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Over the past 40 years, ultrasound has become an important diagnostic modality. Its potential as a leader in the medical diagnostics was recognized in the 1930's and 1940's, when Theodore Dussik and his brother Frederick tried to use ultrasound to diagnose a brain tumor. However, only in the 1970's, the results of work of these and other pioneers of ultrasound study was really recognized.
Along with technological improvements, ultrasound modality has progressed from the big machines, reproducing the non-optimal images to a portable, easy to use and complex instrument. This evolution was due to technological progress and new inventions in physics, physiology, medicine, engineering.
This research covers the main achievements in the evolution of ultrasound, and covers some of the outstanding contributions made in the use of ultrasound modality.
DISCOVERIES and THE EVOLUTION OF ULTRASOUND
Long before modern scientists examined the importance of ultrasound in medicine, a step towards this was a study of sound. In 1880, Pierre and Jacques Curie made an important discovery, which ultimately led to the development of modern ultrasound transducer. Brothers Curie noticed that when putting pressure on quartz crystals, or Rochelle salt, electrical charge can be generated. This charge was directly proportional to the force applied to the crystal, this phenomenon has been called "piezoelectricity". In addition, they demonstrated the inverse piezoelectric effect, which occurred when rapidly changing the electrical potential was applied to the crystal, making it vibrate. Current transducers contain piezoelectric crystals that expand and contract, to convert the electrical and mechanical energy, which is the essence of the ultrasonic transducer. Unfortunately, due to weak development of electronics at that time, these effects were not fully developed and used.
During the First World War, the French explorer Paul Langevin proposed to use the piezoelectric effect to detect submarines. If the piezoelectric encounters in its path ultrasonic wave from a boat propeller, which propagates with speed 1460 km / s, it squeezes it that leads to electric charges. Opening and closing, the crystal generates an alternating electric current, which can be measured by sensitive instruments.
Ultrasound proved to be a godsend for the solution of technical, scientific and medical challenges.
The most important time for the ultrasound development were 1950-s , as lot of advances in ultrasound technology were made during that decade, and that have found new applications in the 1960's and 1970's. In 1955 Yaffe discovered the piezoelectric properties of polarized solid solutions of lead zirconate, titanate. This important discovery eventually led to improvements of ultrasonic sensors. Turner from London, Leksell from Sweden, and Kasner from Germany used these advanced devices to perform encephalography median line for the detection of epidural hematomas in patients with traumatic brain injuries. Encephalography median line has remained the standard diagnostic technique for examination of patients with traumatic brain injury before the 1970's, when CT was introduced (computed tomography).
In the 1960's, the use of ultrasound technology was limited because of slow and tedious collection and study of images and resolution of the images. Despite these difficulties, ultrasound has earned the respect of the medical community and rapidly became a routine method of display. Over the next two decades, advances in ultrasound technology were continued, and its use in many medical specialties has become a standard.
Early display systems consisted of conventional cathode-ray oscilloscopes, which were exposed to photographic shutters open to capture the image on the screen. Significant turning point in the development of ultrasound was revolving sonographic image, or operational mapping. This technique allows the selection of scanning and displaying images so quickly that its formation and displaying seem to appear simultaneously. Operative mapping was initiated in the mid 1950-s by J.J. Wild, but this breakthrough was ignored for more than ten years due to improved image produced by ultrasonic machine of Howry. First commercially available ultrasound machine was operating machine "Vidoson" (Siemens Mecical Systems, Iselin, NJ). This machine had a rotating sensor in a water tank and first used by Hoffman in 1966 and Hollander in 1968 in order to outline the structure of the renal pelvis in women. "Vidoson" produces 15 images per second, creating a relatively flicker-free cinematic image of the displayed body. With operational imaging, the specialist examiner could receive immediate feedback, which was an important mean of creating an ultrasound image, which was not so dependent on the operator.
