ultra sound ppt and class notes for binani technology

Ppt on ultrasound

1. Ultra sound Imaging

2. Various sound waves: Audible  20Hz and 20 000Hz.  I nfra sound  Below 20Hz Ultrasound  Above 20 000Hz Ultrasound is a high frequency mechanical vibration waves above a frequency the human ear can hear.  Ultrasound uses a pulse-echo technique of imaging the body.  Pulses transmitted into patient and give rise to echoes when they encounter interfaces/reflectors.   These interfaces/reflectors are caused by variations in the  " acousitc impedence "  between different tissues. Echo signals are amplified electronically and displayed on a monitor using shades of grey (from black to white),  stronger reflectors = brighter shades of grey   and appear white in an image . Those with  no echoes will appear black , such as a full bladder.

3. Acoustic impedance interactions of ultrasound with tissue Acoustic Impedance (Z) is a measure of the resistance to the sound passing through a medium. Z = density x speed of sound. It is similar to electrical resistance. Materials with a higher density causes higher acoustic impedance, eg bone. Gases have low acoustic impedance. Impedance mis -match A difference in acoustic impedances cause some portion of the sound to be reflected at the interface. Whenever a sound wave encounters a material with a different density (acoustical impedance), part of the sound wave is reflected back to the probe and is detected as an echo. The greater the difference between acoustic impedance, the larger the echo will be. If the pulse hits gases or solids, the density difference is so great that most of the acoustic energy is reflected and it becomes impossible to see deeper. 

4. Properties of an ultrasound wave Frequency higher than 20 000Hz (20kHz) Propagation of sound waves longitudinal A medium is needed for sound waves to go through, no medium = no sound waves Interactions of ultrasound with soft tissues When an ultrasound wave passes through tissues the following things can occur Reflection Scattering Absorption Refraction:  Change in direction & velocity of wave

5. Working Principle of Ultrasound Imaging: Ultrasound waves are produced by a transducer, which can both emit ultrasound waves, as well as detect the ultrasound echoes reflected back. In most cases, the active elements in ultrasound transducers are made of special ceramic crystal materials called piezoelectrics . These materials are able to produce sound waves when an electric field is applied to them, but can also work in reverse, producing an electric field when a sound wave hits them. When used in an ultrasound scanner, the transducer sends out a beam of sound waves into the body. The sound waves are reflected back to the transducer by boundaries between tissues in the path of the beam (e.g. the boundary between fluid and soft tissue or tissue and bone). When these echoes hit the transducer, they generate electrical signals that are sent to the ultrasound scanner. Using the speed of sound and the time of each echo’s return, the scanner calculates the distance from the transducer to the tissue boundary. These distances are then used to generate two-dimensional images of tissues and organs.

6. Commercially available contrast media are gas-filled  microbubbles  that are administered intravenously to the  systemic circulation . Microbubbles have a high degree of  echogenicity  (the ability of an object to reflect ultrasound waves). There is a great difference in echogenicity between the gas in the microbubbles and the soft  tissue  surroundings of the body. Thus,  ultrasonic imaging  using microbubble contrast agents enhances the ultrasound  backscatter , (reflection) of the ultrasound waves, to produce a  sonogram  with increased contrast due to the high echogenicity difference. Targeting  ligands  that bind to  receptors  characteristic of  intravascular  diseases can be conjugated to  microbubbles , enabling the microbubble complex to accumulate selectively in areas of interest Microbubble contrast agents General features There are a variety of microbubble contrast agents. Microbubbles differ in their shell makeup, gas core makeup, and whether or not they are targeted. Microbubble shell : selection of shell material determines how easily the microbubble is taken up by the  immune system .  Microbubble gas core : The gas core is primary part of the ultrasound contrast microbubble that determines its echogenicity . 

7. Untargeted microbubbles are injected intravenously into the systemic circulation in a small bolus. The microbubbles will remain in the systemic circulation for a certain period of time. During that time, ultrasound waves are directed on the area of interest. When microbubbles in the blood flow past the imaging window, the microbubbles '  compressible  gas cores  oscillate  in response to the high frequency sonic energy field, as described in the  ultrasound  article. The microbubbles reflect a unique  echo  that stands in stark contrast to the surrounding tissue due to the orders of magnitude mismatch between microbubble and tissue echogenicity . The ultrasound system converts the strong echogenicity into a contrast-enhanced image of the area of interest. In this way, the bloodstream's echo is enhanced, thus allowing the clinician to distinguish  blood  from surrounding tissues. Source: https ://en.wikipedia.org/wiki/Contrast-enhanced_ultrasound