Single X-ray absorptiometry of the forearm: Precision,correlation, and reference data

The performance of a single X-ray absorptiometry (SXA) device incorporating an X-ray tube as a photon source was evaluated with respect to precision in vivo and in vitro, scan time, image quality, and correlation with an existing dual energy X-ray absorptiometry (DXA) device. SXA precision in vivo, expressed as a coefficient of variation (CV), was 0.66% for bone mineral content (BMC) and 1.05% for bone mineral density (BMD). Precision in vitro, based on 78 BMC measurements of a forearm phantom over 195 days, was 0.53%. Correlation with DXA at the 8 mm distal forearm site was high (r=0.97 for BMC and r=0.96 for BMD). A preliminary SXA reference database composed of 151 healthy Caucasian American women was developed to facilitate the interpretation of patient measurements. SXA scan time was 4 minutes and delivered a radiation exposure of 1.68 mrem. SXA image quality and spatial resolution were superior to SPA and comparable to DXA.     

Interpretation of whole body dual energy X-ray absorptiometry measures in children: comparison with peripheral quantitative computed tomography

The assessment of bone health in children requires strategies to minimize the confounding effects of bone size on dual energy X-ray absorptiometry (DXA) areal bone mineral density (BMD) results. Cortical bone composes 80% of the total skeletal bone mass. The objective of this study was to develop analytic strategies for the assessment of whole body DXA that describe the biomechanical characteristics of cortical bone across a wide range of body sizes using peripheral quantitative computed tomography (pQCT) measures of cortical geometry, density (mg/mm³), and strength as the gold standard. Whole body DXA (Hologic QDR 4500) and pQCT (Stratec XCT-2000) of the tibia diaphysis were completed in 150 healthy children 6–21 years of age. To assess DXA and pQCT measures relative to age, body size, and bone size, gender-specific regression models were used to establish z scores for DXA bone mineral content (BMC) for age, areal BMD for age, bone area for height, bone area for lean mass, BMC for height, BMC for lean mass, and BMC for bone area; and for pQCT, bone cross-sectional area (CSA) for tibia length and bone strength (stress-strain index, SSI) for tibia length. DXA bone area for height and BMC for height were both strongly and positively associated with pQCT CSA for length and with SSI for length (all P < 0.0001), suggesting that decreases in DXA bone area for height or DXA BMC for height represent narrower bones with less resistance to bending. DXA BMC for age (P < 0.01) and areal BMD (P < 0.05) for age were moderately correlated with strength. Neither DXA bone area for lean mass nor BMC for lean mass correlated with pQCT CSA for length or SSI for length. DXA BMC for bone area was weakly associated with pQCT SSI for length, in females only. Therefore, normalizing whole body DXA bone area for height and BMC for height provided the best measures of bone dimensions and strength. DXA BMC normalized for bone area and lean mass were poor indicators of bone strength.     

Precision and Accuracy of Computed Digital Absorptiometry for Assessment of Bone Density of the Hand

