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Biomedical subjects

J L Grashuis

Publications and source records attributed to J L Grashuis.

At least 19 recordsLinked to original sources
PubMed2003

Patient-specific DXA bone mineral density inaccuracies: quantitative effects of nonuniform extraosseous fat distributions.

Nonuniform extraosseous fat is shown to raise the magnitude of inaccuracies in DXA in vivo BMD measurements into the range of 20-50% in clinically relevant cases. Hence, DXA-based bone fragility diagnoses/ prognoses and evaluations of bone responsiveness to treatment can be unreliable. Patient-specific DXA in vivo bone mineral areal density (BMD) measurements have been demonstrated to be inherently inaccurate even when extraosseous fat (F) and lean muscle tissue (L) are uniformly distributed throughout the scan region of interest (ROI). The present work extends these investigations to quantitative evaluation of the extent to which clinically realistic soft tissue inhomogeneities external to the bone within the DXA scan ROI affect patient-specific in vivo BMD measurement inaccuracies. The results are particularly relevant to patient-specific lumbar vertebral and proximal femoral sites. Norland, Hologic, and Lunar DXA scans and corresponding DXA simulation studies of the same set of 225 different phantom arrays were carried out. The phantoms were specially fabricated absorptiometric replications of bone mineral material (B), red marrow (RM), and yellow marrow (YM) mixtures, and extraosseous F and L combinations spanning the anthropometric ranges encountered clinically. The three different DXA scanners yielded BMD results that effectively coincided, were in excellent agreement with the findings of the present corresponding DXA-simulation studies in each case, and confirmed the validity of the DXA BMD inaccuracy analysis formalism. It was found that only relatively small extraosseous soft tissue inhomogeneities within the ROI of DXA BMD scans can increase substantially the already sizable BMD inaccuracies shown earlier to pertain for uniformly distributed extraosseous soft tissues. The extent of these in vivo BMD inaccuracies (%) are shown to depend on the mean extraosseous F-to-L areal density ratio and its degree of nonuniformity within the local bone scan ROI, the marrow thickness and specific composition, and the actual BMD in any given case. It was found that patient-specific DXA-measured in vivo BMD inaccuracies can, in many clinically encountered cases, be as large as 20-50%, particularly so for osteopenic, osteoporotic, and elderly patients. It is concluded that, because these DXA in vivo BMD inaccuracies are unavoidable and clinically unpredictable, diagnoses/ prognoses of bone fragility and evaluations of bone responsiveness to treatment of individual patients based mainly on DXA in vivo BMD measurements can be unreliable.

Absorptiometry, Photon↗
PubMed2001

Inaccuracies inherent in patient-specific dual-energy X-ray absorptiometry bone mineral density measurements: comprehensive phantom-based evaluation.

An extensive series of dual-energy X-ray absorptiometry (DXA) scans and dual polyenergetic X-ray simulation studies of 150 different phantom arrays were carried out to evaluate quantitatively the extent of systematic inaccuracies inherent in DXA in vivo bone mineral density (BMD). These measurements are particularly relevant to lumbar vertebral and proximal femoral sites. The phantoms were specially fabricated near perfect absorptiometric representations of bone material, red marrow (RM) and yellow marrow (YM), and extraosseous mixtures of fat (F) and lean muscle that spanned the full range of soft tissue anthropometrics encountered clinically. In each case, the DXA-measured BMD values obtained using Hologic, Lunar, and Norland densitometers were found to be virtually the same and to be in excellent agreement with the corresponding quantitative simulation study BMD results. Comparisons of the known phantom BMD values and DXA-measured BMD in each case allowed the BMD inaccuracies to be evaluated. These present findings show that these ubiquitous inaccuracies in DXA BMD methodology are of in vivo soft tissue anthropometric genesis. It is found that patient-specific DXA-measured in vivo BMD inaccuracies as high as 20% or more can be readily anticipated clinically, particularly in cases of osteopenic, osteoporotic, and elderly patients. As these inaccuracies exceed considerably DXA precision errors, they may compromise patient-specific evaluations of fracture risk and, in prospective studies, mask or exaggerate clinically significant true changes in BMD. It is concluded that the magnitudes and variability of inherent inaccuracies in DXA-measured in vivo BMD underscore the need for prudence and circumspection in interpretations and assessments of DXA-based clinical studies.

