Glen Morrell

Intramuscular adipose tissue, sarcopenia, and mobility function in older individuals.

Objective. Intramuscular adipose tissue (IMAT) and sarcopenia may adversely impact mobility function and physical activity. This study determined the association of locomotor muscle structure and function with mobility function in older adults. Method. 109 older adults with a variety of comorbid disease conditions were examined for thigh muscle composition via MRI, knee extensor strength via isometric dynamometry, and mobility function. The contribution of strength, quadriceps lean tissue, and IMAT to explaining the variability in mobility function was examined using multivariate linear regression models. Results. The predictors as a group contributed 27–45% of the variance in all outcome measures; however, IMAT contributed between 8–15% of the variance in all four mobility variables, while lean explained only 5% variance in only one mobility measure. Conclusions. Thigh IMAT, a newly identified muscle impairment appears to be a potent muscle variable related to the ability of older adults to move about in their community.

A phase-sensitive method of flip angle mapping

A radiofrequency (RF) excitation scheme is presented in which flip angle is encoded in the phase of the resulting excitation. This excitation is implemented with nonselective hard pulses, and is used to give flip angle maps over three‐dimensional volumes. This phase‐sensitive B1 mapping excitation can be combined with various acquisition methods such as gradient recalled echo (GRE) and echo‐planar (EP) readouts. Imaging time depends primarily on the readout method, and is roughly equivalent to the imaging time of conventional double‐angle techniques for three‐dimensional acquisition. The phase‐sensitive method allows imaging over a much wider range of flip angles than double‐angle methods. Phantom and in vivo results are presented comparing the phase‐sensitive method with the conventional double‐angle method, demonstrating the ability of the phase‐sensitive method to measure a wider range of flip angles than double‐angle methods. Magn Reson Med 60:889–894, 2008.

Comparison of combined aerobic and high-force eccentric resistance exercise with aerobic exercise only for people with type 2 diabetes mellitus.

Background and Purpose: The purpose of this study was to compare the outcomes between a diabetes exercise training program using combined aerobic and high-force eccentric resistance exercise and a program of aerobic exercise only. Subjects and Methods: Fifteen participants with type 2 diabetes mellitus (T2DM) participated in a 16-week supervised exercise training program: 7 (mean age=50.7 years, SD=6.9) in a combined aerobic and eccentric resistance exercise program (AE/RE group) and 8 (mean age=58.5 years, SD=6.2) in a program of aerobic exercise only (AE group). Outcome measures included thigh lean tissue and intramuscular fat (IMF), glycosylated hemoglobin, body mass index (BMI), and 6-minute walk distance. Results: Both groups experienced decreases in mean glycosylated hemoglobin after training (AE/RE group: −0.59% [95% confidence interval (CI)=−1.5 to 0.28]; AE group: −0.31% [95% CI=−0.60 to −0.03]), with no significant between-group differences. There was an interaction between group and time with respect to change in thigh lean tissue cross-sectional area, with the AE/RE group gaining more lean tissue (AE/RE group: 15.1 cm2 [95% CI=7.6 to 22.5]; AE group: −5.6 cm2 [95% CI=−10.4 to 0.76]). Both groups experienced decreases in mean thigh IMF cross-sectional area (AE/RE group: −1.2 cm2 [95% CI=−2.6 to 0.26]; AE group: −2.2 cm2 [95% CI=−3.5 to −0.84]) and increases in 6-minute walk distance (AE/RE group: 45.5 m [95% CI=7.5 to 83.6]; AE group: 29.9 m [95% CI=−7.7 to 67.5]) after training, with no between-group differences. There was an interaction between group and time with respect to change in BMI, with the AE/RE group experiencing a greater decrease in BMI. Discussion and Conclusion: Significant improvements in long-term glycemic control, thigh composition, and physical performance were demonstrated in both groups after participating in a 16-week exercise program. Subjects in the AE/RE group demonstrated additional improvements in thigh lean tissue and BMI. Improvements in thigh lean tissue may be important in this population as a means to increase resting metabolic rate, protein reserve, exercise tolerance, and functional mobility.