Widespread osteoporosis testing and diagnosis are currently limited due to the high capital cost and reduced portability of many existing bone densitometry techniques. In this study we evaluated an inexpensive, low radiation, X-ray-based technique for assessing bone density of the middle phalanx. The technique, termed computed digital absorptiometry (CDA), is similar to radiographic absorptiometry (RA), using a single-energy X-ray source, an aluminum alloy step-wedge, and a charge-coupled device (CCD) detector system to automatically compute bone mineral content (BMC, g) and bone mineral density (BMD, g/cm²) in the middle phalanx of the third finger. The potential advantage of CDA over current RA techniques is that by using a filmless detector system, no off-site processing of radiographs is required and bone density results are obtained immediately after the test. Using human cadaveric specimens we determined the accuracy and short-term precision of CDA as well as its correlation with other hand and forearm bone densitometry methods. We obtained 26 cadaveric forearms (50% female, mean age 78 years, range 52–96 years). BMC and BMD of the middle phalanx of the third finger were determined using CDA and using RA. We assessed forearm BMC and BMD using single-energy and dual-energy X-ray absorptiometry (SXA and DXA). Precision of CDA was assessed by measuring ten of the specimens five times each with repositioning between measurements. Finally, the middle phalanx was dissected and incinerated to determine ash weight. BMC estimates from CDA and from RA were strongly correlated with ash weight (r = 0.89, p < 0.001 and r = 0.93, p < 0.001, respectively). The mean coefficients of variation using CDA were 1.36% and 0.70% for phalanx BMC and BMD, respectively. BMC and BMD measured by CDA were strongly correlated with hand and forearm bone mineral measurements performed by SXA, DXA and TA (r = 0.74–0.91). These results indicate that CDA accurately and precisely predicts BMC of the middle phalanx. Thus, with further clinical verification, this technique may prove to be a useful tool for the wide-spread testing and assessment of osteoporotic fracture risk.     

Adhesive Capsulitis of the Shoulder (Frozen Shoulder) Produces Bone Loss in the Affected Humerus, but Long-Term Bony Recovery Is Good

The objective of the study was to assess the short- and long-term effects of adhesive capsulitis (frozen shoulder) on the bone mineral density (BMD) of the affected extremity. BMD and clinical status of 22 patients (group A) with active-phase unilateral adhesive capsulitis and of 31 patients (group B) with a previous adhesive capsulitis (average 9 years before the examination) were determined. BMD was measured from the proximal humerus, humeral shaft, radial shaft, ulnar shaft, and distal forearm of both upper extremities using dual-energy X-ray absorptiometry (DXA). In group A, the mean BMD of the affected extremity, as compared with that of the unaffected side, was significantly lower in the proximal humerus (−5.6%; p = 0.001) and humeral shaft (−3.0%; p = 0.008). The radial shaft, ulnar shaft, and distal forearm showed no significant side-to-side differences. In contrast, in group B, the affected-to-unaffected side BMD differences were small and statistically insignificant. Compared with the 31 patients in group B, the relative side-to-side BMD difference of the 22 patients with active-phase disease (group A) was significantly lower in the proximal humerus (−5.6% vs. −1.5%, p = 0.009). In the other sites, groups A and B showed no significant differences. In conclusion, this study indicates that adhesive capsulitis of the shoulder results in significant bone loss in the humerus of the affected extremity, but in the long term, capsulitis-induced bone loss shows good recovery.     

The accuracy of volumetric bone density measurements in dual X-ray absorptiometry

New developments in dual x-ray absorptiometry (DXA) allow the performance of high precision anteroposterior (AP) and lateral scans of spinal bone mineral density (BMD, units: g/cm²) without the patient moving from the supine position. Data from both projections may be combined to give an estimate of the true volumetric bone mineral density (VBMD, units: g/cm³) of the lumbar vertebral bodies. This report presents a cadaver study designed to validate DXA measurements of volumetric bone density. Sections of whole lumbar spine were scanned in AP and lateral projections in a water tank to simulate soft tissue. Individual vertebrae were then divided to separate the vertebral body from the neural arch, and vertebral body volume was measured using the displacement of sand. The bone mineral content (BMC) of vertebral bodies and neural arches was measured by ashing at 250°C for 60 hours followed by 500°C for a further 24 hours. The results showed that DXA scanning systematically underestimated ashing data by 14% for AP BMC, 33% for vertebral body BMC, 23% for vertebral body volume, and 12% for VBMD. Despite these significant systematic errors, the DXA measurements and ashing values were highly correlated (r=0.979-0.992). The results suggested that after allowing for the systematic errors, lateral DXA parameters related closely to true BMC, volume, and VBMD.     

