A study in vitro of specimens of human aortic and common carotid arteries was carried out to determine the feasibility of direct measurement (i.e., not from residual lumen) of arterial wall thickness with B mode real-time imaging. Measurements in vivo by the same technique were also obtained from common carotid arteries of 10 young normal male subjects. Aortic samples were classified as class A (relatively normal) or class B (with one or more atherosclerotic plaques). In all class A and 85% of class B arterial samples a characteristic B mode image composed of two parallel echogenic lines separated by a hypoechoic space was found. The distance between the two lines (B mode image of intimal + medial thickness) was measured and correlated with the thickness of different combinations of tunicae evaluated by gross and microscopic examination. On the basis of these findings and the results of dissection experiments on the intima and adventitia we concluded that results of B mode imaging of intimal + medial thickness did not differ significantly from the intimal + medial thickness measured on pathologic examination. With respect to the accuracy of measurements obtained by B mode imaging as compared with pathologic findings, we found an error of less than 20% for measurements in 77% of normal and pathologic aortic walls. In addition, no significant difference was found between B mode-determined intimal + medial thickness in the common carotid arteries evaluated in vitro and that determined by this method in vivo in young subjects, indicating that B mode imaging represents a useful approach for the measurement of intimal + medial thickness of human arteries in vivo.

Intimal plus medial thickness of the arterial wall: a direct measurement with ultrasound imaging.

A detailed review of the literature on ultrasonic propagation properties of mammalian tissues and organs has revealed 144 papers containing compilable data. Over 1300 lines of parametric data are listed, including the tissue, species, age, specimen preparation, anatomical structure, pathology, temperature, measurement method, frequency, velocity, attenuation, acoustic impedance, and density.

Comprehensive compilation of empirical ultrasonic properties of mammalian tissues

Iterative reconstruction algorithms.

Computer technology has brought about a revolution in radiology. By combining the computer with X rays it is possible (in principle) to obtain tomographic images of any cross section in the human body. These techniques are now used for medical diagnosis in all the major hospitals of the world. But X rays are not the only kind of radiation for which computer-assisted tomography is feasible. Microwaves, electron beams, ultrasound, fast subatomic particles from accelerators, gamma rays from such sources as positron annihilation, and even magnetic fields can also be used. This paper is mainly concerned with ultrasound. Acoustic energy can often give a view of a cross section not available with X rays or other types of radiation. A mapping of acoustic and elastic discontinuities can be expected to give a basically different pattern than a mapping of X-ray absorption and scattering coefficients. Several methods of ultrasonic tomography are discussed including methods based on geometric optics and a Doppler-oriented approach. A major portion of the paper is concerned with introducing ways to take into account diffraction effects. Because of the wavelength differences, these effects are far more important for ultrasound than for X rays.

Reconstructive tomography and applications to ultrasonics

The propagation of ultrasonic waves is nonlinear. Phenomena associated with the propagation of diagnostic ultrasound pulses cannot be predicted using linear assumptions alone. These include a progressive distortion in waveform, the generation of frequency harmonics and acoustic shocks, excess deposition of energy and acoustic saturation. These effects occur most strongly when ultrasound propagates within liquids with comparatively low acoustic attenuation, such as water, amniotic fluid or urine. Within soft tissues, similar effects occur, although they are limited by absorption and scattering. Nonlinear effects are of considerable importance during acoustic measurements, especially when these are used to predict in situ exposure. Harmonic generation may be used to create images. These offer improvements over conventional B-mode images in spatial resolution and, more significantly, in the suppression of acoustic clutter and side-lobe artifacts. B/A has promise as a parameter for tissue characterisation, but methods for imaging B/A have shown limited success.

Nonlinear acoustics in diagnostic ultrasound.

Reconstruction of Three-Dimensional Velocity Fields and Other Parameters by Acoustic Ray Tracing

Ultrasonic Data Acquisition and Processing System for Atherosclerotic Tissue Characterization

A theory with supporting experimental evidence is presented for reconstructing the three-dimensional fluid velocity vector field in a moving medium from a set of measurements of the acoustic propagation time between a multiplicity of transmitter and receiver locations on a stationary boundary surface. The inversion of the integrals’relating the acoustic propagation path to the propagation time measurements is affected by linearization and discrete approximation of the integrals and application of an algebraic reconstruction technique (ART). The problem of the presence of certain invisible fluid flow functions is treated. Since this technique does not require the presence of scattering centers or the optical transparency of the medium, it may be applied in many cases (i.e., turbid, opaque, or chemically pure media) where Doppler or optical (e.g., laser holography) methods fail.

S.A. Johnson

Papers

Reconstruction of Three-Dimensional Velocity Fields and Other Parameters by Acoustic Ray Tracing

Ultrasonic Data Acquisition and Processing System for Atherosclerotic Tissue Characterization

Reconstructing three-dimensional fluid velocity vector fields from acoustic transmission measurements

Digital image focussing in the near field of a sampled acoustic aperture.