Basic Transthoracic Echocardiography Tutorial | 2D TTE Image Acquisition

Ultrasound (sonogram) produces black-and-white images showing gradients between light and dark areas, with brighter regions representing denser materials like bone. Sound is a longitudinal wave where particles vibrate parallel to wave propagation, creating compression and rarefaction regions. Waves have three key characteristics: wavelength (cycle length), frequency (cycles per second), and speed, related by speed = frequency × wavelength. Ultrasound operates at frequencies around 2 million Hz, far above human hearing range (20 Hz to ~20,000 Hz). The speed of sound varies with medium density—higher density allows faster sound transmission because particles transfer energy more efficiently. Acoustic impedance (Z = ρ × v) measures a material's resistance to sound wave movement. When sound encounters boundaries, reflection and transmission occur according to R = [(Z₂ - Z₁)/(Z₂ + Z₁)]². Large impedance differences cause high reflection, while similar impedances allow greater transmission. Medical ultrasound relies on detecting reflected waves from tissue boundaries; strong signals appear at large impedance differences (skin-air, bone-tissue), while weak signals appear where impedances are similar. Coupling gel removes air gaps between transducers and skin, enabling efficient sound transmission into the body for diagnostic imaging.

Attenuation (scatter + absorption) limits imaging depth - higher frequencies attenuate more rapidly. Water and fluid attenuate minimally, causing posterior acoustic enhancement where tissues behind cysts appear brighter. Bone and calcium strongly attenuate transmitted sound, creating acoustic shadows. Time gain compensation electronically amplifies deeper signals. Piezoelectric transducers convert electrical to acoustic energy and vice versa. Spatial pulse length (wavelength × cycles) determines axial resolution - higher frequencies provide better resolution but less penetration. Lateral resolution depends on beam width and focusing capability. Harmonic imaging improves contrast by detecting higher-frequency harmonics generated in tissues.

Ultrasound operates above 20 kHz, typically using megahertz frequencies. The piezoelectric effect enables transducers to both emit and detect ultrasound: crystals generate voltage when compressed and vibrate when subjected to electrical potential at their natural frequency. Ultrasound reflects at tissue boundaries with different acoustic impedances (Z = ρ×v), with reflection intensity given by ir/i₀ = (Z₂-Z₁)²/(Z₂+Z₁)². A-scans display voltage versus time, with spike positions indicating boundary locations. Thickness is calculated using d = (v×t)/2. Most ultrasound reflects at air-skin interfaces due to impedance mismatch, requiring ultrasound gels for effective penetration. Doppler ultrasound measures blood velocity using frequency shifts: v = (Δf × c)/(4f₀cosθ), requiring angled positioning (typically 45°) to avoid zero Doppler shift at perpendicular incidence.

Ultrasound operates on pulse-echo principle and piezoelectric effect (crystals convert electrical to acoustic signals). Transducers contain PZT crystals, backing material (absorbs vibrations for wide bandwidth), matching layer (impedance bridge), and acoustic lens. Resonant frequency is where amplitude is maximum; bandwidth is the frequency range where amplitude decreases by 50%. Resolution is the ability to distinguish two reflectors: axial resolution (along beam) depends on spatial pulse length - higher frequency improves resolution; lateral resolution (perpendicular) depends on beam width; elevational resolution (vertical plane) represents slice thickness. Beam profile describes wave spreading - focused beams have narrowest point at focal point. Diffraction bends waves through aperture. Frame rate decreases with increased depth and scanning area.

Acoustic impedance is the product of tissue density and sound velocity, determining how much ultrasound energy is reflected versus transmitted at tissue interfaces. Different tissues (muscle, tendon, bone, air, blood) have different acoustic impedances, creating the interfaces that generate ultrasound images. Attenuation is the progressive loss of ultrasound energy as the beam propagates through tissue, with three components: absorption, scattering, and reflection. Attenuation increases with depth and frequency. Higher frequencies experience greater energy loss at each interface. The half-power distance varies by tissue: water (380 cm), bone (0.2-0.7 cm), and lung (0.05 cm).

The standard anatomical position is the reference posture for describing all body structures: standing upright, facing forward, with arms at sides and palms facing forward, legs together but slightly separated, and feet pointing forward and slightly outward. Three basic anatomical planes facilitate structural description: the sagittal plane (vertical, parallel to midline, dividing body into left and right portions), the coronal or frontal plane (vertical, perpendicular to sagittal, dividing body into anterior/ventral and posterior/dorsal parts), and the transverse or horizontal plane (dividing body into superior and inferior portions). The sagittal plane is always parallel to the median plane, making the term 'parasagittal' redundant. An oblique plane does not conform to any of the basic planes and is commonly used in radiological imaging.

