MHz System Research Articles

Hyperthermic therapy of deep seated tumors: Comparison of the heating efficiencies of an annular array applicator and a capacitively coupled radiofrequency system

Among 82 cases of deep seated tumors treated by hyperthermia with an annular array applicator (AA) and/or a capacitively coupled 8 mHz system (CCS) combined with radiation therapy, 13 cases were treated by both devices. The efficiencies of tumor heating were compared in terms of the time required to attain 42°C, the duration of heating time and the thermal dose as determined by a biological iso-effect formula for equivalent minutes at 42.5°C. Temperature profiles and percent of temperature levels > 42°C were better in the cases treated by the AA, but higher thermal doses were obtained with the CCS because longer treatment times were tolerated with the CCS than with the AA. Methods are necessary to prevent excess elevation of body temperature in the case of the AA, and to reduce superficial pain where the applicators contact the skin in the case of the CCS.

A VLA Search for Cosmological H I

The recent commissioning of the 327 MHz (or P band) system at the NRAO Very Large Array opens the possibility for a new search for the 21 cm of H I redshifted to z ≈ 3.3 and perhaps observing the birth of galaxies as initially suggested by Sunyaev and Zel'dovich (1972, 1975). We present and discuss the results of our first observing run in January 1986, and report on the progress on our second run in April 1987.

Microprocessor based polarity correlation using the skip algorithm

A real-time multiprocessor-based polarity correlator is described which uses MC68000 microprocessors to estimate and display simultaneously the coefficients of a polarity correlation function implemented by the Skip algorithm. The prototype system is capable of sampling the input signals and simultaneously displaying a 128-point correlation function at a maximum rate of approximately 60 kHz when an 8 MHz system clock frequency is used. The additional hardware required by the multiprocessor correlator was implemented on a specially designed single-chip ULA which can be configured to interface directly to the address and data bus of the system.

Sonographic appearance of extra-axial fluid collections in the infant: further observations.

Extra-axial fluid collections were identified in six infants by transfontanelle cranial sonography. Confirmatory computer tomography (CT) scans were performed following the sonograms in five of these patients. These extra-axial fluid collections were varied in appearance and could be divided into two types depending on their sonographic characteristics. The first group consisted of large, usually concave anechoic collections and the second of small extra-axial fluid collections best seen in the interhemispheric fissure. The large collections were easily identified using a routine 5 MHz transducer system. The smaller collections were not well visualized with a 5 MHz system and required a 7.5 MHz transducer to identify the fluid in the interhemispheric fissure. Additionally, the lateral extent of these small collections could not be visualized through the anterior fontanelle using either transducer and CT was required for definitive evaluation of their lateral extent.

Stochastic cooling in the CERN ISR during pp colliding beam physics

When the ISR is used as a pp collider a high-intensity proton beam in R1 collides with a low-intensity antiproton beam in R2 for periods of up to two weeks. The luminosity lifetime is increased with a vertical stochastic cooling system in R1 designed for currents up to 10 A with a total bandwidth of 3.3 GHz. Cooling rates up to 0.7%/h have been obtained. The R2 antiprotons are cooled vertically with a 100-600 MHz system which decreases the initial beam height by up to a factor 7 and increases the luminosity by a factor 1.3-1.4. A momentum cooling system in R2 (frequency range: 55-155 MHz) creates empty space within the p stacking aperture. This allows several stacks from the antiproton accumulator (AA) to be stored in the ISR. With this system which uses the Palmer method it has been proved experimentally that momentum cooling and horizontal betatron cooling are obtained simultaneously if the betatron phase between pick-up and exciter is an odd number of half-betatron wavelengths. The cooling rate of the momentum cooling system which is power-limited is typically 4%/h at 26 GeV/c. The layout of the cooling systems is shown schematically in Fig. 1. The position of the various elements is mainly determined by the available free space and the lattice parameters. Future applications include vertical cooling of α-particles and cooling of antiprotons in all three planes in an experiment where a circulating 3.5-7.5 GeV/c p beam collides with a hydrogen gas jet target.

