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Hitachi Medical Systems America, Inc. (HMSA) provides a complete range of ultrasound-based systems covering the entire spectrum from compact black and white systems at entry price level up to premium class systems for the most demanding users. As a full-line supplier of medical imaging equipment in Japan, Hitachi Medical Corporation (HMC) founded HMSA to provide a direct link to the U.S. marketplace. Hitachi consolidates his distribution channels in the US by transferring the Hitachi line of Ultrasound products to HMSA in October of 2002. HMSA is responsible for the sales, marketing and service of all Hitachi Ultrasound products in the United States.

Ultrasound Systems:

Huygens principle states that an expanding sphere of waves behaves as if each point on the wave front were a new source of radiation of the same frequency and phase. The principle explains how a flat ultrasound transducer can transmit a narrow ultrasound beam, which in the near field is confined to the dimensions of the transducer surface.
Spherical wavelets are emitted from numerous point sources on the transducer surface. They interfere to form a narrow, slightly converging beam of ultrasound in the near field. The wavefronts in the beam are nearly parallel. A precondition for this interference is that the transducer surface is much larger than the ultrasound wavelength.

See also Interference Artifact.

A hydrophone is a special transducer for underwater measurement of acoustic fields. The diameter of a hydrophone should be smaller than the wavelength of the measured ultrasound, in combination with a large bandwidth.

The term hyperechogenic or hyperechoic is used if there are many internal echoes. Hyperechoic tissues appear bright in ultrasound imaging. Tendons are hyperechoic because of the fibrillar pattern. Ligaments appear hyperechoic when the beam is perpendicular to the tissue. Peripheral nerves are hyperechoic relative to muscle. Liver angiomas, tumor cells, blood vessels, fibrosis, and liver steatosis appear diffuse hyperechoic.

Solid regions have internal ultrasound echoes and are classified as echo poor, hypoechoic or hypoechogenic if there are few internal echoes. Hypoechoic structures appear dark in ultrasound imaging, more homogeneous structures are darker than heterogeneous.
Soft atherosclerotic plaque, liver adenoma or FNH appear with a nodular hypoechogenicity. As metastases close the blood vessels they infiltrate, tumor tissues become hypoechogenic after injection of contrast agent. Muscle appears relatively hypoechoic to tendon fibers, also articular hyaline cartilage appears hypoechoic.