Thermoacoustic sensor for ultrasound power measurements and ultrasonic equipment calibration.

This paper describes a thermoacoustic sensor developed for measurements of the acoustic power and calibration of ultrasonic transducers in the medical imaging and nondestructive testing frequency range. It is shown that the equilibrium temperature produced by ultrasound absorption in an absorbing material and detected by a copper-constantan thermocouple is proportional to the square of the current applied to the acoustic source. It is also demonstrated that the simultaneous measurement of this current and the corresponding equilibrium temperature at a given frequency allow the transmitting current sensitivity of the acoustic source to be calculated. The sensor thus provides a useful and low-cost alternative to the expensive calibration methods such as those based on the reciprocity technique, the planar scanning technique and the radiation force balance. The principles of the sensor's operation are outlined and its construction and characteristics are described. Experimental data in the frequency range of 1-8 MHz are presented and the advantages and disadvantages of the sensor are discussed.

The effect of spatial orientation on the perception of moving tactile stimuli.

Previous studies have shown that the perception of spatial patterns, such as letters, presented to the hand is affected by the spatial orientation of the hand. The present study investigated how the perception of direction of motion across the fingerpads changes with the position of the hand in space. The moving stimuli were generated on two displays. In one condition, the displays were placed horizontally in front of the subject, with the subject's thumb (target site) and index finger (nontarget site) placed flat on the displays. In a second condition, the displays were vertically oriented and gripped between the thumb and index finger. Using a selective-attention paradigm in which subjects are instructed to respond only to the direction of motion at the target site, performance was still affected by the direction of motion at the nontarget site. Changing the orientation of the displays changed the effectiveness of the nontarget in interfering with the identification of the target movement. Nontarget stimuli that produced no interference in the horizontal orientation did so in the vertical, and vice versa. It appears that subjects are not using the local direction of movement across the fingerpads to judge the relative direction of movement at the two sites; rather, they are using the external direction of movement.

Perceptual processing of adjacent and nonadjacent tactile nontargets.

Previous research has shown that subjects appear unable to restrict processing to a single finger and ignore a stimulus presented to an adjacent finger. Furthermore, the evidence suggests that, at least for moving stimuli, an adjacent nontarget is fully processed to the level of incipient response activation. The present study replicated and expanded upon these original findings. The results of Experiment 1 showed that an equally large response-competition effect occurred when the nontarget was presented to adjacent and nonadjacent fingers (on the same hand). The results of Experiment 2 showed that the effects observed in Experiment 1 (and in previous studies) were also obtained with stationary stimuli. Although small, there was some indication in the results of Experiment 2 that interference may dissipate more rapidly with distance with stationary stimuli. An additional finding was that interference effects were observed in both experiments with temporal separations between the target and nontarget of up to 100 msec. In Experiment 3, target and nontarget stimuli were presented to opposite hands. Although reduced, interference was still evident with target and nontarget stimuli presented to opposite hands. Varying the physical distance between hands did not produce any change in the amount of interference. The results suggest that the focus of attention on the skin extends nearly undiminished across the fingers of one hand and is not dependent upon the physical distance between sites of stimulation.

Amplitude and period discrimination of haptic stimuli.

As part of a project to examine the ability of the hand to receive speech information, the present study examined subjects' ability to discriminate finger movements along the dimensions of amplitude and period (movement duration). The movements consisted of single-cycle, sinewave movements and single-cycle, cosine movements presented to the index finger. Difference thresholds were collected using an adaptive, two-interval, temporal forced-choice procedure. Amplitudes from 6 to 19 mm were examined, and the difference thresholds ranged from 10% to 18%. The thresholds were unaffected by the period of the movement. Periods from 3000 to 111 ms (0.33-9 Hz) were examined, and thresholds ranged from 6% to 16%. The thresholds were unaffected by the amplitude of the movement. Further measurements in which period was varied in the amplitude discrimination task and amplitude was varied in the period discrimination task indicated that subjects were not using peak velocity as the basis for discrimination. These measurements were collected using a display specifically designed for the examination of haptic stimulation and capable of presenting controlled patterns of movement and vibration to the fingers.

Donor selection process for allogeneic hematopoietic stem cell transplantation at the university hospital of Düsseldorf (1997-1998).

BACKGROUND: Transplantation of hematopoietic stem cells (HSC) is an effective treatment for a number of patients with life-threatening hematologic diseases. HSC donors can be found in the family of the patient or in registries of unrelated donors. In the present study, the search procedure within the last two years for an allogeneic HSC donor at the University of Düsseldorf is analyzed. PATIENTS AND METHODS: During 1997 and 1998, an early search for a related HSC donor in the family was performed for 70 high risk pediatric patients. During the same period, the search for an unrelated HSC donor for 116 adult and pediatric patients was performed. Low resolution HLA-A and -B typing was performed by serology in combination with DNA-typing. High resolution typing of HLA-A, -B and -C was carried out by DNA-sequencing. Low resolution HLA-DRB- und HLA-DQB1-typing was done solely by DNA-typing and high resolution typing of these genes was performed by DNA-sequencing. MAIN RESULTS: For 51 of 70 high risk pediatric patients (73%), no family donor could be defined, 16 of 70 patients (23%) had a genotypically identical sibling and for three of 70 patients (4%) an HLA-acceptable donor in the extended family could be identified. The search for an unrelated HSC donor was successful in 74% of the adult and pediatric patients lacking such a family donor. Most noteworthy, nearly all of the HLA-acceptable donors were identified from that group of donors in the registries, which were not only HLA-A and HLA-B, but also HLA-DR pretyped. CONCLUSION: These data show, that a growing number of pediatric patients with high risk leukemia need an unrelated HSC donor and that HLA-ABDR-pretyped registries present the optimal prerequisite to identify an HSC donor for most of the patients. In addition, 25% of the patients with no family or unrelated HSC donor require HSC transplants from alternative donors like unrelated Cord Blood (CB) from high quality cord blood banks.