A Five-Octave Level Control Circuit for Broadband Coaxial Cable Distribution Systems

Digital communications with an equal amount of data flowing in either direction over a single coaxial cable have been proposed, and a few pioneering systems have already been installed by cable television companies. Broadband distribution for this purpose is certainly attractive. Fifteen-mile-long systems with cascades of thirty or more trunk stations are not uncommon, and in a splitband 450 MHz system, the reverse passband spans more than five octaves of frequency typically ranging from 5 to almost 200 MHz.

Auxiliary heating results from PDX and PLT

Auxiliary heating experiments are continuing on both PLT and PDX. PLT has increased the available ICRF power delivered to the plasma to 3 MW for the 42 MHz system and to 1.6 MW for the 25 MHz system. Deuteron and electron heating are observed in the minority 3He (Td approximately 2.8 keV, Te approximately 2.2 keV) and H (Td approximately 2 keV, Te approximately 2.2 keV) heating regimes. In addition, ion heating has been observed in the second harmonic regime (Teff=2/3 (Eh)=3.3 keV). Recent auxiliary heating of low q(<or approximately=2) discharges on both PLT and PDX have resulted in substantial plasma beta in both machines, PDX has used an absorbed beampower of 5.0 MW at a field of 1.0 T with qphi =1.8 to obtain a beta of 3.2% measured magnetically. PLT has used combined beam and ICRF heating in the minority mode to obtain a toroidal beta in the range of 1.6 to 2.2% with approximately 3 MW total power, 1.7 T field, and qphi =2.2.

Detecting ductal shunting in premature infants by range-gated Doppler echocardiography.

Range-gated pulsed Doppler echocardiography has been reported to be a useful noninvasive bedside technic for detecting ductal left-to-right shunting in premature infants. We studied 30 premature infants with a birth weight of less than 1,500 gm, using a 5 MHz system developed by Advanced Technology Laboratories. An umbilical artery catheter was used to obtain a contrast aortogram. Twenty-three infants had both a positive flush aortogram and a continuous turbulence documented by Doppler echocardiography. A clinically audible murmur was present in 17 of these patients. In six infants there was no Doppler evidence of PDA. In five of this last group there was also a negative flush aortogram. The excellent correlation found between the Doppler and aortographic studies suggests that this noninvasive technic is very sensitive for detecting ductal left-to-right shunting, even in the absence of an audible murmur.

400 MHz System Design

Alternative approaches to headend arrangements in designing 400 MHz cable systems are presented. The trade-offs between coherent and non-coherent headends are discussed and the operating output level of distribution amplifiers (bridgers and line extenders) is shown to be a critical parameter in designing a 400 MHz system to meet performance and operating margins that are comparable to presently operating 300 MHz cable systems.

PIA, the Positron Intensity Accumulator for the PETRA Injection

The storage ring PETRA is designed to store 4.1012 electrons and positrons in 2xfour 500 MHz rf buckets. Since the intensity of the positron linac is about 2.107 particles per 500 MHz bucket, 2.105 bunches are required for injection and accumulation in PETRA. In order to get reasonably short filling times the storage ring DORIS presently is acting as an intermediate bunch accumulation facility. This scheme has been successfully in operation since September 1978. Now the increased demand for elementary particle physics and for synchrotron radiation experiments at DORIS has motivated the construction of the small 450 MeV intermediate storage ring PIA, located between the positron linac and DESY. The circumference is 28,8 m. About 1 . 109 positrons will be injected at a rate of 50 Hz. A first harmonic cavity (10,4 MHz) accumulates positrons in a 0,8 m long bunch which is further compressed to 0,25 m length by a 12th harmonic rf system (125 MHz) for injection into the DESY 500 MHz system. After acceleration to 6,5 GeV in DESY single positron bunches are injected into PETRA.

