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D Felsenberg

Publications and source records attributed to D Felsenberg.

At least 91 records · Page 5Linked to original sources
PubMed1991

Global and regional variations in the spinal trabecular bone: single and dual energy examinations.

Two hundred and sixty-eight vertebrae from 92 subjects (42 males and 50 females) were used to assess inter- and intravertebral variations in the mineral content of spinal trabecular bone from L1-L3. Using a computer-generated grid superimposed on the trabecular bone, the spatial distribution of the mineral content was computed for 48 subdivisions of the grid for single and dual energy computed tomographic examinations. In addition, the age dependence of the mineral content was assessed by regression analysis from each subdivision. The results demonstrated a nonhomogenous distribution of mineral density within the trabecular bone. The lateral and anterolateral subcortical regions show significantly lower mineral density than the posterolateral or anterior subcortical domains. Moreover, with increasing age, bone density was also lost in a nonuniform fashion. Finally, the analysis of regional intervertebral change for the L1-L3 vertebrae revealed a nonhomogeneous pattern of mineral distribution.

Adolescent↗
PubMed1990

[CT examinations using a reduced radiation dosage].

An experimental method was used to determine which diagnostic CT problems could be solved while using reduced radiation doses. The examinations were carried out using 85 kv and 1.7 to 3.0 mGy (instead of the usual 125 kv and 20 to 50 mGy). More than 500 patients have been investigated so far. The method has been used successfully for bone mineral estimations and for otorhinologic and orthopaedic problems. All examinations with high contrast (bones, sinuses) and small diameters (extremities) produced adequate images compared with the usual pictures. With the exception of cerebral CT for demonstrating the brain (structures with little contrast), the method can also be used for children and infants. During the first phase of this study the role of this method has been evaluated. Subjective impressions and demonstration of detail, when compared with a 'normal' image for a corresponding cut, were satisfactory. Signal-to-noise ratio was measured by a quantifiable parameter of image quality.

Humans↗
PubMed1989

[Computerized tomography determination of bone mineral content in quantitative diagnosis of osteoporosis].

Quantitative determination of bone mineral content has become important for the early diagnosis of osteoporosis prior to radiological evidence of vertebral deformities. Quantitative CT (QCT, computer tomometry), whether the single-energy (SE-QCT) or the dual-energy (DE-QCT) technique is used, yields volume-related values that can be used for accurate and reproducible assessment of spongious and cortical vertebral bone mineral. QCT seems to be superior to photon absorptiometry for early detection and follow-up of osteoporosis.

Adult↗
PubMed1989

Reference values for trabecular and cortical vertebral bone density in single and dual-energy quantitative computed tomography.

The validity of reference values for vertebral bone mineral density (BMD) reported in the literature has frequently been questioned. The introduction of dual-energy methods, new calibration systems, and automated image evaluation algorithms, has also made it necessary for us to re-evaluate BMD values in a normal population. We present patient selection criteria, CT measurement and evaluation protocols and results of single energy (SEQCT) and dual energy quantitative CT (DEQCT) for trabecular (tBMD) and cortical (cBMD) bone density in 135 males and 139 females. For SEQCT, tBMD loss rates of 1.7 and 1.8 mg/ml per year for males and females, respectively, were determined by linear regression. The respective DEQCT data show smaller decrements with age. Different statistical models for tBMD in females were tested; models based on a multiphase variation of tBMD yielded an improvement of the fit. For cBMD the percent rate of loss with age is much smaller than for tBMD; females showed a significantly higher loss rate than males, however. A comparison of our results with published data is included.

Absorptiometry, Photon↗
PubMed1988

[Quantitative computerized tomographic determination of bone mineral content].

Quantitative computed tomography (QCT) for measuring bone mineral content of lumbar vertebrae is increasingly used internationally. The effect of using conventional CT (single energy CT, SE-CT) and dual energy CT (DE-CT) on reproducibility has been examined. We defined a standard measurement protocol, which automatically evaluates a calibration phantom. This should ensure an in vivo reproducibility of 1 to 2%. Reference data, which has been obtained with this protocol from 113 normal subjects, using SE-CT and DE-CT, are presented.

Adult↗
PubMed1988

[Tele-thermography in the diagnosis of deep leg and pelvic venous thrombosis].

The results of thermography were compared with those of phlebography in 235 patients with suspected deep venous thrombosis in the legs. Any thermal difference between the two sides was regarded as abnormal. On this basis, thermography had a sensitivity of 97%. Thermography is therefore a reliable, simple, non-invasive and repeatable examination for the exclusion of leg vein thrombosis.

Adult↗
PubMed1988

Bone mineral measurement: automated determination of midvertebral CT section.

The selection of the computed tomographic (CT) section can introduce errors in reproducibility of several percent for bone mineral measurements. An algorithm for automated determination of the midvertebral CT section from survey radiographs was developed; it is based on ridge-line tracking of the vertebral end plates. The midvertebral section is defined by all points with equal perpendicular distance to the regression lines fitted through these end-plate contours. The algorithm can be corrected by manual interaction in case of failure. It was tested on T-12 to L-4 vertebrae on 25 randomly selected localizer radiographs. Of the 250 endplate contours, 223 (89.2%) were tracked automatically; the remaining 27 (10.8%) required user interaction for successful completion.

Algorithms↗
PubMed1988

Günther vena caval filter: results of long-term follow-up.

