Measurement of intervertebral disc pressure with T1ρ MRI

The aim of this study is to demonstrate T_1ρ MRI's capability for measuring intervertebral disc osmotic pressure. Self‐coregistered sodium and T_1ρ‐weighted MR images were acquired on ex vivo bovine intervertebral discs (N = 12) on a 3 T clinical MRI scanner. The sodium MR images were used to calculate effective nucleus pulposus fixed‐charge‐density (mean = 138.2 ± 27.6 mM) and subsequently osmotic pressure (mean = 0.53 ± 0.18 atm), whereas the T_1ρ‐weighted images were used to compute T_1ρ relaxation maps. A significant linear correlation (R = 0.56, P < 0.01) between nucleus pulposus fixed‐charge‐density and T_1ρ relaxation time constant was observed. More importantly, a significant power correlation (R = 0.72, P < 0.01) between nucleus pulposus osmotic pressure as predicted by sodium MRI and T_1ρ relaxation time constant was also observed. The current clinical method for assessing disc pressure is discography, which is an invasive procedure that has been shown to have negative effects on disc biomechanical and biochemical properties. In contrast, T_1ρ MRI is noninvasive and can be easily implemented in a clinical setting due to its superior signal‐to‐noise ratio compared with sodium MRI. Therefore, T_1ρ MRI may serve as a noninvasive clinical tool for the longitudinal evaluation of disc osmotic pressure. Magn Reson Med, 2010. © 2010 Wiley‐Liss, Inc.     

Early marker for Alzheimer's disease: Hippocampus T1rho (T1ρ) estimation

Purpose

To evaluate the T1rho (T_1ρ) 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_1ρ 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_1ρ MRI on a Siemens 1.5T Scanner. T_1ρ 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_1ρ value among the different cohorts.

Results

Significantly higher T_1ρ values were observed both in AD (P = 0.000) and MCI (P = 0.037) cohorts compared to control; also, the T_1ρ in AD was significantly high over (P = 0.032) MCI. Hippocampus T_1ρ was 13% greater in the AD patients than control, while in MCI it was 7% greater than control. Hippocampus T_1ρ in AD patients was 6% greater than MCI.

Conclusion

Higher hippocampus T_1ρ 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_1ρ values as a predictor of developing AD in the control and MCI individuals. J. Magn. Reson. Imaging 2009;29:1008–1012. © 2009 Wiley‐Liss, Inc.     

Spatial distribution and relationship of T1ρ and T2 relaxation times in knee cartilage with osteoarthritis

T_1ρ and T₂ relaxation time constants have been proposed to probe biochemical changes in osteoarthritic cartilage. This study aimed to evaluate the spatial correlation and distribution of T_1ρ and T₂ values in osteoarthritic cartilage. Ten patients with osteoarthritis (OA) and 10 controls were studied at 3T. The spatial correlation of T_1ρ and T₂ values was investigated using Z‐scores. The spatial variation of T_1ρ and T₂ values in patellar cartilage was studied in different cartilage layers. The distribution of these relaxation time constants was measured using texture analysis parameters based on gray‐level co‐occurrence matrices (GLCM). The mean Z‐scores for T_1ρ and T₂ values were significantly higher in OA patients vs. controls (P < 0.05). Regional correlation coefficients of T_1ρ and T₂ Z‐scores showed a large range in both controls and OA patients (0.2–0.7). OA patients had significantly greater GLCM contrast and entropy of T_1ρ values than controls (P < 0.05). In summary, T_1ρ and T₂ values are not only increased but are also more heterogeneous in osteoarthritic cartilage. T_1ρ and T₂ values show different spatial distributions and may provide complementary information regarding cartilage degeneration in OA. Magn Reson Med, 2009. © 2009 Wiley‐Liss, Inc.     

