Specialized/alternative imaging Flashcards
Fluoroscopy is
Form of radiography that uses real time imaging of internal structures with a continuous beam of x-rays
Not still pictures as traditional radiography
Primary function is to provide dynamic real-time imaging of anatomical structures
Diagnostic process is enhanced if veterinarian able to view certain activities within the body as they happen
How does fluoroscopy work
Uses low mA and high kV settings
Time not independently selected as image is created in real time
Controlled by radiographer through use of a foot switch
As long as foot switch is depressed an exposure is occuring
How does the fluoro table work to produce images
Radiation comes from under the table through the patient and onto an image intensifier
Image intensifier receives radiation and converts it to a visible light image – called photoemission
Image sent to a monitor
Image viewed is the opposite of an x-ray – positive image
Black and white areas are reversed
C-arms are an example of type of fluoroscopic unit
When to use fluoroscopy
Minimally invasive repair
Intraluminal stenting for treatment of tracheal collapse
Urethral and colonic obstructive disease
Vascular procedures
Contrast studies of the GIT
Safety concerns for fluoroscopy
Very similar to general radiography, but has real-time component
Recognize radiation generally comes from beneath table (opposite of regular radiography) so use appropriate safety measures
ie: don’t cover hands with gloves
Exposure times are much longer – try to minimize as much as possible for safety of both worker and patient
ALARA
What is computed tomography showing
Technique used to show, in detail, images of structures that lie in structures that lie in predetermined plane of tissue while blurring or eliminating structures above and below that set plane
Uses same principles with advantage of computer to enhance image and ability to show multiple images or “slices” of structures of interest
How does a CT scan work
Works by having x-ray tube connected to image receptor
X-ray tube moves in an arc across table and image receptor follows that arc exactly (but in opposite direction)
Structures at a set point (fulcrum) will remain in focus and structures above and below that point will be blurred
Object of interest is positioned at focal plane (fulcrum)
Tube and receptor are attached
As long as tube and receptor move in unison they will maintain uniform focal plane and produce an image in focus
Image blur of a CT is
Slice thickness determined by operator of CT
Slices thinner than a mm are able to be acquired
Employs x-ray machine that acquires images that look like slices in loaf of bread
Uses detectors and computer
X-ray tube rotates 360 degrees around a gantry (opening in center of machine where table enters)
Opposite the tube are several detectors that rotate at the same speed as the x-ray tube
Two types of CT
Conventional
Spiral/helical
Conventional CT images are
table moves in increments so that several images/slices are taken for a complete examination (start-stop)
Spiral/helical CT is
continuous rotation of tube head/detectors and motion of table
How does CT produce an image
The detector will translate the image into shades of grey on a matrix
Original tomographic principle remains: 1 tube – 1 detector
X-rays pass through patient and the attenuated beam is collected by detectors
Detectors convert photons to an electrical signal, which is then converted to digital signal, which is transmitted to the computer
Computer reconstructs the image
What happens to CT after image is taken
Scan data (raw data) from detectors is used to create the image
This information is very large so is only temporarily available from the scanner
Final image is either photographed onto films or saved on a network (PACS) as picture files
Newer technology able to convert 2D images into 3D
When would you use CT
Can be used for special contrast procedures such as:
Angiograms
Used to visualize abdominal organs
Infections within extremities
Cross-section imaging of both soft tissue and bone
Safety considerations for CT
kV and mAs used in CT much higher than standard radiography
Higher the technical factors in CT, the nicer the image
ALARA!
Scan time
Usually means the time it takes the x-ray tube to rotate 360 degrees around the patient
How does an MRI work
Similar to CT in that takes thin slice of cross-sectional anatomy
Differs from CT in that does not use ionizing radiation to create image
Uses powerful magnetic field to align patient’s molecules based on polarity
Radio wave pulse then used to disrupt magnetic rotation in various tissues
Difference between tissues can be detected and imaged
Superior in imaging the brain and spinal cord, as well as soft tissue structures such as ligaments and cartilage in joints
Higher subject contrast than CT due to ability to show the concentration of free-floating hydrogen molecules within tissue
What types of signals are given during magnetic direction changes of MRI
T1 decay which is the direct magnetic movement of the center of the atom back to its original state
T2 decay is the signal received from the spinning of the atom back into its original state
Why can MRI see different tissues so well
Tissues and molecules in body have different responses with regard to T1 and T2 decay
This difference is what allows MRI to show various tissues so well
Various shades of gray seen in MRI image are referred to as “signal intensities”
Bright (white) portions have high signal intensity
Use of contrast with MRI
Contrast agent called gadolinium used to highlight infection, tumors or vascular disease
Gadolinium alters properties of specific tissues so that they enhance or light up
Gadolinium removed from body via kidneys
Renal function should be tested prior to using
What happens if magnet is near MRI
Magnet will forcefully pull these objects into itself, injuring or potentially killing anyone in its path
Oxygen tanks, pacemakers, orthopedic pins, plates, leashes, collars, horseshoes, beepers, etc cannot be used/present
Safety concerns with MRI
Deep general anesthesia
Difficulty in monitoring due to size of gantry
Most monitoring equipment is outside of the room
Scans take 20-60 minutes of general anesthetic and beyond
Magnets are always on
The most dangerous aspect of MRI is projectile effect – object launches into a magnet
Implanted metal can heat up possibly burning the patient
Metal surgical clips, gun shot remnants
Heat dissipation in patient – interaction of magnet and radio frequencies can produce heat
More important in newer, stronger machines
Noisy – ear protection necessary for patient and anyone staying in room
Pregnant personnel should not remain in room while MRI operating
Nuclear medicine and positron emission tomography is
Noninvasive imaging procedure that employs administration of small amount of radioactive material (radioisotope)
Very effective way to localize pathology or the results of trauma
Radioisotope carried to area with the most active blood supply
What is the difference between nuclear medicine and CT
More sensitive but less specific than radiography or CT
Images do not provide anatomic detail of radiographs or CT but do provide physiologic information about function of specific organs
Hospital or clinic that uses radioisotopes must be registered with the Canadian Nuclear Safety Commission
How does nuclear scintigraphy work
Technetium and Iodine are most common radionuclides used in veterinary medicine
Iodine mainly used to treat hyperthyroidism in felines
Not used for imaging
Technetium used predominantly in equine studies
Patient ingests or is injected with radionuclide and nuclear medicine camera detects the emission of the radioactivity from patient
