Transcript Digital fluoro - El Camino College

Digital FLUORO
Summer 2008
DIGITAL FLUORO
• Digital fluoroscopy is currently most commonly
configured as a conventional fluoroscopy system in
which the analog video signal is converted to a digital
format with an analog-to-digital converter (ADC). An indepth discussion of digital detector technologies (eg,
flat-panel "direct" detection of x rays and charge-coupled
device technology) is beyond the scope of this article.
After a review of several fundamental digital imaging
concepts including binary numbers, pixels, and gray
levels, emphasis will be placed on discussions of the
digital imaging tools specific to digital fluoroscopy and
digital subtraction angiography (DSA).
• Digital fluoroscopy is currently most commonly
configured as a conventional fluoroscopy
system in which the analog video signal is
converted to a digital format with an analog-todigital converter (ADC).
• With discussions of the digital imaging tools
specific to digital fluoroscopy and digital
subtraction angiography (DSA).
Early Fluoroscopy
CONVENTIONAL FLUOROSCOPY
INVENTED BY THOMAS EDISON
Direct Fluoroscopy: obsolete
In older fluoroscopic examinations radiologist stands
behind screen and view the picture
Radiologist receives high exposure; despite protective
glass, lead shielding in stand, apron and perhaps goggles
Main source staff exposure is NOT the patient but direct beam
pixels
• the smallest element of a digital image.
• A digital image is normally composed of a twodimensional (square) matrix of pixels.
• The matrix size of an image is used to describe
the number of pixels in each row and column of
the image.
The size of a pixel determines the smallest detail visible in the
image,
the number of pixels (of a given size) determines the field of view
of the image.
pixel value is assigned to a certain color or gray level for
visualization.
The imaged object is more faithfully reproduced as matrix size
increases and pixel size decreases.
63 K
1024
Digital fluoroscopy
• is most commonly configured as a conventional
fluoroscopy system (tube, table, image
intensifier, video system) in which the analog
video signal has been digitized with an ADC.
• Alternatively, digitization may be accomplished
with a digital video camera (eg, a chargecoupled device) or via direct capture of x rays
with a flat-panel detector.
• For digital fluoroscopy systems in which the
analog video signal is digitized with an ADC, the
resolution is limited by the resolution of the video
camera, which is typically 1–2 line pairs per
millimeter.
Digital Image recording
• In newer fluoroscopic systems film recording
replaced with digital image recording.
• Digital photospots acquired by recording a
digitized video signal and storing it in computer
memory.
• Operation fast, convenient.
• Image quality can be enhanced by application
of various image processing techniques,
including window-level, frame averaging, and
edge enhancement.
• But, the spatial resolution of digital photospots
is less than that of film images.
Digital radiography principle
ANALOGUE
SIGNAL
I
ADC
t
Memory
DIGITAL
SIGNAL
Iris
Clock
See more in Lecture L20
t
Digital spot film images
• and photospot images may be acquired by using
the same digital fluoroscopy system.
• Individual frames from a digital fluoroscopy
sequence can be stored digitally and can be
used instead of conventional spot film and
photospot images.
• Digital photospot images will have the same
characteristics (eg, resolution) as digital
fluoroscopic images.
Digital format – print to film
Remote – over the table tube
Different fluoroscopy systems
• Remote control systems
– Not requiring the presence of
medical specialists inside the
X Ray room
• Mobile C-arms
– Mostly used
theatres.
in
surgical
• The digital image data from digital
fluoroscopy may be processed by using many
useful image processing techniques.
• These techniques may serve to decrease
radiation exposure to the patient and medical
imaging staff or improve visualization of
anatomy.
• Processing options include last image hold,
gray-scale processing, temporal frame
averaging, and edge enhancement.
• Additional processing is available when digital
fluoroscopy data are used to perform DSA.
RADIATION PROTECTION
STAT CH 7 & 8
DHS-RHB
RAD PROT/FLUORO SYLLABUS
Radiation Safety
and Fluoroscopy
Time
Distance
Shielding
Also see Intro to Fluoro Lecture
From RT 124 Spring 2007
Patient Protection
• Tabletop exposure rate
– Maximum 10 R/min
– Typically 1 – 3 R/min
Patient Protection
• Minimum source-to-skin distance
– 12” for mobile equipment
– 15” for stationary systems
• Audible alarm at 5 mins.
• Same rules for collimation
Patient Protection
• Typical exposure rates
– Cinefluorography
• 7.2 R/min
– Cassettes
• 30 mR/exposure
– 105 mm film
• 10 mR/exposure
Protection of Radiographer
and Radiologist
• Lead apron
– 0.25 mm Pb/eq
• Highest energy scatter
– 90o angle to the incident beam
– Same level as radiographer /radiologist’s
gonads
The Patient & Scatter
WHATS WRONG?
Remote – over the table tube
Under table tube vs
Over table tube (remote units)
Need moving shield for
Remote rooms
IsoExposure Curves
Where is it SAFE??
ISOEXPOSURE CURVES
Patient entrance skin exposure
(ESE) is higher when the
fluoroscopic x-ray tube is too close
to the tabletop.
KEEP I.I. CLOSE TO PATIENT
PATIENT EXPOSURE
• REDUCE DISTANCE OF
IMAGE INTESIFIER
• INCREASE DISTANCE
FROM THE TUBE
PATIENT EXPOSURE
• REDUCE SIZE OF
COLLIMATED BEAM
WHEN POSSIBLE
ESE FOR FLUORO
• TLD PLACED AT SKIN ENTRACE POINT
• 1 – 5 R/MINUTE AVE IS 4 R/MIN
• INTERGRAL DOSE –
• 100 ERGS OF TISSUE = 1 RAD EXPOSURE
• OR 1 GM RAD = 100 ERGS
1 RAD -100 ERGS – 1 GRAM
1 rad (of ionizing radiation) deposits 100 ergs of energy per gram
DOSE REGULATIONS
• BEFORE 1974 - AT TABLETOP
• 5R/MIN (WITHOUT AEC)
• 5R/MIN (WITHOUT AEC) – BOOST
MODE
• After 1974 with AEC
• 10 R/MIN
20R/MIN BOOST
SSD – TUBE TO SKIN DISTANCE
• FIXED UNITS
• 18” PREFERRED
• 15 “ MINIMUM
MOBILE UNITS ( C-ARMS)
• 12’ MINIMUM
Conventional “FIXED” Fluoro
Mobile – C- arm fluoro
FLUOROSCOPY –
ABOVE AND BELOW THE TABLE
TUBE EXPOSURE TO TECH
Pulsed Fluoro
• Some fluoroscopic equipment is designed for
pulsed-mode operation. With the pulsed mode, it
can be set to produce less than the conventional
25 or 30 images per second. This reduces the
exposure rate.
• Collimation of the X ray beam to the smallest
practical size and keeping the distance between
the patient and image receptor as short as
possible contribute to good exposure
management.
Dose rate to patients
Mini c-arm