Intro to Imaging Flashcards
Describe the basic principles of conventional radiography
heated cathode -> electrons beam b/c thermal energy -> tilted anode -> photons deflected to produce image
Electromagnetic waves transilluminate patient, behaves like shadows
Best image = beam perpendicular to object as close as possible to film
Advantages of conventional radiography
inexpensive & accessible, good view of bones (fractures/joints), cardiopulmonary assessment
Disadvantages of conventional radiography
ionizing radiation, avoid during pregnancy, limited soft tissue view & overlapping structures
Describe the basic principles of CT
x-ray beam rotates around patient, data reconstructed by computer
water = 0
air = -1000 (black)
bone = 1000 (white)
Advantages of CT
short scan time, more soft tissue detail
Disadvantages of CT
ionizing radiation
Describe the basic principles of MRI
imaging of protons (H+) manipulated by magnetic field
p+ align with magnet turning on -> p+ absorb wave energy and turn to RF pulse -> p+ return to magnet when RF pulse ends (intensity & duration of return = digitized tissue type)
Advantages to MRI
highly manipulative, great tissue detail (brain), no known damaging effects
Disadvantages to MRI
long and loud scan, enclosed (claustrophobia), no metal implants/pacemakers
Difference between T1 and T2 weighted MRI
T1: water = dark (good for soft tissue)
T2: water = bright (good for contrast)
Describe the basic principles of ultrasound
high frequency sound waves = echograms
image = attenuation (energy loss) + reflection (energy coming back)
Advantages to ultrasound
non-ionizing waves (safe), real-time, portable & cheaper
Disadvantages to ultrasound
operator dependence (training), poor image of air & bone, static images difficult to interpret
Compare/contrast appearance of air in CT and MRI images
CT: black
T1-MRI: dark
T2-MRI: dark
Compare/contrast appearance of fat in CT and MRI images
CT: black
T1-MRI: very bright
T2-MRI: bright
Compare/contrast appearance of water/CSF in CT and MRI images
CT: grey-black
T1-MRI: dark
T2-MRI: bright
Compare/contrast appearance of muscle in CT and MRI images
CT: grey
T1-MRI: dark
T2-MRI: dark
Compare/contrast appearance of bone marrow in CT and MRI images
CT: gray
T1-MRI: bright
T2-MRI: intermediate
Compare/contrast appearance of bone cortex in CT and MRI images
CT: white
T1-MRI: dark
T2-MRI: dark
Define radiographic progection
based on direction of beam
posteroanterior, anteroposterior, lateral
Define radiographic view
how image is viewed, always anterior (patient facing you)
Describe the anatomic planes of section and explain the radiologic conventions for viewing sectional images
Transverse/axial: (inferior view) as if standing at supine patient’s feet
Coronal: as if patient facing you
Sagittal: standing at patient’s left side (can change to right)
Describe how contrast media are employed to make tubular structures more visible in radiographic and CT images
increased density iodinated drugs enhance absorption = tissue appear whiter (angiogram, venogram, lymphangiogram)
GI tract: metal compound (barium) defines mucosa; double contrast = air + barium (more detailed, given via oral, tube, or enema)
Describe how contrast media are employed to make tubular structures more visible in MRI images.
magnetically active compounds useful - gadolinium/iron oxide
(iodination = useless b/c MRI not reliant on tissue density)
