DICOM PS3.3 2019b - Information Object Definitions

C.34.10 Performed CT Acquisition Module

This Module contains acquisition parameter values for a performed CT imaging procedure. The purpose of this Module is to record all relevant parameters, not just to record the values that were constrained in the executed Defined Protocol (if any).

This Module contains Attributes that are "set" on the machine, e.g., to affect its behavior, but not those that describe the results. The latter may be found in the reconstructed images.

Table C.34.10-1. Performed CT Acquisition Module Attributes

Attribute Name

Tag

Type

Attribute Description

Acquisition Protocol Element Sequence

(0018,9920)

2

Parameter values for each Protocol Element in the acquisition protocol. Each Item in the Sequence describes one Element. Elements are performed in the order of their Protocol Element Number (0018,9921).

See Section C.34.9.1.

Zero or more Items shall be included in this Sequence.

>Include Table 10.28-1 “Protocol Element Identification Macro Attributes”

>Acquisition Type

(0018,9302)

1

Description of the method used during acquisition.

See Section C.8.15.3.2.1 for Defined Terms.

>Tube Angle

(0018,9303)

1C

The constant angle at which the X-Ray source is located during acquisition. 0 degrees means that the source is located at the highest point of the gantry orbit. Degrees increase from 0 to positive 360 in a clockwise direction as viewed when facing the gantry where the table enters the gantry.

Required if Acquisition Type (0018,9302) is CONSTANT_ANGLE.

>Constant Volume Flag

(0018,9333)

1

Identifies that the acquisition was performed by repetitively acquiring the same volume set over a period of time.

Note

The Acquisition Type (0018,9302) value may be SEQUENCED, SPIRAL or STATIONARY depending on whether table movement is necessary to cover the volume.

Enumerated Values:

YES

NO

>Fluoroscopy Flag

(0018,9334)

1

Identifies that near real-time display of a block of continuously acquired data was performed.

Enumerated Values:

YES

NO

>Revolution Time

(0018,9305)

1C

The time in seconds of a complete revolution of the source around the gantry orbit. This value is independent of the Reconstruction Angle (0018,9319) of the frame.

Required if Acquisition Type (0018,9302) is other than CONSTANT_ANGLE.

>Single Collimation Width

(0018,9306)

1

The width of a single row of acquired data (in mm).

Note

Adjacent physical detector rows may have been combined to form a single effective acquisition row.

>Total Collimation Width

(0018,9307)

1

The width of the total collimation (in mm) over the area of active X-Ray detection.

Note

This will be equal to the number of effective detector rows multiplied by single collimation width.

>Table Height

(0018,1130)

1

The distance in mm from the top of the patient table to the center of rotation of the source (i.e., the data collection center or isocenter). The distance is positive when the table is below the data collection center.

>Gantry/Detector Tilt

(0018,1120)

1

Nominal angle of tilt in degrees of the scanning gantry. Not intended for mathematical computations. Zero degrees means the gantry is not tilted, negative degrees are when the top of the gantry is tilted away from where the table enters the gantry.

>Table Speed

(0018,9309)

1

The distance in mm that the table moves in one second during the gathering of data.

>Table Feed per Rotation

(0018,9310)

1

Motion of the table (in mm) during a complete revolution of the source around the gantry orbit.

>Spiral Pitch Factor

(0018,9311)

1

Ratio of the Table Feed per Rotation (0018,9310) to the Total Collimation Width (0018,9307).

>CTDIvol

(0018,9345)

1C

Computed Tomography Dose Index (CTDI vol), in mGy according to IEC 60601-2-44, Ed.2.1 (Clause 29.1.103.4), The Volume CTDI vol.

It describes the average CTDIvol for this AcquisitionProtocol Element for the selected CT conditions of operation.

Required if Acquisition Type (0018,9302) is not CONSTANT_ANGLE. May be present otherwise.

>CTDI Phantom Type Code Sequence

(0018,9346)

1C

The type of phantom used for CTDI measurement according to IEC 60601-2-44.

Required if CTDIvol (0018,9345) is present.

Only a single Item shall be included in this Sequence.

>>Include Table 8.8-1 “Code Sequence Macro Attributes”

Defined CID 4052 "Phantom Devices".

>CTDIvol Notification Trigger

(0018,9942)

3

The threshold for the CTDIvol value, in mGy, at which a dose notification is triggered for this Acquisition Protocol Element.

See Section C.34.10.2.

>DLP Notification Trigger

(0018,9943)

3

The threshold for the DLP value, in mGy.cm, at which a dose notification is triggered for this Acquisition Protocol Element.

See Section C.34.10.2.

>Acquisition Motion

(0018,9930)

1

Motion of scan progression.

See Section C.34.10.1.