Comparative assessment of bone mineral density of the forearm using single photon and dual X-ray absorptiometry

Summary Forearm bone mineral density (BMD) was measured at proximal and distal sites by ¹²⁵I single photon absorptiometry (SPA) and by dual energy X-ray absorptiometry (DXA) in 67 consecutive subjects, aged 18–75 years. Correlations and regression equations between these two techniques were determined. All forearm measurements were significantly correlated with each other (r=0.599–0.926; P0.0001). Although SPA and DXA correct for fat in different ways, we found similar correlation and regression equations in women with body mass index measurements above and below the mean. In addition, forearm measurements by both techniques were moderately correlated with vertebral spine and hip BMD. We conclude that overall, SPA forearm measurements in a population can be calibrated to DXA measurements if necessary, and that DXA forearm measurements are as predictive of the remainder of the skeleton as SPA measurements.     

Dual X-ray absorptiometry total body bone mineral content and bone mineral density in 18- to 22-year-old caucasian men

Eighty-six healthy, young Caucasian 18-year-old men with no known disease or bone injury were recruited to this study at the United States Naval Academy. Change in bone mineral density (BMD) of the hip, lumbar spine, and distal tibia, and total body bone mineral content (TBMC) was measured by dual-energy X-ray absorptiometry (DXA). BMD and TBMC of these men were measured within 2 months (67 ± 3 days) of entering the Academy, and, at the end of their first, second, and fourth years. Hip BMD was unchanged during the study period (p > 0.05). Lumbar spine BMD increased 3% (p < 0.001) and distal tibia BMD increased 5% (p < 0.001). TBMC showed a 7.5% increase over the study period. In this group of young men, gain in BMD and TBMC is greatest to age 21 years, with minimal further increase after age 21. The significance of this rise in bone mass during early adulthood on risk for osteoporotic fractures in later life or its impact on exercise-related bone injuries is unknown and warrants further examination.     

Evaluation of vertebral volumetric vs. areal bone mineral density during growth

Bone mineral “density” (BMD) measured by dual-energy X-ray absorptiometry (DEXA) does not represent the volumetric density (grams per cubic centimeter), but rather the areal density (grams per square centimeter). This distinction is important during growth. The purpose of this study was to measure vertebral dimensions in cadavers of young pigtail macaques (Macaca nemestrina), and to derive equations to predict the volumetric bone density from noninvasive measurements. We measured the areal bone density by DEXA, vertebral volume by underwater weighing, mineral content by ashing, dimensions of lumbar vertebrae by calipers, and dimensions of vertebrae by radiography. Somatometric measurements of the female lumbar vertebral bodies showed that the shape changed during growth. The bone mineral content from the densitometer correlated significantly with the ash weight (r = 0.99, error 8.7%). The correlation coefficient between the volumetric bone mineral density and areal BMD measurement was significant (r = 0.68, p < 0.0001) with a 9.5% error; this improved significantly to 0.82 (7.2% error) when the BMD was divided by the vertebral depth from the radiograph. Areal BMD showed a strong correlation with age (r = 0.82, p < 0.0001), with an average increase of 7.4%/year. In contrast, volumetric mineral density showed a weak relationship with age (r = 0.43, p < 0.01), for an average increase of 1.5%/year. When studying bone mineral density during growth, the differences between volumetric and areal bone mineral density should be taken into consideration. (     

A Pilot Study of Body Composition and Bone Mineral Density in Healthy Men From Argentina

A precise assessment of bone mineral density (BMD) and body composition can be performed using dual-energy X-ray absorptiometry (DXA). Values of body composition for males would be useful to evaluate the occurrence of alterations in body composition in a number of diseases. The objectives of this study were to establish BMD and body composition values in healthy men and to analyze age-related changes. BMD and body composition of total body and subareas were determined in 116 healthy men (aged 20–79 yr) using DXA. Comparison between 20–29- and 70–79-yr-old men showed that older subjects were shorter (p < 0.03), and had a higher body mass index (p < 0.01). Fat mass increased (+46.7%; p < 0.001) especially in the trunk. Lean mass (LM) decreased (−9.4%; p < 0.05) mainly in the arms and legs. Bone mineral content (BMC) and BMD decreased (−15.3% [p < 0.001], −6.3% [p < 0.05], respectively). Correlation was observed between BMC and LM (r = 0.7, p < 0.01). Values of BMD and body composition in healthy men were obtained. A relation was observed between bone mass and body composition, suggesting that the age-related decrease in LM may be associated to bone mass loss. Further studies should be conducted to elucidate the role of body composition in the occurrence of osteoporosis in men.     

