Four patterns of distribution of left ventricular hypertrophy were identified by a wide angle, two dimensional echocardiographic study of 125 patients with hypertrophie Cardiomyopathy. Most commonly (52 percent of patients) hypertrophy involved substantial portions of both the ventricular septum and anterolateral left ventricular free wall (type III). In other patients, hypertrophy was confined to the anterior portion of the ventricular septum (type I), involved the entire ventricular septum but not the left ventricular free wall (type II) or was identified in regions of the left ventricle other than the basal anterior ventricular septum (type IV). In patients with the latter type, conventional M mode echocardiography failed to identify the presence of hypertrophy and therefore the diagnosis of hypertrophic Cardiomyopathy could be established only with two dimensional echocardiography. Patients with the most widespread hypertrophy involving most of the ventricular septum as well as portions of the free wall (type III) differed from patients having the other patterns of hypertrophy. (1) They more commonly experienced moderate to severe functional limitation (38 of 65 [58 percent]versus 16 of 60 [27 percent]; probability [p]

Patterns and significance of distribution of left ventricular hypertrophy in hypertrophic cardiomyopathy. A wide angle, two dimensional echocardiographic study of 125 patients.

The objective of this paper is to show that time reversal invariance can be exploited in acoustics to create a variety of useful instruments as well as elegant experiments in pure physics. Section 1 is devoted to the description of time reversal cavities and mirrors together with a comparison between time reversal and phase conjugation. To illustrate these concepts, several experiments conducted in multiply scattering media, waveguides and chaotic cavities are presented in section 2. Applications of time reversal mirrors (TRMs) in hydrodynamics are then presented in section 3. Section 4 is devoted to the application of TRMs in pulse echo detection. A complete theory of the iterative time reversal mode is presented. It will be explained how this technique allows for focusing on different targets in a multi-target medium. Another application of pulse echo TRMs is presented in this section: how to achieve resonance in an elastic target? Section 5 explores the medical applications of TRMs in ultrasonic imaging, lithotripsy and hyperthermia and section 6 shows the promising applications of TRMs in nondestructive testing of solid samples.

https://iopscience.iop.org/article/10.1088/0034-4885/63/12/202/pdf

Time-reversed acoustics

Transducer design and phased array beam steering are developed for a volumetric ultrasound scanner that enables the 3-D visualization of dynamic structures in real time. The authors describe the design considerations and preliminary evaluation of a high-speed, online volumetric ultrasound imaging system that uses the principles of pulse-echo, phased array scanning with a 2-D array transducer. Several 2-D array designs are analyzed for resolution and main lobe-side lobe ratio by simulation using 2-D fast Fourier transform methods. Fabrication techniques are described for 2-D array transducer. Experimental measurements of pulse-echo point spread responses for 2-D arrays agree with the simulations. Measurements of pulse-echo sensitivity, bandwidth, and crosstalk are included. >

High-speed ultrasound volumetric imaging system. I. Transducer design and beam steering

To study endocardial wall motion and thickness as indexes of infarction, we used two-dimensional echocardiography to examine regional percentages of systolic wall thickening (%Th) and endocardial motion (%EM) in infarcted canine hearts. Thirteen dogs were studied 48 hours after occlusion of the circumflex or left anterior descending coronary artery. Two-dimensional echocardiographic cross sections obtained every 16 msec at 1-cm intervals from apex to base in an open-chest, anesthetized preparation were analyzed with a computer-aided contouring system for quantification of segmental %EM and %Th at 16 equally spaced points per slice. Slices corresponding to each two-dimensional echocardiographic cross section were examined pathologically for evidence of infarction.Comparing histologically infarcted with distant normal zones in each slice, %Th and %EM both yielded clear separation with little overlap (−12.5% infarcted vs 37.4% normal for thickness; −11.3 vs 25.7% for motion, p ≪ 0.001 for both). Endocardial motion was less precise than thickening, however, in distinguishing infarct from either distant normal zones or zones directly adjacent to infarct.Although wall thickening was useful in separating out true subendocardial infarct, change in systolic thickening was not accurate in detecting the transmural extent of infarction. In 827 individual two-dimensional echocardiographic segments with varying degrees of transmural involvement, segments with 1–20% extent of transmural infarction showed reduced thickening compared with noninfarcted segments (39.9 vs 15.2%, p < 0.001), whereas myocardial segments with 21–100% transmural infarction showed systolic thinning (−8.9 to − 13.3%). There was no significant augmentation in the severity of systolic thinning as the extent of transmural infarction increased from 21% to 100%.We conclude that: (1) Wall motion abnormalities are less precise than thickening in discriminating between infarcted and noninfarcted zones and could lead to overestimation of infarct size. (2) There is an abrupt deterioration in systolic thickening in segments containing more than 20% transmural extent of infarction. (3) There is no significant augmentation in the degree of systolic thinning as the transmural extent of infarct increases from 21% to 100%. This \"threshold\" phenomenon may therefore preclude accurate estimation of infarct size by two-dimensional echocardiography. (4) Evidence of any systolic thickening indicates less than 20% transmural extent of infarction.

