GE Logiq 3 Instruction Manual

							Bioeffects
LOGIQ 3 Expert/LOGIQ 3 Pro/LOGIQ 3 Advanced Reference Manual 1-5
Direction 5122542-100 Rev. 2
Mechanical Bioeffect
In a similar manner ,the interact ion of ultrasound energy with 
tissue can produce a number of non-thermal or mechanical 
effects.The most significant is cavitation which results from the 
action of the oscillating ultrasou nd pressure on tiny gas bubbles 
with in the tissues. Cavitation has caused mechanical damage 
on a cellular level such as microscopic tears and hemorrhage in 
laboratory tests with small animals.t he major contributing factors 
can again be categorised as either tissue characteristics or 
control parameters:
• The physical characterist ics of tissue such as the 
presence and size of micr oscopic gas bubbles and the 
sensitivity of the tissue to th e effects of cavitation will 
influence the potential for and magnitude of cavitation.
• Acoustic field parameters like output frequency,peak  pulse amplitude s and perhaps pulse length are the 
primary parameters effecting the onset of 
cavitation.these are controlled by the operator through 
appropriate equipment selections.
Althogh it is generally accepted that no harmful biological effects 
have been demonstrated at the frequency ,intensity,and 
exposure times used in diognostic examinations,research in to 
the potential for harmful effects continues.The operator is 
encouraged to survey the literature for future developments on 
bioeffects and to become familiar with the references at the end 
of this section.
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							Acoustic Output
1-6LOGIQ 3 Expert/LOGIQ 3 Pro/LOGIQ 3 Advanced Reference Manual
Direction 5122542-100 Rev. 2
Operator Awareness and Actions to Minimize bioeffect 
The operator must be aware of the particular conditions that 
exist during the examination to recognize the potential for 
bioeffect and then take appropriate action to reduce the risk.The 
recognization of potential harm comes from an understanding of 
tissue characteristics and a re al-time knowledge of acoustic 
output.Taking appropriate action requires familiarity with 
equipment operation  and examination skills  like implementing 
alternative techniques for obtaining the same diognostic 
information.
Tissue Characteristics
Tissue Characteristics vary  considerably throughout the 
body.they influence the acoustic  field and determine the heating 
/ cooling rates and cavitation potential.Ultrasound energy 
dissipates as it passes throug h the tissue causing the deeper 
tissue to encounter much lowe r levels.Some tissues like bone 
readiy convert ultrasound energy to heat,while others like blood 
and amniotic fluid pass the  energy on to adjucent tissue 
relatively unattenuated.
A perticular situation that represents a tissue combination 
requiring extra precaution is a third trimester transabdominal 
fetal examination where there is a very thin abdominal wall and 
a long fluid path.The relative lack  of attenuating tissue along the 
acoustic path will significantly  increase the available energy in 
the fetal tissue.Additionally,fetal tissues are more susceptible to 
long term injury due to nature of developing tissue.focussing the 
ultra sound beam on or near fetal bone further increases the 
risk.
Otherthan fetal tissue,there is increased susceptability for 
heating in any tissue that cannot easily conduct or distribute 
heat due to low blood perfusion.As the examination 
progresses,the operator must be aware of changing tissue 
conditions.
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							Bioeffects
LOGIQ 3 Expert/LOGIQ 3 Pro/LOGIQ 3 Advanced Reference Manual 1-7
Direction 5122542-100 Rev. 2
Acoustic Output
awareness of the acoustic output level can be a difficult task for 
the operator,espcially when the objective is to obtaine a quality 
image.Older ultrasound equipment had limited means,if any,for 
indicating the acoustic output le vel.In most cases ,the operator 
had to be familiar with the output intensities as described in the 
operator manual.To improve op erator awareness of acoustic 
output,this system incorporates an  output display that directly 
indicates the potential for mechanical and thermal bioeffects as 
equipment controls are adjusted.
The output display consists of four numeric index values that 
indicate the potential for producing bioeffects(three indices are 
for heating effect and one for cavitation).As the user changes 
equipment settings that alter the acoustic output,the output 
display indices are immediately updated to reflect the changes 
in potential for producing .The indices are based on 
mathematical models and each is normalized so that the 
potential for bioeffect becomes more significant as the indices 
reach a value 1.0 or larger.
A mechanical index (MI) provides an indication of the potential 
for the possible onset of transient cavitation within tissue while 
the three thermal indices provide an indication of the potential 
for heat generation within tissue.The different thermal indices 
may be used depending on the type of tissue being examined:
• Soft Tissue Thermal Index (TIS) is used as an indicator ofthe potential to generate heat within soft tissues.this is 
the most used thermal indicator.
