Rationale and Objectives:To characterize and compare commercially available contrast media (CM) for magnetic resonance imaging (MRI) in terms of their relaxivity at magnetic field strengths ranging from 0.47 T to 4.7 T at physiological temperatures in water and in plasma. Relaxivities also were quan

Comparison of magnetic properties of MRI contrast media solutions at different magnetic field strengths.

A comprehensive classification of contrast agents currently used or under development for magnetic resonance imaging (MRI) is presented. Agents based on small chelates, macromolecular systems, iron oxides and other nanosystems, as well as responsive, chemical exchange saturation transfer (CEST) and hyperpolarization agents are covered in order to discuss the various possibilities of using MRI as a molecular imaging technique. The classification includes composition, magnetic properties, biodistribution and imaging applications. Chemical compositions of various classes of MRI contrast agents are tabulated, and their magnetic status including diamagnetic, paramagnetic and superparamagnetic are outlined. Classification according to biodistribution covers all types of MRI contrast agents including, among others, extracellular, blood pool, polymeric, particulate, responsive, oral, and organ specific (hepatobiliary, RES, lymph nodes, bone marrow and brain). Various targeting strategies of molecular, macromolecular and particulate carriers are also illustrated.

Classification and basic properties of contrast agents for magnetic resonance imaging

Dynamic contrast-enhanced magnetic resonance imaging (DCE-MRI) is the acquisition of serial MRI images before, during, and after the administration of an MR contrast agent. Unlike conventional enhanced MRI, which simply provides a snapshot of enhancement at one point in time, DCE-MRI permits a fuller depiction of the wash-in and wash-out contrast kinetics within tumors, and thus provides insight into the nature of the bulk tissue properties. Such data is readily amenable to two-compartment pharmacokinetic modeling from which parameters based on the rates of exchange between the compartments can be generated. These parameters can be used to generate color-encoded images that aid in the visual assessment of tumors. DCE-MRI is used currently to characterize masses, stage tumors, and noninvasively monitor therapy. While DCE-MRI is in clinical use, there are also a number of limitations, including overlap between malignant and benign inflammatory tissue, failure to resolve microscopic disease, and the inconsistent predictive value of enhancement pattern with regard to clinical outcome. Current research focuses on improving understanding of the meaning of DCE-MRI at a molecular level, evaluating macromolecular and targeted contrast agents, and combining DCE-MRI with other physiologic imaging techniques such as positron emission tomography. Efforts to standardize DCE-MRI acquisition, analysis, and reporting methods will allow wider dissemination of this useful functional imaging technique. J. Magn. Reson. Imaging 2003;17:509–520. Published 2003 Wiley-Liss, Inc.

https://onlinelibrary.wiley.com/doi/pdf/10.1002/jmri.10304

Functional tumor imaging with dynamic contrast-enhanced magnetic resonance imaging.

Objectives:We sought to determine the relaxivity and accurate relaxation rates of Gd-DTPA, Gd-BT-DO3A, and Gd-BOPTA at 0.2, 1.5, and 3 T in human blood plasma.Materials and Methods:Contrast media concentrations between 0.01 and 16 mM in human plasma were used for relaxation measurements. The R1 and

Relaxivity of Gadopentetate Dimeglumine (Magnevist), Gadobutrol (Gadovist), and Gadobenate Dimeglumine (MultiHance) in human blood plasma at 0.2, 1.5, and 3 Tesla.

Time-resolved contrast-enhanced 3D MR angiography (MRA) methods have gained in popularity but are still limited by the tradeoff between spatial and temporal resolution. A method is presented that greatly reduces this tradeoff by employing undersampled 3D projection reconstruction trajectories. The variable density k-space sampling intrinsic to this sequence is combined with temporal k-space interpolation to provide time frames as short as 4 s. This time resolution reduces the need for exact contrast timing while also providing dynamic information. Spatial resolution is determined primarily by the projection readout resolution and is thus isotropic across the FOV, which is also isotropic. Although undersampling the outer regions of k-space introduces aliased energy into the image, which may compromise resolution, this is not a limiting factor in high-contrast applications such as MRA. Results from phantom and volunteer studies are presented demonstrating isotropic resolution, broad coverage with an isotropic field of view (FOV), minimal projection reconstruction artifacts, and temporal information. In one application, a single breath-hold exam covering the entire pulmonary vasculature generates high-resolution, isotropic imaging volumes depicting the bolus passage.

https://www.onlinelibrary.wiley.com/doi/pdf/10.1002/mrm.10212

Time-resolved contrast-enhanced imaging with isotropic resolution and broad coverage using an undersampled 3D projection trajectory

The purpose of this review is to outline recent developments in contrast agents for magnetic resonance angiography (MRA) and to give some idea of what the future might hold. Up to now, non-binding gadolinium (Gd) chelates have been the agents used for MRA. Modified paramagnetic Gd-based agents with varying degrees of protein interaction have been developed, and these, together with new superparamagnetic compounds, are currently under clinical evaluation. It is likely that two different types of contrast agent will soon be available: extracellular agents for first-pass MRA and intravascular agents mainly for steady-state MRA. Several agents also exhibit certain tissue specific properties in addition to conventional extracellular properties. This will lead to more comprehensive imaging approaches.J. Magn. Reson. Imaging 10:314–316, 1999. © 1999 Wiley-Liss, Inc.

