Vasovist-enhanced MR angiography

Long-term safety of Gadofosveset in clinical practice

PURPOSE

The purpose of this study was to systematically search for long-term complications, including Nephrogenic Systemic Fibrosis (NSF), in patients who were previously administered the gadolinium-based contrast agent Gadofosveset at our institute.

MATERIALS AND METHODS

All patients who were administered Gadofosveset at our institute between 2006 and 2009 were identified in our Radiological Information System (RIS). Clinical data such as cause of death during follow-up, and dermatological or nephrological diseases were systematically searched for in electronic patient records (EPR).

RESULTS

During 2006-2009, Gadofosveset was administered a total of 67 times to 62 patients. One patient was unavailable for follow-up. The remaining 61 patients were followed up for up to 14 (median 12) years based on RIS and EPR data. There were 13 deaths among the 61 patients, all assessed as unrelated to Gadofosveset administration. No dermatological or renal disease suggestive of NSF, or potentially related to Gadofosveset administration, was found. At the time of examination, six patients were diagnosed with various stages of renal insufficiency, three of whom were on hemodialysis. Another three patients were diagnosed with renal insufficiency during the follow-up period, but none of these diagnoses were suspected to be related to the administration of Gadofosveset.

CONCLUSIONS

Based on the results of this retrospective safety analysis of up to 14 years following 1-2 exposures, we conclude that Gadofosveset in clinical practice is safe in the long-term.

The CAM cancer xenograft as a model for initial evaluation of MR labelled compounds

Non-invasive assessment of the biodistribution is of great importance during the development of new pharmaceutical compounds. In this contribution, the applicability of in ovo MRI for monitoring the biodistribution of MR contrast agent-labelled compounds was investigated in mamaria carcinomas xentotransplanted on the chorioallantoic membrane (CAM) exemplarily for Gd-DOTA and cHSA-PEO (2000)16-Gd after systemic injection of the compounds into a chorioallantoic capillary vein. MRI was performed directly prior and 30 min, 3 h, 5 h, 20 h, and 40 h after injection of the compound. The biodistribution of injected compounds could be assessed by MRI in different organs of the chicken embryo as well as in xenotransplanted tumors at all time points. A clearly prolonged enhancement of the tumor substrate could be shown for cHSA-PEO (2000)₁₆-Gd. In conclusion, high-resolution in ovo MR imaging can be used for assessment of the in vivo biodistribution of labelled compounds, thus enabling efficient non-invasive initial testing.

Incidence and Risk Factors for Gadolinium-Based Contrast Agent Immediate Reactions

Since their clinical introduction in 1988, gadolinium-based contrast agents (GBCAs) have demonstrated an excellent safety profile with a reported acute adverse reaction rate ranging from 0.01% to 2%. By comparison, the acute adverse reaction rate of low osmolar nonionic computed tomography contrast agents (CTCs) ranges from 0.7% to 3.1%. Many of the risk factors associated with CTC reactions (drug allergies, asthma, atopy, prior contrast reaction) also point toward an increased incidence of acute adverse events to GBCAs. With CTCs, an increased adverse event rate was associated with ionic preparations and high osmolality. In response to concerns for nephrogenic systemic fibrosis, GBCAs are now selected for their augmented chemical stability. These agents possess some combination of macrocyclic chelates or ionic preparations. With their improved chemical stability, these agents also possess higher osmolality and the increased potential to elicit an acute adverse reaction. In light of these concerns, researchers are now focusing greater efforts on reexamining acute adverse reactions to GBCAs and whether there is an increased association with certain agents. In addition to hypersensitivity reactions, this article will also discuss contrast extravasations, safety of GBCAs for pregnant and nursing patients, and the potential nephrotoxic effects of GBCAs.

Magnetic Resonance-Guided Passive Catheter Tracking for Endovascular Therapy

The use of MR guidance for endovascular intervention is appealing because of its lack of ionizing radiation, high-contrast visualization of vessel walls and adjacent soft tissues, multiplanar capabilities, and potential to incorporate functional information such as flow, fluid dynamics, perfusion, and cardiac motion. This review highlights state-of-the-art imaging techniques and hardware used for passive tracking of endovascular devices in interventional MR imaging, including negative contrast, passive contrast, nonproton multispectral, and direct current techniques. The advantages and disadvantages of passive tracking relative to active tracking are also summarized.

Mapping of autogenous saphenous veins as an imaging adjunct to peripheral MR angiography in patients with peripheral arterial occlusive disease and peripheral bypass grafting: prospective comparison with ultrasound and intraoperative findings

BACKGROUND

Mapping of the great saphenous vein is very important for planning of peripheral and coronary bypass surgery. This study investigated mapping of the great saphenous vein as an adjunct to peripheral MR angiography using a blood pool contrast agent in patients who were referred for evaluation of peripheral arterial occlusive disease and bypass surgery.

