Tumor angiography using high-resolution, three-dimensional magnetic resonance imaging: comparison of gadopentetate dimeglumine and a macromolecular blood-pool contrast agent

Gd Complexes of DO3A-(Biphenyl-2,2'-bisamides) Conjugates as MRI Blood-Pool Contrast Agents

We report the synthesis of DO3A derivatives of 2,2'-diaminobiphenyl (1a,b) and their Gd complexes of the type [Gd(1)(H2O)]·xH2O (2a,b) for use as new MRI blood-pool contrast agents (BPCAs) that provide strong and prolonged vascular enhancement. Pharmacokinetic inertness of 2 compares well with that of structurally related Dotarem, a DOTA-based MRI CA currently in use. The R 1 relaxivity in water reaches 7.3 mM(-1) s(-1), which is approximately twice as high as that of Dotarem (R 1 = 3.9 mM(-1) s(-1)). They show interaction with HSA to give association constants (K a) in the order of two (∼10(2)), revealing the existence of the blood-pool effect. The in vivo MR images of mice obtained with 2 are coherent, showing strong signal enhancement in both heart, abdominal aorta, and small vessels. Furthermore, the brain tumor is vividly enhanced for an extended period of time.

High-resolution magnetic resonance angiography in the mouse using a nanoparticle blood-pool contrast agent

High-resolution magnetic resonance angiography is already a useful tool for studying mouse models of human disease. Magnetic resonance angiography in the mouse is typically performed using time-of-flight contrast. In this work, a new long-circulating blood-pool contrast agent-a liposomal nanoparticle with surface-conjugated gadolinium (SC-Gd liposomes)-was evaluated for use in mouse neurovascular magnetic resonance angiography. A total of 12 mice were imaged. Scan parameters were optimized for both time-of-flight and SC-Gd contrast. Compared to time-of-flight contrast, SC-Gd liposomes (0.08 mmol/kg) enabled improved small-vessel contrast-to-noise ratio, larger field of view, shorter scan time, and imaging of venous structures. For a limited field of view, time-of-flight and SC-Gd were not significantly different; however, SC-Gd provided better contrast-to-noise ratio when the field of view encompassed the whole brain (P < 0.001) or the whole neurovascular axis (P < 0.001). SC-Gd allowed acquisition of high-resolution magnetic resonance angiography (52 x 52 x 100 micrometer(3) or 0.27 nL), with 123% higher (P < 0.001) contrast-to-noise ratio in comparable scan time ( approximately 45 min). Alternatively, SC-Gd liposomes could be used to acquire high-resolution magnetic resonance angiography (0.27 nL) with 32% higher contrast-to-noise ratio (P < 0.001) in 75% shorter scan time (12 min).

MR angiography of tumor-related vasculature: from the clinic to the micro-environment

Angiogenesis is a very important process for tumor growth and proliferation. Given its high temporal and spatial resolution, magnetic resonance (MR) imaging is well suited for use in the assessment of angiogenesis. MR angiography can be used clinically and experimentally for identification of tumor feeding and draining vessels, for tumor characterization, and for treatment planning. The morphologic structure of tumor vessels can be investigated in relation to tumor vessel permeability with use of specific contrast agents. To gain insight into tumor angiogenesis in vivo, the authors compared images obtained with digital photography, high-resolution MR angiography, and intravital microscopy through a dorsal skin-fold window in a rodent model. The close correlation between images obtained with these various modalities, with regard to the depiction of the developing tumor vasculature, indicates that noninvasive quantification of angiogenesis may be possible with MR imaging. Future directions in tumor imaging may include so-called four-dimensional MR angiography, in which high-resolution three-dimensional MR angiography is combined with dynamic contrast-enhanced MR imaging.

Quantitative assessment of uptake and distribution of iron oxide particles (NC100150) in human melanoma xenografts by contrast-enhanced MRI

The intratumor heterogeneity in uptake of iron oxide particles (NC100150) in human melanoma xenografts was studied by MRI and the uptake was related to the blood volume fraction, BV, and the permeability surface area product, PS, in an attempt to identify transport barriers limiting the delivery of large macromolecular therapeutic agents to tumors. Dynamic MRI was performed by using spoiled gradient recalled sequences and the extravascular uptake of NC100150, BV, and PS were calculated for each tumor voxel by using a two-compartment tissue model. The uptake of NC100150 and BV were low in the tumor center and increased gradually towards the tumor periphery, whereas there was no radial gradient in PS. Significant correlations were found between the voxel values of the parameters. Thus, PS was inversely correlated to BV, and this correlation was stronger in the center than in the periphery of the tumors. The uptake of NC100150 was positively correlated to PS and this correlation was strong in the tumor periphery, where the blood perfusion is high, and weak in the tumor center, where the blood perfusion is low. In contrast, the uptake of NC100150 was not correlated to BV in any tumor region. These observations suggest that the extravascular uptake of NC100150 was limited primarily by the microvascular permeability in the tumor periphery and primarily by the blood perfusion in the tumor center.

