Search PubMed⌕ Search

Biomedical subjects

J B Liu

Publications and source records attributed to J B Liu.

At least 37 records · Page 2Linked to original sources
PubMed2001

Experience with endoluminal ultrasonography in the urinary tract.

Ultrasonography has been an invaluable tool in the field of urology for its noninvasiveness, safety, and relatively low cost. However, examination of the ureter with ultrasound is difficult because of the distance of the transducer from the ureter and because of intervening structures such as nonconductive bowel gas. As smaller probes have become available, attempts have been made to apply them to endoluminal use. Endoluminal ultrasonography has been employed in urology to examine the proper placement of injected collagen, diagnose urethral diverticula, diagnose and stage upper tract transitional-cell carcinoma, locate crossing vessels to guide endopyelotomy, diagnose submucosal calculi, and examine the severity and length of ureteral strictures.

Collagen↗
PubMed2001

Local longitudinal muscle shortening of the human esophagus from high-frequency ultrasonography.

We analyzed local longitudinal shortening by combining concurrent ultrasonography and manometry with basic principles of mechanics. We applied the law of mass conservation to quantify local axial shortening of the esophageal wall from ultrasonically measured cross-sectional area concurrently with measured intraluminal pressure, from which correlations between local contraction of longitudinal and circular muscle are inferred. Two clear phases of local longitudinal shortening were observed during bolus transport. During luminal filling by bolus fluid, the muscle layer distends and the muscle thickness decreases in the absence of circular or longitudinal muscle contraction. This is followed by local contraction, first in longitudinal muscle, then in circular muscle. Maximal longitudinal shortening occurs nearly coincidently with peak intraluminal pressure. Longitudinal muscle contraction begins before and ends after circular muscle contraction. Larger longitudinal shortening is correlated with higher pressure amplitude, suggesting that circumferential contractile forces are enhanced by longitudinal muscle shortening. We conclude that a peristaltic wave of longitudinal muscle contraction envelops the wave of circular muscle contraction as it passes through the middle esophagus, with peak longitudinal contraction aligned with peak circular muscular contraction. Our results suggest that the coordination of the two waves may be a physiological response to the mechanical influence of longitudinal shortening, which increases contractile force while reducing average muscle fiber tension by increasing circular muscle fiber density locally near the bolus tail.

Deglutition↗
PubMed2001

Blood flow estimation with harmonic Flash Echo Imaging.

Blood volume flow estimation remains an important task for the functional evaluation of internal organs. In vitro and in vivo flow estimation has been carried out using Flash Echo Imaging in harmonic mode after the administration of microbubble-based ultrasound contrast agents. The in vitro flow volume rate correlated with the constant replenishment level but less so with the video intensity decay rate. The in vivo volume flow rates obtained in four dogs agreed well with CVI-Q (time domain correlation) based flow measurement. Our experimental results indicate that the volume flow rate can be accurately estimated in vitro and in vivo using harmonic Flash Echo imaging.

Animals↗
PubMed2001

The role of contrast-enhanced sonography for radiofrequency ablation of liver tumors.

OBJECTIVE: To assess the feasibility and usefulness of contrast-enhanced sonography for tumor detection and guidance of liver VX2 tumor ablation and to evaluate post radiofrequency ablation effectiveness. METHODS: VX2 tumors were implanted into the livers of 6 rabbits. Both conventional and harmonic gray scale and power Doppler imaging were performed with a commercially available scanner to evaluate the liver tumors before and after intravenous injection of a sonographic contrast agent before and after radiofrequency ablation. Contrast-enhanced imaging was used to detect the tumors before ablation, to guide needle insertion, and to measure the ablation sites after radiofrequency ablation. Pathologic examination was performed for comparison. RESULTS: Three tumors were seen without contrast enhancement, whereas 10 tumors (<1 cm) were detected with contrast enhancement. Intentionally, 2 tumors were completely ablated and 5 tumors were partially ablated. In 3 cases, incompletely ablated tumors could only be identified on contrast-enhanced Doppler imaging by enhancing the detection of residual tumor vascularity. There was excellent concordance between sonographic imaging and gross pathologic findings. CONCLUSIONS: Contrast-enhanced sonographic imaging appears useful for detection of liver tumors and for guiding and monitoring tumor ablation therapies.

