Week 10 Flashcards
what is msk ultrasound imaging?
msk ultrasound imaging uses sound waves to produce pictures of muscles, tendons, ligaments and joints throughout the body, it is used to help diagnose sprains, strains, tears and other soft tissue conditions
US imaging
traditionally performed by diagnostic radiologists
increasingly available to physiotherapists and other medical practitioners with appropriate training
-aim to improve diagnosis/classification of msk disorders which, theoretically at least, should lead to improved clinical outcomes
post grad cert in msk imaging
research higher degree (masters/PHD)
US imaging history
derived from technology used in military and metallurgy applications
Began as science of navigation - first form was SONAR used on war ships WWII
- bounced sound waves off ocean floor and interpreted ‘echoes’
US imaging history
late 1940s scans performed as a new way to ‘image’ patient
- subject immersed in water bath
- produced single, static cross - sectional image
- early images looked like seismograph output
US imaging - history
1950s-1960s used by doctors for
- cardiac patients
- –progressing rto
- obstetrics gynaecology
- abdominal application
1970s
-greyscale images depicting cross section of patient anatomy
1980s
-computer technology added to produce ‘modern ultrasound’ image
1990s
-addition of colour Doppler to black and white images
US imaging history - today
dynamic visual images that provide insight human body
continually evolving
- software to measure tissue elasticity
-3D and 4D imaging
US imaging history
physiotherapy applications began in 1980s
-direct visualisation of muscle size and activity
high portability + low cost +excellent resolution = useful tool
How does it work
scanner includes
- hand held probe + central unit that displays image
- probe commonly used are linear or curvilinear
- you need to understand the machine settings
how does it work
Uses high frequency sound wave with short focused pulses to generate images
-no radiation
sound waves passes through body
-percentage is reflected back (normally 1%)
sound waves reflected back to probe by varying boundaries are recorded
- each pulse produce a single line
- single (greyscale) image = multitude of lines (can be >100)
What is wavelength
spatial period of wave
-distance over wave shape repeat
what is amplitude
measure of change over specific period
-peak & peak to peak
How does it work
Probe operates at specific frequencies
- higher frequency = shorter wavelength - shorter pulses
- – higher resolution of image but limited depth of vision
- lower frequency = longer wavelength - longer pulses produced
- –less absorption of US meaning lower resolution but allows vision of deeper structures
Depth of image demonstrated as scale of distance from probe
Linear probe
normal operational frequency >7.5 MHz
Produce high resolution images
rectangular images
approximate depth of vision =5cm
Curvilinear probe
normal operational frequency between 2-5 MHz
lower resolution images
fan shaped image
depth of vision up to 15cm
Doppler imaging
used to detect flow of blood
measure change in soundwave frequency reflected by moving structure
displayed as colour and pulsed Doppler
Doppler imaging cont
colour
- added as colour to greyscale image
- blue and red commonly used to represent flow towards and away from probe
pulsed
-displays spectrum of velocity vs time
Terms relevant to US imaging
attenuation
- weakening of sound wave passing through tissue due to parts being
- absorbed
- reflected
- scattered
- refracted
- diffracted
Terms relevant to US imaging
reflection
- occurs at boundary of 2 materials creating acoustic impedance
- determines echogenicity of tissue
- –small impedance - weak echo (i.e. soft tissue)
- –Large impedance = strong echo (i.e. bone)
Typical tissue appearance
variation due to
- different individuals
- scanner quality, frequency
- but mostly by amount and nature of tissue
- echogenicity
- -compared to normal/expected
- -diseased states issues can be
- —more echogenic (hyperechoic- brighter)
- —less echogenic (hypoechoic - darker)
- -compared to other tissue types
Typical tissue appearance
skin
- appears smooth bright
- –highly reflecive, hyperechoic
fat
-can be bright or dark
subcutaneous - commonly dark with fine, bright septa throughout
fluid
- normally black (anechoic)
- absorbs less sound than surrounding soft tissue
- –tissue deep to fluid can appear relatively bright
Typical tissue appearance
muscle
- dark in cross section
- long section - internal structure visible due to reflective muscle fibres
tendons
-typically bright but affected by orientation relative to probe
Typical tissue appearance
nerves & bone
Nerves
-peripheral - appear bright or dark depending on orientation
distinguished from tendons by following course through surrounding tissues
bone
- surface appear as bright line
- outer surface reflects sound so unable to see deeper
US imaging uses
physio - biofeedback
diagnostic tool - to an extent (training)
US imaging uses cont
it is important to consider that diagnostic US is a user dependant modality
- skill and experience of operator has considerable influence on outcome
radiologists are still the experts
if you plan to use diagnostic US, it is a skill that requires training and experience
- consider courses, guidance, and mentoring, especially amongst those from radiology community
- formal training is optimal for valid and reliable diagnosis