Development of ultrasound modality in medicine
Nearly half a century ago an ultrasound was first used in veterinary medicine to determine the thickness of subcutaneous fat in pigs. This prosaic method prompted researchers to develop new transmitters and receivers of ultrasound and gave an opportunity to "consider" the internal organs. It's much simpler procedure than surgery, in addition, it provided an opportunity to see the body of a man at work. It was possible to even study the movement of blood in the vessels, to determine the state of bone tissue, and even the interior walls of the heart - so that loss of the mitral valve of the heart was first detected by ultrasound. In 1958, one of the specialized medical English-language journal published an article of Scottish scientists Brown and Donald McVicar, that discussed the prospects of ultrasound in medicine. It is considered that from that moment began the development of ultrasound era in medicine.
Currently, ultrasound modality is widely used and it is difficult to imagine modern medicine without ultrasound, in almost every hospital there is any ultrasonic device (ultrasound scanner). Ultrasonography is widely used in medical practice for the diagnosis of various diseases. Ultrasound is acoustic oscillations with a frequency higher than the human ear can perceive (above 20 kHz), but in medicine ultrasound equipment is generally used in the frequency range of 10.02 MHz. Basically, for the recognition of pathological changes in organs and tissues are used ultrasound frequencies from 500 kHz to 15 MHz. Sound waves of this frequency have the ability to pass through body tissues, reflecting from all surfaces that lie at the interface of tissues of different composition and density.
The principle of ultrasound is based on the fact that different tissues of the body in different ways to drop / reflect ultrasonic waves. Important part of every ultrasound machine is the sensor, which is both the emitter and the ultrasonic receiver, and the reflected signal. Produces by a sensor signal is displayed on the device as an image of the investigated organ.
On the physical there are two types of ultrasound: ultrasound location and ultrasound scanning. When ultrasound location, the ultrasonic pulses are reflected from the materials with different acoustic properties. Displacement sensor can detect the size, shape and location of the object. Ultrasound scanning is based on the different absorption properties of ultrasound in different tissues of the body. In the study of the internal organs an ultrasonic wave of a certain intensity is send, and specialists scan the intensity of the transmitted signal from a sensor located on the opposite side of the body. By the degree of intensity change is reproduced the picture of the internal structure of the scanned body. The received signal is processed by an electronic device, and the result is given in the form of the curve (echogram) or two-dimensional images (called a sonogram - ultrasonic scanning image).
Modern equipment allows to produce an ultrasound scan with a large number of frames per 1 second, which provides direct observation of the movements of organs (a study in real time). From such scans can be judged the location, shape and size of the examined organ, the homogeneity or heterogeneity of its tissues.
In recent years especially popular is Doppler method, based on the use of both continuous and pulsed ultrasound. It allows to record changes in blood flow even in small blood vessels, so Doppler is used in obstetrics - it can help assess the flow of blood through the umbilical cord, heart and blood vessels of the child. This approach proved to be valuable for cancer - after developing a tumor "cluttered" with blood vessels, within it there are small haemorrhages, formed areas of dead tissue. All this causes changes in blood flow in the vessels and can be easily detected by Doppler method. (Takeda)
Modern ultrasonic device (ultrasound scanner) can provide virtually complete information about the object of study, and studies with the use of ultrasound scanner do not cause pain and, importantly, pose absolutely no threat to the patient's life.
With the help of ultrasound apparatus it became easier to make more accurate diagnosis of many diseases at an early stage of development that had previously been diagnosed with difficulty. Ultrasensitive sensors detect ultrasound hypertension, migraine, cerebrovascular accident (which helps prevent stroke). Ultrasound machine also will help the doctor diagnose the lesion as the venous system, ischemic arterial disease, prostatitis, erectile potency disorders and more. In a study renal ultrasound machine allows you to identify at an early stage of renal cysts or hydronephrosis.
The most famous area of ultrasound is an examination of women during pregnancy. With ultrasound you can install the pregnancy from the first days of menstruation, to control the process of fetal development, its position in the womb, to reveal the many evils of child development. With ultrasound technology it has become possible to see what happens inside the bone. The speed of ultrasound propagation in bone provides information about their structure, content of organic and mineral substances. Any pathological changes, aging, tumor development are reflected immediately on the acoustic properties of bone. For example, when there is a tumor inside the bone, the ultrasound velocity is increased by 9 - 10%. Effectiveness of treatment of such tumors using hormones, chemotherapy or radiation may be in parallel with control with ultrasonic methods. (Takeda)
Often, the methods of ultrasonic diagnosis are used to examine the abdominal organs (liver, gallbladder, pancreas, spleen), genitourinary system (kidney, bladder, adrenal gland, uterus, ovaries, prostate), thyroid, hips, breasts.
