Excellent image resolution of superficial structures at expense of tissue penetration
Use: vascular, lung (specifically pleura)
Commonly referred to as cardiac probe
Small footprint; sound waves originate from single point and fan outward
Low frequency (typically 1–5 MHz)
Excellent tissue penetration at expense of image resolution
Use: cardiac, lung, abdomen
Large footprint; sound waves originate from large area and fan outward
Low frequency (typically 2–5 MHz)
Excellent tissue penetration at expense of image resolution
Transducer (probe): sends out US waves that pass through tissue; also senses sound waves reflected back to transducer.
Structures closest to transducer are displayed at top of US screen in ‘near field.’
All probes have an ‘indicator’ (typically a bump or groove) on one side of the transducer that corresponds to an index marker on the US screen. Types of probes: see Figure 4.1 and Table 4.2.
General radiology convention is to position the screen index marker on left side of screen, and ‘point’ the probe indicator to patient’s right side or head. This means images on left side of screen correspond to structures on patient’s right side or toward patient’s head, respectively.
Cardiologists use an opposite convention (discussed in more depth in Procedure section).
It is critical to confirm your probe orientation with gel prior to any US exam or procedure. Relative to you, with the probe placed just above the intended point of contact, tapping under the right side of the probe should result in movement on the right side of the ultrasound screen. If movement occurs on the left side of the screen, rotate the probe 180°.
Depth: adjusts depth of field of view by increasing or decreasing depth of US beam. Increasing depth will visualize deeper structures and decreasing will enlarge superficial structures.
Gain: adjusts brightness of image by changing amplification of returning echoes.
Time‐gain compensation: adjusts gain at selective depths to account for tissue attenuation; echoes returning from deeper tissues will be weaker.
Freeze: creates ‘still’ or ‘frozen’ 2D images.
B‐mode (brightness): standard scanning mode using different shades of gray to provide structural information in 2D image.
M‐mode (motion): temporal measurement of structures moving toward or away from probe.
Color Doppler: distinguishes vascular from non‐vascular structures and shows direction of flow.
Echogenicity: brightness (amplitude) of image.
Hyperechoic/echogenic: structure appears brighter/whiter by generating more echoes than surrounding tissue.
Hypoechoic: structure appears darker than surrounding tissue by generating few echoes.
Isoechoic: same brightness as surrounding tissue.
Anechoic: area appears black due to complete absence of echoes.
Artifacts of US imaging
Shadowing: partial or total reflection of US waves (gallstones, ribs).
Posterior enhancement: area behind anechoic fluid‐filled structures appears brighter (bladder).
Edge artifact: shadow formed by refraction of US wave at edge of rounded structure.
Mirror artifact: image of structure duplicated as US wave reflects off highly reflective surface (diaphragm).
Reverberation artifact: US wave bounces between two highly reflective surfaces (pleura).
Ring‐down artifact: appearance of needle tip as a hyperechoic structure casting a narrow shadow.
Probe selection and orientation
Use phased array ‘cardiac‘ probe.
Conventional cardiology screen/probe orientation is to position the screen index marker on the right side of the screen (reverse of general radiology convention).
Parasternal long axis. Position probe just left of sternum at the third or fourth intercostal space. When using conventional cardiology orientation (marker on right side of screen), point probe indicator towards patient’s right shoulder. If you prefer keeping the screen marker fixed on the left side while obtaining views consistent with conventional cardiology imaging, simply point probe in opposite direction towards patient’s left hip. Otherwise, images will be reversed.
Parasternal short axis. Rotate probe 90° from long axis view to obtain circular short axis view of left ventricle. For conventional cardiology orientation, this means pointing probe towards the patient’s left shoulder. For general radiology orientation, point probe towards patient’s right hip. Angling probe through short axis views allows visualization of different segments of the left ventricle, including apex, papillary muscles (mid‐section), mitral valve (base of heart), and aortic valve (‘Mercedes Benz’ sign).
Apical four chamber. Using same orientation as short axis view, slide probe leftward – lateral to nipple line (men) or inframammary crease (women) – to point of maximal impulse. Position probe so ventricular septum is in center of US screen. The left heart will be on right side of screen and vice versa.
Subxiphoid. Position probe just below subxiphoid and angle cephalad toward the patient’s left shoulder using the liver as an acoustic window. If using conventional cardiology orientation, point probe towards patient’s left side. Otherwise, point probe towards patient’s right side. Transition to evaluating the inferior vena cava (IVC) from this view.
Assess for pericardial effusion or tamponade:
Effusion appears as anechoic area within pericardial space.
Large effusions tend to wrap circumferentially around heart.
Clotted blood or exudates appear more echogenic.
If effusion is identified, observe closely for diastolic collapse of right heart which indicates tamponade physiology.
Determine global left ventricular (LV) function, systolic function and size:
Contractility is best determined using parasternal views.
‘Good’ contractility: LV walls almost touch during systole and nearly obliterate ventricular cavity; anterior leaflet of mitral valve moves vigorously in parasternal long axis view.
‘Poor’ contractility: minimal wall movement or change in ventricular cavity between systole and diastole.
Small ventricular cavity in hypovolemic conditions.
Assess for right ventricular (RV) strain (Figure 4.3):
Classic sign of massive pulmonary embolus.
RV dilation: RV size exceeds LV size.
Paradoxical septal wall motion or ’D’ sign: best seen in parasternal short view; normal LV is circular but increased RV pressure flattens or bows interventricular septum into LV during diastole.
McConnell’s sign: RV dysfunction with characteristic sparing of apex; often described as ‘invisible man jumping on trampoline at RV apex’.