Radiologia si ecografia animalelor de companie - diagnostic imagistic, Kardiologia Weterynaryjna, Materiały ...

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SAUNDERS
An Imprint of Elsevier Science
11830 Westline Industrial Drive
St. Louis, Missouri 63146
Small Animal Radiology and Ultrasonography
ISBN 0-7216-8177-8
A Diagnostic Atlas and Text
Copyright © 2003, Elsevier Science (USA). All rights reserved.
No part of this publication may be reproduced or transmitted in any form or by any means, electronic or
mechanical, including photocopying, recording, or any information storage and retrieval system, without
permission in writing from the publisher.
Notice
Veterinary medicine is an ever-changing field. Standard safety precautions must be followed, but as new
research and clinical experience broaden our knowledge, changes in treatment and drug therapy may become
necessary or appropriate. Readers are advised to check the most current product information provided by the
manufacturer of each drug to be administered to verify the recommended dose, the method and duration of
administration, and contraindications. It is the responsibility of the treating veterinarian, relying on experi-
ence and knowledge of the animal, to determine dosages and the best treatment for each individual animal.
Neither the publisher nor the editor assumes any liability for any injury and/or damage to animals or prop-
erty arising from this publication.
Previous edition copyrighted 1996
International Standard Book Number 0-7216-8177-8
Acquisitions Editor:
Ray Kersey
Developmental Editor:
Denise LeMelledo
Publishing Services Manager:
Pat Joiner
Project Manager:
David Stein
Designer:
Renée Duenow
KI/MVY
Printed in the United States of America
Last digit is the print number: 9 8 7 6 5 4 3 2 1
P R E F A C E
for its contents. We are grateful to Dr. Norman Ackerman–our good friend and
the co-author of prior editions of this book–for his previous contributions
This edition was written to further the original goal of the first book (i.e., to be a pic-
torial atlas that illustrates the radiographic and sonographic abnormalities of the common
diseases of dogs and cats). The complementary role that radiography and sonography
share is difficult to demonstrate in a limited number of illustrations, but it should be
emphasized that in most cases both radiographic and sonographic information should be
obtained and integrated to reach a complete diagnosis. As before, the text is offered to sup-
plement the pictorial information.
We continue to believe that every radiographic study should have at least two views
taken at right angles to each other and that every sonographic study should have multiple
imaging planes assessed. However, due the limitations of cost, we have limited the images
in the book to those best illustrating the lesions. We have also excluded computed tomog-
raphy, magnetic resonance imaging, and nuclear scans. Access to these modalities is still
limited, but they are becoming more available and we anticipate that future editions will
need to include these modalities.
As in the previous books, the author with primary responsibility for an area was
accorded final discretion relative to the method of presentation and ultimate importance
of specific material. Fortunately, disagreements were rare.
We appreciate all the work done by those who have directly or indirectly helped with
this project. We hope that we do sufficient honor to all those who have contributed to the
literature in our extensive references. We are deeply indebted to those individuals and
institutions (Henry Bergh Memorial Hospital of the ASPCA, Purdue University, University
of Missouri, University of Georgia, the University of Minnesota, and the Animal Medical
Center) that have provided training and support in our past. We are also grateful to our
current institutions (Veterinary Specialists of South Florida and the University of
Minnesota) for their support. We are particularly grateful to Tacy Rupp, DVM, DACVIM
(Cardiology), for her review of the material on echocardiography. Any errors in this area
are solely Dr. Burk’s responsibility.
Finally, we are exceedingly grateful to our spouses (Lisa Burk, VT, and Janet Feeney, BS)
for their support, patience, and encouragement. We are both very lucky to have someone
who has the love and patience to endure the trial that is a book.
Ronald L. Burk, DVM, MS
DACVR (Radiology, Radiation Oncology)
Daniel A. Feeney, DVM, MS
DACVR (Radiology)
V
W
e (RLB and DAF) are the co-authors of this edition and are solely responsible
C H A P T E R O N E
INTRODUCTION
GENERAL CONTRIBUTION OF RADIOLOGY TO VETERINARY
MEDICINE
The art and science of radiology became an integral part of veterinary medicine and sur-
gery shortly after the exposure of the first radiographic films. This subsequently led to the
publishing of the first English language text on the subject of radiology in canine prac-
tice.
