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D L Liu

Publications and source records attributed to D L Liu.

At least 37 records · Page 2Linked to original sources
PubMed1997

Harmonic amplitude distribution in a wideband ultrasonic wavefront after propagation through human abdominal wall and breast specimens.

The amplitude characteristics of ultrasonic wavefront distortion produced by transmission through the abdominal wall and breast is described. Ultrasonic pulses were recorded in a two-dimensional aperture after transmission through specimens of abdominal wall or breast. After the pulse arrival times were corrected for geometric path differences, the pulses were temporally Fourier transformed and two-dimensional maps of harmonic amplitudes in the measurement aperture were computed. The results indicate that, as the temporal frequency increases, the fluctuation in harmonic amplitudes increases but the spatial scale of the fluctuation decreases. The normalized second-order and third-order moments of the amplitude distribution also increase with temporal frequency. The wide range variation of these distribution characteristics could not be covered by the Rayleigh, Rician, or K-distribution because of their limited flexibility. However, the Weibull distribution and especially the generalized K-distribution provide better fits to the data. In the fit of the generalized K-distribution, a decrease of its parameter alpha with increasing temporal frequency was observed, as predicted by analysis based on a phase screen model.

Abdomen↗
PubMed1997

[Epidemiological analysis on the rising of brucellosis prevalence in the area already under controlled].

An epidemiological analysis was made on the outbreak of brucellosis in Sui-de County, Shaanxi Province in 1995-1996. Result showed that it was one of the most serious brucellosis outbreaks since 1986 when national brucellosis under controlled critiria had been met in the province, and the number of cases was continuously spreading and growing. The incidence was up to 84.8 per 10(5) and the prevalence rate reached 17.5 percent. Patients had typical symptoms with bad conditions. Most all the cases were those who had vocations such as shepherds, etc. Patients' antibody titers were very high with the highest one approached 1:25,600. Two strains of B. melitensis, type III were isolated from the blood of patients.

Adolescent↗
PubMed1996

Repeated immunotherapy using intratumoural injection with recombinant interleukin-2 and tumour-infiltrating lymphocytes inhibits growth of breast cancer and induces apoptosis of tumour cells.

This study tested the effect of repeated intratumoural injection with recombinant interleukin-2 (rIL-2) and tumour-infiltrating lymphocytes (TILs) on inhibition of growth of breast cancer and on induction of apoptosis of tumour cells. The tumour cell line LDLX43 was used to induce breast cancer in Wistar rats. Group I (10 rats) was the control. Group II (12 rats) received repeated intratumoural injection with rIL-2 and TILs. rIL-2 at the dose of 5 x 10(5) IU/day was given for 7 days, and 1 x 10(7) TILs were injected on the second day of each rIL-2 therapy, for a treatment session. Overall, two treatment sessions of immunotherapy with rIL-2 and TILs were given in all treated animals. Rapid increased tumour volume was found in the control group. In the treated group the total response rate was 42%, of which 25% tumours showed partial regression and 17% tumours reached complete remission where infiltration of plenty of T lymphocytes was detected, indicating that T cell-mediated antitumour immunity is primarily responsible for tumour rejection. Further investigation showed the repeated immunotherapy using intratumoural injection with rIL-2 and TILs could induce the development of apoptosis of breast cancer cells.

Animals↗
PubMed1996

Multiple-system organ damage resulting from prolonged hepatic inflow interruption.

