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Accuracy: the
quality of adhering closely to a standard of correctness.
Absolute Accuracy: the accuracy of an
instrument's measurement at most physiological flows; offset error is
insignificant compared to slope error. The term absolute accuracy has
therefore evolved as a synonym for the range of error resulting from an
incorrect slope.
Relative Accuracy: the accuracy of the
instrument: often a linear correction with a slope and offset. Relative
accuracy is often known as linearity.
Acoustic Couplant: Gel, such as
Surgilube, H-R Jelly or NALCO 1181, used during acute use in the
acoustic window to surround flowprobe to complete the acoustic pathway.
Acoustic gel: see Acoustic couplant.
Acoustic Window/Field: the area defined by
the pathway of the ultrasound beam between the transducers in the
flowprobe body and the acoustic reflector.
Acute: short-term use of a device as
for intraoperative studies under anesthesia, typically less than one
day. (Also see chronic & sub-acute.)
Analog Output Signal: voltage output
corresponding to the parameter measured by a device. The signal
generated is calibrated by a scaling factor. The voltage range of
Transonic ultrasound flowmeters is -5 to +5 volts DC with 1 volt
equivalent to full scale of the flowprobe used. Transonic laser Doppler
flowmeters operate in a voltage range of 0 to +5 volts DC and are
scaled to 0 - 100 Tissue Perfusion Units.
Applications: documented uses for
Transonic Systems' flowmeters.
Bi-directional Flow: flow measured in
positive and negative directions.
Bi-directional illumination: with ultrasonic
transit-time, Transonic flowprobes, a tube or vessel is positioned
between transducers which generate wide beams of ultrasound to fully
illuminate the vessel or tube. The ultrasound beams alternately
intersect the flowing liquid in upstream and downstream directions. The
flowmeter derives an accurate measure of the changes in "transit time"
(time it takes for the wave of ultrasound to travel from one transducer
to the other) influenced by the motion of the liquid.
BLF: Transonic Systems' laser
Doppler flowmeter employing the Bonner algorithm.
BLF-FLOW: red blood cell flow reported in
tissue perfusion units by BLF21 Laser Doppler Flowmeters. This is
proportional to volume flow in the tissue sampled.
BLF-Perfusion Units: units used to report
flow in BLF Laser Doppler Flowmeters. Since the volume and mass of a
tissue sample vary based on the tissue's optical properties, an
across-the-board calibration in ml*min-1*100g-1 is not valid. The
Tissue Perfusion Unit is equivalent to milliliters per minute per 100
grams of tissue (the amount of tissue actually sampled).
BLF - VELOCITY: mean velocity of the
moving red blood cells within a sampled tissue. Mean velocity is
proportional to the mean Doppler shift of the received light.
BLF - VOLUME: in this context, volume refers
to the volume or mass of blood corresponding to the number of moving
red blood cells within the sampled tissue. The volume of the red blood
cells is proportional to the number of shifted photons in the received
light. Volume is reported in BLF21 flowmeters with the -V Option in
unit-less values.
Calibration: (often misused as a
synonym for validation)
In Situ: adjustment or correction made
to a measurement device for errors produced under actual conditions of
use by comparing the measurement with a known standard.
In Vivo: adjustment or correction made
to a measurement device during use in a "living body".
Chronic: long in duration. Long-term
studies generally involving implanting a flowprobe so that measurements
made be made in the conscious animal. (Also see acute & sub-acute.)
Cuff (Saddleback): for chronic implants,
a silicone sleeve is used to stabilize a Transonic probe's CM4
connector that has been tunneled subcutaneously to the exit site. The
cuff is then sutured to the skin.
Electrical Isolation: grounding of the
flowmeter circuitry to prevent accidental electrical conductance
between the flowmeter and the test subject.
EPROM: (Acronym for "electrically
erasable programmable read only memory") programmed component that
contains the identification and calibration information specific to
each flowprobe.
Extension cable: cable, one end of
which plugs into the connector of a Transonic flowprobe and the other
end of which plugs into the flowmeter; generally 1, 2, or 3 meters long.
Extracorporeal: measurements outside
of a body.
Filters: in electronics, a circuit that
only passes certain signals. For blood flow measurement, a low pass
filter is often used to strip out high frequency noise, leaving only
the biological components of interest.
