Intro Flashcards
Imaging modalities
-Radiography
-fluoroscopy
-sonography (US)
-cross sectional imaging (CT, MRI
-nuclear medicine (Scintigraphy, PET-CT)
X-rays
-electromagnetic radiation (waves in classical physics, photons in quantum physics)
-xrays have higher frequency and wavelength than visible light
*higher energy=detach electrons and leads to ionization radiation
How X ray machine works?
Tube consists of cathode (neg) and anode (pos) made of tungsten (high melting point)
-electric current passes through cathode and releases electrons from it
-electrons are attracted to the anode with a max energy determined by tube potential (kVp)= results in photons (1%) and heat (99%) being produced. Photons released in a beam out of the window of the tube
Collimator
Controls the size of the xray beam and the field of view
Why do you want a smaller field of view?
Better image resolution
Less scatter radiation
Machine settings
- mA
- kVp
mA (miliampere) and s (second
mA= regulates the current that goes through cathode
s=exposure time
**together controls the number of electrons released and the amount of x-ray photons produced
kVp (kilovoltage peak)
regulates the voltage potential between the cathode and the anode and therefore the speed of electron bombardment/energy of the x-rays
X-ray interaction with tissues
Can be transmitted, absorbed, attenuated, scattered as it interacts with tissues
-depends on beam energy, tissue density, atomic number
-bone is higher density and will absorb more and less reaches plate beneath= white
-grey areas= because most tissues are not homogenous so get a mix
White radiopaque areas
Regions with complete absorption/attenuation (no x rays reaches the detector)
Radiolucent (dark areas)
Regions without absorption/attenuation (all x ray reaches detector)
Image storing and viewing
-digital imaging in DICOM; include all patient information
-need specific software
-Storage: A PACS (picture archiving and communication system)
DICOM
Digital imaging and communications in medicine
Workstation factors
- Lighting -needs to be ambient and adjustable
- Monitor quality- LCD screens; diagnosis needs brightness monitors of 350cd/m2, 3 megapixel resolution or higher, 32” monitors preferred
Fluoroscopy
A series of low dose x rays which allows for the capture of xrays in motion = “x ray movie”
*allows for structural function of organs
Common uses of fluoroscopy
- Swallow study- give positive contrast, observe motion; for dysphagia and regurg
- Dynamic airway study- watch airways during breathing and coughing; good for suspected airway collapse
- Intra-operative orthropedic procedure
Sonography (US)
-widely used, inexpensive, portable, non invasive, no radiation, real time imaging, can be used for lesion sampling, most commonly used for abdomen but others as well
*but diagnostic value is dependent on operator experience
Ultrasound physics
-like ordinary sound but much higher frequency (MHz)
-images are produced by a pulse-echo technique employed by transducers (probes). US pulse from probe interacts with tissues, and echos return back
What determines the image produced by US?
Timing and strength of returning echos
-less time=more superficial object
-more strong= very bright image
US terminology
Hyperechoic- more white
Hypoechoic- darker
Anechoic- completely black/no echo= fluid
Isoechoic- same echogenicity as surrounding structures
US probes
Probe frequency range: 5-18MHz
*most probes now are multifrequency probes
-Lower frequency probes= better depth penetration but reduced image resolution
-higher frequency= less depth penetration, but better image resolution
Shapes of US probes
- Curvilinear- usually lower frequency
- Linear- usually higher frequency; more crisp images
US machine knobs
- Gain- controls overall brightness of image
2.Time gain compensation- controls gain at different depths of tissues; helps make a more uniform image
*often auto adjusted on machines
- Depth- controls field of view size (zoom)
- Focus- allows image to be clearer
How much of screen should the image of interest take up?
Image of interest should cover 2/3rds of screen
Patient prep
-Prefer fasted patients to avoid gas and ingesta from blocking view
-Sedation- better image quality, less scan time, less stress
-often done in dorsal recumbency
-clip fur
-coupling gel
US guided FNA
- selected acoustic window should be prepared aseptically
-often 22G, 1.5 inch needles
-can see needle going into the target
Cross sectional imaging (MRI, CT)
-Allows you to see patient in transverse slices
*eliminates superimposition and allows for reformatting images into different planes
*has increased contrast resolution making it easier to see subtle variations in tissues
Contrast agents
Positive contrast medium injected IV allows for improved visualization of vascular structures and highlight lesions
Contrast used for CT
Iodine based
Contrast for MRI
gadolinium based
Adverse effects of contrast agents
-mild: rash, hives, local swelling
Severe: anaphylaxis, acute kidney injury, acute neutral signs
**need to make sure patient has adequate renal and liver function and is well hydrated
CT
-great for osseous structures, and 3D reconstructions
-emits radiation like x rays
-can be done under sedation
-less than 1 min
-less expensive than MRI
-artifacts from metallic devices but can be decreased with computer algorithms
MRI
-excels for soft tissues (neural or MSK)
-no ionizing radiation
-need GA
-scan time=30min
-expensive
-artifact from metallic devices which cant be avoided unless remove device
-potential risk of metallic device migration and heating up
Nuclear imaging types
-scintingraphy
-PET-CT
Nuclear imaging
Give patient radiopharmaceuticals that bind to the target molecule which allows for image and measure of metabolic functions of organs
*patient will be radioactive after imaging so want compound to have a short half life so that they can go home quickly after imaging
Parts of radiopharmaceuticals
- radioactive isotope that creates image by releasing gamma rays
- A pharmaceutical that targets organ or disease of interest
Nuclear scintigraphy
-use gamma camera
-limitation: gives a low spatial resolution, no clear anatomical reference
-used for equine bone scans and thyroid scans in cats
PET-CT
-observes metabolic activity of body. Can detect anatomical information but not lesions
-radiopharmaceutical: 18F-FDG (glucose monolog) that gets trapped in the cells and can be seen on image. Cells that have higher metabolic activity= more trapped
*common in oncology, and then orthropedics, disease/infection