Synchronized pulsed Doppler blood flow and ultrasonic dimension measurement in conscious dogs

An ultrasonic pulsed Doppler system for sensing blood flow in several vessels simultaneously has been developed and applied in the measurement of blood flow through the smaller vessels of chronically instrumented animals. The range gated, 20 MHz system is directional and can sense Doppler frequencies up to 25 kHz. The probes are single piece cuffs ranging in size from 2 to 8 mm diameter and contain a single piezoelectric crystal 1–2 mm 2. Calibration curves produced in vivo in dogs show good linearity and reproducibility and agree closely with theoretically predicted values. The pulsed Doppler technique is uniquely suited for synchronization with an ultrasonic transit-time dimension gauge allowing the simultaneous measurement of multiple flows and dimensions. The system has proved to be simple and reliable, and excellent quality signals have been recorded from multiple vessels for periods of several months.

The 50 MEZ Transverse Feedback System in the CERN ISR

One of the intensity limits in the ISR is imposed by the transverse coherent instability. The intensity at which the instability occurs may be raised by Landau damping, i.e. increasing the tune spread of the stacked beam. However, due to non linear resonances, the maximum tune spread is limited. A vertical feedback system which detects and damps the first eight modes of the instability has succeeded in increasing the intensity limit by a factor of ~1.6. Recently this factor has once again become insufficient due to the increase in intensity resulting from improvements in the longitudinal density and vacuum system. A new 50 MHz feedback system has now been installed which damps the first 166 modes of the instability. Hence at low chromaticity values the critical intensity is raised by around another factor of two. The electronic gain of this system decreases with frequency in order to limit the blow-up of vertical oscillations due to electronic noise and to reduce phase errors at high frequencies. The 50 MHz system has been used to explore the ISR vacuum limit to intensities of 39 A.

RANGE-GATED PULSED DOPPLER ECHOCARDIOGRAPHY: ITS ROLE IN DETECTING DUCTAL SHUNTING IN PREMATURE INFANTS

To evaluate the effectiveness of the range-gated pulsed doppler system in detecting the presence of ductal shunting in small pre-term infants on assisted ventilation for respiratory insufficiency, 21 infants with BW under 1500 grams were studied with a 5MHz system developed by Advanced Technology Laboratories, Inc. In each, an umbilical or radial artery catheter was used to obtain a contrast aortogram. Also, a two year old child with a documented aortopulmonary (AP) window was studied. Nine of the infants had no doppler evidence of patent ductus arteriosus (PDA), 8 had negative aortograms. In 13 there was an audible continuous turbulence superior to the pulmonary valve approximately 2 cm below the transducer. Each had a positive aortogram. Auscultation revealed a systolic or continuous murmur at the ULSB in 9 of the 13 infants; in 3, no murmur was appreciated. In the child with an AP window, there was a continuous turbulence at the level of the pulmonary valve. This noninvasive bedside technique appears to be very sensitive and specific for detecting the presence of ductal shunting, even in the absence of an audible precordial murmur. Its use permits the expedient indentification of a PDA in the patients who cannot be weaned from the ventilator and it facilitates appropriate timely therapy, such as the phannacologic manipulation or surgical ligation of the ductus, as a means of preventing the complications of protracted ventilation.

Digital acquisition and interactive processing of ultrasonic echoes.

The requirements for an interactive digital signal processing system for ultrasonic pulse-echo signals are discussed. A system based on an Interdata Model 80 mini-computer and micro-processor interface is described. The system is capable of acquiring ultrasonic data at a sampling rate of 6 MHz. Ultrasonic B-mode data may be acquired in Line Mode, when echo waveform data and transducer position and orientation are stored, or in Section Mode when the data is converted directly into picture form in memory in the same way that a standard echogram is formed on the screen of an oscilloscope. In each case the data for single complete high resolution echogram may be acquired in less than 15 sec. It is shown that the 6 MHz sampling rate is sufficient to faithfully preserve the echo waveshape of a 2 MHz system independently of the relation to the phase of the sampling. Also shown is a cross-sectional echogram of the pregnant uterus, and its digital representation with a raster density of 80 × 100 and 160 × 200 picture elements. The computer is programmed with an interactive program to allow ultrasonic signals to be acquired, stored, processed and examined with the convenience of a desk calculator. Sample operations are illustrated including data interpolation, spectrum analysis, filtering and complex signal deconvolution. The ability of deconvolution techniques to resolve targets separated by less than one wavelength in depth is demonstrated. Possibilities of further processing techniques are outlined.