X-Ray Exposure doubt

[Jordi Huguet]

Hi all,

I'm working on extracting radiation information from IODs containing X-RAY ACQUISITION DOSE MODULE to feed a radiation dose record. I have for those specific images radiation dose info contained in DICOM headers which I would like to process and store in a dose record database. At this point I've made some assumptions on how to deal with certain data elements but please correct me if something of what I say isn't right.

As I've seen so far in the definition of such Module, Exposure (0018,1152) is the total amount of current at the XRay source during the whole radiation event the image represents. Thus, could be calculated (approximately) by ExposureTime * XRayTubeCurrent. Is that true?

Exposure (0018,1152) and RelativeXRayExposure (0018,1405) attributes have slightly similar naming and I was wondering what's the (effective) difference between them. I understand they should have different meaning since their values normally differ markedly. 

The Standard definition of RelativeXRayExposure states it is the "Indication of the applied dose, in manufacturer specific units". Why should anyone (NOT being the manufacturer himself) be interested in such an attribute that quantifies exposition in unspecified units? 

cheers,

Jordi

[Michael Flynn]

RelativeXRayExposure (0018,1405) has been used to store the exposure indicators that report measures of the x-ray energy deposited in the detector in segmented regions of the recorded image. They are used in the field a indicators of appropriate exposure levels with acceptable quantum noise. In the past, each manufacturer has their own measure to report and the metrics varied significantly. AAPM address this in the TG116 report that is available on their web-site. This includes an appendix with the metrics used by different manufacturers. A summary  of this report was published in Med. Phys. 36, 2898-2914 (2009). AAPM recommended a standardized metric that is consistent with an IEC standard that was issued at the same time, IEC-62494-1. DICOM subsequently defined new tags for the standardized exposure indicator: Exposure Index (0018,1411), Target Exposure Index (0018,1412), Deviation Index (0018,1413). Most systems now being delivered (or having recent software upgrades) are including these tags.

 

David Leong and Jeff Shepard gave a CE course at the 2011 AAPM annual meeting that provides an excellant overview. Jeff reported on a survey of manufacturers with respect to their status in implementing standardized measures. The slides are available on the AAPM web site, although only if logged in as a member,

 

 MJF

[Jordi Huguet]

Thank you Michael for clarifying it out a bit more, I'll def. have a look at the AAPM TG116 report. 

I understand that having the proper standardized metric DICOM tags would be the desired approach for gathering X-ray exposure indicators. Nevertheless, I'm afraid that those images with solely RelativeXRayExposure values will lack of interest for my purposes. 

regards,

Jordi

[Michael Flynn]

Both the RelativeXrayExposure and the new ExposureIndex tags do NOT
provide
information relevant to the radiation exposure of the patient and
associated organ dose.
They are used to monitoring image quality. Low values imply that the
image will
have high noise. High values imply low noise and suggest that a lower
technique could be used.

We post acceptable range for our technologists. If a radiograph is
below the bottom limit,
they are asked to repeat it. If it is above, they are told to
definitely not repeat it, but
to monitor subsequent studies to see if their techniques should be
systematically reduced.

We are just now setting up to extract these from DICOM tags and manage
them
within a dB as a few other sites have done. The legacy values are
still useful if
reports are compared against the high/low limits for the manufacturer.
Moreover, the legacy units can also be converted to standardized units
since
the manufacturers have been open about the relations between their
indices and the
air kerma in the calibration beam.

Entrance exposure (ESAK) estimation still needs kVp, ma, sec (ma-S)
information
that is generally only available from integrated system like a DR
room.
Even with the technique, a good estimate still needs output
calibration data.

> >> The Standard definition of **RelativeXRayExposure states it is the

[Kevin O'Donnell]

Hi Jordi,

So if you want to database the legacy values in the Relative X-Ray Exposure attribute,
make sure to also record the attribute values for Manufacturer, Model Name and
Software Version (see the General Equipment Module).  Those, combined with the
manufacturer documentation will allow you to interpret the contents of the Relative
X-Ray Exposure.

As Mike has said, for newer systems, the attributes in the Exposure Index Macro are
preferred over the vendor specific metrics.

Best Regards,
  Kevin

Michael Flynn <mi...@rad.hfh.edu> Sent by: medical-imaging-radia...@googlegroups.com 03/09/2012 08:57 AM Please respond to medical-imaging-radia...@googlegroups.com

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[Adam Łutkowski]

Hello everybody,

I have small problem with that field as well because my dicom files were made by older machine which doesn't use "Exposure Index" but "Relative X-Ray Exposure (0018,1405)".

This value varies between files in range 100-6000. In the TG116 report I couldn't find any metric, nor unit for such value. Could you give me any information what is the unit for that field or where I can find metrics?

Machine which generate that files is:
Manufacturer    Philips Medical Systems
Manufacturer's ModelName    DigitalDiagnost
Software Version '3.1.2', 'PMS81.101.1.1 GXR GXRIM9.1'

Best regards,
Adam

W dniu piątek, 9 marca 2012 18:07:50 UTC+1 użytkownik Kevin O'Donnell napisał:

Hi Jordi,

So if you want to database the legacy values in the Relative X-Ray Exposure attribute,
make sure to also record the attribute values for Manufacturer, Model Name and
Software Version (see the General Equipment Module).  Those, combined with the
manufacturer documentation will allow you to interpret the contents of the Relative
X-Ray Exposure.

As Mike has said, for newer systems, the attributes in the Exposure Index Macro are
preferred over the vendor specific metrics.

Best Regards,
  Kevin

Michael Flynn <mi...@rad.hfh.edu> Sent by: medical-imaging-radiation-dose-informatics@googlegroups.com 03/09/2012 08:57 AM Please respond to medical-imaging-radiation-dose-informatics@googlegroups.com

To medical-imaging-radiation-dose-informatics <medical-imaging-radiation-dose-informatics@googlegroups.com>

[Volker]

Hi Adam,

please get in contact with your national Philips service support. They will provide you the answer.

Best regards,

Volker