BACKGROUND: It has been reported that patients undergoing major hepatectomy tolerated 90 and 127 minutes of continuous hepatic inflow interruption with no evidence of permanent damage to the liver. We questioned the safety and feasibility of the interruption beyond 90 minutes in normothermic human beings. We also postulated that, besides injury to the liver per se, extended continuous hepatic inflow interruption would cause extrahepatic multiple-system organ damage in subjects exposed to continuous hepatic inflow interruption for 90 or 120 minutes. DESIGN: Fifty Sprague-Dawley rats were divided into three groups. Group 1 served as controls that had only laparotomy. Group 2 underwent continuous hepatic inflow interruption for 90 minutes, and group 3 was subjected to continuous hepatic inflow interruption for 120 minutes. Scanning electron microscopy and transmission electron microscopy were used to evaluate ultrastructural alterations in the liver, lung, heart, and intestine. SETTING: Lund (Sweden) University Hospital and Top Cancer Institute, Lund. INTERVENTIONS: Intraoperative and postoperative infusion and blood transfusion were given in all experimental animals. MAIN OUTCOME MEASURES: Animal survival and manifestations of multiple-system organ failure. RESULTS: In rats with continuous hepatic inflow interruption for 90 or 120 minutes, scanning electron microscopy showed a necrotic surface of the liver cells together with fibrin exudation. Hepatic sinusoids and intrahepatic nerves also had severe injury. Destruction of pulmonary structures and breakdown of microcirculation in the lung were characterized by thinned and ruptured walls of alveoli and a greatly decreased number of capillaries in the damaged alveolar wall. Transmission electron microscopy showed four types of ultrastructural changes, ie, necrosis of epithelial cells, extremely swollen mitochondria in intestinal cells, death of mucosal cells, and increased permeability of vessels in the injured intestine. The affected heart manifested highly enlarged mitochondria in myocardial cells, thickened vascular walls, and scattered necrotic lesions in myocardial tissue. CONCLUSIONS: Multiple-system organ failure resulting from ischemia-reperfusion injury and obstacle of portal hemodynamics in a subject subjected to an extended continuous hepatic inflow interruption is an unrecognized new disorder that may cause a high mortality rate. Our preliminary results indicated that animals subjected to continuous hepatic inflow interruption for 90 or 120 minutes developed various injuries to the liver, lung, heart, and gut. Therefore, we believe that continuous hepatic inflow interruption exceeding 90 minutes could also be hazardous in human beings.

Animals↗
PubMed1996

Anatomy of vasculature of 850 spleen specimens and its application in partial splenectomy.

BACKGROUND: Anatomic knowledge of vasculature of the splenic lobe and segment is of great clinical significance in partial resections and transplantation of the spleen. METHODS: The methods of two-colored corrosion casting, roentgenography, and anatomic dissection were used to evaluate the vasculature of the splenic hilum and intraspleen. On this basis splenic lobectomy and segmentectomy were performed on 42 patients with traumatized spleens. RESULTS: In the observation of 850 spleen specimens the spleen showed a single lobar artery in 7 cases (0.8%), two lobar arteries in 730 cases (86%), three lobar arteries in 104 cases (12.2%), and multiple lobar arteries (i.e., more than three lobar arteries) in 9 cases (1%). In a subgroup of 276 specimens 17%, 53%, 24%, 4%, 1%, and 1% of spleen specimens had three, four, five, six, seven, and eight segmental arteries, respectively. The result from a subgroup of 280 specimens indicated that mean percentages of the existence of the superior and inferior polar arteries and of the coexistence of both polar arteries were 31.3%, 38.8%, and 13.3%, respectively. Relative avascular planes between segments or lobes were seen. Basic steps of splenic lobectomy or segmentectomy include mobilization of the injured spleen, ligation of vessels in the lobe or segment, transection of the splenic parenchyma, and sutures of the cut surface of the remaining spleen. The postoperative courses of all 42 patients undergoing partial splenectomy were uneventful. No postoperative bleeding and necrosis of the remaining spleen or infectious complications were registered. CONCLUSIONS: Anatomically the spleen is defined with two primary lobes (the superior lobe and inferior lobe), one accessory lobe, and three to five segments. This new classification facilitates surgeons to perform partial resections of the spleen and allotransplantation of the hemispleen from a living related donor in human beings.

Adolescent↗
PubMed1996

Two isozymes of P450nor of Cylindrocarpon tonkinense: molecular cloning of the cDNAs and genes, expressions in the yeast, and the putative NAD(P)H-binding site.

