SPI CTL: Ultrasound Transducers
If a 4MHz transducer is used for an abdominal exam, the wavelength will be approximately _____________ . A. 0.4 mm B. 0.8 mm C. 0.4 cm D. 4 mm
A. 0.4 mm Note: Velocity = frequency x wavelength 1540m/s = 4,000,000Hz x wavelength 1540 / 4,000,000Hz = wavelength 0.000385m or 0.4 mm
When using a 3 to 6 MHz transducer, which frequency will offer the best penetration? A. 3 MHz B. 4 MHz C. 5 MHz D. 6 MHz
A. 3 MHz Note: Lower frequencies offer better penetration, but degraded spatial resolution.
Which of the following transducer frequencies can be used for imaging or therapeutic purposes? A. 3 MHz B. 15 MHz C. 5 MHz D. 1 MHz
A. 3 MHz Note: therapeutic transducers average 0.7 - 3 MHz; imaging transducer's average 2.5 to 15 MHz.
Transducers can be electronically focused by: A. Adding an acoustic lens to the face of the transducer B. Varying timing of the release of the pulses C. Using a convex shaped PE element D. Using a concave shaped element
A. Adding an acoustic lens to the face of the transducer. Note: varying the timing of the production of sound pulses is a type of electronic focusing. Lenses and curved elements are examples of mechanical focusing.
What type of transducer has a cylindrical beam profile? A. Annular array B. Phased array C. Linear array D. Curved array
A. Annular array Note: annular array as usually composed of five circular PE elements that produce a cylindrical shaped beam.
The linear transducer you are using has a 7 to 5 MHz printed on the side of the housing. What pro characteristic is this? A. Bandwidth B. Duty Factor C. System sensitivity D. Dynamic range
A. Bandwidth Note: the megahertz range listed on the side of the transducer housing is the bandwidth of the transducer. The probe has a 2 MHz bandwidth.
Which of the following is necessary for a multihertz transducer? A. Broad bandwidth B. Two piezoelectric elements C. Two different sizes of piezoelectric elements D. Narrow bandwidth
A. Broad bandwidth Note: broadband with allows for multi hertz transducer capabilities and the transducer can operate at two or more different center frequencies.
Which of the following transducers is capable of electronic beam steering? A. Curvilinear phased array B. Linear sequential array C. Curvilinear sequential array D. Mechanical
A. Curvilinear phased array Note: Sequential arrays in the mechanical transducers cannot vary the time of the voltage to the elements with electronic beam steering. The sequential arrays excite their elements in the same order constantly. They are all unable to steer electronically, but can use mechanical steering. phased arrays can electronically focus and steer the beam.
What determines the transducer frequency used for the evaluation of a foreign body? A. Depth of the foreign body B. The radiologist reading the exam C. Age of the foreign body D. Composition of the foreign body
A. Depth of the foreign body Note: depth of a foreign body dictates transducer frequency. Higher frequency = less penetration = more superficial foreign body. Lower frequency = more penetration = deeper foreign body. Preliminary x-rays taken in 2 planes are helpful for guidance on location, depth and composition. Organic foreign bodies are not well seen on radiography, but easily detected on sonography. Metal and inorganic foreign bodies, such as gravel or glass, are radiopaque on an xray and more easily identified.
Spatial compounding requires a transducer that can perform: A. Electronic steering B. Electronic focusing C. Harmonic imaging D. Dynamic frequency tuning
A. Electronic steering Note: the technique uses electronic steering to produce multiple pulses from different angles. The reflections from these pulses are average to produce each frame.
Which of the following can be used for backing material in a PW transducer? A. Epoxy B. Air C. Quartz D. Backing material is only necessary in CW transducers
A. Epoxy Note: PW Doppler requires a backing/damping material that reduces the ring effect of the pulse. Typical substances used include cork, putty, or epoxy. Using air as the backing material is the same as using NO backing material.
Which of the following describes a multi dimensional array? A. Has thousands of elements arranged in a matrix pattern B. Offers increased slice thickness and improved spatial resolution C. Has less than 100 elements that can be fired simultaneously D. Has less than 100 elements that can be fired sequentially
A. Has thousands of elements arranged in a matrix pattern Note: a multi dimensional transducer has thousands of elements arranged in a matrix pattern. The element arrangement improves elevational resolution by reducing the slice thickness. They are used to produce 3D/4D images.
Increasing the angle of electronic steering causes _________ production of lobe artifact. A. Increased B. Decreased C. No change D. Limited
A. Increased Note: Lobe artifacts are an unwanted part of the ultrasound beam, emitted off axis, that produce image artifacts due to errors and positioning the returning echo. Steering causes diffraction of the beam to occur leading to the formation of lobe artifacts.
Which of the following is an advantage of harmonic imaging? A. Increased signal to noise ratio B. Increased beam width C. Increased beam penetration D. Increased lobe artifact
A. Increased signal to noise ratio Note: harmonic imaging refers to processing the returning waves at double the frequency and will not increase beam penetration. The resulting harmonic beam is narrower, has smaller side lobes, offers better lateral resolution, improved signal to noise ratio, less clutter with improved contrast resolution. Higher signal to noise ratio's are preferred because that means there is more signal than noise.
During an exam, you change from a 5 MHz transducer to a 3 MHz transducer. What happens to the period of the waves produced from the new transducer? A. Increases B. Decreases C. Remains constant D. Unable to determine
A. Increases Note: the period is the reciprocal of the frequency. A frequency decreases, the period the waves produced will increase. If the frequency increases, the period of the waves produced will decr
A linear transducer providing a trapezoidal image demonstrates degraded _________ resolution in the far field of the image. A. Lateral B. Elevational C. Axial D. Contrast
A. Lateral Note: A trapezoidal field of view from a linear array leads to degraded lateral resolution in the fire field. Contrast, axial and elevational resolution are not affected by trapezoidal field of view.
All of the following transducers can be focused at multiple depths, except: A. Mechanical single element B. Linear phased C. Curvilinear phased D. Annular phased
A. Mechanical single element Note: mechanical single element transducers have a single set focus because they cannot be focused electronically.
Which of the following occurs with the implementation of backing material in a transducer? A. Shorter pulses B. Higher Q-factor C. Improved sensitivity D. Increased Duty factor
A. Shorter pulses Note: the backing material or damping layer reduces system sensitivity by preventing the lowest intensity waves from forming. The layer reduces the "ringing" effect to create shorter pulses and reduce duty factor.
