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