Ultrasonic methods have been useful for the analysis of human blood. The fact that the membranes of red blood cells are becoming more "fragile" in various diseases, infections, alcohol intake and this has long been used in medicine. Before blood was mixed in a test tube with an anticoagulant, intensively shaking and from disintegrating cells freeds hemoglobin, which is dyed blood plasma, usually colorless, red. According to the intensity of this color you can judge the speed and extent of the destruction of red blood cells.
Shung (2006) informs that it is much easier to destroy red blood cells of low-intensity with ultrasound - the result is a so-called erythrograms. This method gives more accurate information about the strength of the membranes. In combination with the computer analysis, it helps not only improve diagnosis of blood diseases such as leukemia, but also to judge the other pathologies that do not have a clear clinical picture. For example, it is really difficult to find the early stages of cirrhosis of the liver, but the toxic products, that appear in the blood due to malfunctioning of the liver, destroy the red blood cell membranes, and erythrograms changes dramatically. And for example in cancer patients the strength of the membrane of red blood cells, by contrast, is greatly increased.
Hoskins (2003) points that modern ultrasound equipment allows to use one ultrasonic scanner in virtually all areas of medicine. The ultrasonic device is equipped with a sensor that is best suited for this type of research. Ultrasonic sensors can be convex, micro, line, pie, Doppler and other sensors of different types are used in research and diagnosis of different types of diseases. Ultrasonic sensors are electronic and mechanical. Mechanical sensors scan, based on the motion transmitter (the rotation or rolling), which is equipped with an ultrasonic device. In connection with the shortcomings of the mechanical method, the mechanical sensors now no ultrasound scanner does not use, they are considered obsolete. Electronic ultrasonic sensors produce scan, which then ultrasound device "decodes" electronically.
It is important to mention that virtually every modern ultrasound machine has not only change the ultrasonic sensors, but also equipped with a computer, which helps medical staff in diagnosis and research. Powerful microprocessors, which is equipped with an ultrasonic device, process the data and display the end user a "picture" that is adapted to the human eye.
Also Hoskins (2003) informs that there are ultrasonic sensors that are designed to be put directly into the body. For example, using a probe introduced through the rectum, it is possible to detect colon cancer and even its size. Also there are special ultrasound sensors created for being used directly in the operating table during surgery, allowing to determine the number and location of stones in the kidney and bile ducts. In clinical practice is sometimes used the method of puncture of internal organs and pathological formations (tumors, abscesses, etc.) under the control of an ultrasound scan.
Though it is important to remember that with ultrasound modality it is impossible to examine hollow organs (lungs, trachea, intestine, stomach, esophagus) as ultrasound has almost no effect. Also is impossible to use it to examine "a bone", so, for example, an ultrasound of the brain is only possible in young children, through the open fontanel.
Ultrasound examination does not always allow to make an accurate diagnosis. For example, one only ultrasound can not determine the nature of the tumor (benign or malignant). Even if you use the most modern equipment, sometimes it is impossible to interpret the study results due to excess gas in the gastrointestinal tract or because of the high degree of obesity of the patient. That limitations nevertheless lead to development and improvement of ultrasound modality, which are discussed in the next section
Main trends in the development of ultrasound diagnostic modalities
Modern ultrasound diagnosis is based on two pillars: the methods of obtaining two-dimensional images and Doppler modes. In a relatively short time (about 40 years) it passed a huge technological and methodical way. Major high-tech instrumentation companies of East and West have included ultrasound diagnostic devices into the nomenclature of its products, and invest many tens of billions of dollars for their improvements and development.
Currently, ultrasound diagnostic equipment, according to experts, occupies 25% of the global market of medical technology. (Cheeke 2000)
The development of ultrasound methods can not be separated from the major medical problems - the causes of diseases, their early diagnosis and objective treatment efficacy. Achievement of substantial progress in ultrasound images requires significant increase in volume and accuracy of the information that it contains. That is an increase in volume and accuracy of diagnostic information on the ultrasound image that serves as the main goal of modern technology. Currently, new approaches to obtaining and analyzing information can be divided into relating to the visualization in two-mode investigation and relating to Doppler mode investigation.
