Chapter 5. Ultrasound Machines and Components

Women’s Point of Care Ultrasound

Essential Concepts Made Clear

This chapter reviews different types of ultrasound machines and compares them by size, function, and uses for different types of scanning. All machines are meant to essentially do the same thing – image the body in a way that creates an image to be used to help examine body structures. With these images we can learn that a pregnancy is progressing normally, or we can detect possible complications.

By the completion of this Section the participant will:

Understand the interaction of the various main components of the ultrasound machine in how it produces an image
Compare function and complexity of ultrasound machine types, from console to handheld
Begin to navigate basic functions for point of care ultrasound on a handheld
Select appropriate transducer based on structure to be imaged

Machine Essentials^1,2

Simply put, the ultrasound machine is a specialized computer that links a device (transducer) that sends sound into the body, interprets the returning echo, and provides an image that represents the structure of the body it encounters. These images are then interpreted by the person doing the scan, either in real time, or in review of still images. Image recognition enables users to discern normalcy versus pathology.

Sidebar 1. Ultrasound machine diversity analogous to motor vehicles

An analogy sometimes used with ultrasound machines is comparing them to motor vehicles. They all operate in similar ways. They have engines that cause them to move, they have wheels, steering wheels, and they perform the function of transporting people and things to where they want to go.

Sidebar 2. Analogy to dashboard and control differences.

However, there are differences in how some are driven. For example, on the dashboard of a car you can have either a very simple or very complex set of controls. Some cars have steering wheels on the left, and some on the right, depending on how they are driven in different countries.

This analogy can be extrapolated to ultrasound machines. All ultrasound machines have the same essential functions: of sending sound waves into the body and translating the returning echoes into meaningful signals. But they come in various sizes and complexity based on their specific uses. And the controls or consoles help to “drive” them. Although this course will instruct on the basics of ultrasound, it is up to the learner to master the machine that will be used in practice.

Figure 1. Ultrasound machines

Note: It is not the intent of this program to promote or recommend a specific manufacturer of ultrasound machines or supplies. The photos and illustrations represent a variety of machines available at the time this course was developed to use as examples.

Figure 2. Ultrasound machine process.

Here is how the ultrasound machine works: (Figure 2)

1. Master synchronizer – controls most of the functions – tells the pulse transmitter how to shape the beam to adjust the beam width and focus. Part of this synchronizer includes a timer that communicates to the pulse transmitter how much time to pulse and how much time to rest. It also assists with timing in how the image is created – adjusting return time of the signals

2. Pulse transmitter – Generates the electrical pulses sent to the transducer

3. Transducer – transfers the electric charges to the crystals, which vibrate based on the voltage that was applied to them. In between pulses sent into the body, the transducer receives echoes by listening and amplifying the tiny sound waves that return as echoes. Those sound waves are then sent to the receiver as electrical signals.

4. Receiver – accepts voltage from the transducer and prepares signal for display. amplifies the returning signal many times and sends it to the image processor. It compresses the signal to minimize signal noise, compensates for deficiencies (applies gain to increase or decrease signal strength)

5. Image Processor – The processor digitalizes the images by generating pixels based on an 8-bit system of processing, allowing for 256 shades of grey per pixel. This is more detail than what the human eye can distinguis, since the human eye can only process about 100 shades of grey.

Display – Signals coming from the image processor create the display from the pixels created by the image processor, creating both still and video images

Figure 3. Full console machine.

Figure 3 is a photo of what is termed a “full console” machine. It has many capabilities for enhancing and storing images, with features that are used primarily for more sophisticated diagnostic uses like those provided in radiology clinics and hospital radiology units. Some of them even have 3D/4D imaging capability, which will not be discussed in this course since most machines used for point of care ultrasound do not have this feature. Console machines have the ability to connect more than one probe so that the sonographer can switch between probes simply by using a button or switch on the console. Since they are quite large, they are most often parked in a room and are not as likely to be moved from room to room. They usually have the capability of utilizing a system of sending images securely by way of DICOM (Digital Imaging and Communications in Medicine) format so that the images can be interpreted remotely by a radiologist or other provider.

