Physic's - Transducers

The correct answer is "Near Zone." The Fresnel zone, also known as the near zone, is the region close to a transmitting antenna where the radio waves are not fully developed and can experience interference and diffraction. This zone is important for determining the quality of wireless communication signals and is crucial for proper antenna placement and alignment.

Lead Zirconate Titanate (PZT) is the most common piezoelectric material used in ultrasound imaging. PZT is preferred due to its high piezoelectric coefficient, which means it can efficiently convert electrical energy into mechanical vibrations and vice versa. This property allows PZT to generate ultrasound waves when an electrical signal is applied and also to produce electrical signals when it is subjected to ultrasound waves. Additionally, PZT has good mechanical properties, such as high stiffness and low acoustic impedance, making it suitable for ultrasound transducers.

Huygen's Principle explains away diffraction by stating:
Each point on the surface of the transducer is a separate & individual point of sound.
Sound wavelets inferface & overlap.
Overlapping & interference of wavelets cause the US beam to assume its typical hourglass shape

Destructive inferface is out of phase. Occurs when 2 waves are not in same place at same time. Result is negative (cancel each other out, intensity)

The focal point refers to the narrowest point of the beam diameter. This is the point where the beam of light converges or comes together to form a focused spot. It is the point where the intensity of the beam is highest and where the beam can be most effectively used for applications such as focusing, cutting, or heating.

Attached to back of Piezoelectric element. Limits the ringing of pulse. Muffles the sound wave so carries more frequency. Controles the # of cycles, makes pulse shorter or the length/duration of the pulse shorter. Limits the DP and makes DF shorter. Backing/damping controls the DF

Axial resolution refers to the ability of an imaging system to distinguish between two closely spaced objects along the direction of the ultrasound beam. It is determined by the spatial pulse length, which is the distance between two consecutive pulses emitted by the transducer. To calculate the axial resolution, the spatial pulse length needs to be divided by 2. This is because the axial resolution is half the spatial pulse length, indicating the minimum distance between two reflectors that can be resolved by the system. Therefore, the correct answer is "spatial pulse length divided by 2".

Azimuthal resolution refers to the ability of a system to distinguish between two closely spaced objects in the azimuthal direction, which is the horizontal plane or the plane of rotation. It is a measure of the system's ability to resolve details in the horizontal direction. Lateral resolution, on the other hand, refers to the ability of a system to distinguish between two closely spaced objects in the lateral or transverse direction. Since both terms describe the same concept, azimuthal resolution can be considered another name for lateral resolution.

The piezoelectric effect refers to the phenomenon where certain materials generate an electric voltage when subjected to mechanical deformation. This effect is widely utilized in various applications such as sensors, actuators, and transducers. It is not related to the curie point, photomagnetic effect, or bandwidth. Therefore, the correct answer is the piezoelectric effect.

Annular array are elements arranged in form of concentric rings. Image format is sector, sound beam is focused, steered mechanically and usually used for endo vag.

The correct answer is "Beam diameter." Lateral resolution refers to the ability of an imaging system to distinguish between two separate objects that are located side by side. In ultrasound imaging, it is determined by the width of the ultrasound beam. A smaller beam diameter results in better lateral resolution, as it allows for better differentiation between adjacent structures. Therefore, the beam diameter is directly related to the lateral resolution of the imaging system.

A phased array scanner consists of multiple active elements that can be fired simultaneously. This allows for faster scanning and data acquisition compared to traditional scanning methods where only one element is fired at a time. The simultaneous firing of multiple elements enables the scanner to cover a larger area in a shorter amount of time, making the statement true.

Spatial Resolution is Detail Resolution. Spatial resolution is the ability to distinquish structures clearly from a spatial perspective. The Higher the Frequency, the better the Image Quality.

The Quality Factor (Q) is a dimensionless parameter that describes the sharpness or selectivity of a resonant system. It can be calculated mathematically by dividing the resonant frequency of the system by its bandwidth. This ratio determines how much energy is stored in the system compared to how quickly it dissipates. A higher Q value indicates a more selective and efficient resonant system, while a lower Q value indicates a broader and less efficient system.

The best choice for the thickness of the matching layer(s) is one fourth the wavelength because it helps to minimize the acoustic impedance mismatch between the transducer and the medium being imaged. This impedance matching allows for efficient transmission of ultrasound waves and reduces the amount of energy that is reflected back to the transducer. Therefore, using a matching layer thickness of one fourth the wavelength optimizes the performance of the ultrasound system.

