Regional measurement of bone calcium accretion rate and exchangeable pool with a whole-body counter: method and studies in subjects without bone disease

Use of dual-energy computed tomography to measure skeletal-wide marrow composition and cancellous bone mineral density

Temporal and spatial variations in bone marrow adipose tissue (MAT) can be indicative of several pathologies and confound current methods of assessing immediate changes in bone mineral remodeling. We present a novel dual-energy computed tomography (DECT) method to monitor MAT and marrow-corrected volumetric BMD (mcvBMD) throughout the body. Twenty-three cancellous skeletal sites in 20 adult female cadavers aged 40-80 years old were measured using DECT (80 and 140 kVp). vBMD was simultaneous recorded using QCT. MAT was further sampled using MRI. Thirteen lumbar vertebrae were then excised from the MRI-imaged donors and examined by microCT. After MAT correction throughout the skeleton, significant differences (p < 0.05) were found between QCT-derived vBMD and DECT-derived mcvBMD results. McvBMD was highly heterogeneous with a maximum at the posterior skull and minimum in the proximal humerus (574 and 0.7 mg/cc, respectively). BV/TV and BMC have a nearly significant correlation with mcvBMD (r = 0.545, p = 0.057 and r = 0.539, p = 0.061, respectively). MAT assessed by DECT showed a significant correlation with MRI MAT results (r = 0.881, p < 0.0001). Both DECT- and MRI-derived MAT had a significant influence on uncorrected vBMD (r = -0.86 and r = -0.818, p ≤ 0.0001, respectively). Conversely, mcvBMD had no correlation with DECT- or MRI-derived MAT (r = 0.261 and r = 0.067). DECT can be used to assess MAT while simultaneously collecting mcvBMD values at each skeletal site. MAT is heterogeneous throughout the skeleton, highly variable, and should be accounted for in longitudinal mcvBMD studies. McvBMD accurately reflects the calcified tissue in cancellous bone.

Comparison of bone formation rates measured by radiocalcium kinetics and double-tetracycline labeling in maintenance dialysis patients

We report 23 prospective studies on 18 maintenance dialysis patients in whom we measured skeletal mineralization rate (m) using 47Ca, analyzed by the expanding pool model, and compared it with the histologic bone formation rate (bfr), volume referent, estimated on tetracycline-labeled iliac crest bone. The patients showed a spectrum of bone disease types including adynamic bone, aluminum-related osteomalacia, and various degrees of secondary hyperparathyroidism. The mean width between double labels, on which mineral apposition rate depended, was estimated using a simple formula relating area to perimeter for each feature enclosed by the labels. Values for m ranged from 0 to 155 mmol calcium per day and for bfr from 0 to 124% per year. There was close correlation between m and bfr (r = 0.976), serum alkaline phosphatase (r = 0.968), and serum immunological parathyroid hormone (iPTH) (r = 0.868). When the volumetric bfr was converted to mass units and applied to the whole skeleton, using literature values for mineral density and cortical and trabecular mass, there was close agreement between the histologic and isotopic estimates of m (r = 0.959). The results validate the two methods and suggest they are interchangeable. However, use of a rigorous method to determine bfr appears to be essential.

Whole body and regional retention of Tc-99m-labeled diphosphonates with a whole-body counter: a study with normal males

A collimated whole-body counter was used to measure the retention and distribution of radioactivity along the longitudinal axis of the body at several times during the 24 hours after the intravenous injection of 50 microCi of Tc-99m-diphosphonates. Whole-body retention (WBR) was measured together with regional uptakes in the following four areas: head, chest, bladder, and legs using two structurally related Tc-99m-diphosphonate skeletal imaging agents: 1-hydroxyethylidene diphosphonate (HEDP) and methylene diphosphonate (MDP). The average 24 hour WBR values in young males, reflecting skeletal uptake of these tracers, were 17.7 +/- 2.2% (n = 20) and 31.0 +/- 2.4% (n = 3), respectively. A model of skeletal clearance was developed using the sum of two exponentials. In normal volunteers the initial rapid clearance phase of both tracers had a half-time of about 1 hour, whereas the slower second phase clearance had a half-time of 22 hours with HEDP and 44 hours with MDP. The WBR is usually calculated for the entire body only at 24 hours, but with the improved spatial resolution of a collimated whole-body counter, regional measurements could potentially be done over shorter periods (6-8 hours) in order to simplify the procedure.

Continuous mechanical pressure and joint tissue. Effect of synovial membrane products and indomethacin in vitro

We have previously reported that a continuous mechanical pressure of approximately 30 kgfcm-2 greatly inhibited the degradation of articular proteoglycans in calves. In the present report it is shown that indomethacin (5 micrograms/ml) failed to inhibit cartilage degradation caused by mechanical pressure. It is therefore suggested that prostaglandins do not mediate the inhibition of cartilage degradation exerted by continuous mechanical pressure. We have also reported previously that bovine-conditioned synovial medium (SM) greatly enhances the degradation of calf articular cartilage proteoglycans. We now show that the catabolic activity of SM was greatly (but not entirely) inhibited by the application of a continuous mechanical pressure. Simultaneous addition of indomethacin (5 micrograms/ml) to the cartilage cultures did not affect this result. However, the addition of indo-SM (SM from synovial tissue cultured in the presence of 5 micrograms/ml indomethacin) to cartilage cultures subjected to continuous mechanical pressure did not increase cartilage degradation, compared with the addition of DMEM alone. A hypothesis is proposed that continuous mechanical pressure may cause a change in the state of synovial factor receptors on the membranes of chondrocytes.