10/20/2011
CVM 6101
Normal Radiographic
Anatomy
CVM 6101 Normal Radiographic Anatomy
» Lecture and laboratory course
 Utilizes Moodle
» Read syllabus and course schedule carefully
» Address questions to:
 For course: Dan Feeney, course coordinator
 For Moodle: Kristy Lashbaugh/Anthony Untiedt
 For lecture/lab material: individual instructors
» Assessments:
 Open book timed quizzes on Moodle
 Closed book proctored and timed final on Moodle

Includes the LA material as closed book
DVM radiology training overview
» 1st yr, fall semester: Normal
» 2nd yr, spring semester: Physics, alternate
imaging intro, cardiopulmonary, urogenital
» 3rd yr, fall semester: Abdomen/GI,
musculoskeletal
» 3rd yr, spring semester: ultrasound elective
» 4th yr: core radiology rotation, SA
ultrasound elective
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10/20/2011
Introduction to
Radiographic Imaging
Making sense of the shadows
Kari L. Anderson, DVM, Dipl ACVR
Clinical Professor
Introduction to Radiographic
Imaging
» Lecture 1: image formation
» Lecture 2: image interpretation
Introduction to
Radiographic Imaging
Image Formation
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Objectives
» The student will be able to explain:
 Basic concepts of x-ray production and x-ray
interactions
 Making of a radiographic image
 Foundations for the appearance of the
resultant image
 Consequences of the two-dimensional image
 ALARA concept
Which tibia is fractured?
Discovery of x-rays
» November 8, 1895
 Wilhelm Conrad Roentgen
 Refused
to patent x-ray apparatus
believing that this new discovery
should be used for “the good of
man”
» 1901 Nobel Prize in Physics
» First documented use in
veterinary radiology in 1896
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Mini-Physics Tutorial
Definition of x-ray
» X-rays are a form of
electromagnetic
radiation

Combination of electric
and magnetic fields that
travel together
 “sine
wave” with
frequency and
wavelength
Production of x-rays
X-rays produced in a vacuum tube
» Heating (milliamperes or mA) filament (anode)
produces electrons
» Electrons accelerated across a potential difference
(kilovolts peak or kVp) toward target (cathode)
» Interaction at target (focal spot) produces heat and
x-rays (1%)
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Properties of x-rays
»
»
»
»
»
»
»
»
»
»
No mass
Travel at speed of light
Invisible
Cannot be felt
Travel in straight line
Cannot be deflected by magnetic field
Penetrate all matter to some degree
Cause certain substances to fluoresce
Can expose photographic emulsions
Can ionize atoms
Interaction of x-rays with matter
» Interact with matter similar to light photons
 Absorbed
 Reflected (scattered)
» BUT can also pass through patient’s body
 Can be absorbed or scattered by deeper
structures
 Can pass through unchanged
Basic concept of making
radiograph
» Beam of x-rays created and directed toward
image detector
» Object to be imaged placed in the x-ray beam
path

X-ray tube
Between x-ray tube and
image detector
Object to be
imaged
Image detector
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Basic concept of making
radiograph
» Radiographic image possible only
because of differential absorption of x-rays
by patient
» Radiograph is visible image of internal
make-up of an object
» Some method of recording the image
(image detector) of the patient must occur
if it will be assessed critically
Basic concept of making
radiograph
Production of an image
– image detector
» Conventional film/screen radiography
 Radiographic film similar to photographic film
 Chemical
reactions take place in response to
energy being added to the film emulsion
 Negative image formed which is then developed

Intensifying screens fluoresce when impacted
by x-rays
 Visible
light exposes radiographic film
efficiency of system
 Improves


Film and screen held in supporting cassette
Film developed
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Conventional film/screen
radiography
Production of an image
– image detector
» Computed radiography
 Cassettes similar to FSR
 Imaging plate (instead of film) traps x-ray
energy on photostimulable phosphor as latent
image
 Imaging plate put into a reader
 Scanning
laser beam causes light to be released
which is then converted into electrical signal for
image


Imaging plate is “cleared” and reused
Radiograph is a digital image
Computed Radiography
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Production of an image
– image detector
» Digital radiography
 Special digital panel (solid state detector) with
cable directly to computer (some are wireless)
 No reader step needed – x-rays direct to
digital
 Digital panel reused
 Radiograph is a digital image
Digital Radiography
Radiographic Image
» Radiograph is picture of x-rays able to
penetrate object – literal shadow of object

Resulting image is “what is left over” – x-rays
that can get through (penetrate) the object
 What
gets through the patient and is recorded on
image detector is what creates the radiographic
image

