Basics of Ultrasound Dr Mohan Kumar M S
Basics of Ultrasound Dr. Mohan Kumar M. S. (Ay. )
History The bat use Ultrasound for navigation
ULTRASOUND: BASIC DEFINITION Ultrasound is acoustic(sound) energy in the form of waves having a frequency above the human hearing range(i. e. 20 KHz) Ultrasound is a way of using sound waves to look inside the human body.
Pan-Scanner - The transducer rotated in a semicircular arc around the patient (1957)
Scan converter allowed for the first time to use the upcoming computer technology to improve US
Ultrasound Parts
The Ultrasound Machine A basic ultrasound machine has the following parts: 1. Transducer probe - probe that sends and receives the sound waves 2. Central processing unit (CPU) - computer that does all of the calculations and contains the electrical power supplies for itself and the transducer probe 3. Transducer pulse controls - changes the amplitude, frequency and duration of the pulses emitted from the transducer probe 4. Display - displays the image from the ultrasound data processed by the CPU 5. Keyboard/cursor - inputs data and takes measurements from the display 6. Disk storage device (hard, floppy, CD) - stores the acquired images 7. Printer - prints the image from the displayed data
ULTRASONOGRAPHY • Ultrasonography or diagnostic sonography is an ultrasound based diagnostic imaging technique used for visualizing internal body structures.
MAIN IMAGING MODES GREY SCALE IMAGING A-Mode B-Mode M-Mode DOPPLER IMAGING Continuous wave Doppler Power Doppler Color Doppler Duplex Doppler Pulsed wave Doppler
A MODE Simplest form of ultrasound imaging which is based on the pulse-echo principle. A scans can be used to measure distances. A scans only give one dimensional information Not so useful for imaging Used for echoencephalography and echoophthalmoscopy
B MODE B stands for Brightness B scans give two dimensional information about the crosssection. Generally used to measure cardiac chambers dimensions, assess valvular structure and function.
Development of the B-mode Ultrasound image quality
M MODE M stands for motion This represents movements of structures over time. M Mode is commonly used for measuring chamber dimensions. This is analogous to recording a video in ultrasound.
DOPPLER IMAGING It is a general term used to visualize velocities of moving tissues. Doppler ultrasound evaluates blood velocity as it flows through a blood vessel. Blood flow through the heart and large vessels has certain characteristics that can be measured using Doppler instruments.
BLOOD FLOW PATTERNS LAMINAR FLOW • Layers of flow (normal) • Slowest at vessel wall • Fastest within center of vessel TURBULENT FLOW • Obstructions disrupt laminar flow • Disordered directions of flow
TYPES OF DOPPLER ULTRASOUND 1. CONTINUOUS WAVE DOPPLER (CW) Uses different crystals to send and receive the signal One crystal constantly sends a sound wave of a single frequency, the other constantly receives the reflected signal
2. PULSED WAVE DOPPLER Produces short bursts/pulses of sound Uses the same crystals to send and receive the signal This follows the same pulse-echo technique used in 2 D image formation.
3. COLOR DOPPLER Utilizes pulse-echo Doppler flow principles to generate a color image. Image is superimposed on the 2 D image. The red and blue display provides information regarding DIRECTION and VELOCITY of flow. Used for general assessment of flow in the region of interest Gives only descriptive or semi quantitative information on blood flow.
4. POWER DOPPLER 5 times more sensitive in detecting blood flow than color doppler. It can get those images that are impossible with color doppler. Used to evaluate blood flow through vessels within solid organs.
APPLICATIONS Obstetrics and Gynecology 1. Measuring the size of the fetus 2. Determining the sex of the baby 3. Monitoring the baby for various procedures Cardiology 1. Seeing the inside of the heart to identify abnormal functions 2. Measuring blood flow through the heart and major bloo vessels Urology 1. Measuring blood flow through the kidney 2. Locating kidney stones 3. Detecting prostate cancer at early stage
RISKS The two major risks involved with Ultrasound are: Development of heat: Tissues or water absorb the ultrasound energy which increases their temperature locally. Formation of bubbles ( cavitation): When dissolved gases come out of solution due to local heat caused by Ultrasound.
BENEFITS Images muscle, soft tissues very well Renders “live images” where most desirable section is selected Shows structure of organs No long-term side-effects Widely available and comparatively flexible Highly portable Relatively inexpensive Spatial resolution is better in high frequency ultrasound scanners
LIMITATIONS Sonographic devices have trouble penetrating bone Sonography performs very poorly when there is a gas between the transducer and organ of interest Body habitus has large influence on image quality Method is operator-dependent No scout image as there is with CT and MRI
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