Coronary arteries: contrast-enhanced MR imaging with SH L 643A--experience in 12 volunteers

Chemistry of MRI Contrast Agents: Current Challenges and New Frontiers

Tens of millions of contrast-enhanced magnetic resonance imaging (MRI) exams are performed annually around the world. The contrast agents, which improve diagnostic accuracy, are almost exclusively small, hydrophilic gadolinium(III) based chelates. In recent years concerns have arisen surrounding the long-term safety of these compounds, and this has spurred research into alternatives. There has also been a push to develop new molecularly targeted contrast agents or agents that can sense pathological changes in the local environment. This comprehensive review describes the state of the art of clinically approved contrast agents, their mechanism of action, and factors influencing their safety. From there we describe different mechanisms of generating MR image contrast such as relaxation, chemical exchange saturation transfer, and direct detection and the types of molecules that are effective for these purposes. Next we describe efforts to make safer contrast agents either by increasing relaxivity, increasing resistance to metal ion release, or by moving to gadolinium(III)-free alternatives. Finally we survey approaches to make contrast agents more specific for pathology either by direct biochemical targeting or by the design of responsive or activatable contrast agents.

Improved large-scale synthesis and characterization of small and medium generation PAMAM dendrimers

Dendrimers are promising polymers for biomedical applications; however, most dendrimer formulations have failed to move from laboratory science to upscaled products for preclinical testing or GMP production. This publications reports on an improved large-scale PAMAM dendrimer synthesis that is suitable to manufacture large amounts of highly pure and monodisperse dendrimers of generations G0–G5. Furthermore, an extended analytical guideline how to characterize PAMAM dendrimers with NMR, HPLC, SEC-MALS, ESI, MALDI, UV–vis, fluorescence, and IR spectroscopy is provided.

In vivo studies of nanostructure-based photosensitizers for photodynamic cancer therapy

Animal models, particularly rodents, are major translational models for evaluating novel anticancer therapeutics. In this review, different types of nanostructure-based photosensitizers that have advanced into the in vivo evaluation stage for the photodynamic therapy (PDT) of cancer are described. This article focuses on the in vivo efficacies of the nanostructures as delivery agents and as energy transducers for photosensitizers in animal models. These materials are useful in overcoming solubility issues, lack of tumor specificity, and access to tumors deep in healthy tissue. At the end of this article, the opportunities made possible by these multiplexed nanostructure-based systems are summarized, as well as the considerable challenges associated with obtaining regulatory approval for such materials. The following questions are also addressed: (1) Is there a pressing demand for more nanoparticle materials? (2) What is the prognosis for regulatory approval of nanoparticles to be used in the clinic?

Design of nanovectors for therapy and imaging of cardiovascular diseases

Cardiovascular diseases are widely prevalent in western societies, and their associated costs number in the billions of dollars and affect millions of patients each year. Nanovectors targeted to tissues involved in cardiovascular diseases offer great opportunities to improve cardiovascular treatment through their imaging and drug delivery capabilities. Vascular-targeted imaging particles may permit the early identification of atherosclerosis, discriminate between stable and vulnerable atherosclerotic plaques, or guide surgeons as they work on fragile vasculature. Tailored therapeutic nanoparticles may provide safer, more efficient and effective intervention through localization and release of encapsulated therapeutics. Nanovector design involves numerous considerations such as fabrication material, particle size, and surface-modification with ligands for targeting and increasing blood circulation times. Complex blood rheology may affect the efficiency with which dissimilarsized particles target ligand receptors associated with disease. Additionally, the intended use of a nanovector is a critical factor in its design as some materials with poor drug-loading qualities or release kinetics may be suitable for imaging purposes only. Overall, vectors targeted to the vasculature will need to be efficient in avoiding blood clearance, honing to the target location, and binding at the desired site.

Contrast-enhanced cardiac magnetic resonance imaging

Cardiac magnetic resonance (CMR) imaging has significantly evolved in the past decade and is well established in the evaluation of coronary artery disease (CAD). The evaluation of cardiac anatomy and contractility by high-resolution CMR can be improved by using intravenous administration of gadolinium-based contrast agents. Delayed enhancement CMR imaging has become the gold standard for quantification of myocardial viability in CAD. Contrast-enhanced CMR imaging may circumvent the need for endomyocardial biopsy or localize the involved regions, thereby improving the diagnostic yield of this invasive procedure. The application of contrast-enhanced CMR as an advanced imaging technique for ischemic and nonischemic diseases is reviewed.

Dendritic nanoparticles: the next generation of nanocarriers?

Dendritic polymers have attracted a great deal of scientific interest due to their well-defined unique structure and capability to be multifunctionalized. Here we present a comprehensive overview of various dendrimer-based nanomaterials that are currently being investigated for therapeutic delivery and diagnostic applications. Through a critical review of the old and new dendritic designs, we highlight the advantages and disadvantages of these systems and their structure-biological property relationships. This article also focuses on the major challenges facing the clinical translation of these nanomaterials and how these challenges are being (or should be) addressed, which will greatly benefit the overall progress of dendritic materials for theranostics.

