Use of Ultrasound in Medicine
P.K. Ghatak, M.D.
Ultrasound is a portion of sound that is beyond human ears can hear. The human hearing range is 20 to 20,000 Hz, and the intensity 2 to 120 decibels (dB). A decibel named after Alexander Graham Bell, the telephone, telegram, and audiometer inverter.
Ultrasound is used in medicine in two separate fields.
Imaging.
Therapeutic.
The images are called Sonograms, and the process of generating the images is called Sonography or Ultrasound study.
There are many ways Ultrasound is utilized in the medical field. It will be discussed later in this article.
What is Sonogram:
The sound waves are generated by vibrating crystals. The desired diagnostic sound waves are directed to the organ or organs under examination. The sound waves after encountering a barrier reflect back some or nearly all sound waves back. These reflected waves are collected and a computer generates pictures in great detail.
The reflected sound waves are often called Echo and the images generated are called Echogram, for example, Echocardiogram. The Echo has a special quality, among the reflected sound waves, which must reach the human ears after some delays for it to be registered as a separate sound. This delay is called Impedance and the impedance is variable depending on the tissue, air and fluid; this characteristic allows sonography to construct an image.
Who introduced Sonography in medicine:
Dr. Karl Dusskil, a Neurologist used sound waves in 1942, in his attempts to locate brain tumors. He took this idea from studying a publication of an Italian scientist, Spallanzani who discovered bats use ultrasound to locate insects and this process is called Echolocation.
How it is possible to image brain matter which is encased in a cranium, made of bones.
It uses the same principle as is used in the Subtraction Angiography. If the parameters of ultrasound of the cranial bones are known then, they are subtracted from the final scan and the true image of the brain emerges.
The science behind the conversion of electricity to sound.
When asymmetrical crystals, eg, Quartz or Polycrystalline Ceramics are subjected to physical stress, they are polarized and generate electricity which is called Piezoelectric.
In a reversed situation, when these crystals are placed in an electric field, they begin to vibrate and generate sound waves. By varying the crystals, frequency and amplitude of the electrical field, the sound waves of various frequencies and variable strength can be generated.
Components of Ultrasound (US) instrument:
The basic components are ultrasound the Generator, also called the Transducer or Probe and the Receiver. The receiver is also incorporated into the transducer. The other parts are the monitor and controls. The transducer contains an assortment of crystals, and it comes in various shapes and sizes to fit the part of the body to be examined, eg, the neck is a small saddle-shaped gadget and a large gently curved transducer is used in the abdomen and pelvis examination.
In addition, there are specially designed probes for special locations to name a few - transthoracic esophageal ultrasound for examination of the left atrial chamber of the heart, and transrectal for examination of the prostate gland.
Ultrasound images:
US imaging is used for every organ system of the entire body, beginning from the time of conception to the last illness. US study is also useful for the evaluation of the functional status of an organ, detection of motion and direction of blood flow.
The special uses are called by different nomenclatures, eg, Echocardiogram, Doppler study of carotids or aortic valve, etc.
Advantages of Sonography:
1. The instrument is not expensive and the machine is portable.
2. There is no special reparation required for most studies and repeated examinations can be done to watch the progress of a disease or the state of recovery with treatment.
3. Patients are not exposed to radiation.
4. The technology is easy to teach and teaching facilities are locally available and not expensive.
5. The patient does not require to lie down for a US scan, in fact it is an advatade to scan when the patient is sitting or standing to detect small plural effusion or ascites, also, the venous obstructions in legs are better imaged is upright position.
Disadvantage:
1. Air does not produce echo and any structures next to a pocket of air in the body like the Pancreas and Lungs are difficult to visualize.
2. The image quality is very much dependent on the technical skill of the operator. It is like a good professional photographer setting up his camera for a portrait – the aperture, duration of exposure, power of the flash or lighting, etc. The image quality of US varies greatly on the frequency and strength of US generated by different probes, the depth and direction and the focal point; the angle the transducer makes with the body at the contact point. The direct end-on-view makes a clear image and increasing the angle makes the image fainter. The echo and artifacts can be manipulated to enhance the image brighter.