The cDNAs and genes for two isozymes of cytochrome P450nor of the fungus Cylindrocarpon tonkinense, P450nor1 and P450nor2, were cloned and sequenced. Their deduced amino acid sequences respectively showed 83 and 70% identity to that of P450nor of Fusarium oxysporum, and 69% identity to each other. The genes for P450nor1 and P450nor2 were termed, respectively, CYP 55A2 and CYP 55A3. The cDNA for P450nor1 contained a targeting-like presequence upstream the N-terminus of mature protein whereas that for P450nor2 did not, suggesting their different intracellular localisations. We also succeeded in expressing these P450nor isoforms in the host-vector system of the yeast Saccharomyces cerevisiae. We purified one of the recombinant proteins, P450nor of F oxysporum. Little difference could be observed between the native and recombinant proteins in catalytic and spectroscopic properties. We constructed chimeric proteins of P450nor of F oxysporum and P450nor2 which are different in their specificity against the electron donors: reduced pyridine nucleotides. The specificity of chimeric proteins against NADH/NADPH showed that the specificity is determined by the N-terminal half of protein. We found a consensus amino acid sequence between three isoforms of P450nor, A-X-G-X-X-A, similar to the NAD-binding motif G-X-G-X-X-G/A in the region that corresponds to the B'-helix in P450cam.

Amino Acid Sequence↗
PubMed1996

Photodynamic therapy using intravenous delta-aminolaevulinic acid-induced protoporphyrin IX sensitisation in experimental hepatic tumours in rats.

The efficacy of photodynamic therapy (PDT) using delta-aminolaevulinic acid (ALA)-induced protoporphyrin IX (PpIX) sensitisation and laser light at 635 nm was investigated in the treatment of experimental hepatic tumours. The model of liver tumours was induced either by local inoculation or by administration of tumour cells through the portal vein in rats. ALA at a dose of 60 mg kg(-1) b.w. was intravenously administered 60 min before PDT. PpIX accumulation in tumour, normal liver and abdominal wall muscle was detected by means of laser-induced fluorescence (LIF). Laser Doppler imaging (LDI) was used to determine changes in the superficial blood flow in connection with PDT. Histopathological examinations were performed to evaluate the PDT effects on the tumour and the surrounding liver tissue, including pathological features in the microvascular system. The accumulation of PpIX, as monitored by LIF, showed high fluorescence intensities at about 635 nm in both the hepatic tumour tissue and normal liver and low values in the abdominal wall. LDI demonstrated that the blood flow in the treated tumour and its surrounding normal liver tissue decreased immediately after the PDT, indicating an effect on the vascular system. A large number of thrombi in the irradiated tumour were found microscopically 3 h after the PDT. The tumour growth rate showed a marked decrease when evaluated 3 and 6 days after the treatment. These results show that the ALA-PDT is effective in the inhibition of growth of experimental hepatic tumours.

Aminolevulinic Acid↗
PubMed1995

Immunotherapy in liver tumors: III. A new experimental model of metastatic liver tumors from colorectal carcinoma for cytokine therapy.

A new model of metastatic liver tumors in Wistar/Furth rats is introduced. A colorectal adenocarcinoma cell line (LDLX40) induced by 1,2-dimethylhydrazine was injected through one of the branches of the ileal mesenteric vein to develop metastatic liver tumors in rats. On day 30 after the inoculation of tumor cells, micrometastases were detected under microscopy in all animals that received tumor inoculation. Macrometastases in 87.7% of animals were found by either the tumor staining test or ultrasonography. No extrahepatic tumor developed in this tumor model. To observe the effects of different treatment strategies on metastatic liver tumors, 35 animals were randomly divided into four groups. Group I served as control. Group II underwent hepatic artery ligation (HAL). Group III received intraportal administration of recombinant interleukin-2 (rIL-2) and interferon-alpha (IFN-alpha). Group IV had intraportal medication of rIL-2 and IFN-alpha + HAL (the IIH protocol). Results indicated that rapid tumor growth was seen in the control tumors. HAL produced little response to metastatic liver tumors as compared to the control group (P > 0.05). The combined application of rIL-2 and IFN-alpha showed an improved result, with 22% of tumor growth inhibition or regression (P < 0.05 compared to the control group). Twenty-eight percent of tumor growth restraint or regression was found in the group treated with the IIH protocol (P < 0.05 compared to the control group). We conclude that this new experimental model of metastatic liver tumors is reproducible, and that the IIH protocol is effective in the treatment of metastatic liver tumors in rats. These beneficial effects from the IIH protocol may be introduced into patients with metastatic liver tumors.