A smaller version is the portable laptop machine (Figure 4). This unit has the same basic features as the full console, but in a smaller, more portable machine. Some laptops have only one port for probes, so any time a probe is changed, it must be done manually. Screen size differs based on the size of the laptop, just as with laptop computers in general.

Figure 4. Portable laptop ultrasound machine.

Another portable unit is the touchscreen or tablet-sized machine (Figure 5). These can be used on a tabletop or connected to a special stand as shown in this picture. It usually has only one port for a single probe at a time, like the laptop. Some of these machines can accommodate other types of probes, but they must be connected one at a time. The primary difference with this machine is that most of the controls are on the screen and activated by touch, rather than using knobs or a manual keyboard.

Figure 5. Touchscreen ultrasound machine.

The smallest, most portable machine is known as a handheld unit. Figure 6 shows examples of a few models. These have become very popular and very affordable for use in emergency rooms, remote areas, and even in obstetrics. They are simple to use and have most of the basic functions needed for point of care ultrasound. Each type of handheld has advantages and disadvantages, and these will be reviewed in this chapter.

Figure 6. Handheld ultrasound machine.

All ultrasound machines have the following basic parts and capabilities:²

transducer (probe) - probe that sends and receives the sound waves

central processing unit (CPU) - computes the calculations and contains the electrical power supplies for itself and the transducer (probe)

transducer pulse controls - changes the amplitude, frequency and duration of the pulses emitted from the transducer probe

display - displays the image from the ultrasound data processed by the CPU

keyboard/cursor - inputs data and takes measurements from the display

disk storage device (hard drive, CD) - stores the acquired images

printer - prints the image from the displayed data

Figure 7. shows the usual locations for the basic machine components on a full-console machine: the screen, computer, keyboard, transducer, and the control buttons or knobs used to adjust and improve an image.

Figure 7. Console components.

Figure 8 shows a closer view of the console, showing the trackball that is used to steer the cursor on the screen. It is used to either place measuring calipers for measurements, or to type text annotations on the images. This also shows two different types of probes connected to the machine. We will be reviewing specific functions of all the buttons and knobs in another Section.

Figure 8. Knobs and adjustments

Figure 9 shows the back of the machine where the transducers are connected. This larger machine has ports for several transducers to be connected at the same time.

Figure 9. Transducer ports on console machine.

Figure 10 is a closeup of a typical keyboard. It has many of the same keys as a regular keyboard but with special function keys for specific ultrasound functions.

Figure 10. Console keyboard.

Figure 11 shows a CD recorder and thermal printer attached to the machine. Some older machines use these to store and archive images. Thermal printers print on thermal paper. The purpose for thermal printing is that it is less expensive to print white on black images on this rather than use a huge amount of black ink on plain printer paper to create a mostly black image with a small amount of white on it.

Thermal paper is relatively expensive and is used where paper copies are the only way to store an image. The important thing to keep in mind with thermal print paper is that it is heat sensitive. Over time, and with exposure to increased temperatures, the printed white or grey image will fade or eventually turn totally black. Most newer machines, however, do not have physical printers or even CD writers; instead, they utilize USB ports to download images that are not stored in the machine hard drive, or transferred to an archiving system via DICOM (Digital Imaging & Communication in Medicine)

More recently, most machines (especially portable ones) have USB ports to allow for downloading of images to an external source rather than storing them in the device.

Figure 11. CD recorder and thermal printer.

It is important to protect the machine and its parts, since these machines are very costly. They are built to be sturdy under normal conditions, but some parts are easily damaged and not easily repaired or replaced. It is important for EACH person to take extra care in maintaining the machine. Some machines have gel cradles to hold bottles of gel to keep them from dropping or spilling. Some have transducer cradles, where the transducers are placed when not being used. The transducers are the most fragile and most expensive parts to replace, so it is critical that they are protected (Figure 12) Laying them on a bed or table is not recommended since it is too easy for them to fall off. When a transducer is dropped the delicate crystals in the head can be broken, making the transducer non-functional. For portable machines, you can devise a band of some sort as shown above to hold the transducer. Other important features are wheel locks to prevent the machine from moving while it is being used. And it is also very important for the transducer cords and the power cord to be kept OFF THE FLOOR. This is to prevent them from being accidentally rolled over by the heavy machine, causing damage.

