Part 1 - Physic's

The receiver in a communication system performs several functions. Amplification is the process of increasing the strength of the received signal. Compensation is used to correct any distortions or impairments in the signal. Compression is the process of reducing the dynamic range of the signal. Demodulation is the extraction of the original information from the modulated carrier signal. Rejection refers to the elimination of unwanted signals or interference. Therefore, the correct list of functions performed by the receiver is amplification, compensation, compression, demodulation, and rejection.

B-mode display refers to brightness mode in medical imaging. This mode is commonly used in ultrasound imaging to display the intensity of the returning ultrasound signal as shades of gray. It allows for a clear visualization of the internal structures of the body based on the differences in the brightness levels. This mode is particularly useful in detecting abnormalities or changes in tissue density.

The duty factor of a pulsed echo system refers to the ratio of the pulse duration to the pulse repetition period. A duty factor of less than 1% means that the pulse duration is significantly shorter than the time between pulses. This indicates that the system is primarily operating in a pulsed mode, where the pulses are transmitted and received with long intervals in between. A duty factor less than 1% is commonly observed in ultrasound imaging systems, where short pulses are used to minimize tissue heating and maximize image resolution.

Artifacts appearing as parallel, equally spaced lines (like a ladder) are characteristic of reverberation. Reverberation occurs when sound waves bounce off multiple surfaces before reaching the receiver, causing multiple reflections. These reflections create parallel lines on the image, giving the appearance of a ladder-like artifact. This phenomenon is commonly seen in ultrasound imaging and can affect the clarity and accuracy of the image.

The correct answer is SATA because it has the fewest number of consonants (2) compared to the other options. SPTP has 3 consonants, SEPTA has 3 consonants, and SPAT has 3 consonants. Therefore, SATA has the lowest intensity as it has the least number of consonants.

The strength of an echo as related to the height of the vertical deflection on the monitor is called A mode. A mode is a display mode in ultrasound imaging that represents the amplitude of the echo signal as a vertical deflection on the screen. It is commonly used in ophthalmology and cardiology to measure the thickness of tissues or the distance between structures. The height of the deflection corresponds to the strength of the echo, providing valuable information about the reflectivity of the tissue being examined.

The PRP (Pulse Repetition Period) is the time interval between consecutive pulses in a pulse train. In this question, the PRF (Pulse Repetition Frequency) is given as 5 MHz, which means that there are 5 million pulses per second. To calculate the PRP, we need to find the reciprocal of the PRF. Since 1 MHz is equal to 1 million hertz, the reciprocal of 5 MHz is 1/5 million seconds. Converting this to microseconds, we get 0.2 us (microseconds). Therefore, the correct answer is 0.2 us.

The correct answer is "demodulation and compression". Demodulation is the process of extracting the original signal from a modulated carrier wave, and compression is the reduction in dynamic range of a signal. Both of these processes are typically fixed and cannot be adjusted by an operator. On the other hand, compensation and rejection as well as amplification and rejection can be adjusted by an operator to modify the characteristics of a signal.

The wavelength of an ultrasound wave in soft tissue is inversely proportional to the frequency of the transducer used. Since a 3 MHz transducer is used, the wavelength can be calculated using the formula: wavelength = speed of sound / frequency. The speed of sound in soft tissue is approximately 1540 m/s. Therefore, the wavelength would be approximately 0.51 mm.

Beam steering refers to angling the beam by sequentially firing the elements. This means that the ultrasound beam is directed in a specific direction by activating the transducer elements in a sequential manner. By controlling the timing and intensity of the elements, the ultrasound beam can be steered to focus on a specific area of interest. This technique allows for better visualization of structures and improved image quality in ultrasound imaging.

A real-time image needs to be displayed at a high frame rate to appear smooth and flicker-free to the human eye. The human eye can generally perceive flicker at a rate of around 10-15 frames per second. Therefore, to ensure a flicker-free experience, the number of frames per second needed for a real-time image should be more than 15.

The correct answer is converting the voltage delivered to the receiver from one form to another. Demodulation is the process of converting a modulated signal back to its original form. In this case, it refers to converting the voltage signal received by the receiver from its modulated form to its original form. This is necessary in order to extract the original information or data that was transmitted.