Animals↗
PubMed2001

[PACS-based endoscope image acquisition workstation].

A practical PACS-based Endoscope Image Acquisition Workstation is here introduced. By a Multimedia Video Card, the endoscope video is digitized and captured dynamically or statically into computer. This workstation realizes a variety of functions such as the endoscope video's acquisition and display, as well as the editing, processing, managing, storage, printing, communication of related information. Together with other medical image workstation, it can make up the image sources of PACS for hospitals. In addition, it can also act as an independent endoscopy diagnostic system.

Computer Communication Networks↗
PubMed2000

Comparison of fundamental and wideband harmonic contrast imaging of liver tumors.

Wideband harmonic imaging (with phase inversion for improved tissue suppression) was compared to fundamental imaging in vivo. Four woodchucks with naturally occurring liver tumors were injected with Imagent (Alliance Pharmaceutical Corp., San Diego, CA). Randomized combinations of dose (0.05, 0.2 and 0.4 ml/kg) and acoustic output power (AO; 5, 25 and 63% or MI < or = 0.9) were imaged in gray scale using a Sonoline Elegra scanner (Siemens Medical Systems, Issaquah, WA). Tumor vascularity, conspicuity and contrast enhancement were rated by three independent observers. Imagent produced marked tumor enhancement and improved depiction of neovascularity at all dosages and AO settings in both modes. Tumor vascularity and enhancement correlated with mode, dose and AO (P < 0.002). Fundamental imaging produced more enhancement (P < 0.05), but tumor vascularity and conspicuity were best appreciated in harmonic mode (P < 0.05). Under the conditions studied here, the best approach was wideband harmonic imaging with 0.2 ml/kg of Imagent at an AO of 25%.

Analysis of Variance↗
PubMed2000

Three-dimensional esophageal varix model quantification of variceal volume by high-resolution endoluminal US.

BACKGROUND: The purpose of this study was to evaluate the accuracy and reproducibility of three-dimensional volume measurements by high-resolution endoluminal ultrasound in an esophageal varix model. METHODS: An esophageal varix model was made by filling three esophageal dilatation catheters with various volumes of water. A 20 MHz ultrasonography transducer was then pulled along the length of the catheters at a constant rate (1.25 mm/sec) while videotaping the procedure. Cross-sectional surface area measurements of each catheter were taken every second and the cross-sectional surface area was multiplied by the length of each catheter, as determined by high-resolution endoluminal ultrasound, to determine the volume in each catheter. Interobserver variability was calculated, and three-dimensional reconstruction was performed. RESULTS: The measured volumes corresponded closely with the actual volumes with an error ranging from 0% to 15.4%. The correlation between actual and measured volumes was r = 0.988. The interobserver variability ranged from r = 0.951 to r = 0.994. Actual esophageal varices were then imaged in a similar fashion to determine the feasibility of this method in patients with esophageal varices. CONCLUSIONS: High-resolution endoluminal ultrasound is an accurate and reproducible method of measuring volumes in an esophageal varix model and can be used in a clinical setting to determine variceal volume. Volume studies are now underway in human subjects.

Endosonography↗
PubMed2000

Enhanced detection of blood flow in the normal canine prostate using an ultrasound contrast agent.

RATIONALE AND OBJECTIVES: To evaluate the sonographic appearance of normal prostate vascularity in dogs before and after injection of a new ultrasound contrast agent, NC100100. METHODS: Thirty-five intravenous injections of NC100100, in doses ranging from 0.00625 to 0.05 microL microbubbles/kg, were administered to seven anesthetized mongrel male dogs. Transrectal color Doppler imaging and power Doppler imaging were used to perform the assessment. The visibility of the vascular pattern of the prostate was assessed, including dynamics of contrast inflow, blood flow symmetry, and duration times. RESULTS: Before contrast administration, the vascular pattern was poorly visualized in all cases. After contrast injection, the visibility of the vascular architecture improved significantly for both modalities. Independent of the imaging method used, higher doses tended to be more effective than lower doses. Contrast kinetics in the prostate vessels was demonstrated with a mean time from injection of the ultrasound contrast agent to enhancement of the Doppler signals in the subcapsular arteries (+/-1 SD) of 13+/-3 seconds, and the ultrasound contrast agent reached the central periurethral veins 3 to 6 seconds later. A spokelike radial pattern of internal prostatic vessels observed with enhanced ultrasound could also be seen on silicone microfil x-ray images. The Doppler enhancement persisted for a mean time ( +/-1 SD) of 904 seconds (approximately 15 minutes) +/- 225 seconds and tended to increase with increasing dose. CONCLUSIONS: NC100100 significantly improves the detection of blood flow in the normal canine prostate and allows more accurate depiction of the vascular architecture of the prostate.

