INTERVENTIONAL RADIOLOGY Flashcards
In DF, the spatial resolution is determined both
image matrix and by the size of the image intensifier
Spatial resolution is limited by
pixel size
A major change from conventional fluoroscopy to DF is the use of a ___ instead of a TV camera tube
charge-coupled device (CCD)
Military applications ___
night vision scopes
The sensitive component of a CCD is a layer of __.
Crystalline Silicon
When this silicon is illuminated, ___ is generated, which is then sampled, pixel by pixel, and manipulated to produce a digital image.
electrical charge
Spatial resolution of a CCD: determine by
its physical size and pixel count
1024 matrix can produce images with __ spatial resolution.
10 lp/mm
Television camera tubes: __
“pin cushion” or “barrel” artifact
The CCD has greater sensitivity to
light
Because of heated filaments and voltage differences, a very small electric current always is flowing in any circuit
This is called
background electronic noise
The tube with a __ SNR provides five times the useful information and is more compatible with computer-assisted image enhancement
1000 : 1
The __ from the image-intensified digital image receptor is transmitted to an analog-to digital converter (ADC)
output signal
To be compatible with the computer, the __
ADC must have the same dynamic range as the DF system.
An 8-bit ADC would convert the analog signal into values between __
0 and 255
A 10-bit ADC would be more precise, with an ADC range from__
0 to 210 or 0 to 1023.
The output of the ADC is then transferred to ___ and is manipulated so that a digital image in matrix form is stored.
main memory
__ is amplified and is transmitted by cable to the television monitor, where it is transformed back into a visible image.
video signal
television monitor forms
one end of a closed-circuit television system. The other end is the television camera tube or CCD.
Two differences between closed-circuit television fluoroscopy and home television are
no audio and no channel selection
Usually, the radiologic technologist manipulates only two controls:
contrast and brightness
The principal advantages of DF examinations are the ___ that are possible and the enhanced visualization of vasculature that results from venous injection of contrast material
image subtraction techniques
Refers to a number of computer-assisted techniques whereby an image obtained at one time is subtracted from an image obtained at a later time.
Temporal Subtraction
Two methods are commonly used: the __ in temporal subtraction
a.) mask mode and the b.) time-interval difference (TID) mode
results in successive subtraction images of contrast-filled vessels
Mask Mode
Each image was obtained from a __ x-ray pulse. The time required for one video frame is __
33-ms; 33 ms
Imaging sequence after acquisition of the mask can be ___
controlled manually or pre-programmed
the use of later images as mask image.
Remasking
Produces subtracted images from progressive masks and following frames
Time-Interval Difference Mode
Occurs if patient motion occurs between the mask image and a subsequent image.
Misregistration artifact
Same anatomy is not registered in the same pixel of the image matrix
This type of artifact frequently can be eliminated by __ of the mask. Done by shifting the mask by one or more pixels so that __ of images is again obtained
re-registration; superimposition
Uses two different x-ray beams alternately. Images are results of differences in __
Energy Subtraction; photoelectric interaction
When the incident x-ray energy is sufficient to overcome the K-shell electron binding energy of iodine, an abrupt and large increase in absorption occurs
Graphically, this increase is known as the
K absorption edge.
Other methods: FOR ENERGY SUBTRACTION
(1) Alternately pulsing the x-ray beam at 70 kVp and then 90 kVp and
(2) Introducing dissimilar metal filters into the x-ray beam alternately on a flywheel
Combining temporal and energy subtraction techniques
hybrid subtraction
the components
used in conventional fluoroscopy
X-ray source, image intensifier, TV camera, TV monitor
___ is a digital x-ray imaging
system that produces dynamic images obtained with
an area x-ray beam. The difference between conventional fluoroscopy and DF is the __
Digital fluoroscopy (DF); nature of the image and the manner in which it is digitized
Images from DF are obtained by
pulsing the x-ray beam in a manner called
pulse progressive fluoroscopy
During DF, the x-ray tube operates in the __
radiographic mode
__ is required to produce a single video frame, x-ray exposures longer than this can result in unnecessary
patient radiation doses. This is a theoretical limit, however, and longer exposures may be necessary to ensure low noise and good image quality
33 ms
The time required for
the x-ray tube to be switched on and reach selected
levels of kilovolt peak (kVp) and mA is called
interogation time
The time required for the x-ray tube to be switched off is the
extinction time
DF systems must incorporate high-frequency generators with interrogation and extinction times of less than __
1 ms
The fraction of time that the x-ray tube is energized is called
duty cycle
When this silicon is illuminated, electrical charge is generated, which is then sampled, pixel by pixel, and manipulated to produce a __.
digital image
The CCD is mounted on the __ and is coupled through fiberoptics or a lens system
output phosphor of the image-intensifier tube
Advantages of Charge-Coupled
Devices for Medical Imaging
High spatial resolution
* High SNR
* High DQE
* No warm-up required
* No lag or blooming
* No spatial distortion
* No maintenance
* Unlimited life
* Unaffected by magnetic fields
* Linear response
* Lower patient radiation dose
Advantages of Flat Panel Image
Receptors Over Charge-Coupled Device
Image Intensifiers in Digital Fluoroscopy
- Distortion-free images
- Constant image quality over the entire image
- Improved contrast resolution over the entire image
- High DQE (see Chapter 16) at all radiation dose
levels - Rectangular image area coupled to similar image
monitor - Unaffected by external magnetic fields
__ is particularly helpful for digital subtraction angiography (DSA) and results in improved
dynamic range and better contrast resolution.
linear response feature
flat panel image receptor (FPIR). Such an image receptor is composed of
cesium iodide (CsI)/amorphous
silicon (a-Si) pixels
The __ is much smaller and lighter and is manipulated more easily than an image intensifier. The __ imaging suite provides easier patient manipulation and
radiologist or technologist movement, and there are no
radiographic cassettes.
FPIR
The image intensifier is limited by__ from the center to the
periphery of the circular image
nonuniform spatial
resolution and contrast resolution
The video system used in conventional fluoroscopy is
usually a ___ system. Such a system is inadequate
for DF.
525-line system
It is similar to the noise (fog) on a radiograph in that it conveys no information and serves
only to obscure the electronic signal and reduce image
contrast.
background electronic noise
The tube with a 1000:1 SNR provides __ the useful information and is more compatible with computer-assisted
image enhancement
five times
Important characteristics of a DF
system that are computer controlled include the
image matrix size, the system dynamic range, and the image
acquisition rate.
The output signal from the image-intensified digital
image receptor is transmitted to an __
Analog-to-Digital converter
The dynamic range of each pixel, the number of pixels, and the method of storage determine the
__ with which the image can be acquired, processed, and transferred to an output device.
speed
DF provides better contrast resolution through __ of image subtraction
postprocessing
__ mode produces subtracted images from
progressive masks and following frames.
TID
The probability of photoelectric absorption in
all three decreases with increasing x-ray energy. At an
energy of __
33 keV
___ is a special application of DSA. A mask
image is acquired and stored
roadmapping