The Effect of Peritoneal Dialysate on DXA Bone Densitometry Results in Patients with End-Stage Renal Disease

The bone mineral density of patients undergoing peritoneal dialysis (PD) is low compared to a healthy population. No studies have been conducted to investigate whether the presence of peritoneal dialysate affects dual-energy X-ray absorptiometry (DXA) results. We hypothesized that the presence of peritoneal dialysate would not affect the measurement of bone mineral density (BMD) or bone mineral content (BMC) in the spine. Thirty patients on PD had DXA scans of the lumbar spine and hip completed before and after the drainage of peritoneal dialysate. A paired t-test was used to compare the difference in area, BMC, and BMD before and after drainage of dialysate. A significant difference was found in the BMC of the spine before and after the drainage of dialyzate. We recommend that peritoneal dialyzate be removed prior to scanning patients on PD and that densitometry technologists should be observant about the presence of peritoneal dialysate.     

Switching from DXA pencil-beam to fan-beam. I: Studies in vitro at four centers

The performance of the Hologic QDR-2000 DXA osteodensitometer was critically evaluated at four centers, using at all four centers one bone equivalent humanoid spine phantom supplied by the manufacturer. Results were compared with results from Hologic QDR-1000/W using that phantom tested at the same centers.

It appears that the concept of fan-beam scanning—as used in the QDR-2000: a fan-beam, a linear array detector above the phantom, and an x-ray tube located rather close to the spine below the phantom—creates problems due to the magnification effect of the fan beam. The effect of decreasing the distance between the “vertebrae” of the phantom and the couch are: bone mineral content (BMC) increases by 2.8% per cm, projected area (Area) by 2.8% per cm, and bone mineral density (BMD) is unchanged.

When QDR-1000/W is upgraded to QDR-2000, BMD is relatively constant, but there are shifts of BMC and Area which are partly due to the magnification effect of the fanbeam. Replacement of a QDR-1000/W with a QDR-2000 can invalidate longitudinal measurements, even for BMD, unless the proportionality factors of the QDR-2000 are checked and, if necessary, changed. This is true for switching from QDR-1000/W to pencil-beam mode of QDR-2000 or to fanbeam mode of QDR-2000.

Even with pencil-beam mode, the long-term precision error with phantoms is higher for QDR-2000 than for QDR-1000/W (for BMD, 0.47% versus 0.35%).     

Comparison of bone densitometry of the phalanges,distal forearm and axial skeleton in early postmenopausal women participating in the EPIC study

We present baseline bone densitometry from the Early Postmenopausal Interventional Cohort study (EPIC, sponsored by Merck, Sharp & Dohme) for the first time, in which 1609 women from England, Oregon, Hawaii and Denmark are participating to investigate the efficacy of daily oral alendronate to prevent early postmenopausal bone loss. We compared radiographic absorptiometry (RA) of the phalanges for bone mineral density (BMD) measurement with single-energy X-ray absorptiometry (SXA) of the distal forearm, and dual-energy X-ray absorptiometry (DXA) of the lumbar spine, proximal femur and distal forearm. In a random subgroup of 308 women, aged 45–60 years, on average 6 years since menopause (YSM), bone densitometry was measured once at baseline by RA of the phalanges besides the mandatory measurements by DXA. Bone densitometry was furthermore measured by SXA at the Danish site (89 women). Sixty-eight of the women had duplicate measurements performed within 1–3 weeks to evaluate the short-term precision error (CV%). One hundred and one healthy premenopausal women, aged 25–48 years, were recruited at the Danish and Hawaiian sites to establish a reference group. The precision error was 1.5% for RA of the phalanges and in the range 1.0–2.2% for SXA and DXA. BMD by RA correlated with BMD measured by SXA and DXA in the range 0.45<r<0.72 (p<0.001). In conclusion, bone densitometry by RA of the phalanges is highly correlated with bone densitometry by SXA and DXA. RA of the phalanges has a short-term precision error comparable to that of SXA and DXA.     

