fetal ultrasound doppler dictionary of terms


American Institute of Ultrasound in Medicine

the gradual decrease in the magnitude or intensity of a sound wave as it passes through its medium; in the case of ultrasound this is caused by a combination of energy absorption by the medium as heat and sound wave scattering

range sound waves that are generated having frequencies within the audible range are capable of being perceived or "heard"

baby heartbeats per minute

the effects of a transmitted ultrasound wave on gas bubbles present in the imaged medium; generally it causes them to expand and contract as well as to increase in pressure and temperature

class II device
Class II devices are those for which general controls alone are insufficient to assure safety and effectiveness, and existing methods are available to provide such assurances. In addition to complying with general controls, Class II devices are also subject to special controls. Examples of Class II devices include powered wheelchairs, infusion pumps, surgical drapes, and fetal dopplers.

an increase in pressure within a section of a medium created when its composite particles are pushed closer to one another

a form of sound generation in which a waveform of single frequency is generated non-stop. Graphically this waveform would appear as a sine wave

continuous wave doppler
This type of Doppler ultrasound uses the change in pitch of the sound waves to provide information about blood flow through a blood vessel. The doctor listens to the sounds produced by the transducer to evaluate the blood flow through an area that may be blocked or narrowed. This type of ultrasound can be done at the bedside in the hospital to provide a rapid estimate of the extent of blood vessel damage or disease.

This is the type of ultrasound used by your hand-held fetal ultrasound doppler.

critical angle
defined such that for an incident beam striking an interface at an angle equal to greater than this angle, no transmission will occur and only a reflected beam will result

a unitless term of measure that expresses a value as a fraction or multiple of a standard unity value. Decibel notation allows an extremely wide dynamic range to be represented by a much smaller data set.

refraction of the incident sound beam causes objects to be imaged at a location different from their actual location

the part of the ultrasound machine that produces a viewable image by interpreting intensity values onto a screen

doppler effect
is the shift in frequency and wavelength of waves which results from a source moving with respect to the medium, a receiver moving with respect to the medium, or even a moving medium.

doppler ultrasound
A special form of ultrasound that uses sound waves to measure the velocity of blood flow. Doppler ultrasound can be used to listen to the fetal heart beat, examine the fetal heart for defects, and estimate placental blood flow.

dynamic range
the difference between the maximum possible value in a set and the minimum possible value; essentially the width of the data set

a sound wave generated by a reflection off of an interface and received back at the transducer

electronic fetal monitor
An electronic device that is used to monitor the heart rate of the fetus before delivery. The electronic fetal monitor is usually used in labor and can identify fetal problems before delivery. There is some evidence that monitoring the fetal heart rate electronically may increase the rate of cesarean delivery. Most obstetricians believe that it identifies serious fetal problems earlier than other methods, thus improving outcome. Another method for monitoring the fetus' health during labor is listening to the fetal heart beat with a special fetal stethoscope or fetal ultrasound doppler device at regular intervals. There are two types of fetal monitors: 1) external, which are attached to the mother's abdomen and 2) internal, which attach to the infant's scalp inside the uterus.

Food & Drug Administration

Fetal Heart Rate

fetal monitoring
Monitoring of the baby before birth. This usually refers to monitoring of the fetal heart beat. There are two ways to do this. Before the mother's membranes have ruptured (water has broken) a belt containing a receiver similar to an fetal ultrasound doppler can be strapped to her abdomen and used to monitor the fetal heart rate and uterine contractions. After the membranes have ruptured and the cervix has dilated, an internal monitor can be attached directly to the baby's scalp. There are other tests that can be used to monitor the fetus during and before labor such as ultrasound , scalp pH measurements, and others.

fetal heartbeat sounds
A galloping horse is what your baby's heartbeat will sound like and will be about twice as fast as the mother's heart rate. An average normal fetal heart rate is between 120-180 BPM (Beats Per Minute). Where as an average adult heart rate at rest is between 60-100 BPM

fetal ultrasonic monitor
is a device designed to transmit and receive ultrasonic energy into and from the pregnant woman, usually by means of continuous wave (doppler) echoscopy. The device is used to represent some physiological condition or characteristic in a measured value over a period of time (e.g., perinatal monitoring during labor) or in an immediately perceptible form (e.g., use of the ultrasonic stethoscope). This generic type of device may include the following accessories: signal analysis and display equipment, electronic interfaces for other equipment, patient and equipment supports, and component parts. This generic type of device does not include devices used to image some relatively unchanging physiological structure or interpret a physiological condition, but does include devices which may be set to alarm automatically at a predetermined threshold value.

This is a special type of stethoscope used for listening to a baby. There are many types of fetoscopes available, and a regular stethoscope works as well. This can usually be used after about 18 weeks.

the rate at which oscillations governed by a sine wave occur in a given property, measured in cycles per second. A cycle is the process of shifting from minimum value up to a maximum value and then back down to the initial minimum value.

high-risk pregnancy
Pregnancies at high risk of fetal or maternal complications. There are many factors that contribute to complications during pregnancy and delivery. Chronic medical problems in the mother, past history of repeated preterm delivery, and abnormalities of the fetus or placenta all increase the risk of complications. Women with high-risk pregnancies should be seen and treated by someone who is experienced in caring for complicated pregnancies. Usually, this is an obstetrician or a perinatologist, an obstetrician with additional training in treating high-risk pregnancy problems. In some cases a consultation with neonatologist (specialist in the care of sick newborns) can prepare you for what to expect if your baby has problems. Some hospitals have high-risk pregnancy units, where mothers stay during part of their pregnancy to receive the care they need. This is one of those conditions that is best treated by a hospital that has a high volume of these types of patients.

