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Biomedical subjects

B Bai

Publications and source records attributed to B Bai.

At least 19 recordsLinked to original sources
PubMed2002

Model-based normalization for iterative 3D PET image reconstruction.

We describe a method for normalization in 3D PET for use with maximum a posteriori (MAP) or other iterative model-based image reconstruction methods. This approach is an extension of previous factored normalization methods in which we include separate factors for detector sensitivity, geometric response, block effects and deadtime. Since our MAP reconstruction approach already models some of the geometric factors in the forward projection, the normalization factors must be modified to account only for effects not already included in the model. We describe a maximum likelihood approach to joint estimation of the count-rate independent normalization factors, which we apply to data from a uniform cylindrical source. We then compute block-wise and block-profile deadtime correction factors using singles and coincidence data, respectively, from a multiframe cylindrical source. We have applied this method for reconstruction of data from the Concorde microPET P4 scanner. Quantitative evaluation of this method using well-counter measurements of activity in a multicompartment phantom compares favourably with normalization based directly on cylindrical source measurements.

Algorithms↗
PubMed2001

Augmentation of anterior vertebral body screw fixation by an injectable, biodegradable calcium phosphate bone substitute.

STUDY DESIGN: A biomechanical study to evaluate the effects of a biodegradable calcium phosphate (Ca-P) bone substitute on the fixation strength and bending rigidity of vertebral body screws. OBJECTIVES: To determine if an injectable, biodegradable Ca-P bone substitute provides significant augmentation of anterior vertebral screw fixation in the osteoporotic spine. SUMMARY OF BACKGROUND DATA: Polymethylmethacrylate (PMMA) augmented screws have been used clinically; however, there is concern about thermal damage to the neural elements during polymerization of the PMMA as well as its negative effects on bone remodeling. Injectable, biodegradable Ca-P bone substitutes have shown enhanced fixation of pedicle screws. METHODS: Sixteen fresh cadaveric thoracolumbar vertebrae were randomly divided into two groups: control (no augmentation) (n = 8) and Ca-P bone substitute augmentation (n = 8) groups. Bone-screw fixation rigidity in bending was determined initially and after 10(5) cycles, followed by pullout testing of the screw to failure to determine pullout strength and stiffness. RESULTS: The bone-screw bending rigidity for the Ca-P bone substitute group was significantly greater than the control group, initially (58%) and after cyclic loading (125%). The pullout strength for Ca-P bone substitute group (1848 +/- 166 N) was significantly greater than the control group (665 +/- 92 N) (P < 0.01). Stiffness in pullout for the Ca-P bone substitute groups (399 +/- 69 N/mm) was significantly higher than the control group (210 +/- 51 N/mm) (P < 0.01). CONCLUSION: This study demonstrated that augmentation of anterior vertebral body screw fixation with a biodegradable Ca-P bone substitute is a potential alternative to the use of PMMA cement.

Absorbable Implants↗
PubMed2001

The effect of stem modularity and mode of fixation on tibial component stability in revision total knee arthroplasty.

The effect of stem length, diameter, and mode of fixation on the motion and stress transfer of a cemented tibial tray were evaluated for in 12 cadaver knees. There was a significant decrease in motion of the tibial tray with increasing press-fit stem length (75-150 mm) and increasing stem diameter (10-14 mm). Cemented tibial stems showed significantly less tray motion than uncemented stems. The short cemented stems produced tray stability equivalent to long press-fit stems. Although there was a trend for increased proximal tibial stress shielding with the use of cement and longer, wider stems, the trend was not statistically significant. Modular, press-fit stems can achieve tray stability similar to a smaller cemented stem and can avoid the potential problems with cement.

Adult↗
PubMed2001

Effect of articular step-off and meniscectomy on joint alignment and contact pressures for fractures of the lateral tibial plateau.