Figure 12. Machine component protection.

The next section shows images of typical touchscreen screens, where the controls are located. These units are simpler to carry around and use, and there are fewer functions on these units, making them ideal for POCUS.

Figure 13. Touchscreens.

Figure 14. is an example of a handheld unit being used on a patient and the image created on the screen. As you can see, there are lines at the bottom of the screen that are used to control some of the features that enhance an image. Some of these machines even allow you to transmit both image and view of how you are scanning to a remote supervising physician or sonographer. This is done with a special platform allowing for real-time supervision and collaboration while scanning. Teleradiology is useful for more remote settings, where images can be sent electronically for review. It is also useful for after-hours units to be able to access a radiologist at all hours of the day or night, when an in-house radiologist may not be available. Sometimes hospitals will use radiologists in other countries across the globe due to time differences in working hours.

Figure 14. Handheld attached to tablet.

Image Storing and Archiving

Most newer ultrasound machines have the capability for at least one of these methods of archiving images outside of the computer’s own hard drive

--DICOM (Digital Imaging & Communication in Medicine): used primarily in hospital or large inter-hospital groups to send images to a central office for review by radiologists or technicians. The ultrasound machine must have proprietary DICOM software or licensing to be able to send images this way.

--PACS (Picture Archiving & Communication Systems) more widely accessible within a given hospital setting.

Sidebar 3. Digital storing.

SUMMARY ON MACHINE BASICS

Ultrasound units are sophisticated machines that translate reflected ultrasound beams to create images.

Machines vary in terms of size, portability, and extra functions.

All ultrasound machines have basic functions in common:

-Computer

-Pulse generator

-Transducer

-Receiver

-Amplifier

-Image processor

-Storage or image transfer capability

HAND-HELD ULTRASOUND MACHINES

Many providers performing POCUS will be using hand-held units. The following section will demonstrate what the screen could look like, and how to navigate the basic functions.

Not all handhelds have the exact same display, but all will have similar functions on how to enter information prior to a scan.

On this machine a dial is turned to the type of ultrasound to be performed. When doing ob ultrasound, touch is used to select the desired function on that dial (ob, abdomen, lung, etc). The body system icon illuminates when selected.

Figure 15. Handheld screen example: opening page

Touching another part of the dial brings up the “create a patient’ page where demographics and image description can be entered (Figure 16). Some units have other ways to create a patient, or to pull up a previous scan on the same patient.

Figure 16. Handheld screen example: creating a patient.

Patient data is important to enter, since some machines will not archive images if this information is missing. Some machines will assign the patient an arbitrary patient ID, but then it becomes difficult to retrieve or send these images later. Completing patient information uses the keyboard at the bottom of the screen (Figure 17).

It is important to include birthdate since you may have patients with similar names, and some facilities require a patient medical record number to be entered.

For tracking purposes, you also need to include the name of the person who performed the scan, who referred the patient to you (if this is the case), the indication of the exam, and any other pertinent information.

Most machines will date and time-stamp the images so there is no need to enter those.

Figure 17. Handheld screen example: patient data.

After completing patient data, find the “START EXAM” text on the display. Pressing it will bring you to your scan starting view

When starting the exam, be certain that the patient ID is shown at the top of the screen on the display. If it is not there, it may mean that the machine did not register that patient and your images may not save or archive.

Depth on handheld

Depth is sometimes important to be able to focus in or out on an image to see it better.

The depth scroll is indicated at the bottom left of the screen in this view, and it is activated by “rolling” it with a finger.

The image on the right of Figure 18 demonstrates how the depth has changed to make the image larger by decreasing the depth. This also widens the footprint of the image on the screen (white arrows).

Figure 18. Adjustments: Depth.

Gain is a function that brightens or darkens the image.Changing gain (or brightness) is done by rolling the gain scroll at the bottom of the screen (indicated by the green arrow).

Figure 19. Adjustments: Gain.

Greater detail of the use of gain is presented in Chapter 7. Knobs and Adjustments.

Functions

Each machine manufacturer typically supplies in person demonstration and instructional videos about navigating the features. This section gives examples of a screen view from handheld machines.

