Osteoporosis is characterized by decreased bone mass that may lead to an increased risk of fractures. In addition, osteoporosis and ageing is associated with a reciprocal decrease of osteogenesis and an increase of adipogenesis in bone marrow, being driven by respective key molecules Runx2 and PPARγ.¹ Parathyroid Hormone (PTH), a bone anabolic agent, increases osteogenic cells, thereby leading to a rapid increase in trabecular bone, in addition to adipocytes number reduction, in bone marrow.^2-3 Osteoporosis is commonly diagnosed by assessing Bone Mineral Density (BMD) with dual-energy X-ray absorptiometry (DEXA).⁴ This method is effective when significant loss of bone is present. Although MRI scan is capable of quantifying the amount of adipocytes in marrow, the procedure is costly. Here we present, a low-field NMR measurement that is capable of detecting changes in adipogenic population in the bone marrow during early stages of ovarectomy (OVX) induced osteoporosis in rats. Moreover, OVX rats treated with PTH showed significant decrease of adipogenesis correlated with osteogenesis of trabecular bone. NMR scans were performed on an NMR-MOUSE (Mobile Universal Surface Explorer, Magritek, NZ). The device consists of a permanent U-shaped magnet, resulting in B₀=0.3T, with highly flat sensitive volume at a distance of 25 mm parallel to the magnet surface (XY plane), and with a strong stray-field gradient of ~8T/m (see Figure 1). An NMR signal profile was acquired along the radial axis of the bone, for definition of the scanning zones (either the center or periphery of the marrow cavity, shown in Figure 2). Then, T2 was acquired using a CPMG-like sequence with 200 averages, 700 echoes, TR=1800 ms, TE=65 , scan time ~ 6 min. An estimation method based on statistical signal processing was applied to the acquired CPMG train.⁵ T1 was acquired using a saturation recovery pulse sequence with 18 different recovery times spaced exponentially between 0-2200 ms with 36 averages, 350 echoes, TR=2500 ms, TE=65 , scan time ~ 27 min. ADC was acquired using a static gradient stimulated echo with 14 different B-values between 50 and 1000 $$$\frac{s}{\mu m ^2}$$$ with 200 averages, 250 echoes, TR=400 ms, TE=65 , scan time ~19 min. The ability of the low-field portable NMR scanner to detect bone marrow changes was tested. A comparable time series experiment was performed on 3-month-old, female Sprague Dawley rats (n=32), which were divided into two equal groups ovariectomized (OVX) and sham-operated (sham) rats. The femur and tibia from both hind limbs were isolated and underwent ex-vivo NMR scans, BMD measurements, and histology. In the first experiment the scans were performed in the central zone of the marrow cavity at 1 week, 1.5, 3.5 and 4.5 months post operations. A second experiment was performed aimed to find whether treatment with PTH during five weeks, starting one week post operation prevented the adipogenic pathway that is observed in OVX and whether it can be detected early by NMR scans in both the central and peripheral zones.Significant changes in the center of the marrow cavity of OVX bones were observed after 3.5 and 4.5 months, relative to sham operated rats. Two NMR relaxation times, T1 and ADC, decreased in the OVX bones, while T2 increased. The significant separation of the groups revealed by a multidimensional analysis justifies an automated classification for future measurements, as shown in figure 4. In the PTH treatment experiment significant differences are shown after only 1.5 months, when measured in the peripheral zone. T2 values of OVX bones are significantly higher than PTH treated and sham operated rats (see figure 5). There are some indications that by analyzing separately femur and tibia bones, the latter allows a more sensitive detection of changes, however it requires a broader sample group. These results are in correlation with a drop in BMD value and decreased red bone marrow, as shown in figure 6.This study suggests a potential use of a tabletop NMR device for detecting the early bone marrow changes that occur as osteoporosis develops. Clinical translation resulting in an affordable version of this device in the future could facilitate continuous monitoring of treatment efficacy. Future work will focus on expanding peripheral results, with additional NMR relaxation times and will further examine varying effects of the disease and PTH treatment on the femur and tibia bones.