Donald W. Baker

Ultrasonic Duplex Echo-Doppler Scanner

Ultrasonic B-mode displays are produced by a new diagnostic scanner that yields dynamic Doppler information from blood flow in addition to both static and dynamic echo information from stationary and more slowly moving tissues. The effect is produced by combining the flow imaging capability of a multigate pulse-Doppler flow detector with a fast rotational pulse-echo B-mode scanner. The duplex system was designed for performing ultrasonic echo-Doppler arteriography where the location and geometry of the interface between occlusive atherosclerotic tissue and blood is of prime concern. Initial results on normal arteries in vivo are illustrated. Spatial alignment of echo and Doppler images is obtained by using the same transducer and scanning mechanism for both. However, clinical trials on patients with verified occlusive arterial disease indicated a two-transducer system would be more desirable. It is concluded that superposition of images of both tissue and blood decreases the uncertainties inherent in the display of either image alone.

Initial Ventricular Impulse A Potential Key to Cardiac Evaluation

During the early stages of ventricular systole, myocardial tension develops very rapidly, ventricular pressure rises steeply to exceed arterial pressure, and momentum is then rapidly imparted to the blood flowing out of the ventricles. The acceleration of blood out of the ventricles is an expression of the force being applied by the contracting myocardium, and the peak flow velocity can be regarded as the product of the net force applied over the time from the onset of ejection to the peak. The product of force and time is designated by a well-established physical term: impulse (I=Ft). Thus, “initial ventricular impulse” appears to be an appropriately descriptive term for the dynamic properties of ventricular ejection. Direct and continuous records of acceleration, the outflow rate of blood, and the rates of change of ventricular and arterialpressure demonstrate that ejection of blood from both ventricles (particularly the left) is more like striking a piston with a mallet than like squeezing blood out of a chamber. These dynamic characteristics of ventricular ejection are greatly altered by autonomic control and by simulated disease conditions.Initial ventricular impulse is greatly augmented during exercise, by stimulation of sympathetic nerves to the heart, and following long diastolic intervals. On the contrary, initial ventricular impulse is markedly depressed during premature ventricular contractions, acute coronary occlusion, exsanguination hypotension, general anesthesia, etc. Thus, signs of changing ventricular impulse may have significant value in assessing the performance capability of the heart. For this purpose, certain clinical tests of cardiac performance (e.g., arterial pressure pulses, electrokymograms, precordial displacements, ballistocardiograms) may have unsuspected importance. Experiments on animals have considerable value in suggesting measurements that might be appropriately employed on human subjects and patients, but because of species differences, the validation of initial ventricular impulse as clinical test of value must ultimately be accomplished by appropriate measurements conducted on human subjects. For this reason, a specific experimental design is suggested for the evaluation of certain indirect indicators that may have potential value in routine assessment of the cardiac status. By means of modern high-speed computers, cross correlations, and factor analysis could bring to light the aspects of peripheral arterial pulse waves, kinetocardiograms, electrokymograms, and ballistocardiograms of reliable predictive value in assessing initial ventricular impulse in man.

Pulsed Doppler echocardiography: principles and applications.

A new recording and display system is described for use with pulsed Doppler blood flow velocity detectors in the diagnosis of valvular and septal defects. The principles of the pulsed Doppler device are described along with the methods used to analyze and display the Doppler shifted signal from flow jets resulting from various valve defects. An M-mode display is combined with blood flow display to provide a convenient record of the clinical procedure. Examples of aortic stenosis, aortic insufficiency, mitral stenosis and regurgitation are presented along with signals from other valves.

Doppler Echocardiography The Localization of Cardiac Murmurs

A range-gated pulsed Doppler flowmeter has recently been developed that measures the average velocity of blood flow within a small tear-drop shaped (4 mm by 2 mm) sample volume. Unlike the continuous wave Doppler, the distance from the transducer face to the sampling site can be continuously varied by a range adjustment knob.Twenty patients with cardiac murmurs were evaluated in a noninvasive laboratory by brief cardiac physical examination, abbreviated phonocardiogram, complete echocardiogram, and localization of the murmurs by Doppler echocardiography. The localization depends on the detection of turbulent flow or jets at the sampling site. The murmurs included the diastolic rumble of mitral stenosis, mitral regurgitation, the murmur of left ventricular outflow tract obstruction, aortic stenosis, aortic insufficiency, diastolic rumble of tricuspid stenosis, augmented right ventricular filling sound in atrial septal defects, pulmonic stenosis, pulmonic insufficiency, and high velocity flow through the obstruction in ccarctation of the aorta.

