Purpose To develop a semi-quantitative MR-based hip osteoarthritis (OA) evaluation system (Scoring hip osteoarthritis with MRI, SHOMRI), and to test its reproducibility and face validity. Material and Methods The study involved 98 subjects with informed consent. Three-Tesla MR imaging of hip was performed in three planes with intermediate-weighted fat saturated FSE sequences. Two radiologists assessed cartilage loss, bone marrow edema pattern, subchondral cyst in 10 subregions, and assessed labrum in 4 subregions. In addition, presence or absence of ligamentum teres integrity, paralabral cysts, intraarticular body, and effusion in the hip joint were analyzed using the SHOMRI system. The reproducibility was assessed with intra-class correlation coefficient (ICC), Cohen’s Kappa values and percent agreement. SHOMRI scores were correlated with radiographic Kellgren-Lawrence (KL) and OARSI atlas gradings, and clinical parameters, the hip osteoarthritis outcome score (HOOS) and hip range of motion (ROM), using Spearman’s rank correlation and ordinal logistic regression. Results ICC values were in excellent ranging from 0.91 to 0.97. Cohen’s Kappa values and percent agreement ranged from 0.55 to 0.79 and 66 to 99 %, respectively. SHOMRI demonstrated significant correlations with KL and OARSI gradings as well as with clinical parameters, HOOS and ROM (P < 0 .05). Among the SHOMRI features, subchondral cyst and bone marrow edema pattern showed the highest correlation with HOOS and ROM. Conclusion SHOMRI demonstrated moderate to excellent reproducibility and significant correlation with radiographic gradings and clinical parameters.

Purpose To develop a robust sequence that combines T1ρ and T2 quantifications and to examine the in-vivo repeatability and diurnal variation of T1ρ and T2 quantifications in knee cartilage. Materials and Methods Six healthy volunteers were scanned in the morning and afternoon on two days using a combined T1ρ and T2 quantification sequence developed in this study. Repeatability of T1ρ and T2 quantification was estimated using root-mean-square coefficients-of-variation (RMS-CV). T1ρ and T2 values from morning scans were compared to those from afternoon scans using paired t-tests. Results The overall RMS-CV of in-vivo T1ρ and T2 quantification was 5.3% and 5.2% respectively. The RMS-CV of AM scans was 4.2% and 5.0% while the RMS-CV of PM scans was 6.0% and 6.3% for T1ρ and T2 respectively. No significant difference was found between T1ρ or T2 values in the morning and in the afternoon. Conclusions A sequence that combines T1ρ and T2 quantification with scan time less than 10 minutes and is robust to B0 and B1 inhomogeneity was developed with excellent repeatability. For a cohort with low-level daily activity, although no significant diurnal variation of cartilage MR relaxation times was observed, the afternoon scans had inferior repeatability compared to morning scans.

Objective To evaluate the relationship of hip radiographic osteoarthritis (ROA) and MR findings of cartilage lesions, labral tears, bone marrow edema like lesions (BMEL) and subchondral cysts with self-reported and physical function. Design Eighty five subjects were classified as controls (n= 55, KL 0, 1) or having mild-moderate ROA (n = 30, KL 2, 3). T2-weighted MR images at 3-Tesla were graded for presence of cartilage lesions, labral tears, BMELs and subchondral cysts. Posterior wall sign, cross-over sign, center-edge angle and alpha angle were also recorded. Function was assessed using Hip Osteoarthritis Outcome Score (HOOS), Timed-Up and Go (TUG) test and Y-Balance Test (YBT). Analysis compared function between subjects with and without ROA and those with and without femoral or acetabular cartilage lesions, adjusted for age. Non-parametric correlations were used to assess the relationship between radiographic scores, MR scores and function. Results Subjects with acetabular cartilage lesions had worse HOOS (Difference = 5–10%, P = 0.036–0.004), but not TUG or YBT, scores. Acetabular cartilage lesions, BMELs and subchondral cysts were associated with worse HOOS scores (ρ= 0.23–0.37, P = 0.041–0.001). Differences in function between subjects with and without ROA or femoral cartilage lesions were not significant. Other radiologic findings were not associated with function. Conclusions Acetabular cartilage defects, but not femoral cartilage defects or ROA, were associated with greater self-reported pain and disability. BMELs and subchondral cysts were related to greater hip related self-reported pain and disability. None of the radiographic or MR features were related to physical function.

OBJECTIVE To evaluate the longitudinal reproducibility and variations of cartilage T1ρ and T2 measurements using different coils, MR systems and sites. METHODS Single-Site study: Phantom data were collected monthly for up to 29 months on four GE 3T MR systems. Data from phantoms and human subjects were collected on two MR systems using the same model of coil; and were collected on one MR system using two models of coils. Multi-site study: Three participating sites used the same model of MR systems and coils, and identical imaging protocols. Phantom data were collected monthly. Human subjects were scanned and rescanned on the same day at each site. Two traveling human subjects were scanned at all three sites. RESULTS Single-Site Study: The phantom longitudinal RMS-CVs ranged from 1.8% to 2.7% for T1ρ and 1.8% to 2.8% for T2. Significant differences were found in T1ρ and T2 values using different MR systems and coils. Multi-Site Study: The phantom longitudinal RMS-CVs ranged from 1.3% to 2.6% for T1ρ and 1.2% to 2.7% for T2. Across three sites (n=16), the in-vivo scan-rescan RMS-CV was 3.1% and 4.0% for T1ρ and T2, respectively. Phantom T1ρ and T2 values were significantly different between three sites but highly correlated (R>0.99). No significant difference was found in T1ρ and T2 values of traveling controls, with cross-site RMS-CV as 4.9% and 4.4% for T1ρ and T2, respectively. CONCLUSION With careful quality control and cross-calibration, quantitative MRI can be readily applied in multi-site studies and clinical trials for evaluating cartilage degeneration.