Uncertainty in T1 mapping using the variable flip angle method with two flip angles

Propagation of errors, in conjunction with the theoretical signal equation for spoiled gradient echo pulse sequences, is used to derive a theoretical expression for uncertainty in quantitative variable flip angle T(1) mapping using two flip angles. This expression is then minimized to derive a rigorous expression for optimal flip angles that elucidates a commonly used empirical result. The theoretical expressions for uncertainty and optimal flip angles are combined to derive a lower bound on the achievable uncertainty for a given set of pulse sequence parameters and signal-to-noise ratio (SNR). These results provide a means of quantitatively determining the effect of changing acquisition parameters on T(1) uncertainty.

New magnetic resonance imaging methods in nephrology

Established as a method to study anatomic changes, such as renal tumors or atherosclerotic vascular disease, magnetic resonance imaging (MRI) to interrogate renal function has only recently begun to come of age. In this review, we briefly introduce some of the most important MRI techniques for renal functional imaging, and then review current findings on their use for diagnosis and monitoring of major kidney diseases. Specific applications include renovascular disease, diabetic nephropathy, renal transplants, renal masses, acute kidney injury and pediatric anomalies. With this review, we hope to encourage more collaboration between nephrologists and radiologists to accelerate the development and application of modern MRI tools in nephrology clinics.

Synthesis and Evaluation of Globular Gd-DOTA-monoamide Conjugates with Precisely Controlled Nanosizes for Magnetic Resonance Angiography

The purpose of this study was to design and prepare macromolecular contrast agents (CAs) with a precisely defined globular structure for MR angiography and tumor angiogenesis imaging. Generations 1 through 3 (Gd-DOTA-monoamide)-poly-L-lysine octasilsesquioxane dendrimers were prepared as nanoglobular MRI CAs. The nanoglobular Gd(III) chelates had a well-defined compact globular structure and high loading of Gd-DOTA-monoamide at their surface. The size of the G1, G2, and G3 nanoglobular MRI CAs was approximately 2.0, 2.4, and 3.2 nm, respectively. The T1 relaxivity of G1, G2, and G3 nanoglobular MRI CAs was approximately 6.4, 7.2, and 10.0 mM(-1) sec(-1) at 3T, respectively. The nanoglobular MRI CAs showed size-dependent contrast enhancement within the mouse vasculature, which gradually decayed to baseline after a 60 min session. The G3 nanoglobular CA resulted in more significant and prolonged vascular enhancement than the smaller nanoglobular agents at 0.03 mmol Gd/kg. The G3 agent also provided significant and prolonged contrast enhancement in the heart and vasculature at a dose as low as 0.01 mmol Gd/kg, 1/10th of the regular clinical dose. Significant enhancement was observed in tumor for all CAs. The nanoglobular CAs cleared via renal filtration and accumulated in the urinary bladder as shown in the dynamic MR images. The nanoglobular Gd(III) chelates are effective intravascular MRI CAs at substantially reduced doses. The nanoglobular MRI CAs are promising for further preclinical development for MR angiography and MR imaging of tumor angiogenesis.

Pharmacokinetic Mapping for Lesion Classification in Dynamic Breast MRI

To prospectively investigate whether a rapid dynamic MRI protocol, in conjunction with pharmacokinetic modeling, could provide diagnostically useful information for discriminating biopsy‐proven benign lesions from malignancies.

An analysis of the accuracy of magnetic resonance flip angle measurement methods.

Several methods of flip angle mapping for magnetic resonance imaging have been proposed. We evaluated the accuracy of five methods of flip angle measurement in the presence of measurement noise. Our analysis was performed in a closed form by propagation of probability density functions (PDFs). The flip angle mapping methods compared were (1) the phase-sensitive method, (2) the dual-angle method using gradient recalled echoes (GRE), (3) an extended version of the GRE dual-angle method incorporating phase information, (4) the AFI method and (5) an extended version of the AFI method incorporating phase information. Our analysis took into account differences in required imaging time for these methods in the comparison of noise efficiency. PDFs of the flip angle estimate for each method for each value of true flip angle were calculated. These PDFs completely characterize the performance of each method. Mean bias and standard deviation were computed from these PDFs to more simply quantify the relative accuracy of each method over its range of measurable flip angles. We demonstrate that the phase-sensitive method provides the lowest mean bias and standard deviation of flip angle estimate of the five methods evaluated over a wide range of flip angles.

