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K Engelke

Publications and source records attributed to K Engelke.

At least 19 recordsLinked to original sources
PubMed1998

Accuracy and diagnostic sensitivity of radiographic absorptiometry of the second metacarpal.

The accuracy of a radiographic absorptiometry (RA) technique called digital image processing (DIP), discriminative ability of RA for osteoporotic fracture, and the relationship between RA and dual X-ray absorptiometry (DXA) of the spine and forearm were evaluated. We measured 16 cadaver hands, 32 healthy non-black premenopausal women, 39 healthy non-black postmenopausal women, and 35 non-black osteoporotic postmenopausal females. The overall correlation between the ash weights of the entire metacarpal and the DIP values was excellent (r = 0.954, P < 0.001, SEE = 0.14, CV = 6.4%). Short-term precision error of DIP was 3.5%. Age-related bone loss determined by DIP is comparable to that of spinal and forearm DXA: annual BMD decreases were 0.46% for DIP, 0.45% for forearm, and 0.32% for the spine. DIP of the 2nd metacarpal shows a gradient of risk for spinal fracture only slightly below that of forearm DXA, but substantially below that of spinal DXA. Age-adjusted odds ratios were 1.81 for RA, 2.45 for spinal DXA, and 1.94 for forearm DXA.

Absorptiometry, Photon↗
PubMed1997

High resolution magnetic resonance imaging of the calcaneus: age-related changes in trabecular structure and comparison with dual X-ray absorptiometry measurements.

A high-resolution magnetic resonance imaging (MRI) protocol, together with specialized image processing techniques, was applied to the quantitative measurement of age-related changes in calcaneal trabecular structure. The reproducibility of the technique was assessed and the annual rates of change for several trabecular structure parameters were measured. The MR-derived trabecular parameters were compared with calcaneal bone mineral density (BMD), measured by dual X-ray absorptiometry (DXA) in the same subjects. Sagittal MR images were acquired at 1.5 T in 23 healthy women (mean age: 49.3 +/- 16.6 [SD]), using a three-dimensional gradient echo sequence. Image analysis procedures included internal gray-scale calibration, bone and marrow segmentation, and run-length methods. Three trabecular structure parameters, apparent bone volume (ABV/TV), intercept thickness (I.Th), and intercept separation (I.Sp) were calculated from the MR images. The short- and long-term precision errors (mean %CV) of these measured parameters were in the ranges 1-2% and 3-6%, respectively. Linear regression of the trabecular structure parameters vs. age showed significant correlation: ABV/TV (r2 = 33.7%, P < 0.0037), I.Th (r2 = 26.6%, P < 0.0118), I.Sp (r2 = 28.9%, P < 0.0081). These trends with age were also expressed as annual rates of change: ABV/TV (-0.52%/year), I.Th (-0.33%/year), and I.Sp (0.59%/year). Linear regression analysis also showed significant correlation between the MR-derived trabecular structure parameters and calcaneal BMD values. Although a larger group of subjects is needed to better define the age-related changes in trabecular structure parameters and their relation to BMD, these preliminary results demonstrate that high-resolution MRI may potentially be useful for the quantitative assessment of trabecular structure.

Absorptiometry, Photon↗
PubMed1997

Assessment of osteoporosis: comparison of radiographic absorptiometry of the phalanges and dual X-ray absorptiometry of the radius and lumbar spine.

PURPOSE: To evaluate radiographic absorptiometry (RA) of the phalanges in healthy women and in women with osteoporosis and to compare the results of RA with those of dual x-ray absorptiometry (DXA) of the radius and spine. MATERIALS AND METHODS: Thirty-two healthy premenopausal women, 39 healthy postmenopausal women, and 35 postmenopausal women with osteoporosis underwent RA of the phalanges and DXA of the radius and lumbar spine. Pairwise comparisons, age-related bone losses, and percentage decrements and Student t values for intergroup discrimination were calculated. The ability to identify patients with osteoporotic fractures was evaluated by using receiver operating characteristic and age-adjusted logistic regression analyses. The diagnostic agreement for osteoporosis was assessed with kappa statistics. RESULTS: Findings from RA were correlated with those from spinal DXA (r = .56). The annual bone losses in healthy women, as measured with RA, radial DXA, and spinal DXA, were 0.47%, 0.47%, and 0.32%, respectively. Intergroup percentage decrements and t values obtained with RA were comparable to those obtained with radial and with spinal DXA. Receiver operating characteristic analysis showed no statistically significant differences. The odds ratios for RA, radial DXA, and spinal DXA were 2.1, 1.9, and 2.4, respectively. The kappa scores were 0.44 for both RA versus radial DXA and RA versus spinal DXA, and the score was 0.22 for radial DXA versus spinal DXA. CONCLUSION: RA appears to be a useful technique for assessing age- and menopause-related bone loss and for identifying women with osteoporosis.

