13 Duplex Ultrasound (Kim)

Transcription

2015 Phlebology Review Course
Duplex Ultrasound
Esther Kim, MD, MPH, RPVI
Cleveland Clinic
Disclosures:
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Consultant ‐ Philips US
Topics
• Duplex Ultrasound • Instrumentation • Ultrasound Physics and Safety
• Ultrasound Interpretation • Limitations • Quality Assurance • Vascular Lab Development
Duplex Ultrasound
• Several important roles in phlebology
• Assist in the evaluation of
• Deep venous disease
• Superficial venous disease
• Mapping prior to intervention
• Peri‐procedural imaging
• Post‐procedural imaging (success, complications, failure)
Duplex Ultrasound
• Combination of two imaging modalities
• Doppler
• B mode imaging
Ultrasound Imaging
Pulses of sound waves are transmitted into the body and the returning “echoes” from various structures are detected by the probe and converted into images on a screen
Piezoelectric crystal
Sound
• Mechanical wave created by vibration of a moving object; series of pressure waves propagating through a medium
• Ultrasound is a high frequency sound above the limits of human hearing (>20,000 Hz)
• Diagnostic US: 2MHz‐10MHz
Sound ‐ Definitions
• Period: time to complete a single cycle
• Frequency: number of wavelengths in 1 second (Hertz, Hz) • Affects penetration and axial resolution
• 1/period
• Intensity (power, amplitude): concentration of energy in a sound beam
• Wavelength: length of a single cycle • Higher frequency, shorter wavelength
• Affects axial resolution
• Propagation Speed: rate that sound travels through a medium
• Determined by the medium
• All sound travels at the same speed through any specific medium
• Speed of sound is faster with increasing stiffness and decreasing density
• Air << fat < soft tissue << bone
Ultrasound Physics (in a nutshell)
• CW Doppler cannot create anatomic images; pulses of sound are used in ultrasound imaging
• Pulse Duration: time from start to end of a pulse
• # cycles in a pulse x period of each cycle
• Spatial Pulse Length: distance from start to end of a pulse
• Determines axial resolution; shorter pulses create more accurate images
• Pulse Repetition Period: time from the start of one pulse to the start of the next pulse
Spatial pulse length
Pulse Duration
• Pulse duration + listening time
• Increase imaging depth  increase PRP by increasing the listening time
• Pulse Repetition Frequency: Number of pulses that occur in one second; 1/PRP
• Increase imaging depth  decrease PRF
• Duty Factor: Fraction of time the system transmits sound • (100% for CW Doppler, <1% for PW Doppler)
Pulse Repitition Period
Period
Wavelength
• CW Doppler cannot create anatomic images; pulses of sound are used in ultrasound imaging
• Pulse Duration: time from start to end of a pulse
Determined by the transducer
• # cycles in a pulse x period of each cycle
• Spatial Pulse Length: distance from start to end of a pulse
• Determines axial resolution; shorter pulses create more accurate images
• Pulse Repetition Period: time from the start of one pulse to the start of the next pulse
• Pulse duration + listening time
• Increase imaging depth  increase PRP by increasing the listening time
• Pulse Repetition Frequency: Number of pulses that occur in one second; 1/PRP
Determined by the operator by adjusting imaging depth
• Increase imaging depth  decrease PRF
• Duty Factor: Fraction of time the system transmits sound • (100% for CW Doppler, <1% for PW Doppler)
Shallow imaging = short PRP = high PRF = high duty factor
• Attenuation: decrease in intensity, power, and amplitude of a sound wave as it travels. Sources of attenutation are absorption, reflection, scattering, refraction
• Attenuation limits the maximum imaging depth
• length of travel  attenuation
• frequency  attenuation
• Absorption: conversion of acoustic energy into heat
• Reflection: sound energy strikes a boundary between 2 media and some bounces back to the transducer as an “echo” at an angle of incidence identical to the angle of the reflection
• Scattering: chaotically redirected sound waves occurring when waves encounter a medium with a nonhomogenous surface
• Refraction: sound energy traveling trhough the second medium (tissue) is “bent” from its path with an angle of incidence different from the angle of transmission
www. sonoguide.com
Instrumentation (affect image brightness)
• Output Power: adjusts the strength of the sound pulse sent out by the transducer
versus
• Receiver Gain: adjusts the amplification of the ultrasound signals after returning to the receiver
• Compensation: amplifies deep echoes
• Deeper structures are affected by attenuation
• Compensation makes all echoes from similar reflectors the same brightness regardless of depth
• Aka “time gain compensation (TGC), depth compensation (DGC)
ALARA: As Low As Reasonably Achievable
*Adjustment in either output power or receiver gain can correct an image that is too dark or too bright. According to ALARA, always choose the option that minimizes bioeffects (patient exposure).