METHODS

38 patients with peripheral arterial occlusive disease (21 men; mean age: 71 years, range, 44-88 years) underwent peripheral MR angiography using the blood pool contrast agent Gadofosveset trisodium. Apart from primary arterial assessment images were evaluated in order to determine great saphenous vein diameters at three levels: below the saphenofemoral junction, mid thigh and 10 cm above the knee joint (usability: diameter range: >3 and <10 mm at one level and >3.5 and <10 mm at a neighboring level). Duplex ultrasound was performed by an independent examiner providing diameter measurements at the same levels. Additionally, vessel usability was determined intraoperatively by the vascular surgeon during subsequent bypass surgery.

RESULTS

Mean venous diameters for MR angiography/duplex ultrasound were 5.4±2.6/5.5±2.8 mm (level 1), 4.7±2.7/4.6±2.9 mm (level 2) and 4.4±2.2/4.5±2.3 mm (level 3), respectively, without significant differences between the modalities (P = 0.207/0.806/0.518). Subsequent surgery was performed in 27/38 patients. A suitable saphenous vein was diagnosed in 25 and non-usability was diagnosed in 2 of the 27 patients based on MR angiography/duplex ultrasound, respectively. Usability was confirmed by intraoperative assessment in all of the 24 patients that received a venous bypass graft in subsequent bypass surgery. In 1 case, in which the great saphenous vein was assessed as useable by both MR angiography and duplex ultrasound, it was not used during subsequent bypass surgery due to the patients clinical condition and comorbidities.

CONCLUSION

Simultaneous mapping of the great saphenous vein as an imaging adjunct to peripheral MR angiography with a blood pool contrast agent is an alternative to additive duplex ultrasound in patients undergoing subsequent peripheral bypass grafting.

The importance of the costoclavicular space in upper limb primary deep vein thrombosis, a study with magnetic resonance imaging (MRI) technique enhanced by a blood pool agent

BACKGROUND

Primary upper extremity deep vein thrombosis (UEDVT) can be divided into idiopathic and effort thrombosis. Anatomical factors probably play an important role in effort thrombosis, whereas the cause remains mostly unknown in idiopathic thrombosis.

OBJECTIVES

The primary objective of this study was to examine the anatomy of the subclavian region and evaluate how these factors contribute to primary UEDVT. The secondary objective was to investigate if venous compression correlates with post thrombotic syndrome (PTS).

PATIENTS AND METHODS

Fifteen patients and 15 controls were enrolled in the study. The subclavian region (the costoclavicular distance and vessel area) was examined by MRI enhanced by a blood-pool contrast agent (Vasovist). The MRI was performed in two arm positions: alongside and elevated. PTS and disability were quantified with the modified Villalta score and the Disability of the Arm, Shoulder and Hand (DASH) test.

RESULTS

The costoclavicular distance was significantly narrower in the UEDVT patients with the arms alongside the body but there was a significant difference only in the left arm with the arms elevated. Area of the subclavian vein: When comparing the patients non-thrombotic arm with the controls, there was a significant difference only when the arms in the supine position. Disability: There was a high correlation between DASH, Villalta and VAS but no correlation between the MRI measurement and patient's symptoms or the Villalta Score.

CONCLUSION

Our results suggest that primary UEDVT is dependent on the subclavian anatomy and area of vena subclavia.

0.125 mm(3) spatial resolution steady-state MR angiography of the thighs with a blood pool contrast agent using the quadrature body coil only at 1.5 Tesla

PURPOSE

To implement and evaluate high spatial resolution three-dimensional MR contrast-enhanced angiography (3D-CEMRA) of the thighs using a blood pool contrast agent (BPCA) using the quadrature body coil only in patients with peripheral arterial occlusive disease (PAOD) in cases receiver coils cannot be used at 1.5 Tesla (T).

MATERIALS AND METHODS

Nineteen patients (mean age: 68.7 ± 11.2 years; range, 38-83 years) with known PAOD (Fontaine stages; III: 16, IV: 3) prospectively underwent 3D-CEMRA at 1.5T with a noninterpolated voxel size of 0.49 × 0.49 × 0.48 mm(3) . Digital subtraction angiography (DSA) was available for comparison in all patients. Two readers independently evaluated movement artifacts, overall image quality of 3D-CEMRA, and grade of stenosis as compared to DSA. SNR and CNR levels were quantified.

RESULTS

The 3D-CEMRA was successfully completed in all patients. Patient movement artifacts that affected stenosis grading occurred in 3/38 thighs. Overall image quality was rated excellent in 15/38, good in 12/38, and diagnostic in 8/38 thighs. Stenosis grading matched with that in DSA in 35/38 thighs. High SNR and CNR were measured in all vessels.

CONCLUSION

The 0.125 mm(3) spatial resolution 3D-CEMRA of the thighs with a BPCA is feasible using a quadrature body coil exclusively with excellent image quality despite long acquisition times. J. Magn. Reson. Imaging 2014;40:996-1001. © 2014 Wiley Periodicals, Inc.

