Transcript No Slide Title

Chapter 3: Factors of Image Quality
1. Interlaced vs. progressive scanning
2. Matrix size
3. Vertical resolution
4. Horizontal resolution
5. Field of view (FOV)
The next slide demonstrates the transfer of energy though the fluoroscopic imaging chain.
Even the most primitive system may be digitized by capturing the video signal from the
vidicon or plumbicon camera, and sending it through the analog to digital converter (ADC)
The next two slides are not covered in the text of chapter 3, but are included as a quick review
of the fluoroscopic system before discussing the factors of image quality.
The transfer of energy through the imaging chain follows these basic steps.
1.
2.
3.
4.
5.
6.
Remnant x-ray to light at the input phosphor
Light to free electrons at the photocathode
Electrons with added kenetic energy from their attraction to the anode
Intensified light at the output phosphor from flux and minification gain
Light incident on the target of the camera excites electrons of the target material (globules)
A separate source of electrons from the cathode of the camera (electron gun) scans
the target and discharges the globules one by one (left to right, top to bottom).
7. As each globule discharges, an electrical current flows from the cameral as the video
signal. Each pulse of the signal varies in intensity (modulates) in accord with the
excited state of the globule it came from.
8. The video signal energizes the control plate of the cathode (electron gun) of the monitor.
9. Electrons are shot toward the phosphor in the same pattern (left to right, top to bottom) as
they were scanned by the camera.
10. Each pixel on the monitor fluoresces with an intensity proportional to the strength of
the pulse of the video signal that struck it.
Remember all that?
Fluoroscopic imaging chain converted to digital
Camera lens
6
5
7
Light
ADC
1
0
1
1
4
8
ALU
CU
DAC
Primary
Memory
(RAM)
Secondary
Memory
3
9
10
A digital to analog
converter is needed
if the monitor is not
digital
2
1
Interlaced scanning
provides low resolution
fluoroscopic monitoring
and is used for
conventional
(not high definition) TV
Interlaced Scanning
Line 1
Line 2
From the next slide on
we will look at high
definition systems in
conjunction with the
discussion in chapter 3
Line 511
Line 512
262 1/2 Odd Lines scanned = Field 1
262 1/2 Even Lines scanned = Field 2
2 Fields = 1 Frame. The screen is blanked between fields, so with
interlaced scanning there is never a full picture (frame) on the screen. There are 60
60 fields per second, and 30 frames.
Control room
CCD image intensifiers
are easily identified by
their shape
High resolution
flat screen monitors
Spatial Resolution
Measured in line pairs.
One line and one space is a line pair
1 mm
=1
line pair per millimeter
of spatial resolution
A Line Pair Test Tool
(for Testing Spatial Resolution)
The Test Tool provides line pairs of various
sizes to measure spatial resolution
Progressive Scanning
Question: Is the interlaced scheme desirable?
No
Then why is it used?
It is a remnant of the original technology.
What is better than interlaced?
Progressive scanning, which requires a faster
of the electron beams
Bandpass or bandwidth = Horizontal resolution
Matrix Size
(Vertical resolution = number of lines)
Matrix size expresses the number of pixels.
A standard TV matrix is 525 x 525.
A high resolution matrix is 1024 x 1024 or
larger.
A large matrix displays better spatial
resolution than a small matix.
Matrix Size and pixel size
Smaller pixels make an image
look better when viewed close,
and larger pixels provide good
detail viewed further away.
Nevertheless, matrix size alone
determines spatial resolution.
Field of View (FOV)
Image intensifier example
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9”
11”
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11” mode
7”
7” mode
Field of View (FOV)
Computation of Spatial Resolution
You need to know
1. How large is the field of view?
2. How many pixels is it displayed in?
Field of View (FOV)
A simple example to compute spatial resolution
If the FOV is 100 mm
and it is displayed in 400 pixels
100 mm/400 pixels = .25 mm of anatomy per pixel
How many line pairs?
The Grand Canyon from Landsat
Excellent spatial resolution may be measured in meters
or kilometers, depending on the field of view.
Colorado River
The Canyon averages
19km from rim to rim.
AP report March 31, 2002
Quickbird satellite picture from 280 miles can resolve a object
of 2 feet: a person on a golf course appears as a spot, an SUV
can be distinguished from a pickup.
Can you name the Factors of Image Quality?
1. Interlaced vs. progressive scanning
2. Matrix size
3. Vertical resolution
4. Horizontal resolution
5. Field of view (FOV)