A subjective and objective comparison of tissue contrast and imaging artifacts present in routine spin echoes and in iterative decomposition of asymmetric spin echoes for soft tissue neck MRI.

OBJECTIVE: FSE sequences play key roles in neck MRI despite the susceptibility issues in neck region. Iterative decomposition of asymmetric echoes (IDEAL, GE) is a promising method that separates fat and water images resulting in high SNR and improved fat suppression. We tested how neck tissue contrasts, image artifacts and fat separation as opposed to fat suppression in terms of image quality compare between routine and IDEAL FSE. METHODS: IDEAL based and routine T1 and T2-weighted FSE sequences were applied for neck MRI at 1.5T and 3T. Overall image quality including fat suppression, tissue contrast, image artifacts and lesion conspicuity were subjectively assessed for 20 patients clinically indicated for neck MRI. Quantitative tissue contrast estimates from parotid area were compared between IDEAL and routine FSE for 7 patients. Four patients with oncocytoma were also reviewed to assess benefits of separately reconstructed fat specific image sets. RESULTS: Subjective tissue contrast and overall image quality including image sharpness, fat suppression and image artifacts were superior for IDEAL sequences. For oncocytoma fat specific IDEAL images provided additional information. Objective CNR estimates from a central slice were equivalent for IDEAL and routine FSE at both field strengths. CONCLUSIONS: We demonstrated that high SNR inherent in IDEAL FSE consistently translates into high tissue contrast with image quality advantages in neck anatomy where large susceptibility variation and physiological motions reduce image quality for conventional FSE T1 and T2. However, the objective contrast estimates for parotid gland at isocenter were statistically equivalent for IDEAL and conventional FSE perhaps because at or near isocenter routine FSE works well. Additionally, fat specific IDEAL image sets add to diagnostic specificity for fat deficient lesions.

The potential role of IDEAL MRI for identification of lipids and hemorrhage in carotid artery plaques.

Hemorrhage and lipid deposits contribute to instability in atherosclerotic plaques. Unstable carotid artery plaques can lead to cerebral ischemic events. While MRI studies have shown the ability to identify plaque components, the identification of hemorrhage and lipids has proven to be problematic. The purpose of this study was to quantitatively evaluate the potential of the MRI fat/water separation method known as iterative decomposition of water and fat with echo asymmetry and least squares estimation (IDEAL) to complement and improve existing methods for the identification of hemorrhage and lipids in carotid artery plaques. Fifteen asymptomatic subjects with 50-79% stenosis of at least one carotid artery were enrolled. Hemorrhage and lipid components within carotid plaques were identified using previously published criteria based on the multiple contrast-weighted (MCW) method (3D Time-of-Flight (3D-TOF), T1-Weighted (T1W) and T2-Weighted (T2W)). The hemorrhage:muscle, lipid:muscle and intra-plaque lipid:hemorrhage signal intensity ratios (SIR) and contrast to noise ratios (CNR) were measured on MCW and compared to IDEAL black-blood images. No differences were found between any of the MCW methods for any of the SIRs measured. The IDEAL Fat images had higher lipid:muscle and lipid/hemorrhage SIRs (p<0.001) compared to IDEAL Water and all MCW image sequence types. The mean values of IDEAL Fat hemorrhage:muscle SIR and CNR were nearly unity (1.1±0.6) and nearly zero (0.1±1.1), respectively. The IDEAL Water imaging was not significantly different than any of the MCW methods for any of the SIRs or for the hemorrhage:muscle CNR of 3D-TOF, while its CNRs were significantly higher than IDEAL Fat lipid:muscle (p<0.05) and lipid:hemorrhage (p<0.001) and all MCW methods (p<0.001). The addition of IDEAL Water and Fat imaging to the MCW method shows potential to improve the identification of hemorrhage and lipid structures in carotid artery plaques.

Effects of Coenzyme Q10 on Skeletal Muscle Oxidative Metabolism in Statin Users Assessed Using 31P Magnetic Resonance Spectroscopy: a Randomized Controlled Study.

