Introduction & Physics of ED Ultrasound. Objectives. What? - Limited Studies. Who? - ED Docs

Transcription

1 Introduction & Physics of ED Ultrasound Martine Sargent, MD Ultrasound Director, Assistant Professor UCSF Department of Emergency Medicine San Francisco General Hospital & Trauma Center Objectives Who? - ED Docs What? - Limited Studies When? - Real Time integrated assessment Where? - Bedside Why? - Save time, $$, radiation How? - Physics, probes, knobology, artifacts Who? - ED Docs ACEP, SAEM Supported RRC Requirement Fellowships 34% of community EPs have access* NOT radiologists *Ultrasonography in community emergency departments in the United States: access to ultrasonography performed by consultants and status of emergency physician-performed ultrasonography. Moore 2006 What? - Limited Studies Aorta - AAA: YES or NO? Biliary - Stones, thick wall, big CBD, Sono Murphy s, PCCF: YES or NO? Cardiac - Motion, Fluid: YES or NO? DVT - Vein compression: YES or NO? FAST - Free Fluid, Effusion: YES or NO? Pelvic - IUP: YES or NO? Procedures - Localized, success: YES or NO? Renal - Hydro, Stones: YES or NO?

2 When? - Now & Later there is the danger that use by inexperienced practitioners will lead to errors... its use must be restricted -JAMA, circa 1900 Where? - Bedside Real time integrated assessment As you would use your stethoscope Serial exams Trauma - ABCD FAST Codes - YES/NO cardiac activity Procedures - increase safety, success Where? - Bedside Avoid Radiology trip Facilitate procedures Save time Show patients, family Teach Field - Remote areas, underserved, rural, combat/triage Why? Call Codes - PEA Differentiate Hypotension Decrease diagnosis time Increase revenue Increase safety Avoid Radiation!

3 How? - Mechanical pressure waves traveling through a medium Crystal Piezo-electric Transducer (Pressure/Sound) (Electricity) Electricity Crystals vibrate Sound 99% is listening for returning echoes When certain types of crystals are charged with electricity, they vibrate and cause sound (pressure) waves Amplitude = peak pressure of the wave Echogenicity = strength of returning echoes Low = weaker intensity of returning echo High = stronger intensity of returning echo Hyperechoic = Brighter Hypoechoic = Darker Isoechoic = Consistent with Anechoic = No echoes

4 Frequency Low = less resolution more penetration (conserve energy) MHz Frequency = cycles/second Human hearing 16-20,000 Hz Low 2-5 MHz High = more resolution less penetration (use more energy) 5-10 MHz Ultrasound > 20,000 Hz Medical MHz High 5-10 High frequency Low frequency High frequency Low frequency

5 Attenuation Attenuation Superficial structures create echoes that return quickly to the probe Echoes from deeper structures take longer to return to the probe Pixels are translated ted onto a screen en as a function of the elapsed time and intensity nsit of sound waves striking the object and returning rn n to the ultrasound system Air Fluid filled structures Bone Homogeneous structures

6 Orientation, Planes, & Knobs Screen Orientation Transverse Sagittal - Longitudinal RIGHT LEFT HEAD (CRANIAL) FEET (CAUDAL) Oriented perpendicular to long axis of the body Convention probe indicator to patients RIGHT Oriented parallel to long axis of body Convention probe indicator to patients HEAD

7 Coronal Moving the Probe VENTRAL sliding CRANIAL CAUDAL DORSAL rotating Oriented lateral to long axis of body fanning Gain Brightness: Changes echo displayed on screen

8 Time Gain Compensation Depth Differentially amplifies echoes returning from deeper tissues Accounts for attenuation of these echoes Modes A = Amplitude B = Brightness M = Motion D = Doppler CF = Color Flow CPD = Color Power Doppler Real time (B mode) Range of echo strength or the amplitude of waveforms converted into a gray scale continuum

9 M-mode Normal M-mode of Lung Soft Tissue Ocean Normal Lung Beach

10 Color Flow Frequency shifts to and from transducer converted into color Blue Away Red Towards Spectral Doppler Color Power Doppler Frequency shifts between transmitted and received Doppler signal converted into audible or graphical peaks Form of color doppler which is more sensitive to low flow states but has less ability to demonstrate directionality.

11 Artifacts EDGE ARTIFACT Edge Artifact Mirror Artifact Posterior Enhancement Reverberation Shadowing Side Lobe Artifact MIRROR ARTIFACT ENHANCEMENT

12 REVERBERATION COMET TAIL & RING DOWN SHADOWING Shadowing SIDE LOBE ARTIFACT

13 Whew! Now that we know the Who What Where When Why & How... Let s learn the applications and have some hands on fun! Practice will put the physics in perspective References American College of Emergency Physicians. Ultrasound Guidelines [policy statement] American College of Emergency Physicians. Emergency Ultrasound Imaging Criteria Compendium [policy statement] Andrulis DP. Study of How Urban Hospitals Address Sociocultural Barriers to Health Care Access : filename=023299s.htm&iaid=133 Edelman, SK. Understanding Ultrasound Physics. 3rd Edition. Moore C, Molina A, Lin H. Ultrasonography in community emergency departments in the United States: Access to ultrasonography performed by consultants and status of emergency physician- performed ultrasonography. Ann Emerg Med. 2006; 47: Moore CL. Utility of portable ultrasound in patient care in a remote area of Nicaragua. Ultrasound Med Biol. 2003; 29:S152 Abstract.