ULTRASOUND : Color and Doppler Imaging in Ultrasound

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                                    Ultrasound uses no ionizing radiation, and it can image directly in any body plane practice, an ultrasonographer (either an ultrasound technologist called a sonographer or a physician) places on the patient's skin and moves a transducer across the of the patient's body. 

The gel forms an acoustic seal between the transducer and the skin for better transmission of sound, which results in better The transducer can both send out and receive high-frequency sound waves, which transmit through, or reflect off, structures in the body .

The returning sound waves are categorized by their intensity (referred to as echogenicity) and duration of time that it takes for them to return. It is the time that it takes for the echo to return from its encounter with an acoustic interface (a structure within the body which reflects sound) that allows its location within the image to be assigned. 

The intensity of the returning echo (echogenicity) of tissues varies greatly Some tissues, like abdominal fat, are higher in echogenicity than other soft On the ultrasound image, such structures will appear whiter and are described as being increased in echotexture or that return echoes of lower intensity displayed as darker on ultrasound images and are described as decreased in echotexture or By evaluating the echotexture of tissues, we can distinguish one organ from another and look for pathologic processes.

 Fluid-filled structures (such as the gallbladder or urinary bladder) have few or no internal acoustic interfaces and hence appear clear black or sonolucent on . Sound waves traveling through the fluid-filled cyst lose less energy (since they encounter fewer acoustic For this reason, they can pass through with more intensity when they reach the far wall of the cyst. This phenomenon is referred to as "acoustic (arrows)

Some structures that are very dense, such as calcified structures or bone, will prevent sound waves from passing beyond As a result, there is no imaging information that can be obtained deep to those structures. A dark band-like is produced beyond the echo dense This dark shadow can be quite prominent, helping identify even very small calcifications, such as kidney stones Orientation of the plane of section on an ultrasound image is indicated by the sonographer, who annotates the plane of section on images, either with text or with an indicator image.

Scans are normally viewed in real This means that structures can be seen to move in the image cardiac valves) and structures can pass into and out of the field of view. The images that the ultrasonographer records are only selected frozen images from an extensive examination In some situations, it may be advantageous to record the examination in real known as a video or cine clip

Ultrasound weakens or attenuates rapidly by the inverse square law with distance from the transducer, therefore, structures closer to the transducer are better Many transducers have been adapted to get them close to the imaged structures.

Color and Power Doppler Imaging in Ultrasound 

When an ultrasound beam encounters a moving structure a change in the pitch or frequency of the returning echo, compared to the echo sent out by the transducer, occurs This is called the Doppler shift and it is encountered in real life when you hear a siren from a police car as it drives past you the pitch or frequency of the sound you hear changes as the vehicle passes By using information generated by this Doppler shift images can be generated, giving information about the speed and direction of the moving structure. 

This is most commonly used in evaluating blood vessels and blood flow, In conventional color Doppler, the displayed color identifies the direction of now as well as the speed of flow. Power Doppler, which measures the concentration of moving structures is more sensitive to low-flow states, but does not allow an evaluation of direction or speed Calculating the velocity of moving red blood cells numerically can allow an estimation of the diameter of the vessel in which the cells are flowing. 

This is the basis of arterial spectral (duplex) assessment of vessels such as the carotids A spectral Doppler study will display grayscale images, color images, and waveform images of the vessel being evaluated. As the vessel lumen narrows, generally the velocity of red cells moving through it increases. By using multiple calculations along the path of the vessel, multiple velocity measurements and ratios of velocities can be calculated, allowing one to diagnose, quantify, and monitor focal areas of vascular narrowing.

Color power Doppler and spectral imaging are used to assess for possible clot in veins, to evaluate areas of arterial narrowing/stenosis, and to determine if masses and organs have increased blood flow. You might see increased blood flow in a malignant tumor or reduced blood flow in a torsed testicle or ovary Doppler imaging is also used to diagnose vascular malformations and assess for the presence of varicose veins.