Assessment of tissue repair in full thickness chondral defects in the rabbit using magnetic resonance imaging transverse relaxation measurements

2008 ◽  
Vol 86B (2) ◽  
pp. 375-380 ◽  
Author(s):  
Sharan Ramaswamy ◽  
Ilksen Gurkan ◽  
Blanka Sharma ◽  
Brett Cascio ◽  
Kenneth W. Fishbein ◽  
...  
Keyword(s):  
Magnetic Resonance Imaging ◽  
Magnetic Resonance ◽  
Tissue Repair ◽  
Full Thickness ◽  
Resonance Imaging ◽  
Transverse Relaxation ◽  
Chondral Defects ◽  
Relaxation Measurements

scholarly journals High-Resolution CMRO2 Mapping in Rat Cortex: A Multiparametric Approach to Calibration of BOLD Image Contrast at 7 Tesla

2000 ◽  
Vol 20 (5) ◽  
pp. 847-860 ◽  
Author(s):  
Ikuhiro Kida ◽  
Richard P. Kennan ◽  
Douglas L. Rothman ◽  
Kevin L. Behar ◽  
Fahmeed Hyder
Keyword(s):  
Magnetic Resonance Imaging ◽  
Magnetic Resonance ◽  
Spin Echo ◽  
7 Tesla ◽  
Relaxation Rates ◽  
Resonance Imaging ◽  
Gradient Echo ◽  
Transverse Relaxation ◽  
Physiologic Parameters ◽  
Spin Echo Sequences

The blood oxygenation level-dependent (BOLD) functional magnetic resonance imaging (fMRI) method, which is sensitive to vascular paramagnetic deoxyhemoglobin, is dependent on regional values of cerebral metabolic rate of oxygen utilization (CMRO2), blood flow (CBF), and volume (CBV). Induced changes in deoxyhemoglobin function as an endogenous contrast agent, which in turn affects the transverse relaxation rates of tissue water that can be measured by gradient-echo and spin-echo sequences in BOLD fMRI. The purpose here was to define the quantitative relation between BOLD signal change and underlying physiologic parameters. To this end, magnetic resonance imaging and spectroscopy methods were used to measure CBF, CMRO2, CBV, and relaxation rates (with gradient-echo and spin-echo sequences) at 7 Tesla in rat sensorimotor cortex, where cerebral activity was altered pharmacologically within the autoregulatory range. The changes in tissue transverse relaxation rates were negatively and linearly correlated with changes in CBF, CMRO2, and CBV. The multiparametric measurements revealed that CBF and CMRO2 are the dominant physiologic parameters that modulate the BOLD fMRI signal, where the ratios of (ΔCMRO2/CMRO2)/(ΔCBF/CBF) and (ΔCBV/CBV)/(ΔCBF/CBF) were 0.86 ± 0.02 and 0.03 ± 0.02, respectively. The calibrated BOLD signals (spatial resolution of 48 μL) from gradient-echo and spin-echo sequences were used to predict changes in CMRO2 using measured changes in CBF, CBV, and transverse relaxation rates. The excellent agreement between measured and predicted values for changes in CMRO2 provides experimental support of the current theory of the BOLD phenomenon. In gradient-echo sequences, BOLD contrast is affected by reversible processes such as static inhomogeneities and slow diffusion, whereas in spin-echo sequences these effects are refocused and are mainly altered by extravascular spin diffusion. This study provides steps by which multiparametric MRI measurements can be used to obtain high-spatial resolution CMRO2 maps.

Absolute radiation dose verification using magnetic resonance imaging: feasibility study

2003 ◽  
Vol 3 (3) ◽  
pp. 123-129 ◽  
Author(s):  
G. P. Liney ◽  
A. Heathcote ◽  
A. Jenner ◽  
L. W. Turnbull ◽  
A. W. Beavis
Keyword(s):  
Magnetic Resonance Imaging ◽  
Magnetic Resonance ◽  
Transverse Relaxation Time ◽  
Three Dimensions ◽  
Radiation Doses ◽  
Transverse Relaxation Rate ◽  
Dose Verification ◽  
Atmospheric Conditions ◽  
Resonance Imaging ◽  
Transverse Relaxation

This work describes the feasibility of using a polymer-based tissue equivalent gel for measuring radiation doses in situ. The gel is based on the MAGIC formulation thereby enabling it to be manufactured under normal atmospheric conditions. Its composition has been altered to achieve a similar sensitivity to the more widely used, but technically more difficult to produce, PAG gels. Irradiation of the gel material causes polymerisation of the molecular structure resulting in a shortening of transverse relaxation time (T2), which can be imaged using Magnetic Resonance Imaging (MRI). This work calibrates the radiation response in terms of transverse relaxation rate (R2) and uses this information to provide absolute dose verification in a separate gel, which has been previously irradiated to a known configuration. Results demonstrate that this technique is able to verify radiation doses to within a few percent of delivered intent in three dimensions and with high spatial resolution. This work may be followed by anyone with an interest in the quality assurance of advanced conformal radiotherapy delivery methods.

Noninvasive measurement and imaging of liver iron concentrations using proton magnetic resonance

Blood ◽  
2005 ◽  
Vol 105 (2) ◽  
pp. 855-861 ◽  
Author(s):  
Timothy G. St. Pierre ◽  
Paul R. Clark ◽  
Wanida Chua-anusorn ◽  
Adam J. Fleming ◽  
Gary P. Jeffrey ◽  
...  
Keyword(s):  
Magnetic Resonance Imaging ◽  
Magnetic Resonance ◽  
Needle Biopsy ◽  
Hereditary Hemochromatosis ◽  
Iron Concentration ◽  
Relaxation Rates ◽  
Resonance Imaging ◽  
Liver Iron ◽  
Transverse Relaxation

AbstractMeasurement of liver iron concentration (LIC) is necessary for a range of iron-loading disorders such as hereditary hemochromatosis, thalassemia, sickle cell disease, aplastic anemia, and myelodysplasia. Currently, chemical analysis of needle biopsy specimens is the most common accepted method of measurement. This study presents a readily available noninvasive method of measuring and imaging LICs in vivo using clinical 1.5-T magnetic resonance imaging units. Mean liver proton transverse relaxation rates (R2) were measured for 105 humans. A value for the LIC for each subject was obtained by chemical assay of a needle biopsy specimen. High degrees of sensitivity and specificity of R2 to biopsy LICs were found at the clinically significant LIC thresholds of 1.8, 3.2, 7.0, and 15.0 mg Fe/g dry tissue. A calibration curve relating liver R2 to LIC has been deduced from the data covering the range of LICs from 0.3 to 42.7 mg Fe/g dry tissue. Proton transverse relaxation rates in aqueous paramagnetic solutions were also measured on each magnetic resonance imaging unit to ensure instrument-independent results. Measurements of proton transverse relaxivity of aqueous MnCl2 phantoms on 13 different magnetic resonance imaging units using the method yielded a coefficient of variation of 2.1%.

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