MODE selection

A menu allows selection of the “Mode” you want to use. The machine will always default to the 2D or basic ultrasound mode to begin. The machine will automatically display 2D mode as a default setting.

Other modes commonly used in POCUS are M-Mode and Color flow (sometimes called Color Doppler) mode. M-mode captures the heart rate (mostly used for fetal heart rate in women’s pocus). Greatere detail on this function is included in Chapter 7.

Figure 20 . Mode: M-mode

If color flow is required, press the color flow icon. This machine allows for selecting either fast or slow flow. For POCUS purposes, slow flow is best. When pressing that icon, it will pull up the screen allowing the user to make a color flow image. Whatever is located within the white outline will have color flow applied.

Figure 21. Color flow mode.

Freeze Function

Figure 22 shows the freeze button. On many hand-held machines it is designated with a snowflake symbol. On this machine, when it is blue, you are scanning live. When the desired image is seen, pushing the freeze button will halt the scan and freeze that image. The snowflake icon will change color when the image is frozen.

Once the image is frozen as a still image, the active transmission of sound from the transducer is stopped (no energy is sent to the patient). From the freeze frame, other functions can be accessed, such as measurements and annotations, further described in Chapter 7.

Figure 22. Freezing.

Measurements

When the measure icon is selected, it will pull up a menu to allow selection of how you want to measure your object of interest. You can select either a line, an ellipse, or a “trace” line, as shown in Figure 23 Figure 24 demonstrates the types of fetal measurement options that can be selected.

Figure 23. Measuring.

Figure 24. Fetal measuements.

ULTRASOUND TRANSDUCERS^2-5

By the completion of this Section the participant will be able to:

1. Describe the piezoelectric effect and the basic function of an ultrasound transducer

2. Differentiate the three primary types of transducers that can be used on OB/GYN scanning

3. Decide which transducer is most appropriate for the desired type of image

4. Learn how to change transducers on machines with interchangeable transducer ports

Sidebar 3. Transducers.

An ultrasound transducer (sometimes called probe) is the hand-held part of the machine. It converts electrical energy into mechanical (sound) energy and vice versa, based on the principle of piezoelectric effect. The transducer both transmits and receives or detects the return ultrasound waves. It is often referred to as a “probe”, so these two words are used interchangeably.

In review, the time that it takes for a sound to return to the transducer (after being reflected by a tissue) is what the machine uses to determine the depth and texture of the tissue.

Figure 25. How transducers work.

Piezoelectric effect refers to the application of a tiny electrical charge to a crystal, which causing the crystal to “realign its molecules” and vibrate. This vibration converts electrical energy into kinetic or mechanical energy, causing a mechanical wave of sound. A transducer may have as many as 250 crystals, each connected to a single electrical element.

The reverse of the piezoelectric effect happens when a returning echo is detected by the crystal and causes it to mechanically vibrate. This is then converted into electrical pulses that are sent back to the computer processor. These electrical bits of information are translated in real time to a processor that creates a pixel for every bit, creating an image matrix made up of thousands of pixels. The pixels are created to represent varying shades of white, black and grey, creating a grey-scale image

There is much more detail about how ultrasound images are formed, but the information in this course is all that is necessary to know when performing a POCUS exam. Diagnostic ultrasound courses dive into complex mathematical formulas required for in-depth learning of machine processing. But basic understanding of concepts covered in these chapters enable the learner to have enough understanding to use the machine to its fullest potential for a POCUS exam.

TO REVIEW:

When a transducer is placed on the patient, a pulse of sound energy is transmitted

The energy sent into the patient is mechanical – in other words it sends an energy wave that moves molecules in its path.

Internal structures encountered in the path of this wave either reflect, refract, scatter, or absorb the pulse’s energy.

Returning echoes stimulate the transducer, but the echoes are very faint. The machine has to greatly amplify these signals to make them detectable by the computer. Most transducers send pulsed signals – the transducer sends a pulse, listens for a pulse, and then sends another. This was discussed in an earlier chapter. This entire cycle is called the pulse-echo process (Figure 26).

Figure 26. Pulse echo process.

