NCE PRACTICE EXAM

Sonographic quality assurance devices include use of phantoms, such as tissue equivalent, slice thickness, and Doppler phantoms. Alternative answer choices pertain to phantoms used in other imaging modalities. Quality assurance is necessary to ensure imaging in the medical setting is of diagnostic quality and to reduce downtime and repeat scans. Through routine, periodic QA testing observation of gradual equipment, changes may be detected, allowing for necessary modifications to be made for appropriate system operation.

Tissue equivalent phantoms should mimic the speed of sound in soft tissue, which is expressed as an average of 1,540 m/s or 1.54 mm/us. Tissue equivalent phantoms evaluate phased array transducers for demonstration of appropriate soft tissue texture and gray scale imaging. Within a tissue equivalent phantom are structures of varying echogenicity to ensure equipment detection of cystic versus solid masses within soft tissues.

More than 75% of sonographers cope with musculoskeletal injury pain during the span of their career. For this reason, sonographic equipment has evolved in its ergonomic design for sonographer safety. Adaptive devices integrated into sonographic equipment include cable braces, articulation of the sonographic display and control panel, including extension and swivel features, and lightweight transducers. Additional ergonomic devices, although not integrated into the sonographic machine, include: support cushions, wrist braces, and adjustable ergonomic chairs, among others.

Duty factor, pulse duration, spatial pulse length, PRP, and PRF describe pulsed sound. The seven acoustic parameters that characterize non-pulsed acoustic waves are period, propagation speed, frequency, wavelength, power, intensity, and amplitude.

Compared to other biologic tissues listed, bone has the highest speed of sound at 3,500 m/s. The average speed of sound in fat is 1,450 m/s, whereas the speed of sound in the liver and blood are both 1,560 m/s. The average speed of sound in soft tissue is 1,540 m/s. Metallic devices implanted in the body also demonstrate substantial speed of sound, ranging from 2,000 to 7,000 m/s.

Pulse repetition frequency (PRF) and pulse repetition period (PRP) have an inverse, reciprocal relationship. Therefore, the lowest value for PRF - 7 Hz - would have the longest PRP.

Frame rate, or number of images (frames) per second, determines temporal resolution. Temporal resolution improves as frame rate increases and is reduced as frame rate decreases. Factors that determine frame rate include: imaging depth, pulses per frame, a medium's speed of sound, single vs. multi-focus, line density, and sector size. Essentially, any adjustment that adds more detail or asks for more information to be displayed decreases frame rate and temporal resolution. Spatial, elevational, and lateral are also forms of sonographic imaging resolution but temporal resolution has to do with how "fast" an image is.

Mechanical transducers have a single active element (PZT crystal). Therefore, when the crystal is damaged the entire image display is lost.

The active elements (PZT crystals) in convex array transducers are positioned in an arched line, like a rainbow. Synonyms for convex array include curved array or curvilinear array transducers. The top of the displayed image appears as a blunted sector. Alternatively, the active elements in linear array transducers are positioned in a straight line, with the resulting image depicting a rectangular shape. The active elements in an annular array are arranged in a bullseye pattern, and the resulting image is a sector-shape.

Active elements in an annular array transducer are positioned in a bullseye fashion. When damage occurs to the innermost element, the displayed image will have a horizontal band of dropout in the near field. The middle ring correlates to mid-image display. The outermost crystal correlates to the far field in the displayed image. A vertical band of dropout would occur in damage to a linear or convex array transducer, directly under the location of the damaged active element.

This transducer has 280 channels. For each active element, there is a channel. A channel consists of the PZT crystal, system electronics, and connecting wire. Each crystal is connected to the system electronics via the wire, allowing each element to be individually excited which produces a sound wave for transmission into the body. This allows for electronic steering and focusing in the array transducer.

A 3D transducer is essentially a 2D transducer with numerous PZT crystals positioned in a checkerboard pattern. There are typically thousands of individual active elements in a 3D transducer. The acoustic beam is electronically steered and focused, while rendering produces the final image from captured data.