Absorptiometry, Photon↗
PubMed1997

A new trabecular region of interest for femoral dual X-ray absorptiometry: short-term precision, age-related bone loss, and fracture discrimination compared with current femoral regions of interest.

We defined a new region of interest (ROI) for femoral Ward's triangle, centered on the femoral neck axis including comparatively trabecular-rich bone. Forty-seven premenopausal, 39 healthy postmenopausal, and 35 osteoporotic postmenopausal women with vertebral fractures were evaluated comparing the new with the standard femoral ROIs, using a Hologic QDR-2000. Additionally, spinal dual X-ray absorptiometry (DXA) was performed. The short-term precision error of the new ROI expressed as the root mean square of the coefficient of variations was 1.34% for premenopausal women, 1.69% for healthy postmenopausal women, and 2.46% for osteoporotic postmenopausal women. Bone mineral density (BMD) values of the new ROI correlated highly with those of the standard femoral ROIs (r = 0.91 - 0.96) and the spinal BMD (r = 0.74). Age-related bone loss of the new ROI was 0.75% per year (r = 0.66) in healthy women, which was approximately 1.5 times higher than the bone loss of the standard femoral ROIs, except for Ward's triangle. Regarding the intergroup discrimination, the t-value of the new ROI was similar to the t-value of Ward's triangle, and the intergroup percent decrements in BMD of the new ROI approximated those of Ward's triangle. For discriminating women with vertebral fractures, the new ROI demonstrated odds ratios of 1.6 similar to most ROIs but lower than that of the trochanteric region. The new, substantially trabecular ROI appears to be an alternative to the Ward's ROI traditionally used in femoral DXA having improved short-term precision and comparable sensitivity.

Absorptiometry, Photon↗
PubMed1996

A digital model of trabecular bone.

A 3D microCT dataset of bovine bone was used to create a digital 3D model simulating trabecular bone. The model serves a dual purpose: It allows for standard quantitative histomorphometric analysis and it approximates the reality e.g. of high resolution CT in vivo datasets of trabecular bone. Thus the model can potentially be used as a reference to develop 2D and 3D structural analysis algorithms applicable in vivo while it simultaneously allows verification of the results of these algorithms by standard histomorphometry. The model can be used as a standard to evaluate the impact of image processing techniques and of restrictions of imaging systems on the quantitative analysis of structural parameters describing a trabecular network. The model can be used for a comparison of 2D and 3D structural analysis methods and for an analysis of decreasing spatial resolution. The effects of segmentation and filtration can be studied separately and grayscale analysis is possible. As examples standard 2D histomorphometry and the analysis of topological parameters like node number and trabecular network length were applied to the model. The influence of spatial resolution was investigated by decreasing the spatial resolution of the digital model. The bone surface area determined by 3D surface triangulation was only 4% smaller than the surface area determined from the traditional 2D bone histomorphometric parameter bone surface/tissue volume (BS/TV) when 2D results were averaged over all slices of the 3D volume. However, BS/TV showed large (10%) variations among slices within the volume. Both histomorphometric and topological parameters were heavily influenced by spatial resolution and image segmentation. Our initial experience with the digital model indicates a need to investigate bone microstructure based on volume data or to average the 2D results of many slices.

Algorithms↗
PubMed1996

Accuracy and precision study in vitro for peripheral quantitative computed tomography.

We evaluated the accuracy and precision of a peripheral quantitative computed tomography (pQCT) scanner, the Stratec XCT-960, using 12 human cadaveric forearms. The accuracy was determined by comparing the total bone mineral content (BMC) with the ash weight (AW). We scanned and ashed three consecutive slices (thickness 2.5 mm) at the standard position (s-position) and at 2.5 mm both proximal and distal to the s-position. The correlation coefficient between the AW and total BMC using slices at the s-position was r = 0.87 with an accuracy error (random component) of 15.5%. The correlation coefficient using all slices was r = 0.90 with an accuracy error of 14.3%. The correlation coefficient improved to r = 0.95 with an accuracy error of 9.7% after averaging the results of all three slices for each forearm. The short-term precision error expressed as the coefficient of variation (CV) of bone mineral density (BMD) and BMC was determined by measuring the forearms five times either with repositioning or without repositioning. The CVs with repositioning were 2.77 and 1.15 for total BMD and BMC, 1.85 for trabecular BMD; without repositioning they were 0.29, 0.58 and 0.69 respectively. To further evaluate the influence of positioning, additional scans were performed at 1, 2 and 5 mm proximal, and 1 and 2 mm distal to the s-position. BMD and BMC were greatly influenced by the scan location; for example, the percentage differences in trabecular BMD 1 mm distal and proximal relative to the s-position were 2.5% +/- 5.1% and 0.18% +/- 6.3%, respectively. The Stratec XCT-960 appears to be a moderately accurate and highly precise scanner with potential usefulness for evaluating BMC and BMD of ultradistal radius.

