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Fluoroscopy

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Fluoroscopy Robert Metzger, Ph.D. Real-Time Imaging Fluoroscope Imaging Chain The Image Intensifier The Input Screen The Input Screen The Input Screen The Input ... – PowerPoint PPT presentation

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Title: Fluoroscopy


1
Fluoroscopy
  • Robert Metzger, Ph.D.

2
Real-Time Imaging
  • Fluoroscopy is an imaging procedure that allows
    real-time x-ray viewing of the patient with high
    temporal resolution
  • Use TV technology, which provides 30 frames per
    second imaging
  • Allows acquisition of a real-time digital
    sequence of images (digital video), that can be
    played back as a movie loop
  • Cine cameras offer up to 120 frame per second
    acquisition rates using 35-mm cine film. Digital
    cine also available

3
Fluoroscope Imaging Chain
c.f. Bushberg, et al. The Essential Physics of
Medical Imaging, 2nd ed., p. 232.
4
The Image Intensifier
  • There are 4 principal components of an II
  • (a) a vacuum bottle to keep the air out
  • (b) an input layer that converts the x-ray signal
    to electrons
  • (c) electronic lenses that focus the electrons,
    and
  • (d) an output phosphor that converts the
    accelerated electrons into visible light

c.f. Bushberg, et al. The Essential Physics of
Medical Imaging, 2nd ed., p. 233.
5
The Image Intensifier
CCD TV CAMERA
MIRROR
ADC
LENS
OUTPUT PHOSPHOR
APERTURE
FOCUSING ELECTRODES
DISPLAY
ELECTRONS
PHOTO-CATHODE LAYER
INPUT PHOSPHOR ...CsI
X-RAYS
6
The Input Screen
  • The input screen of the II consists of 4
    different layers
  • (a) vacuum window, a 1 mm aluminum window that is
    part of the vacuum bottle
  • keeps the air out of the II, and its curvature is
    designed to withstand the force of the air
    pressing against it
  • a vacuum is necessary in all devices in which
    electrons are accelerated across open space

c.f. Bushberg, et al. The Essential Physics of
Medical Imaging, 2nd ed., p. 233.
7
The Input Screen
  • The input screen of the II consists of 4
    different layers
  • (b) support layer, which is strong enough to
    support the input phosphor and photocathode
    layers, but thin enough to allow most x-rays to
    pass through it
  • 0.5 mm of aluminum, is the first component in the
    electronic lens system, and its curvature is
    designed for accurate electronic focusing

c.f. Bushberg, et al. The Essential Physics of
Medical Imaging, 2nd ed., p. 233.
8
The Input Screen
  • The input screen of the II consists of 4
    different layers
  • (c) input phosphor, whose function is to absorb
    the x-rays and convert their energy into visible
    light
  • cesium iodide (CsI) is used
  • long, needle-like crystals which function as
    light pipes, channeling the visible light toward
    the photochathode with minimal lateral spreading
  • 400 mm tall, 5 mm in diameter

c.f. Bushberg, et al. The Essential Physics of
Medical Imaging, 2nd ed., p. 233.
9
The Input Screen
  • The input screen of the II consists of 4
    different layers
  • (d) photocathode is a thin layer of antimony and
    alkali metals that emits electrons when struck by
    visible light
  • 10 to 20 conversion efficiency
  • 23 to 35 cm diameter input image (FOV)

c.f. Bushberg, et al. The Essential Physics of
Medical Imaging, 2nd ed., p. 233.
10
Input Phosphor Energy Conversion
Aluminum Support
Photocathode
CsI Needles
Figure courtesy from Jonathan Tucker, Brooke Army
Medical Center, SA, TX
11
Input Phosphor Energy Conversion
60 keV X-Ray
Aluminum Support
Photocathode
Figure courtesy from Jonathan Tucker, Brooke Army
Medical Center, SA, TX
CsI Needles
12
Input Phosphor Energy Conversion
Aluminum Support
3,000 light photons ? 420 nm
Photocathode
Figure courtesy from Jonathan Tucker, Brooke Army
Medical Center, SA, TX
CsI Needles
13
Input Phosphor Energy Conversion
Aluminum Support
Photocathode
400 electrons
To Anode
CsI Needles
Figure courtesy from Jonathan Tucker, Brooke Army
Medical Center, SA, TX
14
Electron Optics
  • Electrons are accelerated by an electric field
  • Energy of each electron is substantially
    increased and this gives rise to electron gain
  • Focusing is achieved using an electronic lens,
    which requires the input screen to be a curved
    surface, and this results in unavoidable
    pincushion distortion of the image

