Pleural effusion on a Suresult handheld convex probe: collapsed lung drifting inside the fluid above the bright curve of the diaphragm, 160 mm depth at 5 MHz harmonic, gain 86 dB

Every thoracic frame this library holds for pleural fluid, in order: the finding first, then the same window with the air still in it, then collapsed lung drifting inside the collection. Six of the seven carry the depth, frequency and gain on their own screen.

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Dr. Fernando MarizDr. Fernando MarizGynecology, pelvic surgery, sonography
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I am Dr. Fernando Mariz, a gynecology and pelvic surgery physician practicing in New York City. Before my medical career, I served in the U.S. Marine Corps, where I developed the discipline, focus, and steadiness that continue to shape the way I care for patients today. At Maiden Lane Medical, my work covers women’s health, preventive care, sonography, pelvic pain, abnormal uterine bleeding, and minimally invasive gynecologic procedures.

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Dra. Jailyn AvilaDra. Jailyn AvilaEmergency medicine, POCUS education
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I am Dr. Jailyn Avila, an emergency medicine physician, educator, and digital health innovator based in Southern California. My clinical work is rooted in emergency care, while my teaching focuses on point-of-care ultrasound, residency education, and practical training for physicians. Through my roles with Emergent Medical Associates, UHS SoCal MEC Emergency Medicine Residency, Core Ultrasound, and FemInEM, I work at the intersection of patient care, medical education, and accessible digital learning.

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Verified authorsUpdated September 14, 2026

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A pleural effusion on ultrasound is a collection of fluid between the chest wall and the lung, sitting above the diaphragm, that returns no echo and lets the beam through where air normally stops it dead. The finding is that you can suddenly see structures at a depth where a normal chest shows only shadow. Thoracic ultrasound detects an effusion with a pooled sensitivity of 0.94 and a specificity of 0.98, against 0.51 and 0.91 for chest radiography. Collapsed lung inside the collection appears as a wedge of tissue density that drifts with respiration, because airless lung conducts sound instead of blocking it. Volume can be estimated from a single measurement, but the formula and the measurement travel together: the Balik formula multiplies the maximum separation between the two pleural surfaces at the lung base, measured supine at end expiration, by 20. Fluid on the abdominal side of the diaphragm is ascites, not effusion, and mistaking one for the other is the classic error on this exam. My own habit is to find the diaphragm before I look at anything dark, and to keep it in the frame while I decide.

After the hardware instead of the exam? Chest probe choices sit on the pulmonology hub, and the D3Ultra product page sets out what the head is specified to reach and what it sells for now.

Image atlas

Seven frames, the finding first

These are the thoracic recordings in the Scan Library for pleural fluid, in teaching order. Six of the seven carry the acquisition settings burned into their own panel, read off the screen rather than typed in afterwards, and six of the seven are shown exactly as the library holds them, at their own true size. Figure 6 is the exception on both counts: its export arrived with the parameter panel cropped away, and its caption says so. Figure 1 is the finding and figure 2 is the same window with the air still in it; if you only study two frames here, study that pair, because the second is what makes the first mean anything.

Two limits, stated before the first image. Five of these seven recordings come from one study on 2018-03-19, made inside three minutes of one another, so they are five windows on one chest rather than five patients; the captions say which. And the device model was not recorded for any frame on this page, so none of them names one.

Pleural effusion on ultrasound: dark fluid opening a window above the bright curved diaphragm with solid organ below, 5 MHz harmonic at 160 mm depth, gain 75 dB
Figure 1. Fluid, and the window it opens. The bright curved diaphragm runs across the lower sector with solid organ underneath it. Above it the beam is getting through instead of stopping, which is the whole finding. The control in figure 2 is a different patient on a different device in a different year, at 200 mm rather than 160, DR 60 rather than 80 and ENH 4 rather than 2 — which is the page’s own thesis working on it: the settings change the picture, so both panels are printed under both frames.