Animals↗
PubMed2000

Gray scale second harmonic imaging of acoustic emission signals improves detection of liver tumors in rabbits.

This study evaluates a new reticuloendothelium specific sonographic contrast agent NC100100 (Sonazoid) for detection of liver VX-2 tumors in rabbits. Gray scale imaging of five groups of three rabbits, with hepatic VX-2 tumors implanted 7, 10, 12, 14, and 18 days previously, was performed prior to injection of Sonazoid (dosages, 0.01-0.5 ml/kg). Sonazoid produces induced acoustic emission after uptake in the liver. Therefore, harmonic gray scale images were obtained immediately after injection as well as delayed (by up to 2(1/2) h). Five rabbits (one from each group) also had angiography performed, while all animals were evaluated by pathologic examination. Non-contrast enhanced sonography detected 17 of 61 tumors (29%), as well as three false-positives, while the addition of Sonazoid detected 57 tumors (93%) and one false-positive (P<0.001). Acoustic emission made 2 x 2 mm tumors (invisible in conventional B-mode sonography) clearly perceivable in harmonic gray scale. In the subgroup that received angiography, 12 of 36 tumors (33%) were detected with conventional sonography compared to 22 tumors (61%) seen with angiography (P = 0.002). After injection of Sonazoid the ultrasonographic detection rate increased to 97% (35 of 36 tumors), which was a significant improvement over angiography (P = 0.00024). Improved detection of hepatic VX-2 tumors with second harmonic gray scale imaging of Sonazoid is possible because of this agent's acoustic emission capabilities.

Animals↗
PubMed2000

[Expression and characterization of t-PA in insect cells].

With the RT-PCR technique, human tissue-type plasminogen activator (t-PA) cDNA was amplified from human melanoma cells. The sequence was proved to be the same as those reported by foreign researchers. The t-PA cDNA containing whole reading frame was inserted into the transfer vector pBacPAK8. The constructed pBac-tPA and the linear BacPAK6 virus DNA were cotransfected with Tn-5B-1 insect cells by lipofectin-mediated transfection method. Eleven pure recombinant viruses were isolated by plaque assay, and one of them, nominated BactPA3, was selected by PCR identification and biological activity comparison. The t-PA activity expressed in serum-containing media reach the highest level at 72 h postinfection. The activity was 3.04 x 10(3) IU/ml, e.g. 1.8 x 10(4) IU/10(6) cells. The highest expression level in serum-free media was almost the same, but needed more time (at 132 h postinfection). SDS-PAGE fibrin autography showed that the molecular weight of the expressed t-PA was about 68 kDa. Its stimulation by fibrinogen, affinity with fibrin and inactivation in plasma were almost the same as the native t-PA purified from human melanoma cell culture. The half-life of t-PA expressed in serum-free media was seven minutes.

Animals↗
PubMed2000

[The development of a new version of multifunctional radioactive nuclide diagnostic instrument].

A new kind of multifunctional radioactive nuclide diagnostic instrument is described here, which can make noninvasive measurements on the metabolic functions of five most important inner organs which are kidney, liver, heart and thyroid. The design of the hardware and software of the new instrument embodies many advanced advantages such as multifunctional integration, high accuracy and high reliability, computer controlled, automatic data-processing, easy to use and manage, and so on. Applications show that this is an advanced and efficient radioactive medical diagnostic instrument.

Equipment Design↗
PubMed1999

High-resolution endoluminal sonography assessment of the hematocystic spots of esophageal varices.