OBJECTIVES: Statins partially block the production of coenzyme Q10 (CoQ10), an essential component for mitochondrial function. Reduced skeletal muscle mitochondrial oxidative capacity has been proposed to be a cause of statin myalgia and can be measured using 31phosphorus magnetic resonance spectroscopy (31P-MRS). The purpose of this study is to assess the effect of CoQ10 oral supplementation on mitochondrial function in statin users using 31P-MRS. DESIGN/SETTING: In this randomized, double-blind, placebo-controlled pilot study, 21 adults aged 47-73 were randomized to statin+placebo (n=9) or statin+CoQ10 (n=12). Phosphocreatine (PCr) recovery kinetics of calf muscles were assessed at baseline (off statin and CoQ10) and 4 weeks after randomization to either statin+CoQ10 or statin+placebo. RESULTS: Baseline and post-treatment PCr recovery kinetics were assessed for 19 participants. After 4 weeks of statin+ CoQ10 or statin+placebo, the overall relative percentage change (100*(baseline-follow up)/baseline) in PCr recovery time was -15.1% compared with baseline among all participants, (p-value=0.258). Participants randomized to statin+placebo (n=9) had a relative percentage change in PCr recovery time of -18.9%, compared to -7.7% among participants (n=10) receiving statin+CoQ10 (p-value=0.448). CONCLUSIONS: In this pilot study, there was no significant change in mitochondrial function in patients receiving 4 weeks of statin+CoQ10 oral therapy when compared to patients on statin+placebo.

Effect of Linagliptin on Vascular Function: A Randomized, Placebo-controlled Study.

CONTEXT: The dipeptidyl peptidase-4 inhibitor, linagliptin, possesses pleiotropic vasodilatory, antioxidant, and anti-inflammatory properties in animals, independent of its glucose-lowering properties. Although large, randomized clinical trials are being conducted to better evaluate the efficacy and safety of linagliptin on cardiovascular outcomes, little is known about its effects on vascular function in humans. OBJECTIVE: This study sought to evaluate the effect of linagliptin on surrogates of vascular and mitochondrial function. DESIGN AND SETTING: This was a randomized, double-blind, placebo-controlled trial at a tertiary care center with a large type 2 diabetes referral base. PATIENTS AND INTERVENTION: Forty participants with type 2 diabetes were included in a 12-wk treatment of either linagliptin 5mg/d or placebo. MAIN OUTCOME MEASURES: Micro- and macrovascular functions were assessed using laser Doppler coupled with iontophoresis and with brachial flow-mediated dilation, respectively. Mitochondrial function was assessed by phosphorus-31 metabolites changes in the calf muscle measured by magnetic resonance spectroscopy. Circulating endothelial progenitor cells, as well as inflammatory cytokines, growth factors, and biomarkers of endothelial function were also quantified. RESULTS: Linagliptin was associated with an increase in axon reflex-dependent vasodilation, a marker of neurovascular function (P = .05). A trend indicating increased endothelium-dependent microvascular reactivity was observed (P = .07). These were associated with decreases in concentrations of IFNγ (P < .05), IL-6 (P = .03), IL-12 (P < .03), and MIP-1 (P < .04) following linagliptin treatment when compared with placebo. CONCLUSIONS: This study demonstrates that linagliptin tends to improve endothelial and neurovascular microvascular function and is associated with decreased markers of inflammation in patients with type 2 diabetes. There was no significant effect of linagliptin on mitochondrial function, macrovascular function, or endothelial progenitor cells.

MRI assessment of regional differences in phosphorus-31 metabolism and morphological abnormalities of the foot muscles in diabetes.