A higher frequency transducer will result in more absorption of ultrasound energy because higher frequency waves have shorter wavelengths and higher energy. This allows for better penetration and resolution in tissues, as well as increased absorption of energy by the target area.

The most acceptable choice for the matching layer will be 1,400,000 Rayls because it is closest to the impedance of the transducer's piezoelectric element (1,600,000 Rayls) and provides a better match compared to the other options. A matching layer is used to minimize the reflection of sound waves at the interface between the transducer and the skin, and a close match in impedance helps to optimize the transmission of sound waves into the body.

All annular must be mechanically steered

NLZ is affected by the transducer diameter and frequency

Subdicing refers to the process of dividing a larger ultrasound element into smaller elements and then wiring them back together. This technique allows for improved resolution and focusing capabilities in ultrasound imaging. It helps to reduce the effects of aliasing, which is the distortion or artifact that occurs when the frequency of the ultrasound waves exceeds the Nyquist limit. Dynamic focusing, on the other hand, refers to the ability to electronically focus the ultrasound beam at different depths. Channeling is not a term commonly used in the context of ultrasound imaging.

Arrays have grating lobes which are weaker beams of sound traveling into additional beams resulting from their muli-element structure

Sector scan

This type of external beam focusing uses an acoustic lens in front of the piezoelectric crystal. The acoustic lens helps to focus and direct the ultrasound waves produced by the piezoelectric element. Placing the lens in front of the crystal allows for better control and manipulation of the ultrasound beam, resulting in improved imaging and targeting capabilities.

Worse temporal resolution, makes machine slow down

The terms "depth," "longitudinal," and "radial" all relate to different aspects of axial resolution, which refers to the ability to distinguish between objects along the axis of imaging. However, "angular" does not relate to axial resolution. Angular resolution refers to the ability to distinguish between objects at different angles or orientations. Therefore, "angular" is the term that does not refer to axial resolution.

The given answer states that the thickness of the piezoelectric element in a 3.5 MHz transducer is thicker than that in a 7.5 MHz transducer. This implies that the lower frequency transducer requires a thicker piezoelectric element compared to the higher frequency transducer. This is because the thickness of the piezoelectric element is inversely proportional to the frequency of the transducer. Higher frequency transducers require thinner elements to produce the desired frequency, while lower frequency transducers require thicker elements.

An annular phased array must be steered mechanically. Focused is electronically

Intensity varies greatly in the near zone

A duplex scanner is the correct answer because it refers to an ultrasound unit that can display two-dimensional images and A mode simultaneously. This term is commonly used in medical imaging to describe a specific type of ultrasound machine that offers both modes of imaging at the same time. The other options, such as a compound scanner or C mode scanner, do not accurately describe this specific capability of displaying both two-dimensional images and A mode.

Lateral resolution refers to the ability of an imaging system to distinguish between two closely spaced objects in the horizontal direction. It is determined by factors such as frequency, focal depth, beam diameter, and damping. However, damping has the least influence on lateral resolution. Damping refers to the reduction of vibration or oscillation in the system, which primarily affects the image quality in terms of reducing noise and improving contrast. While damping is important for overall image quality, it has a minimal impact on lateral resolution compared to the other factors mentioned.

NZL is the length of space between the transducer's face & focus. 2 factors affect NZL, transducer diameter and frequency. NZL is equal to transducer diameter squared times frequency divided by 6. OR NZL is equal to diameter squared divided by 4 wavelength

Apodization is the correct answer because it refers to the process of varying the voltage to the transducer elements in order to form a real-time pulse. This technique is commonly used in ultrasound imaging to improve the resolution and focus of the image. By selectively changing the voltage applied to different transducer elements, the beam shape can be modified to reduce side lobes and improve the overall image quality. Apodization helps to optimize the ultrasound beam and enhance the accuracy of the imaging results.

A mechanical transducer has a focus that is preset at a fixed point. This means that the transducer is designed to emit and receive sound waves at a specific depth within the body. Unlike other types of transducers, such as phased array or annular array, which have the ability to change their focus point electronically, a mechanical transducer is fixed and cannot be adjusted. Therefore, it is the correct answer to the question.