Flange: a silicone rim or collar that
can be cemented around Transonic R-or S-Series probes to suture the
probe to surrounding tissue; used in coronary artery and umbilical
artery applications.
Flow: volume or velocity movement of
a liquid (blood, saline, isotonic solutions) passing a given point in a
given time (measured in L/min or ml/min).
Flow dilution sensor: sensor used in
conjunction with the HD01 Hemodialysis Monitor. The sensor measures
volume flow by transit-time ultrasound technology and concentration of
the blood by standard dilution technique.
Flow velocity profile: the distribution of
velocity across the vessel.
Flowmeter: a device for measuring
velocity or volume of flow of liquids or gases passing a given point
per unit of time. Specifically, with regard to Transonic flowmeters,
the box which houses the power supply and signal processing circuitry;
a digital readout of the flow is displayed on the front panel (e.g..
T106/T206 Research Flowmeter).
Flowmetry: the monitoring or study of flow
parameters.
Flowprobe: a device (sensor) which
measures flow. Transonic ultrasound flowprobes contain the ultrasonic
transducers for insonating vessels or tubing to measure volume flow of
blood, buffers and other liquids; Transonic BLF laser Doppler
flowprobes contain the fiber optic cables for transmitting a laser beam
to measure perfusion of red blood cells in tissue by analysis of
Doppler-shifted light and the Bonner algorithm.
Flowsensor: a device (probe) which measures
flow; i.e. sterile tubing flowsensor which measures the volume of a
liquid passing through tubing by transit time ultrasound technology.
Gain: in electronic circuitry, a
linear factor that is used in a device as a multiplier after
calibration. The sensitivity of a probe is adjusted by changing the
gain.
Hz: a cycle or repetition per
second. In ultrasound: Transonic Systems' specification for the
frequency of the ultrasound from the probe crystals is listed in
Megahertz (MHz). A typical value is 2.4 MHz (for a 4S probe - that is
2,400,000 cycles per second). In Data Acquisition: Sampling rates are
reported in hertz; 100 Hz means 100 data points recorded per second.
Key: eeprom dipswitch separate from
and specific to each flowprobe that contains the identification and
calibration information for probes with 4-pin miniature connectors used
in chronic applications. This programmed device plugs into a port on
the extension cable to be read by the flowmeter.
Microprocessor: miniaturized
integrated circuit capable of processing a high volume of signals to
report results or control functions of instruments or machines.
NMR: (acronym for Nuclear Magnetic
Resonance);
MRI: (acronym for Magnetic Resonance
Imaging): diagnostic imaging modality using nuclear magnetic resonance
technology in which a patient's body is placed in a magnetic field and
its nuclei (hydrogen) are excited by radio frequency pulses at angles
to the field's axis; resulting signals are processed through a computer
to produce an image. Transonic ultrasonic transit time flowmeters are
compatible with MRI via its
(-G) Gating Option.
OEM Systems: Original Equipment
Manufacturer (OEM) systems are custom engineered by Transonic Systems
to be embedded within clinical OEM products such as bypass pumps, ECMO
apparatus, infusion/transfusion/perfusion systems, dialysis apparatus
and organ preservation apparatus.
Perfusion: the supplying of fluid to an
organ or tissue. The passing of blood through the vasculature of an
organ or tissue.
Perivascular: surrounding a blood
or lymph vessel as in Transonic perivascular flowprobes
Precision: the quality of repeatable
recognition of minute changes in measuring a parameter. An instrument
may be precise but inaccurate and vice versa.
Pulsatile Flow: biological flows vary
instantaneously throughout the cardiac cycle. The analog output can be
filtered to give a pulsatile or mean flow signal.
Range: the set of numbers between the
limits of the maximum and minimum values measurable.
Reflector: stationary plate component of
Transonic R- and S-Series flowprobes; Each transducer alternately emits
an ultrasound beam which is reflected from a stationary plate
(reflector) to the receiving transducer. The fixed distance of the
reflective pathway is critical to the measurement of the ultrasonic
transit time and thus, the accurate measurement of volume flow.
Repitition Rate: The number of times
per second that a probe "fires" an ultrasound burst. The rate is equal
to the probe's ultrasonic frequency divided by 1024 or lower as
required by ultrasonic conditions.
Resolution: represents the smallest
detectable change in flow. Probe resolutions are generally specified at
0.1Hz filtering.
