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Biomedical subjects

P Van den Winkel

Publications and source records attributed to P Van den Winkel.

11 recordsLinked to original sources
PubMed2002

Magnesium bioavailability from mineral water. A study in adult men.

OBJECTIVE: To assess magnesium enteral absorption from a magnesium-rich mineral water. DESIGN: Experimental study. SETTING: Department of Nuclear Medicine, Brugmann Hospital, Brussels, Belgium. SUBJECTS: Ten healthy male volunteers in the age range 25-42 y. INTERVENTION: Each subject completed two sessions in a random order. At one session, they received an oral load of 300 ml of water (containing 1.2 mmol Mg), traced with (28)Mg, and at the other session they received an intravenous injection of (28)Mg, in order to take into account the metabolism of endogenous magnesium. The dietary consumption was further noted on a weekly diary. RESULTS: The mean bioavailability was 59.1% (s.d.+/-13.6). Magnesium absorption and age were significantly inversely correlated (r=-0.68, P=0.035). CONCLUSION: Magnesium-rich mineral water is a reliable source of magnesium. Our observation of decreased magnesium absorption with age deserves further investigations. SPONSORSHIP: The study was sponsored by SEV, Bourg la Reine, France.

Administration, Oral↗
PubMed1996

Cortical and total bone mineral content of the radius: accuracy of peripheral computed tomography.

The aim of the study was to evaluate the accuracy of an XCT 960 Stratec peripheral quantitative computed tomography (pQCT) device in assessing bone mineral content of the radius. We scanned 27 left forearm specimens excised from cadavers and focused on cortical bone mineral content (BMCc) at the junction of the middle and distal third and on total bone mineral content (BMCtot) at the distal end of the radius. Cylindrical specimens matched with those two sites were cut using a diamond circular saw, embedded in a polyester resin and subsequently submitted to two reference methods, nondestructive neutron activation analysis and flame atomic absorption spectrometry. Mineral contents measured by pQCT were closely correlated with those assessed by using the two reference methods, with correlation coefficients ranging from 0.862 to 0.960. The standard error of the estimate amounted 7-10% for the BMCc (junction of the middle and distal third), and 17-18% for the BMCtot (distal end). We conclude that pQCT is able to measure either cortical or total mineral content of the radius with a high degree of accuracy.

Aged↗
PubMed1995

Cortical thickness assessed by peripheral quantitative computed tomography: accuracy evaluated on radius specimens.

The purpose of the present study was to evaluate the accuracy of peripheral quantitative computed tomography (pQCT) in measuring the thickness of the radial cortex. Thirty left forearm specimens were scanned on an XCT 960 Stratec pQCT device using a 2.5 mm thick slice at the junction of the middle and the distal third of the radius. Cortical and trabecular areas were assessed using a threshold procedure; cortical thickness was subsequently calculated assuming a circular ring model for the radius. Cortical thickness was also measured on the true shape of bone using an iterative contour detection procedure. Subsequently 2.5 mm thick resin-embedded cylindrical radial specimens, matched with the site of pQCT examination, were obtained and contact radiographs were performed. After tenfold magnification, the cortical and trabecular areas of the specimens were measured using computerized planimetry and cortical thickness was calculated assuming a circular ring model. The cortical thickness could be assessed by pQCT in all cases using the threshold algorithm (mean (SD) 2.51 (0.58) mm) and in 21 cases could be directly measured on the true shape of bone (2.62 (0.32) mm). The cortical thickness of the specimens showed good correlation and high proportionality with that measured using pQCT with either the threshold algorithm (r = 0.941, slope = 0.976) or the iterative contour detection procedure (r = 0.883, slope = 0.987). In conclusion, pQCT is able to assess the thickness of the radial cortex, at the junction of the middle and the distal third, with high accuracy.

Aged↗
PubMed1995

Cortical mineral content of the radius assessed by peripheral QCT predicts compressive strength on biomechanical testing.

Our aim was to evaluate the role of cortical bone in resistance to compression in the human radius. Thirty-three left cadaver forearms were scanned on an XCT 960 Stratec CT scanner. Cortical density and cortical thickness were measured at the junction of the middle and distal third of the radius. Subsequently, 2-cm-high cylindrical specimens, centrated on the level of the CT slice, were cut. After removal of the endosteal trabecular bone, the specimens were submitted to compressive testing, using an Instron machine, and load deformation curves were obtained. Maximal stress (load corrected for cross-sectional area) showed a significant relationship with the density (r = 0.78) as well as with the thickness (r = 0.74) of the cortex. The closest correlation involved the maximal load and the mineral content of the cortex specimens (r = 0.87). We conclude that the mineral content of these radius cortex specimens, measured using peripheral QCT, predicts their compressive strength on biomechanical testing.

Aged↗
PubMed1993

Excision of a trabecular ROI from resin-embedded vertebrae: report on a computer-assisted method.

A major problem when evaluating the accuracy of quantitative computed tomography (QCT) against chemical analysis of bone mineral is to ensure that the same region of interest (ROI) is measured with two techniques. The method described here attempts to reach this objective. Forty-nine lumbar vertebrae were scanned. The mid-vertebral portion was sawed and embedded in a polyester resin. The ROI defined with an automated contour detection was transmitted, using a Hewlett-Packard scanjet, to a computer-assisted milling machine which excised a trabecular ROI sample. The volume of each trabecular sample was determined using an Archimedian method. ROI volumes assessed on QCT were highly correlated with those obtained with the Archimedian method (r = 0.98). The standard error of the estimate was 170 mm3 (4.5%). These results suggest that trabecular samples obtained with this method optimally agree with the ROIs selected on QCT examination.