Thoracic magnetic resonance imaging: pulmonary thromboembolism

Ongoing technical developments have substantially improved the potential of magnetic resonance imaging (MRI) in the assessment of the pulmonary circulation. These developments includes improved magnet and hardware design, new k-space sampling techniques (ie, parallel imaging), and alternative contrast materials. With these techniques, not only can pulmonary vessels be visualized by MR angiography with high spatial resolution but also the perfusion of the lungs and its changes in relation to pulmonary thromboembolism (PE) can be assessed. Considering venous thromboembolism as a systemic disease, MR venography might be added for the diagnosis of underlying deep venous thrombosis. A unique advantage of MRI over other imaging tests is its potential to evaluate changes in cardiac function as a result of obstruction of the pulmonary circulation, which may have a significant impact on patient monitoring and treatment. Finally, MRI does not involve radiation, which is advantageous, especially in young patients. Over the years, a number of studies have shown promising results not only for MR angiography but also for MRI of lung perfusion and for MR venography. This review article summarizes and discusses the current evidence on pulmonary MRI for patients with suspected PE.

Synthesis and evaluation of a polydisulfide with Gd-DOTA monoamide side chains as a biodegradable macromolecular contrast agent for MR blood pool imaging

Macromolecular Gd(III)-based contrast agents are effective for contrast-enhanced blood pool and cancer MRI in preclinical studies. However, their clinical applications are impeded by potential safety concerns associated with slow excretion and prolonged retention of these agents in the body. To minimize the safety concerns of macromolecular Gd contrast agents, we have developed biodegradable macromolecular Gd contrast agents based on polydisulfide Gd(III) complexes. In this study, we designed and synthesized a new generation of the polydisulfide Gd(III) complexes containing a macrocyclic Gd(III) chelate, Gd-DOTA monoamide, to improve the in vivo kinetic inertness of the Gd(III) chelates. (N6-Lysyl)lysine-(Gd-DOTA) monoamide and 3-(2-carboxyethyldisulfanyl)propanoic acid copolymers (GODC) were synthesized by copolymerization of (N6-lysyl)lysine DOTA monoamide and dithiobis(succinimidylpropionate), followed by complexation with Gd(OAc)3. The GODC had an apparent molecular weight of 26.4 kDa and T1 relaxivity of 8.25 mM(-1) s(-1) per Gd at 1.5 T. The polymer chains of GODC were readily cleaved by L-cysteine and the chelates had high kinetic stability against transmetallation in the presence of an endogenous metal ion Zn(2+). In vivo MRI study showed that GODC produced strong and prolonged contrast enhancement in the vasculature and tumor periphery of mice with breast tumor xenografts. GODC is a promising biodegradable macromolecular MRI contrast agent with high kinetic stability for MR blood pool imaging.

An intravascular MRI contrast agent based on Gd(DO3A-Lys) for tumor angiography

An intravascular MRI contrast agent Gd(DO3A-Lys), Gadolinium(III) (2,2',2″-(10-(3-(5-benzamido-6-methoxy-6-oxohexylamino)-3-oxopropyl)-1,4,7,10-tetraazacyclododecane-1,4,7-triyl)triacetate), has been studied for tumor angiography based on its high relaxivity and long blood half-life. The preparation procedures of the contrast agent have been modified in order to achieve higher yield and improve the synthetic reproducibility. High relaxivity of Gd(DO3A-Lys) has been confirmed by measurements at 3 T, 7 T and 9.4 T magnetic fields. The relaxivity-dependent albumin binding study indicated that Gd(DO3A-Lys) partially bound to albumin protein. In vitro cell viability in HK2 cell indicated low cytotoxicity of Gd(DO3A-Lys) up to 1.2 mM [Gd] concentration. In vivo toxicity studies demonstrated no toxicity of Gd(DO3A-Lys) on kidney tissues up to 0.2 mM [Gd]. While the toxicity on liver tissue was not observed at low dosage (1.0 mM [Gd]), Gd(DO3A-Lys) cause certain damage on hepatic tissue at high dosage (2.0 mM [Gd]). The DO3A-Lys has been labeled with (68)Ga radioisotope for biodistribution studies. (68)Ga(DO3A-Lys) has high uptake in both HT1080 and U87MG xenograft tumors, and has high accumulation in blood. Contrast-enhanced MR angiography (CE-MRA) in mice bearing U87MG xenograft tumor demonstrated that Gd(DO3A-Lys) could enhance vascular microenvironment around the tumor, and displays promising characteristics of an MRI contrast agent for tumor angiography.

Gadofosveset trisodium: abdominal and peripheral vascular applications

OBJECTIVE

The purpose of this review is to illustrate various applications of gadofosveset trisodium in evaluating abdominal and peripheral vascular disease. The basic properties, technical considerations, and clinical and potential future applications of gadofosveset are described.