What changes occurred to the ultrasound beam one time pulses are emitted from right to left from the elements of the phase transducer? A. The beam is steered to the left B. The focal depth moves closer to the transducer face C. The beam is steered to the right D. A trapezoidal image is displayed
A. The beam is steered to the left Note: when time pulses are emitted from right to left from the elements of the phase transducer, the beam is stair to the left. When timed pulses are emitted from left to right from the elements of the faced transducer, the beam is stair to the right. When timed pulses are emitted from the edge elements to the center elements of the phase transducer, focusing occurs.
As the area of the beam increases, ______________________ . A. The intensity of the beam decreases B. The frequency increases C. The intensity of the beam increases D. The wavelength increases
A. The intensity of the beam decreases Note: beam area is inversely proportional to intensity. As area increases, beam intensity decreases. The greater the beam area, the more the intensity is "spread" out across it.
An ultrasound system/transducer that performed acoustic radiation forced impulse AFRI is used to assess? A. Tissue stiffness B. Speed of sound in tissue C. The sensitivity of the ultrasound system D. Tissue composition
A. Tissue stiffness Note: Acoustic radiation forced impulse (AFRI) is typically used to assess the liver for signs of chronic disease. It is similar to shear wave elastography because it provides a quantitative assessment of tissue stiffness. Cirrhosis, fibrosis, and chronic hepatitis are examples of chronic conditions that would benefit from an AFRI evaluation. Other applications in renal, thyroid and breast tissues are being explore
Which of the following can be used to eliminate the dead zone on the image? A. Use a standoff pad B. Place multiple focal zones at the top of the image C. Decrease the depth to the lowest setting and turn of harmonic imaging D. Not possible to eliminate the dead zone from an image
A. Use a standoff pad Note: the dead zone is an area a very poor resolution at the top of the image. It is caused by the delay in time that it takes for the PE Crystal to switch between transmit and receive functions.
Transducers can be electronically focused by: A. Varying timing of the release of the pulses B. Adding an acoustic lens to the face of the transducer C. Using a convex shaped PE element D. Using a concave shaped element
A. Varying timing of the release of the pulses Note: varying the timing of the production of sound pulses is a type of electronic focusing. Lenses and curved elements are examples of mechanical focusing.
Which of the following statements correctly describes annular arrays? A. an annular array can electronically focus the beam. B. an annular array can use phasing to electronically steer the beam. C. Annular arrays provide the lowest slice thickness resolution. D. annular arrays usually contain 30 or more circular elements.
A. an annular array can electronically focus the beam. Note: phasing refers to firing elements and groups at different time intervals in order to steer the beam. Annular arrays usually contain 5 circular elements. The annular array does not have enough different elements to effectively use the phasing technique. Annular Arrays provide the highest slice thickness resolution of all arrays.
Diagnostic ultrasound is described as frequency is greater than: A. 1 MHz B. 2 MHz C. 2.5 MHz D. 3 MHz
B. 2 MHz Note: diagnostic ultrasound is described as frequencies greater than 2 MHz.
Which of the following transducers will produce the highest frequency sound waves? A. 2mm element thickness, 2mm/us propagation speed of the element B. 2mm element thickness, 6mm/us propagation speed of the element C. 6mm element thickness, 2mm/us propagation speed of the element D. 6mm element thickness, 6mm/us propagation speed of the element
B. 2mm element thickness, 6mm/us propagation speed of the element. Note: thinner elements with higher propagation speeds produce highest frequency waves.
Line density is constant at two lines per degree and you change from a 90° sector to a 45° sector how many lines will now be produced? A. 45 B. 90 C. 180 D. 360
B. 90 Note: Constant line density if the degree of the sector angle decreases by half the number of pulse is produced with decreased by half also to scan lines per degree equals 45×2 = 90
Which statement regarding high frequency transducers is correct? A. higher frequency transducers provide improved image resolution because the sound travels faster through the tissues to provide a more accurate display. B. A multi-hertz transducer operates at multiple frequencies and offers a broad band with. C. Harmonic imaging should never be used on transducers over 12 MHz. D. Higher frequency transducers always have low signal to noise ratio.
B. A multi-hertz transducer operates at multiple frequencies and offers a broad band with. Note: Multi hurts transducers produce a range of frequencies centered around the main frequency equals wider band width. The larger the bandwidth, the better the spatial and contrast resolution. Higher frequency transducers provide improved image resolution because the sound travels and tighter pulses for a shorter distance to provide a more accurate display. The speed of sound is constant in each medium. Higher frequency transducer's always have higher signal to noise ratio. There is more reflected "signal" and less noise on the image than with low frequency transducers. Harmonic imaging can be used at any diagnostic frequency to improve the image resolution and signal to noise ratio.
Which transducer component improves elevational resolution? A. Pulser B. Acoustic lens C. Matching layer D. Damping layer
B. Acoustic lens Note: Poor elevational resolution = increased slice thickness = inability to demonstrate small structures correctly. Elevational resolution is accomplished using a form of fixed mechanical focusing on a linear, curved or phased array; ER is a measure of the beam width perpendicular to the image plane.
Which of the following is true regarding annular arrays and linear arrays? A. Annular arrays and linear arrays can be electronically steered B. Annular arrays must be mechanically steered, linear arrays use electronic steering. C. Annular arrays can be electronically steered, linear arrays must be mechanically steered D. Annular arrays have multiple elements, linear arrays have a single element.
B. Annular arrays must be mechanically steered, linear arrays use electronic steering. Note: annular arrays can be electronically focused but must be steered mechanically with a lens or scanning wedge. Linear arrays can be electronically focused and steered by using varied timing to the elements in the array.
To obtain a longer near zone: A. Add a lens to the transducer face. B. Change from a 3MHz to a 6MHz transducer C. Decrease the transducer element diameter D. Use a linear transducer instead of a curved transducer.
B. Change from a 3MHz to a 6MHz transducer Note: higher frequency and larger element diameter probes provide the longest near zones.
As the quality factor increases, the bandwidth ______________. A. Does not change B. Decreases C. Increases
B. Decreases Note: the band width refers to the range of frequencies produced by the transducer. The quality factor refers to the purity of the sound produced. Narrow bandwidth leads to an increase in the Q Factor and special pulse length = poor image quality. Broad bandwidth decreases Q Factor and improves image quality.