T1ρ-relaxation in articular cartilage: Effects of enzymatic degradation

Spin-lattice relaxation in the rotating frame (T_1ρ) dispersion spectroscopy and imaging were used to study normal and enzymatically degraded bovine articular cartilage. Normal specimens demonstrate significant T_1ρ “dispersion” (～60 to ～130 ms) in the 100 Hz to 9 kHz frequency range. Proteoglycan-degraded specimens have 33% greater T_1ρ values than collagen-degraded or normal samples. T_1ρ-weighted images reveal structure not found in conventional T₁-or T₂-weighted images. Our results suggest that T_1ρ measurements are selectively sensitive to proteoglycan content. The potential of this method in distinguishing the early degenerative changes in cartilage associated with osteoarthritis is discussed.     

T1ρ MRI of human musculoskeletal system

Magnetic resonance imaging (MRI) offers the direct visualization of the human musculoskeletal (MSK) system, especially all diarthrodial tissues including cartilage, bone, menisci, ligaments, tendon, hip, synovium, etc. Conventional MRI techniques based on T₁‐ and T₂‐weighted, proton density (PD) contrast are inconclusive in quantifying early biochemically degenerative changes in MSK system in general and articular cartilage in particular. In recent years, quantitative MR parameter mapping techniques have been used to quantify the biochemical changes in articular cartilage, with a special emphasis on evaluating joint injury, cartilage degeneration, and soft tissue repair. In this article we focus on cartilage biochemical composition, basic principles of T_1ρ MRI, implementation of T_1ρ pulse sequences, biochemical validation, and summarize the potential applications of the T_1ρ MRI technique in MSK diseases including osteoarthritis (OA), anterior cruciate ligament (ACL) injury, and knee joint repair. Finally, we also review the potential advantages, challenges, and future prospects of T_1ρ MRI for widespread clinical translation. J. Magn. Reson. Imaging 2015;41:586–600. © 2014 Wiley Periodicals, Inc.     

Proton T1ρ-dispersion imaging of rodent brain at 1.9 T

Detection of H₂¹⁷O with proton T_1ρ-dispersion imaging holds promise as a means of quantifying metabolism and blood flow with MRI. However, this technique requires a priori knowledge of the intrinsic T_1ρ dispersion of tissue. To investigate these properties, we implemented a T_1ρ imaging sequence on a 1.9-T Signa GE scanner. A series of T_1ρ images for different locking frequencies and locking durations were obtained from rat brain in vivo and compared with 5 % (wt/vol) gelatin phantoms containing different concentrations of ¹⁷O ranging from .037 % (natural abundance) to 2.0 atom%. Results revealed that, although there is considerable T_1ρ-dispersion in phantoms doped with H₂¹⁷O, the T_1ρ of rat brain undergoes minimal dispersion for spin-locking frequencies between .2 and 1.5 kHz. A small degree of T_1ρ dispersion is present below .2 kHz, which we postulate arises from natural-abundance H₂¹⁷O. Moreover, the signal-to-noise ratios of T_1ρ-weighted images are significantly better than comparable T2-weighted images, allowing for improved visualization of tissue contrast. We have also demonstrated the feasibility of proton T_1ρ-dispersion imaging for detecting intravenous H₂¹⁷O on a live mouse brain. The potential application of this technique to study brain perfusion is discussed.     

Assessment of intervertebral disc degeneration with magnetic resonance single‐voxel spectroscopy

