By Michael Macias
Welcome to the Ultrasound Leadership Academy (ULA) summary blog series. I just recently joined the ULA which is essentially an online advanced ultrasound education experience put on by the team from Ultrasound Podcast which brings cutting edge learning to emergency medicine personnel through a variety of interactive platforms including video lectures, google hangouts with experts, simulation, live conferences and real time scanning with a pocket-sized ultrasound device known as a Vscan.
Over the next year I will be posting summaries of the key learning points from my experience. If you want to learn more about the program you can visit Ultrasound Leadership Academy or Ultrasound Podcast to see more from the hosts of this awesome program.
The idea of performing ultrasound in the emergency room isn't that new. We can trace back its history to a radiologist by the name of Golderberg in the 70s, who had the outlandish idea of injecting saline into the abdomens of cadavers and using an ultrasound to detect it. Here in lied the birth of the FAST exam.
But ultrasound in the emergency room isn't simply an extension of the physical exam. We don't bring it along and slap in on everyone's abdomen or chest just to take a peak inside. We can think of Emergency Ultrasound as something slicker and a bit more tailored, designed to answer a specific question.
Emergency Ultrasound should be:
- Performed for a clearly defined condition (Is there a pericardial effusion?)
- A focused, goal-directed exam (I am not going to scan this persons entire body.)
- Characterized by 1-2 features (Is there fluid around the heart? Is the RV collapsing?)
- Easily learned and performed (I am not going to determining the exact EF of a patient.)
- Quick (You have 10 other patients your seeing, let's make this quick.)
- Have a direct impact on patient care (A urgent pericardiocentesis may save this patient's life)
- Point of Care (At the beside, reliable and available)
Choosing the right ultrasound machine can be difficult. Ultimately if you want to incorporate ultrasound into your practice you need to find what purposes you will be using it for, what features you must have and also think about how much money you can spend.
Some features to consider:
- Image quality (This will often be synonymous with more money but you need to also consider additional features such as M-mode)
- User interface (Mac vs Windows...same concept, make sure your interface shows you want to want to know when scanning)
- Boot and battery (Are you in an office or a ED? What is the battery life like?)
- Transducers (You need a linear and phased array probe at minimum)
- Connectivity (What are you going to do with your images? How do you want to export them? Wired vs wireless?)
- Durability/Service (Are you going to destroy your US machine? May want to consider something sturdy...In-house service versus ship out?..cost plays into this as well)
All transducers were not made equal.
Piezoelectric crystals- Vibrate to generate sounds waves which will go out to hit tissue and bounce back and be converted to electric signal and thus an image
Matching layer- Allows easy transmission of sound waves just as US jelly does
- Backing material- Dampening agent that gives time for the PZT crystals to 'listen' for return signal
- High resolution
- Shallow penetration
- Vascular access
- Skin/MSK/small parts
- Linear or intracavitary probes
- Low resolution
- Deep penetration
- Abdominal imaging
- Pleural spaces
- Curvilinear or phased-array probes
1 minute synopsis I promise.
- Frequency: Number of cycles over a period of time measured in Hertz (cycles/second)
- Period- Time from beginning of wave to the end
- Wavelength: Distance from beginning of wave to the end (which is inversely proportional to period)
- Amplitude: Height of the wave
Take Home: Long wavelength will penetrate deep into body and have low resolution since it cannot discriminate between closes structures while short wavelength will penetrate shallow and discriminate highly between close structures.
Speed: US travels through different mediums at different speeds. This will be important when thinking about artifacts created during scanning.
- Air 500 m/s -> Soft Tissue 1540 m/s -> Bone/Solids 3000 m/s
Pulsed Ultrasound: Most of the time the ultrasound is listening for returning echoes. For example, a pulse may be sent from PZT for 1 msec and will listen for the next 999 msec for returning sound waves.
Time = Distance: The US machine determines how far from probe objects are based on the time it takes for sound wave to return after hitting that object.
More terminology: Make sure you know how to describe what your seeing.
- Near field: Half of US screen closest your probe.
- Far field: Half of US screen farthest from your probe.
- Hyperechoic: Appears bright and white which means that it contains high calcium content such as bone/stones/tendons.
- Anechoic: Appears black on screen which means it is fluid or artifact known as shadowing
- Grey areas: The inbetween. Describe these areas with respect to surrounding tissue
The art of turning knobs. There are several knobs that we need to know how to use to make our images look better but first a quick look at probe terminology.
- Gain: This determines overall brightness. Optimal gain allows for proper distinction of structures while too much gain leads to artifact
- Time Gain Compensation: This allows you to vary the gain according to depth. For instance you may have a bright structure in the near field and want to see the far field. You can preferentially turn down gain in the near field or turn up gain in the far field independently.
- Depth: This determines essentially how long the US machine will listen for returning signals. Make sure to decrease depth to optimally characterize necessary structures. Your point of interest should be in the middle of the screen ideally.
- Focus: This allows you to heighten resolution of particular depth within the particular view on your screen. If this doesn't matter then place focus at bottom of the screen.
- Modes: Different modes serve a particular function
- B Mode/2-D/Grey scale is our standard mode.
- M Mode stands for motion mode which allows us to look at a particular line of interest on the screen and observe this line over time
- Color doppler analyzes fluid flow towards and away from probe and displays this as a color gradient.
- Power doppler is useful for presence of absence of flow but does not show direction.
- Pulsed Wave doppler is useful for fluid velocity, assessing hemodynamics and cardiac function.
These are tricky little things. In a nutshell, artifacts are structures that don't represent true anatomic structures.
- Shadowing:Represent areas where acoustic signal is not penetrating. This is not limited to bony structures but rather anything with a high calcium content, such as those gallstones you're seeing in the gallbladder.
- Reverberation: Ultrasound pulse strikes tissue and bounces back to transducer and then back into tissue and back to transducer again taking 2x,3x,4x as long making it seem as if there are multiple similar appearing structures. This is often seen when evaluating the pleural surface. Since these are in multiples, the distance between each artifact should be equal.
- Edge artifact: This occurs as a result of refraction as wave changes medium from air-sold or air-fluid interface leading to shadowing behind structure as sound waves at bent in a different direction. This is often seen along the edge of the gallbladder, do not confuse this with a gallstone shadow.
- Acoustic enhancement: This results from the fact that when ultrasound waves travel through fluid there is not as much attenuation as compared to tissue. Therefore tissue deep to fluid filled structures will appear brighter. You may see this when looking at the bladder or gallbladder.
- Ringdown: This is in essence a very rapid reverberation and is often seen with metallic objects or pulmonary edema. For example, b-lines seen in pulmonary edema are actually constructed of very tightly bound horizontal lines.
- Mirror image: This is often seen around the heart or the diaphragm. When an ultrasound beam hits the diaphragm it reflects off and changes direction, hits tissue, bounces back and hits diaphragm and then returns back to transducer. Remember that time = distance so therefore the machine will assume that this object is past the diaphragm given the time it took to return. When you see a mirror image of liver on the other side of the diaphragm this lets us known that there is no consolidation or fluid in the lung base.
That's it for this week.
If you are interested in learning more about the ULA learning experience, visit their website below:
If you are interested in purchasing eBooks 'Introduction to Bedside Ultrasound', Volume 1 & 2, from Dr. Mallin and Dr. Dawson, for less than $1, visit Ultrasound Podcast Consumables.