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lecturee 6
lecture 6
| Question | Answer |
|---|---|
| the four main parts of the ultrasound | Beam former, signal processor, image processor, and display |
| the beam former has 6 components first one | pulser |
| the beam former has 6 components second | channels |
| the beam former has 6 components third | transmit/receive switch |
| the beam former has 6 components fourth | amplifier |
| the beam former has 6 components fifth | digitizer (ADC) |
| the beam former has 6 components sixth | Summer (Adder) |
| the signal processor has 3 components first of | filter (rejection) |
| the signal processor has 3 components second | demodulation (detection) |
| the signal processor has 3 components third | compression |
| the image processor has 5 components first | scan converter |
| the image processor has 5 components second | preprocessor |
| the image processor has 5 components third | image memory |
| the image processor has 5 components fourth | post processor |
| the image processor has 5 components fifth | digital-to-analog converter (DAC) |
| What does the pulser do? | The pulser produces electronic voltage pulses that are sent to the transducer. |
| The transducer takes those electrical pulses and converts them into | ultrasound |
| The pulser also determines the | amplitude/intensity of the ultrasound being transmitted. |
| Gain | Increases amplification of the received echoes Does NOT increase the ultrasound sent into the patient |
| Power | Increases the strength of the original ultrasound pulse DOES increase the ultrasound sent into the patient |
| Increasing output power: | ➡️ increases transmitted ultrasound strength ➡️ makes image brighter ➡️ broadens transducer bandwidth |
| What determines PRF? | The frequency of pulsing, or the number of pulses sent per second. |
| What happens to PRF when imaging depth increases? | PRF decreases because the machine needs more time for deeper echoes to return. |
| What happens to PRF when depth decreases? | PRF increases because echoes return sooner. |
| What does the POWER control change? | It changes the amplitude/strength of the original ultrasound being transmitted. |
| What is the difference between power and gain? | Power: increases the strength of the ultrasound being sent into the body. Gain: amplifies the echoes that have already returned. |
| Which should generally be increased first: power or gain? | Gain/TGC should be maximized first. Power should be increased only as a last resort. |
| : What else happens when output power is increased? | The image becomes brighter and the transducer's bandwidth broadens. |
| Why is PRF limited by depth? | Because the machine must wait long enough for echoes from the previous pulse to return before sending another pulse. |
| What happens if a second pulse is sent before echoes from the first pulse return? | The machine may not know which pulse an echo came from, producing erroneous information. |
| What is range ambiguity artifact? | An artifact caused when PRF is too high and echoes from different pulses become confused. |
| What is another name for range ambiguity artifact? | High PRF error |
| n which type of imaging can range ambiguity occur according to the lecture? | Doppler imaging |
| Why does the pulser create tiny time delays? | For electronic focusing and steering and for certain apodization and variable-aperture functions. |
| What is coded excitation? | Using a complex pattern of cycles, pauses, and sometimes inverted cycles to create an ultrasound pulse. |
| What is a Barker Code? | A specific coded pattern of ultrasound cycles used in coded excitation. |
| What does a matched filter do to returning coded pulses? | It simplifies the longer coded pulse into a shorter, higher-amplitude pulse. |
| What are the benefits of coded excitation? | Better signal-to-noise ratio Cleaner/sharper images Helps reduce confusion about which echoes came from which pulse |
| What is a channel? | |
| Why does each transducer element need its own channel? | Because each element may receive slightly different information and needs its own transmission and reception pathway. |
| Can a machine have more channels than transducer elements? | No. The total number of channels cannot exceed the total number of transducer elements. |
| Why does the ultrasound machine need a transmit/receive switch? | to protect the receiver from the very high voltages used during transmission. |
| What happens to the receiver during transmission? | it is turned off |
| What happens during reception? | The receiving function is turned ON to detect the weak returning echoes. |
| What are two other names for amplification? | Receiver gain and overall gain. |
| What unit is used to express amplification? | Decibels (dB). |
| What does overall gain do? | Amplifies the tiny voltages from returning echoes. |
| What is TGC | Time-Gain Compensation, which allows echoes from different depths to be amplified by different amounts. |