PURPOSE: To assess differences in the phosphorus-31 (31 P) metabolism and morphology in multiple muscle regions in the forefoot of diabetic patients and normal subjects. MATERIALS AND METHODS: Fifteen diabetic patients and 15 normal subjects were assessed for muscle atrophy by 1 H magnetic resonance imaging (MRI) at 3T to grade the flexor hallucis, adductor hallucis, interosseous regions, and entire foot cross-section. Each region and the entire foot were also quantitatively evaluated for metabolic function using 31 P imaging for spatial mapping of the inorganic phosphate (Pi) to phosphocreatine (PCr) ratio (Pi/PCr). The ratio of viable muscle area to the predefined region areas (31 P/1 H) was calculated. The variability of each method was assessed by its coefficient of variation (CV). RESULTS: Muscle atrophy was significantly more severe in diabetic compared to normal subjects in all regions (P < 0.01). The 31 P/1 H area ratio was significantly larger in the adductor hallucis than in the other two regions (P < 0.05). The Pi/PCr ratio was significantly different between the two groups in the flexor hallucis and interosseous regions (P < 0.05) but not adductor hallucis region. The CV for Pi/PCr ranged from 10.13 to 55.84, while it ranged from 73.40 to 263.90 for qualitative grading. CONCLUSION: Changes in atrophy and metabolism appear to occur unequally between different regions of the forefoot in diabetes. The adductor hallucis region appears more capable of maintaining structural and metabolic integrity than the flexor hallucis or interosseous regions. The CV analysis suggests that the quantitative 31 P methods have less variability than the qualitative grading. J. Magn. Reson. Imaging 2016;44:1132-1142.

Assessment of aged mdx mice by electrical impedance myography and magnetic resonance imaging.

INTRODUCTION: Similar to magnetic resonance imaging (MRI), electrical impedance myography (EIM) is dependent on the presence and location of water in muscle to assess neuromuscular diseases. We compared the 2 technologies in mdx mice to better understand their relationship. METHODS: EIM and MRI, using T2 relaxation and diffusion-weighted imaging (DWI), were performed on the gastrocnemius of 10 mdx and 10 wild-type mice. Muscle function and tissue composition measurements were compared with the EIM and MRI data. RESULTS: EIM reactance and T2 relaxation mapping can discriminate healthy from diseased mice (P < .001 for both), but DWI could not. Both T2 relaxation and EIM reactance also correlated closely with muscle function/composition and with each other. CONCLUSION: Given the low cost of EIM and the simplicity of application, it may be a valuable alternative to muscle MRI in Duchenne muscular dystrophy, where simple cumulative indices of muscle health are being sought.

Simultaneous acquisition of phosphocreatine and inorganic phosphate images for Pi:PCr ratio mapping using a RARE sequence with chemically selective interleaving.

The ratio of inorganic phosphate to phosphocreatine (Pi:PCr) is a validated marker of mitochondrial function in human muscle. The magnetic resonance imaging rapid acquisition with relaxation enhancement (RARE) pulse sequence can acquire phosphorus-31 ((31)P) images with higher spatial and temporal resolution than traditional spectroscopic methods, which can then be used to create Pi:PCr ratio maps of muscle regions. While the (31)P RARE method produces images that reflect the content of the (31)P metabolites, it has been limited to producing an image of only one chemical shift in a scan. This increases the scan time required to acquire images of multiple chemical shifts as well as the likelihood of generating inaccurate Pi:PCr maps due to gross motion. This work is a preliminary study to demonstrate the feasibility of acquiring Pi and PCr images in a single scan by interleaving Pi and PCr chemical shift acquisitions using a chemically selective radiofrequency excitation pulse. The chemical selectivity of the excitation pulse evaluated and the Pi:PCr maps generated using the interleaved Pi and PCr acquisition method with the subject at rest and during exercise are compared to those generated using separate Pi and PCr acquisition scans. A paired t test indicated that the resulting Pi:PCr ratios for the exercised forearm muscle regions were not significantly different between the separate Pi and PCr acquisition method (3.18±1.53) (mean±standard deviation) and the interleaved acquisition method (3.41±1.66). This work demonstrates the feasibility of creating Pi:PCr ratio maps in human muscle with Pi and PCr images acquired simultaneously by interleaving between the Pi and PCr resonances in a single scan.

The feasibility of measuring phosphocreatine recovery kinetics in muscle using a single-shot (31)P RARE MRI sequence.

