LESSON 2 IMAGING METHODS OF ACOUSTIC FIELDS Currently, the system of ULTRASONIC imaging has the important technical tool for doctors. These systems are complementary to x-ray or nuclear device display. Using these techniques it is possible to see internal organs. Visualization is a very good diagnostic tool in modern medicine. .

MODES OF SONOGRAPHY A-mode: A-mode (amplitude mode) is the simplest type of ultrasound. A single transducer scans a line through the body with the echoes plotted on screen as a function of depth. Therapeutic ultrasound aimed at a specific tumor or calculus is also A-mode, to allow for pinpoint accurate focus of the destructive wave energy. B-mode or 2D mode: In B-mode (brightness mode) ultrasound, a linear array of transducers simultaneously scans a plane through the body that can be viewed as a two-dimensional image on screen. More commonly known as 2D mode now. C-mode: A C-mode image is formed in a plane normal to a B-mode image. A gate that selects data from a specific depth from an A-mode line is used; then the transducer is moved in the 2D plane to sample the entire region at this fixed depth. When the transducer traverses the area in a spiral, an area of 100 cm2 can be scanned in around 10 seconds.[14] M-mode: In M-mode (motion mode) ultrasound, pulses are emitted in quick succession – each time, either an A-mode or B-mode image is taken. Over time, this is analogous to recording a video in ultrasound. As the organ boundaries that produce reflections move relative to the probe, this can be used to determine the velocity of specific organ structures. Function of the echo-signal amplitude from distance is called the A-scan. M-mode is the display mode of the moving organs, such as fluctuations of the heart B-scan is a two-dimensional image of the scanned object in the plane of its cross section C-scan is a two-dimensional image of the object in a rectangular coordinate system A-mode: A-mode (amplitude mode) is the simplest type of ultrasound. A single transducer scans a line through the body with the echoes plotted on screen as a function of depth. Therapeutic ultrasound aimed at a specific tumor or calculus is also A-mode, to allow for pinpoint accurate focus of the destructive wave energy. B-mode or 2D mode: In B-mode (brightness mode) ultrasound, a linear array of transducers simultaneously scans a plane through the body that can be viewed as a two-dimensional image on screen. More commonly known as 2D mode now. C-mode: A C-mode image is formed in a plane normal to a B-mode image. A gate that selects data from a specific depth from an A-mode line is used; then the transducer is moved in the 2D plane to sample the entire region at this fixed depth. When the transducer traverses the area in a spiral, an area of 100 cm2 can be scanned in around 10 seconds.[14] M-mode: In M-mode (motion mode) ultrasound, pulses are emitted in quick succession – each time, either an A-mode or B-mode image is taken. Over time, this is analogous to recording a video in ultrasound. As the organ boundaries that produce reflections move relative to the probe, this can be used to determine the velocity of specific organ structures.

A-scan The most simple method of ULTRASONIC imaging is the a-scan. Function of the echo-signal amplitude from distance is called the A-scan In this image the distance between the sensor and different reflectors is the horizontal axis, the amplitude of the echo signal is the vertical axis. A typical sample image of the type As shown in figure. The ULTRASONIC pulse propagating in the object or body is reflected from different reflectors. It can be interface between media with different acoustic impedances (muscle, liver and others). Part of the ULTRASONIC wave energy go to through to interface between two media and continue to propagation in the second medium, and part of the energy of the elastic wave reflect from the interface. If the angle of incidence of ultrasonic waves at the interface of two media is equal to zero, then the reflected part of ultrasound wave energy return to the transducer and is displayed on the screen.

Kidney – почки Liver – печень Stomach – желудок Skin – кожа, adipose tissue, muscle at the bottom of this figure shows the internal organs and on top of this figure shows the a-scan At the interface of two media is formed by reflected signal

M-scan Development of A-mode is the display mode of the moving bodies. It is developed to study the heart and diagnose of heart valves. This mode is called M-mode (motion mode). This method is effective in diagnosis of various heart problems, which cause abnormal working of the heart valves. Using this method you can detect a tumor (опухоль) of the heart. Butб its location and size must be carried out others methods. In M-mode the amplitude of the signal modulates the brightness of the row. All rows retrieved horizontally, forming a characteristic M-echo, shown in figure

M-mode if the transducer is moved the patient's body and at the same time M-echo is displayed to the screen, it gets a dynamic picture, it is called of the "time-movement" (TM–move time). Such an echogram the same by the electrocardiograph.

B-scan there are a line, sector and arc scanning line scanning sector scanning A two-dimensional image is called b-scan. The image In the scan is created by moving the narrow acoustic beam in a given plane. The received echo signals are arranged on the screen of the display device so that there was conformity between the scan lines on the screen and the direction of propagation of the ultrasound in the object. If the transducer is moved in a straight line than it is a linear scan If the transducer is placed in one point on the object and and turn at an angle, it is a sector scan In this case the field of view increases with increasing depth. However, if you increase the angle, the distance between lines in the raster is reduced (the number of rows is constant). This type of scanning is especially helpful for viewing the object through a narrow opening, for example for observation of the heart through the chest. In arc scanning transducer moves along the arc of a circle, whereby the form image is the reverse of the form of an image in sector scan [20]. Where the field of vision as close to the transducer and decreases with depth of penetration. Arc scanning and its modification is most often used for manual scanning of the abdominal cavity, the surface of which is close to the arc of a circle. arc scanning

sector scanning A two-dimensional image is called b-scan. The image In the scan is created by moving the narrow acoustic beam in a given plane. The received echo signals are arranged on the screen of the display device so that there was conformity between the scan lines on the screen and the direction of propagation of the ultrasound in the object.

