Imaging Modalities and Ultrasound Imaging Flashcards
Digital systems are classified into 2 types:
-Computerized/computed radiography (CR)
-Digital radiography (DR)
List the factors that the quality of digital images is related to.
-Resolution
-Image noise
-Pixel size and number
-Field of view
Digital image is recorded as a combination of rows and columns known as ___.
Matrix
Smallest component of matrix is the ___.
Pixel (picture element)
Location of the pixel within the image matrix corresponds to ___.
An area within a 3-dimensional volume of tissue referred to as voxel
Each pixel represents ___.
-Different shades of gray
The number of shades of gray is determined by the grayscale bit depth, which can range from ___ bits.
8-32 bits
___ is related to the size of the pixels that makes up an image.
Resolution
What is image noise?
Unwanted random variations in shades of gray produced on a digital radiograph
Image noise is inversely related to ___.
Image contrast
Increased image noise ___ image contrast.
Decreases
How can electronic noise be produced?
It can be produced by a number of sources within the system, such as image processing units and monitors
How can quantum noise be produced?
-Quantum noise results from random distribution of electrons striking the image receptor
-Use of higher mAs or kVp can minimize this type of noise
What is dose creep?
Term used to to describe increases in exposure factors made in an attempt to reduce the amount of image noise
Describe computed radiography (CR) systems and film.
-CR systems are similar to standard film-based systems in that they require a cassette with an intensifying screen
-The difference is that the screen is composed of photostimulable phosphors and is referred to as a photostimulable storage phosphor imaging plate (PSP) or simply an imaging plate (IP)
-The plate is located in the cassette and the cassette is placed either in the Bucky tray or on the tabletop, depending on the size of the body part being radiographed
List the layers and their function that make up the imaging plate in computed radiography systems.
-The protective layer helps shield the plate from handling damage
-The phosphor layer contains the stimulable phosphors
-The conductor layer aids in minimizing electrostatic interference with image formation
-There is also a light-shielding layer to protect the plate from light damage
How are images formed in a computed radiography system?
-Electrons in the IP become excited when they interact with X-rays
-Some of those electrons are elevated into a high energy state that essentially leaves gaps in the phosphor layer
-These gaps are what produce the latent image
-The remainder of the excited electrons emit light and fall back to their stable state
How are images formed in a computed radiography system (Part 2)
-IP is processed by loading the cassette into the image reader
-IP must be processed shortly after exposure since the electrons only retain the latent image for a few hours
-The image reader uses a red focused laser beam to release the high-energy electrons, which causes additional release of light in proportion to the amount of radiation to which the electrons were exposed
-Released light is directed to a photodetector that converts the visible light into an electronic signal, which is then converted to a digital signal
Within about ___, approximately __% of the image taken with a CR system will be lost.
-8 hours
-25%
How do you prepare an IP for reuse?
The plate is exposed to a bright flash of white light that returns all the electrons to their stable state, fully erasing the image and making the IP ready to re-use
What are some special considerations for imaging plates?
-Imaging plates are sensitive to scatter radiation and should be flashed prior to use, especially if they are not used frequently
-The IP is also prone to wear and “ghosting,” a situation where the prior image cannot be fully erased. The plate may have to be replaced when this occurs
Describe digital radiography (DR).
-With digital radiography, the image receptor is built into the X-ray table
-Cassettes and separate image processing units are not required
-Image receptor interfaces with the processing system that converts and displays the image
What are the 2 types of DR systems?
-Direct detector systems
-Indirect detector systems
___ describes the sensitivity and accuracy of the system.
-Detective quantum efficiency (DQE)
What is the DQE normally expressed as? What is a normal DQE?
-Usually expressed as a percentage of the X-ray energy that strikes the detector and is ultimately converted to the final image
-Most digital systems have a DQE of about 80%
-20% of the image that is not a direct result of the X-ray beam interaction with the detector is then filled in by the computer software programs
Describe direct detector systems.
-Utilize a thin-film-transistor (TFT) device to detect and display the image
-The IP contains amorphous selenium, which releases electrons when they interact with the X-ray beam
-The TFT collects the electrons and directly converts that electronic signal to the digital image for display
Describe indirect detector systems.
