Ultrasound

The information presented in this article has been gathered by Sofian Zeina and Abram Shihata and was presented in the Biomedical Engineering meeting on November 2017.  The article is posted by Nikhil Kanamala.

Ultrasound waves are acoustic waves which are mechanical vibrations inducing alternating refraction and compression of the medium through which they pass.  Ultrasound waves have frequencies higher than the limit of the human hearing typically between 1 – 20 MHz (generally humans can hear between 20 Hz and 20 KHz).

Acoustic waves contain the following properties:

·        Frequency

·        Wavelength

·        Amplitude

·        Propagation Velocity

Ultrasound waves interact with organs and tissues in the human body with the following phenomenon (Figure 1):

·        Reflection

·        Scattering

·        Refraction

·        Attenuation

Figure 1: Ultrasound waves interaction with organs.

Ultrasound imaging contain the following modes:

·        Amplitude (A-mode) - For historical reference. Amplitudes over time were used to show structural shifts. However, A-mode is still in used for Eye ultrasound.

·        Motion (M-mode) - Reflects motion of the heart structures over time. Used for accurate evaluation of rapid movements.

·        Brightness (B-mode) - Most essential modality. Amplitude of reflected signal is converted into gray scale image.

·        Doppler (D-mode) - The Doppler effect describes a change in frequency of sound waves depending on the direction in which they’re travelling (and being recorded).

Doppler (D-mode) contains the following subsections:

·        Doppler Duplex - Based on the simultaneous B-Mode and Doppler imaging

·        Continuous-Wave Doppler (CWD) – Defines blood flow direction, very useful in high velocity signals recording.

·        Pulsed–Wave Doppler (PWD)- Provides both blood flow direction and precise determination of Doppler signal source.

·        Color Doppler – Based on the PWD. Velocities are displayed using color scale. Velocities toward the transducer are red, and velocities away from the transducer are blue.

Figure 2: M-mode, B-mode and D-mode shown.

Ultrasound Transducers construction vary based on the following:

·        Piezoelectric crystal arrangements

·        Aperture (footprint)

·        Operating frequency (related to the penetration depth)

The most popular types of Ultrasound Transducers are:

·        Sector transducer- mainly echocardiography, gynecological, upper body ultrasound

·        Linear transducer – mainly obstetric, breast, thyroid and vascular ultrasound

·        Convex transducer – mainly in all ultrasound types except echocardiography

Implementing multiple point of care ultrasound imaging devices (S-series, Edge II, M-Turbo and Logiq E) has the following advantages:

·        Portability

·        Affordability

·        Time Saving

·        Simplicity

Fusion Ultrasound has combined previously acquired CT, PET or MRI images with real time ultrasound.  However, it does require compatible hardware and software.  The advantages are:

•        More data helps users localize areas of interest.

•        Greater accuracy (either in needle navigation or in diagnostics).

•        Procedure time is reduced

•        Portable