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DMS 200 Test 3
Physics
| Question | Answer |
|---|---|
| Real time imaging? | The production of motion pictures of the anatomy. Consists of a series of frames or pics displayed in a rapid sequence. |
| Motivation for real time scanning | Overcome the shortcomings of B scanning, imaging moving structures and to peform doppler ultrasound |
| The goal of real time scanning | Produce pictures or frames as rapidly as possible, in order to faithfully image moving structures maintain temporal resolution |
| Duplex scanning | 2D also allowed us to be able to scan an anatomical image while also doing another modality on another screen We can add PW or CW spectral traces whle we do 2D; ALso called two modality imaging |
| Temporal resolution? | Temporal resolution is resolution pertaining to time and motion. Ability to accurately locate the positions of moving structures at instants in time. |
| The greater the number of frames created per second the better the? | temporal resolution |
| Frame rate? | The number of frames or images created each second |
| Frame rate equation? | Frame rate (Hz) = 1/Frame time (sec) |
| Frame time equation? | Frame time (sec) = 1/frame rate (Hz) |
| Multiple lines in a frame equation? | Frame time (sec) = time (sec)/line/line/frame |
| Each frame of an ultrasound image is made up of individual____? | scan lines |
| A single scan line (Bmode) is created by ____ pulse from the transducer. | single |
| If there are 100 lines in an image, then ____ pulses are required to the picture. | 100 |
| Scan lines are affected by? | The PRF and the width of the display |
| Frame/sec equation? | Frames/second (sec) = prop. speed (m/s)/ lpf x depth (cm) |
| The maximum frame rate will be less t hen or equal to 77, 000 or ______ | equal to |
| Liens of site and _____ are the same thing. | scan lines |
| Difficulties of two-dimensional imaging. | 1) Ultrasound only travels in a straight line 2) Narrow beam widths are required for high-quality images with good lateral resolution 3) To overcome these difficulties, two dimensional image is constricted from multiple US pulses. |
| Temporal resolution? | Resolution pertaining to time and motion. Defines the ability to accurately locate the position of moving structures at particular instances in time. > the # of frames/second the better the temporal resolution. |
| PRF and frame rate? | -Each frame is made of scan lines -Each focus on each scan line in each frame requires a pulse -The PRF required is determined by number of focuses, lpf, and frame rate, infact these three multiplied together = PRF |
| If frame rate increases PRF? | increases, direct relationship |
| To increase frame rate? | -Increase PRF - Decrease depth - Narrow sector, color box length or width -Decrease line density - Decrease # of foci -Decrease color packet size (pulses/line) |
| By increasing the depth of your image, what happens to the frame rate? | Decreases |
| Give the equation used to calculate frame rate. | Frame (Hz)= Propagation speed/2(depth (cm) x lpf) |
| What is the typical frame rate? | Typically 30 frames per second |
| The greater the number of frame created per second, the ______ the temporal resolution. | Better |
| B scan? | The transducer is attached to the US system by an articulated arm. A memory or scan converter is required to do B scanning. |
| Advantages of Bscan: | -Large images - Good detail resolution |
| Disadvantages of Bscan: | Long time to complete the scan. Patient movement destroys image (poor temporal resolution) cannot image moving structures, and requires a large acoustic window. |
| Mechanical scanning contains one or more active element (disc shaped) that physically ____ or ______ through a pathway. | 1) moved 2) rotated |
| True or False: Mechanical scanning produces pictuers that are similar in shape to linear phased array images. | True: Mechanical scanning and linear phased arrays create sector-shaped images. |
| True or false: Many active elements fire at almost the same time in a mechanical scanner. | False. There is only one active element in a mechanical scanner. |
| True or false: Many active elements fire at almost the same time in a phased array scanner. | True. Many active elements fire at almost the same time in a phased array scanner. |
| Which transducer is best described as mechanically steered and fixed, single focused? | A mechanical transducer steers the sound beam mechanically. The sound beam has a single fixed focuse. |
| Which of the following is best described as mechanically steered and multi-focus? | An annular phased array because those transducers steer the sound beams mechanically. They are, however, multifocused. BTW..no such thing as an annular sequential. |
| Which of the following transducers creates a rectangular shaped image? | A linear sequential array transducer..all of the active elements are fired to create each sound pulse. |
| A linear sequential array transducer has 128 crystals. How many of these crystals are fired to create a single sound beam? | With linear phased array transducers all of the active elements are fired to create each sound pulse. |