CONCLUSION

Gadofosveset trisodium facilitates comprehensive high-resolution arterial and venous MR angiography. Because of its prolonged intravascular residence time, gadofosveset trisodium is particularly useful for evaluating venous, dynamic, and functional vascular disease with a single low-dose contrast injection.

Advantages of blood pool contrast agents in MR angiography: a pictorial review

Gadofosveset trisodium (Ablavar®, formerly Vasovist®) is the first intravascular contrast agent approved for clinical use in peripheral vascular disease. The purpose of this review is to illustrate the clinical uses of gadofosveset-enhanced magnetic resonance angiography in patients referred for assessment of arteriovenous disease. Superior T1 shortening enables first pass renal and peripheral arteriography of quality comparable with larger doses of extracellular agents. In applications such as thoracic outlet syndrome, there may be other advantages such as superior venous imaging and need for only one injection. Steady-state delayed imaging provides high resolution mapping of both arterial and venous systems and imaging of multiple territories. A combination of dynamic and delayed steady-state imaging can provide detailed anatomy and flow characteristics of vascular malformations and mapping for percutaneous sclerotherapy at one investigation. The ability to image in the steady state can provide minimally invasive imaging of thrombo-occlusive disease of central veins.

Rapid size-controlled synthesis of dextran-coated, 64Cu-doped iron oxide nanoparticles

Research into developing dual modality probes enabled for magnetic resonance imaging (MRI) and positron emission tomography (PET) has been on the rise recently due to the potential to combine the high resolution of MRI and the high sensitivity of PET. Current synthesis techniques for developing multimodal probes is largely hindered in part by prolonged reaction times during radioisotope incorporation--leading to a weakening of the radioactivity. Along with a time-efficient synthesis, the resulting products must fit within a critical size range (between 20 and 100 nm) to increase blood retention time. In this work, we describe a novel, rapid, microwave-based synthesis technique to grow dextran-coated iron oxide nanoparticles doped with copper (DIO/Cu). Traditional methods for coprecipitation of dextran-coated iron oxide nanoparticles require refluxing for 2 h and result in approximately 50 nm diameter particles. We demonstrate that microwave synthesis can produce 50 nm nanoparticles with 5 min of heating. We discuss the various parameters used in the microwave synthesis protocol to vary the size distribution of DIO/Cu and demonstrate the successful incorporation of (64)Cu into these particles with the aim of future use for dual-mode MR/PET imaging.

Monitoring antivascular therapy in head and neck cancer xenografts using contrast-enhanced MR and US imaging

BACKGROUND

The overall goal of this study was to non-invasively monitor changes in blood flow of squamous cell carcinoma of the head and neck (SCCHN) xenografts using contrast-enhanced magnetic resonance (MR) and ultrasound (US) imaging.

METHODS

Experimental studies were performed on mice bearing FaDu tumors and SCCHN xenografts derived from human surgical tissue. MR examinations were performed using gadofosveset trisodium at 4.7T. Change in T1-relaxation rate of tumors (ΔR1) and tumor enhancement parameters (amplitude, area under the curve-AUC) were measured at baseline and 24 h after treatment with a tumor-vascular disrupting agent (tumor-VDA), 5,6-dimethylxanthenone-4-acetic acid (DMXAA; ASA404) and correlated with tumor necrosis and treatment outcome. CE-US was performed using microbubbles (Vevo MicroMarker®) to assess the change in relative tumor blood volume following VDA treatment.

RESULTS

A marked decrease (up to 68% of baseline) in T1-enhancement of FaDu tumors was observed 1 day after VDA therapy indicative of a reduction in blood flow. Early (24 h) vascular response of individual tumors to VDA therapy detected by MRI correlated with tumor necrosis and volume estimates at 10 days post treatment. VDA treatment also resulted in a significant reduction in AUC and amplitude of patient tumor-derived SCCHN xenografts. Consistent with MRI observations, CE-US revealed a significant reduction in tumor blood volume of patient tumor-derived SCCHN xenografts after VDA therapy. Treatment with VDA resulted in a significant tumor growth inhibition of patient tumor derived SCCHN xenografts.

CONCLUSIONS

These findings demonstrate that both CE-MRI and CE-US allow monitoring of early changes in vascular function following VDA therapy. The results also demonstrate, for the first time, potent vascular disruptive and antitumor activity of DMXAA against patient tumor-derived head and neck carcinoma xenografts.

CMR assessment of endothelial damage and angiogenesis in porcine coronary arteries using gadofosveset

BACKGROUND

Endothelial damage and angiogenesis are essential for atherosclerotic plaque development and destabilization. We sought to examine whether contrast enhanced cardiovascular magnetic resonance (CMR) using gadofosveset could show endothelial damage and neovessel formation in balloon injured porcine coronary arteries.

