Hewlett E. Melton

Acoustic Lability of Albumin Microspheres

The sonication of human serum albumin produces air-filled microspheres that are used in echocardiographic studies of myocardial perfusion. Recent studies suggest that the microspheres disappear when high pressures are applied, altering the relationship between the administered microsphere dose and the echocardiographic response. Because an ultrasound pulse generates a pressure wave in insonified medium, we hypothesized that with increasing acoustic pulse pressure, the microsphere concentration decreases, hence ultrasonic backscatter decreases. We measured relative integrated backscatter from albumin microspheres diluted in normal saline solution (6152 microspheres/ml) and 5% human plasma protein fraction (24,608 microspheres/ml), with increasing acoustic pulse pressures at the transducers focus. Backscatter was also measured in normal saline solution with increasing concentrations (up to 15,380 microspheres/ml) of albumin microspheres at an acoustic pulse pressure of 0.11 MPa (1.1 atm). Backscatter and microsphere concentration were related logarithmically: y = 3.38 x 0.32; r = 0.93. Backscatter was unchanged over time at acoustic pulse (peak compression) pressures less than 0.15 MPa (1.5 atm). However, backscatter decreased readily at acoustic pulse pressures greater than 0.33 MPa (3.3 atm), which included any mixing effects. Thus, albumin microspheres are acoustically labile.

Ultrasonic output measurements of multiple-mode diagnostic ultrasound systems

Electronic control has brought unprecedented flexibility and complexity in the variety of ultrasonic signals and beams available from a single modern multiple-mode ultrasonic imaging system. The process of measuring the ultrasonic output of these systems is started with the identification of relevant system parameters. Because the combinations of control settings for these parameters can number in the tens of thousands for some of the newer systems, a rational methodology for finding the highest global intensity or pressure values was necessary. To aid in the search, a linear simulation model was developed to predict those control settings that produce the highest relative intensity and pressure levels and their peak locations. This information became the starting point for actual measurements. An equipment setup suitable for multimode measurements is described. Experimental mapping procedures were used to find actual global maxima by varying a smaller subset of control parameters. Data were checked by formulae derived specifically for multimode measurements.<<ETX>>

Techniques for calculating ultrasonic integrated backscatter using frequency or time domain techniques

Apparatus for deriving signals indicating a condition of tissue within an area by launching spaced supersonic pulses into a body under examination and detecting the power of supersonic waves scattered from locations along a plurality of known paths. Gain control elements are provided for compensating for changes in amplitude of the scattered supersonic waves resulting from their passage through blood or tissue, the increased attenuation with frequency of the spectrum of the launched pulses and the focussing of the launched pulses. Compensation for ring-down and the attenuation of the chest wall is also provided.

Undersampled omnidirectional ultrasonic flow detector

A motion detection scheme is described which periodically sends a plurality of pulsed ultrasonic signals from a transducer to a particular range cell to receive a series of backscattered signals from the particular range cell. The time interval between any two pulses is greater than a largest dimension of the range cell divided by a slowest velocity of motion at the particular range cell. A temporal variation between the envelopes of the signals is then determined to detect motion at the particular range cell. This scheme may be applied at all points in an image, to produce images that depict regions undergoing motion.