Absorptiometry, Photon↗
PubMed1998

Vertebral dimensions: influence of X-ray technique and patient size on measurements.

In this study a new reference value, "corrected vertebral dimension," is presented for vertebral height measurements. Of 68 females (age 18-88 years; mean 44.2 years) and 40 males (age 16-81 years; mean 55 years) the projected vertebral dimensions (T4-L5) were measured on lateral radiographs. In addition to this, the vertebra-to-film distances (VFD) were measured and a fixed focus-to-film distance (FFD) was used during the study. Corrected dimensions of the thoracic and lumbar vertebrae (T4-L5) were calculated using the FFD and VFD. These corrected dimensions were then used to recalculate projected vertebral dimensions at different focus-to-film distances. The applied geometric corrections were verified in a phantom study representing an in vitro situation. The results indicate that studies using different X-ray techniques for making lateral radiographs of the spine can become comparable when using corrected vertebral dimensions.

Adolescent↗
PubMed1998

Texture analysis in radiographs: the influence of modulation transfer function and noise on the discriminative ability of texture features.

Tissue structures, represented by textures in radiographs, can be quantified using texture analysis methods. Different texture analysis methods have been used to discriminate between different aspects of various diseases in primarily x rays of chest, bone, and breasts. However, most of these methods have not specifically been developed for use on radiographs. Certain characteristics of the radiographic process, e.g., noise and blurring, influence the visible texture. In order for a texture analysis method to be able to discriminate between different underlying textures, it should not be too sensitive for such processes as image noise and blur. In this study, we investigated the sensitivity of four different texture analysis methods for image noise and blur. First, a baseline measurement was performed of the discriminative performance of the Spatial Gray-Level Dependence method, the Fourier Power Spectrum, the Fractal Dimension, and the Morphological Gradient Method on images, which were not affected by radiographic noise and blur. Two types of images were used: fractal and Brodatz. Whereas the Brodatz images represent very different textures, the differences between the fractal images are more gradual. We assume that the behavior of the different texture analysis methods on the fractal images is representative for their performance on radiologic textures. On these types of images we simulated the effect of four different noise levels and the effect of two different modulation transfer functions, corresponding with different screenfilm combinations. The influence on the discriminative performance of the four texture analysis methods was evaluated. The influence of noise on the discriminative performance is, as expected, dependent on the image type used; the discrimination of more gradually different images, such as the fractal images, is already lowered for relatively low noise levels. In contrast, when the images are more different, only high noise levels decrease the discriminative performance. The discriminative power of the Morphological Gradient Method is least affected by image blur. We conclude that the discriminative performance of the Morphological Gradient Method is superior to that of other methods in circumstances which mimic the conditions prevailing in radiographs.

Biophysical Phenomena↗
PubMed1997

Unraveling the role of structure and density in determining vertebral bone strength.

