First exam U/S and Radiology
Two dimensional mode
"B-mode" Default mode of most machines
M-Mode
"Motion" mode Analyze movement of structures over time I.E. Measure the size of the heart chambers or movement of valves (lung pleural to R/O pneumo)
BART
(Blue Away, Red Towards)
Reflection and propagation of sound waves through tissues depends on?
-Acoustic impedance -Attenuation
What makes a good image?
-Acoustic interfaces perpendicular to the ultrasound beam -Equal brightness from top to bottom -Have less extraneous depth.
Phased Array (footprint)
-Crystal fire at different times -Small footprint; wide field -Ability to focus and steer -Drawback- deeper structure=lower resolution The phased array principle Phased array waves arrive at the target image at the same time- where resolution is best Price of focus is beam divergence.
Linear (Frequency)
-Each crystal creates a single scan line -Rectangular image -Good for imaging small parts & shallow structures -Higher frequency -Good for vascular
Frequency
-Inversely proportional to wavelength -Varies according to the specific velocity of sound in a given tissue.
Gain: Adjust to accentuate the appearance Time gain compensation
-Near gain or far gain -Adjusts the strength (amplitude) of returning signals based on depth -If too low, image will appear dark -If to high, image bright and white
Knobology: Brightness
-Start by adjusting the brightness -Turn the brightness to highest point, then slowly turn it down until the bottom is black or disappears
Intensity
-The concentration of power per unit area -Determines how much heat is generated in tissues.
Transducer movements
1) sliding 2) tilting (framing/sweeping) - used to obtain serial cross-sectional images of solid organs of a fluid collection 3) rocking - often used to center the image on the screen 4) rotating- used to align the US beam with the long or short axis of a structure
Adjusting Gain?
Adjusting gain only manipulates the computer generates image *DOES NOT affect signal quality
Depth of structures?
Along the axis of the US beam is determined by the time delay for echoes to return to the transducer
Power Doppler
Analyzes only amplitude of returning echos Level of brightness correlates with magnitude of flow No info on direction of flow (not used for cardiac) Ex: Venous thrombosis
ALARA
As Low As Reasonably Achievable
Blood flow
Blood moving towards the transducer shifts echos to a higher frequency. Blood moves away - lower frequency. Angling toward the direction of blood flow = Positive doppler shift
High Acouostic Impedence
Calcium, ribs-less sound reflected back to transducer from the calcified area
Depth
Default focal zone depth is typically center of the screen Low frequency Low resolution Longer depth
Resolution: Axial
Determined by soundwave freq.
Resolution: lateral
Determined by the width of US be a, which is influenced by diameter and frequency.
Acoustic impedance
Differences in acoustic impedance determine reflectivity of sound waves at tissue interfaces Greater differences = greater reflection of sound waves
Absorption
Energy transferred from the US beam to tissues as heat
Elevational
Fixed property of the transducer Refers to the ability to resolve objects w the height or thickness of the ultrasound.
Transducer type: Phased array Frequency Range: Imaging Depth: Applications:
Frequency Range: 1-5 MHz Imaging Depth: 35 cm Applications: Heart, inferior vena cava, lungs, pleura, abdomen
Transducer type: Linear Frequency Range: Imaging Depth: Applications:
Frequency Range: 5-10 MHz Imaging Depth: 9cm Applications: arteries/veins pleura, skin/soft tissues, musculoskeletal, testicles/hernia, eyes, breast
Transducer type: Intracavity Frequency Range: Imaging Depth: Applications:
Frequency Range: 5-8 MHz Imaging Depth: 13 cm Applications: Uterus/ovaries, Pharynx
Transducer type: Curvilinear Frequency Range: Imaging Depth: Applications:
Frequency Range:2-5 MHz Imaging Depth: 30cm Applications:Gallbladder, kidney, liver, bladder, abd aorta, abd free fluid, uterus/ovaries
Side Lobes/Grating Lobes
Grating occurs with phased array transducer
Comet tails →
High amplitude tail
Shorter wavelengths
Higher frequency Higher resolution images Penetrate too shallow depths
Transducer Frequency: Higher frequency= Lower frequency =
Higher frequency=better resolution, shorter penetration lower =longer penetration
Overcoming attenuation?