| A linear sequential array transducer has 128 crystals. How many of these crystals are fired to create a single sound beam? | With linear sequential array transducers, a small group of active elements are fired to create each sound pulse. |
| In a linear phased array, what is the firing pattern that steers a beam up or down? | The firing pattern that steers a beam up or down is called the electric slope. |
| In linear phased arrays, what is the fire pattern that focuses a sound beam? | The firing pattern that focuses a sound beam is electronic curvature. |
| True or False: There are large time delays in the firing pattern of a linear phased array transducer. | False. Thre are tiny time delays in the firing pattern of a linear phased array transducer. |
| True or False: A machine that displays A mode and two dimensional images is called duplex scanner. | False. A machine that displays doppler and two-dimensional images is called a duplex scanner. |
| True of False: The acousti impedance of the matching layer is approximately the same as the acoustic impedance of skin. | False. The impedance of the matching layer is greater than the impedance of the skin. |
| Imaging transducers are usually of high rather than low bandwidth. | True. Imaging transducers are high or wide bandwidth. |
| A very high Q factor transducer is used more often in diagnostic imaging transducer thatn a low Q factor. | False. Imaging transducers are low Q. |
| A pulse with a long pulse duration is likely to have a narrow bandwidth. | True. Longer events tend to have a narrow bandwidth. Shorter events tend to have wider bandwidth. |
| The damping material in a transducer increases the sensitivity. | False. Damping decreases sensitivity. |
| The damping material in a transducer decreases the pulse durtion. | True |
| The damping material in a transducer increases the pulse length. | False, damping shortens pulse length. |
| The damping material in a transducer improves the system's lateral resolution. | False, Damping does not affect lateral resolution |
| The damping material in a transducer impoves the system's longitudinal resolution. | True. |
| The damping material in a transducer decreases the quality factor. | True. Damping decreases Q factor. |
| The damping material in a transducer decreases the bandwidth. | False. Damping increases bandwidth. |
| If the frequency of the electrical excitation voltage of a pulsed wave transducer is 6 MHz, then the operating frequency of the transducer is 6 MHz. | False. With pulsed wave transducers, the frequency of sound is not determined by the electrical signal. |
| If the PRF of a transducer is incrased, then the frequency of sound produced by the transducer remains the same. | True. Frequency and PRF are not related. |
| The diameter of the active element of a transducer helps to determine the frequency of the sound produced by the transducer. | False. The diameter of the active element does not determine the frequency of sound created by the transducer. |
| If the frequency of the electrical excitation voltage of a continuous wave transducer is 5 Mhz, thent he operating frequency of the transducer is 6 MHz. | True. The frequency of the electrical voltage and the frequency of the sound beam are indentical with CW transducers. |
| Two PZT cryst are made from the same material. The thicker crystal will make a CW transducer with a lower frequency. | False. With CW transducer, active element thickness does nt determine the sound beam's frequency. |
| The normal propagation speed in PZT material is about 3 to 5 times greater than that in soft tissue. | True. Sound travels much faster in PZT than in soft tissue. |
| The impedance of a transducer active element 1900000 Rayls, and the impedance of the skin 1400000 Rayls. What is an acceptable impedance for the matching layer? | The impedance of the matching layer is between that of the active element and the skin. |
| Which of the following crystals will produce sound with the lowest frequency? | Sound with the lowest frequency is produced by a thick active element in the which sound travels slowly. |
| Which type of transducer has a greater Q factor: therapeutic or imaging? | Therapeutic transducers have a higher Q factor than imaging transducers. |
| Which type of transducer has more backing material: therapeutic or imaging? | Imaging transducers use more backing material than therapeutic transducers. |
| In an imaging transducer, what is the purpose of attaching the backing material to the PZT? | The purpose of the backing material in imaging transducers is to improve image quality. |
| A pulsed wave transducer has a resonant frequency of 5 MHz. The lowest frequency in the pulse is 2 Mhz and highest is 8MHz. What is the bandwidth? | Bandwidth is the range of frequencies found in a pulse, In this case 8 MHz-2Mhz= 6MHz |
| For the transducer described in the last question, what is the main frequency? | The resonant, main, or center frequency, also called operating frequency is 5 Mhz. |
| For the same transducer in described in the last questions, what is the Q factor? | Q factor is resosant frequency divided by the bandwidth, 5MHz/6 Mhz. Bandwidth has not units. No calculations are needed to answer as choice A is only unitless answer with a value less than 1. |
Created by:
ashcamp2180