Imaging Modalities Flashcards
Fluoroscopy
An imaging technique used to obtain real time moving radio graphic images of internal structures, more radiation exposure than radiograph
What is a C-arm
Portable fluoroscopy, used commonly in the OR because can move arm do not need to move patient
What are examples of procedures or illnesses fluoroscopy is helpful with?
Esophagram, collapsing trachea, angiocardogram, orthopedic procedures
What are the basics of CT scanning?
An X ray technique where radiation goes through the body, differentiated by tissues it passes, forms cross-sectional slides, no superimposition, can create 3D images
How does the CT scanner work?
The X-ray tube rotates around the patient and detectors determine amount of radiation absorbed by the patient, then “black box” makes image
What is the old method of CT scanning?
Single slice rotations. The tube would make a complete rotation then the table moves before next rotation.
What is the new method of CT scanning?
The tube continuously rotates while the table continuously moves like a spiral
What is multi-detector CT?
New scanners have multiple rows of detectors - more slices
What is a pixel
Pixel is a picture element and has only 2 dimensions (x, y)
What is a voxel?
Voxel is a volume picture element with three dimensions (x, y, z) pixel with thickness, z is the thickness
Voxel average
Can create inaccuracies, thinner slices prevent this average but higher radiation exposure
What is an isotopic voxel?
X, Y, Z dimensions equal, can do multi-plane reconstructions without loss of resolution
Hounsfield unit
attenuation coefficient, water is 0 HU, range from -2,000 (attenuate less aka air) to 2,000 HU (attenuate more aka metal)
what is the window?
range of Hounsfield units (HU) in a specific image
what is the level
the central value of HUs displayed in CT image
Wide Window
best for imaging tissue that varies greatly
narrow window
best for imaging tissue with similar densities
hyperattenuating
CT term for white, high HU, ex: bone and metal
hypoattenuating
CT term for lowest HU values, black, ex: air
advantages of CT
- more detailed view of anatomy with no superimposition like xray
- faster and less expensive than MRI
- best for bone, lung, abdomen
disadvantages of CT
- radiation exposure
- more expensive than radiographs
- poor soft tissue contrast (compared to MRI)
Basics of MRI
- no ionizing radiation
- involves magnet, computer, radiowave receiver and transmitter, and patient (containing H+)
MRI image formation
H has 1 proton, and is abundant in body can act like tiny magnet, once in magnet machine H atoms line up on magnetic field (some face opposite direction but more line up with field) a radiofrequency coil applies energy causing the non-cancelled H to flip direction, once RF pulse stopped the energy is released goes to receiver coil and H returns to normal orientation, different tissues relax at different rates
weighting
- the use of certain parameters to optimize the different relaxation rates of different tissues to provide contrast
- main weights: T1 and T2