This study examined the feasibility of using short‐echo water‐suppressed point‐resolved spectroscopy (PRESS) on a clinical 3T magnetic resonance (MR) scanner for evaluating biochemical changes in degenerated bovine and cadaveric human intervertebral discs. In bovine discs (N = 17), degeneration was induced with papain injections. Degeneration of human cadaveric discs (N = 27) was assessed using the Pfirrmann grading on T₂‐weighted images. Chemicals in the carbohydrate region (Carb), the choline head group (Cho), the N‐acetyl region (N‐acetyl), and the lipid and lactate region (Lac+Lip) were quantified using ¹H PRESS, and were compared between specimens with different degrees of degeneration. The correlation between the spectroscopic findings and glycosaminoglycan (GAG) quantification using biochemical assays was determined. Significant differences were found between the ratios (N‐acetyl/Cho, N‐acetyl/Lac+Lip) acquired before and after papain injection in bovine discs. For human cadaveric discs, significant differences in the ratios (N‐acetyl/Carb, N‐acetyl/Lac+Lip) were found between discs having high and low Pfirrmann scores. Significant correlations were found between N‐acetyl/Lac+Lip and GAG content in bovine discs (R = 0.77, P = 0.0007) and cadaveric discs (R = 0.83, P < 0.0001). Significant correlation between N‐acetyl/Cho and GAG content was also found in cadaver discs (R = 0.64, P = 0.0039). This study demonstrates for the first time that short‐echo PRESS on a clinical 3T MR scanner can be used to noninvasively and can reproducibly quantify metabolic changes associated with degeneration of intervertebral discs. Magn Reson Med, 2009. © 2009 Wiley‐Liss, Inc.     

T1ρ of protein solutions at very low fields: Dependence on molecular weight,concentration, and structure

The effect of molecular weight, concentration, and structure on 1/T₁ρ, the rotating frame relaxation rate, was investigated for several proteins using the on-resonance spin-lock technique, for locking fields B₁ < 200 μT. The measured values of 1/T₁ρ, were fitted to a simple theoretical model to obtain the dispersion curves 1/T₁ρ(ω₁) and the relaxation rate at zero B₁ field, 1/T₁ρ,(O). 1/T₁ρ, was highly sensitive to the molecular weight, concentration, and structure of the protein. The amount of intra- and intermolecular hydrogen and disulfide bonds especially contributed to 1/T₁ρ. In all samples, 1/T₁ρ(O) was equal to 1/T₂ρ measured at the main magnetic field B_o = 0.1 T, but at higher locking fields the dispersion curves mono-tonically decreased. The results of this work indicate that a model considering the effective correlation time of molecular motions as the main determinant for 1/T₁ρ relaxation in protein solutions is not valid at very low B₁ fields. The underlying mechanism for the relaxation rate 1/T₁ρ at B₁ fields below 200 μT is discussed.     

Ultrashort TE T1ρ magic angle imaging

An ultrashort TE T₁ρ sequence was used to measure T₁ρ of the goat posterior cruciate ligament (n = 1) and human Achilles tendon specimens (n = 6) at a series of angles relative to the B₀ field and spin‐lock field strengths to investigate the contribution of dipole–dipole interaction to T₁ρ relaxation. Preliminary results showed a significant magic angle effect. T₁ρ of the posterior cruciate ligament increased from 6.9 ± 1.3 ms at 0° to 36 ± 5 ms at 55° and then gradually reduced to 12 ± 3 ms at 90°. Mean T₁ρ of the Achilles tendon increased from 5.5 ± 2.2 ms at 0° to 40 ± 5 ms at 55°. T₁ρ dispersion study showed a significant T₁ρ increase from 2.3 ± 0.9 ms to 11 ± 3 ms at 0° as the spin‐lock field strength increased from 150 Hz to 1 kHz, and from 30 ± 3 ms to 42 ± 4 ms at 55° as the spin‐lock field strength increased from 100 to 500 Hz. These results suggest that dipolar interaction is the dominant T₁ρ relaxation mechanism in tendons and ligaments. Magn Reson Med, 2013. © 2012 Wiley Periodicals, Inc.     