Adenocarcinoma↗
PubMed1995

Allotransplantation of whole spleen in patients with hepatic malignant tumors or hemophilia A. Operative technique and preliminary results.

BACKGROUND: It has been reported that the spleen performs a vital function in the fight against malignant tumors. The spleen is the primary producer of tuftsin, which can directly or indirectly kill tumor cells or inhibit their growth. The spleen is also believed to produce coagulating factor VIII. Therefore, allotransplantation of the spleen can be used in the treatment of patients with malignant tumors and hemophilia A. DESIGN: Heterotopic allotransplantation of whole spleen was performed in six patients with advanced hepatocellular carcinoma and hemophilia A. An adjuvant immunotherapy with interferon alfa was simultaneously administered in the patients with liver cancer. SETTING: Tongji Hospital, Tongji Medical University, Wuhan, China. RESULTS: Among six cases of allografting of whole spleen, five grafts were successful; one failed because of torsion of the splenic hilum. Three patients with hepatocellular carcinoma survived 9, 11, and 5 months after transplantation. Marked shrinkage of hepatic tumors and reduced serum alpha-fetoprotein levels were observed in these patients. On 5-year follow-up, three patients with hemophilia who had undergone splenic allografts were alive, and two had experienced substantial clinical improvement. In these two patients, when the grafts were functioning well and the recipients were free of acute rejection or graft-vs-host reaction, the mean plasma factor VIII activity remained between 30% and 36%, with peak factor VIII activities of 53.7% and 66.6%. We also evaluate operative technique and posttransplantation complications. CONCLUSION: Our results strongly imply that the spleen is one of the primary sites of synthesis of factor VIII and that the spleen has an inherent ability to fight malignant diseases. Allografting of whole spleen may be a promising technique for the treatment of patients with unresectable hepatocellular carcinoma and severe hemophilia A.

Adult↗
PubMed1995

Intra-operative laser-induced photodynamic therapy in the treatment of experimental hepatic tumours.

OBJECTIVE: To examine the effect of photodynamic therapy (PDT) on experimental liver tumours in rats. DESIGN: An experimental liver tumour model was used. Each of a group of rats had two tumours simultaneously inoculated into its liver. The tumour located in the left hepatic lobe was used for PDT, and the other one, in the median lobe, as a control. The haem precursor delta-amino laevulinic acid (ALA), at a dose of 30 mg/kg body weight, was injected 60 min before laser irradiation. Rats in group I received ALA through a femoral vein. Those in group II received ALA through the portal vein. Group III had an injection of ALA solution through the portal vein plus hepatic inflow occlusion. Three and 6 days after the treatment, the rats were killed, and the tumours were measured, and ultrastructural changes were examined using scanning electron microscopy. SETTING: Lund University Medical Laser Centre, Lund, Sweden. RESULTS: The mean tumour volume of the treated tumours increased by factors of 1.9, 1.5 and 1.7 in groups I, II and III, respectively, compared with the pretreatment baseline value. However, the mean tumour volume in the control tumours increased by factors of 9.5, 4.3 and 4.8 in the respective groups. Under the light microscope, marked necrosis of the treated tumour and the surrounding liver tissue was observed. Scanning electron microscopy revealed heavy damage to the cells and vessels in the treated tumour. CONCLUSION: PDT with ALA is an effective treatment modality for rat liver tumours.

Aminolevulinic Acid↗
PubMed1995

Measurement and correction of ultrasonic pulse distortion produced by the human breast.

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.

Adolescent↗
PubMed1995

Sexual dysfunction in China.

In recent years, many sexual dysfunction cases cropped up in various parts of China. The number of hospital with sexual dysfunction clinics has also increased. They are concentrated more in the big or coastal cities. In these clinics, compared with those of the west, there is a greater proportion of retarded ejaculation cases and a lower proportion of female patients. Deficient sexual knowledge is the commonest cause of sexual dysfunction especially with respect to the sexual problems of the aged. The treatment approaches used by these clinics combine psychotherapy, behavioural therapy, medication and the application of physical aids, and are in line with modern international trends. However, these clinics are only in their infancy and still face many obstacles. The government is still quite stringent on the control of drugs for treatment of sexual dysfunctions and also sees many sex aids as obscene. However, in view of the rapid development, the Chinese readiness to accept new ideas, the diligence of the Chinese medical professionals and the establishment of the Chinese Sexology Association in 1994, it is hoped that China will soon become one of the more advanced countries in Asia for the treatment of sexual dysfunctions.