RATIONALE AND OBJECTIVES: Heterogeneity of skeletal muscle structure, composition, and perfusion results in spatial differences in oxidative function between muscles and muscle regions. The simultaneous measurement of the postexercise phosphocreatine (PCr) recovery rate across all muscles of a human limb cross-section may provide new insights into normal physiology and disease states. The objective of this work was to assess the feasibility of acquiring PCr rapid acquisition with relaxation enhancement (RARE) images with sufficient temporal and spatial resolution to accurately measure PCr recovery kinetics in a cross-section of a human limb. MATERIALS AND METHODS: One normal subject performed a finger exercise until fatigued. At cessation of exercise surface coil localized pulse-and-acquire phosphorus-31 MR spectra ((31)P- magnetic resonance spectroscopy [MRS]) of the forearm were acquired at 6 S intervals for 4 minutes. The exercise protocol was repeated 7 days later and axial PCr RARE images of the forearm were acquired following exercise with 5.6 cm(3) voxels at 6-second intervals for 4 minutes. RESULTS: The PCr recovery time constants for the PCr RARE and (31)P-MRS measurements were 91.0 and 91.1 seconds, respectively, based on a monoexponential fit. A Pearson correlation test showed that the PCr recovery data that resulted from the RARE PCr imaging were highly correlated with the data resulting from the (31)P-MRS (r = 0.91, P < .0001). DISCUSSION: Data from selected regions of RARE PCr images acquired at 6-second intervals compare well to those acquired using surface coil (31)P MR spectroscopy and can provide an accurate assessment of PCr recovery kinetics.

Evaluation of skeletal muscle during calf exercise by 31-phosphorus magnetic resonance spectroscopy in patients on statin medications.

Muscle pain is a common side effect of statin medications, but the cause is poorly understood. We characterized phosphocreatine (PCr) exercise recovery kinetics in 10 patients with hypercholesterolemia before and after a 4-week regimen of statin therapy using 31-phosphorus magnetic resonance spectroscopy ((31) P-MRS). (31) P spectra were obtained before, during, and after exercise on a calf flexion pedal ergometer. Creatine kinase (CK) serum levels were drawn before and after statin therapy. The mean metabolic recovery time constant in subjects increased from 28.1 s (SE = 6.5 s) to 55.4 s (SE = 7.4 s) after statin therapy. The unweighted mean of the pre/post-recovery time difference was -27.3 s (SE = 12.4 s; P = 0.02). Pre- and post-therapy CK levels were not significantly different (P = 0.50). Metabolic recovery time in the calf is prolonged in patients after statin use. This suggests that statins impair mitochondrial oxidative function, and (31) P MRS is a potential study model for statin-associated myopathy.

Foot muscle energy reserves in diabetic patients without and with clinical peripheral neuropathy.

OBJECTIVE To investigate changes in the foot muscle energy reserves in diabetic non-neuropathic and neuropathic patients. RESEARCH DESIGN AND METHODS We measured the phosphocreatinine (PCr)/inorganic phosphate (Pi) ratio, total (31)P concentration, and the lipid/water ratio in the muscles in the metatarsal head region using MRI spectroscopy in healthy control subjects and non-neuropathic and neuropathic diabetic patients. RESULTS The PCr/Pi ratio was higher in the control subjects (3.23 +/- 0.43) followed by the non-neuropathic group (2.61 +/- 0.36), whereas it was lowest in the neuropathic group (0.60 +/- 1.02) (P < 0.0001). There were no differences in total (31)P concentration and lipid/water ratio between the control and non-neuropathic groups, but both measurements were different in the neuropathic group (P < 0.0001). CONCLUSIONS Resting foot muscle energy reserves are affected before the development of peripheral diabetic neuropathy and are associated with the endothelial dysfunction and inflammation.

An assessment of the sharpness of carotid artery tissue boundaries with acquisition voxel size and field strength.