Contributions of chemical and diffusive exchange to T1ρ dispersion

Variations in local magnetic susceptibility may induce magnetic field gradients that affect the signals acquired for MR imaging. Under appropriate diffusion conditions, such fields produce effects similar to slow chemical exchange. These effects may also be found in combination with other chemical exchange processes at multiple time scales. We investigate these effects with simulations and measurements to determine their contributions to rotating frame (R_1ρ) relaxation in model systems. Simulations of diffusive and chemical exchange effects on R_1ρ dispersion were performed using the Bloch equations. Additionally, R_1ρ dispersion was measured in suspensions of Sephadex and latex beads with varying spin locking fields at 9.4 T. A novel analysis method was used to iteratively fit for apparent chemical and diffusive exchange rates with a model by Chopra et al. Single‐ and double‐inflection points in R_1ρ dispersion profiles were observed, respectively, in simulations of slow diffusive exchange alone and when combined with rapid chemical exchange. These simulations were consistent with measurements of R_1ρ in latex bead suspensions and small‐diameter Sephadex beads that showed single‐ and double‐inflection points, respectively. These observations, along with measurements following changes in temperature and pH, are consistent with the combined effects of slow diffusion and rapid ^?OH exchange processes. Magn Reson Med, 2013. © 2012 Wiley Periodicals, Inc.     

Brain metabolites B1‐corrected proton T1 mapping in the rhesus macaque at 3 T

The accuracy of metabolic quantification in MR spectroscopy is limited by the unknown radiofrequency field and T₁. To address both issues in proton (¹H) MR spectroscopy, we obtained radiofrequency field–corrected T₁ maps of N‐acetylaspartate, choline, and creatine in five healthy rhesus macaques at 3 T. For efficient use of the 4 hour experiment, we used a new three‐point protocol that optimizes the precision of T₁ in three‐dimensional ¹H‐MR spectroscopy localization for extensive, ～30%, brain coverage at 0.6 × 0.6 × 0.5 cm³ = 180‐μL spatial resolution. The resulting mean T₁s in 700 voxels were N‐acetylaspartate = 1232 ± 44, creatine = 1238 ± 23 and choline = 1107 ± 56 ms (mean ± standard error of the mean). Their histograms from all 140 voxels in each animal were similar in position and shape, characterized by standard errors of the mean of the full width at half maximum divided by their means of better than 8%. Regional gray matter N‐acetylaspartate, choline, and creatine T₁s (1333 ± 43, 1265 ± 52, and 1131 ± 28 ms) were 5–10% longer than white matter: 1188 ± 34, 1201 ± 24, and 1082 ± 50 ms (statistically significant for the N‐acetylaspartate only), all within 10% of the corresponding published values in the human brain. Magn Reson Med 63:865–871, 2010. © 2010 Wiley‐Liss, Inc.     

Combined use of T2‐weighted MRI and T1‐weighted dynamic contrast–enhanced MRI in the automated analysis of breast lesions

A multiparametric computer‐aided diagnosis scheme that combines information from T₁‐weighted dynamic contrast–enhanced (DCE)‐MRI and T₂‐weighted MRI was investigated using a database of 110 malignant and 86 benign breast lesions. Automatic lesion segmentation was performed, and three categories of lesion features (geometric, T₁‐weighted DCE, and T₂‐weighted) were automatically extracted. Stepwise feature selection was performed considering only geometric features, only T₁‐weighted DCE features, only T₂‐weighted features, and all features. Features were merged with Bayesian artificial neural networks, and diagnostic performance was evaluated by ROC analysis. With leave‐one‐lesion‐out cross‐validation, an area under the ROC curve value of 0.77 ± 0.03 was achieved with T₂‐weighted‐only features, indicating high diagnostic value of information in T₂‐weighted images. Area under the ROC curve values of 0.79 ± 0.03 and 0.80 ± 0.03 were obtained for geometric‐only features and T₁‐weighted DCE‐only features, respectively. When all features were considered, an area under the ROC curve value of 0.85 ± 0.03 was achieved. We observed P values of 0.006, 0.023, and 0.0014 between the geometric‐only, T₁‐weighted DCE‐only, and T₂‐weighted‐only features and all features conditions, respectively. When ranked, the P values satisfied the Holm–Bonferroni multiple‐comparison test; thus, the improvement of multiparametric computer‐aided diagnosis was statistically significant. A computer‐aided diagnosis scheme that combines information from T₁‐weighted DCE and T₂‐weighted MRI may be advantageous over conventional T₁‐weighted DCE‐MRI computer‐aided diagnosis. Magn Reson Med, 2011. © 2011 Wiley‐Liss, Inc.     

