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USG Basics, Part 5: Ultrasound Modes: A Guide to the Different Types and Applications

 Unlocking the mysteries of ultrasound modes! Discover the different types and applications dr debjyoti dutta

In this article - Unlocking the mysteries of ultrasound modes! Discover the different types and applications in our comprehensive guide. Read more now.

Introduction -

Ultrasound machines can operate in different modes to capture various types of images. Depending on the purpose of the examination, some modes may be more suitable than others. Here are the main modes used in ultrasound and their applications:

B-mode or Brightness Mode produces grayscale images that show the anatomy of the scanned area. It works by displaying the echoes of the sound waves as dots of different brightness on the screen. The images are updated quickly and look like videos.

M-mode or Motion Mode shows the movement of structures over time. It works by displaying a single line of dots that represent the position of the scanned structures along the vertical axis, and the time along the horizontal axis. This mode is useful for studying the motion of the heart valves and other dynamic organs.

Doppler Mode measures the change in frequency of the sound waves caused by the movement of a source, usually blood flow. It works by displaying the frequency shift as a colour or a sound. There are different types of Doppler ultrasound, such as colour Doppler, power Doppler, and spectral Doppler. This mode is useful for assessing the blood flow and detecting any abnormalities.

Doppler Mede ultrasound

Doppler ultrasound is a technique that uses the Doppler effect to measure the speed and direction of moving objects, such as blood cells. The Doppler effect is the change in the frequency of a sound wave when it is emitted or reflected by a moving source. For example, when a train passes by, its whistle sounds higher as it approaches and lower as it moves away. This is because the sound waves are compressed or stretched by the motion of the train.

To perform Doppler ultrasound, the ultrasound probe sends and receives sound waves at an angle to the blood flow. This angle is called the Doppler angle or the angle of insonation. The optimal Doppler angle is between zero and 20 degrees because it minimizes the error in the velocity measurement. If the angle is too large, the error increases. If the angle is 90 degrees, the Doppler effect is zero and no flow is detected.

There are four main modes of Doppler ultrasound that are used for different purposes:

  1. Continuous Wave Doppler (CWD): In CWD, the ultrasound transducer continuously emits and receives ultrasound waves. This allows for the measurement of blood flow velocities at a specific location along the ultrasound beam. CWD is particularly useful for assessing high-velocity blood flow, such as in the evaluation of stenosis in blood vessels.

  2. Pulsed Wave Doppler (PWD): PWD, unlike CWD, emits short pulses of ultrasound waves and then listens for the returning echoes. This enables the measurement of blood flow at a specific depth and location within the body. PWD is commonly used to assess blood flow velocities in smaller vessels and to obtain detailed information about the timing and characteristics of blood flow.

  3. Color Doppler Imaging (CDI): CDI combines standard B-mode (brightness) ultrasound imaging with color-coded representations of blood flow velocities. It provides a real-time, visual depiction of blood flow within a specific area, with different colors representing the direction and speed of blood flow. CDI is valuable for quickly identifying the presence and patterns of blood flow, making it widely used in cardiology, obstetrics, and other medical fields.

  4. Power Doppler Imaging (PDI): PDI, also known as energy Doppler or amplitude Doppler, focuses on detecting the power or amplitude of Doppler signals rather than their frequency shift. It is particularly sensitive to slow-flowing blood and is often used in situations where color Doppler may be less sensitive. PDI is useful for assessing blood flow in small vessels and in areas with weak blood flow signals like when examining structures that are close to the skin, such as the thyroid gland, the testicles, the kidney transplants and the skin lesions. It can also be used to detect blood vessels in tumours, to evaluate low-flow blood in tiny vessels, or to identify areas with poor blood supply.

Colour Doppler Basics: How to Set and Read the Colour Map for Blood Flow Direction and Speed

Colour Doppler is a mode of Doppler ultrasound that uses colour to show the speed and direction of blood flow in a region of interest. It works by measuring the average velocity of the blood cells in each pixel of the image and assigning a colour to it. The colours are updated constantly and create a dynamic display of blood flow. The colour map is a scale that shows the meaning of each colour. The most common colour map is BART, which stands for “Blue Away, Red Toward”. The meaning of “Blue Away, Red Toward” in ultrasound is a way of describing the direction and speed of blood flow in vessels using colour Doppler. Colour Doppler is a mode of ultrasound that uses sound waves to measure the movement of blood cells and display it as different colours on the screen. The colour map is a scale that shows what each colour means. The most common colour map is BART, which stands for “Blue Away, Red Toward”. This means that blue pixels indicate blood flow away from the probe, and red pixels indicate blood flow toward the probe. The darker the shade, the slower the flow. The lighter the shade, the faster the flow. Yellow and green colours indicate turbulent or chaotic flow.

Doppler Components

What is a Colour Box?

Colour Doppler is a mode of ultrasound that uses colour to show the speed and direction of blood flow in a region of interest. The region of interest is also called the colour box because it is a rectangular area on the image where the colour flow is displayed. You can adjust the size, position and angle of the colour box to focus on the area of interest. However, you should not make the colour box too large, because it will reduce the frame rate and slow down the image processing.

What is colour pulse repetition frequency (PRF)?

The colour scale is a setting that controls how fast the blood flow is detected by colour. It is also known as the colour pulse repetition frequency (PRF), because it determines how often the sound pulses are sent and received. You can change the colour scale by using a knob on the machine. The colour scale is shown as a colour bar on the side of the image, with the unit of centimetres per second (cm/s). If you increase the colour scale, you can see higher velocity flows, such as those in the arteries. If you decrease the colour scale, you can see lower velocity flows, such as those in the veins.

What is Aliasing?

Aliasing is a problem that occurs when the colour scale is too low for the blood flow velocity. It makes the blood flow appear to be in the opposite direction of the actual flow. For example, if the blood flow is away from the probe, it may show up as red instead of blue. You can avoid aliasing by increasing the colour scale or PRF. You should also adjust the colour gain, which is the brightness of the colour flow. The colour gain should be high enough to show the blood flow clearly, but not too high to cause colour noise or spillage.

About the Author -

Dr Debjyoti Dutta is a renowned pain specialist and author affiliated with Samobathi Pain Clinic and Fortis Hospital in Kolkata. He currently serves as a registrar at the Indian Academy of Pain Medicine, specializing in musculoskeletal ultrasound and interventional pain management. Globally acknowledged for his expertise, Dr. Dutta has authored significant publications, such as "Musculoskeletal Ultrasound in Pain Medicine" and "Clinical Methods in Pain Medicine," providing profound insights into the field of pain management. Additionally, he is a faculty member of the Asian Pain Academy Courses, contributing to the delivery of top-notch pain management fellowship training in Kolkata, India.

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