Spectral Doppler refers to the combination of either continuous wave Doppler or pulsed Doppler with a spectral display. Spectral Doppler provides a quantitative analysis of the velocity and direction of blood flow.
The Fourier spectrum analyzer performs a fast Fourier transformation on the Doppler signal. The amplitudes of the resulting spectra are encoded as brightness. In the 2D spectral display, the frequency shift is depicted in the vertical and the time in the horizontal axis. The range of blood velocities in the volume produces a corresponding range of frequency shifts.

See also Acceleration Index and Triplex Exam.

Spectral analysis is the quantitative analysis method to display the distribution of frequencies. A difficult Doppler signal is separated into the frequency components so that the range of frequencies in a Doppler shifted signal can be analyzed. This allows measurement of blood flow velocity by positioning of a probing cursor in the artery (on the screen), and the signal representing blood flow velocity is generated. The peaks and ebbs create the spectrum, corresponding to systolic and diastolic blood flow. The signal is both visual and auditory.

The dimension of a spectral reflector is greater than the wavelength of the ultrasound beam. With specular echo reflection, the sound strikes the target at perpendicular incidence and the sound is reflected back towards the receiver. Specular reflections produce bright echoes.

Spectral broadening widens the bandwidth of the returning Doppler shifted signal due to its interaction with scatterers traveling at different velocities. This can be seen with turbulent or disturbed flow distal to an arterial stenosis.

Ultrasound machines, with their various components and types, have revolutionized the field of medical imaging. These devices enable healthcare professionals to visualize internal structures, assess conditions, and guide interventions with real-time imaging capabilities. Today, medical ultrasound systems are complex signal processing machines. Assessing the performance of an ultrasound system requires understanding the relationships between the characteristics of the system, such as the point spread function, temporal resolution, and the quality of images. Image quality aspects include the detail resolution, contrast resolution and penetration. Systems with microbubble scanner modification are particularly suitable for contrast enhanced ultrasound.


In summary, ultrasound machines have diverse performance levels and corresponding price ranges, catering to various medical imaging needs. From low-performance systems with basic imaging capabilities to high-performance and premium systems with advanced features, ultrasound technology continues to advance healthcare imaging capabilities.
See also Ultrasound Physics, Handheld Ultrasound, Environmental Protection, Equipment Preparation.