dr prasanth s. 3d echo basics concept - early 1980s. conventional 2d echo requires cognitive 3d...

3D Echo

Dr Prasanth S

3D Echo BasicsConcept - Early 1980s. Conventional 2D echo requires cognitive 3D reconstruction of

cardiac structures. Real time 3D echo provides anatomically realistic visualization

of structures. Decrease the time required for complete image acquisition. 3D Echo can be viewed from various projections by rotation of

images. A limitation- the information acquired as 3D dataset, must be

displayed as 2D image.

Linear scanning approach

• Earliest approach to dynamic 3D echo.• Based on 3D concepts used in CT and MR imaging.• Acquiring parallel and equidistantly placed 2D images

using transducer mounted on a sliding carriage.• Movement of transducer by a computer controlled

stepper motor.

Fan- like scanning approach • Transducer moved in a fan like arc at prescribed

angles.( manually or by stepper motor)

Hardware used for fanlike acquisition

Rotational scanning approach

• Transducer is rotated in a semicircle around the central axis of imaging plane.

Disadvantages of Initial models– Time consuming– High Cost– Large Machines– Slow processor

RT3DE in 2002– Dense Matrix Array Transducer – 3000 elements– Fast processor

Real Time 3D – Pyramidal Volume

3D volumetric probe- Pyramidal Volume

Technical Issues in Real Time 3D

Full volume images are typically obtained at frame rate of 20-40 Hz.( vary as a

function of depth & size of the volume.)

Either sacrifice frame rate for image quality (spatial resolution) or spatial resolution

for frame rate

Min Frame rate required 20 Hz – 20 frames per sec

Each frame contains beams

1 beam requires .2ms for scanning

If 100 beams / frame – 20 ms time – frame rate – 50Hz

250 beams / frame – 50 ms time – 20 Hz.

Innovations to overcome the limitations

1. Increase the distance between beams.

Blurring of structures that are not adequately sampled.

2. Parallel receive beam processing – Increase frame rate

• 4 or more simultaneous receive beams for each transmitted beam

3. Limit the total number of beams by scanning a smaller volume - 3D

zoom mode

4. Use the patient’s ECG signal to acquire smaller subvolumes for each

R-R interval, and then stitch these subvolumes to produce the

larger volume -full volume dataset

5. Broaden the transmit beam

Transducers

Phased array transducer

Sparse Matrix Array Transducer

Microbeam Former

Dense Matrix Array Transducer

Sparse Matrix Array Transducer:

• Only a small percentage of 2500 (50х50) elements are electrically connected or acoustically active.

• Usually strategically placed 256 elements will be active.

• Loss of signal to noise ratio.• THI not supported- incapable of creating sufficient MI

necessary to create tissue harmonic image.

Micro-beam forming

• Electrically group, small arrays of elements (patches).

• Typical patch contain approx 25 elements(5х5).

• 128 micro-beamformer with 128 wires connecting the transducer to mainframe beamformer- provide a fully sampled array of 3200 elements.

Matrix Array TEE Transducer distal tip

Modes

Real time Mode

• Narrow angle 600:300

• Higher Resolution(high line density

& narrow scan volume)

• No stitching Artifact

• Visualisation of valves,small masses,

vegetations.

• Real time Interventional guidance

Zoom Mode

• Focused – 300: 300

• Enface view of MV

• Masses-

Thrombi,vegetations

• Eliminate need for cropping.

• Low spatial resolution due

to low line density.

Full volume mode

• Covers wider region 900:900 upto

1040 .

• 4 or 7 live 3D subvolumes stitched

together.