You switch from a 5MHz curved probe to a 2.5MHz sector probe to image deeper in the abdomen. How is the attenuation rate affected by the change to the new probe? A. Decreases by 25% B. Decreases by 50% C. Doubles D. Increases by 4 times
B. Decreases by 50% Note: Lower frequency probes offers lower rates of sound attenuation. If the frequency is reduced by half, the attenuation rate will be reduced by half or 50%.
The crystal in the ultrasound transducer converts: A. Mechanical energy into heat energy B. Electrical energy into mechanical energy C Electrical energy into heat energy D. Mechanical energy into sound energy
B. Electrical energy into mechanical energy Note: electrical pulses are applied to the crystal causing the production of mechanical vibrations. The crystal also processes the returning mechanical waves and they are converted back into electrical pulses for image display.
The frequency of the transducer depends primarily on the ______________ . A. Element diameter B. Element thickness C. Thickness of the matching layer D. Thickness of the backing layer
B. Element thickness Note: The frequency of the transducer depends primarily on the element thickness.
All of the following are coupling agents or mediums typically used for ultrasound exams, except: A. KY jelly B. Gastrografin C. Ultrasonic gel D. Water
B. Gastrografin Note: gel in KY jelly can be used in most all ultrasound exams. Some exams use water as a window to evaluate adjacent structures (prostate). Gastrografin is a contrast material normally used in radiology procedures
Which of the following transducers will provide the deepest natural focus? A. Low frequency, large diameter B. High frequency, large diameter C. High frequency, small diameter D. Low frequency, small diameter
B. High frequency, large diameter Note: High frequency, wide diameter transducers will have the deepest natural focus.
Some US transducer arrays allow you to reduce the thickness of the beam as an additional type of focusing. What effect will this change have on the image? A. Degraded temporal resolution B. Improved elevational resolution C. Improved contrast resolution D. Decreased beam attenuation
B. Improved elevational resolution Note: focusing that occurs along the thickness of the beam will decrease the slice thickness and improve elevational resolution.
As the transducer frequency increases, the quality factor _______________. A. Decreases B. Increases C. Does not change D. Changes only if a different PE element is used
B. Increases Note: imaging probes have a low Q factor and a wide band with a frequencies. CW and therapeutic US probes have high Q factor and narrow bandwidth due to the continuous production of the wave at the main frequency. The probe frequency is directly related to the Q factor and indirectly related to bandwidth. The higher the frequency, the higher the Q factor and narrower the bandwidth.
What type of transducer has approximately 200 elements arranged side-by-side and produces only a rectangular shaped field of view? A. Phased linear array B. Linear sequential array C. Annular phased array D. Curved phased array
B. Linear sequential array Note: a sequential linear array contains multiple elements arranged in a line that are fired in a sequential order to produce a rectangular image. The phase linear array has similar construction but the elements are fired and groups to allow a rectangular or trapezoidal field of view.
The wider the element diameter, the A. Longer the near zone. B. Greater the beam intensity. C. Greater the probe frequency. D. Greater the beam divergence in the far field.
B. Longer the near zone Note: intensity is power per unit area. As the area of the beam increases, the total power of the beam is more "spread out" across the larger area. This causes a reduction in intensity. Wider element diameters produced longer near zones with less beam divergence in the far Field. Thinner elements produce higher frequency sound w
The wider the element diameter, the A. Greater the beam divergence in the far field B. Longer the near zone C. Greater the beam intensity D. Greater the probe frequency
B. Longer the near zone Note: wider element diameter is produced longer near zones with less beam divergence in the far field. Intensity is power per unit area. As the area of the beam increases, the total power of the beam is more "spread out" across the larger area. This causes a reduction in intensity. Thinner elements produce higher frequency sound waves.
What is the proper method used to assess the size of the dead zone? A. Measure the width of the area of reverberation at the top of the screen. B. Measure from the top of the image to the depth that uniform tissue is identified. C. Trace the volume of the portion of the image that demonstrates reverberation at the top of the screen. D. trace the area of the portion of the image that demonstrates reverberation at the top of the screen.
B. Measure from the top of the image to the depth that uniform tissue is identified. Note: The dead zone for a transducer is measured by assessing the depth of the area of reverberation at the top of the image. The depth should be measured from the top of the phantom to the depth that uniform tissue is identified.
Which of the following is correct regarding endocavity probes? A. One of the main disadvantages of the tightly curved elements of the endocavity probe is decreased spatial resolution. B. They most commonly incorporate a curved array of elements that are electronically steered to create an extended field of view. C. Endocavity probes offer improved lateral resolution at greater depths. D. They should be cleaned and soaked in a high level disinfectant at least once a day.
B. They most commonly incorporate a curved array of elements that are electronically steered to create an extended field of view. Note: Endocavity probes most commonly used tightly curved element arrays. One of the main advantages of the tightly curved elements of the Endocavity probe is improved spatial resolution. Endocavity probes are limited by degraded lateral resolution at greater depth. They should be cleaned and soaked in a high-level disinfectant after each patient.
Which of the following describes a purpose for applying acoustic gel to the face of the transducer? A. To reduce the beam intensity just before the sound beam enters the patient B. To reduce the difference in impedance between the matching layer and the skin C. To increase the amount of reflection that occurs within the first 2cm of tissue D. To increase the amount of refraction that occurs within the first 2cm of tissue
B. To reduce the difference in impedance between the matching layer and the skin Note: There is a significant difference between the impotence of the PE element and the skin. This will lead to a significant amount of reflection occurring at the boundary between the probe and the skin. The matching layer and acoustic gel help to reduce the difference in importance between the element and skin, therefore reducing the amount of reflection that occurs at the boundary. This allows more of the sound penetrate the tissue
Which of the following transducers provides the best spatial resolution of the cardiac structures? A. Phased sector array B. Transesophageal array C. Vector array D. Curved sequential array
B. Transesophageal array Note: endocavity transducers provide improved resolution. Transesophageal imaging offers the highest probe frequencies and the probe location closest to the heart for the best ultrasound evaluation. Transvaginal imaging offers the highest probe frequencies and the probe location closest to the uterus and ovaries for the best ultrasound evaluation. The Endocavity transducer is also preferred to evaluate the prostate and transrectal ultrasound exams.