X-rays that penetrate the object make the
radiograph black
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Radiographic Image
Radiographic Image
» Number of x-rays penetrating depends on:
 Biologic density of object
 Denser
 Appear
objects absorb (attenuate) more x-rays
whiter on a radiograph
Femur
Bladder
Radiographic Image
» Number of x-rays penetrating depends on:
 Thickness of object
 Thick
piece of material absorbs (attenuate) more xrays
 Appears whiter on a radiograph
Bladder
Fluid filled uterus
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Radiographic Image
» Animals composed of tissues of varying
density and thickness adjacent to each
other
Differential absorption of x-rays passing
through tissues is basis of radiography
 Areas of greater patient density will be whiter
on a radiograph
 Areas of greater patient thickness will be
whiter on a radiograph

Varying patient density and
thickness
Ischium
Spleen
Heart
Liver
Falciform fat
Radiographic opacity
» Definition: the relative ability of a material to
block passage of (absorb) x-rays
» Radiopaque: white (or relatively white) areas on
radiographs

Example tissues: heart, liver, bone
Bone
Heart
Liver
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Radiographic opacity
» Definition: the relative ability of a material to
block passage of (absorb) x-rays
» Radiolucent: black (or relatively blacker) areas
on radiographs

Example tissues: aerated lung, intestines with gas
Stomach gas
Lung
Opacity interface
» Boundary between opacities
» Contrast media can be used to create or
enhance opacity interfaces


Positive contrast is radiopaque (barium, iodine)
Negative contrast is radiolucent (air, CO2)
Contrast
» Definition: the degree of opacity difference
between adjacent areas on a radiograph
» High contrast: lung with liver
» Low contrast: fat with liver
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Radiographic Image
» Radiograph is a two-dimensional depiction of a
three-dimensional object



Shadow puppet – see exterior margin
Photograph – facing exterior surface
Radiograph – margins, exterior surface and some
interior architecture

Basically the 3-D object is compressed into a flat image
Magnification
» Enlargement of image relative to actual size
» Directly related to the distance from the object to
the image detector
» Indirectly related to the distance between the
focal-spot (x-ray tube) and the image detector
» Also results in blurring (decreased clarity) and
distortion


Object should be as close to the image detector as
possible
Distance between focal-spot and image detector
should be as large as practicable
Magnification
Magnified portion of shadow
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Magnification
» R marker placed
on right side of
patient, L marker
placed on left side
of patient
» Markers are same
size
» Right side of
patient closest to
image detector
Distortion
» Image misrepresents true shape or position of
object
» Caused by unequal magnification of the part
being radiographed


Portion of object is farther from the image detector
Keep object parallel to image detector
No distortion
Distortion
Distortion
Distorted femur
*note that femur
also appears shorter
(foreshortening)
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Loss of Depth Perception
» To evaluate depth radiographically, two
radiographs of object necessary

One radiograph made at 90º angle to other

Depth mentally reconstructed

Called orthogonal views
Where is the
identification
marker?
Summation Sign
» Occurs when parts of objects in different planes
are superimposed

Overlapping portions appear to have an opacity equal
to the sum of the individual tissues
Rt kidney
Lt kidney
Summation Sign
» Occurs when parts of object in different planes
are superimposed

Overlapping portions appear to have an opacity equal
to the sum of the individual tissues
Third
kidney?
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Summation Sign
» Occurs when parts of object in different planes
are superimposed

Overlapping portions appear to have an opacity equal
to the sum of the individual tissues
Silhouette Sign
» Materials of the same radiographic opacity
in contact results in the loss of the opacity
interface (no contrast)
Borders of individual materials cannot be
resolved (border effacement)
 May be easier to think of as a “negative
silhouette” sign

Silhouette Sign
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Radiation Safety
»
»
Ionizing properties of x-rays renders
them hazardous
Ionizing in DNA can lead to increased
1)
2)
3)
4)
5)
Rate of mutation
Rate of abortion or fetal abnormalities if
irradiated in utero
Susceptibility to disease and shortened life
span
Risk of cancer
cataracts
Radiation Safety
» Goal:
 Obtain maximum diagnostic information with
minimal exposure of the patient, radiology
personnel and general public
Radiation Safety
» US Nuclear Regulatory Commission
(NRC)
Official source for establishing guidelines for
radiation protection
 Annual occupational radiation dose to
individual adults limited to 0.05 Sv (5 rem)

 Unit
of dose equivalent that weights for the
damage from different types of radiation
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Radiation Safety
ALARA concept
»
As Low As Reasonably Achievable
Practical:


1)
2)
3)
Distance – increase distance from source
Time – reduce duration of exposure
Shielding – use of protective barriers between
individual and radiation source
Which tibia is fractured?
A. Left
B. Right
C.Unable to
determine
Summary
» Basis of the radiographic image is the differential
absorption of x-rays by the object


Beam of x-rays produced by x-ray tube and directed toward the
patient; x-rays that pass through are recorded by image detector
Absorption of x-rays depends upon patient density and thickness
» Radiographic image is two-dimensional

Consequences of this include magnification, distortion, loss of
depth perception, summation sign and silhouette sign
» Radiation safety is important because of the ionizing
properties of x-rays


Distance, time, shielding
ALARA concept
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