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