The strength of bone is determined not only by bone density but also by structure. Therefore, quantification of the structure in radiographs by texture parameters may result in a better prediction of fracture risk. Since in radiographs density and structure are strongly correlated, the predictive power of texture parameters should be corrected for the influence of BMD to determine the additional information conveyed by these parameters. In this study, we evaluated the predictive power of various texture parameters based on the Grey-Level Dependence Method and the Morphological Gradient Method. This study was performed on 67 vertebrae obtained from 20 male and 12 female human cadaver thoracolumbar spines. BMD and area of the vertebral body were determined from QCT images and texture parameters were derived from direct magnification (DIMA) radiographs. The fracture force, measured under conditions simulating the in vivo situation, was corrected with the area of the vertebra to yield the fracture stress (FS). Results of the study indicate that BMD correlates significantly with FS r = 0.82 (P < 0. 001, n = 24) and r = 0.94 (P < 0.001, n = 43) for female and male vertebrae, respectively. Correlation coefficients of the investigated texture parameters were as high as 0.80 (P < 0.001) and 0.67 (P < 0.001) for the female and male vertebrae, respectively. Multiple regression analysis showed that in female vertebrae, the addition of one texture parameter to BMD results in a better prediction of strength. The multiple correlation coefficient was 0. 87 (P < 0.001) in this case. In male vertebrae, BMD was the best predictor of fracture stress. These results suggest that texture parameters, as measured in magnification radiographs, can predict bone strength. Whereas in all cases BMD is the best single predictor of bone strength, for women texture parameters contain useful additional information.

Bone Density↗
PubMed1997

Distribution of trabecular and cortical bone related to geometry. A quantitative computed tomography study of the femoral neck.

METHODS: The relation between geometry and the distribution of trabecular and cortical bone mass and density in the human femoral neck was evaluated with quantitative computed tomography (QCT). Quantitative computed tomography data were obtained from 2-mm thick computed tomography slices of 20 human femur necks in vitro. A standardized scan position in each femur was used with the smallest cross-section as reference point. RESULTS: When trabecular bone mass (TrBM) and cortical bone mass were presented as percentage of total bone mass (ToBM), it was found that, starting at the cranial (head) side, ToBM consists of 78% TrBM. About 21% of ToBM can be found as TrBM at the caudal (trochanter) side. At the smallest cross-sectional volume TrBM is 33% of ToBM. For every 2-mm slice, an average decrease of 5% TrBM can be seen. CONCLUSIONS: These data show that geometry and bone mass distribution are related. Whereas total bone mass remains relatively stable, the cortical and trabecular bone mass changes extensively. This implies that QCT measurements in the femoral neck depend highly on midneck positioning.

Absorptiometry, Photon↗
PubMed1996

Accuracy and the influence of marrow fat on quantitative CT and dual-energy X-ray absorptiometry measurements of the femoral neck in vitro.

Bone mineral measurements with quantitative computed tomography (QCT) and dual-energy X-ray absorptiometry (DXA) were compared with chemical analysis (ChA) to determine (1) the accuracy and (2) the influence of bone marrow fat. Total bone mass of 19 human femoral necks in vitro was determined with QCT and DXA before and after defatting. ChA consisted of defatting and decalcification of the femoral neck samples for determination of bone mineral mass (BmM) and amount of fat. The mean BmM was 4.49 g. Mean fat percentage was 37.2% (23.3%-48.5%). QCT, DXA and ChA before and after defatting were all highly correlated (r > 0.96, p < 0.0001). Before defatting the QCT values were on average 0.35 g less than BmM and the DXA values were on average 0.65 g less than BmM. After defatting, all bone mass values increased; QCT values were on average 0.30 g more than BmM and DXA values were 0.29 g less than BmM. It is concluded that bone mineral measurements of the femoral neck with QCT and DXA are highly correlated with the chemically determined bone mineral mass and that both techniques are influenced by the femoral fat content.

Absorptiometry, Photon↗
PubMed1992

Influence of calibration materials in single- and dual-energy quantitative CT.

With single-energy (SE) quantitative computed tomography (CT), the density of bone mineral in the vertebral body can be estimated. With dual-energy (DE) quantitative CT, both bone-mineral density and fat content can be measured. The calibration device normally used contains materials mimicking trabecular bone, fat, and hematopoietic tissue. To evaluate the influence of different calibration materials on these estimates, theoretical CT numbers were calculated for the trabecular part of the vertebral body and for different calibration devices. Calibration devices were simulated; they contained either identical materials or various accepted tissue-mimicking materials. For all combinations, quantitative CT data were generated for the SE quantitative CT method and for two DE quantitative CT methods. Only one method provided accurate results under ideal circumstances. The selection of tissue-mimicking materials in the calibration devices is important for the interpretation of results of SE and DE quantitative CT. Errors of more than a factor 2 were found when different types of materials were used.