Bone Density↗
PubMed1996

Advances in the noninvasive assessment of bone density, quality, and structure.

Recent advances in the development of methods to assess the skeleton noninvasively have contributed to screening for risk of osteoporosis, early detection of the disease, and effective monitoring of its progression and response to therapy. The capability now exists to evaluate the peripheral, central, or entire skeleton as well as the trabecular bone or cortical bone envelopes accurately and precisely, with the capacity to determine bone strength and predict fracture risk. In this article we examine the current and future capabilities of quantitative computed tomography (QCT), quantitative ultrasound (QUS), and magnetic resonance microscopy (muMR) to assess architectural and densitometric properties of the skeleton to enhance the prediction of fracture risk.

Female↗
PubMed1995

Assessment of the skeletal status by peripheral quantitative computed tomography of the forearm: short-term precision in vivo and comparison to dual X-ray absorptiometry.

In order to assess precision of peripheral quantitative computed tomography (pQCT), duplicate bone mineral density (BMD) measurements at the radius were performed in 20 healthy premenopausal, 20 healthy postmenopausal, and 20 osteoporotic postmenopausal women using a Stratec XCT-960 system. The short-term reproductibility in vivo for the total, trabecular, and cortical regions of interest (ROI) was expressed as the absolute precision error (standard deviation, SD) and as the relative precision error (SD/mean x 100, or coefficient of variation, CV, in %). Reproducibility in vivo was good in all volunteers but was influenced by the study group and the ROI. The precision error for trabecular BMD was 3 mg/cm3, or about 1.6%. This is large relative to the aging decrease of 0.22%/year, or to the difference (12 mg/cm3, or 7%) between osteoporotic women and postmenopausal controls. In order to compare pQCT to dual X-ray absorptiometry (DXA) at the forearm and at the lumbar spine (L1-L4), 40 premenopausal healthy controls, 40 postmenopausal healthy controls, and 35 postmenopausal osteoporotic women were assessed. DXA measurements performed at the ultradistal, middistal, 1/3, and total ROI of the radius showed only moderate correlations between r = 0.38--0.75, r = 0.27--0.64, and r = 0.38--0.53 for the comparison versus pQCT total BMD, versus pQCT trabecular BMD, and versus pQCT cortical BMD, respectively. Correlations of DXA at the lumbar spine and pQCT were between r = 0.18 and 0.44. DXA at radius and spine was able to discriminate between post- menopausal controls and osteoporotic women (p = 0.001--.004),but BMD measurements by pQCT did not show this ability (p = 0.15--0.52). However, two nonstandard pQCT parameters, namely the surface area of the cortical bone and the cortical BMC were factors that discriminated well between these two groups (p = 0.002, p = 0.005, respectively). These pQCT parameters also yielded the highest relative annual changes in pre- and post-menopausal control subjects. The measurement of cortical bone in the distal radius proved to be a good predictor of vertebral fracture status and was a good indicator of age-related skeletal change. Our data emphasize the importance of cortical measurements when using pQCT of the radius to assess osteoporosis.

Absorptiometry, Photon↗
PubMed1995

Factors influencing short-term precision of dual X-ray bone absorptiometry (DXA) of spine and femur.

In this study we analyzed the effect of variations in bone area size, baseline soft tissue composition represented by the R-value, and bone region of interest positioning on the precision in vivo of bone mineral density (BMD) and content (BMC) as measured by dual X-ray absorptiometry (DXA). The posterior-anterior (PA) spine, decubitus lateral, and femur modes were evaluated. Eleven (PA-spine), 9 (dec-lat), and 14 (femur) postmenopausal women were scanned twice on a Norland XR-26 with repositioning to determine short-term precision of BMD, BMC, AREA, and the R-value. Phantom precisions (CV[%] of 10 consecutive scans) for BMD (BMC) were PA spine: 0.66% (0.57%), neck: 1.1% (1.2%), and trochanter: 0.55% (1.0%). Precisions in vivo (CV[%]; two consecutive scans averaged over all patients) were PA spine: 0.9% (1.0%), dec-lat: 7.1% (18%), neck: 1.3% (1.9%), and trochanter: 2.5% (4.9%). BMD precision could be fully explained by BMC and AREA variations. However, BMC alone was a particularly poor predictor of BMD in the dec-lat (r2 = 0.05) and in the neck (r2 = 0.13) modes. AREA was a strong predictor for BMC precision explaining between 41% and 88% of the BMC changes. Changes in soft tissue composition contributed significantly in explaining the BMC changes in the dec-lat projection. A higher dependence of BMC changes on AREA changes resulted in a larger difference between BMC and BMD precision.(ABSTRACT TRUNCATED AT 250 WORDS)