c.f. Bushberg, et al. The Essential Physics of
Medical Imaging, 2nd ed., p. 235.
15
Electron Optics
  • The G1, G2, G3 electrodes along with the input
    screen and the anode near the output phosphor
    comprise the five-component electronic lens
    system of the II
  • The electrons under the influence of the 25K to
    35K V electric field, are accelerated and arrive
    at the anode with high velocity and considerable
    kinetic energy
  • After penetrating the very thin anode, the
    energetic electrons strike the output phosphor

c.f. Bushberg, et al. The Essential Physics of
Medical Imaging, 2nd ed., p. 235.
16
The Output Phosphor
  • The output phosphor is made of zinc cadmium
    sulfide
  • Anode is very thin coating of aluminum on the
    vacuum side of the output phosphor, which is
    electrically conductive to carry away the
    electrons once they deposit their energy in the
    phosphor
  • Each electron causes the emission of
    approximately 1000 light photons from the output
    phosphor
  • 2.5 cm diameter output phosphor

c.f. Bushberg, et al. The Essential Physics of
Medical Imaging, 2nd ed., p. 235.
17
The Output Phosphor
  • The reduction in image diameter leads to
    amplification (analogy magnifying glass and
    sunlight)
  • Minification gain of an II is simply the ratio of
    the area of the input phosphor to that of the
    output phosphor, e.g., 9 input phosphor, 1
    output phosphor, area is square of the diameter
    ratio, minification gain is 81

c.f. Bushberg, et al. The Essential Physics of
Medical Imaging, 2nd ed., p. 235.
18
The Output Phosphor
  • The output phosphor is coated right onto the
    output window
  • Some fraction of the light emitted by the output
    phosphor is reflected at the glass window
  • Light bouncing around the output window is called
    veiling glare, and can reduce image contrast

c.f. Bushberg, et al. The Essential Physics of
Medical Imaging, 2nd ed., p. 235.
19
Image Intensifier Performance Conversion Factor
Light out of image intensifier (cd/m2)
Conversion Factor
Exposure rate into image intensifier (mR/sec)
  • Defined as a measure of the gain of an image
    intensifier
  • ratio of light output to exposure rate input
  • 100 to 200 for new image intensifier
  • Degrades over time, ultimately can lead to II
    replacement

20
Image Intensifier Performance Brightness Gain
  • BG minification gain x electronic gain (flux
    gain)
  • Minification gain increase in image brightness
    that results from reduction in image size from
    the input phosphor to output phosphor size
  • (di/do)2, di is input diameter which varies, do
    is output diameter typically 2.5 cm
  • For 30 cm (12) II, minification gain 144

21
Image Intensifier Performance Brightness Gain
  • BG minification gain x electronic gain (flux
    gain)
  • Electronic gain or flux gain is typically 50
  • The brightness gain therefore ranges from about
    2,500 7,000
  • As the effective diameter of the input phosphor
    decreases (magnification increases), the
    brightness gain decreases

22
Field of View/Magnification
  • FOV specifies the size of the input phosphor of
    the image intensifier
  • Different sizes 23 cm (9), 30 cm (12), 35 cm
    (14), 40 cm (16) FOV
  • Magnification is accomplished electronically
    using electronic focusing that projects part of
    the input layer onto the output phosphor
  • Since brightness gain decreases in mag. mode, the
    x-ray exposure rate is boosted. (12/9)2 1.8,
    (12/7)2 2.9

c.f. Bushberg, et al. The Essential Physics of
Medical Imaging, 2nd ed., p. 237.
23
NON-MAGNIFY MODE OF I.I.
OUTPUT IMAGE
ALL OF INPUT SURFACE USED TO GATHER X-RAYS
24
MAGNIFIED MODE OF IMAGE INTENSIFIER
OUTPUT IMAGE
LESS IMAGED ANATOMY IS EXPANDED OVER THE SAME
OUTPUT SURFACE AND LOOKS MAGNIFIED
ONLY A PORTION OF INPUT SURFACE USED TO GATHER
X-RAYS
25
Magnification
LARGE NON-MAG FoV e.g., 12 INCH
SMALL, MAG FoV e.g., 6 INCH
26
Pincushion Distortion
27
Optical Coupling
  • Parallel rays of light enter the optical chamber,
    are focused by lenses, and strike the video
    camera where an electronic image in produced
  • A partially silvered mirror is used to shunt the
    light emitted by the image intensifier to an
    accessory port

