Transcript
IMAGE OPTIMISATION
CJM STEWART UNIVERSITY OF CAPE TOWN 2010
KNOBOLOGY The basis of ultrasound image optimisation depends on knowledge of your machine. All machines are different. They have different buttons and controls.
Transducers □ Come in different sizes and frequencies. □ FRAGILE AND EXPENSIVE. Most do not come with a warranty. □ Proper care and handling □ Proper cleaning □ A good picture starts with a well cared for transducer. □ Take care of probes to prevent ‘drop-out’.
Transducer safety
YES
NO
Presets □ The manufacturer’s presets are a good starting point. □ Use these to start. □ Customise to suit your own needs. □ Work with the applications specialist to make the machine work for you.
Frequency □ Most transducers have multiple frequencies. □ Always use highest frequency for the part being imaged. □ BUT, know when to lower frequency for penetration.
Higher frequency : superficial structures. Lower frequency : deeper structures
IMPORTANT IN THE OBESE PATIENT
Frequency Evaluate image for adequate penetration
Depth □ Do not want to cut out pertinent information. □ Likewise, do not want too much black or wasted space at the bottom of the image.
Focal zone Focal zone should be at or just lower than the object of interest. Multiple focal zones can be useful but decreases frame rate.
Overall gain □ Overall gain knob usually incorporated into 2D/B mode knob. □ Changes the overall brightness of all the dots on the screen.
Overall gain □ Overall gain too low – image too dark
□ Overall gain too high – image too bright.
Overall gain
TGC □ Time gain compensation (TGC) □ sliders
□ Corrects for the attenuation of the beam as it travels deeper □ Goal is to create uniformity of the brightness of the echoes.
TGC How to use TGC □ Overall gain used to adjust the overall brightness of the image. □ TGC used to compensate for attenuation of the image. □ TGC should never be all the way to the left or right. Centre the sliders, then adjust the overall gain. From there, adjust TGC to correct for attenuation.
Zoom/magnify □ Manufacturers allow zoom or magnification of the image. Different terminology used by different manufacturers. □ Enlarges specific area of interest. □ Usually done on a live image, though some machines can zoom while image is frozen.
Zoom/magnify
Write zoom
Read zoom
□ Redraws image before □ Simply enlarges pixels it is stored in memory. □ Can be done on live or □ Maintains pixel density frozen image □ Image must be live. □ Lower resolution than write zoom □ Best spatial resolution
Other tools □ Tissue harmonics □ Reduces image artifacts □ Increases contrast resolution □ Allows better visualisation of tissue interfaces, especially in technically difficult patients.
□ Speckle reduction □ Eliminates edge shadowing artifact □ Reduces speckling
Cardiac imaging □ Differences between cardiac and no-cardiac imaging □ Cardiac imaging involves maximising the difference between myocardium and blood pools □ This requires maximisation of the frame rate □ Decrease the width of the frame □ Decrease the depth □ Zooming of the image
Increasing frame rate
Decrease width of frame
Increasing frame rate
Properties of the machine □ Tissue harmonics □ Cross beam □ Speckle reduction
Colour doppler imaging □ Gain □ Quality □ Wall motion filter □ PRF (velocity range) □ Invert □ 2D/2D-C □ Threshold
Conclusions □ Take care of the machine □ Know your knobs □ Frequency, depth, overall gain and TGC most commonly used to improve image quality easily □ Check extra features on the machine such as tissue harmonics □ Cardiac imaging often difficult. Optimise settings. □ Obese patient : Adjust depth,TGC, decrease frequency
