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USG Basics, Part 6: Ultrasound Machine Knobology, A Guide to Adjusting Settings

Updated: Nov 29, 2023

Ultrasound Machine Knobology: A Guide to Adjusting Settings and Improving Image Quality dr debjyoti dutta

In This Article - Unlock the secrets of ultrasound machine knobology settings with our comprehensive guide. Learn how to adjust settings for crystal-clear images.

Introduction - Welcome to the intricate world of ultrasound machine knobology, where adjusting settings transforms echoes into crystal-clear images. This guide is your roadmap to navigating the different knobs, dials, and buttons that define ultrasound settings.

Adjusting Gain settings in B Mode

Gain settings in B-mode amplify received sound signals uniformly across the entire image. This adjustment allows for control over the overall brightness of the ultrasound image. Increasing gain enhances brightness while decreasing it results in a darker image. It's crucial to note that manipulating overall gain doesn't impact the rate of ultrasound energy delivered to the patient.

Ultrasound Depth Settings -

Ultrasound depth settings govern the penetration of sound waves into the body, offering operators the ability to enhance visualization of specific areas. Within this setting, two key terms—Near Field and Far Field—describe how close or distant the area of interest is to the transducer's surface. The Near Field signifies proximity, while the Far Field indicates greater depth. During scanning, it's crucial to set the depth at least 1 centimetre beyond the deepest point of interest. For optimal imaging, if exploring a region 4 centimetres deep, set the depth to at least 5 centimetres. Adjustments allow for broader views before zooming in, but deeper depths may impact frame rate due to increased sound pulse travel time.

Time Gain Compensation Knob in Ultrasound with Samobathi Logo
Time Gain Compensation Knob

Time Gain Compensation in Ultrasound

Time Gain Compensation in ultrasound allows operators to adjust the gain settings at different depths to compensate for signal attenuation, resulting in consistent image brightness and improved diagnostic quality across various tissue depths. Time Gain Compensation (TGC) is a crucial feature in ultrasound imaging that allows for the adjustment of signal amplitudes at different depths within the tissue. The purpose of TGC is to compensate for the attenuation of the ultrasound signal as it travels through various tissue depths, ensuring consistent image brightness and quality.

Here's how Time Gain Compensation works:

  1. Signal Attenuation: As ultrasound waves travel through the body, they encounter different tissues with varying acoustic properties. These properties cause the ultrasound signal to weaken or attenuate, leading to a reduction in signal amplitude.

  2. Compensation: TGC compensates for signal attenuation by allowing the operator to manually or automatically adjust the gain settings at different depths. Typically, TGC is represented graphically on the ultrasound system as a set of sliders or controls corresponding to specific depth ranges.

  3. Adjustment of Gain: By manipulating the TGC controls, the operator can increase or decrease the gain (amplification) of the ultrasound signal at specific depths. Increasing gain compensates for signal loss in deeper tissues, ensuring that echoes from deeper structures are appropriately amplified to maintain image brightness.

  4. Improving Image Quality: Properly adjusting TGC helps achieve uniform image brightness throughout the depth of the tissue being imaged. This is crucial for obtaining diagnostically relevant images, as it ensures that structures at varying depths are displayed with adequate contrast and clarity.

Beam spread and beam divergence in ultrasound

Beam spread and beam divergence are concepts related to the behaviour of ultrasound beams as they travel through tissues.

  1. Beam Spread:

  • Definition: Beam spread refers to the widening of the ultrasound beam as it penetrates deeper into tissues.

  • Explanation: In ultrasound imaging, the ultrasound beam originates from the transducer and travels into the body. As it travels deeper, the beam tends to spread out, leading to a larger area of coverage. This phenomenon is influenced by the frequency of the ultrasound waves and the characteristics of the transducer. Higher-frequency waves generally have a narrower beam spread compared to lower-frequency waves.

  1. Beam Divergence:

  • Definition: Beam divergence is the increase in the diameter of the ultrasound beam as it travels away from the transducer.

  • Explanation: As the ultrasound beam propagates through tissues, it naturally diverges or widens. This divergence is a result of the spreading of the wavefront. The rate of divergence can be influenced by factors such as the wavelength of the ultrasound waves and the type of transducer used. Understanding beam divergence is crucial for the accurate interpretation of ultrasound images, especially when considering the resolution and focus at different depths within the body.

Adjusting the focal zone

The focal zone, crucial in ultrasound imaging, is ideally positioned at or slightly below the area of interest to optimize lateral resolution. Visualize the focal zone as the primary focus area of the ultrasound beam. Misplacing the focal zone may lead to blurring in the far field. To enhance resolution at various points within the sound beam, multiple focal zones can be employed. However, this strategy comes at the cost of a reduced frame rate, causing the image to appear in slow motion. Each focal zone necessitates a separate ultrasound pulse for a single scan line, so employing, for instance, three focal zones extend the image construction time threefold.

