focal zone

focal zone,

in ultrasonography, the distance along the beam axis of a focused transducer assembly, from the point where the beam area first becomes equal to four times the focal area to the point beyond the focal surface where the beam area again becomes equal to four times the focal area.

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focal

1. limited to a small area or volume.

2. pertaining to or emanating from focus.

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focal distance

see focal-film distance.

focal length

the distance between the lens and an object from which all rays of light are brought to a focus.

focal liver disease

widely disseminated micro-abscesses or abscesses, migration paths of helminth larvae.

focal macular melanosis

dark colored spots on the skin, not elevated above the skin surface but apt to be confused with melanosis.

focal myelitis-encephalitis

widely disseminated inflammatory lesions, usually the result of blood-borne infection, in brain and spinal cord.

focal symmetrical encephalomalacia

see focal symmetrical encephalomalacia.

focal symmetrical spinal poliomalacia

see focal symmetrical spinal poliomalacia.

focal ulcerative dermatitis

manifest by ulcers in the unfeathered anterior breast skin of 4 to 5 months old male turkeys. The incidence is influenced by litter type. Called also breast buttons.

focal zone

in ultrasound, the area of the transducer where the sound beam is most sharply focussed and where the area under examination will give the best image.