3.0T MR T2 mapping在腰椎间盘退变中的初步研究

目的：运用3.0T MR T2 mapping 成像技术定量研究椎间盘退变及生物力学与腰椎间盘退变的关系。方法分析34例下腰痛(LBP)及(或)坐骨神经痛患者腰椎间盘 T2值与 Pfirrmann 分级、椎间盘部位、年龄的相关性及加压前后腰椎间盘 T2值。结果髓核 T2值与 Pfirrmann 分级、椎间盘部位、年龄存在相关性。结论(1)T2 mapping 可以对椎间盘退变作无创性定量检测;(2)体外压力负荷变化可影响椎间盘 T2值。     

T1ρ MRI quantification of arthroscopically confirmed cartilage degeneration

Nine asymptomatic subjects and six patients underwent T₁ρ MRI to determine whether Outerbridge grade 1 or 2 cartilage degeneration observed during arthroscopy could be detected noninvasively. MRI was performed 2‐3 months postarthroscopy, using sagittal T₁‐weighted and axial and coronal T₁ρ MRI, from which spatial T₁ρ relaxation maps were calculated from segmented T₁‐weighted images. Median T₁ρ relaxation times of patients with arthroscopically documented cartilage degeneration and asymptomatic subjects were significantly different (P < 0.001), and median T₁ρ exceeded asymptomatic articular cartilage median T₁ρ by 2.5 to 9.2 ms. In eight observations of mild cartilage degeneration at arthroscopy (Outerbridge grades 1 and 2), mean compartment T₁ρ was elevated in five, but in all observations, large foci of increased T₁ρ were observed. It was determined that T₁ρ could detect some, but not all, Outerbridge grade 1 and 2 cartilage degeneration but that a larger patient population is needed to determine the sensitivity to these changes. Magn Reson Med 63:1376–1382, 2010. © 2010 Wiley‐Liss, Inc.     

Quantitative cartilage degeneration associated with spontaneous osteoarthritis in a guinea pig model

Purpose:

To determine (i) the feasibility and intra‐ and inter‐scan reproducibility of T_1ρ MRI in assessing cartilage degeneration in a guinea pig model with naturally occurring joint disease that closely mimics human osteoarthritis (OA), (ii) demonstrate the sensitivity of T_1ρ MRI in assessing the age dependent cartilage degeneration in OA progression as compared to histopathological changes.

Materials and Methods:

Duncan‐Hartley guinea pigs were obtained at various ages and maintained under an IACUC approved protocol. The left hind stifle joint was imaged using T_1ρ MRI on a 9.4 Tesla Varian horizontal 20 cm bore scanner using a custom surface coil. Reproducibility of T_1ρ MRI was assessed using 4‐month‐old guinea pigs (N = 3). Three age cohorts; 3 month (N = 8), 5 month (N = 6), and 9 month (N = 5), were used to determine the age‐dependent osteoarthritic changes as measured by T_1ρ MRI. Validation of age‐dependent cartilage degeneration was confirmed by histology and Safranin‐O staining.

Results:

T_1ρ values obtained in the cartilage of the stifle joint in guinea pigs were highly reproducible with an inter‐scan mean coefficient of variation (CV) of 6.57% and a maximum intra‐scan CV of 9.29%. Mean cartilage T_1ρ values in animals with late stage cartilage degeneration were 56.3–56.9 ms (5–9 month cohorts) were both significantly (P < 0.01) higher than that obtained from 3‐month‐old cohort (44 ms) demonstrating an age‐dependent variation. T_1ρ was shown to be significantly greater than T₂. T_1ρ dispersion was observed in this animal model for the first time showing an increase of 45% between 500 Hz and 1500 Hz spin‐locking frequency. Cartilage thickness measurements were calculated from single mid‐coronal histology sections from same animals used for T_1ρ MRI. Thickness calculations showed insignificant differences between 3‐ and 5‐month cohorts and was significantly decreased by 9 months of age (P < 0.01). A moderate correlation (R² = 0.45) existed between T_1ρ values and signal intensity of Safranin‐O stain.

