Biomedical subjects

Alexander J Gougoutas

Publications and source records attributed to Alexander J Gougoutas.

3 recordsLinked to original sources

PubMed2004

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

PURPOSE: To measure T1rho relaxation times and T1rho 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 T1rho-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: T1rho-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 T1rho 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. T1rho is 30% higher in the parenchyma and 78% higher in CSF compared to the corresponding T2 values. T1rho dispersion was observed between spin-locking frequencies 0 and 500 Hz. CONCLUSION: T1rho-weighted MRI provides images of the brain with superb contrast and detail. T1rho values measured in the different brain tissues will serve as useful baseline values for analysis of T1rho changes associated with pathology.

Adult↗

PubMed2004

Correlation of T1rho with fixed charge density in cartilage.

PURPOSE: To establish the specificity of T1rho with respect to fixed charge density (FCD) as a measure of proteoglycan (PG) content in cartilage during the onset of osteoarthritis (OA). MATERIALS AND METHODS: T1rho-weighted and sodium MRI were performed on cartilage samples of enzymatically degraded bovine explants and natural osteoarthritic human samples representing controlled and physiological models of OA, respectively. Spatial maps of T1rho and FCD (measured using the previously validated method of sodium MRI) were calculated from image data. Data were extracted from the maps and subjected to linear regression to compare changes in T1rho with changes in FCD in each model. Tissue samples were subjected to histological staining for a reduction in PG content. RESULTS: Plots of normalized T1rho rate vs. FCD were found to be strongly correlated (R2 > 0.75 and 0.85) in both models with nearly the same slope of approximately 1/2 (P > 0.51). Loss of PG in bovine and human tissue was confirmed by histology. CONCLUSION: The strong correlation of the FCD and T1rho data in both the controlled and physiological models demonstrates that changes in T1rho are due predominantly to changes in PG content. This work is a first step in establishing T1rho as a method of quantifying PG changes in early-stage OA.

Animals↗

PubMed2004

Cartilage volume quantification via Live Wire segmentation.

RATIONALE AND OBJECTIVES: A reduction in cartilage volume is characteristic of osteoarthritis and hence there exists a need for an accurate and reproducible method to measure in vivo cartilage volume. Quantification of cartilage volume from magnetic resonance (MR) images requires a segmentation technique such as the user-driven "Live Wire" strategy that can reliably delineate object volumes in a time-efficient manner. In the present work, the accuracy and reproducibility of the Live Wire method for the quantification of cartilage volume in MR images is evaluated. MATERIALS AND METHODS: The accuracy of the Live Wire method was assessed by comparing the MR-based volume measurement of a patellar cartilage-shaped phantom versus data calculated via water displacement. The inter- and intra-operator reproducibility of the technique was evaluated from Live Wire segmentation of the patellar cartilage volume from fat-suppressed 3-dimensional spoiled-gradient-echo images of five healthy human volunteers performed by three operators. To provide data for analysis of inter-scan reproducibility, the human scans were repeated five times with the aid of a leg-restraining jig to minimize repositioning error. RESULTS: The volume of the patellar cartilage-shaped phantom measured via Live Wire segmentation of MR images was within 97.8% of its true volume. The average inter- and intra-operator coefficients of variation of three operators were 3.0% and 0.4%, respectively. The average inter-scan coefficient of variation of five repeated scans of each volunteer was 2.7%. CONCLUSION: The data suggest that the Live Wire strategy is an accurate, reproducible, and efficient technique to measure cartilage volume in vivo in a feasible amount of operator time.

Adult↗