• Ex: image too bright  decrease output power
• Ex: image too dark  increase receiver gain
Ultrasound Safety
ALARA: As Low As Reasonably Achievable
• Higher power levels expose the patient to the potential biologic effects of ultrasound
• Cavitation: interaction of ultrasound with small gas bubbles or microbubble contrast agents can cause localized energy depositions. “Mechanical index” • Absorption: conversion of sound energy to heat through absorption of waves. “Thermal index”
• No confirmed effects of ultrasound on patients during diagnostic ultrasound exposures
• Ultrasound does not involve ionizing radiation exposure
• Electrical shock related to ultrasound would be exceedingly rare with properly functioning equipment and maintenance
• Ultrasound is safe, however, should be used only when the benefit outweighs the risk, limited prolonged studies
Instrumentation (affect resolution)
Width of beam changes as sound travels.
• Focal zone: where the sound beam reaches its minimum diameter
• Improves lateral resolution ‐ Lateral resolution is directly related to beam width, which is related to US frequency (↑frequency ↓beam width).
Lateral resolution
• Axial resolution (ability to distinguish between two structures along the beam’s main axis)
Axial resolution
• Improved with fewer cycles per pulse
• Improved with higher frequency
• Can only be changed by using a higher frequency transducer.
4 MHz transducer
11 MHz transducer
Pellerito/Polak Introduction to Vascular Ultrasonography 2012
Doppler Shift
• Doppler shift occurs when reflectors move relative to the transducer
• The frequency (fr) of echo signals from moving reflectors (blood cells) is higher or lower than the frequency transmitted by the transducer (ft), depending on whether the blood cells are moving toward or away from the transducer
• The Doppler shift frequency is the difference between the received and transmitted frequencies
http://en.wikibooks.org/wiki/Basic_Physics_of_Nuclear_Medicine
fd = fr‐ft = 2ftVcos
c
Optimal imaging angle
Optimal velocity angle
Angle ()
cosine
90
0
60
0.5
0
1
CW Doppler
• 2 crystals in the transducer, constant transmit, constant receive
• Can capture very high velocities
• Range (depth) ambiguity (echoes from the entire length of the transmitted and received beams)
PW Doppler
• At least 1 crystal alternates between transmitting and receiving
• Can sample a particular area of interest with the sample volume (receive gate)  range resolution
• Subject to aliasing of high velocities
Duplex Ultrasound
• Combination of two imaging modalities
• B mode imaging
• Doppler
Duplex Ultrasound
Color Doppler
Spectral Doppler
Grayscale (B‐mode) imaging
Color Power Doppler
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No velocity or direction information
Any Doppler shift is colorized
Good for detection of low velocity
Ultrasound Interpretation ‐ DVT
• DUS is the test of choice for diagnosis of proximal DVT
Patient, thrombus‐free vein will have complete vein coaptation with compression
Loss of compressibility is the most reliable indicator of the presence of thrombus in the vein
• Sensitivity >95%, Specificity >95%
• Diagnostic components
• Transducer compression maneuvers
• Doppler evaluation (color and spectral Doppler waveform analysis)
• Augmentation maneuvers
• Acute DVT
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Loss of compression
Dilated vein (diameter > artery)
Intraluminal echoes from thrombus
Abnormal/absent color Doppler
Abnormal/absent PW spectral Doppler waveform 1. N Engl J Med. 1989;320(6):342.
2.
Bruit. 1982;7:41–42.
Respirophasic Doppler
Augmentation 
Absent Doppler signal
• Acuity of thrombus
• Acute (<2 weeks)
• Subacute (2 weeks – 6 months)
• Chronic (>6 months)
• Ultrasound parameters
• B‐mode appearance (hypoechoic, isoechoic, hyeprechoic)
• Vein lumen size
• Vein wall appearance
• Venous compressibility
• Function of venous valves
• Presence of collaterals
Circulation. 2014;129:917‐921
Remote
Age indeterminate?
Remote with valvular incompetence
• Limitations
• May miss more proximal DVT (iliacs
veins, IVC)  be alert when seeing a monophasic waveform
• Imaging is limited by body habitus and edema
• Duplicated femoral or popliteal veins may be missed
 Monophasic waveform: more proximal obstruction
 Blunted augmentation: more distal obstruction
Monophasic Doppler signal
Ultrasound – Venous Incompetency • Venous reflux: reversal of flow in the veins of the lower extremity
• Physiologic: fraction of a second it takes for valve leaflets to appose, time varies by location
• Pathologic: reflux of ≥0.5 seconds in superficial veins
Physiologic reflux 
• Reflux can be elicited by
• Valsalva maneuver
• Augmentation: compression and release distal to point of examination
• Best results obtained with patient
• Standing with weight on contralateral limb
• Sitting with torso elevated >45 degrees
• Reverse Trendelenberg
Pathologic reflux
Ultrasound – Venous Incompetency Examination Protocol • Deep system: • CFV, FV, Popliteal vein