Barium Titanate is not naturally piezoelectric. Piezoelectric materials generate an electric charge when subjected to mechanical stress, such as pressure or vibration. Tourmaline, Rochelle Salts, and Amber are all naturally occurring materials that exhibit piezoelectric properties. However, Barium Titanate is a synthetic material that can be made piezoelectric through a process called poling, where an electric field is applied to align the internal structure of the material. Therefore, Barium Titanate is the exception among the given options.

A convex, sequential array transducer will have a rocker top image format. This type of transducer is designed with a curved array of elements that transmit and receive ultrasound waves in a sequential manner. The rocker top image format refers to the shape of the ultrasound beam produced by this transducer, which is wider at the top and narrower at the bottom, resembling the shape of a rocking chair. This format allows for a wider field of view and better visualization of structures at different depths.

Damping material muffles the sound wave to carrier more freuqnecy. It limits the ringing of pulseand shortens pulse by lowering the # of cycles and PD.

Multiple focal zones are advisable in a thyroid ultrasound examination because the thyroid gland is small and has complex anatomy. By using multiple focal zones, the sonographer can capture detailed images of different areas of the thyroid gland, ensuring that no abnormalities or nodules are missed. This approach allows for a more comprehensive evaluation of the thyroid gland and increases the accuracy of the examination.

A pulse of ultrasound contains a range of frequencies because it is composed of multiple waves with different frequencies. This range of frequencies is known as the pulse's bandwidth. The transducer used to generate the ultrasound emits waves with a nominal frequency, but due to factors such as the medium through which the ultrasound travels, the pulse will consist of a range of frequencies. A shorter pulse will have a narrower bandwidth, meaning that the range of frequencies within the pulse will be smaller.

If one of the elements in a linear switched array transducer is damaged, it will result in an area of vertical dropout on the ultrasound image displayed. This means that there will be a portion of the image where the vertical details will not be visible, leading to a loss of information in that specific area. The rest of the image will still be visible, but the damaged element will cause a vertical dropout.

The near zone length is determined by the frequency of the transducer and the properties of the tissue being imaged. In this case, a 5 MHz transducer is being used to image soft tissue. The near zone length is typically calculated as 1.5 times the transducer diameter. Since the transducer diameter is 6 mm, the near zone length would be 1.5 times that, which equals 9 mm. However, the answer options provided do not include 9 mm. The closest option is 30 mm, which is not the exact calculation but may be the closest approximation given the options provided.

Damping material improvs axial resolution
Ax (mm) = SPL (mm) / 2
SPL = # of cycles x wavelength

Focusing the ultrasound beam will not reduce the beam diameter at all distances from the transducer face. When the ultrasound beam is focused, it narrows down at a specific depth or focal point, but beyond that point, the beam starts to diverge again. So, while focusing can reduce the beam diameter at the focal point, it will not reduce the beam diameter at all distances from the transducer face.

The coupling gel is used to eliminate reflection at the skin's surface due to air. When sound waves travel from the transducer into the body, they can encounter air at the skin's surface which causes reflection. This reflection can interfere with the accuracy of the ultrasound imaging. The coupling gel helps to eliminate this reflection by filling the space between the transducer and the skin, ensuring that the sound waves can penetrate the body without any interference from air.

The correct answer is that electrical voltages are converted to acoustic energy. This is known as the indirect piezoelectric effect. When an electrical voltage is applied to a piezoelectric material, it causes the material to vibrate and generate acoustic waves. This effect is commonly used in devices such as speakers and ultrasound transducers, where electrical signals are converted into sound waves.

When element damage occurs with an annular array transducer, it will result in a horizontal area of dropout on the ultrasound display. This means that there will be a portion of the image where no information is displayed, resulting in a gap or "dropout" in the horizontal direction. This can affect the clarity and accuracy of the ultrasound image in that particular area.

Electronic focusing can be moved up and down which is the big advantage that we use.

Narrow bandwidth has a pulse with few frequencies present, longer pulse.

When the diameter of an unfocused circular transducer is increased, the beamwidth in the far field is reduced. This is because the larger diameter allows for a more focused and narrower beam to be produced. As a result, the beam spreads out less in the far field, leading to a reduced beamwidth.

Electronic curvature focuses the beam so can be moved up and down by short time delays

The statement is false. The number of pulses making up the scan is not directly related to the imaging depth or the number of lines in the image. The number of pulses will depend on factors such as the transducer frequency and the desired image resolution.