High-resolution three-dimensional MR angiography of rodent tumors: morphologic characterization of intratumoral vasculature

PURPOSE

To evaluate high-resolution three-dimensional MR angiography (MRA) for the visualization and morphologic characterization of intratumoral vasculature.

MATERIALS AND METHODS

Two subcutaneous rodent tumor models (human skin carcinoma HaCaT-ras-A-5RT3 grown in nude mice and rat prostate carcinoma R3327-AT1 grown in Copenhagen rats) were examined with a clinical 1.5 T MR-system. For MRA a dedicated high-resolution three-dimensional gradient echo pulse sequence with a voxel size of 166 x 206 x 320 microm(3) was performed after injection of Gadomer-17. The image analysis included a correlation of intratumoral vessels with histology. Signal intensity measurements were performed in the vena cava, the tumor underlying muscle, and in various regions of the tumor. Signal-to-noise-ratios (SNR) and contrast-to-noise-ratios (CNR) were calculated from this measurement.

RESULTS

High-resolution MRA allowed a clear distinction of intratumoral blood vessels. The mouse tumor model tended to be strongly vascularized with several intratumoral blood vessels clearly displayed by MRA. When correlated with histology, these intratumoral blood vessels had a size in the range of 300 to 400 microm. In contrast, rat tumors had only sparse capillary intratumoral blood vessels that could only be demonstrated by histology. In both tumor models, dilated blood vessels were observed in the subcutaneous tissue near the tumor. In general, areas with a strong contrast enhancement correlated with viable, well vascularized tumor regions, whereas non-enhancing tumor areas correlated with tumor necrosis or hypoxic areas.

CONCLUSION

High-resolution three-dimensional MRA allows the visualization of intratumoral vasculature in rodent models. With minimal hardware and software modifications, high-resolution MRA could be performed on a clinical 1.5 T MRI scanner. Morphologic characterization of intratumoral blood vessels could add important insights into the process of tumor angiogenesis.

Magnetic resonance imaging of nude mice with heterotransplanted high-grade squamous cell carcinomas: use of a low-loaded, covalently bound Gd-Hsa conjugate as contrast agent with high tumor affinity

RATIONALE

Malignant tumors often show an increased uptake and metabolism of plasma proteins, especially albumin.

OBJECTIVES

Determine whether the accumulation of low loaded Gd-albumin improves visualization of malignant tumors by MRI.

METHODS

Twelve nude mice with heterotransplanted squamous cell carcinomas were studied. The signal intensity of tumor, blood, liver, kidney and muscle tissue was studied in MR images after application of Gd-albumin during a period of 144 hours. MRI results were histologically correlated after simultaneously injection of Gd- and fluorescein-labeled albumins in 9 nude mice.

RESULTS

Although liver and kidney had a maximum increase in signal intensity within 30 minutes, tumors showed a delayed 51% increase in the 24 hours after application. Histologic and fluorescence evaluation demonstrated albumin localization in tumors predominantly in stroma and necroses.

CONCLUSIONS

Gd-albumin is efficiently accumulated in SCC transplants. MRI with low loaded Gd-albumin may offer relevant opportunities for recognizing tumors sensitive to a therapy with cyostic drug-labeled albumins.

Tumor microvascular characterization using ultrasmall superparamagnetic iron oxide particles (USPIO) in an experimental breast cancer model

The diagnostic potential of ultrasmall superparamagnetic iron oxide particles (USPIO) for quantitative tumor microvessel characterization was assessed by kinetic analysis of dynamic magnetic resonance imaging (MRI) in a rodent breast cancer model. Microvascular characteristics (transendothelial permeability (K(PS)) and fractional plasma volume (fPV)) were estimated in 32 female Sprague Dawley rats, bearing breast tumors of varying malignancy. These values were compared to a prototype macromolecular contrast medium standard, albumin-(GdDTPA)(30). Transendothelial permeability (K(PS)) correlated significantly (P < 0.05) with the tumor grade (Scarff-Bloom-Richardson (SBR) score) for the USPIO (r = 0.36), as well as for the reference macromolecule, albumin-(GdDTPA)(30) (r = 0.54). Estimates for the fPV did not show a statistically significant correlation with the tumor grade for either contrast medium. In conclusion, USPIO-enhanced MRI data were capable to characterize tumor microvessel properties in this breast cancer model: microvascular permeability (determined using USPIO) correlated significantly with tumor grade. Thus, quantitative estimation of microvascular characteristics in tumors could provide a surrogate of new vessel formation (angiogenesis) and thus a further important clinical indication for USPIO, in addition to MR angiography. J. Magn. Reson. Imaging 2001;13:882-888.