The influence of PAMAM-OH dendrimers on the activity of human erythrocytes ATPases

Dendrimers are a relatively new and still not fully examined group of polybranched polymers. In this study polyamidoamine dendrimers with hydroxyl surface groups (PAMAM-OH) of third, fourth and fifth generation (G3, G4 and G5) were examined for their ability to influence the activity of human erythrocyte plasma membrane adenosinetriphosphatases (ATPases). Plasma membrane ATPases are a group of enzymes related, among others, to the maintenance of ionic balance inside the cell. An inhibition of their activity may result in a disturbance of cell functioning. Two of examined dendrimers (G4 and G5) were found to inhibit the activity of Na(+)/K(+) ATPase and Ca(2+) ATPase by 20-30%. The observed effect was diminished when higher concentrations of dendrimers were used. The experiment with the use of pyrene as fluorescent probe sensitive to the changes in microenvironment's polarity revealed that it was an effect of dendrimers' self-aggregation. Additional studies showed that PAMAM-OH dendrimers were able to decrease the fluidity of human erythrocytes plasma membrane. Obtained results suggest that change in plasma membrane fluidity was not caused by the dendrimer-lipid interaction, but dendrimer-protein interaction. Different pattern of influence of dendrimers on ATPases activity and erythrocyte membrane fluidity suggests that observed change in ATPases activity is not a result of dendrimer-lipid interaction, but may be related to direct interaction between dendrimers and ATPases.

Coronary MR angiography using citrate-coated very small superparamagnetic iron oxide particles as blood-pool contrast agent: initial experience in humans

PURPOSE

To evaluate very small superparamagnetic iron oxide particles (VSOP-C184) as blood-pool contrast agent for coronary MR angiography (CMRA) in humans.

MATERIALS AND METHODS

Six healthy volunteers and 14 patients with suspected coronary artery disease underwent CMRA after administration of VSOP-C184 at the following doses: 20 μmol Fe/kg (4 patients), 40 μmol Fe/kg (5 patients), 45 μmol Fe/kg (6 healthy volunteers), and 60 μmol Fe/kg (5 patients). In healthy volunteers, contrast-to-noise ratio (CNR), signal-to-noise ratio (SNR), and vessel edge definition (VED) of contrast-enhanced CMRA were compared with non-contrast-enhanced CMRA. In patients, a per-segment intention-to-diagnose evaluation of contrast-enhanced CMRA for detection of significant coronary stenosis (≥50%) was performed.

RESULTS

Three healthy volunteers (45 μmol Fe/kg VSOP-C184) and two patients (60 μmol Fe/kg VSOP-C184) had adverse events of mild or moderate intensity. VSOP-C184 significantly increased CNR (15.1 ± 4.6 versus 6.9 ± 1.9; P = 0.010), SNR (21.7 ± 5.3 versus 15.4 ± 1.6; P = 0.048), and VED (2.3 ± 0.6 versus 1.2 ± 0.2; P < 0.001) compared with non-contrast-enhanced CMRA. In patients, contrast-enhanced CMRA yielded sensitivity, specificity, and diagnostic accuracy for detection of significant coronary stenosis of 86.7%, 71.0%, 73.1%, respectively.

CONCLUSION

CMRA using VSOP-C184 was feasible and yielded moderate diagnostic accuracy for detection of significant coronary stenosis within this proof-of-concept setting.

Contrast-enhanced whole-heart coronary MRI with bolus infusion of gadobenate dimeglumine at 1.5 T

We sought to investigate the T(1) kinetics of blood and myocardium after three infusion schemes of gadobenate dimeglumine (Gd-BOPTA) and subsequently compared contrast-enhanced whole-heart coronary MRI after a bolus Gd-BOPTA infusion with nonenhanced coronary MRI at 1.5 T. Blood and myocardium T(1) was measured in seven healthy adults, after each underwent three Gd-BOPTA infusion schemes (bolus: 0.2 mmol/kg at 2 mL/sec, hybrid: 0.1 mmol/kg at 2 mL/sec followed by 0.1 mmol/kg at 0.1 mL/sec, and slow: 0.2 mmol/kg at 0.3 mL/sec). Fourteen additional subjects underwent contrast-enhanced coronary MRI with an inversion-recovery steady-state free precession sequence after bolus Gd-BOPTA infusion. Images were compared with nonenhanced T(2) -prepared steady-state free precision whole-heart coronary MRI in signal-to-noise ratio, contrast-to-noise ratio, depicted vessel length, vessel sharpness, and subjective image quality. Bolus and slow infusion schemes resulted in similar T(1) during coronary MRI, whereas the hybrid infusion method yielded higher T(1) values. A bolus infusion of Gd-BOPTA significantly improved signal-to-noise ratio, contrast-to-noise ratio, depicted coronary artery length, and subjective image quality, when all segments were collectively compared but not when compared segment by segment. In conclusion, whole-heart steady-state free precision coronary MRI at 1.5 T can benefit from a bolus infusion of 0.2 mmol/kg Gd-BOPTA.

