Ultrasound and CT Scan (Computed Tomography) are two of the most widely used medical imaging techniques. The techniques use different principles to generate an image for diagnostic purposes.
edit How Ultrasounds and CT Scans Work
Different medical imaging principles are applied for ultrasounds and CT scans. As a result, the process of scanning is also different.
The basic principle behind a CT scan relies on the reconstruction of a three dimensional image of an organ, by a computer, after acquiring multiple X-ray images of it. These images are obtained by passing multiple beams of X-rays through the region of interest at different angles.
In an ultrasound, a sound wave is produced in short pulses at the desired frequency and focussed at the region of interest in the body. These sound waves are partially reflected back from the body, received by a transducer and sent to the ultrasonic scanner, where they are processed and transformed into a digital image. The formation of the image depends on the time and the strength of the echo, and is displayed on the computer screen for analysis.
edit CT Scan procedure
During a CT scan, the patient is moved along the scanning system. A source of X-rays and an X-ray detector also rotate in synchrony so that the X-rays that are passed through the region of interest can produce different slices in axial or helical mode, and captured for further computation. The multiple images are then computed to create a view of the organ. The prepared CT image can be immediately viewed on a television monitor or recorded for storage and analysis later.
edit Ultrasound Procedure
During a medical ultrasound, a probe is passed over the region of interest to send sound waves into the area. To minimize air bubbles between the probe and the skin, a jelly is applied to the region first. The patient is sometimes asked to change positions to get a better view of the target area. The images obtained measurements can be viewed or stored for use later.
edit Cost Comparison
CT Scan costs range from $1200 to $3200 - they are usually more expensive than ultrasonography The cost of ultrasound depends on the area examined and usually ranges form $100 to $1000. The cost might vary in different countries.
edit Applications of Ultrasound vs CT Scan
CT Scanning is useful for screening diseases such as colon cancer, detecting injuries and abnormalities in the head, chest, heart, abdomen and extremities. This technique is often combined with other techniques such as MRI, and ultrasonography.
Ultrasound applications are used for diagnostic applications such as visualizing muscles, tendons, internal organs, to determine its size, structures, any lesions or other abnormalities. Obstetric sonography is used to visualize fetuses during pregnancy. Other applications of ultrasound include removing kidney and gall stones, lipectomy and other applications.
edit Advantages and Risks
Due to the high contrast resolution of CT scanning, differences between the tissues are more apparent compared to other techniques. Further, imaging in CT scan removes the superimposition of structures other than the area of interest. The data from a single procedure can be viewed in different planes and thus increases diagnostic ability. This technique is also popular because it can be used to diagnose a number of conditions. This might eliminate the need for other diagnostic techniques such as colonoscopy.
CT scans are associated with the risk of causing cancers, such as lung cancer, colon cancer and leukemia This is mainly due to the use of X-rays. . There are other safety concerns associated with the use of contrast agents which are administered intravenously. However, these disadvantages can be reduced with the use of lower doses.
Ultrasound is less expensive and comparatively safer technique than CT scans. It has a variety of applications in the biomedical, industrial and other areas.
The advantages of ultrasonography far outweigh any risks associated with this technique. However, several studies have highlighted the harmful effects of ultrasound on pregnant mammals such as mice though this effect has not yet been shown in humans. Also, increased exposure to ultrasound waves leads to heating up of tissues, changes in pressure and other mechanical disturbances.
edit Preventative value
A U.S. government-financed study showed that annual CT scans of current and former heavy smokers reduce the risk that they will die from lung cancer by 20 percent.
edit Video explaining the Difference