Biomedical subjects

B D Ward

Publications and source records attributed to B D Ward.

9 recordsLinked to original sources

PubMed2005

Improving the reliability of obtaining tumor hemodynamic parameters in the presence of contrast agent extravasation.

A new approach to improve the reliability of dynamic susceptibility contrast MRI for the evaluation of brain tumor hemodynamics in the presence of contrast agent extravasation is described. This model-based technique simultaneously estimates the voxel-wise tumor residue function and the temporal extravascular T(1) changes following contrast agent leakage. With these estimates the model corrects the measured MRI signal, which is then used to calculate tumor hemodynamic parameters. The feasibility of this technique is demonstrated with computer simulations that cover a wide range of hemodynamic conditions and by application to eight tumor-bearing rats. The simulations demonstrate that the corrected hemodynamic parameters precisely matched the actual values with a maximum percentage error of 4.2% compared to 68.6% for the uncorrected parameters. The corrected parameters are also essentially independent of the tumor hemodynamic state and degree of contrast extravasation. Consistent with these improvements, significant differences between corrected and uncorrected parameters, calculated from a gradient-echo sequence, are shown in a rat 9L gliosarcoma model. This method combined with the hemodynamic parameters derived from GE and SE sequences shows promise as a new tool to evaluate tumor angiogenesis and its therapy.

Animals↗

PubMed2002

Language lateralization in left-handed and ambidextrous people: fMRI data.

BACKGROUND: It is generally accepted that most people have left-hemispheric language dominance, though the actual incidence of atypical language distribution in non-right-handed subjects has not been extensively studied. The authors examined language distribution in these subjects and evaluated the relationships between personal handedness, family history of sinistrality, and a language laterality index (LI) measured with fMRI. METHODS: The authors used whole-brain fMRI to examine 50 healthy, non-right-handed subjects (Edinburgh Handedness Inventory quotient between -100 and 52) while they performed language activation and nonlinguistic control tasks. Counts of active voxels (p < 0.001) were computed in 22 regions of interest (ROI) covering both hemispheres and the cerebellum. LI were calculated for each ROI and each entire hemisphere using the formula [L - R]/[L + R]. RESULTS: Activation was predominantly right hemispheric in 8% (4/50), symmetric in 14% (7/50), and predominantly left hemispheric in 78% (39/50) of the subjects. Lateralization patterns were similar for all hemispheric ROI. Associations were observed between personal handedness and LI (r = 0.28, p = 0.046), family history of sinistrality and LI (p = 0.031), and age and LI (r = -0.49, p < 0.001). CONCLUSIONS: The incidence of atypical language lateralization in normal left-handed and ambidextrous subjects is higher than in normal right-handed subjects (22% vs 4-6%). These whole-brain results confirm previous findings in a left-handed cohort studied with fMRI of the lateral frontal lobe. Associations observed between personal handedness and LI and family history of handedness and LI may indicate a common genetic factor underlying the inheritance of handedness and language lateralization.

Adult↗

PubMed2001

MR-derived cerebral blood volume maps: issues regarding histological validation and assessment of tumor angiogenesis.

In an effort to develop MRI methods for the evaluation of tumor angiogenesis (new blood vessel formation), MRI-derived cerebral blood volume (CBV) information has been compared to histologic measures of microvessel density (MVD). Although MVD is a standard marker of angiogenesis, it is not a direct correlate of the volume measurements made with MRI, and therefore inappropriate for the development and validation of the MR techniques. Therefore, the goal of this study was to develop an approach by which MR measurements of CBV can be directly correlated. To this end, dynamic susceptibility contrast (DSC) MRI experiments were performed in six Fisher rats implanted with 9L gliosarcoma brain tumors. Subsequently, the circulation was perfused with a latex compound (Microfil), after which 50-microm tissue sections were analyzed for vessel count, diameter, and the fraction of area comprised of vessels. The results demonstrate that while fractional area (FA) does not provide a good measure of CBV, FA corrected for section thickness effects does. Whereas the FA in normal brain was found to be 13.03 +/- 1.83% the corrected FA, or fractional volume (FV), was 1.89 +/- 0.39%, a value in agreement with those reported in the literature for normal brain. Furthermore, while no significant difference was found between normal brain and tumor FA (P = 0.55), the difference was significant for FV (P = 0.036), as would be expected. And only with FV does a correlation with the MRI-derived CBV become apparent (r(S) = 0.74). There was strong correlation (r(s) = 0.886) between the tumor / normal blood volume ratios as estimated by each technique, although the MR-ratio (1.56 +/- 0.29) underestimated the histologic-ratio (2.35 +/- 0.75). Thus, the correlation of MRI CBV methods requires a measurement of fractional vessel area and correction of this area for section thickness effects. This new independent correlative measure should enable efficient and accurate progress in the development of MRI methods to evaluate tumor angiogenesis.

Animals↗

PubMed2000

Comparison of simultaneously measured perfusion and BOLD signal increases during brain activation with T(1)-based tissue identification.

Perfusion and blood oxygenation level-dependent (BOLD) signals were simultaneously measured during a finger-tapping task at 3T using QUIPSS II with thin-slice TI(1) periodic saturation, a modified pulsed arterial spin labeling technique that provides quantitative measurement of perfusion. Perfusion and BOLD signal changes due to motor activation were obtained and correlated with the T(1) values estimated from echo-planar imaging (EPI)-based T(1) maps on a voxel-by-voxel basis. The peak perfusion signal occurs in voxels with a T(1) of brain parenchyma while the peak BOLD signal occurs in voxels with a T(1) characteristic of blood and cerebrospinal fluid. The locations of the peak signals of functional BOLD and perfusion only partially overlap on the order of 40%. Perfusion activation maps will likely represent the sites of neuronal activity better than do BOLD activation maps. Magn Reson Med 44:137-143, 2000.

Brain↗

PubMed1975