Measuring and testing – Vibration – By mechanical waves
Patent
1983-02-17
1985-04-09
Ciarlante, Anthony V.
Measuring and testing
Vibration
By mechanical waves
73625, 73628, 73633, 128660, G01N 2904
Patent
active
045093687
DESCRIPTION:
BRIEF SUMMARY
This invention relates to improvements in methods and apparatus for ultrasound tomography, particularly although not exclusively suitable for clinical diagnostics.
Generally speaking non-invasive examination techniques are preferred in humans or other animals to alleviate the risks associated with anaesthetics, infection etc. inherent in surgical techniques. In inanimate bodies, non-destructive examination techniques are preferred from the point of view of cost and practicality. X-ray and gamma-ray techniques have proven effective in obtaining accurate imagery of the internal structures of bodies but of recent years, the use of non-ionizing radiation on animals, particularly humans, is preferred. It is significant to note that those parts of the body which are highly susceptible to radiation damage also statistically show a predisposition to formation of cancers, cysts and other lesions. In a patient suspected of suffering a lesion of the abovementioned kind it is important to conduct regular examinations of the affected region to monitor any changes in the lesion. In women, it is recommended that breast examination be carried out on a regular basis in view of the high incidence of breast cancers.
To accommodate the need for non-invasive examination techniques without the use of ionizing radiation, certain ultrasonic examination and imaging techniques have been developed. These techniques employ levels of ultrasonic energy below those known to be harmful to biological tissues. Although known ultrasound systems have provided information useful in clinical diagnostics, they are not entirely satisfactory in terms of resolution and reproducability of the type and quality of data obtained.
Essentially there are two types of ultrasound imaging systems presently available. These rely on echo reflection information or transmission information for the reconstruction of images representing the internal structure of a body.
At present, the most highly developed and thus most used system is the pulse echo B-scan mode, or variants thereof. In this system an ultrasonic pulse, reflected from a surface or interface within a medium, is detected and represented on a video display with the strength or amplitude of the return echo modulating the brightness of the display. The relative positions of the pulsing/receiving transducer and the reflecting surface are displayed on a video screen in the X and Y axis. In a composite image comprising a plurality of echo signals obtained from scans at different angles within a given plane in a body, the resultant video representation is presented as an image in which each picture element or pixel has a direct geometrical positional relationship to the various reflecting interfaces associated with the body.
The B-scan system is subject to a number of disadvantages resulting from its use of the pulse-echo mode. As the echoes are generated at interfaces between media of different acoustic impedance within a medium, weak reflected signals from some delicate tissue structures may not be detected, particularly after further attenuation in the medium on the reflected signal path. Unless the angle of impingement of a pulse is substantially perpendicular to a reflecting surface or interface, the detected strength of the reflected pulse will be severely attenuated. This makes calibration of such apparatus difficult or impossible due to movement of various parts of the patient's body during breathing, heartbeat etc.
Recent developments in B-scan techniques however have alleviated certain of its inherent shortcomings to some extent. In a manner analogous to X-ray computerized tomography, images representing acoustic impedance distributions within a medium can be reconstructed and displayed as a two dimensional image on a video screen. Acquired data relating to a plurality of tomographic images in the same specimen may then be translated to give a fairly crude three dimensional representation of impedance distributions within the body under examination.
Further improvements in ultrasound image constr
REFERENCES:
patent: 3990300 (1976-11-01), Kossoff
patent: 4074564 (1978-02-01), Anderson
patent: 4105018 (1978-08-01), Greenleaf et al.
patent: 4222274 (1980-09-01), Johnson
patent: 4279157 (1981-07-01), Schomberg et al.
patent: 4338948 (1982-07-01), Perez-Mendez et al.
Koch Rolf H. L.
Whiting James F.
Ciarlante Anthony V.
The Commonwealth of Australia
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