• bone Thermal Index (TIB) is used as an indicator of the  potential to generate heat at the beam focus when 
focussing on or near bone that is adjucent to very 
sensitive tissue.this index  is intended as a thermal 
indicator for second and third trimester fetal examination 
or transfontanelle neonatal cephalic exams.
• Cranial Bone Thermal Index (TIC) is used as an  indicator of the potential to generate heat in the near-
field when the beam passes through bone at the surface 
as with adult or pediatric  cranial applications.
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							Acoustic Output
1-8LOGIQ 3 Expert/LOGIQ 3 Pro/LOGIQ 3 Advanced Reference Manual
Direction 5122542-100 Rev. 2
Acoustic Output(cont’d)
Tissue heating is more of a concern when the acoustic beam is 
stationary, so the thermal index is likely to increase when 
Doppler or M-Modes are selected.The influence of specific 
operator controls on acoustic ou tput is described along with the 
functional purpose of the control through out the user manual 
and a summary is provided in safety.
The operator now has easy access to the status of acoustic 
output and , when combined with the knowledge of tissue 
characteristics and beam location, the risk of potential bioeffect 
can be readily assessed.this di splay conforms to the AIUM/
NEMA Output Display Standard[1] for Ultrasound imaging 
equipment.
Operator Intervention
When conditions indicate a potential for harmful bioeffect, the 
operator should take action promptly to reduce the risk by 
changing equipment settings or altering procedural techniques:
• Output display index values much greater than 1.0 represents an increased risk for tissues in perticular 
beam locations.the potenti al for heating will normally 
only occur near the surface or at the focus,while the 
potential for cavitation is reduced away from the 
focus.selecting non scan operating modes such as PW 
or CW Doppler and M-Mode will significantly increase 
the thermal index because the beam is stationary.
• Optimise gain and other im age enhancement features 
before increasing the acoustic output control or other 
equipment controls that sign ificantly affect the output 
level.Become thoroughly fam iliar with all controls that 
affect output and observe the output display for 
results.controls affecting output are described 
throughout the user manual.
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							Bioeffects
LOGIQ 3 Expert/LOGIQ 3 Pro/LOGIQ 3 Advanced Reference Manual 1-9
Direction 5122542-100 Rev. 2
Operator Intervention(Cont’d)
• Development and practice sk ills to localize anatomy and 
optimize image quality rapidly, then freeze the image as 
soon as the necessary diognostic information is 
obtained.It takes time for tissue temparatures to 
increase ,so reducing exposue r time can significantly 
reduce the potential for injury.
• Avoid susceptible tissues  , if possible ,by changing 
probe position ,entrace angles or probe type. Higher 
frequency probes will not penetrate as deep while linear 
probes have lower near field energy density.Avoid 
focussing on bone or poorly perfused tissue.do not 
allow the acoustic beam to penetrate or focus on or near 
the eye.
Although choices like probe selection , mode of operation and 
other control adjustments have a significant affect on output 
levels, the ability to ch nage these selections is often restricted 
by the type of examination or  clinical objectives.Therefore , 
some examinations may require re latively high output levels to 
achieve success.
The decission to raise acoustic output to potentially harmful 
levels must include an assessment of the risk/benefit potential. 
Such decessions are routine with imaging modalities 
incorporating ionizing radiation such as Nuclear Medicine, X-
Ray and CT.The principle of ALARA is widely used in these 
modalities for minimizing the exposure risk and is now a 
recommended practice with highlevel diagnostic ultrasound.
CAUTION:
During each ultrasound examination , the clinical user is 
expected to weigh the medical benefit of the diognostic 
information obtained against the risk of harmful effects. Once an 
optimal image is achived the need for incresing acoustic output 
or prolonging the exposure can no t be justified. It is important, 
therefore , for the user to be  familiar with system controls that 
affect image quality as well as acoustic output.Complete 
descriptions of image optimization  and acoustic output controls 
are provided in the user interactions.
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							Acoustic Output
1-10LOGIQ 3 Expert/LOGIQ 3 Pro/LOGIQ 3 Advanced Reference Manual
Direction 5122542-100 Rev. 2
Implementing the ALARA Methods
The Primary objective for any ultrasound examination is to 
obtaine diagnostic information of  sufficient quality to benefit the 
patient. Image Quality can usually be improved by increasing 
the acoustic output or taking  more time to refine the 
image.These same actions, however, will also  increase the risk 
of harmful bioeffects when imaging sensitive tissues or when 
high output levels are used.the o perator is therefore encouraged 
to use the lowest acoustic output setting necessary to produce 
clinically acceptable data.
