EDAN DUS 60 - A2.4: TI (Thermal Index)

DUS 60 Digital Ultrasonic Diagnostic Imaging System User Manual Ultrasound Intensity and Safety
- 188 -
Acoustic Output Reporting Table
Transducer Model: L743UA
Operating Model: PW Mode
TIS TIB
Non-Scan
Index Label MI
Scan
A
aprt
≤1 A
aprt
>1
Non-scan
TIC
Global Maximum Index Value 0.4043 0.9339 3.0125 0.8505
P
r.3
MPa 0.9634
W
0
mW 35.2 35.2 35.2
Min
of[W
.3
(z1),(mW)
I
ta.3
(z1)]
Z
1
(cm)
Z
bp
(cm)
Z
sp
(cm) 2.15 2.15
deq(Z
sp
) (cm) 0.0076
f
c
(MHz) 5.6782 5.6782 5.6782 5.6782
X(cm) 1.344 1.344 1.344
Associated
Acoustic
Parameters
Dim of
Aaprt
Y (cm)
0.6 0.6 0.6
PD (usec) 1.5134
PRF (Hz) 6361
P
r
@PII
max
(MPa) 2.35
d
eq
@PII
max
(cm) 0.0076 0.0076
FL
x
(cm) 0.5274 0.5274Focal
Length
Fl
y
(cm) 4.635 4.635
Other
Information
I
pa.3
@MI
max
(W/cm
2
) 0.1433
Control
Conditions
Control1
AP=15; Frequency=6.0MHz;
Depth=78mm; Focus=35mm;
WARNING
The device is not intended for ophthalmic use. Do not use it for examining ophthalmic
vessels, or any other procedures which may cause the ultrasound beam to pass through
the eye.
DUS 60 Digital Ultrasonic Diagnostic Imaging System User Manual Ultrasound Intensity and Safety
- 189 -
A2.4: TI (Thermal Index)
TI is determined by the ratio of the total acoustic power to the acoustic power required to raise
the tissue temperature by 1degree Celsius. Once there is a situation that a TI value is greater than
1.0, the TI value will be displayed in the upper part of the screen.
The adverse biological effects of ultrasound on tissue appear to be, in contrary to what is assumed
for X-ray, threshold effects. When tissue is repeatedly exposed to ultrasound, with intervals in
between, there will likely be no cumulative biological effect. If a certain threshold has been
passed, biological effects may occur. A temperature rise from 37 °C to 41 °C is acceptable for
quite a long time, whereas a temperature rise to 45 °C may not be acceptable. The same counts
for cavitation in that, below a certain level, there will be no cavitation and hence no biological
effect.
A prudent starting-point for each examination would be first to set the machine for the lowest
index setting and then modify from this level until a satisfactory image or Doppler signal is
obtained, keeping track of the TI; and second, the exposure time, during one examination, should
be kept as short as possible. A safety guideline on this should be included.