A measure of the sharpness of vessel wall interfaces in carotid artery MRI may be useful for assessing the conspicuity of the wall's features. An edge detection technique was used to measure the signal intensity gradients in 2D time-of-flight (2D-TOF) and double-inversion recovery black-blood (DIR-BB) carotid artery images of normal subjects that were acquired at 1.5 T with 0.55 x 0.55 x 2.0-mm (0.6 mm3) acquisition voxels and zero filled to reduce the in-plane reconstructed voxel size by one half in each dimension as well as with 0.27 x 0.27 x 2.0-mm (0.15 mm3) acquisition voxels and at 3.0 T with 0.27 x 0.27 x 2.0-mm (0.15 mm3) acquisition voxels using surface coils. The gradient intensities of the lumen-to-background interface varied closely with the contrast-to-noise ratio of the 2D-TOF imaging. For the DIR-BB imaging, in which higher spatial frequency artery structures are visible, the gradient intensities at the interfaces were higher than theoretically predicted at both field strengths with smaller acquisition voxels. The use of acquisition voxels smaller than those previously used at 1.5 T can improve the visualization of carotid artery structures at 1.5 and 3.0 T with surface coil reception.

3T MR of the prostate: reducing susceptibility gradients by inflating the endorectal coil with a barium sulfate suspension.

Most prostate MRI/MRS examinations are performed with an endorectal coil inflated with air, leading to an air-tissue interface that induces magnetic susceptibility gradients within the gland. Inflation of the coil with a barium sulfate suspension is described and compared to inflation with air or liquid perfluorocarbon (PFC). The B(0) field in the prostate gland was mapped for five healthy volunteers when the endorectal coil was inflated with each of the three agents. A marked decrease in the posterior-anterior (P-A) field gradient and a significant improvement in field homogeneity were evident in the presence of a barium suspension and PFC relative to air. MRS data acquired from the prostate gland in the presence of air, PFC, and a barium suspension in the endorectal coil showed similar trends, demonstrating improvement in line-widths and spectral resolution when the barium suspension or the PFC were inflating the endorectal coil. On this basis we conclude that a barium suspension provides an available, cheap, and safe alternative to PFC, and we suggest that inflating the endorectal coil with a barium suspension should be considered for prostate MR studies, especially at high field strengths (such as 3T).

Early changes in the skin microcirculation and muscle metabolism of the diabetic foot.

BACKGROUND: Changes in the large vessels and microcirculation of the diabetic foot are important in the development of foot ulceration and subsequent failure to heal existing ulcers. We investigated whether oxygen delivery and muscle metabolism of the lower extremity were factors in diabetic foot disease. METHODS: We studied 108 patients (21 control individuals who did not have diabetes, 36 patients with diabetes who did not have neuropathy, and 51 patients with both diabetes and neuropathy). We used medical hyperspectral imaging (MHSI) to investigate the haemoglobin saturation (S(HSI)O2; % of oxyhaemoglobin in total haemoglobin [the sum of oxyhaemoglobin and deoxyhaemoglobin]) in the forearm and foot; we also used 31P-MRI scans to study the cellular metabolism of the foot muscles by measuring the concentrations of inorganic phosphate and phosphocreatine and calculating the ratio of inorganic phosphate to phosphocreatine (Pi/PCr). FINDINGS: The forearm S(HSI)O2 during resting was different in all three groups, with the highest value in controls (mean 42 [SD 17]), followed by the non-neuropathic (32 [8]) and neuropathic (28 [8]) groups (p<0.0001). In the foot at resting, S(HSI)O2 was higher in the control (38 [22]) and non-neuropathic groups (37 [12]) than in the neuropathic group (30 [12]; p=0.027). The Pi/PCr ratio was higher in the non-neuropathic (0.41 [0.10]) and neuropathic groups (0.58 [0.26]) than in controls (0.20 [0.06]; p<0.0001). INTERPRETATION: Our results indicate that tissue S(HSI)O2 is reduced in the skin of patients with diabetes, and that this impairment is accentuated in the presence of neuropathy in the diabetic foot. Additionally, energy reserves of the foot muscles are reduced in the presence of diabetes, suggesting that microcirculation could be a major reason for this difference.

Strategies for shimming the breast.