A Pulsed Ultrasonic Flowmeter

A pulsed ultransonic flowmeter has been developed specifically for the simultaneous measurement of blood flow through various major blood vessels in the intact unanesthetized animal. The flow section is a small (1-3 cm) lucite cylinder which is clamped about the blood vessel. Piezoelectric crystals are mounted on the flow section so that bursts of 3-mc sound may be transmitted alternately upstream and downstream. The flowmeter develops a voltage which is proportional to the difference in the upstream and downstream transit times of the sound. This voltage is recorded continuously and calibrated in terms of flow. Under optimal conditions, the output voltage is a linear and accurate representation of volume flow within ±5 per cent, independent of the velocity profile. The flowmeter responds to a step variation in flow within 0.01 second. The maximum noise and baseline drift is equivalent to a flow velocity variation of less than 1 cm/second measured over a 4-hour period.

Color digital echo/doppler image presentation

Abstract Arterial occlusive disease in peripheral blood vessels can be evaluated with an ultrasound scanning system designed to generate real-time cross sectional tissue images and to assess the character of blood flow at any point using multi-gate Doppler methods. A new-generation echo/Doppler system. Duplex scanner IV, incorporates digital display technology to store both echo target location and flow velocity parameters for color composite imaging. Many display formats are possible. In B -mode format echographic tissue images are supplemented with flow information acquired at a specific point in time over 20–30 cardiac cycles by a slow spatial sweep of the Doppler beam in the region of interest. Image storage also makes possible a novel M/Q-mode presentation wherein anatomical interfaces and flow velocities are detected along a single line of sight and displayed as a function of time.

Detection of peripheral vascular disease using the Duplex Scanner III

Abstract Ultrasound provides a convenient means for the clinical evaluation of both the anatomy and the blood velocity patterns in large peripheral blood vessels. Continued development of ultrasound techniques has reached the point of providing useful diagnostic information in a routine fashion. This paper describes the Duplex Scanner III, which provides B -mode images of vascular anatomy combined with a pulsed 5 MHz Doppler to analyze blood flow within those vessels imaged. Improvements over the Duplex Scanner II include: increased scan head reliability; additional operating features and processing techniques to more accurately evaluate anatomy and blood flow characteristics; and display and recording techniques to facilitate clinical use.

EFFECTS OF ACUTE CORONARY OCCLUSION ON PERFORMANCE OF RIGHT AND LEFT VENTRICLES IN INTACT UNANESTHETIZED DOGS.

Abstract Changes in the mechanical performance of the right and left ventricles were studied before, during, and after abrupt occlusion of a major coronary artery, by directly recording from indwelling pressure cannulas and flowmeters. Analogue computers were used to derive additional pertinent variables, so that an engineering type of description of ventricular function was inscribed in as many as 22 variables with standard physical units. In 7 of the 9 animals in the series the anterior descending coronary artery was ligated at the time of operation, days or weeks before the experiment. The principal effects of acute occlusion of the left circumflex coronary artery in unanesthetized dogs were a reduction in peak ejection velocity, peak acceleration, and stroke volume of the left ventricle. These changes may be attributed to interference with the left ventricle as an impulse generator, since the pattern of ejection assumed some of the characteristics of the pattern of normal right ventricular outflow. Sustained tachycardia compensated for the reduction in the stroke volume, so that cardiac output was well maintained. The experiments in which large changes in left ventricular performance occurred were suddenly terminated by ventricular fibrillation within minutes or hours of the experimental coronary occlusion.

Ultrasonic three-dimensional imaging and volume from a series of arbitrary sector scans

Abstract A computer-based system has been developed for generating a three-dimensional reconstruction of an organ as a series of arbitrary outlines from a real-time, two-dimensional ultrasonic sector scanner. This reconstruction can be viewed in perspective or used to find volume by an algorithm which assumes no a priori shape for the organ. The various outlines are obtained by positioning the scan head over the organ to be imaged and tracing the borders with a light pen. The position and orientation of each scan is obtained with a special acoustic position locating system allowing nearly complete freedom of motion of the scan head. An initial feasibility test of this system has been done on seven balloons in a water tank. The correlation between measured and calculated volumes for 30 reconstructions on the seven balloons was R = 0.99, while the range of errors was −9.3 to +7.8%. Possible applications of this system include carotid artery imaging, fetal and liver volumes, and left ventricular volumes.

Doppler echocardiography. Use of a graphical display system.

Pulsed Doppler echocardiography (PDE) is a technique for evaluating blood flow characteristics at specific locations within the heart and great vessels. Because this method assesses blood flow rather than cardiac structures, PDE complements the findings of M-mode echocardiography. A new on-line graphical method for displaying pulsed Doppler information provides 1) a printed, permanent record of flow information, 2) precise timing of blood flow events, and 3) information on the direction of flow in the heart and great vessels.