Absorptiometry, Photon↗
PubMed1992

A new model for diurnal blood pressure profiling. Square wave fit compared with conventional methods.

For the characterization of diurnal blood pressure variation, we developed a simple mathematical model that nevertheless does justice to the specific form characteristics of individual blood pressure registrations. Analysis was based on 24-hour continuous intra-arterial measurement of blood pressure obtained in 23 hospitalized patients with mild-to-moderate untreated essential hypertension (mean +/- SD, 112 +/- 13 mm Hg). The day-night difference for mean arterial pressure varied markedly (mean, 18.6 mm Hg; range, 6.8-36.0). Inspection of profiles suggested a model of blood pressure as two contiguous, complementary periods of constant pressure, a so-called square wave. Determination of the times of transience between both periods (segmentation) was performed individually using a least-square error criterion. Results were compared with those obtained by conventional methods, including analysis by Fourier modeling. The square wave fit accounted for a larger fraction (66%) of circadian variance of mean arterial pressure than modeling based on segmentation by visual inspection (59%, considerable observer bias) or by clock time (50%). Application of the Minnesota Cosinor Method resulted in the poorest description (47%). Segmentation based on harmonic modeling (61%) appeared to be cumbersome (10 harmonics needed), and the significance of additional information offered over the square wave fit is dubious. Observer bias makes segmentation by visual inspection unsuitable for assessment of the circadian variance of blood pressure. Even when daily activities are strictly regulated (hospital environment), circadian variance is not well modeled by clock time. As compared with harmonic analysis, square wave fitting is simple, and it appears to best model the circadian variance. The method can also be applied to data obtained from noninvasive ambulatory blood pressure monitoring.

Blood Pressure Determination↗
PubMed1990

Evaluation of postprocessing dual-energy methods in quantitative computed tomography. Part 1. Theoretical considerations.

Five postprocessing methods for dual-energy quantitative computed tomography of the vertebral body were evaluated theoretically. The methods were compared by transforming the original sets of equations to a standard set. Only two of these methods produced optimal results, namely the basic approach of Goodsitt et al and the method of Nickoloff et al. The calibration approach of Goodsitt et al will produce optimal results only if calibration materials are available that mimic the anatomic constituents of the vertebral body better than those available currently. Theoretically, the methods of Cann et al and of Laval-Jeantet et al will not produce optimal results.

Bone Density↗
PubMed1990

Evaluation of postprocessing dual-energy methods in quantitative computed tomography. Part 2. Practical aspects.

Three facets of dual-energy quantitative computed tomography are studied: (1) the algorithm for postprocessing data (the methods of Cann, Laval-Jeantet et al, Goodsitt et al [two methods], and Nickoloff et al); (2) the influence of choice of tissue-equivalent materials for calibration; and (3) the difference between central and peripheral calibration. The different tissue-equivalent materials include bone mineral-equivalent (K2HPO4 solutions and calcium hydroxyapatite), fat-equivalent (liquid paraffin, polyethylene, and 70% ethanol solution), and red marrow-equivalent (plastic). Deviation from the manufacturer's quoted content is least with central positioning of the calibration materials. The accuracy of estimates is best when the same tissue-equivalent materials are used for calibration that are being measured. The deviations produced by the use of different tissue-equivalent materials indicate the importance of using materials that mimic the components of bone most closely. The two methods of Goodsitt et al and the method of Nickoloff et al produced the best results.

Algorithms↗
PubMed1989

Education in medical informatics in The Netherlands: a nationwide policy and the Erasmus curriculum.

