Digital Imaging and Communications in Medicine (DICOM)

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Chapter 5 Parlez-Vous DICOM?
any conventional monitor (you simply cannot fit more options into a single
available byte). Special radiological monitors and hardware overcome this limitation
by allocating more bytes to grayscale shades.
One byte also gives you enough choices to store all Latin characters (lowercase,
uppercase, punctuation signs), so a byte is often viewed as a single-character
unit. For example, to store 12 characters, a computer uses 12 bytes of
memory; 1 byte per character.
Large data volumes, such as images, can require millions of bytes for storage.
Therefore, binary system counts bytes in larger numbers: 2 10 = 1024 bytes
corresponds to 1 kilobyte (KB), 1024 KB means 1 megabyte (MB), and so on.
Table 1 summarizes this count.
Table 1 Multiples of bytes
Prefix Name Binary meaning Metric meaning Size difference:
binary vs. metric
K Kilo (KB) 2 10 = 1024 1 10 3 = 1000 1 2.40%
M Mega (MB) 2 20 = 1024 2 10 6 = 1000 2 4.86%
G Giga (GB) 2 30 = 1024 3 10 9 = 1000 3 7.37%
T Tera (TB) 2 40 = 1024 4 10 12 = 1000 4 9.95%
P Peta (PB) 2 50 = 1024 5 10 15 = 1000 5 12.59%
In reality, multiples of bytes are counted in two slightly different ways. Information
technology (and DICOM) uses multiples of 2 10 = 1024, which makes
perfect sense from the aforementioned binary system perspective. Hardware
manufacturers use kilo-, mega-, and the others in their metric meaning, as multiples
of 1000. When they sell you a 1-GB flash drive, it contains 10 9 = 1000 3 bytes
(“metric” GB), which according to our table is 7.37% less than 2 30 = 1024 3 bytes
(“binary” GB). This makes nice commission for hardware sales.
When lowercase “b” is used in Kb, Mb, Gb, it commonly stands for “bits”,
and not “bytes”. Consider networks: network bandwidth (unlike computer
storage) is usually measured in “kilobits per second” (Kbs) and “megabits per
second” (Mbs), representing how much data the network can ideally transmit
in one second. For example, dial-up network speed is up to 56 Kbs, which is
identical to 56/8 = 7 KB per second (KBs). A standard computer T1 line delivers
1.544 Mbs; DSL delivers on the order of 10 Mbs; a good PACS network
operates in the range of 1–10 gigabits per second (Gbs).
“Hexadecimal” is a shorthand representation of 2 consecutive bytes, leading
to 65,536 (256 2 = 65,536) possible values. Because of their 16-bit (2-byte)
nature, hexadecimal numbers can be written using a 16-base numerical system