Contrast-enhanced whole-heart coronary MRA using Gadofosveset 3.0 T versus 1.5 T

RATIONALE AND OBJECTIVES

To compare contrast-enhanced coronary magnetic resonance angiography (MRA) at 3.0 T with the same technique performed at 1.5 T using the contrast agent gadofosveset.

MATERIALS AND METHODS

In this prospective randomized study, 19 healthy male volunteers (mean age 28 years, mean weight 79.8 kg), after signing informed consents, underwent contrast-enhanced inversion recovery three-dimensional fast low angle shot (FLASH) MRA at 1.5 and at 3.0 T. Prospective electrocardiogram-triggering was combined with adaptive respiratory gating. For contrast-enhanced images, the intravascular contrast agent gadofosveset was used. Acquisition time, signal-to-noise ratio (SNR) of coronary blood, contrast-to-noise ratio (CNR) between coronaries and adjacent myocardium or epicardial fat and image quality were analyzed for statistical differences by using a two-tailed paired-sample t-test. The ratio calculations were based on measurements performed on the raw data and the image quality was blinded and independently evaluated by two experienced radiologists using a five-point scale.

RESULTS

The mean values for the acquisition time were 14.58 +/- 0.1 minutes at 1.5 T and 16.40 +/- 0.2 minutes at 3.0 T. Overall SNR of all evaluated coronary segments proved higher at 3.0 T compared to 1.5 T (74.0 +/- 42.1 at 3.0 T vs. 50.2 +/- 20.2 at 1.5 T, P = .04). Overall CNR between coronaries and myocardium was significantly increased at 3.0 T in comparison to 1.5 T (40.1 +/- 21.9 at 3.0 T vs. 24.4 +/- 17.2 at 1.5 T, P = .01). Between the two methods, no significant difference in overall CNR between coronaries and epicardial fat was observed (P = .08, NS). The 3.0 T MRA demonstrated superior overall image quality with respect to 1.5 T (2.28 +/- 0.71 at 3.0 T vs. 1.92 +/- 0.38 at 1.5T, P = .004).

CONCLUSION

The use of higher field strength, 3.0 T instead of 1.5 T, resulted in similar CNR between coronaries and epicardial fat, higher SNR values and CNR between blood and myocardium, as well as an improved overall image quality, when gadofosveset in combination with electrocardiogram and respiratory triggering for coronary MRA was used.

Contrast-enhanced whole-heart MR coronary angiography at 3.0 T using the intravascular contrast agent gadofosveset

OBJECTIVES

The purpose of this study was to compare contrast-enhanced (CE) whole-heart coronary magnetic resonance angiography (MRA) at 3.0 T using gadofosveset to noncontrast-enhanced steady-state free precession (SSFP) coronary MRA at 1.5 T.

MATERIALS AND METHODS

A prospective randomized study was conducted among 20 healthy male volunteers. The same group of subjects underwent CE whole heart MRA at 3.0 T employing a 3D FLASH sequence with IR prepulse after gadofosveset injection as well as noncontrast-enhanced coronary MRA at 1.5 T using a 3D SSFP sequence with T2-preparation. Both techniques were performed using prospective ECG-triggering and adaptive respiratory gating. Acquisition time, signal-to-noise ratio of coronary blood, contrast-to-noise ratio (CNR) between coronaries and adjacent myocardium or epicardial fat, and image quality were evaluated in each case.

RESULTS

A significant increase of the overall CNR between coronary blood and adjacent myocardium was measured on images acquired at 3 T in comparison to 1.5 T. The mean values were 38.9 +/- 19.6 and 26.3 +/- 15.4, respectively (P[r] < 0.005). There was no significant difference in CNR between coronary blood and epicardial fat. The mean image quality for the proximal and mid coronary segments was not statistically different between 1.5 T and 3.0 T (P > 0.05), however, the distal coronary segments were rated significantly higher for the CE MRA at 3.0 T (P = 0.02). The average acquisition time (15.29 +/- 5.73 minutes at 1.5 T vs. 17.29 +/- 5.18 minutes at 3 T) and overall image quality (2.15 +/- 0.49 at 1.5 T vs. 2.35 +/- 0.39 at 3 T) were similar for both methods.

CONCLUSIONS

CE whole-heart coronary MRA at 3.0 T demonstrated higher overall CNR between coronary blood and myocardium and an improved image quality of the distal coronary segments compared with noncontrast-enhanced SSFP coronary MRA at 1.5 T.

Coronary computed tomography and magnetic resonance imaging

Cardiac computed tomography and magnetic resonance are relatively new imaging modalities that can exceed the ability of established imaging modalities to detect present pathology or predict patient outcomes. Coronary calcium scoring may be useful in asymptomatic patients at intermediate risk. Computed tomographic coronary angiography is a first-line indication to evaluate congenitally abnormal coronary arteries and, along with stress magnetic resonance myocardial perfusion imaging, is useful in symptomatic patients with nondiagnostic conventional stress tests. Cardiac magnetic resonance is indicated for visualizing cardiac structure and function, and delayed enhancement magnetic resonance is a first-line indication for assessing myocardial viability. Imaging plaque and molecular mechanisms related to plaque rupture holds great promise for the presymptomatic detection of patients at risk for coronary events but is not yet suitable for routine clinical use.