Previously, sound coming from a transducer was described as a single waveform or beam. In reality, the transducer fires a number of lines or beams of sound in sequence, and each line is translated into an image of light and dark spots to translate the depth, outline, and characteristics of the structures being scanned (Figure 27). Each red line in this illustration represents a single sound beam. From the transducer, multiple beams are fired rapidly in sequence, and the computer generates the image, line by line. There are 120 to 200 vertical scan lines per image. This happens so rapidly that it is imperceptible to the viewer. All we see is the final image (without observable lines). There are more than a thousand lines of pixels generated for every ultrasound image.

It is the compression of all these lines into a single display that help us to “see” with sound.

Figure 27. Sound beam sequence.

The portion of the transducer that makes contact with the patient’s skin is known as the footprint, as shown in Figure 28. A larger footprint displays more information close to the surface than a smaller footprint. The shape of the image at the top of the screen tells us what type of transducer was used. You can usually tell by looking at an ultrasound image whether it was created by a curvilinear or a transvaginal probe because the footprint at the top is much smaller in the transvaginal image.

Figure 28. Transducer footprint.

Transducer types

Figure 29. Transducer types.

Transducers used for POCUS can produce an ultrasound beam in 3 configurations:

Linear array (rectangular image)

Curvilinear (most commonly used for abdomen and ob/gyn)

Phased array (most commonly used for cardiac or thoracic)

The following describes each transducer and assists with understanding of how to select the correct transducer for the intent of the exam.

A linear transducer has a “straight down” beam, creating a rectangular or square window on the screen (Figure 30). Its frequency is around 7.5 mHz, which means that it is on the higher end. It is useful for more medium to shallow applications instead of looking deeper into the body.

Figure 30. Linear transducer.

A curvilinear creates a trapezoid-shaped window and has a rounded footprint (Figure 31). The beam widens or diverges as it penetrates deeper into the body. It has a relatively low frequency range (from 2 to 5 mHz) and so it is useful for ob and for looking deeper into the abdomen and pelvis

Figure 31. Curviinear transducer.

A phased array is triangular, with a narrow footprint (Figure 32). Because it is an “array”, the beams widen as they go deeper, allowing for a wider field of view. This allows it to be useful in going between ribs in the near view (avoiding their shadowing) to look at the heart and other thoracic structures. Like the curvilinear, it has low frequency, which allows for deeper penetration. It can be used for obstetrics if this is the only probe available. However, it creates a very narrow view of structures close to the body’s surface. This limits visualization of superficial structures due to the constricted angle at the upper part of the screen.

Figure 32. Phased array transducer.

Another probe that is used in ob and gyn is the transvaginal probe. It has a trapezoid-shaped window, much like a small curvilinear probe. However, it uses a much higher frequency (5-7.5 mHz). It is used for endocavitary scanning (pelvic and ob). It is designed to get closer in proximity to the internal structures to capture more detail using a higher frequency.

Currently, hand-held ultrasound units do not accommodate transvaginal probes. Some providers may be trained to use transvaginal ultrasound, and some may not be allowed to use this method, depending on the local scope of practice definitions. Transvaginal ultrasound, however, is considered to be within the OB/GYN POCUS domain.

Figure 33. Transvaginal transducer.

Figure 34. Probe (transducer) orientation: Curvilinear

A curvilinear abdominal transducer is an arced probe. Each probe has a notch or marker on one side to designate that this is the side you should be pointing either to the woman’s head or toward her right side.

The area toward the notch is called the toe, and the opposite end is called the heel.

Orientation to the Body.

This section provides an overview of general orientation to the body using transducers, but Chapter 6 provides greater detail.

Figure 35. Orientation: sagittal.

In a sagittal plane, the notch on the transducer should be directed toward the woman’s head. (cranial or cephalad)

When the transducer is held transverse to the body (or the structure), the notch should always be directed to the patient’s right.

This gives consistency to all sonograms being performed.

Figure 36. Orientation: Transverse.

Figure 37. Orientation: transverse view showing position indicator (notch).

Figure 38. Transvaginal transducer notch orientation.

This diagram shows that transducer is rotated into a transverse view from the sagittal plane where the notch should be directed toward to the maternal right. The image seen on the screen will be a transverse view of the pelvis.

When scanning, the dot (or marker) in the top left side of the screen always designates which way the probe notch is pointing. It should be oriented either toward the woman’s head, or to the right side of her body.