The curricula of all Medical Faculties still bear the characteristics of an era in which the physician was not educated in managing medical information systems, using communication networks, and processing knowledge. In attempting to formulate the prerequisites for developing and adjusting future curricula, we discuss the evolution of medical information technology during the past 25 years and give examples to illustrate that, by extrapolating current trends, future developments in information technology, medicine and education can be predicted. A plea is made for a strong interaction between scientific developments in medical informatics and academic education. In addition, a model based on our experience in medical informatics education of over 15 years, is pointed out. Furthermore, a nationwide policy on medical informatics in The Netherlands, is discussed. Our treatise is concluded by presenting the outline of the curriculum in medical informatics at the Erasmus University in Rotterdam. Educational recommendations conclude the paper.

Computers↗
PubMed1987

Microdensitometric analysis of bone structures in X-ray images.

The careful evaluation of bony structure is important in the study of normal bone and bone disorders. This study describes bony structure as seen in the X-ray pattern of the phalanges of the hand using quantitative microdensitometry. Normalised scans of bony density show the regular and irregular distribution of the trabeculae. Two properties were determined from these densitometric findings: the mean transverse coarseness (C) indicating fluctuations of horizontal density and the overall standard deviation indicating axial homogeneity (H). This investigation demonstrates the applicability of the method: it shows a significant correlation with radiological diagnosis and that microdensitometry is a reliable method for quantifying the coarseness and homogeneity of bone structure.

Bone and Bones↗
PubMed1986

Electrogastrographic study of gastric myoelectrical activity in patients with unexplained nausea and vomiting.

Using cutaneous electrodes an electrogastrographic study was made of gastric myoelectrical activity in both the fasting and postprandial states in 48 patients with unexplained nausea and vomiting and in 52 control subjects. A gastric emptying study, using a radio-labelled solid phase meal, was carried out in 30 of these 48 patients. A follow up study was done after one year. In 48% of the patients abnormal myoelectrical activity was found which was characterised by: instability of the gastric pacemaker frequency; tachygastrias in both the fasting and postprandial states; the absence of the normal amplitude increase in the postprandial electrogastrogram. This last characteristic was correlated with a delayed gastric emptying of solids. The present study shows that with electrogastrography in a heterogeneous group of patients with unexplained nausea and vomiting a subgroup can be discerned with abnormal myoelectrical activity. Our findings suggests that this abnormal myoelectrical activity is related to these symptoms.

Adolescent↗
PubMed1986

Electrogastrographic characteristics of interdigestive migrating complex in humans.

Interdigestive myoelectric activity and mechanical activity were studied simultaneously by means of cutaneous electrodes (electrogastrography) and intraluminal pressure recording, respectively, in 10 healthy male volunteers. The aims of the present study were 1) to describe the characteristics of the electrogastrogram during the different phases of the interdigestive migrating complex (IMC) in healthy subjects and 2) to determine to what extent these characteristics can be used to identify the different phases of the IMC. The electrogastrograms were analyzed visually and by running-spectrum analysis. It was concluded that in humans the gastric frequency present in the electrogastrogram appears to be less stable during motor activity than during motor quiescence, in particular during phase III, but far more stable than its canine counterpart. A small but consistent drop in gastric frequency was observed in the changeover from motor quiescence to phase II motor activity. The power of the gastric frequency increased with increasing motor activity, except during phase III. A characteristic frequency and power behavior during phase III could only be recognized in a minority of the IMCs. In general, electrogastrography cannot, given the present state of the art, be used to precisely identify the different phases of the IMC.

Adult↗
PubMed1984

Recording of gastrointestinal electrical activity from surface electrodes.

The surface recording of electrical activities generated by the gastrointestinal tract is reviewed, with particular reference to surface recording of gastric electrical activity (electrogastrography or EGG). The available data on interdigestive and postprandial characteristics of the EGG signal in health and disease, including techniques of recording and signal analysis, are summarised.

Animals↗