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Biomedical subjects

N Meier

Publications and source records attributed to N Meier.

At least 19 recordsLinked to original sources
PubMed2003

Evaluation of accuracy of insertion of dental implants and prosthetic treatment by computer-aided navigation in minipigs.

The survival of loaded implants is critically dependent on their biomechanical stability. We have used a computer-guided navigation technique to evaluate the accuracy of computer-assisted insertion for immediately-loaded implants in minipigs. On the basis of computed tomographical data, the Robodent system was used for preoperative planning and guidance of inserting the implant. An optical tracking system allowed positioning of the implant and immediate prosthetic rehabilitation by inserting it in a plaster model and during the operation. Postoperative computed tomograms (CT) showed that the implants were placed precisely in the preoperatively planned position. The accuracy achieved corresponded well with the spatial resolution of the CT used. Immediate placement of the prefabricated crowns resulted in favourable occlusal positioning. Histological cross-sections showed that the implants were biomechanically stable. The accuracy of insertion of oral implants illustrated here suggests that insertion and prosthetic modelling of implants may benefit from computer-assisted navigation.

Animals↗
PubMed2003

Are collimated low-dose digital radiographs valid for performing Delaire's architectural analysis?

Computed radiography (CR) provides the dynamic exposure range to reveal objects in film areas exposed by very low X-ray exposure. Conventional cephalometric radiographs are normally beam limited to the facial skeleton. The cranial vault and cervical vertebra are collimated and only exposed by extra-focal radiation and scatter. We hypothesize that, on conventional cephalometric radiographs obtained with CR, image data of collimated film areas can be enhanced for reliable performance of Delaire's cephalometric analysis of the entire skull. Therefore the aim of the present study was to compare the reproducibility of landmark placement on normal and underexposed film areas of CR images. Intra- and inter-observer reproducibility of landmark identification was evaluated on 200 randomly selected radiographs by calculating the error radius of repeated landmark placements. A paired-samples t-test revealed differences (P< 0.001) between intra- and inter-observer reproducibility. Intra-observer accuracy was influenced (P< 0.001) by variability of suture obliteration (bregma). Identification of landmarks in areas of extra-focal radiation showed no difference (P> 0.05) from that of landmarks inside the normally exposed area. CR offers the opportunity to perform of a full cranial analysis on a cephalometric radiograph collimated to the facial region.

Cephalometry↗
PubMed2003

[Dose reduction of radiographs of the pediatric pelvis for diagnosing hip dysplasia using a digital flat-panel detector system].

PURPOSE: To evaluate a possible dose reduction in pediatric pelvic radiographs in congenital hip dysplasia using a digital flat-panel system instead of a phosphor-storage system. MATERIALS AND METHODS: During a six-month period, all pediatric patients referred for pelvic radiography for the evaluation of congenital hip dysplasia were randomly assigned to be examined by either a phosphor-storage system or a digital flat-panel system, whereby the latter system was operated with half the radiation dose. Thirty pairs of radiographs were assessed for the visibility of 16 anatomic details and for 5 orthopedic-radiographic measurements (5-point scale with 1 = excellent; three independent observers). The projection indices of Ball and Kommenda and of Tönnis and Brunken were calculated for all radiographs. The Student's t-test was used to compare the flat-panel and the phosphor-storage radiographs for observers' assessments, patients' age and projection indices. RESULTS: In a total of 7560 observations, the scores for the visibility of anatomic details and orthopedic-radiographic measurements were respectively 2.72 and 2.64 for the flat-panel system and 2.93 and 2.79 for the phosphor-storage system. No significant differences were found between both systems (p > 0.05) and between patient age and projection indices (p > 0.05). CONCLUSION: Pediatric pelvic radiographs can be obtained with a digital flat-panel system using half the radiation dose instead of a phosphor-storage system without sacrificing relevant information in the diagnosis of congenital hip dysplasia.

