Ultrasound can cause biological effects through thermal and non-thermal mechanisms. Thermal effects are caused by ultrasound energy being absorbed and converted to heat, while non-thermal effects include cavitation and direct mechanical effects. While some studies have reported associations between ultrasound exposure and fetal effects, most clinical studies have found no biological effects, even at higher intensities. Regulatory bodies have established safety indices and output limits, and recommend using the minimum exposure needed for diagnosis. Overall, diagnostic ultrasound is considered safe when used prudently according to established guidelines.

1. Biological
effects of
UltraSound

2. INTRODUCTION
UTZ - HIGH FREQUENCY MECHANICAL WAVE
above human hearing range (>20,000 Hz)
produced by converting ELECTRIC  MECHANICAL energy
BIO-EFFECTS of UTZ – potential BIO consequences
due to interaction b/n UTZ waves & scanned tissues
Concern on:
• biological effects on susceptible structures (fetal tissues)
• No human studies available to establish its effects
• Use of higher acoustic outputs

3. Biological Effects
MECHANISMS
THERMAL
Non – thermal/
MECHANICAL
NON-CAVITATION CAVITATION

4. THERMAL EFFECTS
DEFINITION: Temperature w/in a medium
HOW: SONIC energy absorbed & converted  HEAT
FACTORS TO CONSIDER
1. ACOUSTIC characteristics
• POWER -rate of E transmission Transducer to Medium (mW)
• INTENSITY-rate of E flow through an area (mW/cm2)
Spatial-Peak Temporal Average Intensity (ISPTA)
2. TISSUE characteristics
• Heat generation
• Heat loss

5. A. NON-CAVITATION MECHANICAL (DIRECT) EFFECTS
Eg. Particle Displacement & Fluid Streaming
Target particles pushed away from transducer
acoustic streaming in fluids, cell distortion and lysis.
bubble rotation &
associated fluid
movement along
cell membranes
Microstreaming
NON-THERMAL / MECHANICAL

6. B. CAVITATION
DEFINITION: activity of small gas bodies
w/in tissues in the presence of UTZ waves
HOW: Regions of compression &
rarefaction created in a medium 
Pressure &  formation & size of
gas bodies  STABLE or grow to critical
size then collapse INERTIAL/TRANSIENT
 E generated  mechanical effects …
FACTOR TO CONSIDER:
ACOUSTIC PRESSURE (Mpa)
NON-THERMAL / MECHANICAL

7. STABLE : bubbles oscillating with sound beam.
EFFECT: mechanical damage
membrane rupture
cell lysis.
TRANSIENT : very rapid expansion & violent collapse.
creating high temp. & pressure  release of free radicals
EFFECT: genetic damage in vitro
TYPES OF CAVITATION

8. Some reported fetal effects of US exposure:
Delayed speech, dyslexia, growth restriction,& non-right-
handedness.
EPIDEMIOLOGIC STUDIES
“…no definite causal association to Fetal Growth & development”
IN VITRO CELL STUDIES
“…no biologic effects even at intensities exceeding those
produced by diagnostic UTZ machines”
ANIMAL STUDIES
“…no biologic effects at usual diagnostic levels”
Information regarding
UTZ BIOEFFECTS

9. BUT up to date there is insufficient justification
to conclude that there is a causal relationship
between diagnostic US & long-term adverse fetal
effects THEREFORE exposure to UTZ during
pregnancy appears to be safe
LIMITATION: most studies included were when
Acoustic outputs were LOWER and under strict
regulation
Information regarding
UTZ BIOEFFECTS

10. MAXIMUM ALLOWABLE OUTPUT FDA (USA)
IMAGING ISPTA (mW/cm 2)
1986
ISPTA (mW/cm 2)
1992
ADULT CARDIAC 430 720
PERIPHERAL VASCULAR 720
FETAL 94
OPHTHALMIC 17 50
REGULATION OF
ACOUSTIC OUTPUT LEVELS

11. ACCOUSTIC OUTPUT LEVELS FOR SCANNERS
OPERATING MODE Pressure
Mpa
I (ISPTA)
mW/cm2
POWER
mW
B MODE 1.68 18.7 18
M MODE 1.68 73 3.9
PULSED DOPPLER 2.48 1140 30.7
COLOR FLOW 2.49 234 80.5

12. Safety Indices
Thermal Index (TI) & mechanical Index (MI)
Not perfect; but they are the most common & practical
measurements available at present in estimating risk
Indicate probable thermal & non thermal effects.
Assist sonographers in patient exposure …
…by keeping indices AS LOW AS POSSIBLE
while obtaining the best possible diagnostic images.

