image optimization for critical care ultrasound
DESCRIPTION
Critical Care Ultrasound TrainingTRANSCRIPT
Image optimization for critical Image optimization for critical care UScare US
Critical Care Ultrasound CourseCritical Care Ultrasound Course
SAH & RNSH 2011SAH & RNSH 2011
Summary
Revision: basic image optimizationRevision: basic image optimization
B- mode, M-mode, DopplerB- mode, M-mode, Doppler
LUNGLUNG
IVCIVC
HEARTHEART
Revision: basic image Revision: basic image optimisationoptimisation
Revision: basic image optimisation
Patient position (supine? left lateral?)Patient position (supine? left lateral?) Lighting (dark)Lighting (dark) Enough gelEnough gel Right probeRight probe Right orientationRight orientation Right presetRight preset Right depthRight depth Overall gainOverall gain Individual TGC/DGC slidersIndividual TGC/DGC sliders
Revision: basic image Revision: basic image optimisationoptimisation
FrequencyFrequency Focal Zones (how deep? how many?)Focal Zones (how deep? how many?) Cheat buttons - Cheat buttons -
Auto –optimizeAuto –optimize HarmonicsHarmonics
Change your angle & pressureChange your angle & pressure ZoomZoom
Harmonics (THI)Harmonics (THI) As a sound wave travels through tissue, the high As a sound wave travels through tissue, the high
pressure bit (compressing tissue) moves pressure bit (compressing tissue) moves fasterfaster than the rarefactional component. than the rarefactional component.
This This distortsdistorts the wave! and generates higher the wave! and generates higher frequency components (frequency components (harmonicsharmonics) deep in the ) deep in the tissues.tissues.
eg 3MHz wave creates 6MHz, 12 MHz harmonicseg 3MHz wave creates 6MHz, 12 MHz harmonics
Harmonics (THI)Harmonics (THI)
n Q: So what?Q: So what?n A: it turns out that aberrant/artefact signals are A: it turns out that aberrant/artefact signals are
too too weakweak to generate harmonic waves. to generate harmonic waves.
n THI takes advantage of this: i.e. it displays THI takes advantage of this: i.e. it displays onlyonly the harmonic signals.the harmonic signals.
n THI images have:THI images have:n reduced noise and clutterreduced noise and cluttern improved spatial resolution (harmonic beams improved spatial resolution (harmonic beams
are narrower than the original)are narrower than the original)
Same Kidney, difficult patient
No Harmonics
With Harmonics
Top tip: Top tip: Harmonics (THI) = Harmonics (THI) = another great buttonanother great button
DonDon’’t use it for the lungt use it for the lung For other regions, give it a goFor other regions, give it a go If it makes the image worse, press again to turn it If it makes the image worse, press again to turn it
offoff Best for Best for mid-depth mid-depth images.images.
harmonic generation does not take place near the skin, so harmonic generation does not take place near the skin, so THI no use there. THI no use there.
Also less useful in far field. Also less useful in far field.
M mode
M mode = motion mode
Press Press ‘‘MM ’’ button once & a line appears button once & a line appears Use touch pad / track ball to move the line to area of interestUse touch pad / track ball to move the line to area of interest Press Press ‘‘MM ’’ again to plot a graph of again to plot a graph of what that line sees versus what that line sees versus
timetime Stationary stuff = straight lineStationary stuff = straight line Moving things = curved/ dotsMoving things = curved/ dots
M-mode: what’s the point?
CONSCONS
If angles wrong, If angles wrong, measurements wrong!measurements wrong!
Easier to stuff up than B-Easier to stuff up than B-modemode
IF IN DOUBT, USE B MODEIF IN DOUBT, USE B MODE
PROSPROS
M-mode (motion mode) = M-mode (motion mode) = movement along a movement along a singlesingle line of info against timeline of info against time
Single line therefore much Single line therefore much better sensitivity & better sensitivity & resolutionresolution
More accurate dimensionsMore accurate dimensions
M mode: poorly contractile LV
M mode: IVC changing with respiration
DopplerDoppler
Doppler effect
Probe sends a sound wave of known frequency
If it hits object moving towards probe, the returning sound wave is higher frequency
If object moving away, the returning wave is lower frequency
Today: Today: wewe leave Doppler aloneleave Doppler alone
Master the basics firstMaster the basics first
Know your limitationsKnow your limitations
Sreening exam:Sreening exam:scanning the lungsscanning the lungs
LUNGS: probe & presetLUNGS: probe & preset
PROBEPROBENotNot the linear array (too the linear array (too much fine detail!)much fine detail!) ……False neg PTX False neg PTX
(movement)(movement) ……False pos PTX (pain)False pos PTX (pain)
The The curvedcurved probe is best probe is best Image qualityImage quality AnatomyAnatomy
The The phasedphased array probe array probe fits b/w ribs & gets round fits b/w ribs & gets round the backthe back
PRESETPRESETOne with plenty of One with plenty of greyscale/ dynamic greyscale/ dynamic rangerangeAbdo preset (abdo > Abdo preset (abdo > FAST)FAST)NOT cardiac presetNOT cardiac presetTurn Turn offoff the fancy the fancy filters: THI, filters: THI, compounding/MB etc- compounding/MB etc- they make the artefacts they make the artefacts harder to see!harder to see!