Age Factors↗
PubMed2002

Structure analysis of high resolution magnetic resonance imaging of the proximal femur: in vitro correlation with biomechanical strength and BMD.

The purpose of this study was to use high resolution magnetic resonance imaging (HR-MRI) combined with structure analysis to investigate the trabecular structure of the human proximal femur and to compare this technique with bone mineral density (BMD) using dual energy X-ray absorptiometry (DXA) in the prediction of bone strength in vitro. Thirty-one fresh human proximal femur specimens were examined with HR-MRI using a T1-weighted 3D spinecho-sequence in a coronal plane (voxel size: 0.195 x 0.195 x 0.9 mm and 0.195 x 0.195 x 0.3 mm). In these images structure parameters analogous to standard bone histomorphometry were obtained in a femoral head, neck, and trochanteric region of interest (ROI). In addition, BMD measurements were obtained using DXA and finally, all specimens were tested biomechanically in a materials testing machine, and maximum compressive strength (MCS) was determined. Correlations between BMD and MCS were significant (p <0.01) with R-values up to 0.74. Correlating structure parameters and MCS R-values up to 0.69 (P <0.01) were obtained. Using multivariate regression analysis, combining structure parameters and BMD, improved correlations versus MCS substantially (up to R = 0.93; P <0.01). In conclusion, this study showed that in an experimental setting, structure parameters determined in high resolution MR images of the proximal femur correlated significantly with bone strength. The highest correlations, however, were obtained combining BMD and structure measures.

Aged↗
PubMed2002

First experience with a public domain computer-aided surgical system.

The outcome of complex craniofacial operations is critically dependent on careful and accurate preoperative planning. Recent advances in computer technology enable the surgeon to do surgical simulations directly on to a computer terminal. We describe the clinical application of a public domain-based computer-aided system in craniofacial surgery. Operation planning was based on clinical investigations and radiological images, with particular use of a virtual three-dimensional surgical simulation. Three patients with complex craniofacial malformations were admitted for orbital correction. Surgical simulation defined numerically the extent of bone movements and the extent of resection areas. Operations were guided by the virtual planning. The outcome was compared with the planning to assess the accuracy of the operative correction. Our first experience confirms that computer-assisted simulation is a reliable and useful tool that improves surgical planning and helps to evaluate the surgical outcome.

Adult↗
PubMed2001

[An extended CT scale technique for evaluating periprosthetic bone lesions - an in vitro study].

PURPOSE: In the present study the reduction of artifacts using an extended CT scale technique was examined in 5 vitallium and 5 titanium-aluminium-vanadium tumor prostheses. METHODS: 5 titanium-aluminium-vanadium and 5 vitallium distal femur Mutars(R) tumor prostheses (Mutars(R) - Modular Universal Tumor And Revision System) were implanted in 10 human femur specimens. 110 artifical drill hole lesions of 1 mm, 2 mm, 3 mm, 5 mm and 8 mm diameter were placed in the bone around the hexagonal stem of the tumor prosthesis and furthermore in the proximal part of the femur. All specimens were examined using conventional CT and an extended CT scale technique in a slice thickness of 3 mm. RESULTS: In the proximal part of the femur all drill holes could be detected using 3 mm slices, no artefacts were observed. Along the hexagonal stem smooth lines arising from each hexagonal plane could be observed. This made it impossible to detect a 1 mm drill in 1 vitallium and in 1 titanium-aluminium-vanadium stem. There was no difference between the extended CT scale and conventional CT. CONCLUSION: The extended CT scale did not significantly (p > 0.05, t-test) improve the imaging of artificial drill hole lesions along the hexagonal Mutras(R) stem.

Aged↗
PubMed2001

Joint accumulations of FDG in whole body PET scans.