To minimize the adverse effect of the presence of air, in between the transducer and the skin of the patients, a water-based jelly is used. This jelly contains glycerin and propylene glycol in addition to water. It also provides a smooth surface for the probe to glide against the body and minimize patients's discomfort.
Types of Sonography.
A- Mode. A stands for Amplitude. A single pulse is transmitted through the body and the echo is collected and a linear image is produced. It is a one dimensional image.
B- Mode. B stands for Brightness. B-mode images are two dimensional, also called 2-D echo. The amplitude is in the X-axis, Y-axis is time. Using a proper probe and selecting the correct frequency of sound, depending on the depth of the organ located in the body, the technician should able to select echo of adequate amplitude to generate a good picture.
M-Mode. M is for Motion. Over a time period, successive B-mode echos are recorded and placed next to the previous one. Any moving part of an organ, eg, a beating heart, can be imaged like a moving picture taken by a camera put on sport mode.
3-D and 4-D Echo. The 3-D echogram is generated by taking the echo of the same organ or tissue from many angles and then stitching all of them together as one picture. It is like drawing a box on a flat sheet of paper, showing length, breadth and height. A 4-D echogram is a series of 3-D echograms over a time, depicting changes in volume or size over a specific time frame. The time is the 4th dimension.
Other echograms for special purposes.
Trans Thoracic Echocardiogram (TTE). A narrow probe is introduced through the mouth into the esophagus and positioned just behind the Left Atrium and various aspects of this chamber are examined. This is useful in atrial fibrillation, pulmonary embolism, infra-atrial shunt and heart failure.
Trans-rectal. This is a standard for evaluation of the size, volume and consistency of the prostate gland and is utilized in transrectal biopsy of the prostate gland.
Transvaginal and or, Pelvic ultrasound: This is a standard imaging technology for the evaluation of every aspect of pregnancy, size and shape and growth growth of the fetus, placental health, blood flow, status of amniotic fluid and ectopic pregnancy. In other situations, any pelvic mass, ovarian pathology and ascites can be imaged with clarity.
Doppler Ultrasound:
Vesto Melvin Slipher discovered when a planet was moving away from the Milky Way, the light waves emitted from the planet, were less frequent and appeared Red than when the planet was moving towards the telescope of the observatory and the light waves had higher frequencies and appeared Blue.
In an Ultrasound study, the same phenomenon is utilized to detect whether the blood is moving forward in the blood vessels or falling backward. The Red Blood Cells (RBC) scattered US waves when hit by the US and the receiver records reflected waves and plots the blood movement towards the probe or away from the probe.
The Doppler US is useful in evaluating Aortic stenosis, Aortic and Mitral valve incompetence, Deep vein thrombosis of thigh and pelvic veins, Inferior Vena cava obstruction, the patency of the bile duct and many other uses.
Echocardiography:
A Swedish cardiac surgeon, Dr. Inge Edler, was searching for ways to investigate the Mitral valve function before surgical repair of mitral stenosis, which was a common malady of that time. A scientist named Carl Hellmuth Hertz was using Refected Palatinoscope for testing metal properties. These two scientists teamed together and took a moving echocardiogram of the Mitral valve. They published their findings in 1953, the echocardiogram generated was a 2-D motion image, and with this, the Echocardiography was born. They were awarded the Lasker Prize in 1977 but many scientists lamented that they deserved the Nobel prize in medicine.
What echocardiogram is used for:
This is a versatile machine for evaluating both the structure and functions of the heart as a whole and of its parts. The wall motion abnormality, following a suspected coronary event, indicates possible MI. Excess blood left in ventricular chambers indicates poor contralie function of ventricluar muscles as happens in heart failure. The functional status of all cardiac valves, the size and shape of valves, and the prolapse of valves due to papillary muscle damage can be easily detected. Individual ventricular systolic output or ejection can be studied by moment by moment and used every day for follow-up care in coronary artery disease and following bypass surgery. Interested readers may read many excellent articles published by the American College of Cardiology.
Medical Uses of Ultrasounds.