The principle of ALARA , which stands for As low as reasonably 
achievable, is to keep the radi ation exposure at the minimum 
level necessary to obtain the diagnostic information.This 
principle is widely practiced in medical x-ray protection where 
exposure at any level is potentially harmful.Historically,ALARA 
was initiated as a cautions approachfor dealing with uncertain 
hazards but has since become the principle method for reducing 
the risk of injury from hazard s that do not have safe minimum 
threshold.
While no minimum thresolds for harmful bioeffects have been 
established with the use of diagn ostic ultrasound, the principle 
of ALARA can be readily implemented on equipment 
incorporating an output display. As the operator adjusts the 
equipment to optimize the image quality, the display interactively 
updates to indicate the effect on output.
Controls that have no noticeable impact on image quality should 
be set to minimize the output while controls that improve the 
image quality and also increase acoustic output should be set 
no higher than needed to achive a diagnostic quality image. If 
the output display indicates values much greater than 1.0 , the 
operator should reduce the exposure time and freeze the image 
as soon as possible.
At very low levels(
						

							Bioeffects
LOGIQ 3 Expert/LOGIQ 3 Pro/LOGIQ 3 Advanced Reference Manual 1-11
Direction 5122542-100 Rev. 2
Clinical Instruction for Fetal Use
Following are illustrative examples  of clinical instructions for 
fetal Doppler use which were prepared by Harold 
Schulman,M.D. and Jhon Hobbins,M.D.
Umbilical artery
To Obtain a signal:
For continuous wave doppler instrument , Place the pencil probe 
with appropriate conducting gel on the meternal abdomen. The 
volume should be at a comportable level and the power output 
and gain at a mid-setting. Slowly move the pencil probe by 
changing the angle or location on the meternal abdomen until 
the characteristic sound of the fetal umbilical flow can be 
heard.This is a swishing sound witha rate usually between 120 
and 160 BPm. It should be lack ing in discernible clicks or 
sounds similar to valve moveme nt on cordiac auscultation. 
When the image is obtained , adjust the controls in order to 
optimize the imageby reducing the power output to the lowest 
setting at which a good qualitysignal is obtained.The gain setting 
should also be reduced to make the signal appear crisp with 
minimal background noise. If diagnostic flow signals are not 
obtained, the angle of the beam  incident to the ubbilical cord 
should be examined to determine whether diognostic flow is 
present. When a good quality signal is obtained all the way 
across the display screen , the image amy be frozen.
Prior to taking measurements, the signals should be examined 
to exposure that the variations  in wave form size that may be 
caused by fetal breathing movements are not present.Fetal 
breathing movements will invalidat e any measurements due to 
the variations they cause in umbilical flow.
If a duplex doppler system is being  used, then the umbilical cord 
should be visualized and attempted to be seen in as much of its 
length as is feasible, Considering its usual cooling.The sample 
volume size(“gate”) should be adjusted to encompass the entire 
vessel. If this vessel is being  seen only in crossection , and 
diastollic flow is not seen, this ma y be an artifact caused by the 
angle between the beam and the vessel and anothersampling 
site should be examined.when this crosssectional view is 
obtained, rotating the transducer 90 degrees may bring a 
greater length of the cord into view and permit examination of an 
area where the artery can be seen at a more advantageous 
angle.Indices of pulsality , if calculated, should be determined 
for each of several heartbeats and averaged.
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							Acoustic Output
1-12LOGIQ 3 Expert/LOGIQ 3 Pro/LOGIQ 3 Advanced Reference Manual
Direction 5122542-100 Rev. 2
Uterine artery 
For Continuous wave doppler systems,place the pencil probe in 
the lower lateral portion of the mother’s abdomen.generally just 
above the groin and directed toward the cervix.Adjust the angle 
or position until the characterist ic wave form of the uterine/ 
arcuate artery is obtained.Without visualization, it is important to 
search carefully for the wave form with the greatest amount of 
diastolic flow compared to the systolic flow in a way that might 
appear abnormal if obtained from the uterine artery itself. The 
power and gain settings should be adjusted to the lowest levels 
at which adequate signals are obtained with a minimul amount 
of noise relative to the signal. The image may be frozen when 
the desired number of waveforms are present on the screen.