Understanding Resolution in Ultrasound

Image quality in ultrasound is significantly impacted by resolution, which can be categorized into three types:

  1. Temporal Resolution: This involves visualizing moving objects, like blood, without blurring. Enhancing temporal resolution can be achieved by increasing the frame rate for real-time observation or adjusting factors such as depth, focal zones, persistence, or scan line density.

  2. Lateral Resolution: This type focuses on differentiating between two adjacent reflectors perpendicular to the ultrasound beam. Depth, beam frequency, focal zone placement, and beam width influence lateral resolution.

  3. Axial Resolution: Here, the goal is to distinguish between two reflectors in the direction parallel to the ultrasound beam. Ultrasound frequency and pulse length play pivotal roles; higher frequency waves with shorter pulse lengths yield superior axial resolution compared to lower frequency waves.

Axial and lateral resolution in ultrasound are influenced by various factors that impact the ability to distinguish structures along the length and width of the ultrasound beam, respectively.

Factors Affecting Axial Resolution:

  1. Ultrasound Frequency: Higher-frequency waves provide better axial resolution. Shorter wavelengths associated with higher frequencies allow for the differentiation of structures positioned closely along the axis of the ultrasound beam.

  2. Pulse Length: Shorter pulses contribute to improved axial resolution. As the pulse length decreases, the ability to differentiate between two reflectors positioned one behind the other in the direction of the ultrasound beam is enhanced.

Factors Affecting Lateral Resolution:

  1. Beam Width: A narrower ultrasound beam width results in better lateral resolution. A focused, narrower beam allows for improved differentiation between two reflectors situated side by side in a direction perpendicular to the ultrasound beam.

  2. Ultrasound Frequency: Higher-frequency waves also impact lateral resolution positively. The ability to distinguish structures situated laterally improves with shorter wavelengths, characteristic of higher-frequency ultrasound.

  3. Focal Zone Placement: Proper placement of the focal zone is essential for optimizing lateral resolution. Placing the focal zone at or near the region of interest enhances the ability to differentiate structures in the lateral direction.

Frame Rate in Ultrasound

The Frame Rate, denoting the number of images captured by the ultrasound machine per second, is within the control of the operator through adjustments in ultrasound settings. As previously mentioned, altering the scan depth impacts the frame rate—greater depth results in a slower frame rate and vice versa. Additionally, the quantity of focal zones influences the frame rate; a higher number of focal zones leads to a slower frame rate. Notably, the frame rate itself plays a role in shaping the image characteristics, with a positive correlation existing between frame rate and temporal resolution, which is the ability to visualize moving objects without blurring.

Freeze Button of Ultrasound with Samobathi Logo
Freeze Button

Using Freeze Button

The freeze button on an ultrasound machine serves a crucial function in the imaging process. When the freeze button is activated, it essentially "freezes" the real-time ultrasound image that is continuously updated on the screen. This is important for several reasons: Image Capture, Analysis, Measurement and Documentation.

Adjusting Gain settings in Doppler Mode

In Spectral Doppler, adjusting gain can influence the appearance of the spectral window. Setting the gain too high may introduce noise while setting it too low can result in an absent image. In the case of Colour Doppler and Power Doppler, users also have the capability to fine-tune the gain setting for optimal imaging results.

Within Colour Doppler, the gain setting amplifies the colour signal, offering operators control over the intensity of the colour displayed. When the colour gain is excessively high, there's a risk of colour bleeding beyond vessel walls. To rectify this, reducing gain and simultaneously increasing the colour scale becomes necessary. Conversely, when utilizing Colour Doppler to identify slow or low flow, the approach shifts – raising colour gain and lowering the colour scale proves effective. It's evident that there exists an inverse relationship between colour scale and colour gain, a crucial insight for optimizing settings and achieving accurate Doppler imaging.

About the Author -

Dr. Debjyoti Dutta, a distinguished pain specialist and author, is associated with Samobathi Pain Clinic and Fortis Hospital in Kolkata. Serving as a registrar at the Indian Academy of Pain Medicine, he is an expert in musculoskeletal ultrasound and interventional pain management. Dr. Dutta, acknowledged on a global scale, has authored notable publications, including "Musculoskeletal Ultrasound in Pain Medicine" and "Clinical Methods in Pain Medicine," offering profound insights into the realm of pain management. Dr Debjyoti Dutta is one of the faculty of Asian Pain Academy Courses which provides the best pain management fellowship training in Kolkata, India.

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