radiology and ultrasound Flashcards
which unit of measure quantifies occupational exposure to electromagnetic radiation
Rem (radiation equivalent)
yearly max 5 rem
pregnant/fetus: .5rem/year or .05rem/month
roentgen (R)
unit of radiation exposure
Rad
radiation absorbed dose/amount of radiation received by individual
Curie (Ci)
quantity of radioactive material
describe xrays
short wavelength, high frequency ionizing radiation that penetrate matter at the molecular level
-can damage cellular components (DNA/RNA), cause reactive oxidizes species, and predispose someone to cancer
effective barriers between X-rays or gamma rays
lead or concrete
very high sensitivity to biological effects of EMR
bone marrow
intestinal epithelium
reproductive cells
fetal tissue
high sensitivity to biological effects of EMR
optic lens
thyroid epithelium
mucous membranes
medium sensitivity to biological effects of EMR
glial cells
liver
lung
pancreas
low sensitivity to biological effects of EMR
mature RBC’s, bone, cartilage
3 ways to limit radiation exposure
distance (6ft)
duration
shielding
review parts of normal CXR
review A part of ABCDEFGHI approach
assessment of quality and airway
airway: trachea, carina, mainstem bronchi, ETT
PIER: position, inspiration, exposure, rotation
adequate inspiration on X-ray is determined by ID’ing right hemidiaphragm at 9th or 10th rib counted posteriorly
review B part of ABCDEFGHI approach
bones examination for symmetry and fractures. examine for foreign bodies and SQ air
review C part of ABCDEFGHI approach
cardiac
normal: width of heart is less then 50% the width of the thorax (PA) and 60% (AP)
PA view most accurate assessment of heart size
ID RA, ascending aorta, aortic arch, pulmonary arteries, LV borders
review D part of ABCDEFGHI approach
diaphragm
-right is usually higher than left due to liver
-bilateral flattening consistent with chronic COPD or asthma (picture)
-look for air
review E part of ABCDEFGHI approach
effusions
-costophrenic angles are formed where chest wall and diaphragm meet. sharp, clearly defined angles are normal while blunted angles signify effusions
-effusions tend to rise higher on sides creating a U shape- also need to verify with a lateral angle
review F part of ABCDEFGHI approach
fields, fissures, foreign bodies
-infiltrates, masses, consolidation, PTX, vascular markings
-interstitial pulmonary edema ex LV failure is characterized by peribronchial cuffing and/or linear patterns (Kerley lines)
-kerley A lines are 2-6cm oblique lines in upper lobes, kerley B lines are 1.5-2cm horizontal lines in lung periphery
review G part of ABCDEFGHI approach
great vessels and gastric bubble
-size and shape of aorta as well as outline of pulmonary vessels.
-aortic knob (distal aortic arch that becomes descending thoracic aorta)
-gastric bubble is radiolucent region under left hemidiaphragm caused by gas in fundus of stomach
what causes enlargement of aortic knob (4)
aortic dissection, valvular insufficiency, PDA, or severe TOF
review H part of ABCDEFGHI approach
hila and mediastinum
-hila consist of major pulmonary vessels and bronchi
-eval mediastinum for widening (aortic dissection) or tracheal deviation
review I part of ABCDEFGHI approach
impression overall- synthesize findings
what type of appliance is present on this xray
PAC and ETT
ID of properly placed ETT on CXR
mid trachea about 4-5cm above carina (can use T4-T5 as surrogate and count up 4-5cm from there)
ID of properly placed CVC on CXR
distal tip of CVC should be in distal 1/3 of SVC between right atrium and most proximal venous valves. usually 1 inch from end of SC and IJ veins before they join brachiocephalic vein
ID of properly placed PAC on CXR
from SCV though RA to pulmonary artery. think of anatomy as you look for placement
ID of properly placed cardiac implantable device on CXR
need 2 views (usually PA and lateral) to eval misplaced lead
what’s going on in this CXR
single lead coming from pacer with two shocking coils- one in SVC and one in RV
what is the first radiographic sign of p.edema
cephalization aka redistribution of vascular markings in upper lung
describe the abnormality occurring in this CXR
atelectasis, which features segmental, sub segmental, or lobar opacities with loss of volume and displacement of fissures on affected side
-cannot see anesthesia induced bibasilar atelectasis on CXR
describe the abnormality occurring in this CXR
PTX.
-pleural line beyond which no vascular markings are seen (region appears hyper lucent)
-collapsed lung retains general shape of lung
-deep sulcus sign: air collects in anterior inferior thorax adjacent to the diaphragm. abnormal lucency on costophrenic angle of affected side.
describe the abnormality occurring in this CXR
tension PTX.