OBJECTIVES: To determine the effects of intraarticular step-off and lateral meniscectomy on the alignment of the articular axis, contact area, and pressures for lateral tibial plateau fractures. DESIGN: Biomechanical cadaver study. INTERVENTION: Six fresh cadaveric knees were used. A simulated split fracture of the lateral tibial plateau was reproducibly created by osteotomies, and articular step-offs of zero, one, two, four, and six millimeters were achieved by using support shims. The knee was loaded with 500 newtons in 0 degrees and 350 newtons in 30 degrees of flexion. A digital camera determined changes in the alignment of the articular axis, and F-Scan sensors were inserted into the medial and lateral joint compartments to determine the pressures and pressure distributions. MAIN OUTCOME MEASUREMENT: Each specimen was tested at step-offs of zero, one, two, four, and six millimeters, with the presence or absence of the lateral meniscus. The changes in alignment of the articular axis, the contact area, and the average and maximum contact pressures for each condyle were obtained. RESULTS: Increased articular step-off heights progressively increased valgus angulation and average and maximum contact pressures and progressively decreased contact areas in lateral compartment. At a six-millimeter step-off with 0 degrees of flexion, the valgus angle increased an average of 7.6 degrees, and average contact pressures and maximum contact pressures increased an average of 208 percent and 97 percent, respectively, and contact area decreased an average of 33 percent (p < 0.05). Meniscectomy increased valgus angles by an average of 38 percent and contact pressures by an average of 45 percent and decreased contact areas by 26 percent in the lateral compartment at the same articular step-off heights (p < 0.05). CONCLUSION: The results of this study show the importance of decreasing articular step-off heights in treating lateral tibial plateau split fractures, particularly if a meniscectomy is performed.

Adult↗
PubMed2001

[Studies on insulin-like growth factor I receptor in fetal rats with intrauterine growth retardation].

OBJECTIVE: This study was conducted to detect the localization of the insulin-like growth factor I receptor (IGF-I R) in the cells and tissues in the rats with intrauterine growth retardation (IUGR) and normal growth rats. METHODS: 21 pregnant rats were randomly divided into the experimental group (IUGR) (n = 12) and the control group (n = 9). Animal models for IUGR were established by clamping the uterine vasculature of pregnant rats for 20 minutes on day 14 of gestation. The control group rats were subjected to Sham-operation. On day 22 of gestation, fetal rats were delivered by cesarean section. Immunohistochemical assay was performed to detect the IGF-I R expression on liver and lung using specific polyclonal antibodies to rat IGF-I R. RESULTS: In the experimental group, the IUGR rats' body weight, height, and the weight of their liver, lung and the placenta were significantly lower than those in the control group. In the IUGR rats' liver, the area ratio of IGF-I R was increased and the average gray level was decreased, compared with those in the control group. In the IUGR rats' lung, the area ratio of IGF-I R was increased, compared with that in the control group, but no difference of average gray level was observed between the two groups. CONCLUSION: The increased expression of IGF-I R in rats with IUGR, may be due to the decrease of IGF-I and the compensative mechanism of the body.

Animals↗
PubMed2001

[The relationships of the serum concentrations of insulin-like growth factors in fetal rats with intrauterine growth retardation].

OBJECTIVE: To observe the alterations of serum insulin-like growth factor-I,-II (IGF-I, IGF-II) in rat fetus and to investigate the relationship of serum IGFs with intrauterine growth retardation (IUGR). METHODS: 21 pregnant SD rats were randomly divided into control group (n = 9) and experimental group (IUGR group, n = 12). On day 14 of gestation, the bilateral uterine arteries and veins of experimental group were clamped for 20 minutes to build the rat IUGR models and sham surgeries were performed on control group. Fetal serum concentrations of IGFs, birth weight, the length and weight of fetal liver, lung, brain and placenta of all rats in the two groups were measured and compared. RESULTS: The serum concentrations of IGF-I,-II of IUGR group were 117.92 +/- 26.58 ng/ml and 223.19 +/- 33.35 ng/ml, respectively, which were significantly lower than those of control group (234.43 +/- 70.65 ng/ml and 397.74 +/- 23.69 ng/ml, respectively, P < 0.01). Likewise, birth weight, the length and weight of liver, lung, brain and placenta in IUGR group were significantly lower than those in control group (P < 0.05). CONCLUSION: The decrease of fetal serum concentrations of IGF-I,-II may be one of the internal factors contributing to fetal IUGR, and IGFs may play an important role in fetal growth.