Two-dimensional echocardiography and infarct size: relationship of regional wall motion and thickening to the extent of myocardial infarction in the dog.

Methods for correction of phase aberrations induced by near-field variations in the index of refraction are explored. Using signals obtained from a sampled aperture (i.e. transducer array), phase aberrations can be accurately measured with a correlation approach similar to methods used in adaptive optics and radar. However, the method presented here has no need for a beacon or an ideal point reflector to act as a source for estimating phase errors. It uses signals from random collections of scatterers to determine phase aberrations accurately. Because there is no longer a need for a beacon signal, the method is directly applicable not only to medical ultrasound imaging but also to any coherent imaging system with a sampled aperture, such as radar and sonar. >

Phase-aberration correction using signals from point reflectors and diffuse scatterers: basic principles

A new two-dimensional ultrasound imaging system capable of producing high resolution tomographic images of the heart in real time has been developed. This system relies on phased array principles to rapidly steer the ultrasound beam through the structures under investigation. A hand-held linear array of 16 ultrasound transducers with overall dimensions of 14 mm at the site of contanct may be readily manipulated to image various cardiac structures. The resulting images are displayed in a circular sector format, 60 degrees in azimuth and typically 15 cm in range. At his maximum range, image frames consisting of 256 lines are generated at the rate of 20 frames/second. High azimuthal resolution throughout the field of view is assured by a focused transmit beam and by sweeping the focus of the receiver is synchrony with the range of returning echoes. Azimuthal resolution varies from 2 to 5 mm throughout the field of view while range resolution is 1.5 mm. This imaging system has proven particularly useful for the delineation of left ventricular spatial geometry by the identification of endocardium, myocardium, papillary muscles and interventricular septum. High quality images of anterior and posterior mitral leaflets, aortic root and aortic leaflets as well as left atrium and other cardiac structures have been obtained.

Cardiac imaging using a phased array ultrasound system. II. Clinical technique and application.

In recent years, ultrasound imaging based on B-mode echosonography has become an accepted and useful technique in medical diagnosis. However, the application of this technique has been limited by the time required to obtain an adequate image, the resolution that can be obtained in the image and problems related to the dynamic range of the echo information. A new ultrasound imaging system which removes or substantially reduces many of these limitations has been developed in the hope that ultrasound tomography may find even more widespread application and greater diagnostic value.

A New Ultrasound Imaging Technique Employing Two-Dimensional Electronic Beam Steering

Whereas A-mode echoencephalography has been found diagnostically useful, B-mode displays for similar object volumes have not yet provided the additional information that might be expected from a two-dimensional presentation. Poor image quality results from a number of causes stemming from the presence of skull bone (White, 1967; 1968). Large differences in specific acoustic impedance between skull bone and soft tissue combined with irregularities of skull bone surfaces result in unfavorable reflections and reverberations of acoustic energy. Severe attenuation of ultrasound at diagnostically useful frequencies further reduces system sensitivity and target acquisition. Additionally, significant differences between acoustic velocities in bone and tissue result in beam degradation and registration errors in the B-mode image. With one possible exception (Somer, 1969), the nature and extent of these aberrations have thus far limited practical utilization of B-mode scanners in clinical examinations of head structure.

Sampled Aperture Techniques Applied to B-Mode Echoencephalography

Abstruct-In the design of phased linear array sector scanners for medical applications, it is important to preserve uniform response at each angle throughout the sector scan of k45". Examination of Linear array transducers showed reduced transmit pressure and receive sensitivity a t angles beyond * 20" by individual array elements. The angular response of piezoelectric elements, many wavelengths long and approximately one wavelength or less in width, do not agree with the predictions of simple diffraction theory for plane apertures. Continuous wave (CW) angular response measurements using the RCA Ultrasonovision of individual piezoelectric elements 0.6 h t o 2 h wide indicated this behavior was independent of inter-element coupling and pulse excitation effects within a linear array transducer. Spectral analysis of isolated elements showed a significant amount of energy coupled into the transverse mode due to the small aspect ratio of width to thickness dimensions of the piezoelectric elements. A fist-order hvo-dimensional numerical model, based on thickness mode and transverse mode vibrations, resulted in angular response functions which agree well with experimental measurements.

Angular Response of Piezoelectric Elements in Phased Array Ultrasound Scanners

Time quantization errors in phased array systems can cause increased sidelobe amplitude, thereby limiting the dynamic range of the ultrasound system. A simulation program predicting the position and amplitude of these anomalous quantization error grating lobes has been developed to study the effects of transmitted pulse length on the ampli- tude of these anomalous lobes. Three parallel processing techniques for decreasing these sidelobe amplitudes while smoothing the speckle pat- tern are investigated.

F. L. Thurstone

Papers

Cardiac imaging using a phased array ultrasound system. II. Clinical technique and application.

A New Ultrasound Imaging Technique Employing Two-Dimensional Electronic Beam Steering

Sampled Aperture Techniques Applied to B-Mode Echoencephalography

Angular Response of Piezoelectric Elements in Phased Array Ultrasound Scanners

Delay Quantization Error in Phased Array Images