Contrast agents for MRA: future directions.

Multiphase contrast-enhanced 3D MR angiography (MRA) data sets allow the separate visualization of the arterial and venous pulmonary vasculature. However, due to short arterial-to-venous bolus transit times in the lung, the generation of pure venograms without arterial overlay is difficult. To suppress arterial signal in venograms, early arterial phase data are typically subtracted from peak venous phase images. In this study, a correlation algorithm is used to postprocess the multiphase 3D MRA data sets. The cross-correlation between a measured arterial or venous reference function and the local signal-time course is computed which highlights image locations with a similar signal-time curve as the reference function and suppresses constant signal. Conventional maximum intensity projections (MIP) are generated from the arterial and venous correlation maps. In a study with five volunteers, an increase in SNR by a factor of 2.1 (1.8) of arterial (venous) correlation MIP images over subtraction MIP images was observed.

Separation of arteries and veins in 3D MR angiography using correlation analysis

RATIONALE AND OBJECTIVES. To assess the vascular contrasting properties of a new MR contrast agent (gadobenate dimeglumine [Gd-BOPTA]), which presents higher relaxivity because of reversible, weak protein interaction, and, to compare these properties with a standard gadolinium agent. MATERIALS AND METHODS. Two phase I trials compared intraindividually: (A) the vascular contrasting properties of Gd-BOPTA at three doses (0.0125, 0.05, and 0.2 mmollkg body weight) and two flow rates (0.5 and 2.0 mL/s) in 10 volunteers; and (B) 0.1 mmollkg body weight doses of Gd-BOPTA and Gd-DTPA at 2.0 mL/s using a modified magnetic resonance angiography (MRA) sequence with a temporal resolution of 1 s/f. Quantitative (ROI analysis) and fully blinded qualitative (reader review) assessment of images was performed. RESULTS. A dose of 0.2 mmol/kg resulted in higher maximum intensities, longer median peak widths, and larger areas under the curve than did the lower doses (0.0125 mmollkg and 0.05 mmollkg). In the intraindividual comparison, Gd-BOPTA demonstrated significantly better vascular enhancement characteristics in terms of signal peak duration (p < 0.05), maximum signal intensity (p < 0.05), and area under the enhancement curve (p < 0.01). The multireader assessment for overall vascular contrast preferred Gd-BOPTA at p < 0.03. CONCLUSIONS. Gd-BOPTA was shown to exhibit preferential and different vascular enhancement properties as compared with Gd-DTPA for MRA.

Assessment of gadobenate dimeglumine for magnetic resonance angiography: phase I studies.

The purpose of this study was to demonstrate selective visualization of pulmonary arteries and veins with high spatial resolution for improved detection of vascular pathologies. Time-resolved pulmonary three-dimensional gadolinium-enhanced magnetic resonance angiograms (3D-Gd-MRA) were acquired with an ultrashort 3D fast low-angle shot (FLASH) sequence (TR/TE 2.3/0.9 msec) using asymmetric k-space sampling in readout, phase-encoding, and partition directions. In a single breath-hold four consecutive acquisitions were performed with a scan time of 6.28 seconds for each phase. A spatial resolution of 1.9 x 1.4 x 2 mm(3) could be achieved for a 12 cm thick 3D volume. To exploit the intrinsic enhancement kinetics of the pulmonary vascular system, the infusion of two gadolinium chelate boli was synchronized with the acquisition of the first and third data sets. This infusion strategy created two predominantly pulmonary arterial and venous data sets with the arterial and venous signal being maximally anti-correlated in time. A further separation of arterial and venous signal could be achieved by means of a correlation analysis. Eight patients with suspected thrombi in the pulmonary veins were studied. The calculated correlation angiographies provided high-quality pulmonary arterio- and venograms. Background signal was completely eliminated, allowing maximum intensity projection analysis of the full data set. In 7/8 patients no venous contamination of the arterial phase and vice versa was found. Patency of the pulmonary arteries and veins could be reliably assessed to the level of the segmental vessels. The combination of ultrafast multiphase 3D-Gd-MRA and dual-bolus injection with a correlation analysis of vascular signal provides high-resolution pulmonary arterio- and venograms. This imaging strategy initiates a new competitor to X-ray angiography.

/pdf/high-resolution-pulmonary-arterio-and-venography-using-23t8v3jjm4.pdf

High-resolution pulmonary arterio- and venography using multiple-bolus multiphase 3D-Gd-mRA.

Schoenberg SO, Floemer F, Kroeger H, Hoffmann A, Bock M, Knopp MV. Combined assessment of obstructive sleep apnea syndrome with dynamic MRI and parallel EEG registration: Initial results. Invest Radiol 2000;35:267–276.RATIONALE AND OBJECTIVES.To detect obstructive pharyngeal changes in sleeping pati

F. Floemer

Papers

Contrast agents for MRA: future directions.

Separation of arteries and veins in 3D MR angiography using correlation analysis

Assessment of gadobenate dimeglumine for magnetic resonance angiography: phase I studies.

High-resolution pulmonary arterio- and venography using multiple-bolus multiphase 3D-Gd-mRA.

Combined Assessment of Obstructive Sleep Apnea Syndrome with Dynamic MRI and Parallel EEG Registration: Initial Results