Bone and Bones↗
PubMed1993

Size of cortical bone and relationship to bone mineral density assessed by quantitative computed tomography image segmentation.

RATIONALE AND OBJECTIVES: The accuracy of the measurement of the size of cortical bone on computed tomography (CT) images of human vertebrae was evaluated using an automated contour detection and segmentation procedure. METHODS: Forty human lumbar vertebrae were scanned using 8-mm slices and an automated detection for definition of trabecular and cortical region of interest. The vertebrae were embedded in a polyester resin and 8-mm-thick midvertebral specimens were excised using a diamond circular saw. Contact radiographs of these specimens were performed and, after photograph magnification, the cortical area was measured using computerized planimetry. RESULTS: Cortical area measured on CT images was highly correlated with the area measured by planimetry on the specimens (r = .91; P < .001) with, however, a systematic over-estimation. A significant relationship was found between density and width of the cortex (r = .56; P < .001). CONCLUSIONS: Computed tomography is able to assess the size of cortical bone in human vertebrae, but a threshold detection algorithm, as used in the current study, is not adequate to obtain the precise anatomic dimensions.

Aged↗
PubMed1992

Dual-energy X-ray absorptiometry of lumbar vertebrae: relative contribution of body and posterior elements and accuracy in relation with neutron activation analysis.

The bone mineral content of 34 lumbar vertebrae obtained from ten cadavers (three men, seven women; age 61-88 years) was measured using a pulsed source dual-energy X-ray absorptiometry (DEXA) apparatus. Scanning was performed in the frontal projection and was repeated on the vertebral bodies obtained after removal of the posterior elements of the vertebrae. Subsequently a nondestructive neutron activation analysis (NAA) was performed. The mineral content of the vertebral bodies was found to represent (mean, SEM) 53.0% (1.9%) of the content of the whole vertebrae. The mineral content of the vertebral bodies assessed with NAA (BMC NAA) and with DEXA (BMC DEXA) showed a high correlation: BMC NAAA = (1.016 x BMC DEXA) + 0.990 r = 0.949 (p less than 0.001). We conclude that the mineral content of lumbar vertebral bodies can be accurately measured in vitro in a water environment by DEXA, and that the mean contribution of the posterior elements of the vertebra to the calcium hydroxyapatite content of whole vertebrae measured in the frontal projection is as high as 47.0%.

Absorptiometry, Photon↗
PubMed1989

Interaction between the microtubule inhibitor tubulozole and gamma-irradiation in murine tumors in vivo.

The combined effect of the microtubule inhibitor tubulozole and gamma-irradiation has been investigated in vivo in subcutaneous MO4 fibrosarcomas and Lewis Lung carcinomas. A marked interactive effect on tumor growth was observed when 160 mg/kg tubulozole was orally administered before the tumors were treated with 10 Gy radiation. Dose dependency and optimal effect were obtained on tumor growth of MO4 tumor bearing animals when the drug treatment was given 6 hr prior to the irradiation. The optimal pretreatment time coincided with the time at which a peak mitotic index in the tumor tissue was observed. An enhancing effect is also noticed at other doses of radiation in MO4 tumors pretreated 6 hr before with 160 mg/kg tubulozole. The interactive effect is maintained in a clinically relevant dose fractionation schedule whereby 8 fractions of 2 Gy each were pretreated 6 hr before with 80 mg/kg tubulozole. Tubulozole-T, the stereo-isomer of tubulozole, neither exhibits any antimicrotubular action nor exerts an antitumoral effect on its own or in combination with gamma-irradiation. The possible mechanisms of interaction between tubulozole and gamma-irradiation in tumor tissue are discussed.

Animals↗
PubMedDate not supplied

Mineral content of vertebral trabecular bone: accuracy of dual energy quantitative computed tomography evaluated against neutron activation analysis and flame atomic absorption spectrometry.

The goal of this study was to evaluate the accuracy of preprocessing dual energy quantitative computed tomography (QCT) for assessment of trabecular bone mineral content (BMC) in lumbar vertebrae. The BMC of 49 lumbar vertebrae taken from 16 cadavers was measured using dual energy QCT with advanced software and hardware capabilities, including an automated definition of the trabecular region of interest (ROI). The midvertebral part of each vertebral body was embedded in a polyester resin and, subsequently, an experimental ROI was cut out using a scanjet image transmission procedure and a computer-assisted milling machine in order to mimic the ROI defined on QCT. After low temperature ashing, the experimental ROIs reduced to a bone powder were submitted to either nondestructive neutron activation analysis (n = 49) or to flame atomic absorption spectrometry (n = 45). BMC obtained with neutron activation analysis was closely related (r = 0.896) to that derived from atomic absorption spectrometry, taken as the gold standard, with, however, a slight overestimation. BMC values measured by QCT were highly correlated with those assessed using the two reference methods, all correlation coefficients being > 0.841. The standard errors of the estimate ranged 47.4-58.9 mg calcium hydroxyapatite in the regressions of BMC obtained with reference methods against BMC assessed by single energy QCT, 47.1-51.9 in the regressions involving dual energy QCT. We conclude that the trabecular BMC of lumbar vertebrae can be accurately measured by QCT and that the superiority in accuracy of dual energy is moderate, which is possible a characteristic of the preprocessing method.

Aged↗