13.  indicator of possible TEMPERATURE increase
at a particular equipment setting.
 FORMS:
 Soft tissues (TIS) - < 8wks
 Bone (TIB) – 2nd-3rd Trimester
 Neonate/Adult Cranial exposure (TIC).
Safety Indices
THERMAL Index (TI)

14.  indicator of the probability of cavitation events
… this may not be important for FETAL
scanning as risk is probably remote in OB
scans since FETAL LUNG & INTESTINES
contain NO AIR/GAS bodies yet
Safety Indices
MECHANICAL Index (TI)

15. •MI & TIS
are displayed
on screen.

16. ACCOUSTIC OUTPUT as measured by
MI & TI during ROUTINE OB UTZ
EXAM MEAN Duration MI TI
1ST TRIM (11) 8.9 min 0.73 (0.3-1.3) 0.34 (0.1-1.7)
2ND TRIM (14) 31.8 min 1.04 (0.5- 1.5) 0.28 (0.1-2.4)
3RD TRIM (12) 16.3 min 1.06 (0.2-1.5) 0.32 (0.1-2.4)
Danao, LB, Teotico AR, Sumpaico, WW(2006) Bioeffects & Safety of Ultrasound
Obstertic & Gynecologic Ultrasound for the Practicing Clinician (2nd ed.) pp 9-22
MCU-FDTMF Ultrasound services, Inc

17. RECOMMENDED SCANNING TIME
at any given TI for OB SCANS
BMUS Safety guidelines on the safe use of diagnostic ultrasound equipment 2009

18. BMUS Safety guidelines on the safe use of diagnostic ultrasound equipment 2009

19. SOGC (2005)
UTZ should only be used when BENEFIT OUTWEIGHS RISK
Exposure should be As Low As Reasonably Achievable
DWELL TIME & OUTPUT CONTROL
Dx UTZ device should comply w/ ODS (MI & TI)
Avoid Pulsed/Color doppler in 1st trimester
SATEMENTS ON
CLINICAL SAFETY OF UTZ

20. ISUOG (2003)
ODS is accepted as most practical/understandable in estimating RISK
M MODE / B MODE is safe in all stages of pregnancy
DOPPLER use should be with VALID indication
requiring a knowledgeable Operator
1st TRIMESTER has the highest risk of damage
Exposure & acoustic output should be kept at the LOWEST possible
consistent with obtaining Dx information ,
limited to MEDICALLY indicated procedures rather than entertainment
SATEMENTS ON
CLINICAL SAFETY OF UTZ

21. AIUM (1997)
“There is NO CONFIRMED BIO EFFECT on patients/instrument operators caused by
EXPOSURES from DIAGNOSTIC UTZ INSTRUMENTS.
Although the possibility exists that such BIO EFFECTs may be Identified in the future
Current DATA indicate that the BENEFITS to patients on the prudent use of Diagnostic UTZ
OUTWEIGH RISKS if any that may be present “
SATEMENTS ON
CLINICAL SAFETY OF UTZ

22. DO NOT hesitate to use DIAGNOSTIC UTZ when the situation warrants
FAMILIARIZATION w/ the equipment to know the OPERATING MODES & CONTROL
SETTINGS will result to HIGH/LOW acoustic INTENSITIES
Know & recognize the controls to adjust acoustic POWER
Decreased EXPOSURE TIME by decreasing REPEAT SCANS
avoid a stationary transducer in contact w/ patient = DWELL TIME unless warranted
… keep indices AS LOW AS POSSIBLE
while obtaining the best possible diagnostic images
ALARA PRINCIPLE
(As Low As Reasonably Achievable)
MAXIMUM RECOMMENDED EXPOSURE
TIME (BMUS 2000)
TI MINUTES
0.7 60
1.0 30
1.5 15
2.0 4
2.5 1

23. “UTZ machine MANUFACTURERS are expected to design
their equipment so as to deliver the lowest possible
acoustic exposure consistent w/ diagnostic expectations
of that equipment.
HOWEVER, user awareness & responsibility are major
elements in ensuring patient safety during UTZ
examinations”
Danao, LB, Teotico AR, Sumpaico, WW(2006) Bioeffects & Safety of Ultrasound
Obstertic & Gynecologic Ultrasound for the Practicing Clinician (2nd ed.) pp 9-22
MCU-FDTMF Ultrasound services, Inc

24. THANK YOU