c.f. Bushberg, et al. The Essential Physics of
Medical Imaging, 2nd ed., p. 239.
28
Video Camera
c.f. Bushberg, et al. The Essential Physics of
Medical Imaging, 2nd ed., p. 240.
29
Video Camera
  • Analog video systems typically have 30 frames/sec
    operation, but they work in an interlaced fashion
    to reduce flicker, the perception of the image
    flashing on and off
  • The human eye-brain system can detect temporal
    fluctuations slower than about 47 images/sec, and
    therefore at 30 frames/sec flicker would be
    perceptible
  • With interlaced systems, each frame is composed
    of two fields and each field is refreshed at a
    rate of 60 times per second, which is fast enough
    to avoid perception of flicker

30
Lag
  • Lag means that each new TV image actually
    contains residual image information from the last
    several frames
  • Lag is good and bad
  • Lag acts to smooth the quantum noise in the
    image, but can also cause motion blurring

31
Lag
  • Effect of camera lag. Angiogram of a rapidly
    moving coronary artery shows a trailing "ghost"
    due to excessive camera lag (the direction of
    travel is from right to left).

32
Video Resolution
  • Spatial resolution of a video in the vertical
    direction (top to bottom) of the TV image is
    governed by the number of scan lines
  • By convention, 525 lines are used in N. America
    for TV
  • 490 lines usable
  • In the early days of TV, a man named Kell
    determined that about 70 of theoretical video
    resolution is appreciated visually, and this
    psychophysical effect is now called the Kell
    factor
  • 490 x 0.7 343 lines or 172 line pairs useful
    for resolution
  • For 9 field, resolution 172 lp/229 mm 0.75
    lp/mm
  • 17 cm or 7 field, resolution is 1.0 lp/mm
  • 12 cm or 5 field, resolution is 1.4 lp/mm

33
Video Resolution
  • The horizontal resolution is determined by how
    fast the video electronics can respond to changes
    in light intensity
  • This is influenced by the camera, the cable, the
    monitor but the horizontal resolution is governed
    by the bandwidth of the system
  • The time necessary to scan each video line (525
    lines at 30 frame/sec) is 63 msec
  • 11 msec required for horizontal retrace, 52 msec
    available
  • To achieve 172 cycles in 52 msec, the bandwidth
    required is 172 cycles/52 x 10-6 sec 3.3 x 106
    cycles/sec 3.3 MHz
  • Higher bandwidths are required for high-line
    video systems

34
TELEVISION IMAGE
HORIZONTAL DIRECTION
RASTER LINE
VERTICAL DIRECTION
TV LINES ARE COMPOSED OF DOTS
35
INTERLACED SCANS
36
INTERLACED SCANS
37
TYPICAL MEASURED RESOLUTION
1023 LINE T.V.
  • FoV T.V. I.I. CINE
  • 9 INCH 1.8-2.2 LP/mm 2.7-3.2 LP/mm
  • 6 INCH 2.5-2.8 LP/mm 3.7-4.5 LP/mm
  • 4.5 INCH 3.2-3.7 LP/mm 5.0-6.0 LP/mm

38
Summary
  • Fluoroscopy is a live imaging procedure
  • Image Intensifier main component and consists of
    the input phosphor, electronic lens system and
    output phosphor
  • Input phosphor Cesium Iodide, converts x-rays
    to light
  • Photocathode converts light into electrons
  • Output phosphor Zinc cadmium sulphide, converts
    electrons into light
  • Artifacts pincushion distortion, veiling glare,
    lag
  • Brightness gain minification gain x electronic
    (flux) gain
  • Several magnification modes available, typically
    exposure rate increases with magnification
  • Video camera produces the electronic image which
    we see on the TV monitor
  • Use interlaced scanning to avoid flicker
  • Horizontal (determined by bandwidth) and vertical
    (determined by the number of scan lines) video
    resolution

