intro Flashcards
FOV from the x-ray machine
-The collimator (four lead leaflets) controls the size of the X-ray beam and the field of view
-Smaller FOV**
Better image resolution
Less scatter radiation, safer which is why we do smaller rads on specific body part not whole body
X-Ray Interaction with Matter
and Image Formation
-interaction depends on X-ray beam energy, tissue density, and
atomic number
-Regions with complete absorption/ attenuation (no X-ray reach the
detector) = radiopaque (white areas)
-Regions without absorption/ attenuation (all X-ray reach the
detector) = radiolucent (dark areas)
-Because most tissues are not homogenous, there are lots of shades of
grey
Fluoroscopy
-A series of low-dose X-rays which allows us to capture motion in real time (X-ray movie)
-Provides information about structural function of organs
-Many set-ups, C-arm units are most used in veterinary hospitals
common indications for fluroscopy
Swallow study:
-Used to watch the swallow motions and phases from the oral cavity to the stomach
-Used for patients with dysphagia and regurgitation
Dynamic airway study:
-Used to watch the airways during breathing and cough
Used for patients with suspected airway collapse
Intra-operative orthopedic procedure:
ultrasound physics
-Ultrasound is like ordinary sound, but at a much higher frequency
-images are produced by a pulse-echo technique employed by the transducers (probes)
ultrasound terminology
hyperechoic: white,
hypoerchoic: darker
anechoic: black (fluids)
ultrasound transducers
-Probe frequency is measured in
MHz (megahertz)
-Need transducers in the frequency
range of 5-18 MHz
-Lower frequency = better depth
penetration, but reduced image
resolution
-High frequency = less depth
penetration, but better image
resolution
-Most probes nowadays are
multifrequency probes
gain on ultrasound
gain: controls overall brightness of the image
Time Gain Compensation (TCG)
-Control of gain at different depths
-Helps to make a more uniform image
-Automatically adjusted on higher end machines
depth and focus on US
-depth controls the field of view size (zoom)
-Focus allows the image to be the clearest at the indicated level
cross sectional imaging
-CT and MRI
-Computed Tomography and Magnetic Resonance Imaging are the two
principle cross-sectional imaging modalities
-Major advantage over radiographs are:
-Tomographic nature
-Eliminates superimposition
=Reformatting abilities
-Increased contrast resolution
-Easier to identify subtle variations in tissues
contrast agents
-Positive contrast medium can be given intravenously to improve visualization of vascular structures, to highlight lesions, and to evaluate vascularity of lesions
-Contrast used for CT is iodine based
-Contrast used for MRI is gadolinium based
-Both have potential for adverse effects
Mild: rash, hive, local swelling
Severe: anaphylaxis, acute kidney injury, acute neural signs
-Make sure patient has adequate renal and liver function, and is well-hydrated before contras
CT
-Great for osseous structures, can make 3D recon
-Emits radiation (same physical principle as radiographs)
-Can be done under sedation mostly
-Scant time <1 minute
-$$
-Artifacts from metallic devices (can be decreased with computer algorithms)
MRI
-Excels in soft tissues (neural, MSK)
-No ionizing radiation (use radiofrequency rather than EMR)
-Requires general anesthesia
-Scan time 30 min +
-$$$
-Artifact from metallic devices, can’t be avoided unless remove device
-Potential risks with metallic devices (migration, heat)
nuclear imaging
-Administer to the patient substances (radiopharmaceuticals)
that bind to a target molecule to image* and measure* metabolic functions* of organs to diagnose diseases
-a radioactive isotope creates the image, and a pharmaceutical targets the organ or disease of interest
Nuclear scintigraphy
-Use Gamma camera
-Major limitation is low spatial resolution (no clear anatomical reference)
-Many tests are less commonly done now due to advances in other
imaging technologies and availability
-Tests still performed nowadays:
Bone scan – equine
Thyroid can – cats
Radiographic opacities
-The X-ray photons that reach the detector after interacting with the body determine the image opacity (darkness/ brightness)
-More X-ray photons reach detector = darker (radiolucent)
-Less X-ray photons reach detector = brighter (radiopaque)
-Overall 5 opacities can be seen radiographically
-Fluid and soft tissues are the same opacity Soft tissue
radiograph protocol
-Lateral images of any body part should be oriented with the patient’s head facing the viewer’s/ screen’s left
-VD or DV images of body cavities should be oriented with the patient’s head up/ top of the screen, and patient’s right on viewer’s left
-CC (DP) images of the limbs should be oriented with the proximal end of the extremity pointing up/ top of the screen
thinking in 3D for rads
-Limitation of radiographs: patient
is in 3D and images are 2D
-Important to keep in mind several
principles when translating 3D
information onto a 2D image:
Magnification
Distortion
Superimposition
magnification of rads
-Enlargement of a structure in the image relative to its actual size
-Due to increased distance between the object and the plate
-Also important to note, as distance increases, resolution decreases
-This means the area of interest should be placed closest to the plate
superimposition
Roentgen signs
-X-ray is discovered by German physicist, Wilhelm Roentgen, in 1895
-This is how we describe radiographic abnormalities:
Number: change in expected 3 of structures
Size
Shape: change in shape
Margination: changes in expected outline of a structure, well defined or ill defined
Opacity: change in expected opacity
Location: change in the expected location
