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Understanding Ultrasound: Near Zone, Far Zone, and Types of Spatial Resolution

This guide explains key concepts of ultrasound imaging, including the near zone, far zone, and focal zone. It outlines how transducer types (linear, concave) affect near zone length and methods to focus the ultrasound beam using concave crystals or acoustic lenses. Additionally, we explore the four types of resolution in ultrasound: spatial, contrast, temporal, and energy resolution, detailing their significance and examples. Understanding these elements is crucial for improving image quality and accuracy in ultrasound diagnostics.

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Understanding Ultrasound: Near Zone, Far Zone, and Types of Spatial Resolution

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  1. US PRACTICAL

  2. * NEAR ZONEis the nearest area to the transducer & it always has the same diameter of the transducer, BUT if the transducer: • Linear the near zone length is long (Deeper). • Concave the near zone length is short. • * FAR ZONEis the farthest area from the transducer.

  3. Focal zone: is amethod of focusing the U/S beam by Concentrating the acoustic energy over a small area at Specific distance from the transducer . WE CAN MAKE THE FOUCSE BY TWO WAYS: • 1) Concave crystal. • 2) Acoustic lens .

  4. RESOLUTION: We have four different types of resolution: spatial, contrast, temporal, and energy resolution . *Spatial resolution : It is the ability to image small or high contrast objects. E.g., the best spatial resolution found in Mammogram. * Contrast resolution : It is the ability to distinguish one similar tissue from another. E.g., the best contrast resolution found in MRI.

  5. * Temporal resolution:It is the ability to measure & count motion.E.g., the best temporal resolution found in US "Doppler".* Energy resolution:It is the ability to measure & count energy.E.g., the best energy resolution found in NM.N.B.We consider all the resolution types in US EXCEPT Energy resolution.

  6. WE HAVE TWO TYPES OF :SPATIAL RESOLUTION(1) Axial (2) lateral

  7. AXIAL SPATIAL RESOLUTION : it could also call range, depth or longitudinal . • It is the ability to distinguish between two objects close to each other & located along the main axis .Factors affecting axial spatial resolution are: • 1) Spatial pulse length"if SPL increase, ASR will decrease" • 2) Frequency"if freq. increase, ASR & penetration decrease" • 3) pulse duration“ if PP increase, ASR will decrease • 4) Damping material has an affect also, "how quickly a pulse of US can be initiated & extinguished. • 5) Distance between 2 reflectors “ more D, more ASR

  8. *LATERAL SPATIAL RESOLUTION:It could also call transverse or asemouthal.It is the ability to distinguish between two objects close to each other & located perpendicular on the main axis.

  9. Factors affecting lateral spatial resolution are:1) Size (crystal diameter) "smaller diameter, more LSR"2) Beam width 3) Frequency" more freq, more LSR" 4) Distance between 2 reflectors" more D, more ASR"

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