METHODS AND RESULTS

Data were obtained from seven pigs that all underwent balloon injury of the left anterior descending coronary artery (LAD) to induce endothelial damage and angiogenesis. Between one - 12 days (average four) after balloon injury, in vivo and ex vivo T1-weighted coronary CMR was performed after intravenous injection of gadofosveset. Post contrast, CMR showed contrast enhancement of the coronary arteries with a selective and time-dependent average expansion of the injured LAD segment area of 45% (p = 0.04; CI95 = [15%-75%]), indicating local extravasation of gadofosveset. Vascular and perivascular extravasation of albumin (marker of endothelial leakiness) and gadofosveset was demonstrated with agreement between Evans blue staining and ex vivo CMR contrast enhancement (p = 0.026). Coronary MRI contrast enhancement and local microvessel density determined by microscopic examination correlated (ρ = 0.82, p < 0.001).

CONCLUSION

Contrast enhanced coronary CMR with gadofosveset can detect experimentally induced endothelial damage and angiogenesis in the porcine coronary artery wall.

Diffusion magnetic resonance imaging with gadofosveset trisodium as a negative contrast agent for lymph node metastases assessment

PURPOSE

The aim of this study was to assess the feasibility of using intravenously administered gadofosveset trisodium as a negative contrast agent for lymph node (LN) assessment with diffusion-weighted imaging (DWI) using a VX2 tumor model in rabbits.

MATERIALS AND METHODS

VX2 cells were injected in the right hind limb of five Japanese white rabbits to induce ipsilateral popliteal LN metastasis. DWI was performed before and every 7.5 min (until 1 h) after intravenous gadofosveset trisodium administration, at 1.5 T. Signal intensities (SIs) of right (metastatic) and left (nonmetastatic) popliteal LNs at each time point were measured and compared to each other using two-sided unpaired t-tests.

RESULTS

The SIs of metastatic lymph nodes were significantly higher (P < 0.05) than those of nonmetastatic LNs at each time point after intravenous gadofosveset trisodium administration. Although the SI of metastatic LNs was significantly higher (P = 0.0237) than that of nonmetastatic LNs before contrast injection, this difference became even more significant (P ≤ 0.0105) after gadofosveset trisodium administration.

CONCLUSION

The SI of metastatic LNs at DWI is less suppressed than that of nonmetastatic LNs after the intravenous administration of gadofosveset trisodium. Therefore, intravenously administered gadofosveset trisodium shows promise for use as a negative contrast agent for discriminating metastatic from nonmetastatic LNs at DWI.

Evaluation of rHA labeled with Gd-DTPA for blood pool imaging and targeted contrast delivery

A new contrast agent was developed by linking Gd-DTPA chelate to recombinant human albumin in the laboratory. The molar relaxivity of the new agent was tested in aqueous solution at B(0) 1.5 T and temperature 20 degrees C. The soluble compound had a higher molar longitudinal relaxivity and molar transverse relaxivity in water (r(1) = 7.2 s(-1) mM(-1), r(2) = 18.4 s(-1) mM(-1)) than those measured for Gd-DTPA solution (r(1) = 3.5 s(-1) mM(-1), r(2) = 5.5 s(-1) mM(-1)). The performance of the compound as a blood pool agent was investigated with soluble and microparticulate forms of the compound and comparisons were made with Gd-DTPA and the polymeric blood-pool agent, Gadomer. T(1)-weighted imaging experiments show that the soluble compound acts as a highly effective blood pool agent with hyperintensity in the vasculature persisting beyond 2 h post administration, compared with free Gd-DTPA, which was cleared from the blood pool after approximately 10 min. The clearance kinetics of the new agents were examined, due to the incomplete elimination within 14 days post injection; both rHA labeled compounds are probably not suitable for development as routine blood pool contrast media. However, with free sites on the Gd-loaded rHA molecule, there are possibilities for binding the agent to antibodies in the laboratory, which was demonstrated, and thus there exist potential applications for in vivo molecular imaging with this agent.

Perforator flap magnetic resonance angiography for reconstructive breast surgery: a review of 25 deep inferior epigastric and gluteal perforator artery flap patients

PURPOSE

To evaluate the accuracy of magnetic resonance angiography (MRA) for preoperative mapping of rectus and gluteal muscle perforating arteries prior to autologous flap breast reconstruction.

MATERIALS AND METHODS

Preoperative MRA on 25 consecutive patients undergoing perforator artery-based autologous breast reconstruction was performed at 1.5 T using 3D liver accelerate volume acquisition (LAVA) of abdominal or gluteal regions acquired during injection of 20 mL of gadobenate dimeglumine with bolus timing optimized using MR fluoroscopy or SmartPrep. Perforator artery size and coordinates relative to umbilicus or top of gluteal crease on 3D MRA were compared to findings at surgery. Reconstructed breast volume estimates from MRA were also compared to weights at harvesting.

RESULTS

In all, 132 perforator arteries were found at surgery to be located within 1 cm of the coordinates measured on MRA and were surgically verified to be suitable for flap perfusion. Surgery verified the arterial course and caliber through the rectus and gluteal muscles visualized on MRA in 48 of 49 arteries. Volume rendering of 3D MRA predicted a breast reconstruction volume with a mean difference of 47 g compared to measurements at harvesting.

