**Part 1**

**Basic Science** 

Joao L. A. Carvalho1 and Krishna S. Nayak2

**Spiral Fourier Velocity Encoded MRI** 

Aortic stenosis consists in a narrowing or incomplete opening of the aortic valve. This typically alters the blood flow, causing turbulent and/or complex flow jets. Such jets display peak velocities considerably higher than those of normal flow, and a much broader range of flow velocities. Another form of aortic valve disease is aortic insufficiency, or regurgitation. This condition occurs when the aortic valve fails to close completely. This is also known as "leaky valve", as flow jets in the reverse direction are observed when no flow should occur. The visualization and quantitation of cardiovascular blood flow is an important component of the assessment of aortic valve disease. For example, peak velocity measurements in flow jets are used to estimate pressure drop, which is an indicator of the hemodynamic load of a

**Rapid Quantitation of Aortic Valve Flow Using** 

The current non-invasive gold standard for flow quantitation is Doppler ultrasound. The ultrasound equipment is relatively inexpensive, small, and portable. Measurements are typically obtained in real-time, with excellent temporal resolution. The most popular

Evaluation by ultrasound is impossible when there is air, bone, or surgical scar in the ultrasound path. Examination by ultrasound in obese patients is difficult, as the overlying adipose tissue (fat) scatters the sound waves. Doppler flow measurements may be inaccurate when the ultrasound beam cannot be properly aligned with the vessel axis, requiring measured velocities to be "angle-corrected" by the operator. Peak-velocity overestimation on the order of 18–40% have been reported in the literature (Hoskins, 1996; Winkler & Wu, 1995), usually due to spectral broadening at large insonation angles, and to Doppler gain settings.

Magnetic resonance imaging (MRI) is potentially the most appropriate technique for addressing all aspects of cardiovascular disease examination, which includes assessing myocardial function and perfusion, as well as visualizing and measuring blood flow. MRI overcomes the acoustical window limitations of ultrasound, potentially allowing flow measurements to be obtained along any direction, and for any vessel in the cardiovascular

techniques for ultrasound flow assessment are color Doppler and spectral Doppler.

**1. Introduction**

stenosis (Tsai et al., 1999).

**1.1 Doppler ultrasound**

**1.2 Magnetic resonance imaging**

<sup>1</sup>*Universidade de Brasília*

<sup>1</sup>*Brazil* <sup>2</sup>*USA*

**1**

<sup>2</sup>*University of Southern California*