Note that some machines use a symbol or colored letter (trademark) on the screen in place of a green or blue dot.

The transvaginal transducer/probe also has a designated orientation, or correct positioning, for consistency. If it is held like a gun, then your thumb should be pointing upward, with the toe of the probe angled toward the woman’s front or anterior. If it is rotated, it should be rotated toward the woman’s right, so your thumb is turned toward her right (your left).

When using a transvaginal probe, the “notch” is at the top of the probe when held correctly. It should be pointing toward the anterior surface of the woman, or to the right side of her pelvis in order to keep orientation correct. This means that the dot on the screen indicates that the probe is either angling upward (toward the woman’s abdominal surface) or toward her right pelvis. This will be reviewed again in the next section discussing image capture and orientation.

Selecting the appropriate transducer

The two most used probes in obstetric or gyn scanning are: the curvilinear and the transvaginal.

Review of Tranducers

Curvilinear

Lower frequency
Penetrates deeper into the body
Less resolution

(The phased array can also be used in OB/GYN scanning, but it has disadvantages in that the near field is not seen well)

Transvaginal

Higher frequency
Penetrates more shallowly – limited depth or field of view
Intracavitary so it is physically closer to the object of interest (uterus and ovaries)
Higher resolution (better image)

Knowing these principles, we know to select a curvilinear when you are viewing:

Deeper structures
Posterior placentas
Advanced pregnancy
Large uterine fibroids

We also know that to visualize structures that are either superficial to the body, or closer to the end of the probe, we would select a transvaginal or endocavitary probe. You would select this when you are viewing pelvic structures for gyn, early pregnancy, or searching for an ectopic or abnormal pelvic mass.

Transducer to machine connections

Transducers must be appropriately connected to a machine for them to be used. As described earlier, some machines have a single port for one transducer at a time. Larger machines have multiple ports allowing for 2 or more transducers to remain attached. When selecting a different probe in this case, there is a toggle on the machine console that allows for the switching of transducers (say, from transabdominal to transvaginal) without having to manually change the transducer.

Figure 39. Transducer machine ports.

On some machines, there is a button to push that will allow change of probe from the console. These machines usually have 2 or more ports that other transducers may be attached at one time. The button allows changing the probe without having to manually switch out probes

Figure 40. Probe selection button on console.

Figure 41. Handheld machine probes.

Handheld ultrasound machines have different configurations of probes. With most of them, the probe has the ultrasound “machine” or processor within it. However, all of them must be connected to some sort of display device, such as a cell phone or tablet in order to display the images. The adjustment knobs for these devices are controlled onscreen from the display in the phone or tablet. We will look more closely at these in the next Section.

3D and 4D Transducers

Some machines will have an optional function of performing 3D/4D imaging. This type of scanning requires special probes with that capability. Most 3D probes will also do 2D scanning as well. These probes will automatically scan in 2D or B-mode unless designated on the console to change to the 3D or 4D modes. Because these probes must capture a wider scope of information, they are a bit larger and heavier.

3D is very useful for both obstetric and gyn imaging, but it requires some additional training on how to capture and process images. Although 3D is most widely known for keepsake or entertainment fetal images, it is also useful for GYN diagnosis and for views of certain fetal abnormalities that provide superior views to 2D images

Although 3D ultrasound is not part of this instruction, a basic explanation is here to provide a brief introduction of its functions. Some may have access to these probes and functions, but remember that these probes can also be used for 2D scanning.

Figure 42. Transabdominal and transvaginal 3D probes.

The 3D transducer slices the body in a “box-shaped” manner rather than a tomographic slice as in Figure 43.

Figure 43. 3D and 4D imaging illustration.

SUMMARY – Transducers

-transducers are the parts of the ultrasound that make contact with the woman’s body.

-transducers vary in the frequencies they emit and their overall function

-The most common types of transducers used in OB/GYN ultrasound:

Linear

Curvilinear – most used for OB/GYN

Transvaginal – most used for GYN early OB, and cervical measurement

Phased array - used for cardiac and thoracic but can be used for OB/GYN

Foundations of Women's Point-of-Care Ultrasound

Chapter 5 Ultrasound Machine Basics