ROM: (Acronym for "read only
memory") microchip component in probe connector that contains the
identification and calibration information specific to each flowprobe.
Sampling Rate: number of samples
taken per unit of time. In digital signal processing (Nyquist theory)
it is necessary to sample twice as fast as the highest frequency
component.
Scale: Factor
used to calibrate a voltage signal. Transonic
ultrasound flowprobes operate in either of two scales; low flow or
normal flow scale determined by the range of flow under study.
Sensitivity: amount of voltage
output per unit of parameter measured.
Sensitivity Error: error resulting from
incorrect gain. Total error is the sum of sensitivity error and the
offset error.
Signal-to-Noise Ratio: the ratio of desired
signal to undesired noise; often expressed in decibels, a logarithmic
scale commonly used by engineers.
Silicone Shield: a silicone protective
plate which encapsulates a U reflector on Transonic flowprobes; used to
maintain probe orientation, cushion pulsatile vessels and retard fat
ingress.
Silicone Wrap: a reinforced mesh
which is wrapped around a Transonic flowprobe at an implant site to
retard fat ingress and stabilize the probe's position.
Sub-acute: duration longer than acute, but
not as long term as chronic; typically 8 hours to 3 days. In this
context, subacute applications of Transonic ultrasound instruments are
similar to acute applications where the implanted flowprobe is not
stabilized by fibrotic tissue ingrowth, and the ultrasound signal may
yet be interrupted by the presence of air.
Timed Collection: a calibration
technique combining a known volume with a measured time, as in the use
of a beaker and stopwatch.
Transducer: a device that transforms a
physical parameter into an electrical signal, as in a Transonic
ultrasound flowprobe; the ultrasound signal produced by the
piezoelectric crystals is transformed and converted into an electrical
signal proportional to volume flow.
Transit Times: Transonic Systems'
newsletter distributed periodically to scientists worldwide.
Transit-time: time it takes for a
pulse of ultrasound to travel from one transducer to another.
Ultrasonic: relating to energy waves
similar to those of audible sound but of higher frequency (above 30,000
Hz)
Ultrasonic couplant: a material that
propagates acoustical waves; for blood flow measurement, a material is
chosen that mimics the acoustic characteristics of biological tissue.
Ultrasonic signal coupling: a term used to
describe the state of sound propagation between the transducer and
tissue. Signal coupling is degraded by air bubbles and materials that
do not conduct sound.
Ultrasonic transit time: a technology to
measure volume flow of liquids by using wide-beam illumination;
transducers pass ultrasonic signals back and forth, alternately
intersecting a flowing liquid in upstream and downstream directions.
The Transonic flowmeter derives an accurate measure of the "transit
time" it took for the wave of ultrasound to travel from one transducer
to the other. The difference between the upstream and downstream
integrated transit times is a measure of volume flow.
Ultrasound Dilution: a technology which
unites dilution and ultrasonic transit time to measure the changes that
occur in the velocity of a liquid when diluted with isotonic saline;
measures recirculation, access flow and cardiac output during
hemodialysis.
Validation: test to confirm calibration and
accuracy of a measurement, usually by comparing to a known standard
such as timed collection.
Waveform: the record of a signal that
varies over time. A blood flow signal usually varies periodically with
the cardiac cycle.
Wide-beam illumination: the use of an
ultrasonic beam wider than the vessel of interest. Wide-beam
illumination is necessary for volume flow measurement with the
ultrasonic transit time technique.
X-illumination: ultrasonic
illumination which fully illuminates the vessel or tube to provide a
measure of volume flow by ultrasonic transit time. A vessel or tube is
positioned between four transducers that generate wide beams of
ultrasound that fully illuminate the the vessel or tube. The ultrasonic
beams alternately intersect the flowing liquid in upstream and
downstream directions. The flowmeter derives an accurate measure of the
changes in "transit time" (time it takes for the wave of ultrasound to
travel from one transducer to the other) resulting from the motion of
the liquid. The integrated difference between the two upstream and
downstream transit times is a measure of volume flow.
Zero offset drift: zero offset change
over time.
Zero offset: the measurement
registered by the instrument under conditions of zero input. In blood
flow, this is the flowmeter reading when flow is known to be zero due
to occlusion of the vessel or other means. A two point calibration can
be performed by combining a zero offset determination with a timed
collection.
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