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Alara Principle

The prudent use of ultrasound requires a constant consideration of the risk-benefit ratio for the patient and the conditions of its use along with the employment of the so called alara principle. Alara stands for as low as reasonably achievable—ú. This means that the sonographer only as much ultrasonic power for as long as needed to obtain the necessary clinical information. With training, education, and experience, the sonographer can systematically keep the patient risks for potential boi effects if ultrasound down to a minimum. This means using ultrasound as an effective and often essential source of diagnostic information and not as a source of entertainment.


Summary :

The applications of ultrasound are growing in proportion to design improvements that satisfy specific scanning need. It's also growing in proportion to the imagination of users who experiment and perfect scanning techniques. Understanding the physics of ultrasound & how it affects the basic technologies & instrumentation extends our understanding of how to use the existing & new technologies and instruments as they come available to the user.

Regardless the technology, echo-ranging and Doppler principles remain largely unchanged as fundamental physical processes. Improvements in transducer technology, computer control, and display technology stand to make the techniques even more effective. Even with these improvements, many of the artifacts that arise out of tissue ultrasound interactions have to be understood to avoid making diagnostic errors. The technologies may be better, bur events like reverberations and multipath reflections will continue to plaque the sonographer. And, equipment that is maladjusted or out of registration will still cloud decision-making and diagnosis. Only good techniques and properly adjusted equipment will prevent these artifacts from inserting confusion and error into reading an ultrasound image.

And that brings us to the issue of the seven ways of keeping your imaging balance. The crashed bikes are ready reminders, but we can put these opportunities to crash an image into a slightly different order to keep yourself alert while scanning.

Simply follow the ultrasound in and out of the tissue and into the sonograph.


The sequence is :

  • Select the transducer for shape and frequency
  • Make sure the acoustic coupling is adequate
  • Set the output power to 80% of maximum (or as needed)
  • Set the tgc for image brightness balance using a standard protocol
  • Set the final gain for largest and smallest cho-signals
  • Set the doppler angle to 60 degrees or less(if you are using doppler)
  • Keep an eye out for the image and doppler artifacts.

          In short, keep your imaging balance by keeping these seven point of imaging in mind.


An Easy TGC Setup :

  • Start by turning the system GAIN all the way down. With a low gain, only the brightest echoes will remain on screen. For example, if you are scanning a liver, the skin line, portal vessels, and the diaphragm will remain on the screen, although the diaphragm may look a bit lighter. If these echoes are bright and blooming (that is, each echo signal is so bright that it spreads laterally on the screen), turn the OUTPUT POWER down until the blooming disappears. Conversely, if these echoes are not visible, but not blooming.
  • Now set the TGC so all of these visible echoes have the same brightness, both near and far. For some of the simpler machines, this will require setting a NEAR GAIN and a FAR GAIN to obtain balanced echo signal brightness. All the echoes should appear thin and sharp. If they are not, reduce the OUTPUT POWER further until they do.
  • Now turn the overall GAIN back up until all the soft echoes are visible without producing cystic filling (for example, a healthy gall bladder and vessels should be echo-free). This setup protocol makes sure you will not get into the situation of having too much gain or output power that can make the image look blurry and messy.