Biomedical subjects

Hamied A Haroon

Publications and source records attributed to Hamied A Haroon.

4 recordsLinked to original sources

PubMed2004

A comparison of Ktrans measurements obtained with conventional and first pass pharmacokinetic models in human gliomas.

PURPOSE: To compare in a group of patients with cerebral gliomas the estimates of Ktrans between a conventionally established pharmacokinetic model and a recently developed first pass method. MATERIALS AND METHODS: Glioma patients (23) were studied using T1-weighted dynamic contrast-enhanced magnetic resonance imaging (MRI), and two alternative pharmacokinetic models were used for analysis to derive the volume transfer constant Ktrans. These were a modified version of the established model (yielding KTK) and a recently published method based on first pass leakage profile (FP) of contrast bolus (yielding Kfp). RESULTS: We found a strong correlation between intra-tumoral median KTK and Kfp (rho = 0.650, P < 0.01), but the values from the conventional model were consistently and significantly higher (mean of inter-tumoral Kfp and KTK medians were 0.018 minute(-1) and 0.284 minute(-1), respectively, P < 0.001). The spatial distribution of KTK and Kfp showed poor correlation in the presence of large vascular structures and good correlation elsewhere. CONCLUSION: KTK and Kfp produce similar biologic information within voxels not dominated by vascular tissue. The FP method avoids erroneous overestimation of Ktrans in areas of significant intravascular contrast. Findings are in keeping with the predictions of previous mathematical simulations.

Adult↗

PubMed2004

Comparative study of methods for determining vascular permeability and blood volume in human gliomas.

PURPOSE: To characterize human gliomas using T1-weighted dynamic contrast-enhanced MRI (DCE-MRI), and directly compare three pharmacokinetic analysis techniques: a conventional established technique and two novel techniques that aim to reduce erroneous overestimation of the volume transfer constant between plasma and the extravascular extracellular space (EES) (Ktrans) in areas of high blood volume. MATERIALS AND METHODS: Eighteen patients with high-grade gliomas underwent DCE-MRI. Three kinetic models were applied to estimate Ktrans and fractional blood plasma volume (vp). We applied the Tofts and Kermode (TK) model without arterial input function (AIF) estimation, the TK model modified to include vp and AIF estimation (mTK), and a "first pass" variant of the TK model (FP). RESULTS: KTK values were considerably higher than KmTK and KFP values (P <0.001). KmTK and KFP were more comparable and closely correlated (rho=0.744), with KmTK generally higher than KFP (P <0.001). Estimates of vp(mTK) and vp(FP) also showed a significant difference (P <0.001); however, these values were very closely correlated (rho=0.901). KTK parameter maps showed "pseudopermeability" effects displaying numerous vessels. These were not visualized on KmTK and KFP maps but appeared on the corresponding vp maps, indicating a failure of the TK model in commonly occurring vascular regions. CONCLUSION: Both of the methods that incorporate a measured AIF and an estimate of vp provide similar pathophysiological information and avoid erroneous overestimation of Ktrans in areas of significant vessel density, and thus allow a more accurate estimation of endothelial permeability.

Adult↗

PubMed2003

A framework for a streamline-based probabilistic index of connectivity (PICo) using a structural interpretation of MRI diffusion measurements.

PURPOSE: To establish a general methodology for quantifying streamline-based diffusion fiber tracking methods in terms of probability of connection between points and/or regions. MATERIALS AND METHODS: The commonly used streamline approach is adapted to exploit the uncertainty in the orientation of the principal direction of diffusion defined for each image voxel. Running the streamline process repeatedly using Monte Carlo methods to exploit this inherent uncertainty generates maps of connection probability. Uncertainty is defined by interpreting the shape of the diffusion orientation profile provided by the diffusion tensor in terms of the underlying microstructure. RESULTS: Two candidates for describing the uncertainty in the diffusion tensor are proposed and maps of probability of connection to chosen start points or regions are generated in a number of major tracts. CONCLUSION: The methods presented provide a generic framework for utilizing streamline methods to generate probabilistic maps of connectivity.

Anisotropy↗

PubMedDate not supplied

Is volume transfer coefficient (K(trans)) related to histologic grade in human gliomas?

PURPOSE: The purpose of this study was to examine the relationship between contrast transfer coefficient [K(trans)] and grade in gliomas. MATERIAL AND METHODS: Median values of K(trans), CBV(T1), and of the 95th percentile (95%) of the distribution (K(trans) [95%] and CBV(T1) [95%]) were calculated in 39 patients with glioma. Group comparisons and post hoc pairwise comparisons were performed. The relationship between variables and grade used Spearman rho and canonical discriminant analysis. The separation of high- from low-grade tumors was separately assessed by using Mann-Whitney U tests and logistic regression. Receiver operator curve analysis was performed for high- and low-grade tumors and grade III and grade IV tumors. RESULTS: There were significant differences between grades for all variables (P < .001). Pairwise comparisons demonstrated significant differences between grades II and III and II and IV for all variables except K(trans), which did not show significance in the grade II and III comparison, and between III and IV for CBV(T1) and CBV(T1) (95%; P < .01). All variables correlated with grade (P < .01). Discriminant analysis showed independent relation between both CBV(T1) and K(trans) (95%) and grade, and the canonical function produced a total correct classification of 74.4% of cases. Logistic regression analysis for low- versus high-grade tumors showed K(trans) (95%) and CBV(T1) to be independent factors (P < .01 and P < .05). CONCLUSION: There are strong independent relationships between both CBV and K(trans) and histologic grade in gliomas. Both measurements show good discriminative power in distinguishing between low- and high-grade tumors with diagnostic sensitivity and specificity >90%.

Adult↗