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Depth & alignmentDepth & alignment
DEPTHDEPTH5cm: 5cm: just for pleura eg just for pleura eg slidingsliding10cm: 10cm: to confirm true B to confirm true B lineslines15cm: 15cm: anatomical anatomical relations, diaphragm, relations, diaphragm, effusionseffusions
PROBE ALIGNMENTPROBE ALIGNMENTSurprisingly, stay Surprisingly, stay sagittal (perpendicular sagittal (perpendicular to ribs)to ribs)Only turn parallel if Only turn parallel if interrogating structures interrogating structures further eg solid areasfurther eg solid areas
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Screening exam:Screening exam:the IVCthe IVC
Probe & presetProbe & preset
PROBEPROBECCurvedurved probe is best probe is best Image qualityImage quality AnatomyAnatomy
Phased array probe if Phased array probe if already on TTEalready on TTE
PRESETPRESETWhatever preset you’re Whatever preset you’re on is fineon is fine
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Screening exam:Screening exam:single view heartsingle view heart
Keep it simpleKeep it simpleSame probe & presetSame probe & preset
Trans thoracic echocardiogram Trans thoracic echocardiogram (TTE)(TTE)
WeWe’’re not in Kansas any morere not in Kansas any more
B-mode top tips for cardiac scanB-mode top tips for cardiac scan
Roll the patient to the leftRoll the patient to the left
Sector /phased probeSector /phased probe
Cardiac preset (image Cardiac preset (image ‘‘round the wrong wayround the wrong way’’))
‘‘JerkyJerky’’ image (less averaging) image (less averaging)
Dynamic range decreased (more contrast)Dynamic range decreased (more contrast)
Line density decreasedLine density decreased
Sector width narrowedSector width narrowed
ECG leads can help but we rarely have time!ECG leads can help but we rarely have time!
What does all this mean?What does all this mean?
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The bottom line
The heart beats very quicklyThe heart beats very quickly We need to capture this movement accuratelyWe need to capture this movement accurately So we maximise So we maximise ‘‘temporal resolutiontemporal resolution ’’= increased frame rate= increased frame rate And we turn off averaging = only And we turn off averaging = only ‘‘truetrue’’ images are seen images are seen But we sacrifice something to achieve this: mainly But we sacrifice something to achieve this: mainly spatialspatial
resolutionresolution i.e. the image has less anatomical detail = lower i.e. the image has less anatomical detail = lower ‘‘line densityline density’’ And less greyscale /dynamic range (ie itAnd less greyscale /dynamic range (ie it ’’s a more s a more ‘‘black & black &
whitewhite’’ picture) picture) So we need to try certain So we need to try certain ‘‘trickstricks’’ to improve our image to improve our image within within
these limits e.g:these limits e.g:
- decrease depth- decrease depth
- zoom the image- zoom the image
- decrease sector width- decrease sector width
Why the jerky image?Why the jerky image?
Image not as smoothImage not as smooth
No averaging = no No averaging = no ‘‘fudgingfudging’’
What you see on screen is really thereWhat you see on screen is really there
What’s Line Density?
How many lines per frameHow many lines per frame A high line density is desirable for high resolution imaging of A high line density is desirable for high resolution imaging of
small parts (thyroid, breast testes…), small parts (thyroid, breast testes…), A lower line density is useful inA lower line density is useful in cardiac cardiac applications as it applications as it
allows significantly higher frame rates.allows significantly higher frame rates.
Reference: LOGIQ 9 Basic User Manual, Direction 5140804 -100 Rev.3 5-24Reference: LOGIQ 9 Basic User Manual, Direction 5140804 -100 Rev.3 5-24
Sector Width (Scan Area)
Allows you to widen or narrow the sector angle to maximise Allows you to widen or narrow the sector angle to maximise the region of interest (ROI), and maximise frame rate.the region of interest (ROI), and maximise frame rate.
You can usually steer the narrowed sector as well, useful for You can usually steer the narrowed sector as well, useful for looking in corners!looking in corners!
Top tip: keep sector as Top tip: keep sector as narrownarrow as possible as possible
SummarySummary
Critical care echo is Critical care echo is where itwhere it’’s ats at
TTE is tricky!TTE is tricky!
But screening exam is But screening exam is simplesimple
References
Roger Gent: Applied Physics & Roger Gent: Applied Physics & Technology of Diagnostic UltrasoundTechnology of Diagnostic Ultrasound
19971997
Sam Kaddoura: Echo Made EasySam Kaddoura: Echo Made Easy
Cindy Lucas, senior sonographer Liverpool Hospital