Due to the nature of speckle, the ability to distinguish between regions with little differences in back scattering must be regarded more as a physiological problem than a physical one. If, however, a scanner has some kind of speckle reduction mechanism it can be tested with the low contrast phantom.
The phantom consists of a liver tissue equivalent mass with 3 rows of holes with diameters of 3, 5 and 10 mm. The center hole in each row contains the same material as the surroundings. The neighboring holes differ + and – 1,5 dB in back scattering, but have the same attenuation. The outermost holes differ + and - 3 dB.
Due to the casting, a specular reflex arises from the interfaces, even in the reference holes in the center. Nothing has been added to correct the sound velocity, so the phantom can be scanned through tap water, without risk of damaging the parameters. As a consequence the sound velocity is 3% lower than tissue. This has no impact on the speckle pattern.
Dimensions: 12 * 18,5 * 9,5 cm
Weight: 1,2 kg
Attenuation: 0,5 dB/cm*MHz +/- 0,07 dB/cm*MHz.
Sound speed: 1490 m/sec +/- 15 m/sec.
Density: 1020 kg/m3 +/- 20 kg/m3.
Attenuation, sound speed and density as background
Back scattering is made so that it will be : +3, +1,5, 0, -1,5, -3 dB relative to background, all +/- 1 dB.
Once every month inspect the phantom.
The surface must always be covered with 1/2 - 1 cm preservative fluid. Fluid that disappears by desiccation should be replaced by distilled water.
Once every 3 month replace the preservative fluid.
Please notice that the lid may not be 100 % tight. Drain fluid off before transportation, but never let it stay dry more than a few days.
The phantom will not stand frost. Safe storage temperature: 0 - 45 degrees Celsius.
Prescription for Preservative Fluid
-500 ml Distilled Water
- 2,5 g Acnibio OCS
- 0,5 g Citric ascid