The use of the US is very extensive in daily medical practice. It can be summarized as
Diagnostic
Therapeutic.
Combination of the two.
Many of the diagnostic uses are already mentioned, in short, any diagnosis requiring an image can be accomplished by the use of a US study.
Physiotherapy:
Spain ankles, frozen shoulders, tendinitis, and tennis elbow are treated with low frequency US to increase the blood flow. The same principle is utilized in poor healing of bone fractures.
Tissue Biopsy:
Skinny needle biopsy for any nodules or growth, whether in a deep organ like the kidney or near the shin surface like the thyroid gland and breast tumors, the intervention radiologist accurately maps the tumor and its location then under its guidance introduces the needle and performs biopsy.
Stent placement:
In cases of deepening jaundice due to bile duct obstruction from any cause, including hepatocellular carcinoma, to immediately relieve unremitting symptoms of patients, the doctor locates the intrahepatic dilated hepatic duct by using the US and then threads a probe into it then inserts a stent to drain bile in the duodenum. This kind of procedure is done for obstruction of Cerebrospinal fluid circulation after an attack of meningitis /encephalitis. Renal pelvic obstructions or ureteral obstruction either from tumors or stones. Aspiration of pleura fluid and drainage, pericardial effusion,etc.
Central venous access:
Instead of a blind procedure of placing a Central Venous Line, using the US to locate the subclavian vein or innominate vein is much safer and less likely to produce any complications. In “hard to find veins” US helps to find a vein in the forearm to start an IV line.
Intra-arterial injection of thrombolytic agents:
In cerebral embolism or thrombosis, a Doppler study of the diseased vessel is used and then under US guidance the vessel is catheterized and the thrombolytic agent is infused.
Transdermal administration of medication:
The US is used to improve the absorptive capacity of a patch of skin and then a patch incorporated with medication is applied over it.
US in Surgery:
US energy is used in the ablation of tissues is called High Intensity Focus Ultrasound (HIFU). The high energy sound heats up the target tissue and destroys it, eg, aberrant ectopic focus in atrial fibrillation, Uterine fibroid and Prostatic hypertrophy. Other examples are Tracheal, Laryngeal papillomas, nasal polyps, vocal cord growth, etc
Skin Incision by using the US. Just like a laser beam in making a skin incision, US energy is also used for the same purpose.
Cauterization of bleeding vessels. An easy way to control bleeding is by using US energy.
In Eye surgery:
Phocoemulsifier- In cataract surgery, a needle is inserted into the cataract and it vibrates at US speed and emulsifies the lens. Then the derbies are suctioned out, then an artificial lens is inserted.
In Kidney stone and Gall stones: Extracorporeal shock wave Lithriopsy.
The machine is called Lithotriptor and the process is Lithotriopsy. The body is immersed in water and shock waves are applied to the body to break up stones in smaller fragments and the gravels then pass out easily. The US waves are generated in several ways.
1. Electrohydraulic. The shock waves are created by making tiny sparks underwater between two metal points.
Electromagnetic. An electromagnatic coil generates shock waves.
Piezoelectric. Quartz or ceramic crystals generate the waves.
The other is light. Laser energy is directed toward the stones by breaking them up into small piec
During 1920 to 1940, European soccer teams used Ultrasound as a physiotherapy agent for the treatment of the injuries of their players. In 1958, the US was used in the OBGyn and soon became a standard technology used for various aspects of pregnancy, fetal development and ovarian pathology. The field became wide open with the introduction of Echocardiography and Doppler ultrasound.
Today, the US is the most versatile and often utilized technology in the medical field. Portable US instruments carried by the medical personnel on the nursing floors like a NoteBook and used for diagnostic purposes and also in the therapeutic armament, In a urologists office, the post voided residual urine is determined in patients having voiding problems, just before the urologist sees the patient. Many cardiologist carry similar portable machine, at the point of service, for the evaluation of the many aspects of cardiac functions of their patients, whereas, the stethoscope is progressively becoming a museum piece. In the near future, all medical offices will be using a miniature portable Ultrasound like nowadays the weatherman talks about the weather on TV carrying a small NoteBook in his hand.
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