7.2 Reporting Flashcards
it is a method by which digital radiography manufacturers provide feedback to the technologists regarding the estimated exposure on the detector, as a surrogate for image signal-to-noise ratio and an indirect indication of digital image quality
Exposure Index
The differences in the exposure indicators have created not only confusion but also frustration among users.
This provided the motivation for the development of a standardized EI by the ______
IEC (International Electrotechnical Commission) and the AAPM (American Association of Physicists in Medicine
The IEC standardized EI is _____ to the detector exposure and requires the user to establish EIT values for all examinations in order to ensure optimization of the dose to the patient without compromising the image quality
proportional
provides immediate feedback to the technologist as to whether the correct exposure was used for the examination
Deviation Index
3 Important Aspects of the New Standards
- Exposure Index (EI)
- Target Exposure Index (EIT)
- Deviation Index (DI)
the ability to image two separate objects and visually distinguish one from the other
Resolution
appears as an irregular granular pattern in all images and degrades image information
appears as an irregular granular pattern in all images and degrades image information
Noise can be discussed in terms of:
- Electronic noise (system noise)
* Quantum noise (quantum mottle)
determined by the number of X-ray photons falling upon the detector to create the image
Quantum Noise (Quantum Mottle)
is a measure of the efficiency and fidelity with which the detector can perform the task of receiving an input exposure and converting it into a useful output image
Detective Quantum Efficiency
The ideal detector would have a DQE of ____, meaning all the radiation energy or input exposure is absorbed by the detector and converted into useful image information. This means that there is no loss of information
1 or 100%
The DQE for CR is much ____ than film-screen (F-S) image receptors.
- This means that CR can convert an input exposure into a useful output image over a much wider range of exposures compared to F-S radiography
better
is any feature which appears in an image which is not present in the original imaged object
Image artifact
most common artifact
Motion artifact
devices that either convert x-rays into an electric charge
(direct conversion) or light (indirect conversion) which is then read out through TFTs (Thin Film
Transistors)
Flat panel are digital radiography (DR)
The flat-panel TFT digital detector is designed as a matrix of detector elements, each of which
can be regarded as a pixel. This design principle is referred to as _____
large area integrated circuit
The sensing/storage element of an indirect flat-panel TFT detector is the _____ (photosensitive
storage element)
photodiode
is a semiconductor device that converts light energy into electrical energy
photodiode
Aside from the matrix of pixels, there are other electronic components that are included in the flat-panel detector
gateline or data line
Typical Detector Dimensions
43 x 43 cm
30x 40 cm
18 x 18 cm
Different Matrix Sizes
1920 x 1536, 2000 x 2500, 2736 x 2736, 2560 x 3072, 2688 x 2688, 2836 x 2836, 3121 x 3121
The number of pixels can be obtained by multiplying the dimensions of the ____
matrix size
is the distance from the midpoint of one pixel to the midpoint of the adjacent pixel
Pixel Pitch
Pixel Sizes:
139 mm, 143 mm, 160 mm, 162 mm, 167 mm, 200 mm
An important feature of the pixel in the flat-panel TFT digital detector active
matrix array is the ____
fill factor
is the relationship between the area of the entire pixel and the
active portion of the pixel
fill factor
is fundamentally an image receptor specifically used in the modality of digital
radiography for the indirect conversion of x-ray photons into an electric charge
Charged-Coupled Device Digital Detector
It is primarily composed of silicon chips called ____
Charged-Coupled Device
CCD 3 main technical components:
- Scintillation screen
- Light collection optics
- CCD Chip
Converts x-ray photons to light
Scintillation screen
Disadvantage of light optics
Minification or demagnification
During this process within the CCD, the system electronics provide a
systematic collection of charges on each chip.
This systemic collection is referred to as the ____
Bucket Brigade Scheme
It is a digital detector that is based on an indirect conversion process.
Indirect because the X-ray photons are first converted into light via a scintillation
screen
CCD
Transmits/Focuses/Couples light to the CCD.
Serves to focus light, to ensure that more light is transmitted to the CCD chip;
leading to the added efficiency of the digital detector.
However, since the lens also reduces the size of the projected
visible light image to suit the size of the CCD array, the image
quality is compromised
Light Collection Optics/ Lens / Fiber Optics
Where light is converted to charges.