As depth is increased, the frame rate decreases. As a result, temporal resolution also decreases. However, more information is displayed on the image at a greater depth in the body. For each 1 cm deeper, the go-return time (time of flight) increases by 13 microseconds according to the 13-microsecond rule. Tframe refers to the number of imaging pulses multiplied by the pulse repetition period, therefore deeper imaging results in a longer Tframe.

As output, or transmit, power is increased the overall gain and brightness of the displayed image increases. Additionally, active elements undergo a higher voltage. This increase in energy also results in greater image penetration. The sonographer should be mindful of the ALARA concept in understanding that increasing output power applies more energy to the patient's body.

M-mode is frequently used in cardiac imaging. One common use of M-mode is to obtain a fetal heart rate. This display mode demonstrates variance in position of anatomic structures over a period of time displayed on the X-axis. Depth is displayed on M-mode's Y-axis.

Sliding time gain compensation (TGC) knobs towards the right increases brightness on the displayed image. The upper knobs correlate to the displayed image's near field, whereas the lower knobs correlate to the displayed image's far field at increasing depths. Knobs towards the middle of the TGC curve correlate to the middle of the displayed image. The console's TGC function is useful to compensate for image attenuation, producing a uniformly bright image from top to bottom.

Edge enhancement provides emphasis to the edge of anatomic structure boundaries by modifying contrast and highlighting. This defines the edge of structures in creating a sharp appearance. Edge enhancement may be useful for depiction of near-isoechoic adjacent structures. Frequency and spatial compounding are system technologies that aid to reduce sonographic artifacts, such as shadowing, speckle, and noise. Fill-in interpolation is a preprocessing technology that simulates data between scan lines, increasing the displayed image's spatial resolution.

Spatial compounding is a technology that produces an image using numerous overlapped frames. This overlapping of frames is referred to as compounding. Each of these frames is obtained from varying angles, then compounded to display a single image. Benefits of spatial compounding are decreased in artifacts such as shadowing and speckle, however, as a result, temporal resolution is decreased.

Coded excitation lengthens sound pulses in the pulser, spreading peak energy intensity over with a wide frequency range. Simultaneously, lengthened pulse reflections are shortened by system electronics using a mathematical technique. This aids in improving axial resolution while improving image penetration, signal-to-noise ratio, spatial, and contrast resolutions. Frequency compounding is a system technology that aids in reduce sonographic artifacts, such as shadowing, speckle, and noise. Fill-in interpolation is a preprocessing technology that simulates data between scan lines, increasing the displayed image's spatial resolution. Harmonic imaging refers to a technology in which the image is created via reflected frequencies twice that of the transmitted (fundamental) frequency. There are various forms of harmonic imaging, such as pulse inversion, contrast, tissue, and power modulation harmonic imaging.

Contrast harmonics are produced during the conversion of energy from fundamental to the harmonic frequency as microbubbles interact with the acoustic wave. When microbubbles and the acoustic wave interact, microbubbles react in a nonlinear fashion, expanding and contracting. Contrast harmonics are produced during reflection. The mechanical index (MI) determines harmonic strength and microbubble reaction. Tissue harmonics include harmonics as they relate to energy transfer from the fundamental to harmonic frequency within soft tissues. This results from a nonlinear behavior of acoustic energy compressions and rarefactions while traversing through soft tissue, decreasing the likelihood of artifacts to appear within structures. Pulse inversion harmonics is another technology in which negative and positive acoustic pulses are sent down each individual scan line. These pulses undergo destructive interference, cancelling each other out while the nonlinear, harmonic reflections remain. Fundamental harmonics is not a real term.

Wall filter specifically removes color from areas of slow-moving flow while utilizing the color Doppler application. High velocities are not affected by wall filter adjustments, therefore wall filter is a useful feature for decreasing ghosting artifact.