Bone density of the radius,spine, and hip in relation to percent of ideal body weight in postmenopausal women

Summary Bone mineral content (BMC) and bone mineral density (BMD) of the spine (L2–L4) and hip (at femoral neck, Ward's triangle, and greater trochanter sites) were determined by dual-photon absorptiometry (DPA), and of the radius by single-photon absorptiometry (SPA) in healthy postmenopausal women aged 40–70 years. The relationships of BMC and BMD to years since menopause were examined separately in 97 women who were above 115% of ideal body weight (IBW) and in 128 women below. The heavier women had significantly greater mean BMC and BMD at each site than did the normal-weight women. In the normal-weight women, there was a significant negative correlation between BMD and years since menopause at each measurement site except the greater trochanter. In the obese women, BMD decreased with increasing years since menopause at the radius site only and BMC declined with increasing years after menopause at the hip (femoral neck and Ward's triangle region) as well as the radius. Thus, body size is a significant determinant of BMD in this population. The pattern of loss of BMD from Ward's triangle and femoral neck regions of hip are similar to that of the spine. The BMC and BMD findings in the hip suggest that remodeling occurs at this weight-bearing site which has a favorable effect on bone strength.     

Single X-ray absorptiometry: Performance characteristics and comparison with single photon absorptiometry

The aim of the present study was to evaluate a new device for measurement of forearm bone mass using the technique of single X-ray absorptiometry (SXA, DTX-100; Osteometer A/S, Rødovre, Denmark), and to compare the performance with the more traditional single photon absorptiometry (SPA, DT 100; Osteometer A/S, Rødovre, Denmark). The SPA phantom measurements showed a coefficient of variation of 0.43% and 0.42% for bone mineral content (BMC) and bone mineral density (BMD), respectively (39 months including seven source changes). The SXA precision errors were slightly lower with values of 0.30% and 0.30%, respectively. The patient measurements showed SPA coefficients of variation of 0.85% and 0.99% (BMC and BMD) and SXA coefficients of variation of 0.56% and 0.83%, respectively. The correlation between SPA and SXA values performed in 377 individuals yielded r values of 0.99 an 0.98 for BMC and BMD, respectively. The correlations between SXA measurements of the dominant and non-dominant forearm yielded anr-value of 0.95, with a slope of 0.949 (p<0.001) and an intercept of 0.204 (p<0.05). The non-dominant forearm thus had approximately 3% lower BMC than the dominant (the same was true for BMD). Correlations to spine and femur ranged fromr=0.48 tor=0.75. In conclusion, the new single X-ray absorptiometry forearm bone densitometer described in this paper has performance characteristics which allows it to be used both for diagnostic purposes and for the follow-up of treatment.     

An evaluation of dual-energy X-ray absorptiometry and comparison with dual-photon absorptiometry