Defined Terms:

SINGLE

Scan progresses in a single pass from Acquisition Start Location to Acquisition End Location.

SHUTTLE

Scan progresses from Acquisition Start Location to Acquisition End Location, then reverses direction and scans back to Acquisition Start Location.

NO_MOTION

All slices are acquired simultaneously.

NOT_IMPORTANT

Acan either direction is acceptable.

The value of NOT_IMPORTANT is not permitted in the Performed Procedure Protocol IOD.

>Acquisition Start Location Sequence

(0018,9931)

3

Anatomically oriented transverse location where this acquisition starts.

Note

  1. This represents the nominal start location. Due to overscan, tissue may be irradiated beyond this location.

  2. In a Defined Procedure Protocol, this represents the intended start location. The operator may or may not select a location that exactly matches this anatomical location.

  3. In a Performed Procedure Protocol, this value may have been copied from the Defined Procedure Protocol and may not represent the exact anatomical location selected by the operator.

Only a single Item is permitted in the Sequence.

>>Include Table 10.27-1 “Reference Location Macro Attributes”

BCID 1000 “CT Transverse Plane Reference Basis” for Reference Basis Code Sequence (0018,9902)

BCID 1010 “Reference Geometry - Planes” for Reference Geometry Code Sequence (0018,9903)

>Acquisition End Location Sequence

(0018,9932)

3

Anatomically oriented transverse location where this acquisition ends.

Note

  1. This represents the nominal end location. Due to overscan, tissue may be irradiated beyond this location.

  2. In a Defined Procedure Protocol, this represents the intended end location. The operator may or may not select a location that exactly matches this anatomical location.

  3. In a Performed Procedure Protocol, this value may have been copied from the Defined Procedure Protocol and may not represent the exact anatomical location selected by the operator.

Only a single Item is permitted in the Sequence.

>>Include Table 10.27-1 “Reference Location Macro Attributes”

BCID 1000 “CT Transverse Plane Reference Basis” for Reference Basis Code Sequence (0018,9902)

BCID 1010 “Reference Geometry - Planes” for Reference Geometry Code Sequence (0018,9903)

>CT X-Ray Details Sequence

(0018,9325)

1

Parameter values for each of the X-Ray beams in the Acquisition Protocol Element. Each Item in the Sequence describes one X-Ray beam.

See Section C.34.10.3.

One or more Items shall be included in this Sequence.

>>Beam Number

(300A,00C0)

1

Identification number of the beam.

>>KVP

(0018,0060)

1

Peak kilo voltage output of the X-Ray generator.

>>Exposure Time in ms

(0018,9328)

1

Duration of exposure for this Acquisition Protocol Element in milliseconds.

If Acquisition Type (0018,9302) equals SPIRAL the duration of exposure shall be weighted by the Spiral Pitch Factor (0018,9311).

>>X-Ray Tube Current in mA

(0018,9330)

1

Nominal X-Ray tube current in milliamperes.

>>Exposure in mAs

(0018,9332)

1

The exposure expressed in milliampere seconds, for example calculated from exposure time and X-Ray tube current.

>>Auto KVP Selection Type

(0018,9944)

1

The type of automated selection of the kVp value.

Defined Terms:

NONE

Value is not selected automatically.

CNR_BASED

Value is selected based on Contrast to Noise Ratio.

DIAMETER_BASED

Value is selected based on patient diameter.

>>Auto KVP Upper Bound

(0018,9945)

3

Upper limit on the value of the auto-selected kVp.

Note

Constraints on KVP (0018,0060) represent constraints on the nominal KVP for the scan. Auto KVP Upper Bound (0018,9945) represents a direct constraint on the range of values that may be produced by the automated selection of the kVp value.

>>Auto KVP Lower Bound

(0018,9946)

3

Lower limit on the value of the auto-selected kVp.

Note

Constraints on KVP (0018,0060) represent constraints on the nominal KVP for the scan. Auto KVP Lower Bound (0018,9946) represents a direct constraint on the range of values that may be produced by the automated selection of the kVp value.

>>Exposure Modulation Type

(0018,9323)

1

A multi-valued label describing the type of current modulation used for the purpose of limiting the dose.

Defined Terms:

NONE

ANGULAR

Current is modulated over different tube angles.

LONGITUDINAL

Current is modulated along the axis of the table.

ECG_BASED

Current is modulated based on the cardiac phase.

ORGAN_BASED

Current is modulated based on the organs in the field of view.

>>Focal Spot(s)

(0018,1190)

1

Used nominal size of the focal spot in mm. The Attribute may only have one or two values, for devices with variable focal spot, small dimension followed by large dimension.

>>Data Collection Diameter

(0018,0090)

1

The diameter in mm of the region over which data were collected. See Section C.8.15.3.6.1.