PURPOSE: To retrospectively evaluate FDG accumulations in major joints in a large series of non-absorption corrected partial body and whole body FDG-PET scans, and to determine the frequency and intensity of accumulation. MATERIALS AND METHODS: 354 consecutive PET partial- and whole body non-transmission corrected scans of patients obtained for tumor staging were examined with respect to FDG accumulations in the acromio-clavicular (AC)-, gleno-humeral-, hip-, knee- and talo-tibial joints. FDG-uptake was graded using a semi-quantitative scale from 0 (no accumulation) to 4 (very strong accumulation comparable to brain uptake). RESULTS: Joint activity of grade 1-2 was noted frequently, while grade 3 was rare, occurring only in the knee and shoulder joints, and grade 4 was inexistent. The 43 patients with grade 3 accumulations or with at least 4 joints showing grade 2 uptake were interviewed, but all denied pain specifically referred to a joint. Joint accumulations were seen in 50% of the acromio-clavicular-, 80% in the glenohumeral-, 50% in the hip-, 90% in the knee and 80% in the talo-tibial joints. The intensities of joint accumulations correlated positively and significantly with patient age, ranging from r = 0.7 and p < 0.05 in the knee to r = 0.96 and p < 0.0001 in the AC joint. CONCLUSIONS: FDG accumulations in the joints in whole body FDG-PET scans are frequent and are very likely not related to symptoms. As there is a strong age correlation, and FDG is known to accumulate in inflammatory lesions, the findings are most likely a result of sub-clinical inflammatory synovial proliferation or other chronic inflammatory processes occurring in aging joints.

Adolescent↗
PubMed2000

Cross-sectional area of lumbar vertebrae in peri- and postmenopausal patients with and without osteoporosis.

The purpose of this study was to analyze the midvertebral area of lumbar vertebrae in osteoporotic and nonosteoporotic female patients and to find out whether the midvertebral area may be used as an additional parameter in the diagnosis of osteoporosis. In 195 peri- and postmenopausal patients (average age 51.7 +/- 5.2 years) trabecular and cortical bone mineral density (BMD) were determined using quantitative CT (QCT) in L2-4. In addition, midvertebral cross-sectional area was measured in a standardized fashion on the CT sections and the height of the second lumbar vertebra was determined on the lateral digital radiographs. Body height and weight were obtained and vertebral fracture status was determined. According to WHO criteria 29 patients (average age 57.2 years) were considered osteoporotic, 93 osteopenic (average age 52.2 years) and 73 normal (average age 48.6 years). Body weight and size did not show significant differences between the individual groups. Average midvertebral area was 1278 +/- 173 mm2 in the osteoporotic patients, 1186 +/- 125 mm2 in the osteopenic patients and 1126 +/- 127 mm2 in the normals. A correlation of r = -0.39 (p < 0.05) was obtained between BMD and area. Thirty-six of 195 patients showed osteoporotic vertebral fractures. Midvertebral area in these patients was 1266 +/- 171 mm2 versus 1159 +/- 133 mm2 in the nonfractured females (p < 0.05). We therefore conclude that the lumbar midvertebral area is larger in osteoporotic and osteopenic patients compared with women with normal BMD. In contrast to biomechanical considerations midvertebral area seems not to be suited as an additional measure of bone strength in vivo.

Anatomy, Cross-Sectional↗
PubMed2000

Three-dimensional magnetic resonance imaging of the orbit in craniofacial malformations and trauma.

Craniofacial malformations and trauma often lead to changes in orbital soft tissues, requiring surgical correction of both hard and soft tissues. Computed tomographic scans and 3-dimensional reconstructions are the optimal tools for evaluation of the bony structures. However, there is no equivalent method for the orbital soft tissues. The aim of this study was to establish a 3-dimensional magnetic resonance imaging (3-D MRI) technique that allows a differentiated visualization of the different types of soft tissue in the orbit. A total of 8 patients with different pathologic conditions of the orbit was examined. Five of these patients underwent secondary correction after trauma, and 3 had craniofacial malformations. The 3-D reconstruction was performed in the volume-rendering technique after acquisition of 3-mm axial slices. It was shown that a differentiated visualization of the orbital soft tissues is possible. Although the thin bony structures have a weak signal and, therefore, the imaging is poor, reliable reconstruction of the globe was achieved by different radiologists because of its circular delimitation from the bone. This technique is an additional support in the planning of orbital surgery.

