Biomedical Engineering Reference
In-Depth Information
The minimum information required for image registration applications is
the matrix size and dimensions (or, equivalently, field of view and slice thick-
ness). Other voxel information may also be needed, such as the relationship
of the image coordinates to the absolute coordinate frame of the scanner. This
may be required to correct for image distortion or other hardware limitations
(see Chapter 5).
In addition, the image or separate header file may contain patient-specific
information. This can be convenient and can also be a useful check against
mistakes that may be introduced by copying files and modifying file names.
However, strict laws are now in place to protect the confidentiality of
patients, so that unless the data is held in an appropriately secure location, it
may be necessary to strip out any information that could be used to identify
the subject directly.
Medical images are generally stored and may be archived in a proprietary
format that may not be disclosed to the user by the system manufacturer.
Subsequent processing requires the data to be exported from the scanner, and
this again may be achieved using a variety of data formats. Although manu-
facturers are sometimes reluctant, or at least slow, to provide information on
these file formats, much of this information is now in the public domain, as
many groups have “reverse engineered” these formats. Details of the formats
can be found on various locations on the Internet.* To deal with the require-
ment that images exported from equipment from one manufacturer may
need to be imported to that of another manufacturer, a medical image standard
known as DICOM3** has been devised and has now been widely adopted.
This allows data to be freely exchanged between a wide variety of medical
equipment including scanners and viewing consoles, as well as many pro-
prietary processing software packages intended for use with medical
images. A disadvantage of the DICOM3 standard is that the need to give it
universal applicability makes it complex and unwieldy for many applica-
tions. Also, like many “standards,” individual implementations of
DICOM3 can vary in detail, so incompatibilities still occasionally occur.
Another image format particularly widely used in the nuclear medicine
environment is interfile.***
At the other extreme, there are very simple image formats consisting sim-
ply of pixel intensity values or pixel intensity values combined with rudi-
mentary essential information such as the dimensions of the image pixel
matrix. One popular format of this type is associated with the Analyse image
* Information about a wide range of formats used in medical imaging can be found at
http://www.cica.indiana.edu/graphics/image.formats.html.
** DICOM is an acronym for Digital Information and Communications in Medicine and is a stan-
dard for image transfer developed and sponsored by National Electrical Manufacturers Associ-
ation (NEMA). Information about DICOM standards can be found at
http://medical.nema.org/dicom.html.
*** Information about Interfile can be found at
http://www.keston.com/Interfile/interfile.htm.
For general information see
http://www.cica.indiana.edu/graphics/image.formats.html.
