POCUS Fundamentals

FUNDAMENTALS

The IMBUS program uses several types of ultrasound devices. The chapters in this online textbook cannot describe every detail of performing tasks on each device, and terminology is sometimes different between devices. This text is designed most specifically for the GE Venue.

HANDS: The optimum technique requires the probe to be in the right hand while the left hand performs all tasks on the screen. Becoming accurate and efficient with this technique requires substantial practice.

INDICATOR POSITION: Ultrasound of the heart developed in cardiology and has a long tradition of the screen indicator being upper right for most centers; IMBUS now uses this same convention. The probe indicator positions must match this screen convention, so the long-axis-type views of the heart (e.g., PLAX and apical2) have the probe indicator cephalad. The short-axis-type views (e.g., PSAX and apical4) have the probe indicator toward the patient’s left ventricle.

IMBUS uses radiology convention with the screen indicator in the upper left for exams other than the heart. With this convention and a sagittal, parasagittal, or coronal probe position, the indicator on the screen represents the head (cephalad), and the probe indicator will also be positioned cephalad. A cephalad sliding of the probe shows new tissue entering from the left side of the screen.

For transverse radiology convention views, we want structure movement on the screen to coordinate with probe movement from the physician’s perspective. When the probe moves left, we want new tissue to enter from the left side of the screen. Traditional radiology convention is “probe indicator patient right,” which is accurate for supine and lateral decubitus patient positions. However, when examining a patient from the back (e.g., popliteal vein, posterior lung), the more accurate guidance is “indicator physician left,” which is correct for all transverse probe positions, regardless of patient position.

GEL: Beginners often use too little gel. In some situations, a good amount of gel should be applied directly to the area to be examined rather than repeatedly returning with the probe for more gel. This approach saves time and reduces the risk of losing a good viewing window. If the gel is being loaded onto a probe directly, it should not be done over the patient as it can splatter on their face or clothes. On the left in the image below, the gel was applied to the parasternal area for a cardiac exam, and on the right, the gel was used for a posterior lung exam.

 

PROBE PRESSURE: Increased probe pressure is potentially beneficial only for patients with thick adipose layers or deep abdomens. High probe pressure is uncomfortable for a patient and increases the chance of chronic injury in the physician. Physicians starting advanced IMBUS training often experience cramping of their right hand and arm until they learn to lighten the probe pressure and relax their hand and arm. Light probe pressure with a suitable gel layer is best for locations other than the abdomen.

FREQUENCY: Our Venue presets rarely need frequency adjustment, but in excessively obese patients, lowering the default frequency from RES to GEN or from GEN to PEN may improve views, even though this sacrifices some image resolution.

DEPTH: Structures of interest should be in the lower part of the B-mode sector (called 2D on some devices). The frame rate is better in the lower part of the sector, which is particularly important for any moving structure. This location in the sector also increases the image size of any structure.

FOCUS POSITION: A structure of interest will have the best lateral resolution when it is in the focus position for the sector. The focus position is easily moved on Venue’s depth scale with a finger and brought to the most critical part of the view. On other devices, the focus position is fixed in the center of the screen.

GAIN: The default Venue gain for a preset is usually excellent, but do a quick visual assessment of the fluid in any field (e.g., urine, blood, and cysts). This fluid should be primarily anechoic, but be sure other tissue has good structure. The following images of a left kidney with a parapelvic simple cyst show an under-gained image on the left, an over-gained image on the right, and an acceptably gained image in the middle.

 

Sometimes, just part of the field needs gain adjustment with a control called Time Gain Compensation. For example, the tissue posterior to the cyst in the image above is over-gained because of posterior acoustic enhancement. The TGC control could turn down the gain just for the tissue posterior to the cyst.

WIDTH: The width of a B-mode sector only needs optimization with challenging patients to avoid wasting ultrasound power. A narrower sector width improves the resolution of structures and increases the frame rate. Venue has Width control for the phased array and curvilinear probes.

ZOOM: Zooming is the last step in imaging and is done with Venue using a finger-pinching action on the screen. If a B-mode image has been optimized for depth, focus position, and width, it is unusual to need zooming.

Below is a standard PLAX view of a heart with a Venue device. Assume we want the closest and best view of the aortic valve.

 

To optimize the aortic valve, the depth was decreased to move the valve to the lower part of the sector, the focus position was moved to the valve level, and the sector width was narrowed. Here is the result.