Dual-photon absorptiometry (DPA) is a well-established procedure for measuring bone mineral density (BMD). Recently, dual-energy X-ray absorptiomery (DXA) has become available, which has the ability to measure BMD both regionally and in the total body (TB). We have evaluated the in vivo and in vitro precision of a DXA instrument and compared it with a DPA instrument with similar software characteristics.The short-term precision of BMD measurements using DXA was assessed in 65 postmenopausal women who had duplicate scans performed, with repositioning between scans. Precision was 0.9% in the lumbar spine and 1.4% in the femoral neck.The midterm precision of DXA was compared with DPA by scanning 10 volunteers a mean of four times over 24 weeks, on both instruments. The precision of the bone mineral content (BMC) and area measurements was significantly better (P<0.05) with DXA than with DPA. Long-term in vitro precision was assessed by scanning an aluminium spine phantom over 42 weeks, and a cadaveric sample over 52 weeks, on both instruments. Precision was similar using the aluminium phantom, but was significantly improved (P<0.001) when using DXA for scanning the cadaveric sample.Highly significant correlations (allP<0.001) of BMD, BMC and area measurements were observed when 70 volunteers were scanned on both instruments. However, there was a systematic difference in BMD values between the instruments. The precision of TB composition measurements assessed in 16 volunteers, over a 16-week period, were TB BMD 0.65%, TB lean tissue 1.47%, and TB fat tissue 2.73%. The correlation between weight measured by electronic scales and TB mass as measured by DXA, which was assessed in 70 volunteers, was excellent (r=0.99,p<0.001).We conclude that DXA offers improvements in measuring BMD over DPA in terms of faster scanning times and improved resolution, resulting in better precision, with the additional advantage of the ability to measure TB composition with high precision.     

Bone properties as estimated by mineral density, ultrasound attenuation, and velocity

Quantitative ultrasound (QUS) analysis of bone has been suggested to have a level of performance equal to dual-energy X-ray absorptiometry (DXA) for the assessment of fracture risk. In this study, QUS and DXA measurements were conducted on bovine trabecular bone in vitro using commercially available clinical instruments. The samples were then mechanically tested to obtain Young’s modulus and ultimate strength. In addition, QUS and DXA parameters of the human calcaneus (n = 34) were measured in vivo. The measurements revealed a significant effect of bovine bone size on broadband ultrasound attenuation (BUA) and speed of sound (SOS) in vitro. By normalizing the DXA and QUS results with bone thickness we could systematically improve their ability to predict bone strength. However, in bovine trabecular bone, BUA showed no significant linear correlation with either bone mineral density (BMD), Young’s modulus, or ultimate strength. This finding may be typical of only high-density and low-porosity bovine bone. We significantly improved prediction of ultimate strength by combining density and ultrasound velocity results as compared with assessments of volumetric BMD_vol (p < 0.05) or SOS (p < 0.001) alone. However, the improvement was not significant if BMD_vol, instead of wet density, was used. Altogether, 88% of the variation in the ultimate strength of bovine bone could be explained by combined density and ultrasound velocity. In vivo, SOS showed a weak negative correlation with heel width (r = −0.350). The in vivo measurements also showed a close correlation for BUA with BMD in the human calcaneus. This suggests that BUA is more suitable for quantitative analysis of low-density trabecular bone.     

Changes in muscle mass, fat mass, and bone mineral content in the legs after stroke: a 1 year prospective study

Demineralization and muscle atrophy, common among patients with hemiplegia, may be risk factors for future hip fracture. The aim of this longitudinal study was to investigate changes in lean (muscle) mass and bone mineral content (BMC) of the legs during the first year after stroke according to the patient’s ambulatory level. Twenty-five patients immobilized due to acute stroke were followed. BMC and lean mass of each leg were measured at a mean of 7 days, 2 months, 7 months, and 1 year after the stroke using dual-energy X-ray absorptiometry. Both BMC and lean mass had decreased significantly in the paretic leg (p < 0.05) at the 1 year evaluation and the loss was significantly greater on the paretic side compared with the nonparetic side (p < 0.001). Patients who had not relearned to walk at the 2 month evaluation (n = 12) lost 6% (p < 0.05) of their lean mass in the paretic leg during this time period, and this mass was not regained within the subsequent 10 months. In contrast, a significant 5% loss of lean mass found at 2 months on the nonparetic side was regained completely. With respect to the patients who relearned to walk within the first 2 months (n = 13) lean mass had increased by 5% after 1 year (p < 0.05) in the nonparetic leg, whereas no significant changes were found in the paretic leg during follow-up. Both groups of patients did, however, lose bone mineral in the paretic leg during the first year after stroke (9% and 6%, respectively, p < 0.05), but only the patients who were still unable to walk by 2 months had significant bone loss in the nonparetic leg also (3%, p < 0.05). Thus, lean muscle mass is rapidly lost and may be regained shortly after stroke, whereas loss of BMC appears difficult to prevent, especially on the paretic side. Regaining muscle mass may, however, slow the loss of bone mineral.     