Magnetic resonance cardiac vein imaging: relation to mitral valve annulus and left circumflex coronary artery

OBJECTIVES

To evaluate in vivo anatomical relationships between the coronary sinus-great cardiac vein (CS-GCV), the mitral valve annulus (MVA), and left circumflex coronary artery (LCX) with cardiovascular magnetic resonance.

BACKGROUND

The CS-GCV has become an anatomical structure of interest because it provides a way of access to the heart for a number of interventional procedures. Previous reports demonstrate that the postulated close anatomical proximity of the CS-GCV to the MVA does not always hold true in patients, both in autopsy specimens and in vivo by computed tomography.

METHODS

In 31 participants (24 volunteers and 7 patients; 15 men; 42 +/- 19 years), cardiovascular magnetic resonance was performed for noninvasive evaluation of the coronary sinus and of the coronary arteries using whole-heart imaging and intravascular contrast agents. Three-dimensional reconstructions, standard orthogonal planes, and unprocessed raw data were used to assess CS-GCV anatomy and its relation to the MVA and the LCX along their entire course.

RESULTS

The CS-GCV was located behind the left atrium in all examined participants, at a minimum distance of 8.6 +/- 3.9 mm from the MVA. In 80% of the participants, the LCX crossed the CS-GCV inferiorly, between the CS-GCV and the MVA. The CS-GCV and the LCX had a parallel course for 26.2 +/- 23.0 mm, with great variability of location and length. In several participants, the CS-GCV had a long parallel course, but in other participants, the LCX crossed below the CS-GCV at a discrete point.

CONCLUSIONS

In all participants, the CS-GCV coursed behind the left atrium rather than behind the MVA. In the majority of the participants, the LCX coursed between the CS-GCV and the MVA. These anatomical relationships should be kept in mind when referring a patient for interventional procedures requiring the access to the CS-GCV, and cardiovascular magnetic resonance might provide important information for the selection of candidates for these procedures.

Visualization of the cardiac venous system using cardiac magnetic resonance

We sought to investigate the value of cardiac magnetic resonance to depict cardiac venous anatomy. For cardiac resynchronization therapy the lead for the left ventricle is usually placed by transvenous approach into a tributary of the coronary sinus (CS). Knowledge of the anatomy and variations of the cardiac venous system may facilitate the positioning of the left ventricle lead. The cardiac magnetic resonance examinations of 23 subjects (16 volunteers and 7 patients) were retrospectively analyzed. All examinations were performed using navigator-gated whole-heart steady-state free precession coronary artery imaging after administration of intravascular contrast agents (gadofosveset in volunteers; Gadomer-17 in patients). The cardiac venous system was visualized in all subjects. The most frequent anatomical variant observed (in 12 subjects [52%]) was a connection of the small cardiac vein to the CS at the crux cordis. In 10 subjects (44%) the small veins entered the right atrium independently from the CS, and the posterior interventricular vein was connected to the CS at the crux cordis. Only one subject had a disconnection between the CS and posterior interventricular vein, which entered into the right atrium independently. The mean distance of the posterior vein of the left ventricle and the left marginal vein to the ostium of the CS was 15.2+/-4.7 mm and 49.7+/-14.1 mm, respectively. In conclusion, the anatomy of the cardiac venous system and its anatomical variability can be described using cardiac magnetic resonance. Its preimplantation visualization may help to facilitate the implant procedure and to reduce fluoroscopy time.

Magnetic resonance coronary angiography with Vasovist: in-vivo T1 estimation to improve image quality of navigator and breath-hold techniques

The purpose of the study was to estimate T1 values of blood and myocardium after a single injection of Vasovist and to assess Vasovist for magnetic resonance coronary angiography (MRCA). For all exams 0.05 mmol/kg of Vasovist was injected. T1 values of blood and myocardium were estimated over 30 min after injection. Twelve volunteers were examined on a 1.5-T Siemens system using a SSFP sequence with incrementally increasing inversion times for T1-estimation and a breath-hold 3D IR-FLASH sequence for MRCA. Eleven examinations were performed on 1.5-T Philips system using the Look-Locker approach for T1 estimation and a whole-heart inversion-prepared, 3D SSFP sequence for MRCA. SNR, CNR and image quality were assessed. T1 values of blood (5 min: 230 ms vs. 30 min: 275 ms) and myocardium (5 min: 99 ms vs. 30 min: 130 ms) increased over time. Whereas the blood SNR (1 min: 23.6 vs. 30 min: 21.2) showed no significant differences, the blood-to-myocardium CNR (1 min: 18.1 vs. 30 min: 13.8) and the image quality (1 min: 2.9 vs. 30 min: 3.8) degraded over time. Due to long plasma half-time the T1-shortening effect of Vasovist remains effective over 30 min, which allows for multiple breath-hold or high-resolution MRCA.

