T1rho Magnetic Resonance Imaging at 3T Detects Knee Cartilage Changes After Viscosupplementation

Viscosupplementation may affect cartilage. Changes in T1rho magnetic resonance imaging (MRI) relaxation times correlate with proteoglycan changes in cartilage. The authors hypothesized that T1rho MRI will show an improvement in proteoglycan content at 6 weeks and 3 months after viscosupplementation and that this improvement will correlate with functional outcome scores. Ten patients (mean age, 56 years; Kellgren-Lawrence grade 1 or 2) underwent T1rho MRI at baseline, 6 weeks, and 3 months after viscosupplementation. Volumetric T1rho means were calculated by depth and region. Visual analog scale (VAS), International Knee Documentation Committee (IKDC), and Western Ontario and McMaster Universities Osteoarthritis Index (WOMAC) scores were obtained. Mean T1rho values decreased in the superficial patella at 6 weeks (10.3%, P=.002) and 3 months (7.9%, P=.018) and in the middle patella at 6 weeks (7.0%, P=.014) compared with baseline values. Deep patella T1rho values increased at 3 months compared with 6 weeks (9.9%, P=.033), returning to values similar to baseline. Mean T1rho values increased in the deep tibia at 6 weeks (4.7%, P=.048) and in the middle tibia (5.2%, P=.004) and deep tibia (11.2%, P=.002) at 3 months compared with baseline. At 6 weeks, improvement was seen in VAS (5.9 to 3.9, P<.01), IKDC-9 (55.3 to 63.7, P=.03), and WOMAC (43.9 to 32.8, P=.03) scores. Functional VAS (4.0, P=.02), IKDC-9 (67.8, P=.04), and WOMAC (30.0, P=.04) scores remained better at 3 months. T1rho MRI is a feasible noninvasive method of studying molecular changes in cartilage. Some segments improved after viscosupplementation, and others worsened, possibly reflecting natural history or symptom relief and subsequent increase in activity-related wear.

Novel imaging of the intervertebral disk and pain

T-1-rho (T1ρ) magnetic resonance imaging (MRI) and disc height ratio (DHR) are potential biomarkers of degenerative disk disease (DDD) related to biochemical composition and morphology of the intervertebral disk (IVD), respectively. To objectively detect DDD at an early stage, the hypothesis was tested that the average T1ρ relaxation time of the nucleus pulposus (NP) correlates with the disk height of degenerate IVDs, measured by MRI. Studies were performed on a 3-T Siemens Tim Trio clinical MRI scanner (Siemens Healthcare, Malvern, Pennsylvania, United States) on patients being treated for low back pain whose disks were categorized into (1) painful and (2) nonpainful subgroups based on provocative diskography and (3) age-matched healthy controls. Painful disks presented both low DHR and T1ρ values, nonpainful disks measured the highest DHR and extended to a higher range of T1ρ, and control disks presented a midrange DHR with the highest T1ρ values. T1ρ MRI evaluated in the NP of IVDs may be useful to establish a threshold (120 milliseconds here) above which indicates a healthy disk, and disks measuring low NP T1ρ (50 to 120 milliseconds here) would require disk height analysis to further categorize the disk. Combining T1ρ MRI and disk height analysis may hold promise in predicting painful disks without provocative diskography, and predictive models should be developed.

T(1ρ) MRI in Alzheimer's disease: detection of pathological changes in medial temporal lobe

BACKGROUND

The need of an early and noninvasive diagnosis of AD requires the development of imaging-based techniques. As an alternative, the magnetic resonance image (MRI) relaxation time constant (T1ρ) was measured in brains of Alzheimer's disease (AD), mild-cognitive impairment (MCI), and age-matched controls in order to determine whether T1ρ values correlated with the neurological diagnosis.

METHODS

MRI was performed on AD (n=48), MCI (n=45), and age-matched control (n=41), on a 1.5 Tesla Siemens clinical MRI scanner. T1ρ maps were generated by fitting each pixel's intensity as a function of the duration of the spin-lock pulse. T1ρ values were calculated from the gray matter (GM) and white matter (WM) of medial temporal lobe (MTL).

RESULTS

GM and WM T1ρ values were 87.5±1.2 ms and 80.5±1.4 ms, respectively, in controls, 90.9±1.3 ms and 84.1±1.7 ms in MCI, and 91.9±.8 ms and 88.3±1.3 ms in AD cohorts. Compared to control, AD patients showed 9% increased WM T1ρ and 5% increased GM T1ρ. Compared to control, MCI individuals showed 4% increased T1ρ both in WM and GM. A 5% increased T1ρ was found in WM of AD over MCI.