CONCLUSION

MRA accurately maps rectus and gluteal muscle perforator arteries for preoperative planning of autologous flaps for breast reconstruction.

Gadofosveset-enhanced magnetic resonance imaging of human carotid atherosclerotic plaques: a proof-of-concept study

OBJECTIVE

To investigate the potential of gadofosveset-enhanced MR imaging for the characterization of human carotid atherosclerotic plaques.

MATERIALS AND METHODS

Sixteen (9 symptomatic, 7 asymptomatic) patients with 70% to 99% carotid stenosis (according to NASCET criteria) were included (13 men, 3 women, mean age 67.6 years). All patients underwent baseline precontrast MR imaging of the carotid plaque. Immediately after completion of the baseline examination, 0.03 mmol/kg gadofosveset was administered. At 24 hours postinjection, the acquisition was repeated. Twelve patients were scheduled for carotid endarterectomy. Carotid endarterectomy specimens were HE-, CD31-, CD68-, and albumin-stained to correlate signal enhancement with plaque composition, intraplaque microvessel density, and macrophage and albumin content. A random intercept model was used to compare signal enhancement between symptomatic and asymptomatic patients, adjusting for size of various plaque components. This study was approved by the institutional medical ethics committee. All participants gave written informed consent.

RESULTS

Signal enhancement (SE) of the plaque was significantly higher in symptomatic patients compared with asymptomatic patients (median log SE 0.182 vs. -0.109, respectively, P < 0.001). A positive association (as expressed by a regression coefficient beta = 0.0035) was found between signal enhancement on the log scale and intraplaque albumin content (P = 0.038). There was no association between signal enhancement and various other plaque components.

CONCLUSION

In this study, the potential of gadofosveset-enhanced human carotid plaque MR imaging for identification of high-risk plaques was demonstrated. Signal enhancement of the plaque after administration of gadofosveset was associated with differences in intraplaque albumin content. Although promising, we emphasize that these results are based on a small patient population. Larger prospective studies are warranted.

Gadofosveset-enhanced MR angiography of carotid arteries: does steady-state imaging improve accuracy of first-pass imaging? Comparison with selective digital subtraction angiography

PURPOSE

To evaluate the diagnostic accuracy of gadofosveset-enhanced magnetic resonance (MR) angiography in the assessment of carotid artery stenosis, with digital subtraction angiography (DSA) as the reference standard, and to determine the value of reading first-pass, steady-state, and "combined" (first-pass plus steady-state) MR angiograms.

MATERIALS AND METHODS

This study was approved by the local ethics committee, and all subjects gave written informed consent. MR angiography and DSA were performed in 84 patients (56 men, 28 women; age range, 61-76 years) with carotid artery stenosis at Doppler ultrasonography. Three readers reviewed the first-pass, steady-state, and combined MR data sets, and one independent observer evaluated the DSA images to assess stenosis degree, plaque morphology and ulceration, stenosis length, and tandem lesions. Interobserver agreement regarding MR angiographic findings was analyzed by using intraclass correlation and Cohen kappa coefficients. Sensitivity, specificity, positive predictive value (PPV), and negative predictive value (NPV) were calculated by using the McNemar test to determine possible significant differences (P < .05).

RESULTS

Interobserver agreement regarding all MR angiogram readings was substantial. For grading stenosis, sensitivity, specificity, PPV, and NPV were, respectively, 90%, 92%, 91%, and 91% for first-pass imaging; 95% each for steady-state imaging; and 96%, 99%, 99%, and 97% for combined imaging. For evaluation of plaque morphology, respective values were 84%, 86%, 88%, and 82% for first-pass imaging; 98%, 97%, 98%, and 97% for steady-state imaging; and 98%, 100%, 100%, and 97% for combined imaging. Differences between the first-pass, steady-state, and combined image readings for assessment of stenosis degree and plaque morphology were significant (P < .001).

CONCLUSION

Gadofosveset-enhanced MR angiography is a promising technique for imaging carotid artery stenosis. Steady-state image reading is superior to first-pass image reading, but the combined reading protocol is more accurate.

Atherosclerosis: contrast-enhanced MR imaging of vessel wall in rabbit model--comparison of gadofosveset and gadopentetate dimeglumine

PURPOSE

To investigate the potential of gadofosveset for contrast material-enhanced magnetic resonance (MR) imaging of plaque in a rabbit model of atherosclerosis.