MR angiography with blood pool contrast agents

Contrast-enhanced magnetic resonance angiography (CE-MRA) with standard extracellular contrast material is well established for vascular imaging. Recently, the first blood pool contrast agent (BPA) has become clinically available. This paper reviews characteristics and classification of BPA as well as first clinical experience in various vascular territories. BPAs comprise gadolinium-based compounds, synthetic compounds, and ultrasmall superparamagnetic iron-oxide (USPIO) particles. Such BPAs are retained in blood with a prolonged time-window of enhancement as compared to extracellular gadolinium chelates. Promising results from USPIO at first-pass and steady-state angiography have been published, but no USPIO is approved yet. Gadofosveset is the first clinically approved BPA. After bolus injection, gadofosveset binds noncovalently to serum-albumine, thus enhancing relaxivity. First published results from carotid, coronary, renal, and peripheral angiography are encouraging; particularly helpful is prolonged enhancement during steady state. More BPAs have been clinically evaluated, but no approval has been granted. Bolus-injectable BPAs allow for first-pass CE-MRA similar to standard extracellular contrast media, but with higher relaxivity, allowing lower doses and reduced injection rates. An additional feature of BPA is the steady-state phase with a broad time window enabling high-resolution angiography or double-gated angiography of coronary arteries to compensate for the complex motion pattern.

Patient acceptance of noninvasive and invasive coronary angiography

BACKGROUND

Noninvasive angiography using multislice computed tomography (MSCT) is superior to magnetic resonance imaging (MRI) for detection of coronary stenoses. We compared patient acceptance of these two noninvasive diagnostic tests and invasive conventional coronary angiography (Angio).

METHODS AND FINDINGS

A total of 111 consecutive patients with suspected coronary artery disease underwent MSCT, MRI, and Angio. Subsequently, patient acceptance of the three tests was evaluated with questionnaires in all patients. The main acceptance variables were preparation and information prior to the test, degree of concern, comfort, degree of helplessness, pain (on visual analog scales), willingness to undergo the test again, and overall satisfaction. Preparation for each test was not rated significantly differently, whereas patients were significantly more concerned about Angio than the two noninvasive tests (p<0.001). No pain during MSCT, MRI, and Angio as assessed on visual analog scales (0 to 100) was reported by 99, 93, and 31 patients, respectively. Among the 82 patients who felt pain during at least one procedure, both CT (0.9+/-4.5) and MRI (5.2+/-16.6) were significantly less painful than Angio (24.6+/-23.4, both p<0.001). MSCT was considered significantly more comfortable (1.49+/-0.64) than MRI (1.75+/-0.81, p<0.001). In both the no-revascularization (55 patients) and the revascularization group (56 patients), the majority of the patients (73 and 71%) would prefer MSCT to MRI and Angio for future imaging of the coronary arteries. None of the patients indicated to be unwilling to undergo MSCT again. The major advantages patients attributed to MSCT were its fast, uncomplicated, noninvasive, and painless nature.

CONCLUSIONS

Noninvasive coronary angiography with MSCT is considered more comfortable than MRI and both MSCT and MRI are less painful than Angio. Patient preference for MSCT might tip the scales in favor of this test provided that the diagnostic accuracy of MSCT can be shown to be high enough for clinical application.

Coronary Magnetic Resonance Imaging

This article highlights the technical challenges and general imaging strategies for coronary MRI. This is followed by a review of the clinical results for the assessment of anomalous CAD, coronary artery aneurysms, native vessel integrity, and coronary artery bypass graft disease using the more commonly applied MRI methods. It concludes with a brief discussion of the advantages/disadvantages and clinical results comparing coronary MRI with multidetector CT (MDCT) coronary angiography.

Comparison of the endocytic properties of linear and branched PEIs, and cationic PAMAM dendrimers in B16f10 melanoma cells

Many different polymers and architectures are now being developed as polymer therapeutics and non-viral vectors for cytosolic delivery, and cationic dendrimers, and linear and branched poly(ethylenimine)s (PEIs) have been widely used. For rational design and safe transfer into the clinic, it is important to better understand the cellular pharmacokinetics of the carrier, even if this will likely change when it is conjugated to, or complexed with, a targeting residue or therapeutic payload. The aim of these studies was to compare binding, endocytic capture and intracellular trafficking of linear and branched PEIs (Mw 25,000 g/mol) and cationic PAMAM dendrimers (generations (gen) 2- 4) using B16F10 murine melanoma cells. FITC-dextran was used as a control for comparison. All polymers were first conjugated to Oregon Green (OG) and carefully characterised in respect of pH- and concentration-dependence of fluorescence. Throughout, non-toxic concentrations of polymer were used. Flow cytometry showed that all the cationic polymers were internalised by "adsorptive" endocytosis, with maximum uptake seen for PAMAM gen 4>>branched PEI>linear PEI>PAMAM gen 3>PAMAM gen 2. The PAMAM gen 4 uptake rate was 130 fold greater than seen for FITC-dextran. Branched PEI had the highest extracellular binding (accounting for >50% of total cell-associated fluorescence) whereas for the linear PEI, binding was only 13% of the cell-associated fluorescence. Unlike FITC-dextran, all cationic polymers lacked significant exocytosis over the time period studied. Whereas PAMAM gen 4 and the branched PEI were predominately internalised by cholesterol-dependent pathways, internalisation of linear PEI appeared to be independent of clathrin and cholesterol. A perception of the rate and mechanisms of cellular uptake of these vectors will be important in the context of their proposed use as drug delivery systems.