-depression of diaphragm
-flattening of cardiac border
-mediastinal shift to contralateral side with tracheal deviation
cardiogenic pulmonary edema stage 1
cephalization always occurs first
p. blood vessels larger in upper lobes than in lower lobes
cardiogenic pulmonary edema stage 2
interstitial edema
peribronchial cuffing (donuts)- interstitial edema around bronchial walls
-butterfly pattern around hila
-septal lines:
kerley a lines (oblique lines 2-6cm in upper lobes near hila)
kerley b lines (horizontal lines <2cm long in lung periphery near costophrenic angles
cardiogenic pulmonary edema stage 3
alveolar edema
alveolar consolidation
blunted costophrenic angles
rounded LV (increased heart size)
3 stages of ARDS
stage 1: exudative. diffuse patchy alveolar infiltrates manifest peripherally ~12 hours after initial insult
stage 2: primary alveolar infiltrates with atelectasis and air bronchograms appear after 24-48h
stage 3: complete alveolar consolidation
ID the abnormality in the CXR
fracture boi
compression and rarefaction on sound wave/ultrasound wave
compression is peak (high pressure) while rarefaction is trough (low pressure)
frequency
-measure of pitch
-mesured in hz (cycles/second)
-humans can hear between 20-20,000hz
-ultrasound frequencies range between 1-20million hz (or 1-20Mhz)
wavelength
distance between 2 points on adjacent cycles
-higher frequency = shorter wavelength
amplitude
loudness (measured in decibels)
-determined by degree of pressure fluctuations from the displacement of molecules within the medium
-higher amplitude = greater pressure change and louder sound
propagation velocity of sound through
air
soft tissue
bone
air: 343 m/sec
soft tissue: 1540 m/sec (this is a reference average value)
bone: 3,000-5,000 m/sec
what material is used in modern ultrasounds to employ a piezoelectric effect
lead zirconate titanate
(if you apply electrical current to pizoelectric material, it emits sound waves and vibrates)
what determines the placement of the vertical and horizontal dots on the ultrasound
vertical placement is determined by time delay- how long it takes echo to return to transducer
horizontal placement: determined by which piezoelectric crystal receives the returning echo
examples of things that usually appear hypo echoic
solid organs, skin, adipose, cartilage, muscle itself is hypo echoic but fascial lines appear hyper echoic
examples of things that usually appear anechoic
vessels, cysts, ascites
how to differentiate a tendon versus a nerve
nerves can appear honey comb and as you scan up they dont change in size
-tendons become flat and disappear as they connect to muscle
what does axial resolution help with
beam depth- differentiates structures that exist along the length of the US beam.
-axial resolution is improved by using higher frequency (shorter wavelength)
what does lateral resolution help with
beam width- ability to differentiate structures that exist in the width of the US beam.
-lateral resolution is improved by positioning sonoanatomy of interest in focal zone
what does elevational resolution help with (beam thickness)
ability to differentiate structures in thickness of US beam
fixed value determined by transducer
ID the 3 zones of the US beam
near zone (fresnel zone): region between transducer and focal zone
focal zone: where beam is narrowest (x and y axis) and thinnest (z axis)
far zone (fraunhofer zone): region beyond focal zone
describe attenuation and which structures produce the greatest degree of it
some of the sound waves never return to the transducer.
-bone > soft tissue > fluid
-greater with higher frequency sound waves than with lower frequency sound waves
-can think of it as the process of absorption, reflection, scatter, refraction
absorption
-waves are lost to body as heat
reflection
sound wave bounces off a tissue body of differing acoustic impedance
-applying gel reduces this
scatter
when US wave encounters something smaller than the US wave.
-causes scatter and signal never returns to transducer
-explains why fluid filled structures appear anechoic
refraction
bending of US wave that encounters tissue boundary at oblique angle
-concept is called snells law. formula used to calculate refraction of light when passing between two mediums with different refractive indices
high frequency transducer
mHz
depth range
when to use
> 10mHz
< or = 3cm below skin
when to use: ISB, supraclav, axillary, forearm, wrist, femoral, ankle, superficial blood vessels
medium frequency transducer
mHz
depth range
when to use
5-10mHz
~3-6cm below skin
when to use: infraclav, popliteal, sciatic, deeper BV’s
low frequency transducer
mHz
depth range
when to use
<5mHz
> or = 6cm below skin
when to use: lumbar plexus, celiac ganglion, neuraxial block, patients with high BMI
liner array transducer
piezoelectric crystal arrangement
image specs
frequency
pizoelectric crystals arranged in a linear fashion, flat foot print
image same width as transducer to its geometrically accurate
operate in higher frequencies
curvilinear array transducer
piezoelectric crystal arrangement
image specs
frequency
piezoelectric crystal arrangement convex, has convex foot print
image specs: fan like
frequency: in lower frequency range
phased array transducer
image specs
best used for
frequency
narrow in near field and fans out with increasing depth
used when you have a small acoustic window to visualize deep structures like cardiopulmonary imaging between ribs
frequency: in lower frequency range
B mode
most bedside US procedures use this mode. stands for brightness of pixels on screen. produces real time imaging of sonoanatomy
M mode
M stands for movement. think of it as time lapse that shows relative movement of structures over time.
y axis represents degree of movement, x axis represents time
when to use M mode
frequently used in echocardiography, providing useful information about valve integrity, ventricular function, wall thickness, chamber size, aortic root diameter
-also useful for POC like dx of PTX or evaluating fluid responsiveness
define the doppler effect and when its used
change in perceived frequency of a sound wave when theres relative motion between sounds source and the observer. aka observer will perceive a change in the sounds frequency.