China↗
PubMed1994

Immunotherapy in liver tumours: I. Combined administration of recombinant interleukin-2 (IL-2) and interferon-alpha through the subcutaneous transposed spleen prolongs the half-life of IL-2 in vivo and enhances antitumor effects.

Two modifications in this study, including the use of subcutaneous transposed spleen (STS) as a port for administration of recombinant interleukin-2 (IL-2) and interferon-alpha (IFN-alpha), and the mixture of IL-2 and IFN-alpha with degradable starch microspheres (IIM), for the treatment of rat liver tumor are introduced. Group I is the control. Group II received the IIM schedule through the STS. Group III and group IV received IL-2 and IFN-alpha, diluted with normal saline and injected through the STS or a peripheral vein. The comparative studies indicated that the best result was seen in group II where the elevated concentration of IL-2 in portal blood and massive tumor necrosis with lysis were observed. Inhibitions of tumor growth of 33%, 20% and 13% in group II, III, and IV, respectively, were observed. We conclude that administration of the IIM schedule through the STS is an effective method for the treatment of liver tumor in rats.

Animals↗
PubMed1994

Immunotherapy in liver tumors: II. Intratumoral injection with activated tumor-infiltrating lymphocytes, intrasplenic administration of recombinant interleukin-2 and interferon alpha causes tumor regression and lysis.

This study tested the effect of intratumoral injection with activated tumor-infiltrating lymphocytes (TIL), and simultaneous administration of recombinant interleukin-2 (rIL-2) and interferon alpha (IFN-alpha) (LII protocol), on mouse liver tumor. Group I (n = 10) served as the controls. Group II (n = 17) received rIL-2 + IFN-alpha schedule. Group III (n = 20) received the LII protocol. A total of 5 x 10(6) of TIL were injected into 4 sites of a tumor in a single treatment. rIL-2 (1 x 10(6) IU) on the first day and IFN-alpha (1 x 10(5) IU) on the second day were alternately given with a total of 10 treatment doses that were completed in 20 days. Tumor remission or regression rates of 29% and 40% were obtained in groups II and III, respectively, but no remission was obtained in the controls. A large number of TIL were also observed in the tumors treated with the LII protocol. Making comparisons between the control group and IL-2 + IFN-alpha schedule, and the control group and LII protocol, the ratios of cytolytic activity of TIL in vitro were 0:32 and 0:57, respectively. We conclude that the LII protocol appears to be more effective in the treatment of mouse liver tumor than the IL-2 + IFN-alpha schedule, and that it may be a new promise for the treatment of patients with liver malignancies.

Animals↗
PubMed1994

Measurements of ultrasonic pulse arrival time and energy level variations produced by propagation through abdominal wall.

Ultrasonic pulse arrival time and energy level variations introduced by propagation through human abdominal wall specimens have been measured. A hemispheric transducer transmitted an ultrasonic pulse that was detected by a linear array transducer after propagation through an abdominal wall section. The array was translated in the elevation direction to collect data over a two-dimensional aperture. Differences in arrival time and energy level between the measured waveforms and calculated references that account for geometric delay and spreading were found. Plots of waveforms compensated for geometric path, maps of time delay differences and energy level fluctuations, and statistics derived from these for water paths and tissue paths characterize the measurement system and describe the time delay differences and energy level fluctuations caused by 14 different human abdominal wall specimens. Repeated measurements using the same specimens show that individual tissue path measurements are reproducible, the results depend on specimen position, and frozen storage of a specimen for three months does not appear to alter the time delay differences and energy level fluctuations produced by the specimen. Comparison of measurements at room and body temperature indicates that appreciably higher time delay differences occur at body temperature while energy level fluctuations and time delay difference patterns are less affected. For the 14 different abdominal wall specimens, the rms time delay differences and energy level fluctuations have average values of 43.0 ns and 3.30 dB, respectively, and the associated correlation lengths of the time delay differences and energy level fluctuations are 7.90 and 2.28 mm, respectively. The spatial patterns of time delay difference and energy level fluctuation in the reception plane appear largely uncorrelated, although some background variations in energy level fluctuation are similar to features in time delay difference maps. The results provide important new information about the variety and range of ultrasonic wave front arrival and energy variations caused by transmission through abdominal wall.

