MRI of blood-brain barrier permeability in astrocytic gliomas: application of small and large molecular weight contrast media

Pretreatment evaluation of microcirculation by dynamic contrast-enhanced magnetic resonance imaging predicts survival in primary rectal cancer patients

PURPOSE

To investigate the prognostic value of the perfusion index (PI), a microcirculatory parameter estimated from dynamic contrast-enhanced magnetic resonance imaging (DCE-MRI), which integrates information on both flow and permeability, to predict overall survival and disease-free survival in patients with primary rectal cancer.

METHODS AND MATERIALS

A total of 83 patients with stage cT3 rectal cancer requiring neoadjuvant chemoradiation were investigated with DCE-MRI before start of therapy. Contrast-enhanced dynamic T1 mapping was obtained, and a simple data analysis strategy based on the calculation of the maximum slope of the tissue concentration-time curve divided by the maximum of the arterial input function was used as a measure of tumor microcirculation (PI), which integrates information on both flow and permeability.

RESULTS

In 39 patients (47.0%), T downstaging (ypT0-2) was observed. During a mean (±SD) follow-up period of 71 ± 29 months, 58 patients (69.9%) survived, and disease-free survival was achieved in 45 patients (54.2%). The mean PI (PImean) averaged over the group of nonresponders was significantly higher than for responders. Additionally, higher PImean in age- and gender-adjusted analyses was strongly predictive of therapy nonresponse. Most importantly, PImean strongly and significantly predicted disease-free survival (unadjusted hazard ratio [HR], 1.85 [ 95% confidence interval, 1.35-2.54; P<.001)]; HR adjusted for age and sex, 1.81 [1.30-2.51]; P<.001) as well as overall survival (unadjusted HR 1.42 [1.02-1.99], P=.040; HR adjusted for age and sex, 1.43 [1.03-1.98]; P=.034).

CONCLUSIONS

This analysis identifies PImean as a novel biomarker that is predictive for therapy response, disease-free survival, and overall survival in patients with primary locally advanced rectal cancer.

The blood-brain barrier is intact after levodopa-induced dyskinesias in parkinsonian primates--evidence from in vivo neuroimaging studies

It has been suggested, based on rodent studies, that levodopa (L-dopa) induced dyskinesia is associated with a disrupted blood-brain barrier (BBB). We have investigated BBB integrity with in vivo neuroimaging techniques in six 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) lesioned primates exhibiting L-dopa-induced dyskinesia. Magnetic resonance imaging (MRI) performed before and after injection of Gadolinium-diethylenetriamine pentaacetic acid (Gd-DTPA) revealed an intact BBB in the basal ganglia showing that l-dopa-induced dyskinesia is not associated with a disrupted BBB in this model.

Dynamic T(1) mapping predicts outcome of chemoradiation therapy in primary rectal carcinoma: sequence implementation and data analysis

PURPOSE

To describe details about the implementation of a dynamic T(1)-mapping technique and a simple data analysis strategy that can be used to predict therapy outcome in primary rectal carcinoma and to investigate the physiologic meaning of the obtained parameter.

MATERIALS AND METHODS

Contrast-enhanced dynamic T(1) mapping was achieved with a snapshot fast low-angle shot (FLASH) T(1) mapping sequence implemented on a 1.5 T MR scanner. This method was applied to 58 patients with primary rectal cancer before onset of chemoradiation therapy. A simple data analysis strategy based on the calculation of the maximum slope of the tissue concentration-time curve divided by the maximum of the arterial input function (AIF) was used as a measure of tumor microcirculation (PI values).

RESULTS

The snapshot FLASH (SFL) T(1)-mapping technique is accurate and sensitive enough to detect inhomogeneous uptake kinetics within tumor tissue. Classifying the patients into two groups according to therapy response showed lower mean PI values for responders as compared to nonresponders. PI was found to combine information about permeability surface area product (PS) and blood volume.

CONCLUSIONS

The described method based on dynamic T(1) mapping has the potential to be a clinical tool for predicting therapy outcome of preoperative chemoradiation in patients with primary rectal carcinoma.

Contrast-enhanced MRI of white matter lesions in patients with blood-brain barrier dysfunction

White matter lesions (WMLs) and blood-brain barrier (BBB) dysfunction are common in dementia. Both conditions may be a consequence of small-vessel disease, in which case the BBB damage could be suspected to be located to the WMLs. Magnetic resonance imaging (MRI) can be used to show WMLs as well as to detect BBB damage when using an intravenous contrast agent, gadolinium. We examined 10 demented patients with WMLs, including 5 cases with BBB (elevated CSF/serum albumin ratios). Results showed no significant changes in MR signal in the WMLs after contrast administration. We conclude that WMLs are not related to BBB damage to such a degree that is detectable with this method and that the elevated CSF albumin might have another origin.

Comparison of gadopentetate dimeglumine and albumin-(Gd-DTPA)30 for microvessel characterization in an intracranial glioma model

To compare the performance of macromolecular albumin gadolinium-diethylenetriamine pentaacetic acid (Gd-DTPA)30 and low molecular weight gadopentetate dimeglumine for microvessel characterization, we examined an intracranial 9L glioma model in which increased angiogenesis, hypervascularity, and hyperpermeability mimic characteristics of clinical malignant brain tumors. Dynamic MRI data were analyzed using a bidirectional, two-compartment kinetic model to extract quantitative estimates for fractional blood volume (fBV) and permeability surface area product (PS). Three criteria were used for comparison of contrast agent performance: (a) tumor conspicuity, defined as the contrast-to-noise ratio (CNR); (b) dynamic range of differential permeability estimates between tumor and normal brain; (c) reasonableness of blood volume estimates. Gadopentetate was superior to macromolecular albumin-(Gd-DTPA)30 for detection of 9L brain gliomas and for measurements of hyperpermeability.

Dynamics of tumor imaging with Gd-DTPA-polyethylene glycol polymers: dependence on molecular weight

Macromolecular contrast media offer potential advantages over freely diffusible agents in magnetic resonance (MR) imaging outside the central nervous system. To identify an optimum molecular weight for macromolecular contrast media, the authors studied a novel macromolecular contrast agent, gadolinium diethylenetriaminepentaacetic acid polyethylene glycol (DTPA-PEG), synthesized in seven polymer (average) molecular weights ranging from 10 to 83 kd. Twenty-eight rabbits bearing V2 carcinoma in thighs underwent T1-weighted spin-echo imaging before injection and 5-60 minutes and 24 hours after injection of the Gd-DTPA-PEG polymers or Gd-DTPA at a gadolinium dose of 0.1 mmol/kg. Tumor region-of-interest measurements were obtained at each time point to determine contrast enhancement dynamics. Blood-pool enhancement dynamics were observed for the Gd-DTPA-PEG polymers larger than 20 kd. Polymers smaller than 20 kd displayed dynamics similar to those of the freely diffusible agent Gd-DTPA. Above the 20 kd threshold, tumor enhancement was more rapid for smaller polymers. The authors conclude that the 21.9-kd Gd-DTPA-PEG polymer is best suited for clinical MR imaging.