Absorptiometry, Photon↗
PubMed1995

Which vertebrae should be assessed using lateral dual-energy X-ray absorptiometry of the lumbar spine.

The purpose of this study was to determine precision and diagnostic capability of bone mineral density measurements using lateral dual-energy X-ray absorptiometry (DXA) of the lumbar spine in supine position. Duplicate postero-anterior (PA) and lateral DXA measurements were performed in 60 women. Precision errors of the single vertebral levels using lateral DXA ranged from 3.3% to 4.9%. The combination of all levels improved the precision errors to 2.0%. Paired PA and lateral DXA measurements (Hologic QDR 2000) including the vertebral levels L2 to L4 were performed in 331 postmenopausal women. In 42 women an overlap of L4 by the pelvis was suspected on the lateral DXA images. Vertebral fractures were assessed as a fracture/non-fracture dichotomy. L4 and combinations of vertebrae including L4 showed the best discriminatory capabilities with respect to vertebral fractures in receiver operating characteristic (ROC) analyses, t-tests and Z-scores, with smaller variability of the results when multiple vertebral levels were used. The areas under the ROC curves were 0.662 and 0.639 for lateral and PA measurements of L2 to L4, respectively when all women were included. Excluding the women with pelvic overlap on lateral DXA scans improved the ROC area for lateral scans to 0.686 while that for PA scans remained almost constant (0.641). The differences between PA and lateral measurements were not statistically significant. In 162 women of our study cohort an additional quantitative computed tomography (QCT) measurement of the vertebral levels L2 to L4 was performed and overlapping bony structures at the three levels were studied.(ABSTRACT TRUNCATED AT 250 WORDS)

Absorptiometry, Photon↗
PubMed1994

Dual x-ray absorptiometry forearm software: accuracy and intermachine relationship.

An ash study was performed to analyze the accuracy of forearm measurements at the one-third site of three dual x-ray absorptiometry (DXA) systems using 20 cadavers. A Hologic QDR-2000, a Hologic QDR-1000/W, and a Lunar DPX-L system were used. The correlations between ash weight and DXA BMC were excellent for the three instruments (r > 0.97, p < 0.001), with accuracy errors < 5.2%. To perform a forearm cross-calibration of bone mineral content (BMC) and density (BMD) between the scanners, 10 healthy volunteers were additionally scanned at the distal one-third radius. The correlations among the DXA machines were excellent (r > 0.95); the absolute BMC and BMD values were significantly different between the two Hologics and the Lunar machine. The slope and intercept of both the BMC and BMD between the two Hologic systems were close to unity. In conclusion, the DXA forearm software packages provide accurate methods for assessing bone mineral content and density. The conversion of data among different manufacturers should be performed by careful cross-calibration measurements.

Absorptiometry, Photon↗
PubMed1994

Universal standardization for dual x-ray absorptiometry: patient and phantom cross-calibration results.

The comparison of patient data among different dual x-ray absorptiometry (DXA) scanners is complicated because no universally accepted cross-calibration procedure or standard currently exists. This study was performed under the auspices of the International DXA Standardization Committee to establish appropriate cross-calibration parameters. Posteroanterior (PA) lumbar spine measurements of 100 women, ages 20-80 years (mean 52.6 +/- 16, range of BMD = 0.4-1.6 g/cm2) were obtained on a Norland XR26 Mark II, a Lunar DPX-L, and a Hologic QDR 2000 densitometer using standard procedures (pencil beam mode for all three scanners). Area, BMC, and BMD results from the different scanners were compared for all patients. In addition, the European spine phantom (ESP) and the European spine phantom prototype (ESP prototype), as well as standard phantoms from all three manufacturers, were evaluated on the three systems. To achieve universal scanner calibration, we used the intercept and slope of the patient's correlations and the value of the middle vertebra of the ESP as a reference point in a series of standardization formulas, and we have expressed the results as sBMD (mg/cm2). The correlations of the patients' spinal BMD values were excellent for each of the three scanner pairs. The average absolute difference in patient spinal BMD values (L2-4) between Hologic and Norland was 0.012 g/cm2 (1.3%); it was 0.113 g/cm2 (11.7%) between Hologic and Lunar and 0.118 g/cm2 (12.2%) between Norland and Lunar. The phantoms' regression lines approximated those of the patient regression lines, and the phantoms with only one measurement point were very close to the patients' regression lines. After applying the standardization formulas, the average absolute differences for the 100 patients were 28 mg/cm2 (2.7%) for Hologic/Norland, 23 mg/cm2 (2.2%) for Hologic/Lunar, and 29 mg/cm2 (2.8%) for Norland/Lunar. Average BMD results for the patients before correction were 0.972 mg/cm2 for Hologic, 1.100 g/cm2 for Lunar, and 0.969 g/cm2 for Norland. After correction, sBMD results for patients were 1045 mg/cm2 for Hologic, 1047 mg/cm2 for Lunar, and 1043 mg/cm2 for Norland. The standardization approach as performed in our study provided compatibility of DXA results obtained on different scanners.

