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Biomedical subjects

W A Kalender

Publications and source records attributed to W A Kalender.

At least 19 recordsLinked to original sources
PubMed1992

Compact and trabecular components of the spine using quantitative computed tomography.

A computer algorithm was employed to quantify separately cortical and trabecular bone mineral density (BMD) from single energy computed tomography (CT) scans of 139 vertebrae (L1-L3) of 50 normal female subjects. In addition, the trabecular-to-integral and cortical-to-integral mass ratios were determined using digital image segmentation techniques. They showed that for the central 8-mm vertebral slice, the mass of integral bone consists of about one-fifth trabecular and four-fifth cortical bone. The trabecular-to-integral volume ratios were 0.37 +/- 0.08 and 0.63 +/- 0.08, respectively. Based on cross-sectional data from this subject group, the average annual loss was -2.21 +/- 0.15 mg/cm3 or -1.84 +/- 0.12% for trabecular bone, -3.15 +/- 0.25 mg/cm3 or -1.01 +/- 0.08% for cortical bone, and -2.60 +/- 0.20 mg/cm3 or -1.09 +/- 0.09% for the integral bone. The proportions of the age-related loss of BMD from the integral bone which originated from trabecular and cortical bone were 29.5 and 70.5%, respectively.

Adult↗
PubMed1992

Effective dose values in bone mineral measurements by photon absorptiometry and computed tomography.

A high degree of uncertainty and irritation predominates in the assessment and comparison of radiation dose values resulting from measurements of bone mineral density of the lumbar spine by photon absorptiometry and X-ray computed tomography. The skin dose values which are usually given in the literature are of limited relevance because the size of the irradiated volumes, the relative sensitivity of the affected organs and the radiation energies are not taken into account. The concept of effective dose, sometimes called whole-body equivalent dose, has to be applied. A detailed analysis results in an effective dose value of about 1 microSv for absorptiometry and about 30 microSv for computed tomography when low kV and mAs values are used. Lateral localizer radiographs, which are necessary for slice selection in CT, mean an additional dose of 30 microSv. Lateral X-ray films of the spine which are frequently taken in combination with absorptiometry result in a dose of 700 microSv or more. The concept of effective dose, the basic data and assumptions used in its assessment and a comparison with other dose burdens (for example the natural background radiation, of typically 2400 microSv per year) are discussed in detail.

Absorptiometry, Photon↗
PubMed1992

Evaluation of section sensitivity profiles and image noise in spiral CT.

Spiral computed tomography (CT) offers continuous volume scanning of complete organs or body sections within a single breath hold. Almost all image quality characteristics of spiral CT are identical to those of conventional section-by-section CT; however, there is a change in pixel noise values and degradation in the shape of the section sensitivity profiles (SSPs). Computer simulations, phantom measurements, and clinical studies were used in evaluating the SSP and noise characteristics of two new section-interpolation algorithms. The results were compared with standard CT and spiral CT data processed with the commonly employed linear section-interpolation algorithm. Degradation of SSP quality was insignificant for a table feed distance per 360 degrees revolution equal to the section thickness when the new algorithms were applied; noise values, however, increased. SSP width increased for table feed distances greater than the section width, the effect being less pronounced with the new algorithms. The value of these algorithms is primarily seen in the improved quality of multiplanar reformations and cine and three-dimensional displays.

Algorithms↗
PubMed1991

Accuracy of vertebral mineral determination by dual-energy quantitative computed tomography.

Quantitative computed tomography is an established method for the non-invasive assessment of bone mineral content. Scanning with two different X-ray energies allows material-selective image reconstruction and separation on the basis of differing atomic numbers. As proven by chemophysical analysis of 45 bone samples, dual-energy quantitative computed tomography with basis material decomposition allows highly accurate measurement of bone mineral density with an error of 1.4%, independent of fat and soft tissue content.

Bone Density↗
PubMed1991

[The estimation of the effective dose in bone mineral measurements with photon absorptiometry and computed tomography].

There is still some uncertainty in the assessment and comparison of patient dose which results from bone mineral measurements on the lumbar spine by photon absorptiometry and x-ray computed tomography (CT). In the literature, skin dose values are offered in almost all cases. These are not meaningful, however, as the size of the irradiated volume and the radiation sensitivities of the respective organs are not taken into account. Here, the concept of effective dose has to be applied. An assessment of effective dose resulted in approximately 1 mu Sv for absorptiometry and approximately 30 mu Sv for computed tomography with low kV and mAs values. For lateral lumbar spine films which are often taken in connection with absorptiometry, at least 700 mu Sv have to be added. In CT, additional 30 mu Sv result from the lateral topogram which is required for positioning. The concept of effective dose, the data and assumptions used in its assessment and a comparison to other risk factors, as for example natural background radiation of approximately 2400 mu Sv per year, are discussed in detail.

Absorptiometry, Photon↗
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↗
PubMed1990

Measurement of pulmonary parenchymal attenuation: use of spirometric gating with quantitative CT.

A new approach to reproducible measurement of lung attenuation and structure by means of respiratory-gated computed tomography (CT) was developed. The patient breathes through a microcomputer-controlled pocket spirometer during the complete CT examination, starting with a measurement of the vital capacity. At a user-selected respiratory level, the CT scan is triggered and air flow is inhibited mechanically. To exclude operator-related reproducibility errors, evaluation is based on semiautomated algorithms that isolate lung parenchyma by fast contour tracing. In a study on one volunteer, measurement of lung attenuation changed by a factor of about 2.6 (-895 to -730 HU) as a function of inspirational status. Reproducibility on the order of 5% or better can be achieved only with tight spirometric control of respiration.

Humans↗
PubMed1990

Spiral volumetric CT with single-breath-hold technique, continuous transport, and continuous scanner rotation.

Continuous computed tomographic (CT) scanning of organ volumes during a single breath hold was studied. The authors modified the table feed mechanism of a continuously rotating CT scanner to allow patient transport at low, but accurately controlled, speeds (0.1-11.0 mm/sec) during continuous 1-second scanning. An algorithm was designed to reconstruct artifact-free images for arbitrary table positions from the helical data by interpolating between adjacent scans. Section sensitivity profiles were enlarged; the section width for a 10-mm section and a speed of 10.0 mm/sec was increased by a factor of 1.3, compared with the nominal value. Clinical examples were presented for studies of lung nodules and studies enhanced with contrast medium. Major advantages are the possibility of continuous scanning of extended volumes within a breath-hold period and retrospective, arbitrary selection of anatomic levels.

Humans↗
PubMed1990

Lung: spiral volumetric CT with single-breath-hold technique.

The authors adapted the transport system of a computed tomographic (CT) scanner with continuous rotation capability to examine complete lung subvolumes during a single breath hold. Twenty-four adult patients underwent scanning with up to 12 continuous 1-second rotations, and data acquisition was synchronized with longitudinal patient motion at one section thickness per second. Interpolated planar raw data were obtained retrospectively from any level within the volume, and these afforded high-quality images that were comparable to standard images. Solitary pulmonary nodules were not omitted, their centers could always be depicted, and secondary reformations as well as three-dimensional reconstructions were obtained easily. The authors conclude that spiral volumetric CT, by completely surveying a subvolume of the lung, is an attractive new application of CT.

Female↗
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

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↗