39
Flat Panel Digital Fluoroscopy
  • Flat panel devices are thin film transistor (TFT)
    arrays that are rectangular in format and are
    used as x-ray detectors
  • CsI, a scintillator is used to convert the
    incident x-ray beam into light
  • TFT systems have a photodiode at each detector
    element which converts light energy to an
    electronic signal
  • Flat panel detectors would replace the image
    intensifier, video camera, and other peripheral
    devices

c.f. Bushberg, et al. The Essential Physics of
Medical Imaging, 2nd ed., p. 242.
40
DIAGRAM OF GE FLAT PANEL IMAGE DETECTORS
41
FLAT PANEL-LIGHT SENSOR
Very High Fill Factor
Fill Factor
FROM GE
42
Peripheral Equipment
  • Photo-spot camera
  • used to generate images on photographic film,
    100-mm cut film or 105-mm roll film
  • full resolution of the II system, hardly seen
    nowadays
  • Digital photo-spot
  • high resolution, slow-scan TV cameras in which
    the TV signal is digitized and stored in computer
    memory
  • Or CCD cameras with 10242 or 20482 pixel formats
  • near-instantaneous viewing of the image on a
    video monitor
  • allows the fluoroscopist to put together a number
    of images to demonstrate the anatomy important to
    the diagnosis
  • digital images can be printed on a laser imager

43
Peripheral Equipment
  • Spot-film devices
  • attaches to the front of the II, and produces
    conventional radiographic screen-film images
  • better resolution than images produced by II
  • Cine-radiography cameras
  • attaches to a port and can record a very rapid
    sequence of images on 35-mm film
  • used in cardiac studies, 30 frames/sec to 120
    frames/sec or higher
  • uses very short radiographic pulses
  • digital cine are typically CCD-based cameras that
    produce a rapid sequence of digital images
    instead of film sequence

44
Fluoroscopy Modes of Operation
  • Continuous fluoroscopy
  • continuously on x-ray beam, 0.5 4 mA or higher
  • display at 30 frames/sec, 33 msec/frame
    acquisition time
  • blurring present due to patient motion,
    acceptable
  • 10 R/min is the maximum legal limit
  • High dose rate fluoroscopy
  • specially activated fluoroscopy
  • 20 R/min is the maximum legal limit
  • audible signal required to sound
  • used for obese patients

45
Fluoroscopy Modes of Operation
  • Pulsed fluoro
  • series of short x-ray pulses, 30 pulses at 10
    msec per pulse
  • exposure time is shorter, reduces blurring from
    patient motion
  • Can be used where object motion is high, e.g.,
    positioning catheters in highly pulsatile vessels
  • 15 frames/sec, 7.5 frames/sec also available
  • Variable frame pulsed fluoroscopy is instrumental
    in reducing dose
  • Ex., initially guiding the catheter up from the
    femoral artery to the aortic arch does not
    require high temporal resolution and 7.5
    frames/sec could potentially be used instead of
    30 frames/sec
  • 7.5 frames/sec instead of 30 frames/sec, dose
    savings of (7.5/30) 25

46
Frame Averaging
  • Fluoroscopy systems provide excellent temporal
    resolution
  • However, fluoroscopy images are relatively noisy,
    and in some applications it is beneficial to
    compromise temporal resolution for lower noise
    images
  • This can be achieved by averaging a series of
    images or frames
  • Real-time averaging in the computer memory for
    display
  • Can cause noticeable image lag but noise in image
    is reduced as well
  • Could also reduce dose in some circumstances

c.f. Bushberg, et al. The Essential Physics of
Medical Imaging, 2nd ed., p. 245.
47
Last Frame Hold
  • Last-frame hold
  • when the fluoroscopist takes his or her foot off
    the fluoroscopy pedal, rather than seeing a blank
    monitor, last-frame-hold enables the last live
    image to be shown continuously
  • useful at training institutions
  • no unnecessary radiation used on patient

48
Road-Mapping
  • Road Mapping
  • software-enhanced variant of the last-frame-hold
    feature
  • side-by-side video monitors, one shows captured
    image, the other live image
  • In angiography, subtracted image can be overlayed
    over live image to give the angiographer a
    vascular road map right on the fluoroscopy
    image
  • is useful for advancing catheters through
    tortuous vessels

49
Automatic Brightness Control
  • The purpose of the automatic brightness control
    (ABC) is to keep the brightness of the image
    constant at monitor
  • It does this by regulating the x-ray exposure
    rate (control kVp, mA or both)
  • Automatic brightness control triggers with
    changing patient size and field modes

