Download Chapter 19 - Diagnostic Imaging

Chapter 19
Diagnostic Imaging
Radiology and ultrasonography are the primary diagnostic imaging techniques available
to veterinary hospitals. In order for veterinarians to arrive at a correct diagnosis, high
quality images must be available.
Legal records and film identification
A. Radiographs are part of the medical record and should be clearly labeled.
a. Patient identification
b. Owner identification
c. Date of examination
d. Name of hospital
B. Film Labeling
a. Lead markers
b. Lead tape
c. Photo imprints
C. Film Filing
a. X-ray envelopes
b. Hospital filing system
Production of X-Rays
A. X-rays = form of radiation that results when energy of electrons is converted to
electromagnetic radiation
B. X-rays are produced when fast moving electrons collide with matter (in x-ray
tube)
X-Ray Tube
A. Cathode – electrically negative portion of the x-ray tube; provides source of
electrons
B. Anode – electrically positive portion of the x-ray tube; provides the target for the
interaction of the electrons
a. Stationary Anode – small capacity for x-ray production; dental units and
small portable units for large animals
b. Rotating Anode – more powerful machines; produce higher quality images
C. Tube Rating Chart – provided by tube manufacturers; shows safe exposure time
and maximum kVp (kilovoltage peak) and mA (milliamperage) in a single
exposure
Equipment
A. Portable Unit – light units that can be easily carried/moved; common for large
animal vets
B. Mobile Unit – wheel mounted units that can be moved around the hospital
C. Stationary Unit – large, powerful units that cannot be moved
D. Fluoroscope – presents a continuous moving image; gastrointestinal studies,
myelography, heart and vascular studies; rarely seen due to cost
E. Digital Radiographs – any radiographic technique where images can be
digitalized and displayed on a computer screen
F. Computed (Axial) Tomography (CAT Scan/CT Scan) - X-ray procedure that
combines many X-ray images with the aid of a computer to generate crosssectional views and, if needed, three-dimensional images of the internal organs
and structures of the body; rarely used
G. MRI (Magnetic Resonance Imaging) - uses a powerful magnetic field, radio
frequency pulses and a computer to produce detailed pictures of organs, soft
tissues, bone and virtually all other internal body structures; rarely used
Image Receptors – mechanisms that transfer the invisible radiation into a visible
image
A. Cassette – rigid film holder that keeps the screen and film in close contact
B. Screen – layers of tiny crystals that emit light when stuck by radiation and expose
the film
C. Film – provides a permanent record of the image produced by the radiation
D. Grid – sheet of lead that filters the primary x-ray beam and absorbs most scatter
radiation
Dark Room
Where films are developed. These are rarely seen/used with the invention of digital
radiography.
Radiographic Quality
A. Density – degree of darkness or blackness on the film; the more photons that
affect the film, the darker the image
B. Contrast – visible difference between two adjacent radiographic densities
C. Detail – definition/sharpness of the image
Radiation Safety
A. Hazards – all tissues are sensitive
a. Cells are damaged at the DNA level
b. Younger tissues/organs more sensitive
c. Cells that divide rapidly more sensitive
d. Critical organs = dermis, thyroid, eyes, lymphatic system, blood forming
tissue, bone, gonads
B. Measurement – absorbed dose is measured = unit of radiation that is transferred to
a body part
a. Units are “gray”, “coulomb”, “Sievert”
C. Maximum Permissible Dose – max dos of radiation that a person may receive in a
given period
a. Set by National Council on Radiation Protection and Measurements
D. Practices
a. NEVER allow any body part to be in path of primary beam
b. NEVER permit pregnant women or individuals under 18 to be in the room
c. Remove all unnecessary personnel and rotate personnel
d. Use non-manual restrain when possible (sandbags)
e. ALWAYS wear protection
i. Lead gloves
ii. Lead apron
iii. Thyroid protector
f. Collimate to smallest area possible
g. Wear dosimeter to track exposure
h. Never hand hold a machine
i. Avoid re-takes
Positioning Techniques – see attached
Ultrasonography
A. Use of high frequency sound waves to produce images of internal structures.
B. Patient preparation:
a. Clip surface to be examined
b. Clean skin thoroughly
c. Apply ultrasound coupling gel
C. Ultrasound image:
a. Thin, cross-sectional slice through the body
b. Requires knowledge of anatomy
c. Same equipment used in human medicine