Breath-hold perfusion and permeability mapping of hepatic malignancies using magnetic resonance imaging and a first-pass leakage profile model

A comparison of Ktransmeasurements 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.

New hybrid technique for accurate and reproducible quantitation of dynamic contrast-enhanced MRI data

The accuracy and precision of two major approaches for analyzing dynamic MRI data from the first passage of a Gd-DTPA contrast bolus are examined, using a Monte Carlo simulation. Method 1 fits the contrast concentration curve of the first pass to a two-compartment kinetic model to determine the tissue pharmacokinetic parameters. Method 2 decomposes intravascular and interstitial components of the first-pass curve based on a leakage profile (LP) model. Based on the results of these Monte Carlo simulations, a new "hybrid" method is proposed that combines both analytical approaches to optimize accuracy and precision of estimates of K(trans), v(e), and v(p). The new method was evaluated by computer simulation and used on experimental results from a patient with primary brain tumors. The new method has the potential to provide more accurate quantification of tissue plasma volume and vessel permeability.

Method for quantitation of dynamic MRI contrast agent uptake in colorectal liver metastases

PURPOSE

To investigate the reproducibility of dynamic contrast-enhanced MRI (DCE-MRI) in colorectal liver metastases using a vascular normalization function (VNF) from pixels in the spleen and to compare this with a technique using an arterial input function (AIF) from pixels in the aorta.

MATERIALS AND METHODS

DCE-MRI with gadolinium-DTPA (Gd-DTPA) was performed in patients with colorectal liver metastases. The VNF and AIF were determined using an automated algorithm. The average Gd-DTPA uptake rate (k(ep)) was calculated for the metastases using a physiological pharmacokinetic model. The protocol was repeated on a second day to calculate the repeatability coefficient of the measurements of k(ep).

RESULTS

Using the VNF from the spleen the overall mean k(ep) of the two sessions for 11 patients was 0.033 per second and the repeatability coefficient was 0.009 per second. Using the AIF from the aorta these values were 0.031 per second and 0.028 per second, respectively.

CONCLUSION

The mean Gd-DTPA uptake rate using a VNF taken from the spleen can be determined with adequate reproducibility in colorectal liver metastases. The use of a VNF from pixels in the spleen is better than an AIF from pixels in the aorta in terms of reproducibility, and is recommended when this DCE-MRI technique is used for prediction and monitoring of therapy outcome in colorectal liver metastases.

Reproducibility of quantitative dynamic contrast-enhanced MRI in newly presenting glioma

We have investigated the reproducibility of dynamic contrast enhanced imaging techniques in nine patients with cerebral glioma. Patients were imaged twice with a 2 day interval between scans. Maps were produced of the time taken to achieve 90% enhancement (T90), the maximal intensity change per time interval ratio (MITR), the volume transfer coefficient between plasma and the extravascular extracellular space (K(trans)) and the extravascular extracellular contrast distribution volume, v(e). Measurements of K(trans) greater than 1.2 min(-1) were used to exclude pixels where first pass perfusion effects dominated the measurement. Measures of the test-retest coefficient of variation (CoV) and intraclass correlation coefficients were used to assess reproducibility for measurements from a volume of interest containing enhancing tissue from the whole tumour. MITR showed poor reproducibility (mean CoV 17.9%, 95% confidence limits for group comparisons 20.2%). T90 showed good reproducibility (mean CoV 7.1%, 95% confidence limits for group comparisons 5.2%). Calculated values of K(trans) and v(e) also showed good reproducibility (mean CoV 7.7% and 6.2% respectively, 95% confidence limits for group comparisons 6.2% and 4.8%, respectively). We conclude that the measurements of K(trans) and v(e) derived from pharmacokinetic analysis are sufficiently reproducible to support their use as a biological markers in therapeutic trials.

Molecular imaging and biological evaluation of HuMV833 anti-VEGF antibody: implications for trial design of antiangiogenic antibodies

BACKGROUND

Vascular endothelial growth factor (VEGF) is a potent angiogenic cytokine, and various inhibitory agents, including specific antibodies, have been developed to block VEGF-stimulated angiogenesis. We developed HuMV833, a humanized version of a mouse monoclonal anti-VEGF antibody (MV833) that has antitumor activity against a number of human tumor xenografts, and investigated the distribution and biologic effects of HuMV833 in patients in a phase I trial.

METHODS

Twenty patients with progressive solid tumors were treated with various doses of HuMV833 (0.3, 1, 3, or 10 mg/kg). Positron emission tomography with (124)I-HuMV833 was used to measure the antibody distribution in and clearance from tissues. Magnetic resonance imaging was used to measure the vascular permeability surface area product with a first-pass pharmacokinetic model (k(fp)) to determine tumor vascular permeability.

RESULTS

The antibody was generally well tolerated, although the incremental dose, phase I study design, and pharmacodynamic endpoints could not identify the optimum biologically active dose. Antibody distribution and clearance were markedly heterogeneous between and within patients and between and within individual tumors. HuMV833 distribution to normal tissues also varied among patients, but the antibody was cleared from these tissues in a homogeneous fashion. Permeability was strongly heterogeneous between and within patients and between and within individual tumors. All tumors showed a reduction in k(fp) 48 hours after the first treatment (median = 44%; range = 4%-91%).

CONCLUSIONS

Because of the heterogeneity in tumor biology with respect to antibody uptake and clearance, we suggest that either intrapatient dose escalation approaches or larger, more precisely defined patient cohorts would be preferable to conventional strategies in the design of phase I studies with antiangiogenic compounds like HuMV833.