ urement or categorization based on the waveform data, identification of regions of interest or particular features of the waveform, or​ events during the data collection that may affect diagnostic interpretation (e.g., the time at which the subject coughed).​

Each Annotation Item shall have the following components:​

1.​An annotation Text, Coded Name (only), Coded Name/Coded Value pair, or Coded Name/Numeric Measurement pair (mutually​ exclusive)​

2.​Temporal coordinates in the Waveform to which the annotation applies​

Table C.10-11. Waveform Annotation Module Attributes​

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