Craniofacial Abnormalities↗
PubMed1999

A novel serine protease overexpressed in the hair follicles of nude mice.

We have studied changes in gene expression between normal and nude mouse skin. Using the method of representational difference analysis, a cDNA encoding a novel serine protease designated BSSP was cloned. Our results show that in skin this gene is predominantly expressed in the sebaceous gland of the hair follicle and in the distal part of the outer root sheath. Thus, BSSP is the first serine protease known to be expressed in the sebaceous gland. In nude mouse skin, this gene is overexpressed.

Amino Acid Sequence↗
PubMed1999

Whn and mHa3 are components of the genetic hierarchy controlling hair follicle differentiation.

The molecular basis of the characteristic hair growth disorder in nude mice that carry a defective Whn transcription factor gene is unknown. A comparison of mRNA populations from wild-type and nude mice back skin by representational difference analysis revealed the absence of acidic hair keratin gene 3 (mHa3) mRNA in mutant mice. Whn and acidic hair keratin genes are co-expressed in hair follicles, nail forming regions and filiform papillae of the tongue: expression of the mHa3 gene is generally detectable about 1 day after Whn mRNA and rapidly ceases in its absence. Whn is strongly expressed during the anagen (growth) phase of the hair cycle in matrix, cortex and outer root sheath; its expression rapidly declines during catagen and is undetectable in telogen phases. In nude mice, low levels of mHa3 expression are maintained in nails and whisker follicles, whereas expression is completely absent in pelage hair follicles and filiform papillae. Thus, the nude phenotype represents the first example of an inherited skin disorder that is associated with the loss of expression rather than structural mutation of keratin genes. The distinct molecular difference between pelage and whisker follicles correlates with the improved mechanical stability of vibrissae in nude mice, implicating mHa3 as an important structural component of the hair shaft.

Animals↗
PubMed1999

[The texture-analysis of high-resolution computed tomograms as an additional procedure in osteoporosis diagnosis: in-vitro studies on vertebral segments].

PURPOSE: The purpose of this study was to perform texture analysis of high-resolution CT images obtained from human vertebral specimens and to correlate these parameters with the biomechanical stability of the specimens. In addition, structure data were compared with bone mineral density (BMD) assessed by quantitative CT (QCT). MATERIAL AND METHODS: High-resolution CT images and standard QCT sections were obtained in 36 vertebral motion segments, each consisting of two vertebrae with intact ligaments and intervertebral disc. The trabecular structure in the CT images was assessed using three texture analysis techniques: Trabecular threshold area ratio (TTAR), fractal dimension without thresholding (OTS) and fractal dimension with thresholding (ITS). Finally, the maximum compressive strength (MCS) was determined using a biomechanical testing device. RESULTS: A correlation of r = 0.76 (p < 0.01) was obtained for TTAR versus MCS, of r = 0.83 (p < 0.01) for ITS versus MCS, and of r = 0.35 (p > 0.01) for OTS versus MCS, while r = 0.76 (p < 0.01) was found for BMD versus MCS. Best results were obtained by combining structure measures and BMD (r = 0.85, p < 0.01). CONCLUSIONS: This in vitro study showed a significant correlation between structure measures and biomechanical strength, which was comparable to BMD and strength. However, best correlations were obtained by combining both measures. Using both BMD and structure measures therefore may improve the prediction of biomechanically determined bone strength.

Aged↗
PubMed1998

Computer-aided automated landmarking of cephalograms.

