From Lantheus Medical Imaging.
Activated DEFINITY® Injectable Suspension is indicated for use in patients with suboptimal echocardiograms to opacify the left ventricular chamber and to improve the delineation of the left ventricular endocardial border. The perflutren lipid microspheres exhibit lower acoustic impedance than blood and enhance the intrinsic backscatter of blood.
Echocardiography with Definity produced more detailed images of the heart in difficult-to-image patients versus echocardiography alone, and images obtained with the contrast agent provided a more accurate assessment of segmental wall motion compared with unenhanced images.

See also Coherent Contrast Imaging.

In August 2001 DuPont Pharmaceuticals Company received FDA approval.

Densitometry in ultrasound refers to measurement of the gray level intensity of an image region. Ultrasound image gray levels usually have non-linear relationships to the echo amplitude that makes densitometry not suitable for evaluation of contrast images.

To calculate the echo position, a constant sound speed of 1538.5 m/sec is assumed. Tissue penetration is frequency depended, if the frequency increases, the imaging depth decreases. The range resolution defines the depth. Ultrasound propagating in tissue is attenuated due to scattering and absorption. The attenuation is proportional to depth and frequency and is typically in the range from 0.5 to 1 dB/(MHz cm).

See also Attenuation Coefficient, Proximity Sensor, and Echo Ranging.

A quantity (considering for attenuation) that is measured in water using standard methods and then multiplied by a derating factor. This calculates the attenuation of the ultrasound area of the tissue between the probe and a particular location in the body along the axis of the sound beam.
The 'Guidelines for the Safe Use of Diagnostic Ultrasound' of the Government of Canada recommend a derating factor of 0.3 dB/cm-MHz.

See also Attenuation Coefficient.

The diastole is the period of relaxation in the cardiac cycle which alternates with systole. During diastole, the ventricles fill and the aortic and pulmonary valves are closed. On a Doppler spectrum analysis, diastole can be identified as beginning at the dicrotic notch (a small abrupt upswing in the deceleration phase of systole) and ending with the systolic upstroke.

See also Echocardiography and Cardiac Ultrasound.