MATERIALS AND METHODS

All experiments were approved by the animal ethics committee. Thirty-one New Zealand White rabbits were included in one of four study groups: animals with atherosclerosis imaged with gadofosveset (n = 10) or gadopentetate dimeglumine (n = 7) and control animals imaged with gadofosveset (n = 7) or gadopentetate dimeglumine (n = 7). Aortic atherosclerosis was induced through endothelial denudation combined with a cholesterol-enriched diet. Control rabbits underwent a sham surgical procedure and received a regular diet. After 8 weeks, pre- and postcontrast T1-weighted MR images of the aortic vessel wall were acquired. Relative signal enhancement was determined with dedicated software. Statistical analysis was performed by using a generalized linear mixed model. Immunohistochemical staining with CD31 and albumin was used to assess microvessel density and the albumin content of the vascular wall. Group differences were analyzed by using a chi(2) test. Gadofosveset spatial distribution and content within the vessel wall were determined with proton-induced x-ray emission (PIXE) analysis.

RESULTS

Postcontrast signal enhancement was significantly greater for atherosclerotic than for control animals imaged with gadofosveset (P = .022). Gadopentetate dimeglumine could not enable discrimination between normal and atherosclerotic vessel walls (P = .428). PIXE analysis showed higher amounts of gadopentetate dimeglumine than gadofosveset in both atherosclerotic and normal rabbit aortas. Immunohistochemical staining revealed the presence of albumin and increased microvessel density in the vascular walls of atherosclerotic rabbits.

CONCLUSION

These results suggest that gadofosveset can be used to differentiate between atherosclerotic and normal rabbit vessel walls.

SUPPLEMENTAL MATERIAL

http://radiology.rsnajnls.org/cgi/content/full/250/3/682/DC1.

Macromolecular dynamic contrast-enhanced (DCE)-MRI detects reduced vascular permeability in a prostate cancer bone metastasis model following anti-platelet-derived growth factor receptor (PDGFR) therapy, indicating a drop in vascular endothelial growth factor receptor (VEGFR) activation

The antivascular function of the platelet-derived growth factor receptor (PDGFR) inhibitor imatinib combined with paclitaxel has been demonstrated by invasive immunohistochemistry. The purpose of this study was to 1) noninvasively monitor the response to anti-PDGFR treatment, and 2) understand the underlying mechanism of this response. Thus, response to treatment was studied in a prostate cancer bone metastasis model using macromolecular (biotin-bovine serum albumin [BSA]-Gd-diethylene triamine pentaacetic acid [GdDTPA]) dynamic contrast-enhanced magnetic resonance imaging (DCE-MRI). Human prostate cancer (PC-3MM2) bone metastases that caused osteolysis and grew in neighboring muscle showed a high blood-volume fraction (fBV) and vascular permeability (PS) at the tumor periphery compared to muscle tissue and intraosseous tumor. Imatinib alone or with paclitaxel significantly reduced PS by 35% (one-tailed paired t-test, P = 0.045) and 40% (P = 0.0003), respectively, whereas paclitaxel alone or no treatment had no effect. Based on changes in PS, we hypothesized that imatinib interferes with the signaling pathway of vascular endothelial growth factor (VEGF). This mechanism was verified by immunohistochemistry. It demonstrated reduced activation of both PDGFR-beta and VEGF receptor 2 (VEGFR2) in imatinib-treated mice. Our study therefore demonstrates that macromolecular DCE-MRI can be used to detect early vascular effects associated with response to therapy targeted to PDGFR, and provides insight into the role played by VEGF in anti-PDGFR therapy.

Peripheral MR angiography with blood pool contrast agent: prospective intraindividual comparative study of high-spatial-resolution steady-state MR angiography versus standard-resolution first-pass MR angiography and DSA

PURPOSE

To prospectively compare the accuracy of high-spatial-resolution steady-state magnetic resonance (MR) angiography with standard-resolution first-pass MR angiography in the lower extremities, with digital subtraction angiography (DSA) as the reference standard.

MATERIALS AND METHODS

Institutional ethics committee approval and written informed consent were obtained. Twenty-seven patients (16 men, 11 women; mean age, 64.4 years +/- 14.8 [standard deviation]; range, 26-87 years) suspected of having or known to have peripheral arterial disease underwent first-pass and steady-state MR angiography and DSA. First-pass and steady-state MR angiography were performed in the same patient in the same session and with the same dose of blood pool contrast agent. The most severe stenosis grade of each evaluated segment was measured; sensitivity, specificity, and positive and negative predictive values were calculated at first-pass and steady-state MR angiography, with DSA as the reference standard. The kappa coefficient was used to measure the agreement between first-pass MR angiography, steady-state MR angiography, and DSA.

RESULTS

A total of 334 arterial segments were available for intraindividual comparison of first-pass MR angiography, steady-state MR angiography, and DSA in 27 patients. In 20 (74%) of 27 patients, the stenosis grade of at least one of the evaluated vessels differed at steady-state MR angiography from that at first-pass MR angiography. In total, stenosis grade was judged as higher at first-pass MR angiography than at DSA (overestimation) in 28 of 334 segments and as lower (underestimation) in 15 of 334 segments. The stenosis grade as judged at steady-state MR angiography matched with that at DSA in 334 of 334 vessel segments.

