FYS4250 Fysisk institutt - Rikshospitalet

FYS 4250

FYS4250 Fysisk institutt - Rikshospitalet

Medical instrumentation, intensive care unit

FYS4250 Fysisk institutt - Rikshospitalet

Operating room

FYS4250 Fysisk institutt - Rikshospitalet

Approaches

• Physicians• Physicists, engineers• Researcher• Patients• Functions: diagnostic, therapeutic, support• Invasive / non-invasive• Technology: electromagnetic, optical,

mecanical

FYS4250 Fysisk institutt - Rikshospitalet

FYS4250 Fysisk institutt - Rikshospitalet

Unit of measurement, SI system

U = 5 volt

U is the quantity

5 is the dimension figure

[volt] is the unit

Examples of non SI-units: bar, psi, inch, yard, degrees Fahrenheit, miles, gallon

FYS4250 Fysisk institutt - Rikshospitalet

Interfering modifying desired

FYS4250 Fysisk institutt - Rikshospitalet

Example: modifying,

interfering input

FYS4250 Fysisk institutt - Rikshospitalet

Regulation systems of the body

FYS4250 Fysisk institutt - Rikshospitalet

Servo loop

FYS4250 Fysisk institutt - Rikshospitalet

Servo (negative feedback)

ddf

d xGH

Gy

+=

1Eq.1.3

y = output xd = desired input Gd = gain Hf = part of y back to input

d

dd H

xyG →∞→ ,

FYS4250 Fysisk institutt - Rikshospitalet

Biostatistics

• Sensitivity high → high true positive

• Specificity high → high true negative

FYS4250 Fysisk institutt - Rikshospitalet

Output

Input

Output

Input

(a) (b)

(a) Linear system fits the equation y = mx + b. (b) Nonlinear system does not fit the straight line.

FYS4250 Fysisk institutt - Rikshospitalet

Output

Input

Output

Input

(a) (b)

(a)The one-point calibration may miss nonlinearity. (b)The two-point calibration may also miss nonlinearity.

FYS4250 Fysisk institutt - Rikshospitalet

Sensorsignal

Measurand

A hysteresis loop The output curve obtained when increasing the measurand is different

from the output obtained when decreasing the measurand.

FYS4250 Fysisk institutt - Rikshospitalet

(a) (b)

Precision, (a) low, (b) high

FYS4250 Fysisk institutt - Rikshospitalet

Accuracy: (a) low, (b) high

(a) (b)

FYS4250 Fysisk institutt - Rikshospitalet

Sensitivity

Drifting

FYS4250 Fysisk institutt - Rikshospitalet

Linearity

FYS4250 Fysisk institutt - Rikshospitalet

Dynamic systems

The medical variable to be measured will normally vary as a function of time

The statical and dynamical properties of a measurement instrument can be described with a differeintial equation, usually limited to a 2. order like:

a2d2y/dt2 + a1dy/dt + a0y(t) = b2d2x/dt2 +b1dx/dt + b0x(t)

input x(t), output y(t)

FYS4250 Fysisk institutt - Rikshospitalet

0. order system, static, no energy

storing

FYS4250 Fysisk institutt - Rikshospitalet

1.order system, one energy

storing element, relaxation

FYS4250 Fysisk institutt - Rikshospitalet

2.order system,two energy

storing elements, swinging system

FYS4250 Fysisk institutt - Rikshospitalet

2.order system, blood pressure monitoring

FYS4250 Fysisk institutt - Rikshospitalet

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