There is evidence in the literature indicating a significant static field inhomogeneity in the human breast. A nonhomogenous field results in line broadening and frequency shifts in MRS and can cause intensity loss and spatial errors in MRI. Thus, there is a clear rationale for determining the regional variations in the static field homogeneity in the breast and providing strategies to correct them. Herein, the nature and extent of the static magnetic field at 3 T were measured in central planes of the human breast using both phase maps and multivoxel MRS techniques. In addition, the effect of first- and high-order shimming and of spatial saturation pulses on the static field inhomogeneity was evaluated. Both the theoretical and the measured field were found to be primarily linear in nature, with a reduction of 300 Hz from the nipple to the chest wall. First-order shimming reduced this inhomogeneity by 65%. Interestingly, the combination of spatial saturation pulses and first-order shimming was more effective than high-order shim alone. Since many clinical scanners do not have either higher-order shim or automated higher shimming algorithms that work in the presence of fat, the suggested combination provides an effective means to correct inhomogeneities in the breast.

Concentric coil arrays for parallel MRI.

A new type of coil array is proposed that consists of concentrically placed coil elements, each of which is characterized by symmetrically arranged lobes that have alternating current directions. Symmetries in the coil elements' conductor paths allow for the minimization of mutual inductance and noise correlations. In addition, the concentric arrangement of the coil elements provides spatial encoding capabilities in multiple directions, which is valuable when arrays are used with parallel MRI. Simulations are presented that describe the signal-to-noise ratio (SNR) properties of individual concentric array elements, and a four-element prototype concentric array is constructed. This prototype array is compared experimentally with three alternative four-element array designs. The overall SNR of the concentric array is comparable to the SNR of the competing arrays. Reconstruction of twofold undersampled data using the concentric array yields an average g-factor of less than 1.3 in all directions parallel to the plane of the array. There is some degradation in performance when threefold undersampled data are reconstructed, but the array still shows substantial directional invariance compared to alternative designs. Both fully-sampled and undersampled cardiac images acquired using the concentric array are shown. These results suggest that concentric structures can be useful tools for designing specialized coil arrays for parallel MRI.

Evaluation of the RF field uniformity of a double-tuned 31P/1H birdcage RF coil for spin-echo MRI/MRS of the diabetic foot.

PURPOSE: To evaluate the B1 field uniformity of a double-tuned birdcage coil designed for (31)P/(1)H MRI/MRS spin-echo (SE) imaging of the metatarsal head region of the foot in neuropathic diabetic patients. MATERIALS AND METHODS: A low-pass double-tuned (31)P/(1)H RF birdcage coil was constructed to fit over the adult forefoot. Flip angle (FA) maps were created from B1 data acquired at the 3T (31)P (four normal subjects) and (1)H (five normal subjects) frequencies. T2-weighted (T2-W) (1)H images, (31)P rapid acquisition with relaxation enhancement (RARE) images, and composite SE pulse CSI data were acquired to demonstrate the uniformity of the resulting images and data. RESULTS: The means and standard deviations (SDs) of the range of FAs across the feet of the volunteer subjects indicated good uniformity (the maximum coefficients of variation (CVs) for all of the (31)P and (1)H FA maps were 7.6% and 7.3%, respectively). The FA values across the metatarsal head region indicated a maximum signal intensity variation of +/-3% in a RARE image acquired using an echo train length of 32. CONCLUSION: A (31)P/(1)H birdcage coil constructed for MRI/MRS studies of the human forefoot provided sufficient signal uniformity of SE data to facilitate accurate (31)P concentration measurements in muscle.

Foot small muscle atrophy is present before the detection of clinical neuropathy.

