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HealthPhone™: How to Use the Ultrasound Probe

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Medical Aid Films - The training films charity

Use of the Probe

What is ultrasound?

Ultrasound is high-frequency sound above the range of human hearing An ultrasound probe houses the ultrasound transducer, which is made up of piezo-electric crystals

Ultrasound is generated by the passage of an electronic stimulus through the piezo-electric crystals which then vibrate and a high-frequency sound is emitted.

The soundwave then travels through different tissues in the body, which have a different penetrability, also known as acoustic impedence.

So, part of the sound energy is reflected by the tissues and part continues to travel through until it hits other tissues and is reflected back.

The image is produced from the reflected soundwaves as they come back from the different tissue interfaces, and that impulse is registered on the screen as a dot.

Thousands of these dots produce the complete image, which is a composite of all the returning signals.

Terminology

The terms longitudinal and transverse are used when referring to the position of the probe.

The terms saggital and coronal are used when referring to the view obtained by the probe of the mother or fetus.

Longitudinal

When initiating a scan, one always starts with the probe over the pubic bone of the mother, in a longitudinal plane. This means the long axis of the probe is lined up with the long axis of the mother. We then scan systematically, up and down her abdomen, taking slices lengthways.

Transverse

We then rotate the probe through 90 degrees so it's in the transverse plane. This means the long axis of the probe is lying across the mother. We then scan systematically across the mother's abdomen, taking slices, crossways, giving left to right images.

Saggital

Saggital is used when describing a vertical slice or view of a section that passes through the mother or fetus, from head to foot.

Coronal

Coronal is used when describing the view of a section that passes through the mother or fetus, from left to right.

Anterior and Posterior

If we're considering the antiverted uterus and are scanning in both the longitudinal and transverse planes, then the anterior part of the uterus is the front of the uterus, nearest the mother's belly button, and the posterior is the back of the uterus, nearest the mother's spine.

As an image on the monitor, the anterior part is represented uppermost on the screen and the posterior part is represented on the lower part of the screen.

Superior

This refers to the direction of the mother's head

Inferior

This refers to the direction of the mother's feet.

For example, if scanning the uterus in the longitudinal plane, the superior part of the organ is the end towards the mother's head, and the inferior part is the end towards the mother's feet. As a scan image, superior is represented to the viewer's left on the screen and inferior is represented to the viewer's right on the screen.

Cephalic presentation

Cephalic describes the fetus in the head-down position inside the uterus The head of the fetus is at the birth canal, in other words, just above the pubic bone.

Breech presentation

Breech describes the fetus with its breech or bottom lying close to the birth canal, just above the pubic bone.

Probe Orientation

There is a marker or a dot located on the ultrasound probe and it is always represented on the screen in the same place, usually the top left-hand corner. This dot is crucial when working out the orientation of the organ or the fetus and when interpreting the corresponding image on screen.

If the probe is placed on the mother's pubic bone in the longitudinal plane, one must consider where the dot is on the probe and relate it to the dot on the screen in order to interpret the image.

In the longitudinal plane, the left side of the screen represents the superior part of the mother and the right side represents the inferior part of the mother.

So when scanning in the longitudinal plane, the mother's head is represented to the left of the screen and her feet to the right. The location of the dot on the screen should correspond.

When scanning in the transverse plane, the image on screen is like a mirror image. The left side of the mother is represented on the right side of the screen, and the right side of the mother is represented on the left side of the screen. Again, the location of the dot on the screen should correspond.

Understanding these principles of orientation is important, otherwise it can lead to confusion, for example, where a cephalic presentation could be mistaken for a breech, and vice versa.

Interpreting the image

There are various positions of the back for cephalic or breech presentation.

Cephalic

Back posterior

Scanning in the longitudinal plane, the fetus's back is lying along the mother's back. They are back-to-back. The head will appear to the right of the screen and its back will be on the lower part of the screen.

Back anterior

Scanning in the longitudinal plane, the fetus's spine will be lying just under the mother's abdominal wall. The head will be to the right of the screen and the fetus's back will lie at the top of the screen.

So, to summarise: When scanning in a longitudinal plane, the right side of the screen always shows the inferior part of the mother and the left side of the screen always shows the superior part of the mother. Breech It is essential to identify a breech presentation before delivery.

Regarding the spine position, the same principles apply.

For example, back anterior. Scanning in the longitudinal plane, the fetus's spine will lie just under the mother's abdominal wall. The head will be to the left, and the fetus's back will lie at the top of the screen.

A good way to distinguish a breech presentation from a cephalic presentation is by scanning the fetus's abdomen in the transverse plane. With the back posterior, a cephalic presentation will always show the fetal stomach to the left of the screen, and with a breech presentation, the fetal stomach will always be on the right of the screen.

Twins

During the ultrasound scan of twins, it's important to identify each twin and to describe their positioning.

Twin 1 is traditionally referred to as the twin with the lower-most presenting part So in the case when both are lying longitudinally with a cephalic presentation, twin 1 will be the twin that has its head lowest in the pelvis In the case of breech twins, the same principle applies: the twin with the lowest-most breech will be described as twin 1.

Clearly, in some instances, twin 1 may be cephalic and twin 2 may be breech. The lie of the twin refers to whether the twin is in the longitudinal, transverse or oblique position.

Placenta

The placenta can be located in the upper part or the lower part of the uterus in an anterior or posterior position. A placenta inserted in the lower segment of the uterus is regarded as low or as a placenta praevia if close, reaching or covering the cervix.

Anterior and posterior positions

Scanning in the longitudinal or the transverse plane, the anterior placenta will always be at the top of the screen and the posterior placenta will always lie at the bottom of the screen.

Fundal position

Scanning in the longitudinal plane, the fundal placenta will be displayed on the left side of the screen.

Placenta praevia

Scanning in the longitudinal plane, the praevia position will be shown on the right side of the screen. A low anterior placenta will appear between the bladder, which is seen at the extreme right of the screen, and the fetus on the left.

Fibroids

When scanning fibroids, it's important to describe their size in terms of volume. Two measurements are taken in the longitudinal plane and one measurement is taken in the transverse plane. The fibroid should then be located in relation to the uterus to determine whether it is fundal, anterior, posterior or cervical.

Also described is the fibroid's position within the uterine wall.

Fibroids located in the lower part of the uterus can obstruct labour and therefore need to be identified before birth.

In summary: Before proceeding with the finer points of diagnosis using ultrasound, it is important to clearly understand the orientation of the fetus and its organs within the uterus and to accurately learn the language of its description.

Credits Animation: Alternative View Studios

Consultants: Dr. Natalie Greenwold Prof. Eric Jauniaux, Mr. Raj Dave

Producer & Director: Marissa Lestrade

Special thanks: Gordon Brothers Europe Kirsten and Michael Lathauwer Portland Hospital, London Lisa White, Jessica Phillips

Medical Aid Films – The training films charity

Video Details

Duration: 12 minutes and 30 seconds
Country: United Kingdom
Language: English
Producer: Medical Aid Films
Views: 5,385
Posted by: nand on Mar 29, 2012

To be used when training midwives and clinical officers in basic obstetric ultrasound.

MAF tested this film while training clinical officers and nurses in Mozambique.

Very few people living in low resource areas of the world have any access to obstetric ultrasound. However, on-going studies show that at risk pregnancies can be highlighted and appropriate and timely referral of women can have an impact on the morbidity and mortality rate of women in these countries.

Learning the orientation of the probe is considered to be the most challenging part of learning to scan. This animation is used in conjunction with other formal training to improve the proficiency, uptake and understanding of scanning.

© Medical Aid Films - 2011

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