| Why do deeper echoes usually need more gain? | They have experienced more attenuation. |
| What is another name for TGC? | Depth-Gain Compensation (DGC). |
| What is LGC? | Lateral Gain Control, which allows gain to be increased on one side of the image while leaving the other side alone. |
| What is ADC? | Analog-to-Digital Conversion. |
| What happens during digitization? | The electrical voltage signal is converted into digital information/numbers. |
| When do reception delays for focusing and steering occur? | : Just after digitization. |
| What does the summer/adder do? | Combines all the echo information received for each pulse into information representing an entire scan line. |
| What are the 3 major functions of the signal processor? | Filtering Demodulation/detection Compression |
| What does a bandpass filter reject? | Frequencies outside the transducer's known bandwidth. |
| What does a threshold filter reject? | Echoes with amplitudes/intensities below a predetermined level. |
| bandpass is equal to | frequency |
| threshold is equal to | amplitude |
| What are harmonics? | Waves whose frequencies are multiples of the transducer's operating frequency. |
| What is the second harmonic? | 2 × the operating frequency. |
| What produces harmonics? | Nonlinear propagation as sound travels through a medium. |
| What does the tissue harmonic imaging filter do? | It looks for harmonic echoes, typically the second harmonic, and rejects echoes at the original operating frequency. |
| Why can tissue harmonic imaging improve resolution? | The harmonic echoes have a higher frequency, which provides better resolution. |
| What is another name for demodulation? | detection |
| What does demodulation convert? | RF format to video format |
| What are the two processes of demodulation? | rectification and smoothing |
| What does rectification do? | Converts negative voltage into positive voltage. |
| What is another name for smoothing? | enveloping |
| Can the operator control demodulation? | no it occurs automatically |
| What is dynamic range? | the ratio between the largest and smallest amplitudes/intensities |
| what happens when dynamic range is too large | the machine ha difficulty processing it |
| what does compression do | reduces the dynamic range to a level the machine can handle |
| what is the effect of compression on the image | it allows more shades of gray to appear |
| what happens if there isn't enough compression | the image appears mostly black and white with very few intermediate shades |
| If the original dynamic range is 80 dB and compression is 50 dB, what is the new range? | 30 db |
| what is the job of the image processor | to manipulate the processed data so it can become an image |
| what is the image processor sometimes called on newer machines | image former |
| what does the scan converter do | combines scan lines into one complete image called a frame |
| What is frame rate? | The number of frames displayed per second. |
| What unit is frame rate measured in? | Hertz (Hz) |
| What is preprocessing? | Image manipulation that occurs before the image is stored in memory/frozen. |
| Give examples of preprocessing. | Gain, TGC, focusing, compression, depth adjustment, pixel interpolation, persistence, panoramic imaging, and other machine functions. |
| What is post-processing? | Manipulation performed after the image has been stored/frozen |
| Give examples of post-processing. | Caliper measurements, color maps, text annotation, grayscale mapping, B-color, and read zoom. |
| What does CINE allow you to do? | Review several seconds of previously stored image information. |
| What is a pixel? | A picture element — one individual dot/element of the image. |
| What is a common ultrasound pixel matrix? | 512 x 512 |
| How many pixels are in a 512 × 512 matrix? | 262,144 pixels. |
| How many bits are usually used to describe each pixel? | 8 bits. |
| How many shades of gray can 8 bits represent? | 256 shades. |
| How many bits are in one byte? | 8 bits. |
| What is grayscale mapping? | A post-processing feature that changes how the 256 shades of gray are displayed without changing the actual image data. |
| What is B-color? | a post processing feature that changes grayscale pixels |
| does b-color add new information | no , it only changes the appearance of existing information |
| is B-color the same as color doppler | no |
| what is B-flow | A pre-processing feature that allows blood flow to be seen in real time as part of the grayscale image. |
| How do red blood cells appear with B-flow? | As moving gray dots. |
| When can B-flow be particularly useful? | Small, deep, or tortuous vessels where color Doppler may not be sensitive enough. |
| What does edge enhancement do? | Sharpens the borders/edges of structures. |
| How does edge enhancement make borders more obvious? | It makes pixels on one side of a border slightly brighter and pixels on the other side slightly darker. |