The human body can be divided into sections using three primary anatomical planes: (1) Sagittal plane - divides the body into right and left portions, passing through the midsagittal line between the two parietal bones; (2) Transverse plane - divides the body into upper and lower portions; (3) Coronal (frontal) plane - divides the body into anterior (front) and posterior (back) portions. The term 'median' is sometimes used but 'sagittal' is the authentic technical term.

The human body can be divided by three primary anatomical planes that serve as reference systems for describing body orientation and structure. The median sagittal plane is a vertical plane passing through the body's center, dividing it into equal right and left halves. The frontal or coronal plane is another vertical plane that separates the body into anterior (front) and posterior (back/dorsal) regions. The transverse, horizontal, or axial plane is a horizontal plane that divides the body into superior (upper) and inferior (lower) regions. These three planes intersect at right angles to create a three-dimensional coordinate system essential for anatomical description. Understanding these planes is fundamental for students studying human anatomy, as they provide the spatial framework for locating and describing body structures.

Anatomical planes are hypothetical or imaginary flat surfaces used to dissect the human body for describing the location of structures and the direction of movements. The three principal anatomical planes are: (1) Sagittal plane (longitudinal plane) - divides the body into left and right portions, with the mid-sagittal plane passing through the body's midline to create equal halves, and parasagittal planes creating unequal portions; (2) Coronal plane (frontal plane) - divides the body into anterior (front) and posterior (back) portions; (3) Transverse plane (axial plane) - divides the body into superior (upper) and inferior (lower) portions.

Anatomical terminology provides standardized language for describing body structures, with the anatomical position (standing upright, facing forward, arms at sides with palms forward) serving as the reference point. Key directional terms include superior (above), inferior (below), anterior (front), posterior (back), medial (toward midline), lateral (away from midline), contralateral (opposite side), ipsilateral (same side), proximal (closer to attachment point), and distal (farther from attachment point). Anatomical planes divide the body: sagittal (right/left), coronal/f frontal (front/back), and transverse (upper/lower).

The cardiac cycle consists of systole (contraction and ejection) and diastole (relaxation and filling). During systole, ventricles contract, pressure rises, and blood ejects through semilunar valves. During diastole, ventricles relax, pressure falls, and blood fills through atrioventricular valves. The cycle begins with atrial contraction, followed by ventricular filling, then ventricular contraction, and finally ventricular relaxation. The cycle is coordinated by electrical events that precede mechanical events by milliseconds.

The cardiac cycle alternates between systole (contraction) and diastole (relaxation). Systole begins after ventricular filling during diastole and involves two phases: isovolumic contraction (pressure rises above atrial pressure, closing AV valves with first heart sound) and ejection (pressure exceeds aortic pressure, opening semilunar valves for blood ejection). Diastole follows with four phases: isovolumic relaxation (pressure drops below aortic pressure, closing semilunar valves with second heart sound), rapid inflow (AV valves open, passive filling to 70-80%), diastasis (minimal volume change), and atrial systole (atria contract adding final 20-30%). Diastole constitutes approximately two-thirds of the cardiac cycle.

The cardiac cycle consists of coordinated electrical and mechanical events where atrial and ventricular systole (contraction) and diastole (relaxation) alternate; during diastole, chambers passively fill with blood as they relax, while during systole, contraction increases pressure to eject blood, with key measurements including end diastolic volume (maximum blood volume in ventricles at end of filling) and end systolic volume (minimum blood volume remaining after ejection).

The cardiac cycle encompasses all events from one heartbeat to the next. Electrical systole corresponds to the QT interval (QRS to end of T wave), while diastole spans from end of T wave to beginning of QRS. Ventricular depolarization occurs sequentially: left ventricle first, then right ventricle (opposite to atrial sequence). Mechanical events include isovolumetric contraction (pressure rises, volume constant), ejection (blood leaves ventricle), and isovolumetric relaxation (pressure falls, volume constant). Diastole has three phases: rapid passive filling, diastasis, and rapid active filling with atrial contraction. Excitation-contraction coupling links electrical depolarization to mechanical contraction through calcium release from the sarcoplasmic reticulum.

The cardiac cycle consists of systole (contraction) and diastole (relaxation). Systole includes isovolumetric contraction (ventricular pressure rises, AV valves close, generating S1), rapid ejection (70% of blood pumped), and slow ejection. Diastole includes isovolumetric relaxation (semilunar valves close, generating S2), rapid ventricular filling, slow ventricular filling, and atrial contraction (contributing final 20% of filling). The cycle is driven by spontaneous action potentials from the sinoatrial node.