1
Although many special radiographic procedures have been described since then, sur-
vey radiography remains the standard for the majority of antemortem anatomical
diagnoses.
The computer’s ability to manipulate data has been applied to various imaging tech-
nologies, resulting in new images such as those seen with digital subtraction fluoroscopy,
computed tomography (CT), magnetic resonance imaging (MRI), nuclear scintigraphy,
and diagnostic ultrasonography. This technological explosion has called for an expansion
of veterinary expertise beyond traditional diagnostic radiology to include all types of diag-
nostic imaging. Of these newer technologies, ultrasonography has gained popularity most
rapidly among both veterinary specialists and small animal practitioners. Although future
developments in diagnostic imaging and the role for MRI, CT, and nuclear imaging remain
to be defined, it is clear that diagnostic radiology and ultrasonography will play an impor-
tant and expanding role in the practice of small animal medicine and will contribute to
improved health for pets.
ESSENTIALS OF RADIOGRAPHIC AND ULTRASONOGRAPHIC
PHYSICS
The physics of radiology and ultrasonography are complex, and merely mentioning the sub-
ject to some individuals elicits a response that ranges from fear to boredom. Several text-
books explain radiologic and ultrasonographic physics in detail. Because our purpose is to
emphasize radiographic and ultrasonographic diagnosis, these textbooks and articles should
be consulted if a more complete understanding of radiographic and ultrasonographic
physics is desired.
2-9
A minimal knowledge of the physics of the processes involved is help-
ful for successful radiology procedures. X-rays are electromagnetic radiations with very short
wavelengths (high frequencies) and high energies. They are produced by bombarding a tung-
sten target with a stream of energetic electrons. The resulting x-ray beam is a collection of
photons of different energies. These x-ray photons may pass through or be absorbed by a
substance, depending on their energy and the relative density, thickness, and atomic number
of the substance. In film-based medical radiology, after passing through body fluids, tissues,
and organs, the photons ionize silver, which is contained in the emulsion of a photographic
type of x-ray film. This may occur either directly, by interaction of the x-ray photon with the
silver emulsion, or indirectly, by interaction of the x-ray photon with a fluorescent intensify-
ing screen producing blue or green light that exposes the film. This pattern of ionized silver
(the latent image) becomes visible after the film is chemically developed and fixed. Digital
detectors in lieu of x-ray film may also be used to create images. In this circumstance, the
interaction of the photons that have passed through the patient with a computer-compati-
ble detector creates the latent image, which is then translated into a digital display on a com-
puter screen. The visible image as visualized using film or a computer is a composite picture
of the structures through which the x-rays passed before reaching the film. For the rest of this
1
2
S M A L L A N I M A L R A D I O L O G Y A N D U LT R A S O N O G R A P H Y
text, reference will be made only to film-based radiographs, but it should be noted that the
same general technical and interpretive principles apply to digital radiography. Either type of
radiograph is a two-dimensional representation of three-dimensional structures and repre-
sents the sum of their radiodensities and shapes in that third dimension.
Ultrasonography is based on the pulse-echo principle. A pulse of high-frequency sound
(ultrasound) is transmitted into the body. This pulse travels through the body until it reaches
a reflecting surface, at which time a portion of the ultrasound pulse (the echo) is reflected
back toward the source of the pulse. Piezoelectric crystals, which create sound in response to
electronic stimulation and create electronic signals in response to sound stimulation, are the
two-way conduit between the computer and the patient. A computer tracks the time that
elapses from the beginning of the pulse to the time the echo is received, which allows deter-
mination of the reflecting surface’s position in two-dimensional space viewable on a video
screen. The proportion of the pulse that is reflected is dependent upon the initial strength of
the pulse, the ability of the reflecting surface to transmit sound (its acoustic properties), the
angle at which the pulse strikes the reflecting surface, and the size of the reflecting surface rel-
ative to the thickness of the ultrasound beam (the third dimension not seen in two-dimen-
sional ultrasonographic images). The amount of the ultrasound pulse that is reflected
determines the brightness (difference from the image background and associated with the
mechanical intensity of the reflected sound) of the point produced in the two-dimensional
image and whether or not anything can be seen beyond that point (e.g., acoustic shadow).
