Biomedical subjects

Hee Kwon Song

Publications and source records attributed to Hee Kwon Song.

21 records · Page 2Linked to original sources

PubMed2002

Intratendinous strain fields of the intact supraspinatus tendon: the effect of glenohumeral joint position and tendon region.

Rotator cuff tears are a common shoulder pathology and are hypothesized to relate to excessive tissue deformation. Few data exist, however, describing deformation of the rotator cuff as an intact, functional unit. Our purpose was to determine regional variations of intratendinous rotator cuff strain over a range of clinically relevant joint positions. A novel, MRI-based technique was utilized to quantify intratendinous strains in cadaveric shoulder specimens at 15 degrees, 30 degrees, 45 degrees, and 60 degrees of glenohumeral abduction in the scapular plane. The strain data were grouped into superior, middle, and inferior locations across the region where most rotator cuff tears occur clinically. A repeated measures ANOVA assessed the effects of joint position and tendon region on intratendinous strain. Few differences in intratendinous strain existed across tendon regions, but joint position had a pronounced effect. Specifically, intratendinous strain increased with increasing joint angle, and the 60 degrees strain was significantly greater than the 15 degrees strain across all tendon regions. These data suggest that joint position plays a larger role in rotator cuff mechanics than previously believed. Future studies will utilize this technique for quantifying intratendinous strain to assess the effects of partial-thickness rotator cuff tears.

Adult↗

PubMed2002

Role of magnetic resonance for assessing structure and function of trabecular bone.

The strength of trabecular bone and its resistance to fracture traditionally have been associated with apparent density. This paradigm assumes that neither the ultrastructural nor microstructural make-up of the bone is altered during aging and osteoporosis. During the past decade there has been growing evidence from both laboratory and clinical studies against this view. Recent advances in noninvasive imaging technology, notably micro-magnetic resonance imaging (micro MRI) and computed tomography, offer an opportunity to test the hypothesis that architecture is an independent contributor to bone strength. MRI appears to be ideally suited for this task because bone marrow has uniform high signal intensity while bone appears with background intensity, thus yielding a binary system tomographic system. However, in vivo trabecular bone imaging is hampered by the limited signal-to-noise ratio that precludes voxel sizes much smaller than trabecular thickness, which would be required to yield a bimodal intensity histogram for segmentation of the image into bone and marrow. The resulting partial volume blurring leads to fuzzy boundaries. Successful structure analysis thus demands more elaborate processing strategies. This article reviews new approaches conceived in the authors' laboratory toward acquisition, processing, and structural analysis of trabecular bone images in the limited spatial resolution regimen of in vivo micro MRI. These methods are shown to provide detailed insight into the three-dimensional trabecular network topology and scale at the distal radius or distal tibia that typically serve as surrogate sites. The micro MRI-derived structural parameters are shown to be associated with the bone's biomechanical properties and fracture resistance. Further, the technology has advanced to a stage permitting serial studies in laboratory animals and humans as a means to evaluate the effects of treatment. The method currently is confined to peripheral skeletal sites, and its extension to typical fracture sites such as the proximal femur hinges on further advances in detection sensitivity.

Animals↗

PubMed2002

Quantitative magnetic resonance imaging in the calcaneus and femur of women with varying degrees of osteopenia and vertebral deformity status.

Quantitative magnetic resonance imaging (QMRI) allows measurement of two parameters that are related to the integrity of the trabecular bone: R2*, the rate constant of the free induction signal, and trabecular bone volume fraction (BVF), the counterpart of apparent density. In this work, R2* and BVF were measured in 68 women (mean age, 58.2 +/- 9.5 years) of varying spinal bone mineral density (BMD) T scores (mean, -1.37 +/- 1.54) and vertebral fracture status on a commercial 1.5 T whole-body imager using customized image acquisition and processing techniques. Twenty-five of the patients had vertebral fractures, characterized by the total cumulative deformity burden exceeding 200%. R2* was measured in the calcaneus and proximal femur and BVF could be measured in the calcaneus only. On a pixel-by-pixel basis, calcaneal R2* and BVF within each subject were highly positively correlated (r2 = 0.61 +/- 0.11) but the correlation of region-of-interest (ROI) means for different calcaneal sites among patients was weaker (r2 = 0.34; p < 0.0001). The strongest discriminator of vertebral deformity was R2* of the calcaneus, which was lower in the fracture group, consistent with lower trabecular density. Among the calcaneal sites examined, the subtalar region, a location characterized by dense nearly horizontal trabeculae that transmit the stresses imparted by body weight from the tibia to the heel, best discriminated the two groups (p = 0.0001), with 77% diagnostic accuracy as determined from the area under the receiver operating characteristic (ROC) curve (compared with 66% for vertebral BMD). The cavum calcanei, an anterior site of low trabecular density, and the tuber calcanei (the location ordinarily used for ultrasound measurements) also had significantly reduced R2* in the fracture group (p < 0.005 and p = 0.01, respectively). The R2av*, computed as the average of all pixels in the calcaneus, was a strong discriminator as well (p < 0.005). On the other hand, calcaneal BVF was only marginally discriminating (p = 0.05). Among the BMD sites examined, the lumbar spine (average L1-L4) was significant (p = 0.005, 66% diagnostic accuracy), as was the femoral neck (p = 0.01). The data suggest the calcaneus to be suited as a surrogate site to assess vertebral osteoporosis and that R2* is sensitive to alterations in bone quality not captured by density.

Absorptiometry, Photon↗