DXA、QCT和SPA方法测量47例绝经后妇女骨质疏松症的比较

以骨密度测量应用最广的３种方法（ＤＸＡ─双能ｘ线吸收法，ＱＣＴ─定量ＣＴ法和ＳＰＡ─单光子吸收法）测量绝经后妇女的骨矿密度，比较其测量值、诊断结果和相关关系。首先用ＳＰＡ法测量绝经后妇女１８１例，诊断骨质疏松（ＯＰ）４７例。三种方法测量骨矿密度的均值分别低于峰值骨量的Ｍ─２ｓ的９％、２１．４％和２１％，且ＤＸＡ和ＱＣＴ两种方法测量的均值都在骨折阈值范围内。ＤＸＡ和ＱＣＴ诊断４７例ＯＰ之间无显著性差异，当排除椎骨骨质增生后的ｘ２＝０．２３７，且ＤＸＡ和ＱＣＴ测量值之间为正相关，ｒ＝０．７９９，而ＤＸＡ、ＱＣＴ和ＳＰＡ之间的相关系数，ｒ＝０．１８５和０．２８５，ＤＸＡ诊断ＯＰ的敏感性为８６．６％，特异性为７０％。     

Bone mass changes during pregnancy and lactation in the rat

We examined bone mass changes in the total, axial, and appendicular skeleton as well as in the different subareas of femur and tibia in rats fed on a normal calcium diet. A total of 16 virgin Wistar rats, approximately 5 months of age (270 ± 30 g), were assigned to two groups of eight rats each. One group was mated and, for each pregnant rat, a nonpregnant control rat was studied simultaneously. Weaning was performed when the pups reached 38 ± 3 g body weight. At the beginning (t = 0), on the first day postpartum (t = 22 days), and at weaning (t = 45 days), total skeleton bone mineral content (BMC), area, and bone mineral density (BMD) were determined by dual-energy X-ray absorptiometry (DXA) in vivo under anesthesia. Body weight increased significantly during pregnancy (p < 0.05) and decreased at weaning, whereas control rats showed a slow, gradual increment without reaching a significant difference. During pregnancy, BMC and area of the total skeleton increased significantly in pregnant rats, but the changes in BMD were not different compared with the control group. A completely different pattern was observed between groups during the 23 days of lactation. While the skeleton continued to grow in the control group (BMC and area increased), the total skeleton of lactating rats showed no change in area (size), small decreases in BMC, and a significant decrease in BMD (p < 0.05). Consequently, although BMC and BMD of both groups were similar at the time of delivery, BMC was 12.0% lower and BMD 4.9% lower at the end of lactation in the lactating rats compared with the control group. The contribution of the maternal skeleton to the lactation period was not similar; that is, the areas with the highest trabecular component showed the greater average differences in BMD at the time of weaning (proximal tibia −19.9%, distal femur −12.6%, spine −10.9%) (p < 0.05), compared with relatively minor, nonsignificant losses in areas where cortical bone predominates (distal tibia −5%, middle tibia −5.2%). Our experimental results demonstrated the usefulness of DXA in vivo to visualize changes in BMD during the reproductive cycle of the rat. Moreover, the data confirm that normal pregnancy in the rat appears to exert little influence on bone, whereas lactation induces significant bone loss, mainly in the areas of predominant trabecular bone.