Mode of Echo and their Application

Various modes of elamination performed during a transthoracic echocardiography ade shown in Table

Newer Techniques

Acoustic Quantification

Harmonic Imaging

Tissue Doppler Imaging

M-Mode Echocardiography (Motion Mode)
M-Mode was the earliest form of cardiac ultrasound used clinically. It displays the amplitude signals of various structures along the length of ultrasound beam with distance or depth on vertical axis against the time dimension on the horizontal axis.

Showing M-Mode across aorta

Main features and advantages are:

1) High sampling rate allows for accurate evaluation of rapidly moving valvular structures and endocardium.

2) High temporal resolution that allows visualization of minute changes in wall or valve motion.

3) Accurate and reproducible measurements of various chamber dimensions and wall thickness.

Provides one dimensional ("ice pick") view of the heart only provides information with respect to the distance of each object from the transducer and no information in the lateral dimensions 2D echocardiography. 2DFundamentals of Echocardiography

echocardiographic examinal :ion involves mechanically or electronically sweeping the ultrasound beam across the tomographic plane to generate a real time image of the heart. 2D images are similar to a thin slice of the heart along the tomographic plane and axis of ultrasound beam.

Advantages

1) Allows evaluation of the anatomical details, size and motion of various cardiac stnictures.

2) Valvular morphology, estimation of valve area by planimetry.

3) Cardiac size, volumes and function.

4) lntracardiac hemodynamics.

5) Disorders of pericardium and great vessels.

6) Acts as a guide for the placement of curser and sample volume for accurate

M-Mode and Doppler examination.

Disadvantages
Various structures are seen in two-dimensional planes; hence mental conceptualization is still required because the heart is three-dimensional. Now,newer technology has evolved and live three-dimensional echocardiography is a reality.

Doppler examination' provides hernodynamic information regarding blood flow in the heart and great vessels i.e. comparable to that obtained by cardiac catheterization. It relies on analysis of a shift in the frequency of ultrasound beam due to interaction with moving targets. Doppler studies are usually performed in conjunction with standard echocardiographic imaging. Two types of Doppler examination are:

a) Pulse Wave Doppler (PW) which gives velocity of blood flow at the level of sample volume placed along ultrasound beam

b) Continuous Wave Doppler (CW) which records velocities all along the ultrasound beam.

A proper alignment of ultrasound beam or cursor with the flow of blood under consideration is essential for accurate information.

Schematic representation showing curser position of pulse wave and
continuous wave Doppler from apical view.

A lot of hemodynamic information including maximum and mean velocity,maximum and mean pressure gradients and pressure half time can be obtained from Doppler trace that helps in detection and gradient of valve stenosis and regurgitation, extraction of pulmonary artery pressure and evaluation of aortic,pulmonary venous and hepatic venous flows. Various calculations like stroke volume, cardiac output, valve area, regurgitant fraction and intracardiac shunts can be calculated which can guide the cardiologist and surgeon in taking important decisions regarding timing and type of intervention in individual patients.

Colour Doppler is bbed on principle of pulse wave Doppler and provides a real time display of movilg blood in different colours. By convention the blood flowing towards the transducer is encoded in red and blood flowing away form the transducer is encbded in blue colour. Turbulence is indicated by multicoloured or mo$aic pattem of flow. Colour Doppler imaging makes the detection and estimation of valve regurgitation and shunts simple and accurate. It also guides in correct placement and angulation of cursor for obtaining pulse or continuous wave Doppler traces.