| Why is pixel interpolation used in sector images? | Scan lines become farther apart at greater depths, leaving gaps. |
| What does pixel interpolation add? | Dummy pixels between actual pixels. |
| Does pixel interpolation actually improve lateral resolution? | No |
| what does panoramic imaging do ? | makes the image wider by combining images obtained as the transducer is moved laterally |
| In what direction must the transducer be moved for panoramic imaging? | Laterally, so the images remain in the same scan plane. |
| What is spatial compounding? | Creating multiple scan lines that reach the same tissue from different angles. |
| What happens to lateral resolution with spatial compounding? | improves |
| What happens to frame rate with spatial compounding? | decreases |
| what does persistence do? | averages several frames together |
| what is one benefit of persistance | Reduces random speckle/noise and improves image cleanliness and contrast resolution. |
| what is the disadvantage of persistance | it decreases frame rate |
| what is read zoom? | A post-processing feature that enlarges an already-created image. |
| Does read zoom improve the original spatial resolution? | No |
| what is write zoom? | A pre-processing feature that tells the machine to process only a selected area. |
| Does write zoom improve spatial resolution? | Yes |
| Does write zoom improve temporal resolution? | Yes, because the machine doesn't have to process the entire image. |
| What is temporal resolution? | The ability to capture changes/motion over time. |
| What determines temporal resolution in 2-D imaging? | Frame Rate |
| Approximately what is a good 2-D frame rate according to the lecture? | About 30 Hz. |
| What does M-mode display? | One single scan line displayed across time. |
| What is M-mode useful for? | Showing motion along a single scan line. |
| How do fast movements appear in M-mode? | More vertical |
| How do slow movements appear in M-mode? | More diagonal. |
| How can you improve frame rate by changing line density? | Decrease line density → fewer scan lines → higher frame rate |
| How does decreasing depth affect frame rate? | Increases frame rate because PRF can increase. |
| How does write zoom affect frame rate? | Increases frame rate because the machine only processes the selected area. |
| How does decreasing sector width affect frame rate? | Increases frame rate because fewer scan lines need to be processed. |
| How does decreasing the number of focal zones affect frame rate? | Increases frame rate because fewer focal zones require less processing time. |
| How does decreasing persistence affect frame rate? | Increases frame rate because fewer frames are averaged. |
| What does the "A" in A-mode stand for? | Amplitude. |
| What does A-mode display? | Echo amplitude/intensity along a single scan line. |
| Who commonly uses A-mode according to the lecture? | Ophthalmologists, particularly when scanning the eye. |
| What does elastography show? | The relative stiffness or elasticity of tissues. |
| What is elastography compared to? | The sonographic equivalent of palpation. |
| How does elastography create its information? | The transducer applies a small push, and tissue responses are represented by colors over the grayscale image. |
| What is the basic pathway an ultrasound signal follows through the machine? | Pulser → Transducer → T/R switch → Amplification → ADC → Reception delays → Summer → Filtering → Demodulation → Compression → Scan converter → Image processing → Memory → Display |
| What happens during transmission? | The pulser sends electrical voltage to the transducer, which converts it into ultrasound. |
| What happens during reception? | The transducer receives returning echoes and converts them back into electrical signals. |
| Beam former: | Creates/organizes the ultrasound beam and returning echoes. |
| Signal processor | Processes and cleans the electrical signal. |
| Image processor: | Turns the processed information into an image. |
| What can n represent in ultrasound? | In the scan-converter discussion, n can refer to the number of pulses needed per scan line, especially when multiple focal zones are used. |
| What happens when you increase the number of focal zones? | More pulses are required to create each scan line, so frame rate decreases. |
| What happens to frame rate when you increase the number of scan lines? | Frame rate decreases. |
| What happens when line density decreases? | Frame rate ↑ but Lateral resolution ↓ |
| What is the tradeoff with spatial compounding? | Lateral resolution ↑ but Frame rate ↓ |
| What is the tradeoff with persistence? | Image smoothness/contrast resolution ↑ but Frame rate ↓ |
| Why does write zoom improve frame rate AND spatial resolution? | Because the machine processes a smaller area using the available pixels/scan lines more efficiently. |
| What should the frequency of the pulser's voltage be reasonably close to? | The natural/resonating frequency of the transducer elements. |
| What is bandwidth? | The range of frequencies a transducer can produce/receive. |