Conclusion:

The data presented demonstrate that T_1ρ MRI is highly reproducible in this spontaneous model of OA and may serve as a noninvasive tool to characterize joint cartilage degeneration during OA. Age‐dependent changes, verified with histological measurements of proteoglycan loss, correlated with T_1ρ across different age groups. T_1ρ has adequate dynamic range and is sensitive to detect and track the progression of cartilage degeneration in the guinea pig model before gross anatomical changes such as cartilage thinning has occurred. This study presents a technological advancement that would permit longitudinal studies of evaluating disease‐modifying therapies useful for treating human OA. J. Magn. Reson. Imaging 2012;35:891–898. © 2011 Wiley Periodicals, Inc.     

Reduction of residual dipolar interaction in cartilage by spin‐lock technique

The influence of radiofrequency (RF) spin‐lock pulse on the laminar appearance of articular cartilage in MR images was investigated. Spin‐lock MRI experiments were performed on bovine cartilage plugs on a 4.7 Tesla small‐bore MRI scanner, and on human knee cartilage in vivo on a 1.5 Tesla clinical scanner. When the normal to the surface of cartilage was parallel to B₀, a typical laminar appearence was exhibited in T₂‐weighted images of cartilage plugs, but was absent in T_1ρ‐weighted images of the same plugs. At the “magic angle” orientation (when the normal to the surface of cartilage was 54.7° with respect to B₀), neither the T₂ nor the T_1ρ images demonstrated laminae. At the same time, T_1ρ values were greater than T₂ at both orientations throughout the cartilage. T_1ρ dispersion (i.e., the dependence of the relaxation rate on the spin‐lock frequency ω₁) was observed, which reached a steady‐state value of close to 2 kHz in both parallel and magic‐angle orientations. These results suggest that residual dipolar interaction from motionally‐restricted water and relaxation processes, such as chemical exchange, contribute to T_1ρ dispersion in cartilage. Further, one can reduce the laminar appearance in human articular cartilage by applying spin‐lock RF pulses, which may lead to a more accurate diagnosis of degenerative changes in cartilage. Magn Reson Med 52:1103–1109, 2004. © 2004 Wiley‐Liss, Inc.     

Temporal changes in the T1 and T2 relaxation rates (ΔR1 and ΔR2) in the rat brain are consistent with the tissue‐clearance rates of elemental manganese

Temporal changes in the T₁ and T₂ relaxation rates (ΔR₁ and ΔR₂) in rat olfactory bulb (OB) and cortex were compared with the absolute manganese (Mn) concentrations from the corresponding excised tissue samples. In vivo T₁ and T₂ relaxation times were measured before, and at 1, 7, 28, and 35 d after intravenous infusion of 176 mg/kg MnCl₂. The values of ΔR₁, ΔR₂, and absolute Mn concentration peaked at day 1 and then declined to near control levels after 28 to 35 d. The Mn bioelimination rate from the rat brain was significantly faster than that reported using radioisotope techniques. The R₁ and R₂ relaxation rates were linearly proportional to the underlying tissue Mn concentration and reflect the total absolute amount of Mn present in the tissue. The in vivo Mn r₁ and r₂ tissue relaxivities were comparable to the in vitro values for aqueous Mn²⁺. These results demonstrate that loss of manganese‐enhanced MRI (MEMRI) contrast after systemic Mn²⁺ administration is due to elimination of Mn²⁺ from the brain. Magn Reson Med, 2009. © 2009 Wiley‐Liss, Inc.     

In vivo measurement of T1rho dispersion in the human brain at 1.5 tesla

Purpose

To measure T_1ρ relaxation times and T_1ρ dispersion in the human brain in vivo.

