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
T1 weighted
based on molecular construct
fluid is hypointense (black)
fat is hyperintense (white)
T2 weighted
- based on physical construct
- fluid is hyperintense (white) (liquid soft material)
- fat is hypointense (black) (firm solid tissue)
hypointense
less bright than tissue you compare to
isointense
same brightness as tissue you compare to
hyperintense
brighter than tissue you compare to
advantages of MRI
- better for soft tissue contrast and detail
- noninvasive
disadvantages of MRI
- long scan times
- expensive
- general anesthesia
Choose CT for:
- better bone detail
- good for thorax and abdomen
Choose MRI for:
- better soft tissue
- good for neuroimaging, musculoskeletal (especially horses), CNS
Acquiring CT
- heavy sedation or general anesthesia
- faster scan time (seconds/minutes)
Acquiring MRI
- general anesthesia
- longer scan time (1-2 hours)
safety concerns of CT
ionizing radiation
safety concerns of MRI
projectiles, metal implants
basic of ultrasound
- soon be commonplace like stethoscope
- sound wave frequency bounces off body subjects
ultrasound waves
- sound waves above acoustic level (we cant hear them)
what creates the sound waves?
ultrasound transducers transmit and receive sound waves, transmits 1% of time, receives 99% of time (measures intensity and time of arrival of returning waves
ultrasound frequency
- freq. inverse to wavelength
- lower freq. transducers penetrate farther but lower resolution
- higher freq. transducers do not penetrate far but higher resolution
how is US image formed?
- using the echoes returning from the tissues, sound travels at constant rate in tissue, white means reflection off tissue
how does US interact with matter?
differences in resistance to flow of tissues will alter sound wave direction (refract, reflect, or attenuate)
anechoic
- in US, shows black
- ex: fluid filled cyst
hypoechoic
- in US, darker than compared structure
isoechoic
- in US, same echogenicity to compared structure
hyperechoic
- in US, brighter than compared structure
what is the doppler effect?
- change in frequency occurs as result of motion between sound source and observer
- can determine velocity and direction blood flow
- RBCs sound source, transducer is observer
color flow mapping
- BART: blue away, red towards