Where the readout process occurs (Bucket Brigade Scheme)
CCD chip
the distribution of the charges in the matrix array of pixels represents the so-called ____
latent image
Uses complex and sophisticated electronic circuitry to read out the electrical charges produced and stored in the matrix array
readout electronics
pixels are read out row by row
active matrix readout
Before the flat-panel detector can be used for an X-ray examination, it must be prepared prior to the X-ray exposure
Initialization
examines the response of
the IR to the radiation falling upon it
Exposure Latitude
-Narrow exposure latitude -Fixed -Clearly evident - More critical selection
Film Screen
- Wide exposure latitude
- Adjustable
- Not Evident
- Less critical selection
Digital Radiography
Film screen slope or graph
Sigmoidal (Non-linear)
Digital radiography slope or graph
Straight line (Linear
Exposure latitude for CR/DR detectors:
: 0.1-1000 μGy (0.01-114 mR)
High noise (quantum mottle), low SNR, poor contrast sensitivity
Underexposed in DR
High radiation dose,
high SNR, better contrast sensitivity
Overexposed in DR
The risk of increasing patient dose, possibly without
being aware of it, OR an increase in exposure over
time when using digital systems with manual tube
settings
Exposure/Dose Creep
Unintended excessive exposure & subsequent
unnecessary patient radiation exposure
Exposure/Dose Creep
FPD EIs of Philips Healthcare for 5 μGy, 10 μGy, and 20 μGy
are 200, 100, and 50
EI of Siemens FPD for 5 μGy, 10 μGy, and 20 μGy
are 500, 1000, and 2000
Because of the digital detector’s wide exposure latitude, the image contrast from the detector is ____
poor
is the first subject of pre-processing
Raw
Developed to repair raw data acquired from defective detector elements that might cause difficulties
with the detector’s appropriate operation
Pre-processing
The first image received from the detector is referred to as a _____, which contains artifacts
caused by faulty detector components.
flat field image
It is presented as DICOM “for processing image”
Pre-processing
is tagged as “for presenting image”
Post-Processing
The goal of _____ is to turn the “for processing image” into a “for presentation image” with
improved contras
post-processing
To generate a picture with contrast enhancement, the wide exposure latitude or linear response is
turned into the well-known characteristic curve which is the ______
non linear response
It is basically a process of enhancing a quality of an image itself where the condition is to increase the
spatial resolution, contrast resolution, and edge enhancement parameters
Image Display Optimization
It is mandatory that technologists recognize that the effective use of image post-processing techniques
in a fairly complex process and that image processing is not intended to correct the poor images
routinely due to errors that may have been made during _____
image acquisition
_____ of the image displayed on monitors for viewing by both technologists and radiologists
demands a good working knowledge of not only image processing but also display workstation
principles and technology
(That’s why we have those programs like the quality assurance, quality control and the continuous
quality improvement programs to help us or guide us in our work place)
Optimization
too much editing or optimizing an image can result an _____ background or simply the _____ which can degrade the image diagnostic
quality
halo effect or increased
in image noise,
quantum mottle
ability of the combined components of a system to accurately reproduce the structural details of an object within an image
Modulation Transfer Function
is a ratio of the image to the object
Modulation Transfer Function
a perfect system would have an MTF of ___
1
is a graphical representation or a means of evaluating the spatial resolution performance of an imaging system or detector
Modulation Transfer Function
A higher MTF value at a higher spatial frequency means that the detector provides ____ spatial resolution than lower MTF values at low frequencies
better
Measurement of the MTFs for various detectors demonstrates that as the spatial frequency
increases, the MTF _____
decreases
a higher MTF value at lower spatial frequencies means that the detector provides ____ contrast resolution
better
All digital imaging systems have what is
referred to as the _____, which is the spatial frequency limit that is obtained at an MTF
value of ___
limiting resolution,
0.1
A system that has a higher spatial frequency at an MTF of 0.1 will show ____ spatial resolution than a system that has a lower spatial frequency at an MTF of 0.1.
better
Response of the detector to different levels of radiation exposure
Dynamic Range
Technologist must use detectors wisely in order to avoid _____
Exposure Creep
Refers to the persistence of the image, that is, charge is still being produced after the radiation beam from the X-ray tube has been turned off
Memory Effect
2 Types of Lag Phenomenon
- Instantaneous Lag
- Long-term Lag
lag that occurs within seconds to minutes and disappear instantaneously
Instantaneous Lag
lag that occurs by accumulation of X‐ray information to the FDP over hours, months, and years and is thus
much easier to document
Long‐term Lag
is important in cardiology because the heart has motion and we cannot stop it from beating, therefore we cannot avoid involuntary motion if we do not use fluoroscopy to examine the heart
Fluoroscopy
Flat panel detectors can be used in
Fluoroscopy and Portable Radiography
is used when patients are not able of transporting to the imaging department
Portable Radiography also called Mobile Radiography
Real-time imaging
Fluoroscopy
What are some fluoroscopic applications?
- Gastrointestinal tract fluoroscopy - esophagus, stomach, and intestine
- Angiography - to radiograph of the blood vessels
- Portable fluoroscopy ex. C-arm
worked on establishing a standardized EI for DR
International Electrotechnical Commission (IEC), the American Association of Physicists in Medicine (AAPM) and the Medical Imaging and Technology Alliance (MITA)
standardized EI for DR known as
IEC Exposure Index
EI is obtained from the information in the image by using one of two methods:
histogram method, or region of interest (ROI) method
the computer analyzes the histogram using processing algorithms and compares it with a pre-established histogram specific to the anatomic part being imaged. This are stored histogram models, each having a shape characteristic of the selected anatomic region and projection
histogram method
algorithms detect and eliminate the foreground and background regions from consideration. The remaining image area is evaluated to derive the unique ROI value for that image
Region of Interest Method
refer to them as Pixel values in the original image that correspond to the selected region
Value of interest
- VOI segments the anatomy under study and an average value is obtained from at least ___ of the central region of the image
25%
In establishing a standardized EI for DR, the IEC requires that the following elements be met:
- a direct proportional approach or scale must be used which relates the EI to the detector dose
- the ROI pixel values are used in calculation of the standardized EI.