How can you adjust the elevation focus to a more superficial location in a 1D array transducer? A. Scan the breast from a lateral approach B. Use a stand off pad C. Change the short axis focus setting on the console D. There is no way to adjust the elevation focus in a 1D array
B. Use a stand off pad Note: The elevation focus in a 1D array transducer is set by an acoustic lens inside the transducer and is fixed. Placing a standard 1cm stand off pad in front of the transducer can move the focus to a level that is 1cm more superficial in the tissues being scanned.
The damping material causes a ____________ bandwidth and a ____________ quality factor. A. Narrower, lower B. Wider, lower C. Narrower, higher D. Wider, higher
B. Wider, lower Note: damping produces a wider band with and reduces quality factor (preferred for imaging). The presence of a backing/damping layer reduces the number of cycles in a pulse and broadens the bandwidth. Longer pulses result and narrower bandwidth.
Which of the following exams would benefit from an exam performed with a multi dimensional array? A. carotid exam with a high-grade stenosis B. cardiac exam to evaluate left atrial and ventricular volume C. Abdominal exam on an obese patient D. breast biopsy to localize the lesion and several planes
B. cardiac exam to evaluate left atrial and ventricular volume Note: Multi dimensional arrays can produce a 3D/4D image, which is the preferred method for volume assessment.
Which of the following statements is true regarding the advantage of a mechanical annular probe over the mechanical single element probe? A. the array of elements allows for electronic steering which is not possible with a single element. B. the array of elements allows for electronic focusing which is not possible with a single element. C. The array of elements allows for mechanical steering which is not possible with a single element. D. the single element probe will have higher temporal resolution than the annual array.
B. the array of elements allows for electronic focusing which is not possible with a single element. Note: an array of elements allows for varied voltage timing between elements to be used to focus the beam. If the probe contains only one element, the ability to vary the voltage timing between elements is lost.
Which type of transducer would be used to evaluate a palpable lump in the neck? A. 3MHz curvilinear sequential array B. 12 MHz sector phased array C. 12 MHz linear phased array D. 12 MHz curvilinear phased array
C. 12 MHz linear phased array Note: superficial imaging is best performed with linear transducers. The large near field and rectangular field of view provide improved imaging of superficial structures. Higher frequencies also provide the best resolution.
Which of the following transducers would have the best axial resolution? A. 4mm spatial pulse length B. 2mm element diameter C. 2mm spatial pulse length D. 4mm element diameter
C. 2mm spatial pulse length Note: the axial resolution is determined by the special pulse length of the wave. AR = 1/2 SPL Shorter spatial pulse lengths result in a lower numerical value of axial resolution. Lower numbers indicate the ability to resolve smaller structures correctly. Elements that are THINNER produce a higher frequency beam. Element (width) diameter does not affect the frequency of the sound produced.
Which of the following transducers would be most useful for imaging deeper structures? A. 5 MHz short focus B. 3 MHz short focus C. 3 MHz long focus D. 5 MHz long focus
C. 3 MHz long focus Note: low frequency transducers are better for imaging deeper structures due to increased penetration. A longer focus will improve the resolution ability at the deeper depth.
Which of the following statements is true regarding transducer selection? A. A high frequency transducer has degraded lateral resolution compared to a lower frequency transducer. B. A high frequency transducer has greater field beam divergence than a lower frequency transducer. C. A high frequency transducer has less depth penetration than a lower frequency transducer. D. A high frequency transducer has degraded axial resolution compared to a lower frequency transducer.
C. A high frequency transducer has less depth penetration than a lower frequency transducer. Note: a low frequency transducer has greater depth penetration than a high frequency transducer. A high frequency transducer has improved axial and lateral resolution compared to a lower frequency transducer. A high frequency transducer has less far field beam divergence than a lower frequency transducer.
Which of the following correctly describes phased array transducers? A. A vector phased array can produce a trapezoidal image. B. All phased array transducers are steered electronically. C. All phased array transducers are focused electronically. D. A sector phased array has a trapezoidal field of view.
C. All phased array transducers are focused electronically. Note: A sector phased array has a fan shaped field of view. All phased array transducers are focused electronically. All phased array transducers are NOT steered electronically. Annular phased arrays must be steered mechanically using acoustic lenses. A linear phased array can change to a trapezoidal field of view (FOV) using beam steering.
What type of transducer array has the fewest number of elements? A. Mechanical transducer B. Linear phased array C. Annular array D. Curvilinear sequential array
C. Annular array Note: Annular arrays usually have 5 ring shaped crystals. Linear, curvilinear, sector and vector arrays have an average of 200 elements. If the question asked which type of transducer has the fewest elements instead of which type of transducer ARRAY, the answer would be a mechanical transducer. Mechanical transducers have a single element, not an array of elements.
As transducer frequency increases: A. Lateral resolution will improve, but axial resolution will be degraded B. Lateral resolution will be degraded, but axial resolution will improve C. Axial and lateral resolution will improve D. Axial and lateral resolution will be degraded
C. Axial and lateral resolution will improve Note: Axial and lateral resolution will improve with higher frequency probes.
Which of the following is true regarding continuous wave transducer structure and function? A. CW probes do not require a matching layer. B. CW probes are preferred for detection of low velocity flow. C. CW probes do not require any backing material. D. CW probes have a single PE element.
C. CW probes do not require any backing material. Note: CW probes have two elements, one for transmission and one for receiving signals. The matching layer thickness is related to the wave length of the program. CW versus PW does not affect matching layer thickness. All CW probes have a duty factor of 100% because the beam is constantly "on" (does not pulse on and off). ACW probe does not need a backing because it is constantly producing an ultrasound polls and bring down between pulses is not a concern. Backing material is needed for PW probes to reduce the ringing between pulses.
You switch from a 5MHz curved probe to a 2.5MHz sector probe to image deeper in the abdomen. How is the wavelength affected by the change to the new probe? A. Has no effect when changing from curved to sector transducer B. Decreases by 50% C. Doubles D. Increases by a factor of 4
C. Doubles Note: wavelength and frequency are inversely related. If the frequency is reduced by 50%, the wavelength will double.
_______________ used to form the sector shaped field of view for a phased array transducer. A. An acoustic lens is B. Electronic focusing is C. Electronic steering is D. The curved arrangement of the elements are
C. Electronic steering is Note: Variation and timing of the voltage applied to each element produces the sector field of view. A curvilinear phased array has a curved arrangement of the elements. A sector phased array has a flat arrangement of elements.
