Types of Biomedical Instrumentation Systems
• Direct I Indirect
• Invasive I Noninvasive
• Contact I Remote
• Sense I Actuate
• Dynamic I Static
Direct/Indirect: The sensing system measure a physiologic parameter directly, such as the average
volume blood flow in an artery, or measures a parameter related to the physiologic parameter of interest
(e.g., ECG recording at the body surface is related to propagation of the action potential in the heart but is
not a measurement of the propagation waveform).
Invasive/Noninvasive: Direct electrical recording of the action potential in nerve fibers using an
implantable electrode system is an example of an invasive sensor. An imaging system measuring blood
flow dynamics in an artery (e.g., ultrasound color flow imaging of the carotid artery) is an example of a
Contact/Remote: A strain gauge sensor attached to a muscle fiber can record deformations and forces in
the muscle. An MRI or ultrasound imaging system can measure internal deformations and forces without
contacting the tissue.
Sense/Actuate: A sensor detects biochemical, bioelectrical, or biophysical parameters. An actuator
delivers external agents via direct or indirect contact and/or controls biochemical, bioelectrical, or
biophysical parameters. An automated insulin delivery pump is an example of a direct, contact actuator.
Noninvasive surgery with high intensity, focused ultrasound (HIFU) is an example of a remote,
Dynamic/Static: Static instruments measure temporal averages of physiologic parameters. Real-time
instruments have a time response faster than or equal to the physiologic time constants of the sensed
parameter. For example a real-time, ultrasound Doppler system can measure changes in arterial blood
velocity over a cardiac cycle.