Increase gain Amplify signal in post processing
To Optimize view:
Look at pt position (gastric US - right lateral position), probe
Longer wavelengths
Lower frequency Lower resolution Penetrate deep
Transverse plane *out of plane
Marker should be pointed to operators left side
Longitudinal (coronal & sagittal) *in plane
Marker should be pointed to patients head
Resolution (measured?)
Measured by wave length used
Doppler imaging
Measures a change in freq.
Focal Zone
Narrowest part of the ultrasound beam where resolution is the greatest Region of highest intensity
Color Flow Doppler: Based on PWD with multiple sample volumes Sonographer selects area of interest Multiple lines with multiple sample volumes Mean frequencies are calculated at each spot
RED=blood moving towards the transducer BLUE=blood is moving away from the transducer GREEN= turbulence (left-laminar) (right-turbulent) Brightness corresponds to velocity Color corresponds to direction of flow
Deflection
Results in a reduction in echo amplitude
Resolution: elevational
Slice thickness resolution determined by transducer thickness
Ultrasound Sound waves
Sound waves at a frequency above the average human audible range (>20Hz) Frequencies used in Ultrasound 2-18 MHz U/S images are generated by sound waves reflected and scattered back to the transducer
Piezoelectric effect
The ability of certain crystals to generate vibrations with the application of electricity
Resolution: temporal
The ability of image moving structures
Axial
The ability to differentiate two objects along the axis of the ultrasound beam. -Is the vertical resolution on the screen -Depends on transducer frequency the higher the frequency:, the better axial resolution, shallower penetration
Lateral (horizontal)
The ability to differentiate two objects perpendicular to the US beam Decreases as deeper structures are images d/t divergence and increased. of the ultrasound Optimized Lateral resolution by placing target structure in the focal zone.
Transducers receive and record ?
The intensity of returning sound waves
Attenuation
The loss of energy as sound waves travel through tissues D/T absorption, deflection & divergence of sound
propogation speed
The velocity of sound in tissues (varies depending on physical properties of tissues)
Injuries:
Thermal (heat generation) Nonthermal (Cavation) from contrast enhanced US.
Screen orientation
Top corresponds with probe face Tranduscer marker corresponds with left of screen Heart US - transducer marker corresponds to right of screen
True pathology should be visualized in at least
True pathology should be visualized in at least two planes. Suspected pathology that is not seen in multiple planes is most likely an artifact.
Higher frequencies
Used in Linear array transducers to visualize superficial structures *(vascular & peripheral nerves)
Lower frequencies
Used in curvilinear & phased array transducers to visualize paper structures in the thorax, abdomen & pelvis.
Artifacts arise when
When one or more properties of sound are violated. Artifacts are false images, or parts of images, that do not represent true anatomic structures.
Mirroring artifact-
aorta, pleural, calcified edge of aorta Strong reflector (diaphram, calcified aorta) creates a mirror image that apprears to be behind target image
Resolution of ultrasound images is divided into four different types:
axial, lateral, elevational, and temporal.
Coronal plane
divides body into front and back *frontal plane
Sagittal plane
divides body into left and right.
Transverse plane
divides the body into superior and inferior parts (upper and lower) *Short axis plane
(Artifacts) Reverberation:
equally spaced bright liner echos from repeated reflections from air space Looks like a ladder
Resolution
high frequency high resolution shorter depth
Point-of-care ultrasound
is defined as a goal-directed, bedside ultrasound examination performed by a healthcare provider to answer a specific diagnostic question or to guide performance of an invasive procedure.
Hypoechoic -
iso, various gray shades → muscles, solid organs Reflect some sound waves but less than surrounding structures
Divergance
loss of US be a, intensity as the beam widens
Temporal
refers to clarify or resolutions of moving structures.
Hyperechoic
reflect greater than surrounding structures → bones, nerves, fascial plane Reflect the most sound waves Appear bright on US Calcified & dense
Spectral Doppler
represented graphically Y-axis: Velocity X-Axis: time quantitative assessment of velocities: Pulse wave, continuous wave
Murphys Point:
see more in Trendelenburg position for gastric hemorrhage
Average power
total energy on a tissue in a specific time
Anechoic
transmit all sound waves w/o reflecting → fluid filled structure → vessel Black Structure that transmits all sound waves Fluid-filled structures *blood vessels