Biological tissues usually contain distinct water compartments with different transverse relaxation times. In this study, two-dimensional, multi-slice, ultrashort echo time spectroscopic imaging (UTESI) was used with bi-component analysis to detect bound and free water components in musculoskeletal tissues. Feasibility studies were performed using numerical simulation. Imaging was performed on bovine cortical bone, human cadaveric menisci and the Achilles' tendons of volunteers. The simulation study demonstrated that UTESI, together with bi-component analysis, could reliably quantify both T(2)* and fractions of the short and long (2)* components. The in vitro and in vivo studies each took less than 14 min. The bound water components showed a short T(2)* of ~0.3 ms for bovine bone, ~1.8 ms for meniscus and ~0.6 ms for the Achilles' tendon. The free water components showed about an order of magnitude longer T(2)* values, with ~2 ms for bovine bone, ~14 ms for meniscus and ~8 ms for the Achilles' tendon. Bound water fractions of up to ~76% for bovine bone, 50% for meniscus and ~75% for the Achilles' tendon were measured. The corresponding free water components were up to ~24% for bovine bone, 50% for meniscus and ~25% for the Achilles' tendon by volume. These results demonstrate that UTESI, combined with bi-component analysis, can quantify the bound and free water components in musculoskeletal tissues in clinically realistic times.

Recent proton magnetic resonance (MR) spectroscopy studies have shown that cortical bone exists as different components which have distinct transverse relaxation times (T2s). However, cortical bone shows zero or near zero signal with all conventional MR sequences on clinical scanners and the different water components cannot be assessed with this approach. In order to detect signal in this situation a two-dimensional (2D) non-slice selective ultrashort echo time (UTE) pulse sequence with a nominal TE of 8 μs was used together with bi-component analysis to quantify bound and free water in bovine cortical bone at 3T. Total water concentration was quantified using a 3D UTE sequence together with a reference water phantom. 2D and 3D UTE imaging were performed on 14 bovine bone samples which were subjected to sequential air-drying to evaluate free water loss, followed by oven-drying to evaluate bound water loss. Sequential bone weight loss was measured concurrently using a precision balance. Bone porosity was measured with micro computed tomography (μCT) imaging. UTE measured free water loss was higher than the volume of cortical pores measured with μCT, but lower than the gravimetric bone water loss measured during air-drying. UTE assessed bound water loss was about 82% of gravimetric bone water loss during oven-drying. On average bovine cortical bone showed about 13% free water and 87% bound water. There was a high correlation (R = 0.91; P < 0.0001) between UTE MR measured free water loss and gravimetric bone weight loss during sequential air-drying, and a significant correlation (R = 0.69; P < 0.01) between UTE bound water loss and gravimetric bone weight loss during oven-drying. These results show that UTE bi-component analysis can reliably quantify bound and free water in cortical bone. The technique has potential applications for the in vivo evaluation of bone porosity and organic matrix.

Biological tissues frequently contain different water compartments, and these often have distinct transverse relaxation times. Quantification of these may be problematic on clinical scanners because spin echo sequences usually have initial echo times that are too long to accurately quantify shorter relaxation time components. In this study, an ultrashort echo time pulse sequence was used together with bicomponent analysis to quantify both the short and long T 2 components in tissues of the musculoskeletal system. Feasibility studies were performed using numerical simulation, and on phantoms and in vitro tissues including bovine cortical bone, ligaments, menisci, tendons, and articular cartilage. The simulation and phantom studies demonstrated that this technique can quantify T 2 * and fractions of the short and long T 2 components. The tissues studies showed two distinct components with short T 2 *s ranging from 0.3 ms for bovine cortical bone to 2.1 ms for menisci, and long T 2 *s ranging from 2.9 ms for bovine cortical bone to 35.0 ms for articular cartilage. The short T 2 * fraction ranged from 18.5% for patella cartilage to 80.9% for ligaments. The results show that ultrashort echo time imaging with bicomponent analysis can quantify the short and long T 2 water components in vitro in musculoskeletal tissues. Magn Reson Med 67:645-649,

Background: The objective of this study was to evaluate changes in resting energy expenditure (REE), body composition and metabolic parameters, and to investigate predictors of the results in seriously obese patients after Roux-en-Y gastric bypass (RYGBP).Methods: 31 patients (BMI 44.4 ± 4.8 kg/m 2 ; 27 female, 4 male; 37.3 ± 11.1 y) were evaluated at baseline and 6 months after RYGBP. Weight, REE, waist circumference (WC), fat mass (FM) and fat-free mass (FFM), physical activity, food intake, fasting glucose (GLU), insulin (INS), HOMA-IR and lipid concentrations were measured. Results: At 6 months, percentage of weight loss (%WL) was 29.0 ± 4.4% and percentage of excess weight loss was (%EWL) 59.7 ± 12.3%. FM loss corresponded to 77.1 ± 12.2% of the weight loss. REE decreased from 33.4 ± 4.1 to 30.1±2.6 kcal/kg FFM (P<0.05). Significant decreases (P<0.001) were observed in GLU, INS, HOMA-IR, LDL-cholesterol and triglycerides. %EWL was correlated with baseline INS (r=0.44; P=0.014), baseline HOMA (r=0.43; P=0.017), change in %FM (r=0.67; P<0.001) and change in WC (r=0.5; P<0.01). Decrease in REE/FFM (%) was positively correlated with baseline REE/FFM% (r=0.51; P<0.005) and change in %FM (r=0.69; P<0.001). Initial REE/FFM, baseline energy balance and FM change explain 90% of REE/FFM decrease.Conclusion: RYGBP was an effective procedure to induce significant weight loss, fat mass loss and improvement in metabolic parameters in the short term. Metabolic adaptation was not related to FFM wasting but to a higher baseline REE. Fasting hyperinsulinemia was the best single predictor of weight loss after RYGBP.