- the IEC specifies that other factors must be considered as well in establishing a standardized EI such as the kV, filtration, and so forth
defined the standardized EI
which is, a “measure of the detector response to radiation in the relevant
image region of an image acquired with a digital X-ray imaging system”
International Electrotechnical Commission (IEC)
Both the IEC and the AAPM suggest the following steps to obtain the
standardized EI. First, the detector must be calibrated such that there is a
____ proportional relationship between the EI and the exposure at the
detector, that is, if the detector exposure is doubled, the EI value doubles.
direct
In addition, users must note that the standardized EI depends on _____
X-ray beam quality (kVp)
is a three-dimensional imaging technique based
on the reconstruction of several planar
radiograph
Digital Tomosynthesis
overcomes the problems of conventional two-dimensional (2D) tomography
The technique involves image acquisition, image
reconstruction, and image display and communication
Digital Tomosynthesis
X-ray tube moves through various positions which
describes an angle θ, the _____, while the digital detector remains stationary. In this manner several slices are acquired at low doses and stored
sweep angle
t illustrates both acquisition images of the objects
represented as a white square and a black circle and the resulting tomosynthesis reconstruction images in ___
planes
two
when the X-ray tube is perpendicular to the
detector, structures located at different heights in the
breast are superimposed on that image. These structures
are separated out in the ______
positions of the X-ray tube.
nonzero degree (off axis)
This shows a significant advantage of _____; superimposed tissues from different sections of the breast are clearly demonstrated in the
images compared to the two-dimensional full-field
digital mammography (2DFFDM) or simply a two
dimensional digital mammography (2DDM) image
digital tomosynthesis
digital tomosynthesis parameters
Sweep angle,
Sweep direction,
Patient barrier-object distance, number of projections,
Total radiation dose
refers to the total arc about the center of the detector as
defined by the focal spot position from the
first to the final projection in the tomosynthesis acquisition or sweep
Sweep angle
A sweep angle of 40°
signifies a –20° to +20° sweep. The sweep
angle can be varied between 20° and 40° on
our ______
flat-panel detector system
The direction of X-ray tube
movement relative to the object or body part of
interest during a sweep
Sweep direction
can be arbitrarily determined by altering the position or direction of the object or body part
Sweep direction
Is the minimum distance between the surface of the
patient barrier and the object of interest
Patient barrier-object distance
_____ should be used for
more accurate geometric analysis, but patient
barrier-object distance is convenient because
it can be determined more easily and
accurately
Detector-object distance
is simply the
number of X-ray projection images acquired
during a single sweep
Number of projections and projection density
number of projections divided by sweep
angle
Projection density
is used as an important conceptual
parameter in the minimization of ripple
artifact
Projection density
Is the cumulative sum
of the doses for all projections
Total radiation dose
multiple projection images are acquired at different viewing angles and reconstructed into a 3D dataset,
which can be viewed in thin slices with high
in-plane resolution without suffering from tissue overlap.
Digital breast tomosynthesis (DBT)
FFDM
Full-field Digital
Mammography
It has the potential to improve the
effectiveness of early breast cancer screening
at a similar dose and cost to full-field digital
mammography (FFDM)
Digital breast tomosynthesis (DBT)
The first commercial DBT scanner received FDA approval in early ___
2011
The sweep angle can be varied between _____ on our flat-panel detector system
20° and 40°
potential artifact for Sweep direction, projection density
Blurring-ripple
potential artifact for Sweep direction
Ghost artifact-distortion
potential artifact for Sweep angle, patient barrier-object distance
Poor depth resolution
potential artifact for total radiation dose
Image Noise
potential artifact for sweep direction
Metallic artifact
the distance from the detector imaging plane to the patient barrier is approximately _____ for the wall stand and ____ for the table
- 9 cm,
6. 6 cm
The sweep angle should be _____ to evaluate fine anatomy, such as that of the hand or foot (sweep angle should be 40°), with improved depth resolution
increased
The number of projections and total dose should be ______ for imaging a thin body part, such as the hand or foot (the number of projections should be 30), to reduce unnecessary radiation exposure
decreased
The projection density should be _____ for imaging a thick body part, such as the chest (the number of projections should be 60 and the sweep angle 30°, resulting in a projection density of 2), to avoid ripple in the sections of interest
increased
For the average adult chest examination, the effective dose for tomosynthesis has been determined to be ____
0.124 mSv
is caused by a high-contrast structure that exists outside the section plane and whose long axis is parallel to the sweep direction
Distortion Ghost artifact
can manifest as very low signal along the sweep direction around the edges of a high-attenuation material such as a metal prosthesis or osteosynthetic material
Metallic Artifact
This artifact is caused predominantly by reconstruction of the very low-level signals in the shadow of the high-attenuating object and, to a much lesser degree, by the limited sweep angle
Metallic Artifact
occurs along the sweep direction and results from the imaging of structures that exist outside the section plane
Blurring-Ripple