The computer-aided method presented is able to interpret and measure radiological structures automatically and reproducibly on a large number of randomly selected lateral head films of different film quality. For example the hard and soft tissue expression of the profile is used to discuss method, application and disadvantages. The performance of the system depends on image quality. The algorithm cannot be influenced by opacifications due to metal structure. In 90% of all cases the contours are identified correctly. Even if the image quality is poor, the recognition rate is about 84%. The selected cephalometric landmarks are placed in the right way in 85% of all cases. The constraint mathematical conditions and the high reproducibility improve the quality process of the cephalometric analysis. Recognition rates of 84% to 90% justify even nowadays the routine use of semi-automatic systems in PC-based analysis. With advancing digital radiography and improved computer performance, image interpreting systems will certainly become established.

Cephalometry↗
PubMed1998

[MRI 3D imaging of the orbits in craniofacial abnormalities and injuries].

Craniofacial malformations and trauma often lead to changes in orbital soft tissues that require operative correction of both hard and soft tissues. CT scan and 3D reconstructions are optimal tools for the evaluation of the bony structures but there is no equivalent for the orbital soft tissues. The aim of this study was to establish a 3D-MRI technique that allows differentiated visualization of the different soft-tissue types of the orbit. A total of eight patients with different pathologic conditions of the orbit were examined. Five of these patients came for secondary correction after trauma and three showed a craniofacial malformation. 3D reconstruction was performed in volume-rendering technique after acquisition of 3 mm axial slices. It was shown that differentiated visualization of the orbital soft tissues is possible. Even though the thin bony structures have a weak signal and therefore the imaging is poor, the globe could be reconstructed reliably by different radiologists because of its circular delimitation from the bone. This technique provides additional support in the planning of orbital operations.

Craniofacial Abnormalities↗
PubMed1998

[Computer-assisted structure analysis of trabecular bone in the diagnosis of osteoporosis].

Osteoporosis is characterized by reduced bone mass and a deterioration of bone structure which results in an increased fracture risk. The purpose of this review is to evaluate structure analysis techniques in the diagnosis of osteoporosis. Several imaging techniques were applied to analyze trabecular bone, such as conventional radiography, high-resolution computed tomography (HR-CT) and high-resolution magnetic resonance imaging (HR-MRI). The best results were obtained using high-resolution tomographic techniques. The highest spatial resolutions in vivo were achieved using HR-MRI. These studies show that texture parameters and bone mineral density predict bone strength and osteoporotic fractures in a complementary fashion. Combining both techniques yields the best results in the diagnosis of osteoporosis.

Calcaneus↗
PubMed1998

[Medical cooperation on the internet].

Post-1999, the economically united EEC will pose new challenges to European business, industry and citizen. It is a key objective that in the domain of European "infostructure" these problems are challenged and overcome, and that "advanced communications technologies and services" (ACTS) become the cement which binds the Community together. Within ACTS, 130 different projects are building new services. The consortium Emerald develops a telemedicine platform, setting up teleworking with teleconference, computer supported co-operative work (cscw, joint editing), demonstration and teleteaching for radiology, cardiology, nuclear medicine and radio surgery working environments.

Computer Systems↗
PubMed1997

[Radiologic performance in night and emergency care].

This report deals with radiologic examinations outside official working hours in a German university hospital and the influence of new government regulations. A total of 65,113 radiologic examinations were requested and performed outside official working hours between 1 July 1990 and 30 Juni 1994. The data were analyzed according to the age and sex of this patient population compared with the entire population studied within this 4-year period. Further analysis included the time of the study, the organ systems investigated, and the radiologic technique. About one-third of requests occurred between 16.00 and 20.00 hours on normal working days and, thus, could be taken care of by late shifts. Another third covers the time between 20.00 and 08.00 hours in the morning, which requires inhouse staff (medical and technical). The remainder of the requests occurred during holidays and weekends in the daytime. The most common request in this analysis was for portable chest examination. About 50% of all portable chest examinations were performed outside regular working hours. In all, 17.2% of all requests involved CT and MRT studies. Government regulation did not change the number, technique, and frequency of radiologic examinations outside official working hours.

Adolescent↗