CONCLUSION

The increased T1ρ in WM and GM of MTL in AD may be associated with the pathological changes that are not evident on conventional MRI.

Early marker for Alzheimer's disease: hippocampus T1rho (T(1rho)) estimation

PURPOSE

To evaluate the T1rho (T(1rho)) MRI relaxation time in hippocampus in the brain of Alzheimer's disease (AD), mild cognitive impairment (MCI), and control, and to determine whether the T(1rho) shows any significant difference between these cohorts.

MATERIALS AND METHODS

With informed consent, AD (n = 49), MCI (n = 48), and age-matched control (n = 31) underwent T(1rho) MRI on a Siemens 1.5T Scanner. T(1rho) values were automatically calculated from the left and right hippocampus region using in-house developed software. Bonferroni post-hoc multiple comparisons was performed to compare the T(1rho) value among the different cohorts.

RESULTS

Significantly higher T(1rho) values were observed both in AD (P = 0.000) and MCI (P = 0.037) cohorts compared to control; also, the T(1rho) in AD was significantly high over (P = 0.032) MCI. Hippocampus T(1rho) was 13% greater in the AD patients than control, while in MCI it was 7% greater than control. Hippocampus T(1rho) in AD patients was 6% greater than MCI.

CONCLUSION

Higher hippocampus T(1rho) values in the AD patients might be associated with the increased plaques burden. A follow-up study would help to determine the efficacy of T(1rho) values as a predictor of developing AD in the control and MCI individuals.

T1rho-prepared balanced gradient echo for rapid 3D T1rho MRI

PURPOSE

To develop a T1rho-prepared, balanced gradient echo (b-GRE) pulse sequence for rapid three-dimensional (3D) T1rho relaxation mapping within the time constraints of a clinical exam (<10 minutes), examine the effect of acquisition on the measured T1rho relaxation time and optimize 3D T1rho pulse sequences for the knee joint and spine.

MATERIALS AND METHODS

A pulse sequence consisting of inversion recovery-prepared, fat saturation, T1rho-preparation, and b-GRE image acquisition was used to obtain 3D volume coverage of the patellofemoral and tibiofemoral cartilage and lower lumbar spine. Multiple T1rho-weighted images at various contrast times (spin-lock pulse duration [TSL]) were used to construct a T1rho relaxation map in both phantoms and in the knee joint and spine in vivo. The transient signal decay during b-GRE image acquisition was corrected using a k-space filter. The T1rho-prepared b-GRE sequence was compared to a standard T1rho-prepared spin echo (SE) sequence and pulse sequence parameters were optimized numerically using the Bloch equations.

RESULTS

The b-GRE transient signal decay was found to depend on the initial T1rho-preparation and the corresponding T1rho map was altered by variations in the point spread function with TSL. In a two compartment phantom, the steady state response was found to elevate T1rho from 91.4+/-6.5 to 293.8+/-31 and 66.9+/-3.5 to 661+/-207 with no change in the goodness-of-fit parameter R2. Phase encoding along the longest cartilage dimension and a transient signal decay k-space filter retained T1rho contrast. Measurement of T1rho using the T1rho-prepared b-GRE sequence matches standard T1rho-prepared SE in the medial patellar and lateral patellar cartilage compartments. T1rho-preparedb-GRE T1rho was found to have low interscan variability between four separate scans. Mean patellar cartilage T1rho was elevated compared to femoral and tibial cartilage T1rho.

CONCLUSION

The T1rho-prepared b-GRE acquisition rapidly and reliably accelerates T1rho quantification of tissues offset partially by a TSL-dependent point spread function.

Cross-molecular coupling in combined photoassociation and Feshbach resonances

We model combined photoassociation and Feshbach resonances in a Bose-Einstein condensate. When the magnetic field is far-off resonance, cross coupling between the two target molecules--enabled by the shared dissociation continuum--leads to an anomalous dispersive shift in the position of laser resonance, as well as unprecedented elimination and enhancement of resonant photoassociation via quantum interference. For off-resonant lasers, a dispersive shift and quantum interference appear similarly in resonant three-body Feshbach losses, except that the Feshbach node is tunable with intensity.