Digital Imaging and Communications in Medicine (DICOM)

326
Chapter 16 DICOM Software Development
but it clearly has nothing to do with DICOM software design. And although
needing a DICOM file opener is the most common reason for starting DICOM
development, it is also the worst one. You think small, you neglect the entire
structure of the DICOM standard, and your partial success can create an illusion
of doing it right. I really hope that after reading most of this book you
realize that the DICOM standard expands much farther that your simple MR
file viewer, even if the latter opens all files from your MR scanner. As a result,
the more files you try to open, the more disappointing surprises and failures
you will experience, constantly running into unknown pixel representations,
compressions, and IODs.
In short, you will have to discover the DICOM standard empirically by
learning from your own mistakes. This is the most inefficient way of mastering
something as complex and evolving as DICOM. In fact, by the time you make
your next discovery, the actual items in DICOM and everywhere around you
could change. You will never catch up.
So, if you “just need to open this DICOM file”, use Matlab, Analyze, or some
free DICOM file viewer to solve your problem in a matter of minutes and not
days. Be practical.
16.3
Implementing DICOM
If you have decided to move forward and implement DICOM software, and not
for a small transient need, I respectfully salute you. Go ahead and start from
this book; it was written for you. Read Chap. 5, and while reading it, try to
build a clear object-oriented design of your DICOM implementation. If I were
you, I would consider each of the following guidelines carefully:
1. Implement a class for the binary buffer, paying particular attention to efficient
memory allocation and cleanup. Remember, DICOM reads, writes, and processes
all its data as sequences of binary bytes, and this class will be responsible
for the efficient management of all your DICOM data (Fig. 94). Include
functions such as Big/Little Endian byte swapping and reading/writing to a
file/socket. You can also use a buffer class to implement text strings; and if
you choose to do so, implement DICOM wildcard string matching.
2. Implement VR as the main data type (class), as shown on Fig. 95. The main
work in a VR class is to code functions to read/write data in all possible and
popular formats. For example, time in various versions of DICOM can be
written as HHMMSS, HH.MM.SS, or HHMM, and it is good to make your
VR aware of all of this. Then add implicit/explicit VR encoding as reading/
writing encoded VR data to binary buffers.
3. Ensure that all DICOM attributes (data elements) become instances of your
VR class.
4. Implement the DICOM Data Dictionary as a VR hash table. Pay special attention
to its performance: searching the dictionary by (group, element)