A Günther vena caval filter was implanted in the inferior vena cava in 59 patients to prevent pulmonary embolism. This newly available device, which can be inserted percutaneously via a 10-French introduction system, has three filtering planes. No complications occurred at the puncture site. Follow-up included clinical examinations (54 patients), plain radiographs (50 patients), and CT scans (41 patients); these examinations were performed up to 21 months after implantation. Caudal migration of the filter occurred in 35 (70%) of the 50 patients who had radiographs, but no cranial or oblique movement occurred. Occlusion of the filter was noted in three (7%) of 41 patients who had CT examinations. Thromboemboli were seen inside the filter in 16 (39%) of the 41 patients who had CT scans. Recurrent pulmonary embolism was not observed after filter implantation. The Günther vena caval filter seems to be a satisfactory device for preventing pulmonary embolism.

Adult↗
PubMed1987

Percutaneous transluminal treatment of varicoceles: where to occlude the internal spermatic vein.

Percutaneous transluminal sclerotherapy is an accepted treatment for varicoceles. It is administered by applying a liquid sclerosing agent to the internal spermatic vein. However, the optimal site for the placement of the occlusive material has not been evaluated previously. Therefore, the success rate of sclerotherapy was determined in two groups of patients. In the first group (34 patients), the liquid agent was applied in the cranial part of the internal spermatic vein; in the second group (113 patients), the agent was applied in the caudal part of the vessel at the level of the inguinal ring. The success rate determined 3 months after therapy by telethermography was significantly higher after treatment in the caudal part (82%) than in the cranial part (68%) of the vessel. Sclerotherapy at the level of the inguinal ring appears to be superior to therapy in the cranial part of the internal spermatic vein.

Adolescent↗
PubMed1987

[Material selective imaging and density measurement with the dual energy method. III. Determination of bone mineral of the spine with CT].

Quantitative computed tomography for measuring vertebral bone mineral content offers high sensitivity and reproducibility. However, several systematic errors of the method have to be considered, such as the influence of fat present in the spongiosa in varying concentrations as well as beam hardening effects and different calibration methods. The unknown fat content of the spongiosa of the vertebral bodies can be responsible for errors up to 30%. Beam hardening effects result in comparatively minor errors which can moreover be easily corrected via reference phantoms. The calibration method, on the other hand, results in potentially major systematic deviations due to the necessarily arbitrary determination of the reference points. These deviations must be taken into account especially in cross-comparisons of measured data. Dual energy methods enable a highly selective determination of the density of calcified tissue and soft tissue and decisively reduces the systematic errors mentioned above. The order of magnitude of the individual errors for different CT techniques was assessed by means of phantom studies and clinical studies.

Adult↗
PubMed1987

[Material-selective imaging and density measurement using the dual-energy method. I. Principles and methodology].

The principles of the Dual Energy method are discussed from two perspectives: a clear illustration of the method and an exact presentation of the principles involved. The principles apply to both radiography and computed tomography. The method was implemented on a CT scanner (SOMATOM DR, Siemens AG). Dual Energy images enable highly selective imaging based on the determination of density values for calcified and soft tissue. Images may also be reconstructed that are based on other parameters such as electron density and effective atomic number. The degree to which selective imaging is possible is discussed. Examples of Dual Energy clinical applications for radiography and computed tomography are presented. More detailed information will be available in future contributions.

Humans↗
PubMed1986

Varicoceles: combined sonography and thermography in diagnosis and posttherapeutic evaluation.

One hundred eighteen patients with clinically suspected varicocele were examined with thermography and sonography before phlebography of the internal spermatic vein (ISV). The combination of sonography and thermography led to an exact differentiation among eight patients with normal findings (6.8%), 103 with left-sided varicoceles (87.3%), six with bilateral varicoceles (5.1%), and one with a right-sided varicocele (0.85%). The accuracy of thermography was 98.4% and of sonography, 92.7%. With sonography, venous dilatation was detected when the patients were upright and the Valsalva maneuver was being performed. Thermography was more sensitive than sonography in detecting persistent varicocele in 63 patients reexamined after sclerotherapy. Sclerotherapy within the inguinal segment of the ISV gave better results (82.9%) than that within the proximal segment (77.3%).

Adolescent↗
PubMedDate not supplied

Bone architecture assessment with measures of complexity.

Architectural changes in trabecular bone by osteoporosis were utilized as a model for the changes which probably occur in human bone while exposed to microgravity conditions. Although there are many concerns about microgravity-induced bone loss, little is known about the impact of microgravity on the three-dimensional architecture of the skeleton. 50 (level L3) and 57 (level L4) vertebral bones harvested from human cadavers were investigated by computed tomography (CT) and quantified in terms of bone mineral density (BMD). Based on the symbol-encoded transformed CT-images, five measures of complexity were developed which quantify the structural composition of the trabecular bone. This quantification determines the bone architecture as a whole. Depending on the specific measure of complexity and its relation to BMD, a 5-10% change of BMD is related to a 5-90% change in structural composition. The method requires a non-invasive CT-procedure of the lumbar spine resulting in a radiation exposure of about 30 microSv effective dose. The technique is useful for the evaluation of the bone status of space-flying, personnel as well as for patients on ground. Grant numbers: BMH1-CT92-0296.

Aerospace Medicine↗