Which of the following factors affect the focal length of the transducer? A. Element thickness and diameter B. Element frequency and PRF C. Element diameter and frequency D. Element diameter, frequency and thickness
C. Element diameter and frequency Note: Element diameter and frequency are directly related to the focal length of a transducer. The smaller the diameter of the transducer, the shorter the focal length. The lower the frequency, the shorter the focal depth.
Which two factors determine the focal depth of a transducer? A. Propagation speed and element diameter B. Element thickness and diameter C. Element diameter and frequency D. Element thickness and frequency
C. Element diameter and frequency Note: Element diameter and frequency other determining factors for the focal depth of a transducer.
Which of the following describes the type of focusing used in an annular phased array? A. Mechanical focusing using curved elements B. Fixed focus set by the manufacturer C. Focusing at multiple levels across all depths of the image D. Single focal point that is adjustable by the technologist
C. Focusing at multiple levels across all depths of the image Note: annular arrays are composed of five ring-shaped (flat, not curved) elements. By using varied timing of the pulses applied to the circular ring-shaped elements, focusing occurs at multiple levels across all steps of the image. These transducers offer improved lateral resolution across the image.
Quality factor = _________________ _______________________ . A. Dynamic range / bandwidth B. Bandwidth x frequency C. Frequency / bandwidth
C. Frequency / bandwidth Note: Quality factor is directly related to transducer frequency. Increased frequency = increased QF; Decreased frequency = decreased QF. Quality factor is inversely related to bandwidth. Increased bandwidth equals decreased QF; Decreased bandwidth = increased QF.
Which of the following describes a vector array transducer? A. Used for breast imaging and extremity vascular exams. B. Uses mechanical steering C. Has a sector shaped field of view with a flat top. D. Uses only mechanical focusing.
C. Has a sector shaped field of view with a flat top. Note: a vector transducer combines sequenced linear array and phased array techniques to provide a trapezoidal imaging format with a slightly larger footprint than a phased array transducer. The sector image has a flat top with a wider field of view in the near field. Commonly used for echocardiography, abdominal, pelvic, vascular, transcranial, and neonatal brain imaging.
As frequency increases, the axial resolution will A. Remain unchanged B. Depends on how the PE elements are arranged C. Improve D. Be degraded
C. Improve Note: as frequency increases, the axial resolution will improve. As frequency increases, the numerical value associated with axial resolution will decrease.
Which of the following correctly describes how the elements of a sequential linear transducer are excited? A. varies with exam preset selection on the system. B. varies with transmitted frequency of the transducer. C. In a specific order that does not change. D. elements are excited left to right with a 0.0 1ms between each voltage spike
C. In a specific order that does not change. Note: sequential linear transducers excite the elements in a specific order that is set by the manufacturer. This order can vary between manufacturer. It is not related to the type of exam or transmitted frequency.
As the propagation speed of the crystal increases, the frequency of the transducer: A. Decreases B. does not change C. Increases D. Depends on the thickness and diameter of the crystal
C. Increases Note: PE element propagation speed is directly related to transducer frequency.
The acoustic impedance of the matching layer: A. Must be much thinner than the transducer element B. Usually the same material as the damping layer C. Is usually very low D. Is usually much higher than the acoustic gel applied to the patient
C. Is usually very low Note: The matching layer is designed to assist in US penetration into the body. The acoustic impedance should be low to reducing the difference between the impedance of the PE element and patient's skin. This helps to reduce the amount of sound reflection at the transducer/skin boundary. The matching material should be thin BUT the impedance is not described as being "thin".
Which of the following statements is true regarding damage to the matching layer of the transducer? A. The use of more acoustic gel is required to increase the distance between the probe and the skin surface. B. It causes an increase in the intensity of the beam and increased exposure to the patient. C. It causes an increased risk of electrical shock to the patient. D. it is normal for it to develop small holes after extended use.
C. It causes an increased risk of electrical shock to the patient. Note: The matching layer aids in transmission of the sound and protects the patient from electrical shock. The beam intensity can only be adjusted by the power applied to the PE crystal.
A curved array transducer is preferred over a sector array transducer of the same frequency for fetal and abdominal imaging because: A. It offers less beam divergence B. It offers increased penetration C. It has a wider near field D. It produces a lower intensity beam
C. It has a wider near field Note: Curved array transducers have a wider near field than sector and vector arrays. This characteristic allows for visualization of anatomy closest to the transducer face.
What type of probe is preferred for extremity vascular imaging? A. Phased B. Sector C. Linear D. Curved
C. Linear Note: Linear transducers are used for extremity vascular imaging and superficial structures.
Which of the following correctly describes an annular array? A. Improved temporal resolution is a primary advantage of annular arrays B. Produces a sector shaped field of view with a flat top C. Offers excellent lateral resolution D. Produces a trapezoid shaped field of view
C. Offers excellent lateral resolution Note: Annular arrays offer improved lateral resolution but degraded temporal resolution. A sector shaped field of view is produced.
Which of the following correctly describes how a linear array transducer produces a trapezoid field of view? A. PE elements are stimulated by time voltage spikes produced first on the left and moving to the right side of the array. B. PE elements are stimulated by time voltage spikes produced first on the right and moving to the left side of the array. C. PE elements are stimulated by time voltage spikes produced in a convex pattern. D. PE elements are stimulated by time voltage spikes produced in a concave pattern.
C. PE elements are stimulated by time voltage spikes produced in a convex pattern. Note: the timed voltage is produced in a convex shape will create a wider beam. If the voltages are time to stimulate the elements in a concave pattern, a focused beam as produced.
The matching layer is usually made of _____________ . A. Quartz B. Cork C. Plastic D. Air
C. Plastic
Which system component improves lateral resolution? A. Backing material B. Matching layer C. Pulser D. PE element
C. Pulser Note: through timing of the voltage applied to the elements, the pulser electronically focuses the beam to improve lateral resolution. Thinner elements produce higher frequencies with improved axial resolution.
What shape is the image display from a sequential linear transducer? A. Trapezoidal B. Flat top triangle C. Rectangle D. Wedge shaped with curved top
C. Rectangle Note: a linear sequential transducer will produce a rectangular image. Because the elements are fired in sequential order, instead of phased firing, a linear image is the only field of view it can produce. A linear phased array uses electronic steering to produce a trapezoidal image.
Which type of transducer has the smallest field of view in the near field? A. Linear B. Vector C. Sector D. Curvilinear
C. Sector Note: Sector transducers produce a triangle shaped image and the field of view in the near field is very small compared to the other types of transducers.