50
Automatic Brightness Control
  • The top curve increases mA more rapidly than kV
    as a function of patient thickness, and preserves
    subject contrast at the expense of higher dose
  • The bottom curve increases kV more rapidly than
    mA with increasing patient thickness, and results
    in lower dose, but lower contrast as well

c.f. Bushberg, et al. The Essential Physics of
Medical Imaging, 2nd ed., p. 247.
51
Image Quality Spatial Resolution
  • A 2D image really has 3 dimensions height,
    width, and gray scale
  • Height and width are spatial and have units such
    as millimeters
  • The classic notion of spatial resolution is the
    ability of an image system to distinctly depict
    two objects as they become smaller and closer
    together
  • The closer together they are, with the image
    still showing them as separate objects, the
    better the spatial resolution
  • At some point, the two objects become so close
    that they appear as one, and at this point,
    spatial resolution is lost

52
Image Quality Spatial Resolution
  • The spatial domain simply refers to the two
    spatial dimensions of an image, width
    (x-dimension) and length (y-dimension)
  • Another useful way to express the resolution of
    an imaging system is to make use of the spatial
    frequency domain
  • F (line pairs/mm or cycles/mm) 1/2?, where ? is
    the size of the object (mm)
  • Smaller objects (small ?) correspond to higher
    spatial frequencies and larger objects (large ?)
    correspond to lower spatial frequencies
  • So, objects that are
  • 0.36 mm correspond to 1.4 lp/mm
  • 0.19 mm corresponds to 2.7 lp/mm
  • 1 mm correspond to 0.5 lp/mm

53
Image Quality Spatial Resolution
  • Spatial frequency is just another way of thinking
    of object size
  • A device used to measure the spatial resolution
    is the bar pattern

c.f. Bushberg, et al. The Essential Physics of
Medical Imaging, 2nd ed., p. 249.
54
Image Quality Spatial Resolution
  • The modulation transfer function, MTF of an image
    system is a very complete description of the
    resolution properties of an imaging system
  • The MTF illustrates the fraction (or percentage)
    of an objects contrast that is recorded by the
    imaging system, as a function of the size (i.e.,
    spatial frequency) of the object
  • The limiting spatial resolution is the size of
    the smallest object that an imaging system can
    resolve
  • The limiting resolution of modern image
    intensifiers is between 4 and 5 cycles/mm

c.f. Bushberg, et al. The Essential Physics of
Medical Imaging, 2nd ed., p. 248.
55
Image Quality Contrast Resolution
  • The ability to detect a low-contrast object on an
    image is highly related to how much noise
    (quantum noise and otherwise) there is in the
    image
  • The ability to visualize low-contrast objects is
    the essence of contrast resolution. Better
    contrast resolution implies that more subtle
    objects can be routinely seen on the image
  • The contrast resolution of fluoroscopy is low by
    comparison to radiography, because the low
    exposure levels produce images with relatively
    low signal-to-noise ratio (SNR)

56
Image Quality Contrast Resolution
  • Contrast resolution is increased when higher
    exposure rates are used, but the disadvantage is
    more radiation dose to the patient
  • Fluoroscopic systems with different dose settings
    allow the user flexibility from patient to
    patient to adjust the compromise between contrast
    resolution and patient exposure

57
Noise and Contrast
  • Comparison of x-ray noise amplitudes in coronary
    angiograms acquired at fluoroscopic (2 µR per
    frame) (a) and angiographic (16 µR per frame) (b)
    exposure levels.

58
Noise and Contrast
  • 16 µR per frame. Note improved resolution and
    contrast due to the higher exposure.

59
Digital Image Quality
  • Effect of Matrix Size.
  • 512 x 512 matrix

60
Digital Image Quality
  • Effect of Matrix Size.
  • 256 x 256 matrix

61
Digital Image Quality
  • Effect of Matrix Size.
  • 128 x 128 matrix

62
Digital Image Quality
  • Effect of Matrix Size.
  • 64 x 64 matrix

63
Digital Image Quality
  • Gray Levels at a constant 512 x 512 matrix size.
  • 256 Grey Levels (8 bit)

64
Digital Image Quality
  • Gray Levels at a constant 512 x 512 matrix size.
  • 4 Grey Levels (2 bits)

65
Digital Image Quality
  • Gray Levels at a constant 512 x 512 matrix size.
  • 8 Grey Levels (3 bits)

66
Image Quality Temporal Resolution
  • Fluoroscopy has excellent temporal resolution,
    that is over time
  • Blurring in the time domain is typically called
    image lag
  • Lag implies that a fraction of the image data
    from one frame carries over into the next frame
  • Video cameras such as the vidicon demonstrate a
    fair amount of lag