BACKGROUND: Many variables are associated with an increased potential for esophageal variceal rupture, especially the presence of hematocystic spots and other red signs on upper endoscopy. The etiology of hematocystic spots is unknown. High-resolution endoluminal sonography has been shown to be an accurate and sensitive imaging modality for detection, as well as the qualitative and quantitative assessment of esophageal varices. Because the high-resolution endoluminal sonography transducer permits detailed resolution of submucosal structures thereby allowing more precise examination of the actual wall of the varix, we sought to image variceal hematocystic spots in an effort to better define their anatomy. METHODS: Simultaneous upper endoscopy and high-resolution endoluminal sonography were performed in 68 patients with cirrhosis. Endoscopy was performed as part of screening for varices during evaluation for liver transplantation or in patients with previous presumed variceal bleeding. On endoscopy and high-resolution endoluminal sonography, two independent reviewers identified the same 10 patients having esophageal varices with hematocystic spots. The patients who had bled from their varices had not received prior endoscopic treatment. RESULTS: Hematocystic spots as seen with high-resolution endoluminal sonography imaging appeared as saccular aneurysm like projections on the variceal surface in 6 of 10 patients. Four of six patients would later have recurrent bleeding; two of these patients were again noted to have hematocystic spots on endoscopy with a similar corresponding high-resolution endoluminal sonography appearance. Patients without hematocystic spots did not have similar high-resolution endoluminal sonography imaging. CONCLUSION: Aneurysm-like projections in the wall of varices may represent focal weaknesses of the variceal wall and thus play a role in the pathophysiology of esophageal variceal rupture. The present findings may help to explain why there is an increased risk of variceal hemorrhage associated with the presence of hematocystic spots on esophageal varices.

Endoscopy, Digestive System↗
PubMed1999

2-D and 3-D endoluminal ultrasound: vascular and nonvascular applications.

Endoluminal ultrasound using catheter-based transducers has been used for the evaluation of a wide range of abnormalities. To date, one of the most promising areas of clinical application is its use intravascularly for quantitating the degree of arterial stenosis and for monitoring the therapeutic effects of angioplasty in peripheral and coronary arteries. Uses in the gastrointestinal tract include quantification of the size and wall thickness of esophageal varices, distinguishing between various submucosal lesions and measuring the degree of fibrosis in scleroderma. In the genitourinary system, endoluminal ultrasound provides a unique intraoperative tool allowing the addition of a third dimension (depth) to endourological procedures. The indications for, and the use of, endoluminal ultrasound within the upper urinary tract can be expected to increase with more experience, and the procedure has become an important technique that yields information not available through other modalities. In the bronchotracheal tree, endoluminal ultrasound allows imaging and subsequent biopsy of lymph nodes and tumors that cannot be visualized at routine bronchoscopy. Three-dimensional (3-D) reconstruction of two-dimensional (2-D) ultrasound imaging is a new method in the evolution of intraluminal imaging. It provides information about spatial relationships of anatomic structures that cannot be evaluated using conventional 2-D imaging. Although still in its infancy, 3-D endoluminal ultrasound has the potential to become a dynamic tool in both the research and clinical areas.

Bronchial Diseases↗
PubMed1999

Effect of filling gases on the backscatter from contrast microbubbles: theory and in vivo measurements.

Two surfactant-based contrast agents, ST44 and ST68, were produced according to US Patent # 5,352,436 and filled with either air, C4F10 (perfluorobutane) or SF6 (sulfur hexaflouride). Ten rabbits received i.v. injections of each agent/gas combination with 5 repetitions of each dose (range: 0.005-0.13 mL/kg). A custom-made 10-MHz cuff transducer was placed around the surgically exposed distal aorta and audio Doppler signals were acquired in vivo. Quantitative in vivo dose responses were calculated off-line using spectral power analysis and compared to a theoretical model of microbubble dissolution and enhancement. For qualitative comparisons, 10 rabbits were imaged pre- and postcontrast administration (dose: 0.1 mL/kg) in gray-scale and colour. All agent/gas combinations produced marked Doppler enhancement with air bubbles enhancing least of all (p < 0.0001) and ST68-SF6 best of all (maximum: 27.6 +/- 2.04 dB; p < 0.012). There were no significant differences between other agent/gas combinations (0.30 < p < 0.70). Theoretical enhancement was within 1 order of magnitude of the experimental observations (i.e., deviations of up to 10 dB). The duration of contrast enhancement was 1-2 min for air-filled bubbles, 3-5 min for SF6-filled bubbles and more than 7 min for C4F10-filled bubbles. In conclusion, ST68-SF6 microbubbles produced most in vivo enhancement of the agent/gas combinations studied. Theory matched the measurements within an order of magnitude.