Home uterine monitoring
Measurement of uterine activity at a patient's home. Women wear a special belt that identifies uterine contractions and either notifies the woman directly or transmits the information to the doctor. It can be especially helpful in monitoring women with premature labor. Use of this technique puts patients in daily contact with their health care provider. The contractions are transmitted by telephone to a center so the doctor can evaluate them on a computer. This can be an alternative to hospitalization

incident beam
a sound wave beam generated by a transducer that strikes an interface

instrument noise
The fetal doppler itself may have some background noise, static, popping etc. When the fetal doppler probe is moved on the abdomen, louder popping noises may result. Sometimes, the movements of your baby in later pregnancy also produce louder noises. Ultrasound gel use is integral on cutting down on much of the static produced when positioning the fetal dopplers trasducer during an exam.

internal fetal monitoring
It is an internal monitoring with an electrode attached to the baby's head to record heart tones, and a pressure catheter to record contractions. This is also used during labor and birth, however, it is not used intermittently

maternal sound
You may also hear sounds of your own heart or blood flow. A major artery runs through your abdomen and the swish of your blood through it is sometimes picked up by the fetal doppler. This sound is heard by the baby later in pregnancy and has been recorded and used to calm upset babies after birth.

any suspension comprised of particulate matter that allows an energy source, including sound, to propagate through it

obstetrician-gynecologist (OB-GYN)
A specialist in the medical and surgical problems associated with women's reproductive system. These doctors receive at least four years of specialty training to prepare them to assist women with pregnancy, delivery, postnatal care and other women's health issues. Many OB-GYN serve as primary care physicians for their patients and are viewed as such by insurance plans. During pregnancy, a strong doctor-patient relationship often develops. This relationship can be a source of confidence and trust in dealing with other health issues. Surveys have shown that women often continue to receive care from the same OB-GYN for many years.

the length of time required for one oscillation to occur, symbolized by T. Also equal to the inverse of frequency (T=1/f)

a specialized type of transducer which converts electrical energy into acoustical energy, i.e. sound, and vice versa

placental sounds
The blood flow becomes steadier as it flows through the placenta and has a distinctive sound like wind blowing through the trees.

a form of sound generation in which short bursts of sound, each consisting of several cycles of variable frequency content, are transmitted rather than a single continuous waveform

the part of the ultrasound machine that generates electrical pulses which stimulate the transducer

the part of the ultrasound machine that listens for returning sound waves and converts them to electrical signals. Also performs some preprocessing functions

reflected beam
the portion of an incident sound wave beam which, upon striking an interface, bounces back in the direction of the source

an immediate reverse in direction of an incident beam upon striking an interface such that it is now travels back towards its source

a bending or shifting of the path of an incident beam as it passses through an interface

small deflections of the incident wave caused by the striking of objects or surfaces which are small relative to the wavelength of the incident wave


sonograph (sonogram)

A-Mode - is a one-dimensional display of sound waves.  Each time a sound wave hits a structure, a spike is formed on the examiner's screen.  The height and spacing between each of the echoes provides the examiner with valuable information.  A-Mode scans are now mostly obsolete in medical imaging.

B-Scan - is used to create a two-dimensional, cross-section view.  Multiple sound waves are emitted from the probe allowing the examiner to visualize structures.

 2D - Traditionally fetal ultrasounds are 2D, providing a two dimensional image. These images are made up of image slices of which only one at a time is visible and creates a flat looking image. A 2D fetal ultrasound can display up to 100 images per second.

3D - Recently, three dimensional fetal ultrasounds have become more and more common but due to there high expense ($250,000) haven't made there way into all hospitals. The 3D fetal ultrasound takes thousands of slices and digitally stores and shades them to emulate a more life like image of the baby.

4D - A Four dimensional fetal ultrasound simply means that the images can be seen in real time, allowing for the study of fetal behavior.

telemetry monitoring
It is a lot like the regular Electronic Fetal Monitoring, however, one can maintain mobility

transducer (probe)
any mechanism that transforms one form of energy into another. A basic example could be a stove, which transforms energy in the form of elecricity into energy in the form of heat



transmitted beam
the portion of an incident sound wave beam which, upon striking an interface, continues in the direction of the incident beam

a sound wave having a frequency above the audible human range. Ultrasound can also refer to the medical imaging modality which utilizes these sound waves

Ultrasound imagery is offered to most women between 16--20 weeks but up it's up to the doctor's discretion.

Ultrasounds allow imaging of body parts using sound waves. Ultrasound uses sound waves that are above the range of human hearing to create an image of organs within the body. Sound waves are reflected off internal body structures and back to the ultrasound machine. The reflected sound waves are analyzed by computer and turned into pictures. This method of imaging results in less clearpictures than X-rays, CAT scans or MRI. However, there is no radiation risk with ultrasound and no confirmed adverse effects on the fetus or mother from diagnostic ultrasound examinations in pregnancy.

There are different types of ultrasound exams. They are differentiated by the purpose for which they are done and the level of detail obtained.

Ultrasound can measure fetal size, the amount of amniotic fluid, estimate fetal gestational age, identify multiple fetuses, some fetal abnormalities such as microcephaly or Down Syndrome, and locate the location of the placenta. Although an ultrasound can usually determine gender of your baby, many families do not want to know this information before delivery and some ultrasound centers have a policy of not revealing the gender

ultrasound gel
Ultrasound gel is specially formulated to act as a coupling agent and reduce static that is often caused when using a fetal doppler. To get optimal use and sound out of a fetal doppler monitor use plenty of ultrasound gel. Do not use colored gels or lotions. Any oil based substance used with a fetal doppler will cause excess static and can damage the fetal doppler probe.

Fetal Doppler Facts™ - All Rights Reserved 2007