Note

In the case of an Acquisition Type (0018,9302) of CONSTANT_ANGLE, the diameter is that in a plane normal to the central ray of the diverging X-Ray beam as it passes through the data collection center.

>>Filter Type

(0018,1160)

1

Type of filter(s) inserted into the X-Ray beam.

Defined Terms:

NONE

WEDGE

BUTTERFLY

STRIP

MULTIPLE

BOWTIE

Note

Multiple filters can be expressed by a combination of terms, e.g., BUTTERFLY+WEDGE.…

>>Cardiac Synchronization Technique

(0018,9037)

1

Cardiac synchronization technique applied during acquisition or processing.

Enumerated Values:

NONE

REALTIME

PROSPECTIVE

RETROSPECTIVE

PACED

See Section C.7.6.18.1.

>>Cardiac Signal Source

(0018,9085)

1C

Source of cardiac synchronization signal.

Defined Terms:

ECG

Electrocardiogram.

VCG

Vector cardiogram.

PP

Peripheral pulse.

Required if Cardiac Synchronization Technique (0018,9037) equals other than NONE.

>>Cardiac RR Interval Specified

(0018,9070)

1C

R-R interval in ms measured prior to or during the scan.

Required if Cardiac Synchronization Technique (0018,9037) equals other than NONE.

>>Cardiac Beat Rejection Technique

(0018,9169)

1C

Cardiac arrhythmia rejection technique.

Defined Terms:

NONE

RR_INTERVAL

Rejection based on deviation from average RR interval.

QRS_LOOP

Rejection based on deviation from regular QRS loop.

PVC

Rejection based on PVC criteria.

Required if Cardiac Synchronization Technique (0018,9037) equals PROSPECTIVE or RETROSPECTIVE.

>>Low R-R Value

(0018,1081)

2C

R-R interval low limit for beat rejection, in ms.

Required if Cardiac Synchronization Technique (0018,9037) equals PROSPECTIVE or RETROSPECTIVE.

>>High R-R Value

(0018,1082)

2C

R-R interval high limit for beat rejection, in ms.

Required if Cardiac Synchronization Technique (0018,9037) equals PROSPECTIVE or RETROSPECTIVE.

>>Skip Beats

(0018,1086)

3

Number of beats prescribed to be skipped after each detected arrhythmia.

>>Cardiac Framing Type

(0018,1064)

1C

Type of framing performed.

See Section C.7.6.18.1.1.1 for description and Defined Terms.

Required if type of framing is not time forward from trigger, may be present otherwise.

>>Respiratory Motion Compensation Technique

(0018,9170)

1

Technique to reduce respiratory motion artifacts.

Defined Terms:

NONE

BREATH_HOLD

REALTIME

GATING

TRACKING

RETROSPECTIVE

CORRECTION

See Section C.7.6.18.2.

>>Respiratory Signal Source

(0018,9171)

1C

Signal source from which respiratory motion is derived.

Defined Terms:

NONE

BELT

NASAL_PROBE

CO2_SENSOR

ECG

Required if Respiratory Motion Compensation Technique (0018,9170) equals other than NONE or BREATH_HOLD. May be present otherwise.

>>Respiratory Trigger Delay Threshold

(0020,9256)

1C

Respiratory trigger threshold in percent of the chest expansion for the frame relative to the last Respiratory-Peak.

See Section C.7.6.16.2.17.1 for further explanation.

Required if Respiratory Motion Compensation Technique (0018,9170) equals other than NONE, REALTIME or BREATH_HOLD. May be present otherwise.

>>Respiratory Trigger Type

(0020,9250)

1C

Characteristic of the respiratory signal used to the define the respiratory triggering.

Defined Terms:

TIME

AMPLITUDE

BOTH

Required if the value is not TIME. May be present otherwise.

>Requested Series Description

(0018,9937)

3

Requested text to copy into the Series Description(0008,103E) of raw instances resulting from this Acquisition Protocol Element.

>Content Qualification

(0018,9004)

3

Content Qualification Indicator of instances resulting from this Acquisition Protocol Element.

Enumerated Values:

PRODUCT

RESEARCH

SERVICE

See Section C.34.12.1.


C.34.10.1 Acquisition Motion

The motion, in patient terms, during acquisition progression. For example, due to the direction of contrast propogation or the need to manage equipment connected to the patient, it may be helpful to specify the acquisition progress in the expected direction of contrast propogation.

A scan that shuttles back and forth can be encoded as multiple elements and each specifies the Start Location and the End Location. Alternatively, a scanner may provide the ability to shuttle in a single scan element, in which case this value indicates the initial direction of motion and further details about the shuttling are likely contained in Private Attributes.

DICOM PS3.3 2019b - Information Object Definitions