Animals↗
PubMed2000

Effect of posterior cut angle on tibial component loading.

Although clinical studies have shown that posterior cut angle affects tibial component stability, biomechanical studies are lacking. Fifteen Sawbones tibiae were divided into 5 groups and prepared with 0 degrees , 3 degrees, 6 degrees, 9 degrees, and -5 degrees tibial surface cuts, and a tibial component was implanted with cement. Using a standard and then a highly congruent polyethylene insert, the knee was loaded at 0 degrees and 30 degrees of flexion. There were statistically significant increases in anterior micromotion of the standard polyethylene component for each increase in posterior slope cut angle, which increased for the highly congruent polyethylene component. The anterior slope cut (-5 degrees) led to significant posterior micromotion of the tibial polyethylene component. Increased posterior slope cut angle significantly decreased tibial anterior compressive strains and significantly increased tibial posterior compressive strains. The highly congruent insert significantly increased this posterior strain. The results indicate that cutting the articular surface of the tibia at a 0 degrees or 3 degrees posterior slope provides the greatest tibial component stability.

Arthroplasty, Replacement, Knee↗
PubMed2000

A biomechanical comparison of Schuhli nuts or cement augmented screws for plating of humeral fractures.

Schuhli locking nuts can be used in poor quality cortical bone to enhance fixation stability as an alternative to cement augmented screws. This study compared the fixation strength and stability of plate constructs using Schuhli locking nuts with standard screws and cement augmented screws for fixation of simulated humeral shaft fractures in a test model with osteoporosis. The constructs were tested in axial compression, 4-point bending, and torsion to determine fixation stability. The humeri were cycled in torsion (4.5 Nm) for 1000 cycles to simulate upper extremity use during the early postoperative period and retested for stability. The Schuhli locking nuts and cement augmented screws had significantly greater fixation stability than the standard screws before (range, 6-14 times greater) and after cycling in torsional loading (range, 3-3.6 times greater). Although cement augmented screws and Schuhli augmentation showed increased fixation stability compared with the standard screws in axial and 4-point bending before cycling (range, 1.3-1.4 times greater), this was not significant. Compared with Schuhli fixation, cement augmented screws showed no significant difference in fixation stability in all loading modes before and after cycling. Schuhli locking nuts offer the stability of cement augmentation while avoiding its potential adverse effects on fracture healing with extravasation and thermal necrosis.

Biomechanical Phenomena↗
PubMed2000

New technique for treatment of unstable distal femur fractures by locked double-plating: case report and biomechanical evaluation.

BACKGROUND: A comminuted, intra-articular distal femur fracture was surgically treated by the authors with a locked, double-plating technique because fixation stability could not be initially achieved by using a standard double-plating technique. The purpose of this study was to determine biomechanically whether a locked double-plate construct would enhance fixation stability compared with a nonlocked double-plate construct. METHODS: Six matched pairs of mildly osteopenic femurs were selected and all had a reproducible intra-articular fracture pattern created. Each pair underwent fixation with either a double-plating construct or a locked, double-plating construct that was randomly assigned. The instrumented femurs were then mechanically tested in several loading modes to determine fixation stability. After initial testing, specimens were cyclically loaded and retested for stability. RESULTS: The locked, double-plating construct provided significantly greater fixation stability than the standard double-plating construct in precycling and postcycling biomechanical testing. CONCLUSION: The technique described is particularly applicable for severely comminuted fractures of the distal femur and fractures in osteopenic bone with poor screw purchase. It offers a simple alternative for enhancing fixation stability, which avoids the potential complications of methylmethacrylate-enhanced screw fixation.

Biomechanical Phenomena↗
PubMed2000

[The correlation of serum levels of insulin-like growth factors and intrauterine growth: report of a study in rats].

This animal experiment was designed to investigate the relationship of the serum insulin-like growth factors (IGFs) with fetal intrauterine growth. The serum concentrations of IGF-I, -II in 21 fetal rats were measuerd and their relationships with fetal birth weight, length and tissue weights of brain, lung, liver were analysed respecively. The results showed that both of the serum concentrations of IGF-I, -II were positively correlated (P < 0.01) with fetal birth weight, length and tissue weights of brain, lung, liver respectively. These data suggest that both IGF-I and IGF-II may play an important role in fetal intrauterin growth and their decreased concentrations in serum may be factors contributing to fetal intrauterine growth retardation.