Read off the screen

  • Dispositivo
    Suresult wireless convex probe (clinical reference library; model not recorded)
  • Recorded2018-03-19 08:30:25 (on-screen clock)
  • PanelF H5.0 MHz · D 160 mm · GN 75 dB · DR 80 · ENH 2 · frozen at 30/30
  • FileJPEG 1781 × 1293
Figure 2. The lung base with nothing in it. The same window with the air still in it, and it is mostly black on purpose. Air stops the beam at the pleural surface, so the screen shows a narrow wedge of chest wall and then shadow. The diaphragm, the liver and the spleen are behind that air and cannot be seen from here. Compare it with figure 1: fluid is what opens the window, and this is what the window looks like shut.

Read off the screen

  • Dispositivo
    Suresult wireless convex probe (clinical reference library; model not recorded)
  • Recorded2017-01-07, frames stamped 12:11:53 to 12:12:40 (on-screen clock)
  • PanelF H5.0 MHz · D 200 mm · gain 83 dB · DR 60 dB · ENH 4 · 100 frame cine replay
  • FileMP4 864 × 656 · 10 s · 100 frames
Figure 3. The same chest, swept. Gain is eleven decibels higher here than in the frozen frame above, and the fluid stops looking uniformly black: strands and moving echoes appear inside it. Turning gain up is how a collection that reads as simple starts to read as complex, which is why the number on the screen belongs in the record.

Read off the screen

  • Dispositivo
    Suresult wireless convex probe (clinical reference library; model not recorded)
  • Recorded2018-03-19 08:33:17 to 08:33:24 (on-screen clock)
  • PanelF H5.0 MHz · D 160 mm · GN 86 dB · DR 80 · ENH 2 · 57 frame cine replay
  • FileMP4 480 × 352 · 5.7 s · 57 frames
Collapsed lung sitting inside pleural fluid on ultrasound, a tissue density wedge bounded by dark fluid and a bright curved diaphragm, 5 MHz harmonic at 160 mm depth
Figure 4. Lung inside the fluid. A wedge of tissue that looks like solid organ rather than air, bounded by dark fluid on one side and the bright curved diaphragm below. Airless lung conducts sound, so it draws with texture instead of stopping the beam. Frozen, it is a shape; it is the movement that names it.

Read off the screen

  • Dispositivo
    Suresult wireless convex probe (clinical reference library; model not recorded)
  • Recorded2018-03-19 08:32:56 (on-screen clock)
  • PanelF H5.0 MHz · D 160 mm · GN 86 dB · DR 80 · ENH 2 · cine replay, frame 100/100
  • FileJPEG 1781 × 1293
Figure 5. The same lung, moving. The collapsed lobe drifts inside the collection as the chest moves. The literature calls this the jellyfish sign, and it is a B mode appearance; the M mode trace taken through the same space is a separate finding with its own name, the sinusoid sign. Watch the frequency on the panel as well: the operator runs 3.5 MHz for the first ten frames and switches to harmonic 5.0 MHz at frame 11.

Read off the screen

  • Dispositivo
    Suresult wireless convex probe (clinical reference library; model not recorded)
  • Recorded2018-03-19 08:32:24 to 08:32:28 (on-screen clock)
  • PanelF 3.5 MHz for the first ten frames, then F H5.0 MHz from frame 11 · D 160 mm · GN 86 dB · DR 80 · ENH 2 · 38 frame cine replay
  • FileMP4 912 × 672 · 3.8 s · 38 frames
Second ultrasound study showing pleural fluid with a curled edge of collapsed lung against the bright diaphragm
Figure 6. A second patient, the same pattern. The only frame on this page from a different study than the other effusion images. The curled tissue edge against the bright diaphragmatic line repeats what the first study shows, which is the point of including it. It is also the one frame here whose parameter panel was cropped out of the export, so its settings cannot be read off the screen the way the rest can.

