DICOM PS3.17 2026d - Explanatory Information
UUUU.4.5 Encoding of Distances and Geometry (Current)
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UUUU.4.5 Encoding of Distances and Geometry

To be properly interpreted, an Air Kerma value is provided with the point at which it has been measured or calculated (so-called Reference Point, or RP). Most systems define the Reference Point (RP) at an assumed radiation entrance location for a typical patient, expressed relative to equipment locations (e.g., Isocenter, tabletop, detector plane).

UUUU.4.5.1 Recommended Reference Points

Table UUUU.4.5.1-1 provides recommended Reference Points for different mechanical configurations as encoded in the Content Item (113780, DCM, "Reference Point Definition").

Table UUUU.4.5.1-1. Recommended Reference Points

Modality

Mechanical Configuration

Recommended Reference Point

X-Ray Angiography (XA)

Interventional system with C-arm and Isocenter.

(113860, DCM, "15cm from Isocenter toward Source")

Interventional system without Isocenter and with X-Ray source assembly fixed below table.

(113862, DCM, "1cm above Tabletop")

Radio Fluoroscopy (RF)

C-arm fluoroscopy system without integrated table.

(113861, DCM, "30cm in Front of Image Input Surface")

Lateral-type of fluoroscopy system.

(113864, DCM, "15cm from Table Centerline")

Fluoroscopy system with X-Ray source assembly fixed below table.

(113862, DCM, "1cm above Tabletop")

Fluoroscopy system with X-Ray source assembly fixed above table.

(113863, DCM, "30cm above Tabletop")

Radiography (DX, CR)

Radiography system with mobile cassettes or mobile digital detectors.

(113941, DCM, "In Detector Plane")

Mobile X-Ray sources where the information of the detector location is not available.

(113965, DCM, "100cm from X-Ray Source")

Mammography (MG)

All mammography systems including tomosynthesis.

(113865, DCM, "4.2cm above Breast Support Surface")

(113964, DCM, "At Surface of Patient")

Dentistry (IO, PX)

All dental systems except when performing cone beam CT.

(113941, DCM, "In Detector Plane")

Dental systems performing cone beam CT.

Reference Point is not defined.

Computer Tomography (CT)

All CT systems.

Reference Point is not defined.

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DICOM PS3.17 2026d - Explanatory Information