Biomedical Engineering Reference
In-Depth Information
on input from users of the Standard. These proposals are considered for inclusion in
future editions of the Standard. A requirement in updating the Standard is to
maintain effective compatibility with previous editions [
3
].
Security Issue in Transmission
PS 3.15 of the DICOM Standard specifies security and system management pro-
files to which implementations may claim conformance. Security and system
management profiles are defined by referencing externally developed standard
protocols, such as DHCP, LDAP, TLS, and ISCL. Security protocols may use
security techniques like public keys and ''smart cards''. Data encryption can use
various standardized data encryption schemes.
Choosing Lossless Compression Technique for Medical Images
Medical images are compressed due to their large size and repeated usage for
diagnosing purposes. Certified radiologists and doctors assess the degree of image
degradation resulting from various types and amounts of compression associated
with several different digital image file formats. A qualitative, rather than a
quantitative approach is normally chosen because radiologists typically evaluate
images qualitatively in their day-to-day practice and, also, because common
metrics used for comparing images pre- and post-compression, e.g., mean pixel
error, root mean square error, maximum error, etc., may not correlate well with
visual assessment of image quality. Bitmapped picture (BMP) is Microsoft Win-
dows device-independent bitmap standard for lossless format. Users of this format
can depend on images being displayed on any Windows device [
4
,
5
].
Performance Evaluation Parameters
The effectiveness of lossless compression schemes can be described using the
following parameters:
• Compression Ratio: it is defined as the ratio of original file size to that of
compressed file size.
• Bit Rate: the bit rate is the average number of bits (fractional) required to
encode a pixel and is computed from the total number of bits encoded divided
by the number of pixels.
• Mean Square Error: the cumulative squared error between the original and the
compressed image is shown by MSE
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