* NEAR ZONE is 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 ZONE is the farthest area from the transducer.

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.

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.

* 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.

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

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

*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.

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"