Read off the screen

  • Dispositivo
    Suresult wireless convex probe (clinical reference library; model not recorded)
  • Recordeda different study, on-screen clock 09:23:40; the date digits are cut off by the export
  • PanelSettings panel cropped out of this export; frequency, depth and gain are not legible
  • FileJPEG 590 × 554
Figure 7. Two compartments in one study. Logged in the reference library as pleural fluid with a pericardial collection in the same examination. Which compartment a dark space belongs to is settled by the descending thoracic aorta: pericardial fluid tracks in front of it, pleural fluid behind and lateral to it. What this recording settles is that both compartments can fill in one patient, which is the reason the aorta is worth finding before the fluid is named.

Read off the screen

  • Dispositivo
    Suresult wireless convex probe (clinical reference library; model not recorded)
  • Recorded2018-03-19 08:31:18 to 08:31:28 (on-screen clock)
  • PanelF H5.0 MHz · D 160 mm · GN 82 dB · DR 80 · ENH 2 · 49 frame cine replay
  • FileMP4 480 × 352 · 4.9 s · 49 frames

These frames come from two devices with two panel layouts. The 2018 device writes its parameters in English as GN: and D:, and keeps 冻结 for freeze and 回放 for cine replay: that is figures 1 and 3 to 7. The 2017 device writes the same two values in Chinese, 增益 for gain and 深度 for depth: that is figure 2, the control. Every value that is legible is transcribed into the settings cards above in the usual notation. The on-screen ID, name, gender and age fields are the demonstration values the device ships with, and they are shown as recorded. Three further assets from the same library were reviewed and left out: two are down-scaled crops of frames already published above, and one is an overlapping export of the same cine buffer as figure 1.

Reading the images

What this exam shows

One question, asked at one place. Put a low frequency curvilinear probe in a lower rib space in the mid to posterior axillary line, aim it at the diaphragm, and ask whether you can see past the pleura. In a chest with no fluid the answer is no: air reflects almost all of the beam, so the screen shows a couple of centimetres of chest wall and then shadow, and the diaphragm and the liver or spleen underneath it are invisible from that window. That is figure 1, and it is the reason this exam is quick to learn.

Fluid changes the answer completely. A collection conducts sound, so the beam reaches the diaphragm and everything beyond it, and the image opens into a dark space bounded below by a bright curved line with solid organ under it. Inside that space, lung that has lost its air stops behaving like a mirror and starts behaving like tissue: it draws as a grey wedge with texture, tethered at the hilum, drifting as the chest moves.

Two things the picture alone will not tell you. It will not tell you whether the fluid is transudate or exudate, because an anechoic collection can be either, and a concentrated transudate under diuretics can look echogenic. And it will not tell you which side of the diaphragm you are on unless you find the diaphragm first and keep it on screen, which is why the anchoring step is the whole technique.

Acquisition

How the scan is done

A low frequency curvilinear probe, 2 to 5 MHz, penetrating 10 to 25 cm, because an adult chest needs 10 to 25 cm of penetration. A phased array is an acceptable alternative for slipping between narrow rib spaces. A high frequency linear probe is the wrong tool here: it reaches 2 to 5 cm, which is the chest wall and the pleural surface, not the recess. Depth on the machine is commonly set to 8 to 10 cm.

The European Respiratory Review describes the systematic examination as sitting the patient upright or leaning slightly forward and scanning from behind. For a supine patient, ACEP Sonoguide puts the probe along the posterior axillary line above the diaphragm, because fluid is gravitationally dependent and pools in the costophrenic angle. That choice is not cosmetic: Ko and colleagues measured the pocket by approach in supine patients and found that in 40.6 percent of effusions the depth exceeded 1 cm posteriorly or posterolaterally but not laterally.

Anchor the image before you interpret it. Find the diaphragm with the liver and right kidney below it on the right, or the spleen and left kidney on the left, and keep that landmark in the frame. Everything on the abdominal side of that line is abdomen. Then fan through the recess, and if a measurement is wanted, take the maximum separation between the two pleural surfaces at the base at end expiration and record the patient position alongside it, because the position changes which constant applies.

