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Ultrasound vs X-ray | Difference between Ultrasound and X-ray

This page compares Ultrasound vs X-ray and mentions difference between Ultrasound and X-ray imaging based diagnosis techniques.

Introduction: Various diagnostic techniques are performed on the patients to identify root cause of illnesses. The common diagnostic techniques are ultrasound, X-ray, CT-scan and MRI (Magnetic Resonance Imaging).

Ultrasound uses frequencies above audible range. Ultrasound is non-invasive imaging technique used for internal structures or organs of the body. It provides valuable information of the body organs without performing any surgery or use of harmful radiations. X-rays penetrate opaque objects which provide images of inner structures. They are used for diagnosis and therapeutic medical purposes. CAT (Computerized axial tomography) combines X-ray imaging with computer techniques to provide more accurate information. MRI technique is based on nuclear properties of hydrogen atoms in the body. MRI images are more accurate for tumours, inflammatory, vascular abnormalities etc.

What is Ultrasound imaging ?

The ultrasound used in medical domain works on the same principle of SONAR used by bats and ships. Our audible frequency range is from 20 Hz to 20 KHz. Ultrasound waves use frequencies greater than 20 KHz. Diagnostic ultrasound waves use frequencies from 1 to 10 MHz. These waves travel in longitudinal directions. The propagation of ultrasonic waves depend upon elastic properties of the medium. The average speed of ultrasound waves is given by following equation.
c = (β/ρ)0/5
β = Modulus of elasticity
ρ = Density of medium

Ultrasound imaging system block diagram

As in SONAR, acoustic waves are transmitted in water. The reflected waves from the interface are received by the ultrasonic instrument. All tissues of our body are made of water except bones and lungs. In ultrasound imaging technique, sound waves are transmitted by ultrasonic equipment into the body. As shown, reflected waves are recorded and processed to construct real time visual images by the computer and are displayed on the monitor display.

The figure-1 depicts block diagram of ultrasound imaging system with its components. The returning echoes of sound waves reflect size and shape of the body organs. It also indicates whether the organ is solid or liquid or in between these.
Refer advantages and disadvantages of Ultrasound >>.

What is X-ray imaging ?

The X-ray radiation is electromagnetic radiation which can ionize matter through which it passes due to its high energy content. These ionization can cause damage to the DNA and body cells. Latest X-ray techniques are developed to minimize the effects of radiation dose. X-rays use waves with wavelength from 10 A and 8.01 A.

As X-ray radiation can penetrate the body, it allows non-invasive visualization of internal anatomy of human body. X-ray radiations are produced in a vaccum tube comprising of anode and cathode.

X-Ray Imaging System Block Diagram

The figure-2 depicts block diagram of X-ray imaging system with its components. As shown, X-ray imaging system include X-ray generator, X-ray detector and computer with display.
Refer advantages and disadvantages of X-Ray >>.

Difference between Ultrasound and X-rays

Following table compares ultrasound and x-rays with various parameters.

Parameters Ultrasound X-Rays
Waveform Longitudinal sound waves Electromagnetic (EM) waves
Medium for transmitting waves Required, elastic medium Not required
Waveform generation By stressing the medium By accelerating the electric charge
Velocity Depends on medium through which it propagates Constant
Similar waveforms Acoustic, seismic Radio, light

Difference between Ultrasound and X-ray diagnosis

Following table mentions difference between ultrasound and x-ray based diagnosis techniques.

Ultrasound diagnosis X-ray diagnosis
It is non-invasive and it has no long term side effects. It is non-invasive, but it has harmful effects as body is invaded by ionizing radiation.
It uses sonic energy. It requires medium for propagation. It uses EM energy. It does not require medium.
Imaging is obtained from echoes which are reflected beams from the targets. Imaging is obtained from the radiation which leaves the body.
Ultrasound can not penetrate bones. It images only muscles, soft tissues and bone surface. X-rays show up well the high density parts such as bones and air cavities.
It is used as real time imaging which is highly operator dependent. It is not a real time imaging.
It performs poorly when gas is present between transmitter and organ under imaging. It does not have such problem.
Depth penetration is limited. The quality of image decreases in obese patients. There is no such problem as imaging is achieved from radiation leaving from the body.
It is portable. It is not portable due to heavy weight of equipments.
Displacement of structure and valves as well as blood flow can be imaged. It is not possible.

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