What changes occur to the ultrasound beam when timed pulses are emitted form left to right from the elements of the phased transducer? A. The beam is steered to the left B. A trapezoidal image is displayed C. The beam is steered to the right D. The focal depth moves closer to the transducer face
C. The beam is steered to the right Note: when timed pulses are emitted from right to left from the elements of the phase transducer, the beam is steered to the left. When timed pulses are emitted from left to right from the elements of the phase transducer, the beam is steered to the right when timed pulses are omitted from the edge elements to the center elements of the phase transducer, focusing occur
When scanning the thyroid, you change from a 5 MHz probe to a 10 MHz probe. Which of the following statements is true? A. There will be decreased attenuation with increased penetration with the 10 MHz probe. B. The 2D imaging depth settings are much more limited in the 5 MHz transducer. C. The spatial resolution will improve with the 10 MHz transducer. D. The reflected waves will be more quickly received and processed by the 10 MHz probe.
C. The spatial resolution will improve with the 10 MHz transducer. Note: The spatial resolution will improve with the 10 MHz transducer. The speed of sound and tissue is constant. Changing the transducer frequency does not change the speed of sound in tissue. There will be increased attenuation with decreased penetration with the 10 MHz pro. The 2D imaging depth settings are much more limited in the 10 MHz transducer.
Which of the following statements is true regarding the differences between a vector array compared to a phased sector array? A. the vector array is mechanically steered while the phased sector array is electronically steered. B. the vector array has a smaller near field, field of view than the phased sector array C. The vector array has a smaller footprint than the phased sector array D. the vector array provides better penetration capabilities than the phase sector array of the same megahertz
C. The vector array has a smaller footprint than the phased sector array Note: the vector array has a larger field of view in the near field and a smaller footprint than the phased sector array. The vector array uses electronic focusing and steering. Frequency is indirectly related to penetration. Penetration depths are the similar for all transducers of the same frequency used to scan the same structures.
As the element diameter decreases, the focal length _________________. A. Will increase B. Will remain unchanged unless the element thickness also changes C. Will decrease D. Will remain unchanged unless the frequency also changes
C. Will decrease Note: Element diameter and frequency are directly related to the focal length of a transducer. Changes in either element characteristic will result in focal depth changes. The smaller the diameter of the transducer the shorter the focal length. The lower the frequency, the shorter the focal depth.
The matching layer for a transducer is usually made of plastic and is approximately ___________________ . A. 1/2 of the probe wavelength in thickness B. 4 times the probe wavelength in diameter C. 1/4 of the probe spatial pulse length in thickness D. 1/4 of the probe wavelength in thickness
D. 1/4 of the probe wavelength in thickness Note: The matching layer for a transducer is usually made of plastic and is approximately 1/4 of the probe wavelength in thickness.
A __________ MHz transducer will have the thinnest element. A. 3 B. 5 C. 7 D. 12
D. 12 Note: Higher frequency probes have thinnest PE elements.
Which of the following transducers would be preferred for breast imaging? A. 15 MHz mechanical B. 15 MHz sector array C. 12 MHz curved array D. 12 MHz linear array
D. 12 MHz linear array Note: the linear array is required due to footprint and field of view shape. The American College of Radiology recommends a 12 MHz frequency or higher for the proper penetration vs resolution in breast imaging. Lower frequency transducer's may be necessary for deep imaging on larger breasts.
Which transducer would provide the lowest attenuation rate? A. 10MHz B. 5MHz C. 8MHz D. 2.5MHz
D. 2.5MHz Note: The higher the frequency, the higher the attenuation rate.
Which of the following transducers would have the best axial resolution? A. 2mm element diameter B. 4mm element thickness C. 4mm element diameter D. 2mm element thickness
D. 2mm element thickness Note: The axial resolution is determined by the spatial pulse length of the wave. AR = 1/2 SPL Shorter spatial pulse lengths result in a lower numerical value of axial resolution. Lower numbers indicate the ability to resolve smaller structures correctly. Elements that are THINNER produce a higher frequency beam. Element (width) diameter does not effect the frequency of the sound produced.
If the fundamental frequency of a transducer is 3 MHz, what is the second harmonic frequency for this transducer? A. 12 MHz B. 1.5 MHz C. 4.5 MHz D. 6 MHz
D. 6 MHz Note: In harmonic imaging, the second harmonic frequency is double the fundamental frequency.
Which of the following transducers will produce the lowest frequency sound waves? A. 2 mm element thickness, 6 mm/us propagation speed of the element. B. 2 mm element thickness, 2 mm/us propagation speed of the element. C. 6 mm element thickness, 6 mm/us propagation speed of the element. D. 6 mm element thickness, 2 mm/us propagation speed of the element.
D. 6 mm element thickness, 2 mm/us propagation speed of the element. Note: Thicker elements with slower propagation speeds produce the lowest frequency waves.
Which of the following is an advantage of the new Capacitive Micromachined Ultrasonic Transducers (CMUT) compared to traditional transducer arrays? A. Produces a lower intensity beam than traditional transducer of the same frequency B. A narrow bandwidth and improved detail resolution C. A coupling gel is not needed for sound transmission D. A wider bandwidth and improved detail resolution
D. A wider bandwidth and improved detail resolution Note: Capacitive Micromachined Ultrasonic Transducers (CMUT) use miniature elements that each contain a fixed component in a flexible membrane. Between the two layers there is an insulating layer and a vacuum sealed gap. The layers between the two parts of each element allow the flexible membrane to vibrate and produce the ultrasound pulse. The advantages over lead zirconate titanate elements include the ability to integrate with electrical circuits, a wider band with, improved detail resolution, allowing for 3-D imaging using to Dee array, and improved cost effectiveness.
What transducer component reduces the "ringing" of the crystal, improves axial resolution, and reduces special pulse length? A. Acoustic lens B. Pulse delays C. Matching layer D. Damping material
D. Damping material Note: Damping produces a shorter spatial pulse length. Axial resolution (longitudinal resolution) is equal to 1/2 spatial pulse length. The shorter the spatial pulse length, the better the axial resolution.
As frequency increases, penetration will A. Increase B. Depends on how the PE elements are arranged C. Remain constant D. Decrease
D. Decrease Note: As frequency increases, penetration will decrease. Inverse relationship.
As beam width increases, how is intensity affected? A. Increases B. No change, except in endocavity probes where intensity increases C. No change, except in endocavity probes where intensity decreases D. Decreases
D. Decreases Note: as the beam Wijdan's, the total intensity is spread across the beam width. The narrowest portion of the beam has the highest intensity and this will also decrease as the beam widens.