For pulsed doppler systems, Place the transducer in lower other 
portion of the meternal abdomen. The orientation should be 
towards the parametria area can then be examinedby 
maneuvering the sample volume until the characteristics wave 
forms are obtained.examinations should be confined to the area 
that is composedof the myometrium amd may be most fruitful 
close to the placenta. Indices fo r pulasatility , if calculated, 
should be determined for each of several heartbeats and 
averaged.
Fetal Heart
Fetal cardiac doppler studies can be performed only with duplex 
ultrasound systems. the fetal heart should be carefully examined 
in all standard planes to determine whether or not the anatomy 
is normal. These planes should inclued :four-chamber view, long 
axis left ventricles, short axis of the great vessels, aortic arch, 
and pulmonary artery ductus views. The area for sampling 
should be visualized as clearly as possible to the ultrasound 
beam. The sample volume should be placed in this area with an 
appropriate size selected to samp le as desired. Power output 
control should be at the lowest settingscompatible with obtaining 
an adequate image and the gain setting should be maintained to 
keep an adequate signal without ex cessive noise. Excluding the 
actual valves from the sample  volume will help to minimize 
unnecessary noise from the signals obtained.
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							Bioeffects
LOGIQ 3 Expert/LOGIQ 3 Pro/LOGIQ 3 Advanced Reference Manual 1-13
Direction 5122542-100 Rev. 2
Efficacy Of Fetal Doppler
The following are clinical  obstritrical where ther are experimental 
data that demonstrate the effica cy of Doppler.Provided by Jhon 
C.Hobbins,M.D. and Peter Burns,Ph.D.4
IUGR
Many studies have shown a good correlation between abnorma 
waveform( or decreased blood flow) and increased perinatal 
mortality5, Fetal hypoxia 6,7,8 ,and neonatal eveents such as 
necrotizing entero colitics(NEC), and interventricular 
hemorrhage(IVH)8. It must be pointed out that the doppler 
studies initially designed to identity altered fetal growth had a 
predictably low sensitivity beca use the category of small for 
dates frequently includes genetically small but completely 
normal fetuses and neonates.Thus far, all studies have shown 
that the rare doppler  pattern of reverse diastollic flow in the 
umbilical artery has been very  highly correlated with adverse 
outcome and may warrent immediate intervention. conversely, 
anormal waveform in the umbilic al artery has been rarely 
associated with stillbirth in a high risk pregnancy.
Cardiac Anomalies
Doppler has become an integral part of fetal schocardiaographic 
studies. Its use has been directly derived from well-documented 
pediatric and adult Doppler research.The etiology and 
seriousness of fetal arrhythmias  is relatively easy to determine 
with pulsed doppler interrogation of ventricular diastollic filling 
patterns.Benign patterns such as  premature atrial extrasystoles 
can be more easily diognised with Doppler than with older 
approach of M-Mode echocardiography.Doppler has proven 
useful as well in the understanding and interpretation of 
structural heart disease and the appearence of non-immune 
hydrops. Improved diognostic  and prognostic ability has 
permitted more accurate counseling of parents whose fetuses 
have structural ca rdiac abnormalities.
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							Acoustic Output
1-14LOGIQ 3 Expert/LOGIQ 3 Pro/LOGIQ 3 Advanced Reference Manual
Direction 5122542-100 Rev. 2
Efficacy Of Fetal Doppler(cont’d)
Summary
It is important to realize that current investigation DOES NOT 
support the concept that Doppler waveform analysis in the 
above obestritrical conditions prov ides information that is meant 
to replace other conventional tests, or the biophysical profile, 
also, it should not replace classical non-doppler ultrasound 
scanning methods. Rather , it a ppears that Doppler is of value 
when used in conjuction with thes e other tests. Lastly, there is 
little data to suggest that an is olated Doppler examination of the 
fetus can be used as a screening tool in a low-risk population to 
identify the compromised fetus.
As with the evoluti on of any new diognostic technique, the 
indications for use may change when new experimental data 
become avilable.
Suggested Guiedlines
Following are suggested guidelines prepared by Harold 
Schulman,M.D
Overview
There are two types of Doppler instruments, continuous 
Wave(CW) and pulsed .Modern instruments use directional 
Dopplers, that is they portray forward and reverse flow on a split 
screen.The CW Doppler traverses the entire vessel Diameter 
and summerises a veriety of refl ections, including those from the 
vessel wall and neighboring vess els. The pulsed Doppler is 
focused and may sample the red cell flow in different loci within 
the radius, but has the advantage of rejecting extraneous 
current instrumentation utilize  output energies which exceede 
guidelines for safety  obestrtric ultrasound.
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