In the early 90-ies of XX century. to improve the visualization of internal organs has been proposed a method based on the analysis of harmonics. At the basis of harmonic images lies the effect of nonlinear interaction of ultrasonic waves with the body. Earlier in the construction of B-pictures the nonlinear signals from tissue were not used, being cut off by filter, and the new technology of the second harmonic (or native tissue) use them in constructing an image. That is why the image will contain more information that can improve the image readability. (Applied radiology 1999)
What are the advantages of harmonic B-picture? The classical image always contains a large number of artifacts, but harmonic signal overcomes a way only from the depth of tissue where it actually came to the sensor and construct a harmonious image, without most of the artifacts of the ray path from the sensor to the object. This is especially evident when an image is based solely on the basis of the second harmonic signal, without using the fundamental harmonic. This second harmonic is particularly useful in studying of "difficult to study" patients.
Thus, these harmonics can increase the resolution of the ultrasound system, reduce the artifacts and loss of information due to the depth of the research object in the body, improve contrast resolution and to minimize reverberation. Thereby it increases the quality of diagnosis and reduces the costs of the ultrasound images as a whole.
In determining the performance of ultrasound imaging devices, sensors occupy a fundamental position. Man of the most significant achievements in improving image quality were the result of the growth of clinical opportunities associated with innovation in the development of sensors. Operating frequency range of modern sensors are within 3. 3-15 MHz, and allows to study virtually all internal organs, and superficial anatomical structures and tissues with a resolution of up to 500 microns. But nowadays are being developed laboratory tests for two-dimensional imaging sensors with frequencies of 30-50 MHz. These technologies called "ultrasound biomicroscopy" have not yet found wide application, but it is evident that recently they will help to more closely examine epithelial and endothelial tissues, as well as to investigate clusters of cells.
Three-dimensional ultrasound - a new era in ultrasound modalities
Currently ultrasound method is at the beginning of a large technological leap into a new dimension through the improvement that could change in diagnostic ultrasound as we know it. Three-dimensional ultrasound can provide the clinician of anatomical images that are simply not available with conventional two-dimensional study. Advantage for health systems, physicians and technologists is the possibility to transfer three-dimensional data on a network for consultation and interpretation of data anywhere. (Szabo 2004)
In the traditional two-dimensional ultrasound scanning transducer transmits short packets or pulses of sound waves into the body of the patient and records the reflected signals. The received information is processed and displayed on a monitor screen in the form of pixels or dots of varying degrees of brightness. The same principles are used in three-dimensional ultrasound technology. Three-dimensional technique includes the following components: data scanning - multi-processing - image.
The great future of such programs is beyond doubt, since such technical achievement make the work of diagnosticians easier and graphically represent anatomical features and pathological changes in the organism. Creation of "intelligent" ultrafast electronic sensor, apparently, is one of the most important aspects of a new generation of 3D technology. Apparently, the ideal solution can be 2D matrix transducer with thousands of piezoelectric crystals with electronic control and focus of the acoustic beam.
3D technology is used primarily in gynecology and pediatrics: it allows to improve the examination of children with high risk for some anomalies, to confirm the normal development of the fetal spine. This method can also be used for more detailed study of placenta.
Three-dimensional ultrasound will reduce time of patient scanning, improve documentation of anatomy and allow the doctor to play it again and to evaluate patient data without having to re-survey.
Scanning procedure is similar to the usual research - a doctor or a specialist uses ultrasound device that works in real time for studying the anatomical features of the patient. When the certain area of interest is visualized, the researcher keeps the sensors still and simply selects the bulk of research from the menu. Internal mechanism of the sensor slips inside, moving along the study area, giving information about the internal organs, while the sensor itself remains stationary.
Ultrasonografist can spend a few seconds on a scanning operation, getting a three-dimensional information, and immediately after the scan, information is displayed on the monitor screen in multi-image form. Multiplanar reconstruction at the same time gives the image in three orthogonal planes, allowing to see the transverse, longitudinal and horizontal sections together. (Szabo 2004)
Three-dimensional image has many advantages:
- Firstly, this is the exact anatomical relationship between the structures.
