Differences in ultrasound elevational beam width (slice thickness) between popular handheld devices

Abstract

Background

Handheld ultrasound devices are increasingly used by medical professionals for bedside ultrasound-guided interventions. Especially for vascular access procedures, the width of the imaging plane, known as the slice thickness or elevational beam width is a prominent source for misinterpretation. A wide slice thickness can lead to the interpretation that 2 objects (i.e. needle and vessel) are on the same plane while in fact they are not and thereby negatively influencing the performance of in-plane ultrasound-guided interventions. Therefore, the beam profiles of three popular handheld US devices are tested and compared to a conventional US device.

Methods

The GE VScan, Philips Lumify and Butterfly IQ ​+ ​are tested using a slice phantom to determine the slice thickness. For comparison, a Philips Affiniti machine was investigated. Both linear and curved array settings were analyzed. In a slice phantom, a diffuse scattering plane at an angle of exactly 45° is scanned. For each imaging depth, the vertical height of the imaged rectangle corresponds to the slice thickness at that depth.

Main results

For the linear array transducers, the focus depth ranges from 1.5 to 3.5 cm. At the focus depth, all transducers have a reasonable slice thickness of approximately 1 mm. More superficially, the slice thickness varies between 1 and 4 mm. The curved array probes have larger focus depths, ranging from 2.7 to 7.3 cm. The slice thickness at focus depth varies between 1.4 and 3.8 mm, but at 2 cm depth is even more than 5 mm.

Conclusions

The slice thickness of handheld ultrasound transducers varies between the different devices, and can be suboptimal for superficial in-plane ultrasound-guided interventions. The larger slice thickness of the curved array settings may complicate in-plane guidance. Handheld ultrasound users should be aware of the beam characteristics of their devices to optimize guidance for interventions.