Limited Ultrasound Training Developed by: Dr. David Ying, Radiologist Michelle Zehr, RN, BSN © CompassCare Pregnancy Services The following information.

Limited Ultrasound TrainingDeveloped by: Dr. David Ying, Radiologist Michelle Zehr, RN, BSN

© CompassCare Pregnancy ServicesThe following information is the copyrighted intellectual property of CompassCare Pregnancy Services, and may not be used by any party without the expressed written permission of CompassCare.

Objectives

Describe indications for limited ultrasound exams

Understand and apply the basic principles of ultrasound physics and instrumentation

Understand the implications for patient care from ultrasound findings

© CompassCare Pregnancy Services

Ultrasound Physics and Instrumentation


Sound Wave Propagation


Electromagnetic Wave:Radio Wave, Light Wave

Does not require medium for transmission and is measured in wavelength (distance between two adjacent vibrations)


Mechanical Wave:Sound Wave

Transmitted through a medium such as air, water, solid and is measured in frequency (vibrations per second), or hertz (Hz=1 vibration/second)


Waveforms Compared

Light 370 trillion to 750 trillion Hz Spectrum of visible light

ranges from 780nm to 380nm (Nanometer=I billionth of a meter)

Ultraviolet, X-ray and gamma rays have progressively shorter wavelengths

Infrared and radio microwave have progressively longer wavelengths

Sound spectrum ranges from 20-

20,000 Hz. Ultrasound is in the range

higher than 20,000 Hz Medical ultrasound is in the

range of 2-7 megahertz (MHz= 1,000,000 Hz)


Useful terms:

Attenuation: Weakening of sound as it propagates through a medium

Causes: Absorption, reflection, and scattering

Decibels (dB): units used to relatively quantify intensity of sound for comparison purposes


Frequency: cycle/vibrations per second expressed in hertz (Hz)

1 Hz=1 vibration/second

Intensity: Power (energy/time)/area= Watts/area


Incidence: Direction of sound wave travel to the boundary between 2 media

e.g. perpendicular, oblique angle

Impedance: = density of medium X propagation speed


Inverse square law: intensity of sound varies inversely with the square of the distance from the source

Speed of propagation: depends on the medium. The more solid (high elasticity or stiffness) medium allows faster speed. Decreasing speed in solids, water, air.


Boundary behavior: (interface between media)Reflection: bouncing back from the boundary

Specular: when the boundary is smooth and flat Scattering: when the boundary is rough and

uneven

Refraction: crossing the boundary with change in direction

Transmission: going through the boundary


Transducer Functions

A transducer converts one form of energy to another.

An ultrasound transducer converts sound wave energy to electric energy and vice versa.


Composition of an U/S Probe

Piezoelectric element: Material that is capable to convert pressure and

electricity, such as ceramic or quartz Element (crystal) in linear, curved (sector) and

phased array

Damping/matching, material: To improve transmission


Operating Frequency

The higher the operating frequency, the thinner the transducer element, the greater the attenuation (or the lesser the depth penetration)

3.5 or 5.0 MHz for the abdominal probe

5.0 or 7.5 MHz for the internal/vaginal probe


Beam Focusing:

Focusing electronically to improve resolution at various depths

Coupling Medium:

Gel that is used to eliminate air at transducer-skin interface to maximize ultrasound transmission


Types of transducers

External: Linear array

Flat top, curved top, pointed top

Sector Flat top, curved top,

pointed top

Internal (endo-): Rectal, vaginal,

esophageal, vascular, etc.


Penetration:

Depth of images obtained is directly related to:Attenuation by the mediumPower of the beamFrequency (Hz), inverse relationship


Time-Gain Compensation

To provide a more uniform image by “compensating” the weaker signals from deeper (further from the transducer) tissue as a result of longer time and greater attenuation


Resolution

Detail

Contrast

Temporal


Detail:

Degree of separation of structure echoes or signals Axial resolution: along the beam direction Lateral resolution: perpendicular to the beam direction

Increased frequency means increased resolution but decreased penetration

(useful U/S frequency is 2-15mHz)


Contrast:

Improves with:

Greater gray scale

(U/S signal strength vs. B-W scale)

Color display


Temporal:

Improves with higher frame rate


Artifacts

Types:False (erroneous) signals or imagesMissing signals or structuresWrong locations Incorrect sizes


Artifact Causes:

Section Thickness:

Ultrasound beam is

3-D while the displayed image is

2-D


Artifact Causes:

Acoustic speckles:

Interference effects of scattered sound beams and echoes from various tissues and directions of the ultrasound beam.


Artifact Causes:

Reverberations:

Repeated echoes occur between the transducer and a strong reflector.