If you change from transducer with a 40 mm crystal thickness to one with a 20 mm crystal thickness, the frequency of the sound produced will: A. Decrease by 1/4 B. Increase by a factor of 4 C. Increase by 1/2 D. Double
D. Double Note: iThinner PE crystals produce higher frequency sound. PE crystal thickness is inversely related to the frequency of the sound produced. If the element thickness doubles, the frequency decreases to have the original frequency. If the element thickness is cut in 1/2, the frequency increases by a factor of two.
What changes occur to the ultrasound beam when timed pulses are emitted from the edge elements to the center elements of the phase transducer? A. The beam is steered to the right B. The beam is steered to the left C. A trapezoidal image is displayed D. Electronic focusing occurs
D. Electronic focusing occurs Note: When timed pulses are emitted from right to left from the elements of the phase transducer, the beam is steered to the left. When timed pulses are emitted from left to right from the elements of the phased transducer, the beam is steered to the right. When timed pulses are emitted from the edge elements to the center elements of the best transducer, focusing occurs.
Which of the following system functions allows the linear transducer to offer a trapezoidal field of view? A. Mechanical focusing B. Apodization C. Electronic focusing D. Electronic steering
D. Electronic steering Note: by using timed pulses, the beam can be steered outward on both lateral aspects of the probe to produce a trapezoidal image.
The narrowest point of the ultrasound beam is called: A. Fresnel zone B. Fraunhofer zone C. Focal depth D. Focal zone
D. Focal zone Note: The narrowest point of the ultrasound beam is called the focal zone. Fresnel zone = near zone; Fraunhofer zone = far zone
Which of the following is true regarding the Curie point of a piezoelectric element? A. A quartz transducer Crystal is heated above the Kure point to initiate the PE effect of the Crystal. B. If the active PE crystal is heated to this temperature, the intensity of the being produced will increase. C. If the active PE Crystal is heated to this temperature, the frequency of the Crystal will increase. D. If the active PE crystal is heated to this temperature, the element will lose its piezoelectric properties.
D. If the active PE crystal is heated to this temperature, the element will lose its piezoelectric properties. Note: Certain ceramic elements can be polarized by heating them above their Curie point. If the active element is heated again, it will lose its piezoelectric properties.
Lowering the transducer frequency will: A. Decrease the propagation speed B. Increase the sector size C. Improve temporal resolution D. Increase the mechanical index
D. Increase the mechanical index Note: low transducer frequency will cause an increase in the mechanical index and the rest of cavitation. It will have no effect on the propagation speed, sector size or temporal resolution. It does reduce axial resolution and improve sound penetration.
The coupling gel used for ultrasound exams provides the same function as white transducer component? A. Damping layer B. PE element C. Backing layer D. Matching layer
D. Matching layer Note: Gel provides an additional matching layer. It aids in reducing the acoustic impedance mismatch at the skin, which leads to reduced reflection and improved sound transmission at the skin barrier.
Linear phased arrays utilize what type of focusing? A. Mechanical only B. Electronic only C. Elevational only D. Mechanical and electronic
D. Mechanical and electronic Note: linear phased arrays normally use a mechanical lens to set the elevation focus (focusing along the shore axis of the beam), along with alternating the electronic timing of the firing of groups of elements to accomplish focusing along the width of the beam.
Mirrors and lenses can be used to ________________. A. Increase the PRF of the transducer B. Improve sound transmission into the body C. Electronically focus the US beam D. Mechanically focus the US beam
D. Mechanically focus the US beam Note: Mirrors and lenses are used to mechanically focus the US beam. Transmit and receive focusing are types of electronic focusing.
Which of the following correctly describes a dedicated continuous wave Doppler transducer? A. Cork or epoxy for backing material B. Low quality factor C. Very low duty factor D. Narrow bandwidth
D. Narrow bandwidth Note: CW transducers have no backing material because the sound is not pulsed. This leads to a narrow bandwidth. The duty factor for CW ultrasound is 1 or 100%. CW transducers have a high quality factor (purity of the beam) because they operate continuously at the center frequency.
Which of the following applies to therapeutic ultrasound transducers? A. Frequencies >15MHz used due to the increased potential for focused cavitation B. Low Q factor C. Backing material at least 2X thickness of that used in imaging transducers D. Narrow bandwidth
D. Narrow bandwidth Note: therapeutic probes have a high Q factor and narrow band with due to the continuous production of sound at the main frequency. No backing material is used in the construction of therapeutic transducers. Standard frequencies used are between 0.7 and 3 MHz for increased thermal effects.
The choice of frequency for an exam is dependent on the _______________ needed for an optimal exam. A. type of transducer array B. Number of images C. Size of the transducer footprint D. Penetration and resolution
D. Penetration and resolution Note: the choice of frequency for an exam is dependent on the penetration and resolution needed for an optimal exam. Ultimately you want the best resolution obtained with the penetration needed for a complete exam.
What type of probe is preferred for cardiac imaging? A. Phased curved B. Linear sequential C. curved sequential D. Phased sector
D. Phased Sector Note: The phased sector array with a small footprint and high frame rate is preferred for cardiac structures.
Intensity = ____________________ . A. Density x Propagation Speed B. Frequency x Wavelength C. Power x Beam area D. Power / Beam area
D. Power / Beam area Note: Intensity (mW/mm)^2 = Power (mW) / Beam Area (mm^2)
The operating frequency of the transducer is also called the: A. Piezoelectric frequency B. Pulser frequency C. Vibrational frequency D. Resonance frequency
D. Resonance frequency Note: The operating frequency of the transducer is also called the resonance frequency.
Which of the following transducers uses a beam former? A. Sequential linear array B. Mechanical transducer C. Sequential curved linear array D. Sector phased array
D. Sector phased array Note: The beam former adjust the timing of the pulses to focus and steer the US beam and phased array transducers.
Materials used for the matching layer of a transducer must have an impedance between impedance levels of the ____________ . A. PE element and damping layer B. Skin and acoustic gel C. Acoustic gel and air D. Skin and PE element
D. Skin and PE element Note: the impedance of the matching layer of a transducer is designed to be between the impedance of the skin and PE element. This will minimize the amount of sound reflection that occurs at these boundaries.
