ULTRASOUND IMAGING*
INTRODUCTION:
Ultrasound Imaging is also known as “ultrasound scanning” or “sonography”. Ultrasound imaging is nothing but exposing a part of the body to a high frequency sound waves to produce pictures of inside of the body. This kind of imaging does not use any ionizing radiations like X-rays and so they can report about the structure and motion of internal organs and even the blood flow through the vessels while X-rays do not report about the motion of the organs or blood flow. This is considered as one of the major advantages of Ultrasound Imaging over the X-rays.
Ultrasound Imaging is a non-invasive method of diagnosing that is used by physicians all over the world.
THEORY AND INSTRUMENTATION:
Ultrasound Imaging involves the use of acoustical waves (sound waves) whose frequencies are greater than 20 kHz (20,000Hz). In medicine, generally ultrasound of 1 MHz frequency is used. It is used to determine the location of surfaces within the tissues by detecting the time interval between transmission of the ultrasound and its echoing from those surfaces. By measuring the time interval we can conclude the distance of the tissue from that of the transmitter.
DOPPLER ULTRASOUND:
This is the most important property of the ultrasound waves. If the structure on which the ultrasound is directed is stationary, then the frequency of the reflected ultrasound will be the same as that of the frequency of the transmitted wave. If the structure is under motion, then there will be a shift in the frequency (higher or lower) of the reflected wave depending on whether it is moving towards or away from the transducer that produces the ultrasound. This shift in the frequency of the ultrasound is known as the “Doppler Shift”. For example, if a wave of ultrasound impinges through a blood vessel, a little of the sound energy will be absorbed by the moving erythrocytes (RBCs) and so there will be a shift in the frequency of the ultrasound. Thus the cross-sectional area of the blood vessel, volume of the blood flow and the velocity of the blood cell can be found.
Doppler ultrasound is a special technique that gives us the information about the blood flow velocity as the blood moves through any blood vessel.
There are three types of Doppler Ultrasound. They are:
Colour Doppler
Power Doppler
Spectral Doppler
Colour Doppler:
This method uses computer to convert the Doppler measurements into an array of colours to visualize the speed and direction of blood flow through a blood vessel.
This is a picture of the colour Doppler of the umbilical cord.
Power Doppler:
Power Doppler is the newer technique to Colour Doppler. This method is more sensitive than Colour Doppler that it provides more clear information about the blood flow especially when the blood flow is very less or minimal. But this method is not useful for radiologists as it does not give any information about the direction of blood flow.This is the power Doppler image of the umbilical cord.
Spectral Doppler:
This method has a technique in which instead of displaying the blood flow or its direction visually, they are represented graphically interms of distance traveled per unit time.This is the image of a spectral Doppler.
COMMON APPLICATIONS OF ULTRASOUND IMAGING:
Ultrasound Imaging helps to diagnose the variety of conditions of the organ under examination and also help us to access the organ damage.
It helps the physician to figure out the presence of:
Pain
Swelling
Infection.
Ultrasound is the useful way in examining a number of internal organs or parts like:
Heart and the blood vessels, including the abdominal aorta and its major branches.
Kidney
IMAGE OF THE KIDNEY ULTRASOUND.§ Gall bladder
§ Spleen
§ Pancreas
§ Liver
§ Bladder
§ Uterus, ovaries, unborn foetus in pregnant patients
§ Eyes
§ Thyroid and parathyroid
§ Scrotum.
Ultrasound is also used in:1) Guiding the procedures in the needle biopsies where there is a need to take sample cells from the abdomen for testing.
2) Ultrasound guided breast biopsy where its takes the image of the breast that helps in biopsy for breast cancer.
Ultrasound also helps the physician to evaluate the conditions of:
1) Blockages in the blood vessels
2) Narrowing of the vessels
3) Tumors and congenital malformation.
With the volume of the speed and volume of the blood flow that is got from the Doppler ultrasound, a physician can determine whether the patient is eligible for angioplasty.
PREPARATION FOR ULTRASOUND IMAGING:
§ The patient should wear loose and comfortable clothing.
§ The clothing and jewellery in and around the area of examination should be removed.
§ For some scanning, the doctor may instruct the patient not to eat or drink for atleast 12 hours before the test.
§ In some other type of scanning, the doctor may advise the patient to drink a minimum of six glasses of water and also not to urinate so that the bladder may be full at the time of examination.
WORKING OF THIS PROCEDURE:
The principles of ultrasound imaging is similar to that of the principles in SONAR (Sound Navigation and Ranging), that is used by bats and also in ships. When a sound wave strikes an object, it bounces back producing echoes. These echoes determine the position of the object, its size, its shape and consistency.
In medicine, its is used to detect the change in position, appearance of organs, tissues and blood vessels and also used to report the abnormalities such as the presence of tumors.
The transducer when placed on the skin generates small waves of high frequency sound that are inaudible. When the sound waves bounce back they are recorded through a tiny microphone that indicates the change in sound’s pitch and direction. This change is instantly measured by a computer and can be given out as images that can be monitored.
LIMITATIONS OF ULTRASOUND IMAGING:
Ultrasound waves can be disrupted by air or gas, therefore it cannot be used to figure out bowels or organs obstructed by bowels. Therefore CT scans and MRI scans are used in such cases.
Ultrasounds have difficulty in penetrating through the bones. So only the outer surface of bones can be imaged. Therefore for visualizing the internal structure of the bones other imaging modalities or MRI are often used.
ULTRASOUND SOUND IMAGE OF THE HAND BONE.
Large patients are difficult to be examined because their tissues attenuate (weaken) the sound waves as they pass deeper into the body.BENEFITS OF ULTRASOUND IMAGING:
§ This is a non invasive method of examining the interior of the body without any harm or side effects.
§ Ultrasound imaging is easy to use and less expensive method of diagnosis.
§ It causes no health problems and so can be used as often as necessary.
§ This method uses no ionizing radiations.
§ It is the most preferred imaging modality that is used on pregnant patients and unborn babies. And also for standard ultrasound there are no harmful effects on humans.
CONCLUSION:
Ultrasound imaging is one of the most useful, minimally or non-invasive method of diagnosing and treating most of the health problems. Thus ultrasound imaging is the most effective method prescribed my most of the physicians all over the world.