The correct answer is threshold or rejection level. The threshold or rejection level refers to the minimum level of signals that can be detected or transmitted through an ultrasound receiver. It represents the sensitivity of the receiver and determines the minimum strength of the signal required for it to be considered valid. Signals below this level are not transmitted or processed by the receiver.

The correct answer is "bandwidth." Bandwidth refers to the range of frequencies contained in an ultrasonic pulse. It represents the difference between the highest and lowest frequencies present in the pulse. The average frequency and operating frequency are specific values within the bandwidth range, but they do not encompass the entire range of frequencies. Therefore, the correct answer is bandwidth.

Increased viscosity refers to the thickness or stickiness of a fluid, such as blood. When the viscosity of blood increases, it becomes more resistant to flow through the blood vessels. This is because the thicker the blood, the more friction it encounters as it moves through the vessels. As a result, increased viscosity leads to increased resistance in relation to vascular flow volume.

The velocity of an ultrasound wave is determined by the medium through which it travels. Different mediums, such as air, water, or solids, have different densities and elastic properties, which affect the speed at which the ultrasound wave can propagate. The velocity of the ultrasound wave is not determined by the frequency, period, or Nyquist limit, but rather by the physical properties of the medium.

The beam of an unfocused transducer diverges in the Fraunhofer Zone. In this zone, the beam spreads out due to diffraction, resulting in a wider beam width. This occurs when the ultrasound waves are far away from the transducer, and the beam has had time to fully diverge. In contrast, the Fresnel Zone is closer to the transducer and has a narrower beam width. Inadequate damping or a long pulse length may affect the overall performance of the transducer, but they do not directly cause the beam to diverge in the Fraunhofer Zone.

The correct answer is Fourier transform. Fourier transform is a mathematical technique used by imaging instruments to derive Doppler Shift information from the returning echoes. It is a method that transforms a time-domain signal into its frequency-domain representation, allowing the identification and analysis of different frequency components in the signal. By applying Fourier transform to the returning echoes, the imaging instrument can determine the Doppler Shift and extract information about the velocity and direction of the moving objects.

The echo will take a longer time to arrive back at the transducer because it is located 7 cm deep in the body. The depth of the echo affects the time it takes for the echo to travel back to the transducer. Additionally, the propagation speed of sound in the body is given as 4080 m/s. Therefore, it will take 91 microseconds for the echo to arrive back at the transducer.

Lateral resolution refers to the ability of an ultrasound system to distinguish between two closely spaced objects that are perpendicular to the sound beam. It is determined by the width of the ultrasound beam. As the distance from the transducer increases, the width of the beam also increases, resulting in a decrease in lateral resolution. Therefore, lateral resolution varies the most with distance from the transducer compared to the other options.

The duty factor refers to the fraction of time when the transducer emits pulses. It is a measurement of the "on" time of the pulses compared to the total time. A higher duty factor indicates that the transducer is emitting pulses for a larger portion of the time, while a lower duty factor means that the pulses are emitted for a smaller fraction of the time. Therefore, the duty factor is the correct answer in this case.

The correct answer is "between two consecutive points that are in the same phase on the wave." This is because the wavelength is defined as the distance between two points on a wave that are in the same phase, meaning they have the same position in their respective cycles. This can be two consecutive crests, two consecutive troughs, or any other two points that are in the same phase. It is important to note that the wavelength is not the distance the wave travels in a certain time period or the distance between any two random points on the wave.

Errors relating to propagation speed can cause improper axial position on the display. This means that the ultrasound waves are not traveling at the correct speed, leading to inaccurate positioning of the displayed image. This can result in misinterpretation of the anatomy being examined and potentially lead to incorrect diagnoses or treatment decisions.

The equation for impedance is given by the product of the propagation speed (c) and density (p), or it can be a combination of both. Impedance is a measure of the opposition that a circuit or medium presents to the flow of current or sound waves. The equation accounts for the speed at which the waves propagate and the density of the medium through which they travel.

The acoustic impedance of a medium is equal to the product of density and velocity. Acoustic impedance is a measure of how much a medium resists the transmission of sound waves. It is determined by the density of the medium, which represents how closely packed the particles of the medium are, and the velocity of sound in the medium, which represents how quickly the sound waves can travel through it. The product of density and velocity gives the acoustic impedance, as the two factors are both important in determining how sound waves propagate through a medium.