• Reflux >1.0 sec
• Superficial System: (vein diameter msmts included)
• Entire length of GSV +/‐ entire length of SSV
• Reflux >0.5 sec
• Perforators
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Examine entire calf
Focus on areas of ulcerations
Reflux ≥0.35 sec
Diameter >3.5 mm likely competent
http://intersocietal.org/vascular/standards/
IACVascularTestingStandards2015.pdf
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The location, competency and diameter of the saphenous junctions. The distal extent of reflux in the saphenous veins in the thighs and legs. Recording the saphenous diameter at the mid‐thigh and at the knee is desirable. The location of incompetent perforating veins as measured from the floor
Other named and unnamed veins that show reflux or are varicose should be noted. The source of venous hypertension in varices if not from the veins described above. Saphenous veins that are absent, totally occluded, hypoplastic or atretic should be noted. The state of the deep venous system, including valvular competence and evidence of current or previous venous thrombosis.
http://www.phlebology.org/wp‐content/uploads/2014/11/ACP_Imaging_Guidelines_rev1109_a.pdf
J Vasc Surg 2011;53:2S‐48S
Quality Assurance ‐ Indications
Quality Assurance ‐ Purpose
• Assure that ultrasound exams are • To provide accurate diagnostic accurate compared to other imaging information to referring physicians
modalities
• To ensure patients receive accurate • Identify etiology of error
high quality care
• Initiate corrective measures
• To maintain accreditation of the laboratory by a recognized body
• Review cases in meetings of the medical director and laboratory supervisor, staff
SVU/IAC Quality Assurance Guidelines for Accuracy of Examinations in the Vascular Laboratory 03/13/2012
Quality Assurance ‐ Components
• Correlation of Diagnostic Ultrasound Findings
• Equipment Quality Assurance
• Continuing Professional Education
• Communication of urgent findings
Limitations to accuracy
• No written protocol
• No review of staff knowledge/ability in performing exams
• Lack of CME
• Low volume exams
• Limited knowledge of interpretation criteria
• Limiting exams only to basic protocols
SVU/IAC Quality Assurance Guidelines for Accuracy of Examinations in the Vascular Laboratory 03/13/2012
Quality Assurance ‐ Specifics
• There must be a written policy regarding QI for all procedures performed • A correlation log for each test area must show >70% accuracy agreement
• Minimum of 2 facility QI meetings per year must be held to:
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Review results of comparative studies
Address discrepancies
Discuss difficult cases
Address facility QI issues
• When available, appropriateness criteria published by medical professional organizations should be utilized.
http://intersocietal.org/vascular/standards/IACVascularTestingStandards2015.pdf
JACC 2013;62:649.
Accreditation ‐ Benefits
• Demonstrates commitment to quality care
• Application requires QI programs, identification and correction of potential problems, revise protocls
• Renewal process results in continued self‐assessment
• Allows quality to be evaluated through independent peer review
• Application of standards in imaging
• Acts as a recruiting tool for potential talented hires
• Demonstrates accountability • May be required for payment by insurers
http://www.intersocietal.org/iac/accreditation/whatisaccreditation.htm
IAC Accreditation – Initiating the Application
• IAC is there to help; not to prevent accreditation!
• Organization is key
• Review current lab protocols and policies, identify problems and correct prior to application
• Ensure imaging meets current IAC Standards • Review process takes 12‐16 weeks
• In house review, peer review, board of directors review
http://www.intersocietal.org/vascular/forms/VascularTestingAccreditationChecklist.pdf
• Information you will need
• Equipment information
• Procedure volumes
• Training Qualifications for MDs and sonographers
• Credential information for all medical and technical staff
• CME information for all staff
• Documents you will need (sample documents available)
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Primary source verification policy
Patient complaint policy
Personnel safety policy
Facility‐specific Technical Protocols
Patient safety policy
Patient confidentiality policy
Quality Improvement policy
QI meeting minutes >2/year
QI documentation – Correlation Log
• Case Studies
• Represent best work
• All cases must be abnormal of varying degress of pathology
• Must be from within the past 12 months from the date of application filing
• All medical and technical staff must be represented
• Site visit
• May occur as part of the accreditation process but will occur during 3 year accreditation period
• May occur as “random, investigative, or required” visits
Thank You

13 Duplex Ultrasound (Kim)

Transcription

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