Tuesday, July 26, 2011

Cutlines / Cutline Navigation GE Centricity

What exactly is a 'cutline' or 'cutline navigation'?

GE Centricity Web Manual [1]
If you are a GE Centricity Web user or if you read carefully through the GE's Centricity Web User Manual, you should know that there is a function called 'Displaying Cutlines'.

In the manual, it states that a cutline is the intersection between two planes..

"With Centricity Web you can display cutlines (intersections between two planes) provided your study has images suitable for this... If a series contains images in random order, you will not be able to turn on cutlines..." [1]

But, the explanation is extremely vague.  Two planes.  What kind of planes?  orthogonal planes?  planes between two series? more than two series? just one series?

DICOM Standard
Since the above basically did not help with my concerns, i went back to my favorite source: DICOM STANDARD.

In PS3.3, by searching the keyword 'localizer', you should get quite a number of hits.   You should then start by reading CT Image Type.  There, you should see that  DICOM 3.3 defined CT Image Type (0008,0008) as one of the followings:  AXIAL or LOCALIZER.

In PS3.3, section C., it clearly states that The Referenced Image Sequence (0008, 1140) provides an unambiguous method for relating localizer images.

In PS3.11, section E.3.3.2, it clearly states the localizer related attributes allow the image to be referenced to a localizer image or other orthogonal image.  The Rows (0028, 0010) and Columns(0028, 0011) attributes are required in order to facilitate annotation of such a localizer.  It also refers to the Frame of Reference section in PS3.3

In PS3.16, in the annex, it defines localizer as "Image providing an anatomical reference on the patient under examination, for the purpose of defining the location of the ensuing image".

From the most notable and respectable figure in DICOM, D. Clunie [2]
You will need to make a careful reading in the attached section.  Therefore, i will not repeat the info here.  However, it must not be neglected that the Frame of Reference UID is being used throughout for the projections.   That is, they must be the same for both the localizer and the orthogonal images.

Basically, a cutline maps the orthogonal relationship between two planes that are supposingly orthogonal to each other.  In this situation, those two planes are most likely from two different series that are, perhaps, meant to be registered the moment the DCM files are generated (hence, Frame of Reference UID).    Note that this can lead to co-registrations between multiple series if those multiple series are related but do not provide direct spatial mapping.  And, there is a huge research history of algorithms that produce good results for co-registrations.  

[1] http://pulmonaryfellowship.hms.harvard.edu/NewFiles/CentricityWeb2UserGuideM3.pdf
[2] http://www.dclunie.com/medical-image-faq/html/part2.html#DICOMLocalizers

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