PW-Doppler transducers are subject to aliasing. Aliasing occurs with high velocity flow, when velocity exceeds the Nyquist limit at the top of the spectral Doppler display. To reduce aliasing, the sonographer may utilize a CW-Doppler transducer or with a PW-Doppler transducer move the baseline, increase scale, utilize an alternative sonographic window for a shallower sample volume, or decrease transducer frequency. Range ambiguity is the inability to visualize a sonographic image (i.e. with CW-Doppler transducers) to determine an exact selection point for Doppler sampling within the anatomical region of interest, such as the center of a vessel. The opposite of range ambiguity, which is true with PW-Doppler transducers, is referred to as freedom from range ambiguity artifact, range resolution, or range specificity, all of which are synonyms. A PW-Doppler transducer requires a minimum of one PZT crystal, or active element, which sends out pulses of acoustic energy, alternating between transmission and listening time for the reflected pulse. PW-Doppler transducers have a low Q-factor, versus CW-Doppler transducers which exhibit a high Q-factor. Q-, or quality-factor, is unitless, and refers to a transducer's bandwidth. To determine Q-factor, the transducers primary frequency is divided by the bandwidth, therefore dampened pulses exhibit a low Q-factor whereas long pulses with ringing exhibit a high Q-factor. CW-Doppler transducers create long pulses, as short pulses are not necessary with no image being created. This means a higher Q-factor and increased sampling sensitivity.

Color confetti refers to excess color gain. With color confetti, speckles of color appear throughout the entire color Doppler box rather than solely in the region of interest (vessel). Color funfetti and color bleed are not actual terms. Crosstalk is an artifact that refers to spectral Doppler imaging versus color Doppler imaging and is a mirrored image display of the spectral Doppler waveform.

Demodulation is the removal of the low Doppler frequency from the carrier frequency of the transducer. To better understand demodulation, it is helpful to understand Doppler shift, or Doppler frequency. The Doppler shift is expressed in a unit of Hertz and is equivalent to the reflected frequency minus the transmitted frequency. The Doppler shift is either a negative or positive value. With a positive Doppler shift, the reflected frequency is greater than the transmitted frequency, typically encountered when the direction of blood flow is moving towards the transducer. The opposite is true with a negative Doppler shift. Frequency reflection is not a real term. a made up distractor. Quadrature detection, also referred to as phase quadrature, is a Doppler signal processing technology.

Reverberation is a gray-scale imaging artifact. This artifact has a classic "Venetian blind" or "ladder" appearance, resulting from too many reflections. Reverberation artifact is displayed as numerous echoes that are equally spaced parallel to the main axis of the sound beam. Crosstalk, clutter, and aliasing are all artifacts that can occur with spectral Doppler display.

A color Doppler map is used to display both direction and velocity of blood flow during implementation of color Doppler. Above the black baseline, positive Doppler shifts or flow towards the transducer are demonstrated. Therefore, if color displayed on the color Doppler map above baseline is red, red superimposed color flow within a vessel would indicate blood flowing towards the transducer. As velocity increases, color of flow changes to a variation of hues including yellows, greens, etc.

Multiple pulses utilized with color Doppler in reference to blood velocity is referred to as a Doppler ensemble or packet. Increased packet size or ensemble length provides greater accuracy with measurement of blood velocity. However, as with most applications that require additional processing of data, frame rate and temporal resolution decrease.

Doppler frequencies demonstrate the velocity of blood flow. Whereas speed solely reports distance over a period of time, velocity describes both the speed and direction the blood is flowing.

One of the most beneficial advantages in using a CW-Doppler transducer is the ability to document elevated velocities with a great level of accuracy. CW-Doppler transducers contain two active elements, that constantly receive and transmit acoustic energy. As a result, no anatomic image is created and therefore an exact sampling location within the anatomic structure being evaluated is not possible, referred to as range ambiguity. CW-Doppler transducers are often utilized for vascular studies.

A Reynolds number of less than 1,500 is indicative of laminar flow. Greater than 2,000, however, is indicative of turbulent flow. Reynolds number was designed to predict streamlined laminar versus disrupted turbulent flow within a vessel. Turbulent flow is commonly visualized post-stenosis.