On the safety question the evidence is one directional: a meta-analysis of 24 studies and 6605 procedures put the overall pneumothorax rate after thoracentesis at 6.0 percent and found imaging guidance associated with an odds ratio of 0.3.

Fast comparison

Fluid versus no fluid, structure by structure

Read the fourth column with the other three. On this exam the image is easy and the qualification is where the work is.

What you are looking at No fluid Fluid What the frame still cannot settle
Beyond the pleural surface
 Air stops the beam. A narrow band of chest wall, then shadow, and nothing beyond it. The beam gets through. A dark space with recognisable structures visible behind it. A window says fluid is present. It does not say how much, and it does not say what the fluid is.
The diaphragm
 Not visible from an intercostal window over aerated lung. A bright curved line with liver or spleen immediately below it. Fluid on the abdominal side of that line is ascites. Getting the side wrong is the classic error on this exam.
The lung edge
 Not separately visible, because air and lung are one surface. A wedge of tissue density inside the collection that drifts as the chest moves. A frozen frame gives the shape. Only a clip gives the movement, and the movement is what names it.
The fluid itself
 No collection to characterise. Anechoic in a simple collection, echogenic or septated in a complex one. An anechoic collection can be transudate or exudate, and a concentrated transudate under diuretics can look echogenic.
The depth of the pocket
 No pocket to measure. The separation between parietal and visceral pleura at the base, in millimetres. The Balik multiplier of 20 is tied to this measurement in a supine patient. The sitting rule uses a different constant on a different distance, so the landmark and the position belong in the record with the number.

Echogenicity and what it predicts: Yang et al., 320 cases, with the exception in Hassan and colleagues. The drifting collapsed lobe in B mode, and the sinusoid sign that the M mode trace through the same space produces: Killu and Kakol y Lichtenstein. Separating fluid above the diaphragm from fluid below it: Halvorsen and Thompson y Blanco and Volpicelli. Volume formulas and the effect of patient position, each with the measurement it was derived on: Balik et al. y Usta et al., read alongside Vetrugno and Bove. All sources accessed September 14, 2026.

Hardware

Device and settings

The left column is the published specification; the right column is what the device interface actually showed while these frames were acquired. Look at the depth first. Every frame whose panel is legible ran at 160 or 200 mm, which is a convex-array setting, and it is the single fact that decides the hardware for this exam. A high frequency linear probe is not a good fit for this window at any price: it cannot reach an adult costophrenic recess and no amount of gain repairs that. That depth line is what I would buy on. If chest and abdominal work is the whole job, the convex-only probe below reaches the same depth for less. A head that carries three geometries starts to earn its price only once lines, joints and small parts are on the same list.

Published specification

Suresult D3Ultra

Three geometries, one head — $2,976

  • Convexo3.2 / 5.0 MHz · 90–300 mm · 45°
  • Por fases3.2 / 5.0 MHz · 90–300 mm · 60°
  • Lineal7.5 / 10 MHz · 20–100 mm · 40 mm
  • Signal path192 elements · 64 channels · 256 grey levels
  • Gain range30–105 dB · dynamic range 40–110
  • Efecto DopplerColour, Power and PW, alongside B and M
  • Handpiece156 × 65 × 20 mm · 263 g · 2 h scanning
  • Connects toiOS, Android, Windows · dual-band Wi-Fi

Read off the screens, across the six legible panels

  • PresetNot displayed on these frames
  • ArrayConvex on every frame
  • ProfundidadD 160 mm on the effusion study, D 200 mm on the control; not legible on figure 6
  • FrecuenciaF 3.5 MHz and F H5.0 MHz
  • GaneGN 75 to 86 dB across the six legible panels
  • Dynamic rangeDR 60 and DR 80 · ENH 2 and 4
  • OutputMI and TIS not displayed on these frames
  • ModosB mode throughout · every finding here is settled in grey scale
D3Ultra specification and price →C5SH convex probe — $2,139 →Pulmonology hub →Critical care hub →Scan Library →

The abdominal half of the same probe and the same depth setting is covered on the gallbladder and right upper quadrant image atlas.