-used to ID vascular structures
what determines the degree of doppler shift
- frequency of US beam
- BF velocity.
- angle of insonation (shift is greatest if US beam is parallel to flow, shift is zero if US beam is perpendicular to flow. this is because cosine of 90 degrees is 0.)
negative versus positive doppler shift
remember this is all in relativity so dont assume red = arterial
according to standard convention, orientation marker on US should point towards (2)
patients’ head (long axis)
patients’ right (short axis)
define angle of incidence
highest quality image achieved at perpendicular (90 degree) angle
when is tilting the transducer helpful
optimizing angle of incidence relative to structure you are trying to ID
when is rocking the transducer helpful
promotes better contact between patient and transducer and helpful for imaging inside narrow acoustic window (rocking is in long axis way)
define sliding of transducer
maintaining short axis view
how to remedy this image
more gel, my dude
what artifact is this and how do we fix it
shadow. adjust scanning plane to find a better acoustic window.
what artifact is this and how do we fix it
acoustic enhancement (think of it as opposite of shadow).
when US meets fluid filled structure and underlying tissue, difference in acoustic impedance attenuates the brightness in this region.
what artifact is this
-mirror image. US beam gets trapped between two highly reflective tissues that causes time delay in some returning echoes.
-true anatomy and artifact will be eqidistant from reflector (pleura in this case)
define reverberation
sound waves bounce between two strong parallel reflecting surfaces.
-see this when imaging pleura or using wide bore needle
define bayoneting
-occcurs when needle passes through tissue of different acoustic impedance
-since ultrasound machine assumes that sound travels at 1540 m/sec, it fails to account for the fact that each tissue has unique propagating velocity
3 standard imaging windows for cardiac exam
- parasternal
- apical
- subcostal
POCUS cardiac: parasternal long axis view (PLAX)
patient position
transducer position
structures viewed
interpretation
TEE equivalent
patient position: left lateral
transducer position: just left of sternum at 3rd or 4th ICS
structures: LA, LV, mitral valve, aortic valve, aorta, pericardium
interpretation: LV function, mitral and aortic valve lesions, pericardial effusions
TEE equivalent: mid esophageal long axis
POCUS cardiac: parasternal short axis view (PSAX)
patient position
transducer position
structures viewed
interpretation
TEE equivalent
patient position: left lateral
transducer position: just left of sternum at 3rd or 4th ICS but turn transducer 90 degrees clockwise from PLAX view to have marker point towards patients left shoulder
structures viewed: LV + papillary muscles, RV, pericardium
interpretation: LV and RV function, pericardial effusion
TEE equivalent: trans gastric short axis
POCUS cardiac: apical 4 chamber (A4CH)
patient position
transducer position
structures viewed
interpretation
TEE equivalent
patient position: left lateral
transducer position: PMI. inferolateral to left nipple in men and under inferolateral quadrant of left breast in women. place US orientation mark on patients left side right US beam pointing towards patients right shoulder
structures viewed: RA, RV, LA, LV, mitral valve, aortic valve, pericardium
interpretation: LV and RV function, AV valve lesions, pericardial effusion
TEE equivalent: mid esophageal 4 chamber
POCUS cardiac: subcostal 4 chamber (subcostal 4CH)
patient position
transducer position
structures viewed
interpretation
TEE equivalent
patient and transducer position: with the patient supine, place transducer midline just inferior to xiphoid process. transducer orientation mark should point to patients left side. may need to apply a lot of pressure
structures viewed: RA, RV, LA, LV, mitral valves, aortic valves, liver
interpretation: LV function, pericardial effusion
TEE equivalent: mid esophageal 4 chamber
POCUS cardiac: subcostal IVC
patient position
transducer position
structures viewed
interpretation
TEE equivalent
from subcostal 4 chamber view (patient is supine), rotate transducer 90 degrees to tilt beam in posterior direction
structures viewed: IVC, RA, liver
interpretation: volume status. IVC collapse suggests hypovolemia
TEE equivalent: bicaval
POCUS view to eval for lung sliding/PTX
a lines and b lines in lung POCUS
a lines: horizontal lines that result from reverberation artifact due to pleura acting as strong reflector
b lines: (comet tails) vertical. can be normal or suggest pathology such as p.edema
POCUS: gastric
patient positioning
empty v clears v particulate
how to calculate how much fluid is ok
positioning: right lateral decubitus
gastric volume (mL) = 27 + 14.6 x CSA of stomach - [1.28 x age in years]
