1608098820679_DIGITAL FLUOROSCOPY part 1.pdf

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1. Maria Yaseen
[email protected]
Allied Health Sciences Dept

2. Digital X-Ray imaging system that produce
series of dynamic images with an X-Ray
beam.
Different from conventional fluoroscopy just
because of the nature of image and manner
in which it is digitized.

6. Early approach
TV
CAMER
A TUBE
COMPUTER
TV
MONITO
R

7. Low patient dose
Speed of image acquisition
Post-processing of final image

8. Same as conventional fluoroscopy in first look
Multiple computers added, multiple monitors
and more complex operating console

9. ❑Two monitors used
❑Right for edit patient and examination data
and annotate final image
❑Left for display subtracted images
❑Right module: Alphanumeric and special
function keys, video control options and pad
for cursor and region of interest manipulation
❑Right portion of console: additional special
function keys for data acquisition and image
display

13. Operate in radiographic mode
Tube current in hundreds of mA(as
compared to conventional 5mA)
Images in DF obtained in pulsing X-Ray beam
manner called pulse progressive fluoroscopy
so there will be not big issue as increase
patient dose or tube heating with increase in
mA.

14. Image acquisition rate is 1/s up to 10/s
Flat panels as image receptor( in few systems
other than image intensifier tube) and due to
this exposure time continuously varied for
even greater patient dose reduction because
each time flat panel exposed, it is
immediately readable and image is projected
until next image is acquired.

15. Must be capable of switching on and off
rapidly
Must have interrogation time and extinction
time < 1ms
Interrogation time: time required by X-ray
tube to switch on and reach selected level of
kVpand mA
Extinction Time: time required for X-Ray tube
to switch off
Duty Cycle: fraction of time for which tube is
energized

17. 1. Charge Couple Device (CCD)
2. Flat Panel Image Receptor

18. Fundamentally, a charge
coupled device (CCD) is an
integrated circuit located
onto a silicon surface
forming light sensitive
elements called pixels.
Photons incident on this
surface generate charge
that can be read by
electronics and turned
into a digital copy of the
light patterns falling on
the device.
Developed in 1970s and
since then using in
multiple electronic
devices.

19. In DF, charge-coupled device (CCD) replaces
TV camera tube
Convert light photons into electrical signal
Coupled with image intensifier tube
sensitive component of a CCD is a layer of
crystalline silicon
Working (brief view)
Light from image intensifier tube silicon
of CCD electric charge generated
samplified pixel by pixel digital image

21. Coupled with
output phosphor of
image intensifier
tube via fiber optics
or lens coupling

22. Solid state CCD sensors
are replacing the
electronic TV camera tube.
It has sensitive surface of
silicon upon which light is
incident. It has number of
pixels.
Each pixel in the CCD has
an associated electrode. A
positive bias voltage is
applied to the electrode
that forms a "potential
well" in the region of the
silicon substrate.

23. The light photons (from the II output) are absorbed
into the silicon substrate of the CCD (light-
sensitive array)
Each light photon gives rise to an electron-hole
pair
◦The positive "hole" drains away
◦The negative electrons accumulate in a potential well
These charge packages are then transferred to the
light shielded storage array
The data is then read from the storage section
line-by-line
◦The quantity of electronic charge which accumulates at
each pixel is directly proportional to the intensity of the
incident light

25. With lens coupling only a sample of light from
image intensifier tube is used to stimulate
ABS system.
When CCD is coupled to image intensifier
tube, entire CCD signal is sampled and drive
ABS system.

27. The purpose of the ABC is to maintain constant
viewing condition independent of examination.
This is done by mAand kV regulation. The need
to alter the mAor kV is determined by either
electronically sampling the video signal or by
measuring the II light output with a photo-
sensor.
The allowable dose allowed by the ABC is
determined by the mode used:
Minimum patient dose rate mode
Standard patient dose rate mode
High patient dose rate mode (high image quality)

29. Small size
Can be roughly handle
High spatial resolution
No spatial distortion such as pin cushion or barrel
artifacts
Higher light sensitivity ( Detective Quantum
efficiency)
Lower level of electronic noise so the higher signal to
noise ratio and high contrast resolution
No image lag
Very long lifetime
No maintenance required
Have linear response to light
Better dynamic range

30. Replace CCD coupled Image intensifier tube
Composed of cesium iodide/amorphous
silicon pixel detectors
Smaller, lighter and manioulatedmore easily
than image intensifier
No radiographic cassettes

31. Flat Panel Image Receptor contain a layer
ofscintillatormaterial, typically made of
cesium iodide, which converts the x-rays into
light. Directly behind the scintillatorlayer is
anamorphous silicondetector array.
This array consist of individual detector
elements. The elements are square, 140–200
microns per side.
Each pixel also contains aphotodiodewhich
generates an electrical signal in proportion to
the light produced by the portion of
scintillatorlayer in front of the pixel.

32. The signals from the
photodiodes are
amplified and
encoded by additional
electronics positioned
at the edges or
behind the sensor
array in order to
produce an accurate
and sensitive digital
representation of the
x-ray image

33. Flat Panel Image Receptor Image intensifier CCD
Uniform spatial and
contrast resolution
Does not degrade with
age
Image capture is square
or rectangular just like
flat panel monitors
Insensitive to magnetic
field that’s why possible
application is in image
guided catheter
navigation.
Non-uniform spatial
resolution and contrast
resolution from center
to periphery
Veiling glare and
pincushion distortion
increase with age
Produce circular image
Sensitive to magnetic
field that’s why could
not use with catheter
having magnetic tip

34. Conventional video has 2 limitations
1. interlace mode of reading the target of TV
camera can significantly degrade the digital
image
2. conventional TV camera tubes are noisy.
SNR(signal to noise ratio) in TV camera tube is
200:1 and in DF it is 1000:1
To overcome these issues some modifications
are made in DF.

35. In conventional Fluoroscopy there was interlaced
mode of reading target assembly where two
fields were read individually and finally a 525 line
video frame created in 33ms.
In DF, this interlace mode replaced by
progressive mode in which electron beam of the
TV camera tube swept the target assembly
continuously from top to bottom in 33ms. Video
image formed similarly on TV monitor. Sharper
image with less flicker produced.

36. INTERLACE MODE: it utilizes two video fields
to create one frame
PROGRESSIVE MODE: The whole frame is
scanned at once.

37. Rapidly replacing cathode ray tube
Easier to view and easier to manipulate along
with better image
Lighter in weight and easily mounted in
angiography rooms as well

38. THE END