Should the ultrasound beam encounter tissues or objects with very different acoustic prop-
erties to general soft tissues (e.g., bone, air, metal), near-complete reflection will occur. If an
adequate number of points can be transmitted and received, a composite image of the reflect-
ing surfaces can be displayed. This image is updated by sending multiple pulses and receiv-
ing multiple echoes in a relatively short period. The data are stored in a computer and, when
transferred to a video display in “real time,” a moving, flicker-free image can be seen. This
real-time image can be recorded on videotape or the video display can be “frozen” on an area
of interest and recorded on photographic film or electronic media for future computer-based
transfer, manipulation, and even transmission to a remote site for second opinion.
The echoes reflected from a body part being examined also can be displayed along a mov-
ing, time-oriented graph. This display is referred to as M-mode and is used most often in car-
diology to display quantitatively the size of heart valves, heart chambers, heart walls, and great
vessels, as well as the motion of the ventricular walls, heart valves, and major vessels. The
striplike image that is created parallels the course of an electrocardiogram, which also allows
comparison of electrical and mechanical cardiac activities.
The hand-held transducer, which houses the piezoelectric crystal(s), can vary in fre-
quency (megahertz [MHz]) and crystal configuration. In general, the higher the resonant
frequency the greater the resolution but the lower the penetration of the sound beam. For
most small animals, transducers in the 4- to 12-MHz range are used. The arrangement of
the piezoelectric crystals as well as their number, “firing” sequence and, if applicable,
motion determines the shape of the two-dimensional image display (e.g., sector [pie-
shaped] or rectangular image) (Fig. 1-1). The applicability of these transducer configura-
tions depends on whether a small or large “footprint,” or area of surface contact, is
applicable to the anatomy being imaged and the cost one is willing to encumber for a
machine. Current sector scanners may have transducer configurations ranging, in increas-
ing order of cost, from (1) mechanical sector, moving the piezoelectric crystal(s), through
(2) curved linear/radial array, a series of piezoelectric crystals arranged in a diverging array,
to (3) phased array, a linear series of piezoelectric crystals pulsed in a highly sophisticated
sequence to whip the sound beam back and forth (Fig. 1-2). Current linear-array scanners
(linear series of piezoelectric crystals designed to image flat or nearly flat surfaces and yield
a rectangular image that corresponds to the transducer length) may vary in their overall
size depending on their intended use (e.g., broad surface abdominal imaging for organs not
obscured by ribs, pelvis, gas-containing viscera, or intracavitary imaging such as transrec-
tal). The most versatile transducer configuration for small animal imaging is the sector
scan because the narrow part of the image is at the skin surface and the viewed area gets
wider with increasing depth in the patient. This allows views to be made between bony
structures (e.g., ribs) or gas-filled viscera or both. There are special transducer configura-
C H A P T E R O N E I N T R O D U C T I O N
3
FIG. 1-1
Example of a two-dimen-
sional, sector real-time scan
(A)
and
a two-dimensional, real-time linear-
array scan
(B)
. Each scan was made
of the same spleen
(S).
The ventral
capsule (
arrow
closest to top) and
dorsal capsule (
arrow
lowest on scan
and pointing to the entrance of a
splenic vein) are identified. Note the
difference in the volume imaged in
the near field (just under the skin
surface) in
A
compared with
B.
A
B
tions available including transvaginal, transesophageal, and even intravascular. These are,
however, quite expensive and are designed only for specific use in humans. Although there
may be some applicability of these to select small animal situations, their limited versatil-
ity usually does not justify their cost.
Ultrasonography is subject to many artifacts. These have been described in detail, and
the physical principles governing their production have been explained.
2,3,7-15
Although we
will discuss the effects of these artifacts on the image that is produced, these references
should be consulted if a more complete understanding of the physical principles that pro-
duce these artifacts is desired.
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