# Underatanding digital data acquisition in medical diagnostics by rbt28073

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```									    Understanding digital
data acquisition
in medical diagnostics
technical approaches

Lutz Issler
Martin Baumann
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Same topics as in our introductory seminar:
Part 1: Basics and some theory.
Part 2: Using filters.
Part 3: Real data are real problems.
Finally...

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Part 1:
Basics and some theory.

Bit by bit - some terms.
Analogue vs. digital.

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Bit by bit - some terms.

What are quantisation steps?
ex.: 12 bit resolution  212 = 4096 steps
quantisation error = 1/(212) = 0.024% of
max-value
What is a sampling-rate?
1 kHz acquisition rate  1000 samples per
second
every 1 ms a new value
faster events may remain invisible

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Analogue vs. digital: Example.

1.322
1.412
1.911
2.332
2.627
2.872
2.972
3.099
3.499
3.881
4.007
3.502
2.391
1.000
0.480
0.479
0.653
1.304
1.600
2.099
2.126
1.982
1.578
0.910
0.344
0.107
0.019
0.124
0.299
0.505 mV
Digital
Multimeter

Oscilloscope
Start!
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Analogue vs. digital: Facts.

Transient signals can be followed easier:
slow signal changes
rapid signal changes
“Exact” multimeter values are not that exact:
pretend to be accurate
“jumping” digits
Possibility of further processing of data records

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Part 2:
Using filters.

Fourier, not furious.
Filter - When and why?
Filter - Universal solution?

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Fourier, not furious.
match?
match!   Fourier-Algorithm: build
any signal from an

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Filter - When and why?

Real signal = ideal signal plus noise.
Task: remove noise and keep ideal signal.
There are many different kinds of noise, so
there is no all-purpose filter algorithm!

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Filter - Universal solution?

No, non, nein, non est.
(almost) every filter will change
signal characteristics
one must not trust the filter result in
every case
Yes, oui, ja, sic est.
better to filter and know the possible errors
than not to filter and keep guessing
one must trust own knowledge and
experience

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Part 3:
Real data are real problems.

True lies.
Storage and restoration.

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True lies.

Manipulation is possible:
inserting / deleting data
points
selecting display range
Display of data is possible
in various ways:
can be used to support or

to hide information
may guide the
interpretation
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Storage and restoration.

Acquired data are just - data:
store, compress, calculate, combine, ...
attention: 1hr 10kHz 10dig  >340MByte
Store where?
paper, (hard)disk, (RW)CD, tape, ...
how long do media / technologies survive?
Store what?
raw data, analysed data

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Finally...

Why did I tell you all this?

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Why?

Students should learn good skills in ...
... data acquisition,
... data calculation,
... data interpretation.
Students must learn ...
... how to detect and solve
data acquisition errors,
... a reasonable distrust in any data,
... an effective presentation of data.

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Thank you for listening!

Contact:
Lutz Issler, Martin Baumann
Institute of Physiology
RWTH, 52057 Aachen
phone:      +49/241/80-88823
fax:        +49/241/8888-434
(issler|mbaumann)@physiology.rwth-
aachen.de