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MINUTES-tcon
DICOM WORKING GROUP 21
(Computed Tomography)
Date and Time:
Dec. 19, 2013
Members Present:
Represented by:
AAPM /MD Anderson
Siemens Healthcare
Toshiba Medical Systems
Philips Healthcare
Dianna Cody
For Shuai Leng
Reinhard Ruf
Kevin O’Donnell
Shlomo Gotman
Members Absent:
Represented by:
Pixelmed Publising
GE Healthcare
David Clunie
Balaji Raman (PT)
Alternate Voting Representatives, Observers, and Others Present:
Ami Altman
Don Peck
Stephen Vastagh
Zhou Yu
Philips Healthcare
AAPM / H Ford Health
MITA, Secretariat
Toshiba Medical Systems
Presiding Officers
Reinhard Ruf, Chair
1. Opening
DICOM WG-21, 2013-12-19
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The meeting was called to order at 12.00 USA Eastern time. The Agenda was approved. The
Secretary reviewed the antitrust rules. The approval of the minutes of the last t-con were tabled
in the interest of time. The purpose of the t-con was to discuss image definitions for the new
Multi-Energy Draft Supplement to the DICOM Standard to assure consistent and unambiguous
interpretation of the standard.
2. Image Definitions
The following initial terms were discussed definitions were discussed:
Material-Base
Material-Only
Material-Free
The questions posed before the meeting are shown in Exhibit A.
After a technical discussion it was decided to revise as follows:
Material-Base (there was still an open issue about the usefulness)
Material-Enhanced (also mentioned were material specific and target material)(not HU)
Material-Supressed (HU – Hounsfield Unit))
The discussion included the topics and decisions listed below:
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there is a need to emphasize lack of purity of the definitions, i.e. that more than 2 bases
may be used.
no “poly-enhanced” or “poly-suppressed” meanings, at this time
all three images are “derived” images
there is a need to describe the methods used to create the enhanced and suppressed
iamges in a generic way
presentation units
o HU for single material
o HU is not appropriate for material-base
HU is for original images
Use of a new IOD is still an open issue, there are advantages and disadvantaes to using
current IOD (systems will either accept or choke)
The basic question is how to differentiate between material-base and the other images
3. Next steps
DICOM WG-21, 2013-12-19
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Homework:
by Dec. 30, 2013 S. Gotman will draft and distribute initial draft definitions for
the above three images and for monochromatic and atomic number images as
well.
4. New Business
None
5. Next Meetings and Tcons
Tcon:
Wednesday, 2014-02-05, 10.45-11.45 USA Eastern Time
6. Adjournment
The meeting was adjourned at 13.00
Reported by Stephen Vastagh, Secretary
Reviewed by legal counsel: CRS 2013-12-20
EXHIBIT A
1) “Material-Base” – one primary material with contributions from other materials
One of the outcomes of spectral\dual energy CT is a series of material-specific images. Materialspecific images can be presented either in terms of their partial density (concentration) in each
Voxel in units of mg/cc (may be using a stretched 12-bit scale), or in terms of HU since
theoretically the attenuation coefficient (HU) is linear with the density.
Although the material decomposition into the two base materials is always correct if only these
two base materials are scanned, the equivalent base material concentrations for other materials
depends to some extend (% level) on the attenuation curve of the material.
2) “Material-Only” – a derived image where the intention is to have only this material present
in the pixels
How to differentiate between a “Materiel-Base” image (that may include contributions of other
materials) and Material-Only image?
For Material-Only image – are we putting concentration into the pixels, or HU-based attenuation?
How shall we name them?
So one question is how to tag these two alternatives, or how to differentiate them? And should we
call it Material-Only (e.g. Iodine-Only image), or Material-Map image (e.g. Iodine-Map image)
Note that this is very different from two-material base presentation where the Iodine-base image
includes also most of the Calcium in the image (since Alvarez-Macovski projection-based
decomposition, as well as 2-material-based decomposition in the image domain cannot
distinguish out a third material). Then, the question is how to tag the second-material base
images (which are not single material quantification).
DICOM WG-21, 2013-12-19
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3) “Material-Free” – a derived image where the intention is remove one (or more?) material
from the image
A complementary question is how to call and tag the Material-free images (material free image is
like the term “Caffeine-Free” coffee, which means “everything in, except Caffeine). A good
example for that are Virtual-Non-Contrast (VNC) images that are derived from the images with
contrast-injection, by using the dual-energy analysis to remove all or most of the Iodine contrast
from the image, emulating a non-contrast-injection scan (saving scan dose and time). So VNC
images should contain all the materials and tissues in the body, except the injected Iodine.
Another example, are Calcium-Free images to enable seeing only the blood-vessels lumen from
CT Angiography.
In clinical cases the question is often: which soft tissue density would be seen if a foreign
material was not there. So the other materials are removed but the soft, tissue density is corrected
for the space that was occupied by the other material. However, standard material decomposition
would show a decrease in the soft tissue density if there is more of the other base material. How
can these cases be distinguished? Are there other similar cases?
The most interesting base material decomposition is for iodine and water. But iodine cannot be
produced with variable density and the attenuation of pure iodine. Iodine is too high to be
measured reliably (partial volume effects, scattered radiation, etc.). How can iodine base material
images be evaluated in a simple way (reproducibility)? For some materials (especially contrast
agents) the density of the main atom (iodine) is known, but the exact chemical composition may
be unknown (though reproducible). The resulting density image would show the iodine density
under the assumption that the iodine is contained in the contrast agent and diluted e.g. in water.
How can this case be clearly defined?
The same applies for all other base material with high (effective) atomic number. Seems like it
can be (or will be) diluted to some degree, this is not a significant issue – is this correct?
How can an unambiguous and reproducible definition/decomposition look like? Are there other
procedures possible to standardize such decomposition?
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