Materials and Methods

Magnetic resonance imaging (MRI) was performed on a 1.5‐T GE Signa clinical scanner using the standard GE head coil. A fast spin‐echo (FSE)‐based T_1ρ‐weighted MR pulse sequence was employed to obtain images from five healthy male volunteers. Optimal imaging parameters were determined while considering both the objective of the study and the guarantee that radio‐frequency (RF) power deposition during MR did not exceed Food and Drug Administration (FDA)‐mandated safety levels.

Results

T_1ρ‐weighted MR images showed excellent contrast between different brain tissues. These images were less blurred than corresponding T₂‐weighted images obtained with similar contrast, especially in regions between brain parenchyma and cerebrospinal fluid (CSF). Average T_1ρ values for white matter (WM), gray matter (GM), and CSF were 85 ± 3, 99 ± 1, and 637 ± 78 msec, respectively, at a spin‐locking field of 500 Hz. T_1ρ is 30% higher in the parenchyma and 78% higher in CSF compared to the corresponding T₂ values. T_1ρ dispersion was observed between spin‐locking frequencies 0 and 500 Hz.

Conclusion

T_1ρ‐weighted MRI provides images of the brain with superb contrast and detail. T_1ρ values measured in the different brain tissues will serve as useful baseline values for analysis of T_1ρ changes associated with pathology. J. Magn. Reson. Imaging 2004;19:403–409. © 2004 Wiley‐Liss, Inc.

     

A B1‐insensitive high resolution 2D T1 mapping pulse sequence for dGEMRIC of the HIP at 3 Tesla

Early detection of cartilage degeneration in the hip may help prevent onset and progression of osteoarthritis in young patients with femoroacetabular impingement. Delayed gadolinium‐enhanced MRI of cartilage is sensitive to cartilage glycosaminoglycan loss and could serve as a diagnostic tool for early cartilage degeneration. We propose a new high resolution 2D T₁ mapping saturation–recovery pulse sequence with fast spin echo readout for delayed gadolinium‐enhanced magnetic resonance imaging of cartilage of the hip at 3 T. The proposed sequence was validated in a phantom and in 10 hips, using radial imaging planes, against a rigorous multipoint saturation–recovery pulse sequence with fast spin echo readout. T₁ measurements by the two pulse sequences were strongly correlated (R² > 0.95) and in excellent agreement (mean difference = ?8.7 ms; upper and lower 95% limits of agreement = 64.5 and ?81.9 ms, respectively). T₁ measurements were insensitive to B₁₊ variation as large as 20%, making the proposed T₁ mapping technique suitable for 3 T. Magn Reson Med, 2011. © 2011 Wiley‐Liss, Inc.     

In vivo venous blood T1 measurement using inversion recovery true‐FISP in children and adults

A time‐efficient method is described for in vivo venous blood T₁ measurement using multiphase inversion‐recovery‐prepared balanced steady‐state free precession imaging. Computer simulations and validation experiments using a flow phantom were carried out to demonstrate the accuracy of the proposed method for measuring blood T₁ by taking advantage of the continuous inflow of fresh blood with longitudinal magnetization undisturbed by previous radiofrequency pulses. In vivo measurement of venous blood T₁ in the sagittal sinus was carried out in 26 healthy children and adults aged 7–39 years. The measured venous blood T₁ values decreased with age as a whole (P = 0.006) and were higher in females than males (P = 0.013), matching the expected developmental changes and gender differences in human hematocrit level. The estimated mean blood T₁ values were highly correlated with normal hematocrit levels across age and gender groups (Spearman's r = 0.93, P = 0.008). The longitudinal repeatability of this technique was 4.0% as measured by the within‐subject coefficient of variation. The proposed multiphase inversion recovery‐prepared balanced steady‐state free precession imaging method is a feasible technique for fast (<1 min) and reliable in vivo venous blood T₁ measurement and may serve as an index of hematocrit level in individual subjects. Magn Reson Med, 2010. © 2010 Wiley‐Liss, Inc.