OBJECTIVE: To characterize structural changes and the metabolic profile of foot muscles and correlate them with diabetic neuropathy measurements using phosphorus-31 ((31)P) rapid acquisition with relaxation enhancement (RARE) magnetic resonance imaging (MRI). RESEARCH DESIGN AND METHODS: We studied 12 control subjects, 9 non-neuropathic diabetic patients, and 12 neuropathic diabetic patients using (31)P RARE and proton ((1)H) MRI at 3 Tesla. The ratio of the total cross-sectional area of the foot to that of the muscle tissue was calculated from transaxial (1)H and (31)P images. The average (31)P concentration across the metatarsal head region was measured from the (31)P images. RESULTS: The muscle area-to-total area ratio differed among all three groups (means +/- SD): 0.55 +/- 0.04 vs. 0.44 +/- 0.05 vs. 0.06 +/- 0.06 for control, non-neuropathic, and neuropathic subjects, respectively (P < 0.0001). The average (31)P concentration also differed among all groups: 27.7 +/- 3.8 vs. 21.7 +/- 4.8 vs. 7.9 +/- 8.8 mmol/l for control, non-neuropathic, and neuropathic subjects (P < 0.0001). The muscle area-to-total area ratio strongly correlated with clinical measurements: Neuropathy Disability Score, r = -0.83, P < 0.0001; vibration perception threshold, r = -0.79, P < 0.0001; and Semmes-Weinstein monofilaments, r = -0.87, P < 0.0001. CONCLUSIONS: Small muscle atrophy is present in diabetes before clinical peripheral neuropathy can be detected using standard clinical techniques. The (31)P RARE MRI method evaluates the severity of muscle atrophy, even in the early stages when neuropathy is absent. This technique may prove to be a useful diagnostic tool in identifying early-stage diabetic foot problems.

Quantification of the 31P metabolite concentration in human skeletal muscle from RARE image intensity.

A method is described for quantifying the cellular phosphorus-31 (31P) concentration in human skeletal muscle based on RARE (rapid acquisition with relaxation enhancement) image intensities. The 31P concentrations were calculated using relaxation rates, RF coil spatial characteristics, and RARE signal intensities from foot muscle and an external 31P standard. 31P RARE and 1H T2-weighted images of the foot muscles in 11 normal subjects were acquired at 3.0 T using a double-tuned (31P/1H) birdcage coil. 31P PRESS (point-resolved spectroscopy) spectra were acquired to verify the measurable 31P concentrations in a multiecho acquisition. The mean measured concentration was 26.4 +/- 3.1 mM (mean +/- SD) from RARE signal intensities averaged over the entire imaged foot anatomy and 27.6 +/- 4.1 mM for a 3 x 3 pixel region-of-interest measurement. The 31P RARE image acquisition time was 4 min with a 0.55 cm3 voxel size. These results demonstrate that the 31P concentration can be accurately measured noninvasively in human muscle from RARE images acquired in short scan times with relatively high spatial resolution.

Double inversion black-blood fast spin-echo imaging of the human heart: a comparison between 1.5T and 3.0T.

PURPOSE: To evaluate the effectiveness of blood suppression and the quality of black-blood cardiac images acquired at 3.0 Tesla using a double-inversion recovery fast spin-echo sequence by comparing data acquired at 3.0T to data acquired at 1.5T. MATERIALS AND METHODS: Black-blood T2-weighted fast spin-echo images of the heart were acquired from five normal volunteers at 1.5T and five normal volunteers at 3.0T. Region-of-interest signal intensity measurements were performed at several locations in the suppressed blood regions of the left and right ventricles and around the left ventricle walls to assess the effectiveness and uniformity of the blood suppression, the myocardial signal-to-noise ratio (SNR), and the signal uniformity at both field strengths. B1 field maps were produced in phantoms and in subjects at both field strengths. RESULTS: Blood suppression performance is equivalent at 1.5T and 3.0T. The improvement in SNR at 3.0T compared with 1.5T is less than has been predicted in previous studies. The signal uniformity is significantly poorer at 3.0T than at 1.5T due to dielectric effects and shorter radio frequency wavelengths (P < 0.005). CONCLUSION: Spin-echo and spin-echo echo-train sequences that perform well at 1.5T will produce large signal variations in the chest cavity at 3.0T without modifications. B1 insensitive methods must be explored and implemented for spin-echo sequences to fully realize the advantages of using these sequences for high-field MRI.