Free SPI sample questions

Correct answer: Density and propagation speed

Acoustic impedance (Z) is an intrinsic property of a medium and is defined as the product of the medium's density (ρ) and its propagation speed (c). The formula is Z = ρc. The greater the difference in acoustic impedance between two media, the stronger the reflection at their boundary.

Correct answer: Low quality factor (Q factor) and a short spatial pulse length (SPL)

Wide bandwidth transducers have a low quality factor (Q factor), meaning they produce a wide range of frequencies around the center frequency. This is achieved using a backing material that dampens the crystal's ringing, resulting in a short pulse duration and a short spatial pulse length (SPL). A short SPL is essential for good axial resolution.

Correct answers: Increase the overall gain before increasing the output power.; Decrease the scan time by acquiring images as quickly as possible.

Increasing gain amplifies the returning echoes without increasing the transmitted energy, thus having no impact on patient exposure. This should always be done before increasing output power.

Total exposure is a function of intensity and time. Minimizing the duration of the exam, especially dwelling in one spot, directly reduces the patient's overall exposure to ultrasound energy.

Correct answer: Decrease the color gain

The scenario describes color flash or clutter, which is most often caused by the color gain being set too high. The system becomes overly sensitive and amplifies electronic noise or subtle tissue motion, displaying it as color. The first and most effective step is to reduce the color gain until the random noise disappears, leaving only the signal from true blood flow.

Correct answer: Reduced grating lobe and reverberation artifacts

Tissue harmonic imaging relies on harmonic frequencies generated within the tissue, not transmitted by the probe. These harmonic signals are strongest in the main beam and weaker in the weaker parts like side lobes and grating lobes. Furthermore, since harmonics are generated deeper in the tissue, superficial reverberation artifacts are significantly reduced. This results in a cleaner image with improved contrast resolution and reduced clutter.

Correct answer: -10 dB

The decibel scale is logarithmic. A change of -10 dB corresponds to a tenfold decrease in intensity. Conversely, +10 dB is a tenfold increase. A change of -3 dB corresponds to halving the intensity, and +3 dB corresponds to doubling it. Since the intensity is reduced to 1/10th, the change is -10 dB.

Correct answer: True

This statement is true. The purpose of the matching layer is to reduce the large acoustic impedance mismatch between the high impedance of the PZT crystal and the low impedance of soft tissue (skin). By having an intermediate impedance, the matching layer facilitates more efficient energy transfer from the transducer into the body, improving sensitivity and image quality.

Correct answer: The distance from the transducer face to the first identifiable echo.

The dead zone is the region close to the transducer face where imaging is not possible. It is caused by the time it takes for the system to switch from transmit to receive mode and by reverberation within the transducer itself. Measuring the dead zone on a phantom assesses the system's ability to resolve structures in the extreme near field. A larger dead zone can be caused by a cracked crystal or a detached backing material.

Correct answer: Switch to a lower frequency transducer.

When the PRF is already maxed out, other methods must be used to combat aliasing. The Doppler shift is directly proportional to the transducer frequency. Switching to a lower frequency transducer will decrease the measured Doppler shift for the same velocity, bringing it below the Nyquist limit and resolving the aliasing. Adjusting the baseline only shifts the waveform up or down but does not increase the Nyquist limit. Increasing the wall filter would remove low-velocity signals, not help with high-velocity aliasing. Using CW Doppler is another solution, but switching the transducer frequency is a direct way to solve the issue with PW Doppler.

Correct answer: By averaging frames acquired from different steering angles to reduce speckle and shadowing.

Spatial compounding is a technique where the ultrasound beam is electronically steered to acquire multiple frames of the same anatomical region from different angles. These frames are then averaged together in real-time. This process reduces speckle artifact, minimizes shadowing, and improves the definition of tissue boundaries and specular reflectors. The main trade-off is a reduction in temporal resolution (frame rate).