POCUS image acquisition: probe positions and Doppler sectors
Stem
At the ultrasound station, the POCUS task card describes a 58-year-old man, 90 kg, who is hypotensive in recovery after a laparoscopic colectomy. The standardized patient lies supine. The examiner at the machine asks for a parasternal long-axis view and then a color-flow Doppler sector over the mitral valve. Phased-array, curvilinear and linear probes are on the cart.
Question
Acquire the view for me: which probe, where do you place it, and what do you ask me to set on the machine?
Ideal answer
HeadlineFour narrated steps, probe, position, optimize, color: phased array at the left third or fourth space beside the sternum, marker to his right shoulder.
- Probe for the target. Phased array because this is the heart; curvilinear (or phased) for abdomen, stomach and lung bases; linear for the pleural line only.1
- Name the spot before the probe goes down, then ask you for depth, gain, focus: heart filling two-thirds of the screen, blood black, tissue gray.
- Confirm by proof structures. RV outflow tract, LV, aortic and mitral valves, descending aorta at the bottom.1
- Small color box only over the mitral valve, Nyquist 50–70 cm/s for cardiac flow,2 because a wide box drops the frame rate.
- Freeze, state orientation, name the proof structures.3 If lung gets in the way, one space lower or subcostal.
Breaking down the answer
- I produce the image here — in the monitors station I read one someone else acquired. The examiner names an outline view, such as parasternal long-axis, right upper quadrant or gastric antrum,4 and scores probe, position and marker, settings and the color Doppler box.3
| View | Probe | Position and marker | Proof structures |
|---|---|---|---|
| Parasternal long-axis | Phased, cardiac preset | Left 3rd–4th space, marker to right shoulder | RVOT, LV, aortic and mitral valves, descending aorta at the bottom of the image1 |
| Parasternal short-axis | Phased | Same spot, marker to left shoulder | Round LV, two papillary muscles |
| Apical four-chamber | Phased | Point of maximal impulse, marker to patient's left | Four chambers, apex at the top |
| Subcostal four-chamber and IVC | Phased or curvilinear | Subxiphoid, marker left; then rotate to the head | Liver, RV, IVC into RA, hepatic vein |
| Lung and pleura | Linear (pleura); curvilinear or phased (deeper) | Anterior 2nd–3rd space, marker to the head | Rib shadows, pleural line, A-lines, sliding1 |
| Diaphragm | Curvilinear | Subcostal, angled cranially through liver or spleen | Diaphragm excursion, lung base |
| RUQ / LUQ | Curvilinear | Mid- to posterior axillary line, 8th–11th space, marker to head | Hepatorenal or splenorenal space, diaphragm |
| Pelvis | Curvilinear | Suprapubic, transverse and sagittal | Bladder, rectovesical or rectouterine pouch |
| Gastric antrum | Curvilinear, 2–5 MHz | Epigastric sagittal, supine then right lateral decubitus | Left lobe of liver, antrum, pancreas, aorta or IVC, SMA5 |
- Scale matched to the vessel — a lower scale for veins: too low aliases a normal vessel into a mosaic, too high and slow venous flow disappears.
- Gastric scan in two positions — I never call the stomach empty from the supine view alone;5 right lateral decubitus brings contents to the antrum.5
- What changes the induction — clear fluid in both positions (grade 2) with more than 1.5 mL/kg, or any thick fluid or solid, means a full stomach: rapid sequence induction.6
- FAST sequence — RUQ first, because the hepatorenal space is the most dependent upper abdominal space supine, then LUQ, then pelvis. Free fluid in a hypotensive trauma patient sends them to the operating room.
Follow-up question
The model has poor windows, and the parasternal screen shows only lung artifact. On the next task, vascular access, the examiner asks you to show flow in the IJ, and the screen shows a full-sector color box full of aliasing. What do you do?
Follow-up answer
HeadlineTwo fixable acquisition problems; I narrate the fix rather than fight the machine.
For the heart: "Lung is in the way; I will move one space lower and closer to the sternum, and if that fails I will go subcostal." When the subcostal four-chamber comes up, I name the liver, RV and LV, then rotate to the IVC. For the IJ, I ask the examiner for a narrower box over the vein and a lower scale, then compress to confirm the vein. Asking for the fix aloud scores; quietly fighting the machine does not.
Pitfalls that cost points
- Leaving the target at the bottom of an 18 cm image, or the gain washed out: it hides every finding.
- Calling a red vessel an artery: blue is away, red toward; color gives the angle to the probe.
Rapid-fire
Q: Why does a big color box hurt? A: Every color line needs its own pulses, so a larger box lowers the frame rate and temporal resolution.
Q: Why scan the antrum in right lateral decubitus? A: Gastric contents move to the dependent antrum, so small volumes become visible and the cross-sectional area can be measured to estimate volume.5
Q: Why the hepatorenal space first in FAST? A: It is the most dependent upper abdominal space supine and the most sensitive site for free fluid.
Q: What does aliasing mean? A: Flow velocity exceeds half the pulse repetition frequency, so the color wraps to the opposite direction.
Numbers to know
| Item | Value |
|---|---|
| Cardiac Nyquist | 50–70 cm/s2 |
| Venous Nyquist | Lower scale, roughly 20–40 cm/s |
| Target on screen | ~2/3 depth |
| Gastric volume of concern | ≥1.5 mL/kg6 |
| Probes | Linear 6–15, curvilinear 2–5, phased 1–5 MHz |
Links
- The ultrasound application station: format and tasks, The 5 POCUS cardiac views, Lung ultrasound: pleura, A/B-lines, effusion, pneumothorax, Abdominal free fluid and gastric ultrasound, Volume status, IVC and fluid responsiveness
- Atlas: The 5 POCUS cardiac views
- SHM minimum image quality criteria for POCUS (2025); ASE Focused Cardiac Ultrasound Recommendations (2013)
Sources
- 1.Defining minimum image quality criteria for common diagnostic point-of-care ultrasound images: A position statement of the Society of Hospital Medicine · SHM (J Hosp Med), 2025 · ebi.ac.ukOpen-access full text (PMC12865264) via Europe PMC; Tables 2-4.
- 2.Recommendations for Noninvasive Evaluation of Native Valvular Regurgitation · ASE/SCMR, 2017 · asecho.org
- 3.OSCE Example Scenarios (all stations) · ABA, 2023 · theaba.orgPOCUS task template: probe orientation, two structures, color-flow Doppler sector over a valve.
- 4.APPLIED Exam Objective Structured Clinical Examination (OSCE) Content Outline · ABA · theaba.org
- 5.Gastric ultrasound: image acquisition · gastricultrasound.org (Perlas, Van de Putte) · gastricultrasound.org
- 6.Gastric ultrasound: image interpretation and cut-off values · gastricultrasound.org (Perlas, Van de Putte) · gastricultrasound.org
Facts on this page were checked against these sources on Oct 14, 2026. Guidelines change; confirm doses against current institutional protocols.