Measurement of renal tissue oxygenation with blood oxygen level-dependent MRI and oxygen transit modeling

Blood oxygen level-dependent (BOLD) MRI data of kidney, while indicative of tissue oxygenation level (Po2), is in fact influenced by multiple confounding factors, such as R2, perfusion, oxygen permeability, and hematocrit. We aim to explore the feasibility of extracting tissue Po2 from renal BOLD data. A method of two steps was proposed: first, a Monte Carlo simulation to estimate blood oxygen saturation (SHb) from BOLD signals, and second, an oxygen transit model to convert SHb to tissue Po2. The proposed method was calibrated and validated with 20 pigs (12 before and after furosemide injection) in which BOLD-derived tissue Po2 was compared with microprobe-measured values. The method was then applied to nine healthy human subjects (age: 25.7 ± 3.0 yr) in whom BOLD was performed before and after furosemide. For the 12 pigs before furosemide injection, the proposed model estimated renal tissue Po2 with errors of 2.3 ± 5.2 mmHg (5.8 ± 13.4%) in cortex and -0.1 ± 4.5 mmHg (1.7 ± 18.1%) in medulla, compared with microprobe measurements. After injection of furosemide, the estimation errors were 6.9 ± 3.9 mmHg (14.2 ± 8.4%) for cortex and 2.6 ± 4.0 mmHg (7.7 ± 11.5%) for medulla. In the human subjects, BOLD-derived medullary Po2 increased from 16.0 ± 4.9 mmHg (SHb: 31 ± 11%) at baseline to 26.2 ± 3.1 mmHg (SHb: 53 ± 6%) at 5 min after furosemide injection, while cortical Po2 did not change significantly at ∼58 mmHg (SHb: 92 ± 1%). Our proposed method, validated with a porcine model, appears promising for estimating tissue Po2 from renal BOLD MRI data in human subjects.

Associations of Body Size and Body Composition with Functional Ability and Quality of Life in Hemodialysis Patients

BACKGROUND AND OBJECTIVES Modifiable factors, such as body size and body composition, could influence physical function and quality of life in patients undergoing maintenance hemodialysis (MHD). DESIGN, SETTING, PARTICIPANTS, & MEASUREMENTS From January 2008 to June 2012, in body mass index (BMI), waist circumference (WC), and magnetic resonance imaging measurements of midthigh muscle area (MTMA) and intra-abdominal fat area (IAFA) were obtained at baseline in 105 MHD patients. Six-minute walk distances and physical and mental component scores (PCS and MCS) from the Short Form-12 questionnaire were obtained at baseline and 6 and 12 months. Separate mixed-effects regression models were used to relate baseline BMI, WC, and IAFA with baseline and the average of follow-up 6-minute walk distances and PCS and MCS after adjustment for baseline covariates and MTMA. RESULTS for baseline covariates and baseline MTMA, each SD increase in baseline BMI was inversely associated with baseline (-31.5 m; 95% confidence interval [95% CI], -53.0 to -10.0 m) and follow-up (-36.9 m; 95% CI, -54.6 to -19.2 m) 6-minute walk distances. Results were similar for WC and IAFA. In each of these models, each SD increase in MTMA had a strong positive association with 6-minute walk distance. Adiposity measures were not associated with baseline or follow-up PCS and MCS. After adjustment for baseline BMI, each SD increase in baseline MTMA was associated with higher baseline PCS score (3.78; 95% CI, 0.73 to 6.82) and MCS (3.75; 95% CI, 0.44 to 7.05) but had weaker associations with follow-up PCS and MCS. CONCLUSIONS Body size and composition are significantly associated with physical functioning and quality of life. Interventions that improve muscle mass and decrease obesity might improve these measures in patients undergoing MHD.