Digital Imaging and Communications in Medicine (DICOM)

6.1 DICOM BMPs 89
sion than with chasing lonely interpixel bits. Nevertheless, “bit-squeezing” techniques
are still standard in DICOM, and can be found in many applications and
data, especially if you deal with an older DICOM unit. Appendix D in DICOM
PS3.5 of the standard explains other possible sample encoding schemes.
If you can deal with the various ways of recording image pixels (samples),
you know how to read and write DICOM BMPs. As we have mentioned,
DICOM treats image information like anything else and all important image
attributes are translated into DICOM VRs stored in DICOM objects. These attributes
must be present in any image-containing DICOM object. In DICOM
parlance, these attributes are required. Table 18 provides a more detailed snapshot
of some important image attributes, taken from the DICOM Data Dictionary.
This is but a small fraction of all DICOM pixel-related tags, but if you
have any experience working with other image formats, you should appreciate
the completeness of DICOM. For example, as (0028,0008) suggests, you can
store a sequence of frames (essentially, a digital video) in a simple DICOM
image. You can specify the physical dimensions of pixels in (0028,0030), which
allows you to measure the image objects in their physical units, such as millimeters.
Knowing pixel spacing and spacing between the images (stored in
(0018,0088) and used with all image series such as MR or CT) allows for the
most elaborate 3D reconstructions, because we can preserve the correct sizes of
the objects. We could go on with this list almost indefinitely, but let’s stop here
and conclude.
Table 18 Important image attributes in DICOM Data Dictionary
Tag Name VR VM
(0028,0002) Samples per Pixel US 1
(0028,0004) Photometric Interpretation CS 1
(0028,0008) Number of Frames IS 1
(0028,0010) Rows US 1
(0028,0011) Columns US 1
(0028,0030) Pixel Spacing DS 2
(0028,0100) Bits Allocated B a US 1
(0028,0101) Bits Stored B s US 1
(0028,0102) High Bit B h US 1
(0028,0103) Pixel Representation US 1
(7FE0,0010) Pixel Data OW/OB 1