Animals↗
PubMed1999

The use of an injectable, biodegradable calcium phosphate bone substitute for the prophylactic augmentation of osteoporotic vertebrae and the management of vertebral compression fractures.

STUDY DESIGN: A biomechanical study comparing two materials for augmentation of osteoporotic vertebral bodies and vertebral bodies after compression fracture. OBJECTIVES: To compare an injected, biodegradable calcium phosphate bone substitute with injected polymethylmethacrylate bone cement for strengthening osteoporotic vertebral bodies and improving the integrity of vertebral compression fractures. SUMMARY OF BACKGROUND DATA: Injection of polymethylmethacrylate bone cement into fractured vertebral bodies has been used clinically. However, there is concern about thermal damage to the neural elements during polymerization of the polymethylmethacrylate bone cement as well as its negative effects on bone remodeling. Biodegradable calcium phosphate bone substitutes have been studied for enhancement of fixation in fractured vertebrae. METHODS: Forty fresh osteoporotic thoracolumbar vertebrae were used for two separate parts of this study: 1) injection into osteoporotic vertebrae: intact control (n = 8), calcium phosphate (n = 8), and polymethylmethacrylate bone cement (n = 8) groups. Each specimen then was loaded in anterior compression until failure; 2) injection into postfractured vertebrae: calcium phosphate (n = 8) and polymethylmethacrylate bone cement (n = 8) groups. Before and after injection, the specimens were radiographed in the lateral projection to determine changes in vertebral body height and then loaded to failure in anterior bending. RESULTS: For intact osteoporotic vertebrae, the average fracture strength was 527 +/- 43 N (stiffness, 84 +/- 11 N/mm), 1063 +/- 127 N (stiffness, 157 +/- 21 N/mm) for the group injected with calcium phosphate, and 1036 +/- 100 N (stiffness, 156 +/- 8 N/mm) for the group injected with polymethylmethacrylate bone cement. The fracture strength and stiffness in the calcium phosphate bone substitute group and those in the polymethylmethacrylate bone cement group were similar and significantly stronger than those in intact control group (P < 0.05). For the compression fracture study, anterior vertebral height was increased 58.5 +/- 4.6% in the group injected with calcium phosphate and 58.0 +/- 6.5% in the group injected with polymethylmethacrylate bone cement as compared with preinjection fracture heights. No significant difference between the two groups was found in anterior vertebral height, fracture strength, or stiffness. CONCLUSION: This study demonstrated that the injection of a biodegradable calcium phosphate bone substitute to strengthen osteoporotic vertebral bodies or improve vertebral compression fractures might provide an alternative to the use of polymethylmethacrylate bone cement.

Absorbable Implants↗
PubMed1999

Gelfoam as a barrier to prevent polymethylmethacrylate-induced thermal injury of the spinal cord: in vitro and in vivo studies in pigs.

Gelatin sponge (Gelfoam; Upjohn, Kalamazoo, MI, U.S.A.) is commonly used as an interpositional barrier to shield the spinal cord from thermal injury during vertebral reconstruction with polymethylmethacrylate bone cement. The aim of this study was to record epidural and intradural temperatures during polymethylmethacrylate reconstruction of vertebral corpectomy defects. Three surgical techniques (subtotal corpectomy, total corpectomy with insertion of a Gelfoam barrier, and total corpectomy with no barrier) were compared in vivo and in vitro in a porcine model. As expected, total corpectomy defects cemented without a Gelfoam barrier produced the highest epidural temperatures in vivo (52.8 degrees C) and in vitro (58 +/- 2 degrees C). The Gelfoam barrier provided some protection against heat transfer, but peak temperatures and absolute temperature increases were significantly higher than in defects with an intact posterior cortex (p < 0.05). These results indicate that an intact posterior cortex provides the best protection against heat transfer, whereas the use of a Gelfoam barrier appears to provide only partial protection against thermal injury.