Absorptiometry, Photon↗
PubMed1994

Phantom studies simulating the impact of trabecular structure on marrow relaxation time, T2'.

Phantom studies were conducted to investigate the impact of trabecular structure on the T2' signal measured by MRI. For a separation of density from structural effects, several phantoms were built. They consisted of parallel polyethylene strings arranged in a variety of different patterns to simulate a) a constant uniform trabecular distribution with increasing trabecular thickness and b) different structures with identical overall trabecular density. An asymmetric spin echo sequence was used to determine the apparent relaxation time T2'. Changes in T2' are induced by susceptibility differences between the polyethylene strings simulating trabeculae and Gd-DTPA doped saline simulating bone marrow. The results showed an increasing T2' decay rate with a) decreasing spacing while the string density was constant and b) with increasing string density while the string arrangement was constant. The results demonstrate that the T2' signal is affected not only by density but also by spatial distribution. However, the results also indicate that a separation of the two effects is not possible from a T2' measurement alone, but that e.g., a matching CT slice that would provide purely density information is additionally needed. Theoretical simulations confirmed these results.

Bone Marrow↗
PubMed1994

Radiographic absorptiometry for bone mineral measurement of the phalanges: precision and accuracy study.

PURPOSE: To evaluate the accuracy and precision of a radiographic absorptiometry (RA) method for assessment of bone mineral of the middle phalanges. MATERIALS AND METHODS: Nineteen cadaveric hands were radiographed with an aluminum wedge, once at 50 kVp and 400 mA and once at 60 kVp and 300 mA. Bone mineral content (BMC) and bone mineral density (BMD) of the second to fourth middle phalanges, expressed in arbitrary units (BMC-AU and BMD-AU), were analyzed and averaged in each hand. RESULTS: The precision error of this method was 1.0% for BMC-AU and 0.6% for BMD-AU. A 2.0%-2.4% reduction in BMD-AU seen on radiographs obtained through ethanol thicknesses of 5 and 6 mm compared with that seen on controls was statistically significant (P < .01). The correlation between BMC-AU and forearm BMC determined with dual x-ray absorptiometry was good (r = .887), and that between BMC-AU and ash weight in the phalanges was excellent (r = .983). CONCLUSION: The RA method is precise and accurate for bone mineral assessment of the peripheral appendicular skeleton.

Absorptiometry, Photon↗
PubMed1993

Quality assurance for bone densitometry research studies: concept and impact.

A concept for quality assurance (QA) in bone densitometry has been developed for clinical multicenter studies. Major elements provided by a coordinating center comprise (1) consulting services and certification of participating centers in the start-up phase of the study, (2) review of scan data acquired on QA standards for cross-calibration and longitudinal assessment of scanner stability, (3) review of selected patient data as well as of problem cases during the study, and (4) comprehensive review and correction of patient results based on QA data after conclusion of the study. Limitations of phantom-based QA data should be acknowledged. Typical problems encountered during research studies and guidelines for solutions are presented. Successful implementation of QA measures may yield substantial enhancement of statistical power. Depending on the study design and the variability of response within patient groups, improvement in precision due to QA measures may reduce the smallest detectable difference between subject groups or, alternatively, sample size by a few to more than 50%, and thus may contribute to a substantial reduction in study cost. Formulae for calculation of the magnitude of these effects are presented. To maximize the net benefit, QA efforts have to be limited to levels that assure reliability of the data at acceptable QA cost. While QA programs at individual clinical sites or for local practitioners may not need to be as extensive as for multicenter clinical trials, awareness of the potential problems and implementation of basic QA measures will help in obtaining high-quality bone densitometry results.

Bone Density↗