• Near real time

• Higher temporal resolution

• Spatial relationship of cardiac

structures

• Chamber Quantification

Colour Flow Mode

• Limited angle 60:60

• Limited Temporal resolution

• Shape & extention of jets

Basic 3D analysis

• 3D orientation

– manual free rotation of the dataset to provide the best perspective

of the structures of the heart

• Cropping

– manually moving a cutting plane from outside the 3D volume

towards its center- provide a view from the cutting plane

– cropping can be performed either before (during) or after data

acquisition

• Slicing

– extraction of image planes from the 3D volume in different modes

Full Volume

Artifacts

Stitch artifact

• Lines of disagreement between two neighboring subvolumes.

Dropout artifacts

•Losses of 3D surface information due to poor echo signal intensity.•Structures- too thin to reflect.•Appropriate gain settings, colour doppler can identify false defects.

Blurring and blooming artifacts

• Blurring refers to unsharp or hazy representation of thin structures- appear thicker.

• Eg: Mitral leaflets, mitral valve apparatus.• Blooming: thickened or excessive representation of

high echo density structures like mechanical prosthesis, pacemaker leads.

• Strongly related to the line density.

Blurring and blooming artifacts

Gain artifacts

Protocols

Protocols

Applications

Left ventricular function

• Unlike 2D echo, there is no geometrical assumptions.

• Left ventricular volume can be calculated by,

• 1. Method of discs

• 2. Directly sum the volumetric picture elements enclosed by

endocardial borders of 3D structure.

Global LV function - EDV measurement

Global LV function - ESV measurement

LV Mass

• Currently, 3D TTE and TEE assessment of LV volumes and ejection fraction is recommended over the use of 2D echocardiography, as it has been clearly demonstrated to provide more accurate and reproducible measurements.

European Heart Journal – Cardiovascular Imaging (2012) 13, 1–46 .(EAE/ASE RECOMMENDATIONS)

Parametric imaging

• Assessing segmental contraction of LV.

• 800 endocardial data points - to develop a polar map of

endocardial surface of LV.

• Endocardial motion is displayed as shades of

– Blue - positive excursion values - inward motion

– Red - negative excursion values - outward motion

– Black - no motion

• Akinetic or dyskinetic myocardium - black or red color

• Normal or hypokinetic segment - shades of light to dark blue

Parametric imaging

Normal Apical MI

LA Volume

RV volume & function

• RV has a complex geometrical shape.• RV inflow, outflow and apex do not align in a single 2D plane.• More heavily trabeculated. Normal reference values

Indexed RV EDV 49±10 ml/m²

Indexed RV ESV 16±6 ml/m²

RV EF 67±8%

Valvular Disease

MVP - Mitral Regurgitation

• Accurate anatomy – Scallop

• Surgical View

• Vena contracta area – direct measurement

• TTE is good enough

Important parameters derived by RT3DE before MV repair

1. Anterior-posterior diameter (DAP)

2. Anterolateral-posteromedial diameter (DAlPm)

3. 3D curvilinear length of posterior and anterior leaflet

4. Exposed area of leaflets (A3DE)

5. Minimal area of leaflets within the saddle-shaped annulus (A3Dmin)

6. Volume of leaflet prolapse (VProl)

7. Maximal prolapse height (HProl)

8. Length of antero-lateral and postero-medial chordae tendinae

MVP Multiple jets

Mitral Stenosis

• MVA at smallest orifice

• Better assessment for BMV

• Planimetry from Apical window

• More accurate than Gorlin

• New GOLD STANDARD

Localizing smallest orifice

Aortic Regurgitation

TEE is better

Vena contracta area

Better delineation of Etiology

Aortic Regurgitation

Aortic Stenosis

• AVA measurement

• Assess the noncircular LVOT area

BCAV

DEGENERATIVE

RHEUMATIC

NORMAL

Other Applications

Dysynchrony

VSD

ASD

Thrombus

Myxoma

Intervention

References

• Feigenbaum’s Echocardiography

• Clinical Echocardiography;Otto

• 3D Echo Thomas Buck, Andreas Franke,Mark J. Monaghan

• ASE 2012 Guidelines

• ESC – 3D Echobox

• Cardiology clinics 2007 vol 25