Capillary electrophoresis for the characterization of the complex dendrimeric contrast agent Gadomer

A CE method for the characterization of the complex dendrimeric contrast agent Gadomer has been developed and validated. The method was capable of separating the target substance Gadomer 24 from related dendrimers containing amino or carboxyl functions and from impurities of lower molecular weight. The compounds were separated in a fused-silica capillary. The optimized BGE consisted of 15 mM sodium phosphate, pH 6.3, containing 0.5 mM hexadecyltrimethylammonium bromide. The assay was validated with regard to linearity, specificity, accuracy, LOD and LOQ as well as robustness according to the guidelines of the International Conference on Harmonization. The method allows the determination of the purity and stability of the drug substance Gadomer as well as its injectable formulation. On the basis of the present study, a strategy for the quality assurance and quality control of the complex dendrimeric drug candidate Gadomer may be devised. The method may therefore serve as a key component in a set of analytical methodologies designed to assure and control the reproducible quality and safety of this innovative product. To the best of our knowledge, this is the first work reporting a validated method for the characterization, impurity profiling, and stability testing of a dendrimeric agent designed for clinical use.

MR contrast agents in lymph node imaging

The detection of tumor metastases in lymph nodes is clinically important for tumor staging and therapy planning in cancer patients. However, differentiating between malignant and benign lymph nodes is still a problem because current imaging modalities rely only on the size and shape of the lymph nodes. Thus, small metastases in normal-sized lymph nodes can be missed, and it is difficult to differentiate enlarged nodes (benign hyperplasia versus malignant disease). Therefore, a specific lymphotropic contrast agent is needed to obtain a high contrast between functional and metastatic tissue. Contrast-enhanced MR lymphography is a noninvasive method for the analysis of the lymphatic system after interstitial (intracutaneous or subcutaneous) or intravenous application of contrast media. Interstitial MR lymphography using extracellular, liposomal, polymeric, lipophilic or particulate contrast agents results in high accumulation in regional lymph nodes. The systemic administration of a lymphotropic contrast medium is needed to address each individual lymph node. Ultrasmall superparamagnetic iron oxide particles are in late-stage clinical development for this indication, but they take 24h to show sufficient contrast. Recently, a gadolinium-type contrast agent (Gadofluorine M) was described that detected lymph node metastases within 60 min of intravenous injection.

Breath-hold 3D steady-state free precession coronary MRA compared with conventional X-ray coronary angiography

PURPOSE

To evaluate the use of breath-hold three-dimensional (3D) steady-state free precession (SSFP) coronary magnetic resonance angiography (MRA) in patients with coronary artery disease (CAD) in comparison with conventional coronary x-ray angiography (XRA).

MATERIALS AND METHODS

Twenty-eight patients with suspected CAD were examined with the use of a breath-hold 3D-SSFP-MRA sequence and conventional XRA. To assess the accuracy of MRA, two clinicians who were blinded to patient information independently reviewed the MRA and XRA data, which were presented in a randomized order. To identify discrepancies between MRA and XRA, and assess features of coronary lesions on MRA, two additional clinicians examined MRA and XRA data that were presented side by side, divided into proximal, mid, and distal segments, and compared them segment by segment.

RESULTS

The sensitivity and specificity for diagnosing significant coronary stenoses (> 50% diameter narrowing) were 64% and 94%, respectively. At sites of coronary lesions identified on XRA, bright signals and enlarged vessel profiles, in addition to the characteristic narrow lumen, were frequently observed on MRA.

CONCLUSION

Breath-hold SSFP coronary MRA has good specificity but inconclusive sensitivity in diagnosing significant coronary stenoses, and provides important image features for depicting coronary lesions.

Single-session magnetic resonance coronary angiography and myocardial perfusion imaging using the new blood pool compound B-22956 (gadocoletic acid): initial experience in a porcine model of coronary artery disease

OBJECTIVE

The objective of this study was to evaluate a new blood pool contrast agent, B-22956, for detecting myocardial perfusion abnormality and coronary artery stenosis by magnetic resonance imaging (MRI) in 1 setting.

MATERIALS AND METHODS

Coronary artery atherosclerotic stenoses were created in 6 miniswine. Myocardial first-pass perfusion imaging was performed with a bolus injection of 0.015 mmol/kg B-22956 during pharmacologic stress followed by postcontrast coronary artery imaging after another injection of B-22956/1. The total doses for the 6 pigs were 0.1 mmol/kg (n=3) and 0.15 mmol/kg (n=3). Perfusion upslope maps were analyzed and MR coronary artery images were reviewed by 2 readers.

RESULTS

For all 6 pigs, the normalized upslopes of the perfusion curves were 0.83+/-0.12, 0.74+/-0.15, and 0.52+/-0.05 (P<0.01 vs. normal) with normal or mild (<50% area stenosis), moderate (<50% and <75%), and severe stenosis (>75%), respectively. Mean signal-to-noise ratio (SNR) and contrast-to-noise ratio (CNR) in right coronary artery images improved 90% and 200%, respectively, with a total dose of 0.1 mmol/kg of B-22956. Excellent agreements (kappa=0.82) were achieved for evaluating the grade of stenosis between MR postcontrast coronary artery images and histopathology by 2 reviewers.