Mirror image is a form of reverberation artifact and formed with a strong reflector within a tissue.


Artifact Causes:

Refraction:

Laterally misplaces or mis-shapens a structure when a beam is refracted in the tissue.

e.g. Observed depth of object in water.


Artifact Causes:

Speed error:

Axially misplaces a structure when the speed of the ultrasound beam is miscalculated

Artifact Causes:


Artifact Causes:

Shadowing:

Decrease or loss of ultrasound signal behind a strongly reflecting or attenuating structure, or from the edge of a refracting structure.

Artifact Causes:


Artifact Causes:

Enhancement:

Increase in echo signals behind a poorly attenuating structure.

Artifact Causes:


Artifact Causes:

Grating Lobes:

False duplicated and miscalculated images created by side beams in directions different from the primary beam.

Artifact Causes:


Proficiency in imaging technique:

Patient Interaction Professional, but

friendly Courteous Respectful, esp. in

regard to privacy Informative regarding

the procedure, but not the diagnosis

Proper instrument settings probes and gel. Correct transducer

frequency and type. Adjust field size, near

and far gain settings Contrast, gain and

TGC slope


Scanning Technique:

Patient position: Supine, prone and lateral, to provide shortest distance

to the anatomic structure of interest Image:

In traditional long (sagittal) and transverse (axial) planes. Also oblique, coronal and angle planes if necessary.

Identify anatomic structures and landmarks. Know the pathology (abnormal findings)


Safety:

There is no known risk associated with diagnostic ultrasound since first used in the 70’s.

The possibility of adverse bio-effects from an even low level, delayed harm of the U/S energy transfer can not be absolutely denied.

Minimize use exposure time and intensity of the ultrasound without sacrificing the proper gathering of diagnostic information.


Patient Education


Indication for testing:

Confirm the viability of pregnancy. visualize your baby’s heartbeat within the uterus. 31% of all pregnancies are not viable. (it could be

miscarriage, ectopic pregnancy, or multiple other reasons why the pregnancy hormone would be in the urine).

Confirming how far along she is related to her last menstrual period (LMP).

Explain what you anticipate before the exam.


Gestational Age

Gestational Sac (GS)

Yolk Sac (YS)

Fetal Heart Motion

Movements Development

(visualized)

3-4 wks + - - - -4-5 wks + ? - - -5-6 wks + + ? - -6-7 wks + + + - -8-9 wks + + + + arms, legs

9-10 wks + + + + face

11 wks + + + + arms & legs moving, jaw lines, fingers

and toes

12 wks + + + + More clarity

With each week, size doubles and development is much more defined

Scope of Information Provided:


Ultrasound ExamResults

See What YouExpect to See

Didn’t See WhatYou Expect to See

Confirm ViabilityCan not Confirm

Viability(Before 6 Weeks)

Can not Confirm Viability

(After 6 Weeks)

See What You Expect To See:Confirm Viability

Reiterate what you were able to see.

Explain the development that is there that you can’t see.

Show the model of comparison to where they are, and where they’ll be soon.

See What You Expect to See

Confirm Viability Can’t Confirm Viability

So, You’re Pregnant Brochure

Reschedule for Repeat Ultrasound

Refer to physician for Prenatal Care


Saw What you Expect to See Unable to Confirm Viability: Before 6 Weeks

Say, “You are __far along and I can not confirm viability. I see ___ and would expect to see that.”

i.e.: “You are 5 weeks today by the measurements, I see the yolk sac (point it out), but can not confirm viability because I can not see the heart beat today. We will need to reschedule you for next week in order to confirm viability.”

See What You Expect to See

Confirm ViabilityCan’t Confirm

Viability

Give Miscarriage/Ectopic Pregnancy

Brochure

Reschedule for repeat ultrasound

one week

Refer her to physician


Didn’t See What You Expect to See Unable to Confirm: After 6 Weeks

Say to the patient, “I do not see what I expect to see.”

Reiterate what you would have expected and explain you are not seeing that today.

Follow P&P


Didn’t See What You Expect to See

Can’t Confirm Viability

Symptoms ED No Symptoms

Call Patient’s OBFor Plan

If no OB, ED

What this exam does not include:

Sex of the baby

Diagnosis of pregnancy from an RN or Sonographer

Diagnosis/Opinion of what is wrong if you do not see what you expect to see (to the pt.)


Criteria for Rescheduling an Ultrasound

Limited Ultrasound Training Developed by: Dr. David Ying, Radiologist Michelle Zehr, RN, BSN © CompassCare Pregnancy Services The following information.

Documents

ultrasound transducer

beam frequency hz

sound wave energy

hz medical ultrasound

light wave

intensity of sound

direction of sound wave

radio wave