Abdominal Muscles↗
PubMed1994

Time-shift compensation of ultrasonic pulse focus degradation using least-mean-square error estimates of arrival time.

Focus degradation produced by abdominal wall has been compensated using a least-mean-square error estimate of arrival time. The compensation was performed on data from measurements of ultrasonic pulses from a curved transducer that emits a hemispheric wave and simulates a point source. The pulse waveforms were measured in a two-dimensional aperture after propagation through a water path and after propagation through 14 different specimens of human abdominal wall. Time histories of the virtual point source were reconstructed by removing the time delays produced by geometric path differences and also removing time shifts produced by propagation inhomogeneities in the case of compensation, finding the complex amplitudes of the Fourier harmonics across the aperture, calculating the Fraunhofer diffraction pattern of each harmonic, and summing the patterns. This process used a least-mean-square error solution for the relative delay expressed in terms of the arrival time differences between neighboring points and included an algorithm to determine arrival time differences when correlation based estimates were unsatisfactory due to dissimilarity of neighboring waveforms. Comparisons of reconstructed time histories in the image plane show that the -10-dB effective radius of the focus for reception through abdominal wall without compensation for inhomogeneities averaged 48% greater than the corresponding average effective radius for ideal waveforms, while time-shift compensation reduced the average -10-dB effective radius to a value that is only 4% greater than for reception of ideal waveforms. The comparisons also indicate that the average ratio of energy outside an ellipsoid defined by the -10-dB effective widths to the energy inside that ellipsoid is 1.81 for uncompensated tissue path data and that time-shift compensation reduced this average to 0.93, while the corresponding average for ideal waveforms was found to be 0.35. These results show that time-shift compensation yields a significant improvement over the uncompensated case although other factors must be considered to achieve an ideal diffraction limited focus.

Abdominal Muscles↗
PubMed1994

Correction of ultrasonic wavefront distortion using backpropagation and a reference waveform method for time-shift compensation.

A model is introduced to describe ultrasonic pulse amplitude and shape distortion as well as arrival time fluctuation produced by propagation through specimens of human abdominal wall. In the model, amplitude and shape distortion develops as the wavefront propagates in a uniform medium after passing through a phase screen that only causes time shifts. This distortion is compensated by a backpropagation of the wavefront using the angular spectrum method. The compensation employed waveforms emitted by a pointlike source and measured after propagation through the tissue. The waveforms were first corrected for geometric path and then were backpropagated over a sequence of increasing distances. At each distance, a waveform similarity factor was calculated to find the backpropagation distance at which the waveforms were most similar. A new method was devised to estimate pulse arrival time for geometric correction as well as to perform time-shift compensation. The method adaptively derives a reference waveform that is then cross correlated with all the waveforms in the aperture to obtain a surface of arrival times. The surface was smoothed iteratively to remove outlying points due to waveform distortion. The mean (+/- s.d.) of the waveform similarity factor for 14 specimens was found to be 0.938 (+/- 0.025) initially. After backpropagation of waveforms to the distance of maximum waveform similarity for each specimen, the waveform similarity factor improved to 0.967 (+/- 0.015). The corresponding energy level fluctuation in the wavefront was 4.2 (+/- 0.4) dB initially and became 3.3 (+/- 0.3) dB after backpropagation. For wavefronts focused at 180 mm, the -30 dB mean (+/- s.d.) effective radius of the focus was 4.2 (+/- 1.2) mm with time-shift compensation in the aperture and became 2.5 (+/- 0.5) mm with backpropagation followed by time-shift compensation. These results indicate that a phase screen placed some distance away from the aperture is an improved model for the description of wavefront distortion produced by human abdominal wall and that wavefront backpropagation followed by time-shift estimation and compensation is an effective method to compensate for such distortion.

Abdominal Muscles↗