- Secondly, the ability to visualize structures in the horizontal plane, which can not be achieved with conventional two-dimensional ultrasound systems.
- Third, it allows the physician to move in any plane within the volume that was scanned by simply turning the drive on the remote. Each slice can be rotated on axes x, y and z in order to achieve the perfect image.
After a three-dimensional scanning was carried out in the region of interest, the user has the option to convert the obtained three-dimensional data into three-dimensional image, and the user can rotate the image for better visualization. Usually the doctor, using a two-dimensional ultrasound can only see stark photographic imagery. If the images were performed on the wrong plane or not at optimal projection, the doctor will be difficult to diagnose. This required further investigation, significant inconvenience for the patient, a specialist in ultrasound diagnosis and a doctor, but also reduced the income of health institutions. With the constraints of the health care system, three-dimensional ultrasound will show itself as a cost-effective imaging technique that allows to save time and money.
Three-dimensional ultrasonography has particular value as a tool for solving problems of visualization in gynecology. It involves scanning of three-dimensional ultrasound data that is stored in computer memory, a floppy disk or hard drive. These data can be considered in different ways, and any arbitrary portion may be visualized independently of the other anatomical structures. With the help of three-dimensional ultrasound it is possible to get images that can not be get in the usual two-dimensional method for anatomical restrictions. For example, a coronal image of the uterus is rarely obtained during the two-dimensional scanning, but is the usual image in three-dimensional technology, that is why this method is optimal for visualizing abnormalities of the uterus and determining the state of its appendages (tube or ovary).
Volumetric data can be displayed on the multi-display where simultaneously three orthogonal planes are displayed. They can be rotated in any direction, in order to explore any number of sections. This allows to "cut", for example, the uterus on the set of planes to examine the various projections - so, it is possible to thoroughly investigate the outer contour of the body of the uterus, to distinguish between bicornuate uterus (which has a fundal furrow) and the uterus wall (which has not).
Also can be obtained by three-dimensional image, changing various parameters, the image can be optimized for specific tasks. For example, three-dimensional image can show the details of the bone or painting surface, etc.
Only few decades have passed since the first attempts to obtain information about internal organs using ultrasound. In comparison with radiology it is a little time, but ultrasound technology has developed rapidly. Going from "zigzag images" (in the A-scan mode) through the era of large, sophisticated scanners (scan B-mode) to a compact model that works in real-time diagnostic ultrasound is becoming more widely used.
Given the importance of ultrasound modality in medicine, it is rapidly becoming the method of choice in diagnostics. Ultrasonography have gained much popularity due to its non-invasive metod, has undergone tremendous technological development: scanning in real time, Doppler and color Doppler method have now become the standard types of medical research.
All the said above shows that modern ultrasound equipment allows to expand the boundaries of knowledge about the human organism: with it became possible to get the contrast and three-dimensional images of cells and thin tissue sections. Since there is a special acoustic microscope, which uses ultrasonic waves of high frequency, it can capture the most subtle change in the "architecture" of cells and provide information about events inside the body. Ultrasonic diagnosis is used in many fields of medicine. Ultrasound technologies are used in cardiology, gynecology, and ophthalmology. Ultrasound scanner is also an indispensable assistant in oncology, urology, trauma wards of hospitals. It is impossible to overestimate the role played by the ultrasound scanner in the diagnosis of pregnancy.
One of the technical achievement that opens new perspectives and opportunities in ultrasound diagnosis is a three-dimensional image (3D). Originally it appeared in 3D computed tomography, as computing power enables to measure parallel slices in a single volume unit, and now it has become an integral part of not only scientific research, but also practical diagnosis.
Thus, a review of the history of the development of ultrasound technology and its applications in medicine, showed the serious progress and importance of ultrasonic modality for modern science. For decades after the invention of ultrasound and ultrasound imaging, it has been constantly evolving and improving. These improvements could make the resulting image more clearly, allowed to start and successfully hold new studies of the human body.
In conclusion we can say that the development and improvement of ultrasound technology and modality is an important scientific achievement for medicine, and that in future scientists undoubtedly will achieve new results and progress in this area.