Animals↗
PubMed1999

Tissue-specific US contrast agent for evaluation of hepatic and splenic parenchyma.

PURPOSE: To evaluate the recently developed ultrasonographic (US) contrast agent SHU 563A, which is specifically taken up by the reticuloendothelial system (RES). MATERIALS AND METHODS: Color Doppler imaging (CDI) was performed in a gel phantom, with SHU 563A microbubbles in stationary suspension. CDI was performed in vivo in five woodchucks with natural hepatomas and in 12 rabbits before and after intravenous bolus injections of SHU 563A (0.16-0.48 mL/kg). After a 15-135-minute delay, the liver and spleen were scanned again, and the image findings were compared with pathologic analysis results. RESULTS: Phantom CDI demonstrated a random mosaic color pattern in spite of the lack of flow. This phenomenon, which is associated with bubble rupture, is termed induced acoustic emission. In vivo, delayed imaging demonstrated acoustic emission signals in normal parenchyma, whereas no mosaic color was seen in regions lacking reticuloendothelial cells (e.g., tumors). Four of 12 VX-2 tumors detected with pathologic analysis were detected with US alone; the remaining eight tumors were detected by using US with contrast agent (100%, P = .0078). Nine of 20 hepatomas were detected at baseline US, whereas 17 were detected after administration of SHU 563A (P = .0215). Acoustic emission enabled detection of hepatic tumors as small as 3 mm in diameter. CONCLUSION: CDI with SHU 563A demonstrates a random mosaic color pattern, even without flow. The characteristic appearance of acoustic emission signals provides a distinctive method of visualizing normal hepatic tissues and substantially improves the detectability of hepatic tumors.

Animals↗
PubMed1999

Subharmonic imaging with microbubble contrast agents: initial results.

The subharmonic emission from insonified contrast microbubbles was used to create a new imaging modality called Subharmonic Imaging. The subharmonic response of contrast microbubbles to ultrasound pulses was first investigated for determining adequate acoustic transmit parameters. Subharmonic A-lines and gray scale images were then obtained using a laboratory pulse-echo system in vitro and a modified ultrasound scanner in vivo. Excellent suppression of all backscattered signals other than from contrast microbubbles was achieved for subharmonic A-lines in vitro while further optimization is required for in vivo gray scale subharmonic images.

Animals↗
PubMed1999

Feasibility of three-dimensional intravascular ultrasonography: preliminary clinical studies.

The aim of this study was to demonstrate the clinical utility of reconstructed three-dimensional intravascular ultrasonography using a voxel-based volume rendering technique. Three-dimensional reconstruction of intravascular ultrasonographic data was performed in 12 patients with various vascular abnormalities during interventional radiology procedures. A stepping motor device was used to pull either a 12.5 or a 20 MHz catheter-based transducer through the lumen of a variety of vessels at a rate of 1.5 mm/s. Images were downloaded to a Life Imaging System for three-dimensional reconstruction. The value of three-dimensional ultrasonographic imaging was evaluated in comparison to conventional intravascular ultrasonography. A variety of abnormalities were demonstrated in reconstructed three-dimensional ultrasound imaging, including arterial atheroma and plaque, aneurysm and pseudoaneurysm, aortic dissection and stenosis (May-Thurner syndrome). The vascular branches and accessory vessels, as well as their relationships to each other, were easily demonstrated on three-dimensional imaging by selecting an appropriate angle, plane, and section of the image. The dimensions and shapes of the vascular lumen were determined in the longitudinal view. Three-dimensional information proved useful for determining the distribution and type of plaque in vessels. Reconstructed three-dimensional imaging allows for global evaluation of the dissection entry site, extent of the flap, and the false lumen of a pseudoaneurysm. Intravascular three-dimensional ultrasonography provides information complementary to that obtained with two-dimensional imaging. It supplies information about spatial relationships of anatomic structures that cannot be evaluated using conventional imaging methods.

Adult↗