Tissues containing both water and lipids, e.g., breast, confound standard MR proton reference frequency-shift methods for mapping temperatures due to the lack of temperature-induced frequency shift in lipid protons. Generalized Dixon chemical shift-based water-fat separation methods, such as GE's iterative decomposition of water and fat with echo asymmetry and leastsquares estimation method, can result in complex water and fat images. Once separated, the phase change over time of the water signal can be used to map temperature. Phase change of the lipid signal can be used to correct for non-temperature-dependent phase changes, such as amplitude of static field drift. In this work, an image acquisition and postprocessing method, called water and fat thermal MRI, is demonstrated in phantoms containing 30:70, 50:50, and 70:30 water-to-fat by volume. Noninvasive heating was applied in an Off1-On-Off2 pattern over 50 min, using a miniannular phased radiofrequency array. Temperature changes were referenced to the first image acquisition. Four fiber optic temperature probes were placed inside the phantoms for temperature comparison. Region of interest (ROI) temperature values colocated with the probes showed excellent agreement (global mean ± standard deviation: −0.09 ± 0.34°C) despite significant amplitude of static field drift during the experiments. KeywordsMR thermometry; PRFS; hyperthermia; water-fat separated imaging; chemical shift Hyperthermia shows great promise both as a primary or an adjunct treatment for a variety of malignancies. In addition, high-frequency focused ultrasound has been demonstrated to be effective for treating superficial and deep tumors in soft tissue (1,2). Conventional, lowertemperature hyperthermia therapies have been shown to be effective as an adjunct treatment (3) with radiation or chemotherapy in such cases as recurrent tumors in the chest wall (4) and sarcomas in leg and other extremities.Accurate tumor and normal tissue temperature measurements are necessary to confirm desired thermal dose distributions, a key factor for successful treatment (3,5,6). Invasive thermometry provides accurate but spatially limited measurements. Devices such as fiber optic probes are often limited to a single location or a one-dimensional track through the region of interest, due both to accessibility and patient tolerance. Previous work has shown the value of using the temperature sensitivity of the tissue water proton resonant frequency shift (PRFS) (8-11). The temperature dependency of water protons is approximately 0.01 PPM/°C (12), which in a 1.5-T scanner results in 0.64 Hz/°C. This effect can be observed in its most simple form via a gradient echo data acquisition, where a series of images of a water-based gel phantom is acquired through time while applying heat. If each complex image is subtracted from the first and the phase angle for each time point plotted against time, then the phase change over time directly correlates to the change in temperature. However, tissues with a mix of wa...

The data show that for evaluable treatments, excellent correlation (deltaT < 1 degrees C) of MRTI-ROI and invasive measurements can be achieved, but that motion and other artifacts are still serious challenges that must be overcome in future work.

Objective To evaluate whether baseline T1ρ and T2 relaxation times of hip cartilage are associated with magnetic resonance imaging (MRI) based progression of hip osteoarthritis (OA) at 18 months. Methods 3T MRI studies of the hip were obtained at baseline and 18-month follow-up for 54 subjects without evidence of severe OA at baseline [Kellgren-Lawrence (KL) score of 0–3]. 2D fast spin-echo sequences were used for semi-quantitative morphological scoring of cartilage lesions and a combined T1ρ/T2 sequence was used to quantitatively assess cartilage composition. Progression of hip OA was defined based on incident or progression of morphological semi-quantitative grade at 18 months. Baseline T1ρ and T2 relaxation times were compared between progressors and non-progressors using one-way analysis of variance and Mann-Whitney U tests and used to predict progression with binary logistic regression after adjusting for age, gender, body mass index, and KL score. Additionally, a novel voxel-based relaxometry technique was used to compare the spatial distribution of baseline T1ρ and T2 between progressors and non-progressors. Results Significantly higher baseline T1ρ and T2 values were observed in hip OA progressors compared to non-progressors, particularly in the posterosuperior and anterior aspects of the femoral cartilage. Logistic regression showed that higher baseline T1ρ or T2 values in the femoral cartilage were significantly associated with progression of femoral cartilage lesions at 18 months. Conclusion T1ρ and T2 relaxation parameters are associated with morphological cartilage degeneration at 18 months and may serve as potential imaging biomarkers for progression of cartilage lesions in hip OA.

Purpose To validate six-echo, chemical-shift based MRI with T2* correction for the quantification of bone marrow fat content in the presence of trabecular bone. Materials and Methods Ten bone phantoms were made using trabecular bone cores extracted from the distal femur and proximal tibia of twenty human cadaveric knees. Bone marrow was removed from the cores and the marrow spaces were filled with water-fat gelatin to mimic bone marrow of known fat fractions. A chemical-shift based water-fat separation method with T2* correction was employed to generate fat fraction maps. The proton density fat fractions (PDFF) between marrow regions with and without bone were compared to the reference standard of known fat fraction using the squared Pearson correlation coefficient and unpaired t-test. Results Strong correlations were found between the known fat fraction and measured PDFF in marrow without trabecular bone (R2=0.99; slope=0.99, intercept=0.94) as well as in marrow with trabecular bone (R2=0.97; slope=1.0, intercept=−3.58). Measured PDFF between regions with and without bone were not significantly different (p=0.5). However, PDFF was systematically underestimated by −3.2% fat fraction in regions containing trabecular bone. Conclusion Our implementation of a six-echo chemical-shift based MRI pulse sequence with T2* correction provided an accurate means of determining fat content in bone marrow in the presence of trabecular bone.