Concurrent MRI and diffuse optical tomography of breast after indocyanine green enhancement

We present quantitative optical images of human breast in vivo. The images were obtained by using near-infrared diffuse optical tomography (DOT) after the administration of indocyanine green (ICG) for contrast enhancement. The optical examination was performed concurrently with a magnetic resonance imaging (MRI) exam on patients scheduled for excisional biopsy or surgery so that accurate image coregistration and histopathological information of the suspicious lesions was available. The ICG-enhanced optical images coregistered accurately with Gadolinium-enhanced magnetic resonance images validating the ability of DOT to image breast tissue. In contrast to simple transillumination, we found that DOT provides for localization and quantification of exogenous tissue chromophore concentrations. Additionally our use of ICG, an albumin bound absorbing dye in plasma, demonstrates the potential to differentiate disease based on the quantified enhancement of suspicious lesions.

Prostate cancer tumor grade differentiation with dynamic contrast-enhanced MR imaging in the rat: comparison of macromolecular and small-molecular contrast media--preliminary experience

PURPOSE

To differentiate prostate cancers of different histopathologic grades with dynamic gadolinium-enhanced magnetic resonance (MR) imaging. Results with a conventional small-molecular contrast medium (CM) were compared to those with a prototypic macromolecular CM.

MATERIALS AND METHODS

High- and low-grade tumors, sublines of the Dunning R3327 rat prostate cancer line, were subcutaneously implanted into the flanks of 12 male Copenhagen rats. Dynamic contrast material-enhanced MR imaging was performed with small-molecular CM and macromolecular CM at an interval of 1 day. Microvascular permeability, as estimated with the endothelial transfer coefficient, and fractional plasma volume were calculated for each tumor and each CM by means of a two-compartmental, bidirectional kinetic model.

RESULTS

Mean endothelial transfer coefficient values for both macromolecular CM and small-molecular CM were significantly different between the two tumor sublines (P = .0004 and P = .01, respectively). For the high- and low-grade tumors, no overlap of values was seen with macromolecular CM, but a broad overlap was seen with small-molecular CM despite a significant difference in mean values.

CONCLUSION

Dynamic contrast-enhanced MR imaging permits differentiation of histopathologic prostatic tumor types. Quantitative microvascular permeability characteristics estimated from macromolecular CM-enhanced data were significantly superior to those derived from small-molecular CM-enhanced data.

Physiologic measurements by contrast-enhanced MR imaging: expectations and limitations

Contrast-enhanced magnetic resonance imaging (MRI) offers the opportunity to quantitatively assess physiologic properties of tissue, such as perfusion, blood volume, and capillary permeability. Use of such quantitation potentially allows tissues to be characterized in terms of pathophysiology and to be monitored over time, during the course of therapeutic intervention. The degree to which such quantitation is applicable relies heavily on simplified model descriptions of the tissue space and assumptions relating the signal intensity observed to the contrast agent concentration. This article presents a perspective on the use of quantitative contrast-enhanced MRI, analysis of the accuracy of derived physiologic parameters, and recommendations for pulse sequence choice.

Assessing tumor angiogenesis using macromolecular MR imaging contrast media

MRI enhanced with a macromolecular contrast medium (MMCM) has previously been shown to estimate tumor microvascular characteristics that correlate closely with histologic microvascular density, an established surrogate of tumor angiogenesis. A similar MMCM-enhanced MRI technique has now been used to investigate the acute tumor microvascular effects of antibody-mediated inhibition of vascular endothelial growth factor (VEGF), a well-studied and potent angiogenesis stimulator. Athymic rats xenografted with a human breast carcinoma (MDA-MB-435) were imaged after administration of albumin-gadolinium diethylenetriamine pentaacetic acid (Gd-DTPA30) using a heavily T1-weighted three dimensional-spoiled gradient-refocused acquisition in a steady-state pulse sequence before and 24 hours after treatment with anti-VEGF antibody (single dose of 1 mg). Changes in longitudinal relaxivity (delta R1) were analyzed using a bidirectional two-compartment kinetic model to estimate tumor fractional blood volume (fBV) and permeability surface area product (PS). Data showed a significant decrease (P < 0.05) of tumor PS with respect to macromolecular contrast medium at 24 hours after treatment with anti-VEGF antibody. No significant change was observed in fBV. Suppression of tumor microvascular permeability induced by anti-VEGF antibody can be detected and quantified by MMCM-enhanced MRI. MRI grading of tumor angiogenesis and monitoring of anti-angiogenesis interventions could find wide clinical application.