Asked on this search

Pleural effusion ultrasound questions

Can ultrasound detect a pleural effusion better than a chest radiograph?

Yes, and the gap is wide. A meta-analysis of 12 studies covering 1554 subjects put pooled sensitivity at 0.94 and specificity at 0.98 for ultrasound, against 0.51 and 0.91 for radiography. In ventilated intensive care patients scanned against CT as the reference, ultrasound reached 100 percent sensitivity and specificity while the bedside film managed 65 and 81 percent.

How small a pleural effusion can ultrasound find?

Very small. The original comparative study showed ultrasound detecting as little as 3 to 5 mL of loculated pleural fluid, and a study of healthy volunteers measured normal fluid layers of 2.0 to 4.3 mm. A plain film is far blunter: fluid becomes visible as a meniscus on the lateral view at roughly 50 mL and on the frontal view at roughly 200 mL.

How is pleural effusion volume measured on ultrasound?

The usual shortcut is the Balik formula: volume in millilitres equals 20 multiplied by the maximum separation between the parietal and visceral pleura in millimetres, measured at the lung base at end expiration. It was derived in 81 ventilated patients lying supine with the trunk raised 15 degrees, and its mean prediction error is 158 plus or minus 161 mL. A separate rule exists for the sitting patient, from Usta and colleagues in cardiac surgery, but it multiplies by 16 and it measures a different distance, from the mid height of the diaphragm to the visceral pleura. The two constants are not interchangeable on one measurement.

What can be mistaken for a pleural effusion on ultrasound?

Three things. Fluid below the diaphragm, which is ascites, and the diaphragm sign, the displaced crus sign and the bare area sign are what separate them. A mirror artefact, which repeats the liver pattern above the diaphragm because the diaphragm is a strongly reflective surface. And a pericardial collection, which has been documented reproducing the appearance of a collapsed lung floating in fluid.

How do you tell a pericardial effusion from a pleural effusion?

By where the fluid sits relative to the descending thoracic aorta. The original echocardiographic series showed that isolated pericardial fluid produced an echo free space between the descending thoracic aorta and the posterior wall of the left ventricle, while isolated pleural fluid produced a space behind that aorta. Point of care teaching states the same rule: pericardial fluid tracks in front of the descending aorta, pleural fluid behind and lateral to it.

Provenance

Sources and image provenance

Every frame on this page was recorded by Suresult’s own 2017 to 2020 clinical reference library. Nothing comes from a third-party image bank. The device model was not recorded for any of them and they predate the current product line, so no frame here is attributed to a current model. Six of the seven carry a legible parameter panel, and those settings are transcribed from the frame’s own burned-in display. The finding labels are the labels the library itself recorded. No frame has been retouched or relabelled. One is cropped, and its caption says so: figure 6 reached the library as an export with the parameter panel and the date digits cut away.

How deep does your chest work actually have to reach?

An adult costophrenic recess is a deep target approached between ribs, so the answer starts by ruling a high frequency linear array out rather than in. What is left open is whether one head also has to cover lines, joints and small parts. Say what a normal week on your list looks like and I will tell you which of those depths actually decides it, up to and including the case for buying nothing yet.


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About Dr. Fernando Mariz, MD

Soy el Dr. Fernando Mariz, médico especialista en ginecología y cirugía pélvica que ejerce en la ciudad de Nueva York. Antes de iniciar mi carrera médica, presté servicio en el Cuerpo de Marines de los Estados Unidos, donde desarrollé la disciplina, la concentración y la firmeza que siguen marcando la forma en que atiendo a mis pacientes en la actualidad. En Maiden Lane Medical, mi trabajo abarca la salud de la mujer, la atención preventiva, la ecografía, el dolor pélvico, el sangrado uterino anómalo y las intervenciones ginecológicas mínimamente invasivas.

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