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This paper investigates the properties of highly thinned ultrawideband (UWB) arrays. The design aim is high resolution and very low side radiation levels (SL). One- and two-dimensional ultrasparse UWB arrays can be designed to achieve both. The minimum available pulse-echo SL is shown to approach N(-4) where N is the number of elements in the transmit and receive arrays. Periodic thinning is shown to be superior to random thinning, and amplitude taper is shown to raise the SL. Two-dimensional curvilinear deployment of elements are shown to outperform rectilinear designs, and different transmit and receive arrays in pulse-echo systems are shown to outperform systems that use the same array for transmit and receive. Very low SL is achievable in an ultrasparse UWB system with so few elements that echo signal-to-noise ratio (SNR) rather than SL becomes the constraint on the minimum number of elements required by the system for the array to be useful for imaging. For example, in ultrasonic pulse-echo breast imaging, SL approximately -70 dB is desired to distinguish small cysts from tumors. A 2-D randomly thinned array requires about 10,000 elements. A 2-D ultrasparse UWB periodic array requires less than 100 to satisfy SL, a reduction of 100:1, but provides insufficient SNR. A 500-element, 7.5 MHz array operating with 4 cm penetration depth satisfies both. Experimental results demonstrate the theory.

The effects on array gain and sidelobe level of a practical digital beamforming (DBF) processor under the wideband conditions typical of ultrasound is discussed. It is concluded that a relatively simple design that replaces each analog delay line with a tapped, digital shift register (DSR) and a digital phase shift operation adjusted for midband will provide the desired performance, provided that the sampling rate of the signal at the input to the DSR is 4 to 10 times the bandwidth. More realistically, when nonidealized passbands are taken into account and the typical condition whereby the transducer frequency is about twice the bandwidth is considered, the rule of thumb for the sampling rate is that it must be 4 to 10 times the transducer frequency.

Traumatic carotid-cavernous fistulae are rare yet potentially lethal vascular anomalies in the skull base seen after craniomaxillofacial trauma. This aberrant vascular communication has been extensively evaluated and classified, with a number of treatment modalities available to clinicians. The ultimate and definitive treatment of carotid-cavernous fistulae falls beyond the scope of craniomaxillofacial surgery. Nevertheless, clinicians treating patients with craniofacial injuries should have a complete understanding of this pathological entity, because urgent intervention may improve patient outcome.

A formula is derived for the peak sidelobe level of a phased array in which the elements are randomly located. The parameters of the formula are the number and size of the array elements, size of the array, wavelength, beamsteering angle, and signal bandwidth. The theory is tested by measurement of the peak sidelobe of several hundred computer-simulated random arrays. Unlike the case for the conventional array the effect of spatial taper (nonuniform density of element location) upon the peak sidelobe level is minor. The peak sidelobe of the twodimensional planar array is approximately 3 dB higher than thet of the linear array of the same length and same number of elements.

Ultrasonic wavefront distortion produced by transmission through breast tissue specimens was measured in a two-dimensional aperture. Differences in arrival time and energy level between the measured waveforms and references that account for geometric delay and spreading were calculated. Also calculated was a waveform similarity factor that is decreased from 1.0 by changes in waveform shape. For nine different breast specimens, the arrival time fluctuations had an average (+/- s.d.) rms value of 66.8 (+/- 12.6) ns and an associated correlation length of 4.3 (+/- 1.1) mm, while the energy level fluctuations had an average rms value of 5.0 (+/- 0.5) dB and a correlation length of 3.4 (+/- 0.8) mm. The corresponding waveform similarity factor was 0.910 (+/- 0.023). The effect of the wavefront distortion on focusing and the ability of time-shift compensation to remove the distortion were evaluated by comparing parameters such as the -30-dB effective radius, the -10-dB peripheral energy ratio, and the level at which the effective radius departs from an ideal by 10% for the focus obtained without compensation, with time-shift estimation and compensation in the aperture, and with time-shift estimation and compensation performed after backpropagation. For the nine specimens, the average -10-dB peripheral energy ratio of the focused beams fell from 3.82 (+/- 1.83) for the uncompensated data to 0.96 (+/- 0.18) with time-shift compensation in the aperture and to 0.63 (+/- 0.07) with time-shift compensation after backpropagation. The average -30-dB effective radius and average 10% deviation level were 4.5 (+/- 0.8) mm and -19.2 (+/- 3.5) dB, respectively, for compensation in the aperture and 3.2 (+/- 0.7) mm and -22.8 (+/- 2.8) dB, respectively, for compensation after backpropagation. The corresponding radius for the uncompensated data was not meaningful because the dynamic range of the focus was generally less than 30 dB in the elevation direction, while the average 10% deviation level for the uncompensated data was -4.9 (+/- 4.1) dB. The results indicate that wavefront distortion produced by breast significantly degrades ultrasonic focus in the low MHz frequency range and that much of this degradation can be eliminated using wavefront backpropagation and time-shift compensation.

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A B S T R A C T F, hybrid offspring of New ZealandBlack mothers and New Zealand White fathers [(NZB X NZW)F1] female mice develop antibodies to singlestranded (ss) and native DNA, immune complex glomerulonephritis, massive proteinuria, and premature death with renal failure. By a series of matings, congenic (NZB X NZW)Fj * xid/xid mice were prepared. These mice were different from (NZB X NZW)Fj mice in having the X chromosome-linked immune deficiency gene, xid, in homozygous form. Such congenic (NZB X NZW)F, xid/xid females failed to develop antibodies to single-stranded or native DNA. They also failed to develop fatal renal disease as measured by proteinuria, glomerular histology, glomerular immunofluorescence, and survival.To control for unknown genetic factors, studies were performed with littermates that were derived by mating NZB * xid/+ females with NZW * xid/Y males such that the resulting offspring were either (NZB X NZW)F1. xid/xid (and therefore "defective") or (NZB X NZW)F1 . xid/+ [phenotypically like (NZB X NZW)Fl]. In these and in additional studies, mice were housed in the same cages and identified by ear tagging so as to avoid possible environmental variations from cage to cage. In these studies, xid/xid mice failed to develop the characteristic signs of autoimmunity, whereas the controls did. Similar results were also obtained with (NZW X NZB)F1 xid/xid mice compared with (NZW X NZB)Fj xid/+ mice.The effect of xid/xid upon (NZB X NZW)F1 mice was further investigated by assessing responses to immunization and polyclonal B cell activation in vivo.