Spectral Analysis

Spectral analysis

Separate individual velocities. Arranges flow velocities over time

Importance of Spectral Analysis

Important for diagnosing vascular stenosis

Technique used for spectral analysis?

Fast Fourier Transform.. separates doppler shift frequencies.

Spectral Anylisis is used by what dopplers?

Pulsed wave and color doppler

Spectral doppler display?

Velocities on verticle axis (y) and time on horizontal axis (x) as systole dystole

what is Laminar flow ?

Narrow spectral tracing with a clear spectral window where velocities are well-organized, indicative of a smooth flow.

What is a Spectral window ?

The black area under the spectral trace. Between the baseline and spetrum

What is turbulent flow?

Wide range of velocities and has spectral broadening. obileration of window.

Advantages of spectral analysis?

Selection of exact flow location to measure the velocities

What are disadvantages of spectral analysis?

Angle dependent and subject to aliasing

What is aliasing?

Aliasing is the misrepresentation of velocities due to undersampling the doppler shift

What does aliasing on a spectrum look like?

With higher velocities, it can be cut from the spectrum and be displayed on the other side of the baseline.

What is nyquist limit?

Upper limit of doppler shift that can be detected properly by pw (kind of like frequency)

What is nyquist limit equal to?

The Nyquist limit is equal to half of PRF which defines the maximum frequency that can be accurately sampled without aliasing.

What are two ways to correct aliasing?

1. Increase the nyquist limit (increase prf)

2. Decrease the doppler shift (Low frequency transducer, higher doppler angle)

3. use a continuous wave doppler

How do you increase PRF?

Increase the scale

What are two ways to decrease doppler shift

1. use a higher doppler angle

2. use a low frequency transducer

Spectrum in relation to the cardiac cycle include what ?

Systolic component and diastolic component

What makes up the systolic component?

1. In upstroke: sharp rise with high velocity in early systole

2. In peak systole: Highest velocity achieved by blood cells

3. In downstroke: Decrease in velocity

What does systolic component depend on?

myocardial Force of contraction

What does diastolic component depend on?

Peripheral resistance from the change in diameter of the arteriolies. (vasoconstriction and vasodiolation)

What are two diastolic components?

1. Early diastole

2. late diastole

What are three possibilities of early diastole ?

1. reverse flow

2. forward flow

3. no flow

What is a possibility of late diastole ?

No flow

What is low resistant wave form/ low pulstality characteristics?

broad systolic peak/ continuous forward flow in diastole with good velocity

What are characteristics of high pulsatatlity or high resistant wave form?

1. Systolic peak: pointed narrow peak

2. Early diastole: reverse flow

3. late diastole: foward flow

Typical High wave form is ______

Triphasic

What are moderate resistant waveform characteristics?

1. high systolic peak

2. normal continous flow. no reverse flow in early diastole

What is stenosis ?

Focal narrowing of a blood vessel due to atherosclerosis leading to reduction of vessel lumen

What is the prestetonic stenosis?

Proximal to stenosis (before)

What changes occur in proximal stenosis ?