CONCLUSION

The MR blood pool contrast agent B-22956 demonstrated the ability for detecting myocardial perfusion abnormalities and coronary artery stenosis in 1 setting.

Myocardial infarct: depiction with contrast-enhanced MR imaging--comparison of gadopentetate and gadobenate

Institutional review board approval and patient written informed consent were obtained. On two separate occasions, 24 hours apart, contrast-enhanced cardiac magnetic resonance (MR) imaging was performed prospectively at 1, 3, 5, 10, and 20 minutes after injection of gadopentetate dimeglumine and gadobenate dimeglumine in 15 patients (11 men, four women) with history of myocardial infarction. Both agents allowed detection of infarcted myocardium. T1 values at all times were significantly (P < .05) lower for gadobenate, compared with values for gadopentetate, in both infarcted and noninfarcted myocardium. At 1 minute after administration of both agents, T1 values in left ventricular cavity (LVC) were not different; at 3-20 minutes after injection, values were significantly (P < .05) lower for gadobenate. Differences between contrast-to-noise ratio (CNR) values of infarcted and noninfarcted myocardium were significantly higher on gadobenate-enhanced images (P < .05). CNR values between infarcted myocardium and LVC were significantly higher on gadopentetate-enhanced images (P < .05). Gadopentetate might permit better delineation of infarcts, especially subendocardial infarcts.

Comparison of synchrotron radiation angiography with conventional angiography for the diagnosis of in-stent restenosis after percutaneous transluminal coronary angioplasty

AIMS

Synchrotron radiation angiography (SRA) is a novel tool for minimally invasive coronary artery imaging. The method uses subtraction of two images produced at energies bracketing the iodine K-edge after intravenous infusion of iodinated contrast agent. We investigated the accuracy of SRA for detecting in-stent restenosis (ISR).

METHODS AND RESULTS

We recruited 57 men, 4-6 months after successful PTCA. We visualized the right coronary artery (RCA) in 27 patients with 36 stented segments [12 segments with ISR>50% by quantitative coronary angiography (QCA)], and the left anterior descending artery (LAD) in 30 patients with 37 stented segments (10 ISR). SRA and QCA were performed within 2 days of each other. Two experienced observers unaware of QCA data evaluated the SRA results. Image quality was good or excellent in most patients. Global sensitivity was 64%, specificity was 95%, and positive and negative predictive values were approximately 85%. Inter-observer kappa concordance coefficient was 0.86. False negatives involved short eccentric lesions and superimposed segments, most frequently of the LAD. False positives occurred in intermediate stenoses slightly overestimated by SRA.

CONCLUSION

In men, this minimally invasive approach, using small radiation doses, detects significant ISR in the RCA, but the LAD poses difficulties because of superimposition with others structures.

MR Coronary Angiography with SH L 643 A: Initial Experience in Patients with Coronary Artery Disease

PURPOSE

To prospectively assess the accuracy of breath-hold three-dimensional magnetic resonance (MR) coronary angiography with the gadolinium-based intravascular contrast agent SH L 643 A in patients with coronary artery disease.

MATERIALS AND METHODS

Twelve patients (seven men, five women; age range, 46-78 years; mean age, 61.3 years) with angiographically proved coronary artery disease (luminal narrowing >50%) underwent breath-hold three-dimensional MR coronary angiography before and after injection of SH L 643 A (0.1 mmol gadolinium per kilogram body weight). For all MR examinations, signal-to-noise ratio and contrast-to-noise ratio were measured. Image quality was assessed with a four-point scale. Conventional angiograms and MR angiograms were evaluated for depiction of the left main, proximal and middle left anterior descending, proximal left circumflex, and proximal and middle right coronary artery segments in a blinded fashion by two experienced readers in consensus. Results of this evaluation were compared by using a paired Student t test. P < .05 was considered to indicate a statistically significant difference.

RESULTS

For the 72 coronary artery segments, the contrast-to-noise ratio significantly improved after administration of SH L 643 A, compared with the prior ratio (9.8 +/- 5.1 [standard deviation] vs 23.0 +/- 8.7; P < .01), whereas the difference in signal-to-noise ratio did not reach statistical significance (25.2 +/- 11.4 vs 29.5 +/- 9.8; P > .3). Image quality significantly improved from a mean of 2.0 +/- 0.9 for nonenhanced images to 2.9 +/- 0.9 (P < .03) for contrast material-enhanced images. The proportion of segments for which images were nondiagnostic decreased from 38% to 10% with application of SH L 643 A. Overall sensitivity and specificity of contrast-enhanced MR coronary angiography for detection of coronary artery disease were 80% and 93%, respectively, and accuracy was 87%.

CONCLUSION

Use of SH L 643 A improves detection of coronary artery disease at three-dimensional MR coronary angiography.