67
Image Quality Temporal Resolution
  • Lag in general is undesirable, beneficial for DSA
  • Frame averaging improves contrast resolution at
    the expense of temporal resolution
  • With DSA and digital cine, cameras with low-lag
    performance (plumbicons or CCD cameras) are used
    to maintain temporal resolution

68
Fluoroscopy Suites
  • Gastrointestinal Suites
  • R and F room, large table that can be rotated
    from horizontal to vertical to put the patient in
    a head-down or head-up position
  • II above or under the table, spot film device
    usually there
  • Remote Fluoroscopy Rooms
  • Designed for remote operation by the radiologist
  • Tube above table, II under table
  • Reduce dose to the physician and no lead apron
    needed

c.f. Bushberg, et al. The Essential Physics of
Medical Imaging, 2nd ed., p. 250.
69
Fluoroscopy Suites
  • Peripheral Angiography Suites
  • Table floats, allows patient to be moved from
    side to side and head to toe
  • C-arm or U-arm configuration
  • 30 to 40 cm image intensifier used
  • Power injectors are normally ceiling- or
    table-mounted
  • Cardiology Catheterization Suite
  • Similar to angiography suite, 23 cm II used to
    permit more tilt in cranial caudal direction
  • Cine cameras used, biplane rooms common

c.f. Bushberg, et al. The Essential Physics of
Medical Imaging, 2nd ed., p. 250.
70
Fluoroscopy Suites
  • Biplane Angiographic Systems
  • Two complete x-ray tube/II systems used, PA and
    Lateral
  • Simultaneous acquisition of 2 views allows a
    reduction of the volume of contrast media
    injected in patient
  • Portable Fluoroscopy- C Arms
  • C-Arm devices with an x-ray tube placed opposite
    from the II
  • 18-cm (7-inch) and 23-cm (9-inch) and several
    other field sizes available
  • Operating rooms and ICUs

c.f. Bushberg, et al. The Essential Physics of
Medical Imaging, 2nd ed., p. 250.
71
Radiation Dose
  • Patient Dose
  • The maximum exposure rate permitted in the US is
    governed by the Code of Federal Regulations
    (CFR), and is overseen by the Center for Devices
    and Radiological Health (CDRH), a branch of the
    Food and Drug Administration (FDA)
  • The maximum legal entrance exposure rate for
    normal fluoroscopy to the patient is 10 R/min
  • For specially activated fluoroscopy, the maximum
    exposure rate allowable is 20 R/min

72
Radiation Dose
  • Patient Dose
  • Typical entrance exposure rates for fluoroscopic
    imaging are
  • About 1 to 2 R/min for thin (10-cm) body parts
  • 3 to 5 R/min for the average patient
  • 8 to 10 R/min for the heavy patient
  • Maximum dose at 120 kVp for most vendors

c.f. Bushberg, et al. The Essential Physics of
Medical Imaging, 2nd ed., p. 252.
73
Dose to Personnel
  • Rule of Thumb standing 1 m from the patient, the
    fluoroscopist receives from scattered radiation
    (on the outside of apron) approximately 1/1,000
    of the exposure incident upon the patient
  • The scatter field incident upon the radiologist
    while performing a fluoroscopic procedure is
    shown
  • A radiologist of average height, 178 cm (510)
    is shown overlaid on the graph and key anatomic
    levels are indicated

c.f. Bushberg, et al. The Essential Physics of
Medical Imaging, 2nd ed., p. 253.
74
Dose to Personnel
  • The dose rate as a function of height above the
    floor in the room is shown for 6 different
    distances D, representing the distance between
    the edge of the patient and the radiologist
  • 80 kVp beam and 20 cm patient thickness assumed
    for calculation
  • Roentgen-area product (RAP) or dose-area product
    (DAP) meters can be used to provide real-time
    estimate of the amount of radiation the patient
    has received

c.f. Bushberg, et al. The Essential Physics of
Medical Imaging, 2nd ed., p. 253.
75
Additional Reading
  • Additional topics on digital fluoroscopy and
    digital subtraction angiography can be found at
    the RSNA Education Portal.
  • http//www.rsna.org/education/archive/aapm/toc.htm
    lfluoroscopy
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