-2 types of indirect systems used for DR
-1 uses a TFT detector and the other uses a charged-coupled-device (CCD)
-Both systems use a scintillator
-Light emitted is then detected by the TFT or CCD, depending on the type of system
TFT and CCD convert that light energy to electrical energy, which is processed by the computer to display the digital image
What is a scintillator?
A material that fluoresces when exposed to the X-ray beam
During digital image processing, what is windowing and leveling?
-Windowing controls the range of densities displayed
-Leveling controls the brightness of the image
What monitor are digital radiographs best viewed on?
-Medical grade monochrome LCD monitor
-These are expensive
-Consumer type LCD monitors are commonly used and newer models have acceptable resolution for most routine applications
What is a picture archiving and communication system?
-PACS
-Refers to the processes, procedures, and technology required for creating, distributing, and archiving digital images
PACS includes the imaging device and any associated ___ as well as the computer ___ that store and retrieve the images
-Readers
-Viewers
-Computer servers and workstations
Medical images use a universal format known as ___.
DICOM
DICOM is an acronym that refers to ___.
-Digital imaging and communications in medicine
Although traditional X-ray imaging can be used to visualize the size, shape, and position of organs, ultrasound can ___.
-Generate images that allow for the evaluation of the texture of organs
-Providing real-time visualization of the functional ability of the organs
Describe acoustic principles and how ultrasound imaging works.
-Based on conversion of energy
-Electrical energy is applied in pulses to a probe and is converted to sound waves by crystals within the probe
-Sound waves are directed into the patient
-Specific fate of the sound waves depends on the direction of the wave and the density of the components that the wave encounters (fluid, bone, muscle)
-Waves can be absorbed, scattered, or reflected back as an echo to the transducer
The height of the waves is referred to as ___.
Amplitude
Taller waves are ___ sound waves.
Louder
Wavelength is the ___.
Distance between each of the bands
Frequency refers to the ___. ___ is the measurement for frequency.
-Number of wave cycles that occur each second
-Hertz (Hz)
Areas that do not generate an echo are described as ___.
-Anechoic
-Appear black on the final image and usually represent fluid-filled structures
Areas with a high-intensity echo appear very bright and are referred to as ___.
Hyperechoic
___ areas are those with little returning echo and appear darker gray.
Hypoechoic
___ refers to areas with returning echoes that are the same as the surrounding tissues.
Isoechoic
What are the basic components of an ultrasound machine?
-Power source
-Transducer
-Control panel
The ___, or probe, generates the sound waves and also serves to receive the returning echoes
Transducer
___ within the probe begin to vibrate and emit sound when electrical energy is applied to the probe.
Piezoelectric crystals
The range of frequencies the transducer can generate varies depending on the ___.
Thickness of the crystals
Transducers are composed of several hundred piezoelectric crystals arranged with a specific configuration or array.
The configuration of the array dictates the ___.
-Application it is used for
-Appearance of the image on the monitor
What are the different types of transducers?
-Sector array
-Linear array
-Curvilinear array
-Phased array
-Annular array
What shape image does a sector array produce?
Wedge or pie-shaped image
What shape image does a linear array produce?
-Rectangular-shaped image
-Often useful when assessing blood flow
-Linear arrays are the most common
The curvilinear array is a type of linear array arranged into a convex curve.
Microconvex versions of the curvilinear transducer are ideal for use with ___.
-Most small animal patients
-Abdominal imaging
How are the piezoelectric crystals arranged in phased array transducers? What are they commonly used for?
-Linearly and are activated in sequence
-Cardiac studies
The power control alters the ___ generated by increasing the voltage to the transducer.
Intensity of the sound wave (amplitude)
Applying higher voltage to the transducer generates ___.
-Sound pulses that are louder
Louder pulses generate ___.
Louder echoes and thus a brighter image
The frequency or rate at which pulses are released can also be changed using the ___.
Pulse repetition frequency control
Once the sound pulse is released, the transducer stops transmitting momentarily while ___.
The echoes are returned and detected
The ___ detect the returning echo and generate electrical energy that is then translated to an image on the monitor by the computer software
Piezoelectric crystals
Echoes from deeper tissues take ___ to return to the transducer than from more superficial structures
Longer
The ultrasound waves are ___ as they travel through tissues.
-Attenuated (lose amplitude)
-Degree of attenuation varies with tissues of different densities
The amplitude of the returning echo is used to determine the ___.
Tissue characteristics.
Differences in amplitude are indicated as ___.
Different shades of gray on the monitor