Animals↗
PubMed1999

[Effect of anti-opioid peptide sera on the enhancement of electroacupuncture analgesia induced by neurotensin in PAG of rats].

With the use of potassium iontophoresis induced tail-flick for measuring the pain threshold, the effects of injecting neurotensin (NT), naloxone (NX), anti-metenkephalin serum (AMEKS), anti-beta-endorphin serum (AEPS) and anti-dynorphin A1-13 serum (ADYNS) into periaqueductal gray (PAG) on electroacupuncture (EA) analgesia in rats were investigated. NT administration enhanced EA analgesia remarkably. Pre-injection of NX, AMEKS and AEPS into PAG could significantly attenuate the enhancement of EA analgesia induced by NT, but not by administration of ADYNS. The results indicate that NT in PAG is responsible for the enhancement of EA analgesia. The effect of NT may be partly mediated by met-enkephalin and beta-endorphin.

Acupuncture Analgesia↗
PubMed1999

[Studies on immunoprotection of monoclonal antibodies against Cryptosporidium parvum].

AIM: To explore the immune protection of the monoclonal antibody (McAb) against Cryptosporidium parvum. METHODS: On the basis of Madin-Darby canine kidney (MDCK) cell culture, the immunoprotection of McAb against C. parvum was screened by means of neutralization test in vitro, and verified by rat model and transmission electron microscopy of infected MDCK cells. RESULTS: The number of C. parvum sporozoites recovered on the surface of rat intestinal epithelial cells and the mean output of oocyst were significantly reduced by McAb Z3D2 (P < 0.001, P < 0.05). The decreased Cryptos poridium at each development phase within infected MDCK cells and less damage of cell ultrastructure caused by Cryptosporidium were found in Z3D2 treated group. CONCLUSION: McAb Z3D2 possesses highly effective protection against C. parvum.

Animals↗
PubMed1997

[The role of periaqueductal gray neurotensin in electroacupuncture analgesia].

The effect of periaqueductal gray (PAG) injection of neurotensin (NT), anti-NT serum (ANTS), and naloxone (Nx) on both the pain threshold and electroacupuncture (EA) analgesia in rat was investigated in this study. The potassium iontophoresis-induced tail-flick was used to measure the pain threshold. NT administration induced an increase in pain threshold and enhanced EA analgesia. Injection of ANTS reduced the pain threshold significantly and diminished the effect of EA analgesia. Furthermore, pre-injection of Nx into PAG could weaken analgesia effect of NT and NT-EA analgesia. These results indicate that NT in PAG is involved in pain modulation and plays a role in EA analgesia. The effect of NT may be partly conducted by endogenous opiate peptides.

Acupuncture Analgesia↗
PubMed1997

[Total hip replacement in patients with steroid-induced femoral head necrosis].

In order to evaluate the long-term effect of total hip replacement (THR) in patients with steroid-induced femoral head necrosis, 40 cases of 50 hips received THR patients were followed up for an average of 8.5 years after operation. Evaluation was carried act according to Harris score system. In these cases, average score was seventy-five points. Revision rate among them was 2% after four years and 18% after five to eight and a half years, with as overall rate of 20%. It was found that the main reason for revision was looseness of the prosthesis. In this follow-up, it showed that besides foreigen body reaction, abnormal osseous remodelling was the main factor in long-term failure of this arthroplasty. It was also proved that it was a good selection to perform cemented total hip replacement in younger patients, which could improve living quality.

Adult↗
PubMed1995

[The effect of intrathecal injection of neurotensin on acupuncture analgesia in rats].

The influence of intrathecal injection of Neurotensin (NT) and Anti-NT serum (ANTS) on pain threshold, and electroacupuncture (EA) analgesia in the rat was investigated. The tail-flick induced by potassium iontophoresis was used to measure the pain threshold. The increase of pain threshold was observed within 100 min, after NT injection (2 micrograms), and it was more effective than that of the ACSF injection (P < 0.01). The NT administration could also enhance the EA analgesia. On the contrary, the pain threshold was decreased in ANTS group as compared with that of ACSF control group. The ANTS administration could decreased the role of EA analgesia. Our data show that NT in spinal cord may play an important role in the EA analgesia.

Acupuncture Analgesia↗