Which of the following can be done to reduce the beam divergence? A. Switch to a lower frequency transducer B. Remove an acoustic lens in front of the PE element C. Deactivate dynamic focusing D. Switch to a higher frequency transducer
D. Switch to a higher frequency transducer Note: Lower frequency transducers have more beam divergence and wider beams. Dynamic focusing and adding a lens to the face of the transducer will reduce beam divergence.
Which of the following describes the primary advantage of a 1.5D array over a 1D array? A. The 1.5D array eliminates the need for a stand-off pad for superficial imaging. B. The 1.5D array allows for 3D imaging while the 1D array does not C. The 1.5D array can produce a trapezoid field of view while the 1D array can only produce a rectangular field of view. D. The 1.5D array allows for variable elevation focus while the 1D array has a fixed elevation focus.
D. The 1.5D array allows for variable elevation focus while the 1D array has a fixed elevation focus. Note: A 1D array has elements aligned along the long axis of the transducer. Electronic focusing is used to focus the beam on the long axis. An acoustic lens provides a fixed focus along the short access of the beam (elevation focus). A 1.5D array has elements aligned along the long axis of the transducer but the elements are etched to create groups of the 3 or 8 elements that allow for variable focusing along the short access of the beam. 2D arrays have not yet been developed due to limitations caused by the necessary size of the transducer and electrical wiring.
____________ determines the acoustic power of the transducer. A. The diameter of the matching layer B. The frequency of the transducer C. The size of the PE element D. The magnitude of the voltage spike
D. The magnitude of the voltage spike Note: The magnitude of the voltage spike from the pulser determines the acoustic power of the transducer.
The main advantage of a curvilinear transducer over a vector transducer is: A. The smaller footprint B. The ability to perform CW Doppler with 2D imaging C. The ability to scan at increased frame rates D. The wider near field
D. The wider near field Note: Curvilinear transducers have a wider near field which is very helpful for fetal evaluations. This is the main advantage of a curvilinear array transducer over a vector array transducer. A curvilinear transducer has a larger footprint than the vector transducer.
An 8MHz transducer would have elements that are ________________ than a 4MHz transducer. A. Thicker B. Stiffer C. More dense D. Thinner
D. Thinner Note: The thicker the element, the lower the frequency. An 8MHz transducer would have thinner elements than a 4MHz transducer.
Capacitive Micromachined Ultrasonic Transducer's (CMUT): A. Are no longer used in the field B. Cannot be used to perform 3D imaging C. Use large elements with tiny air pockets in each one D. Use miniature elements that each contain a fixed component and a flexible membrane.
D. Use miniature elements that each contain a fixed component and a flexible membrane. Note: Capacitive Micromachined Ultrasonic Transducers (CMUT) use miniature elements that each contain a fixed component and a flexible membrane. Between the two layers there is an insulating layer and a vacuum sealed gap. The layers between the two parts of each element allow the flexible membrane to vibrate and produce the ultrasound pulse. The advantages over lead zirconate titanate elements include the ability to integrate with electrical circuits, a wider bandwidth, improved detail resolution, allowing for 3-D imaging using 2D array, and improved cost effectiveness.
D. The frame rate will increase for the image. Note: as the number of scan lines decreases, the time to produce a full field of scan lines decreases equals increase in the frame (production) rate. The faster the frames are produced, the faster the real time image information is replaced. High frame rates reduce/eliminate image "drag" during real time scanning with which improves the temporal resolution. Fewer scan lines will degrade spatial resolution. Beam thickness determines elevational resolution.
For each transducer shown, there is an ultrasound image produced. Which of the following statements is true regarding the image produced by the transducer on the left? A. The image will show degraded temporal resolution. B. The image will show improved spatial resolution. C. The image will show degraded elevational resolution. D. The frame rate will increase for the image.
A. Electrical cord
What is the name of the transducer component labeled letter A? A. Electrical cord B. PE element C. Matching layer D. Focusing lens
A. Housing
What is the name of the transducer component labeled letter B? A. Housing B. Damping layer C. Masking layer D. A and B
B. PE element
What is the name of the transducer component labeled letter C? A. Matching layer B. PE element C. Focusing lens D. Damping layer
C. Electrical wiring
What is the name of the transducer component labeled letter D? A. Damping layer B. Matching layer C. Electrical wiring D. PE element
B. Matching layer Note: Positioned in front of the PZT at the face of the transducer. The matching layer: increases the efficiency of sound energy transfer between the active element and the body, and protects the active element. The matching layer is 1/4 wavelength thick and appears as the purple material.
What is the name of the transducer component labeled letter F? A. Focusing lens B. Matching layer C. Housing material D. Damping layer
A. Damping layer Note: also called backing material. Bonded to the back of the active element, it reduces the ringing of the PZT. Backing material is commonly made of epoxy resin impregnated with tungsten filaments. When an electrical spike excites the PZT, the backing material restricts the extent of PZT deformation. The emitted samples is dampened; thus, it is short and duration and length. Crystal damping enhances axial resolution. The damping layer is blue.
What is the name of the transducer component labeled letter G? A. Damping layer B. PE element C. Matching layer D. Insulator
A. Sector phased array Note: dissector phased array uses electronic steering to create the sector shaped image. It has the smallest near Field of all transducers.
What type of transducer produced the image? A. Sector phased array B. Linear sequential array C. Curved sequential array D. Vector phased array
D. Vector phased array Note: Vector array is a type of linear phased array. It combines a sequenced linear array and phased array techniques to provide a trapezoidal imaging format. The probe has a slightly smaller footprint than a sector array transducer. The vector transducer produces a wedge shaped image with a flat top and a wider field of view in the near field than sector array.
What type of transducer produced the image? A. Sector phased array B. Linear sequential array C. Curved sequential array D. Vector phased array
D. Curved phased array Note: The curved top of the image and wide far field. This indicates a curved phased array.
What type of transducer produced the image? A. Vector array B. Sector phased array C. Linear phased array D. Curved phased array
B. Red The Fraunhofer zone is another term for the far field. The Fresnel zone is another term for the near zone.
Which color of line indicates the Fraunhofer zone of the US beam? A. Purple B. Red C Yellow D. Royal blue
A. Royal blue Note: the Fraunhofer zone is another term for the far field. The Fresnel zone is another term for the near zone. The yellow line indicates the focal point and the purple dotted lines indicate the focal zone.
Which color of line indicates the Fresnel zone of the US beam? A. Royal blue B. Red C. Purple D. Yellow