Electronic scanning There are two type system: linear step displacement of the beam phased array Total focusing method There are two types of visualization systems with electronic scanning: system of linear moving step of the beam (usually referred to simply as linear array) and a system of linear phased array. First system needs very many sensor into probe.

SYSTEM OF LINEAR MOVING STEP OF THE BEAM Only four sensors (from 1 to 4) emit elastic wave in one moment, after that first sensor is excluded and fifth sensor is included into group and next four sensors (from 2 to 5) emit elastic wave, so four sensors move along the liner array and the acoustic beam moves along a liner array, but the liner array is constant position. Thus, due to the use of a group of sensors increases the aperture and the sensitivity increases, in accordance with diffraction theory increases the resolution in the far field.

Directional diagram the far field is at a distance x X equals d squared over four lambda (wavelength). D is aperture size. When designing a system with a linear array number of elements to be included in the group are determined based on the requirements to the instrument resolution and the probing depth. All elements one group can be connected in parallel (that is, they must emit in the same phase). therefore, the electronic equipment is elementary. most of the devices with linear array not using electronic focusing of phase change, so the cross-resolution of such systems is usually lower than with a manual scanning, and longitudinal resolution (determined by the duration of the acoustic pulse) may be the same as that of the system with b-scan and manual scanning. As in mechanical systems, the frame rate, probing depth and number of raster lines – correlation parameters. Due to cross-resolution is low, so it does not require a many number of scan lines, so the frame rate can be high. Most of the devices with linear array have from 64 to 128 raster lines and the frame rate from 20 to 40 frames per second (fps). These devices have small weight and cost due to the simplicity of electronic circuits. devices with linear matrix used in obstetrics, particularly for detection of pregnancy and monitoring her progress

Devices with phased array focusing Every sensor of the array emit signal with the different phase, it is the beam deflect at an different angle and it is focused in different areas of the testing zone. In this devices result imaging has the sector scan, as shown in 8 slide. The instruments of this type are often used to visualize the heart. Phase change of the emitted elastic wave is produced by changing the time delay of the electric signal, which goes into the sensor. Time delay is produced two methods: the use a set of time-delay line with constant time-delay; The use time-delay line with electronic control. Changing the angle of the acoustic beam The combination of focus and change the angle of entry focusing

BLOCK DIAGRAM OF Device with time-delay From 1 prime to 5 prime are delay circuit (delay unit) From 1 to 5 are sensor of array (piezoelectric cell) 2a is width of sensor, L is length of sensor M is step of array First type device (the use a set of time-delay line with constant time-delay); Delay unit consists several time-delay line. Result time-delay is produced to connect one or two or three time-delay line. Time-delay line is Second type device (The use time-delay line with electronic control). Delay unit can modify time-delay the use control signal

Set time-delay circuits with constant time-delay

Delay unit with modify time-delay The digital delay line is a digital device designed to delay time a digital signal by a specified number of clocks, and it is shift register. The delay time in such devices is changed from the outside. The same shift register usually has several “outputs" that allows producing several different of the time delay Цифровая линия задержки представляет собой цифровое устройство, предназначенное для задержки цифровых сигналов во времени на заданное число тактов и по сути представляют из себя регистры сдвига. Время задержки в таких устройствах либо фиксированное, либо может настраиваться программным способом извне. Один и тот же регистр сдвига обычно имеет несколько «отводов», что позволяет получить несколько сигналов с разными длительностями задержки

Total focusing method ∑Aij α1 α2 α… αN Информационная матрица Aij 3 4 . . . A21 A22 A23 A24 First sensor (number 1) shoots elastic wave. From 1 to 4 element receive of the echo signals. After that this signals are converted to digital type. The data are saved in the first row of the data matrix A11 - A14. Then, the second sensor shoots elastic wave. From 1 to 4 element receive of the echo signals. After that this signals are converted to digital type. The data are saved in the second row of the data matrix A21-A24. And so on, until the last sensor shoots elastic wave and we have full data matrix. A31 A32 A33 A34 A41 A42 A43 A44

Total focusing method решетка Дефект 4 Дефект 1 Дефект 3 Дефект 2 11x11 1x1 12x12 13x13 14x14 9x9 15x15 8x8 3x3 2x2 5x5 6x6 7x7 16x16 10x10 4x4 решетка Дефект 1 Дефект 2 Дефект 3 Дефект 4 Дефект 5 Дефект 6 The next step is the statistical processing of the data. The tested area is divided into local areas with a predetermined pitch, and then, the total signal amplitude is determined for each of the local areas in accordance with Kirchhoff migration algorithm. The amplitude of the received signals is colour coded and displayed on the screen

Thank you