Color doppler imaging: principles, limitations, and artifacts

Article Abstract:

Color Doppler (CD) imaging is a diagnostic technique that uses ultrasound (US) to visualize or photograph internal organs and tissues. CD can also be used to measure blood flow, and this information may be considered when evaluating whether or not a patient has cardiovascular disease and determining the severity of the condition. The diagnostic use of CD in cardiac disease has not been well studied. A number of variables are involved in measuring blood flow through the coronary arteries (which supply the heart muscle); these variables must be understood and considered when evaluating the CD images. To encourage proper use of this technique, researchers examined variables involved in CD blood flow measurements. US can measure blood flow because its frequency changes when it is reflected from moving blood cells. These changes in frequency are affected by the angle at which US encounters blood flow. Two-dimensional Doppler images can be obtained by US sampling over several intervals. This is important in determining blood flow across vessels or through valves. Blood flow can appear as color-encoded images on a time scale; the different colors represent different rates or directions of flow. However, artifacts (due to the technique) can interfere with Doppler measurements. Sometimes, US is reflected back and results in the transmission of a mirror image. The angle of blood flow and spatial (location) measurements may be difficult to determine. Artifacts may be avoided by changing the angle of the US or by reducing power. In addition, how the image is processed can affect outcome. Choosing color versus gray scale can have important effects on the type of artifacts that are likely to result. Choice of transducer (which sends and receives sound wave signals) affects the sensitivity of the image. Variations in the CD imaging technique are required to get the best results. These variations are dependent on a number of factors such as blood flow rate, depth, location, and others. CD imaging can be a useful tool for examining blood flow in the heart. Knowing what information is being sought and understanding the variables and technical choices involved in this method will increase the accuracy and reliability of the CD images. (Consumer Summary produced by Reliance Medical Information, Inc.)

Cardiovascular diseases, Ultrasound imaging, Blood flow, Measurement, Blood flow measurement, Doppler echocardiography, editorial

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Hemolytic-uremic syndrome: intrarenal arterial Doppler patterns as a useful guide to therapy

Article Abstract:

Ultrasound (US) was used to examine 17 children suffering from acute renal (kidney) failure due to hemolytic-uremic syndrome (anemia, of unknown origin, resulting from destruction of red blood cells, accompanied by decreased urine output). Hemolytic-uremic syndrome is the most common cause of acute renal failure requiring kidney dialysis in children. These young patients commonly suffer from a bout of gastroenteritis (intestinal inflammation) followed by sudden pallor, irritability, and oliguria (reduced urine output) or anuria (lack of urine output). In all forms of the disease a lesion consisting of microscopic damage to a small blood vessel (microangiopathy) contributes to the lack of blood flow in the kidney and the subsequent interruption of urine output. Patients with oliguria or anuria and a normal ultrasound evaluation may not require dialysis since urine flow will usually resume following initiation of diuretic therapy (medication to increase urine excretion). US was used to evaluate renal arterial blood flow as a means of predicting blood flow within the kidney during the course of the hemolytic-uremic syndrome. This predictive value enabled clinicians to plan treatment for the children more appropriately and anticipate their recovery.

Care and treatment, Usage, Causes of, Complications and side effects, Pediatric diseases, Renal artery obstruction, Kidney diseases, Acute kidney failure, Doppler ultrasonography, Hemolytic-uremic syndrome, Urination disorders, Acute renal failure in children

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