MRI in coronary artery disease

Diagnosis of coronary artery disease (CAD) is a major challenge for medical imaging, because CAD is the leading cause of death in developed nations. Several non-invasive tests are used in clinical routine for the detection of CAD. However, due to limited sensitivity and specificity, the reliable diagnosis as well as the exclusion of CAD can only be established by catheter angiography. In patients with known CAD, therapeutic decisions require accurate information on myocardial function, ischemia and viability. Recently, magnetic resonance (MR) imaging has emerged as a non-invasive cardiac imaging technique that provides information on cardiac morphology, cardiac function, myocardial viability, and coronary morphology. This review discusses technical aspects and the clinical impact of different MR techniques.

Magnetic Resonance Imaging of Myocardial Perfusion and Viability Using a Blood Pool Contrast Agent

RATIONALE AND OBJECTIVES

A comprehensive cardiac magnetic resonance (MR) examination should comprise imaging of myocardial perfusion, viability, and the coronary arteries. Blood pool contrast agents (BPCAs) improve coronary MR angiography, whereas their potential for imaging of perfusion and viability is unknown. The abilities to noninvasively image myocardial perfusion and viability using the BPCA P792 (Guerbet, France) were tested in a closed-chest model of nonreperfused myocardial infarction in 5 pigs.

MATERIALS AND METHODS

Two to 3 days after instrumentation, myocardial perfusion imaging with a saturation-recovery steady-state free precession technique and viability imaging with an inversion-recovery fast low-angle shot sequence were conducted on a 1.5-T MR scanner using the extracellular contrast agents (ECCA) Gd-DOTA (0.1 mmol Gd/kg) and blood pool contrast agent (BPCA) P792 (0.013 mmol Gd/kg).

RESULTS

Perfusion defects were visualized in all pigs with good correlation between the ECCA and the BPCA (1.77 +/- 1.16 cm2 vs. 1.80 +/- 1.19 cm2, r = 0.959, P < 0.01). Reduced myocardial perfusion was detected using the ECCA up to 80 seconds after injection. In contrast, BPCA administration enabled visualization of perfusion defects on equilibrium perfusion imaging in all cases for 10 minutes. The size of myocardial infarction detected with viability MR imaging correlated well between the standard method (ECCA) and delayed-enhancement imaging with the BPCA (5.40 +/- 3.16 versus 5.52 +/- 3.13 cm3, r = 0.994, P < 0.002).

CONCLUSIONS

The BPCA investigated in this study allows both reliable detection of perfusion defects on first pass and equilibrium perfusion imaging and characterization of viability after myocardial infarction. Thus, this contrast agent is suitable for a comprehensive cardiac MR examination.

Contrast-enhanced MR imaging of the heart: overview of the literature

The use of magnetic resonance (MR) imaging for cardiac diagnosis is expanding, aided by the administration of paramagnetic contrast agents for a growing number of clinical applications. This overview of the literature considers the principles and applications of cardiac MR imaging with an emphasis on the use of contrast media. Clinical applications of contrast material-enhanced MR imaging include the detection and characterization of intracardiac masses, thrombi, myocarditis, and sarcoidosis. Suspected myocardial ischemia and infarction, respectively, are diagnosed by using dynamic first-pass and delayed contrast enhancement. Promising new developments include blood pool contrast media, labeling of myocardial precursor cells, and contrast-enhanced imaging at very high fields.

Phase I Clinical Evaluation of Citrate-coated Monocrystalline Very Small Superparamagnetic Iron Oxide Particles as a New Contrast Medium for Magnetic Resonance Imaging

RATIONALE AND OBJECTIVES

To evaluate the safety and pharmacokinetics of a newly developed MR contrast medium consisting of very small superparamagnetic iron oxide particles (VSOP) coated with citrate (VSOP-C184) in a clinical phase I trial.

METHODS

A total of 18 healthy subjects received either VSOP-C184 (core diameter: 4 nm; total diameter: 7 +/- 0.15 nm; relaxivities in water at 0.47 T (T1) 18.7 and (T2) 30 L/(mmol*seconds)) at doses of 0.015, 0.045, or 0.075 mmol Fe/kg (n = 5 per dose) or placebo (n = 1 per dose) as intravenous injections. Physical status and vital parameters were recorded, blood samples were collected for clinical chemistry and relaxometry (0.94 T), and urinalyses were performed before and for up to 2 weeks after administration.

RESULTS

No serious adverse events occurred. The most pronounced adverse events occurred in 2 subjects of the highest dose group 45-50 minutes after injection. These were a drop in blood pressure and a drop in oxygen saturation, which were considered to be possibly drug-related and rapidly resolved without medication. Otherwise, no relevant changes in vital and laboratory parameters were observed. The parameters of iron metabolism exhibited short-term, dose-related changes. The injection of VSOP-C184 decreased T1 relaxation time of blood below 100 milliseconds for 18 minutes after a dose of 0.045 mmol [corrected] Fe/kg and for 60 minutes after 0.075 mmol [corrected] Fe/kg.

CONCLUSIONS

The favorable data on the safety, tolerability, and efficacy of VSOP-C184 justify further clinical phase II and III trials as a contrast medium for MRI.