| What does variable aperture allow the system to change? | The number of transducer elements being used, depending on imaging conditions/depth. |
| What is apodization used for? | It changes the relative amplitudes/voltages applied to elements to help control the ultrasound beam. |
| When can the machine apply focusing delays? | During transmission and reception. and Transmission focusing organizes the outgoing beam; reception focusing organizes returning echoes. |
| What is dynamic aperture? | Changing the number of active elements as imaging depth changes. |
| What is a scan line? | Information obtained along one ultrasound beam/path. |
| What is a frame? | A complete image made from multiple scan lines. |
| What does increasing line density do? | More scan lines per frame → better spatial detail, but lower frame rate. |
| Does having more pixels automatically mean better actual ultrasound information? | No. The image can contain interpolated/dummy pixels that don't represent new information. |
| What is bistable imaging? | An image with only two display levels: black or white. Ultrasound normally uses grayscale, which provides many shades between black and white. |
| CRT | Older Bulky Produces more heat Less energy efficient |
| LCD | Flat More energy efficient Common on modern machines |
| PACS | Picture Archiving and Communications System |
| DICOM | Digital Imaging and Communications in Medicine |
| POWER | transmitted ultrasound |
| Gain | received echoes |
| depth increases | Pulse repetition frequency goes down |
| Depth decreases | Pulse repetition frequency goes up |
| pulse repetition frequency too high | echoes can be assigned to the wrong pulse |
| pre | before storage/ freeze |
| post | after storage/ freeze |
| read zoom | enlarge existing image |
| write zoom | create a higher resolution image of selected area |
| spatial | separate structures |
| contrast | distinguish different shades/intensities |
| temporal | see motion |
| Put the components in order based on their function. | Pulser → Amplifier → ADC → Summer → Demodulation → Scan Converter → Post-processing → DAC |
| pulser | starts the ultrasound |
| amplifier | makes the returning electrical signals stronger |
| ADC | analog to digital converter changes analog information into digital information. |
| summer | puts the echo information together to prepare a scan line. |
| demodulation | converts the signal into a form that can be used for image formation. |
| scan converter | puts scan lines together to make the image/frame |
| post processing | allows manipulation after the image is stored /frozen |
| DAC | digital to analog converter |
| Which components are part of the beam former? | Pulser + Channels + Summer |
| What are the three major functions of the signal processor? | Filtering + Demodulation + Compression |
| Which functions are part of the image processor? | Scan converter + Image memory + Post-processing |
| What does CRT stand for? | Cathode Ray Tube It's the older type of monitor |
| deep structure | slow prf |
| shallow structure | fast pfr |
| transmit power | changes the strength of the ultrasound leaving the transducer |
| Gain | amplifies the returning echoes after they come back |
| Why are pulse delays necessary? | Electronic focusing Electronic steering |
| Which beam-former component prevents the strong transmitted pulse from being "heard" by the receiver? | Transmit/Receive switch 🧠 Why? The transmitted electrical signal is extremely strong compared with the tiny returning echo. The receiver needs protection. |
| Digital | Information represented in numbers/code for a computer. |
| Analog | Live streams of waveforms, such as electrical or sound signals. |
| Which beam-former component combines the echo information from each pulse and prepares the scan line? | Summer / Adder |
| What does a bandpass filter do? | It accepts frequencies within the designated bandwidth and rejects unwanted frequencies outside that range. It occurs in the: Signal processor |
| Demodulation | Another name: Detection Two steps: Rectification Smoothing / Enveloping |
| What does the machine do with enormous dynamic ranges? | Compression It reduces the dynamic range to something the machine can process and display. |
| PRF and PRP have an | inverse/reciprocal relationship |
| What formula does your homework give for PRF when maximum depth is known? | PRF = 77,000 ÷ maximum depth (cm) |
| What is coded excitation? | Creating longer-than-normal pulses made of sequences of cycles and partial cycles. These sequences are called coded pulses or Barker codes |
| What is the benefit of coded excitation? | It reduces background noise and improves the signal-to-noise ratio (SNR). |
| Which beam-former component prevents the strong transmitted pulse from being "heard" by the transducer/receiver? | Transmit/receive switch. |
| What is digital data? | Information represented in numerical or code form for a computer. |
Created by:
lupita25