CONCLUSION

High-spatial-resolution steady-state MR angiography allowed for better agreement with DSA regarding stenosis grade in patients with arterial disease compared with standard-resolution arterial-phase first-pass MR angiography.

Time-resolved contrast-enhanced MR angiography of intracranial lesions

PURPOSE

To determine if contrast-enhanced (CE) MRI of intracranial lesions benefits from time-resolved MR angiography (MRA) during contrast agent injection.

MATERIALS AND METHODS

For 126 patients with suspected intracranial lesions undergoing routine CE MRI at 3.0T (N = 88) or 1.5T (N = 38), time-resolved CE MRA (three-dimensional [3D] time-resolved imaging of contrast kinetics [TRICKS]) was performed during injection of the routine gadolinium (Gd) dose of 0.1 mmol/kg. Time to peak (TTP) enhancement of lesions as well as time to internal carotid artery (ICA), middle cerebral artery (MCA), superior sagittal sinus (SSS), and jugular vein enhancement were measured. Source and maximum intensity projection (MIP) images were reviewed to delineate the spatial relationship of lesions and the vasculature.

RESULTS

In 61 patients (48%), additional important findings were detected on time-resolved MRA that were not seen on the routine CE protocol, including aneurysms (N = 6), arteriovenous malformations (N = 7), ICA stenoses (N = 2), vascular anomalies (N = 18), and relationships between lesions and vessels (N = 28). In addition, tumor TTP correlated with glioma grade (r = 0.87) and discriminated epithelial from nonepithelial meningiomas (P = 2.6 x 10(-5)). MRA added eight minutes to the total exam time.

CONCLUSION

Time-resolved MRA performed during contrast agent injection adds information to the routine brain CE MRI examination of intracranial lesions with only a small time penalty and no additional risk to the patient.

Variable echo time imaging: signal characteristics of 1-M gadobutrol contrast agent at 1.5 and 3T

Gadobutrol (Gd-Bt; Gadovist(R), Schering AG) is a 1-M Gadolinium (Gd)-based contrast agent. Its higher Gd concentration allows for reduction of injection volumes in first pass contrast-enhanced MR angiography (CE-MRA) and should increase bolus sharpness and image quality. However, ambivalent results were reported. In order to explore the performance of 1-M contrast agents such as Gd-Bt and its dependence on molecular environment and temperature, signal characteristics were analyzed for a series of increasing Gd-Bt concentrations for different temperature-controlled samples in water and human blood plasma. Relaxation times, relaxivities, and signal-concentration curves were assessed for several Gd-Bt concentrations in water at 20 degrees C and 37 degrees C and in plasma at 37 degrees C for 1.5T and 3T. Gd-Bt concentration influence on signal intensity (SI) could be effectively simulated and compared with experimental measurements as well as simulations with other contrast agents at realistic in vivo concentrations. Particular attention was given to T(2)- and T(*) (2)-induced losses at high concentrations, which annihilate benefits from T(1) shortening. Based on these findings, variable echo time (VTE) approaches with readout bandwidth varying with k-space position were explored in order to enhance the signal to noise performance of gradient echo imaging at high contrast agent concentrations. Results indicate the potential of VTE for imaging with increased SNR at high contrast agent concentrations.

Biochemical safety profiles of gadolinium-based extracellular contrast agents and nephrogenic systemic fibrosis

Gadolinium (Gd)-based paramagnetic contrast agents are relatively safe when used in clinically recommended doses. However, with the rapidly expanding body of literature linking Gd-based paramagnetic contrast agents and nephrogenic systemic fibrosis (NSF), awareness of the potential side effects and adverse reactions from Gd is now an important requirement for practicing radiologists. In addition to the ongoing accumulation and analyses of clinical NSF data, it is also essential for the practicing radiologist to understand the biochemical characteristics of the extracellular Gd-chelates. The purpose of this review is to consolidate and update the available information on known side effects, adverse reactions, and toxicity of the Gd chelates, with particular emphasis on the potential mechanisms of NSF.

MR-guided endovascular interventions: a comprehensive review on techniques and applications

The magnetic resonance (MR) guidance of endovascular interventions is probably one of the greatest challenges of clinical MR research. MR angiography is not only an imaging tool for the vasculature but can also simultaneously depict high tissue contrast, including the differentiation of the vascular wall and perivascular tissues, as well as vascular function. Several hurdles had to be overcome to allow MR guidance for endovascular interventions. MR hardware and sequence design had to be developed to achieve acceptable patient access and to allow real-time or near real-time imaging. The development of interventional devices, both applicable and safe for MR imaging (MRI), was also mandatory. The subject of this review is to summarize the latest developments in real-time MRI hardware, MRI, visualization tools, interventional devices, endovascular tracking techniques, actual applications and safety issues.

MRT der akuten Lungenembolie

Recent technical developments have substantially improved the potential of MRI for the diagnosis of pulmonary embolism. On the MR scanner side this includes the development of short magnets and dedicated whole-body MRI systems, which allow a comprehensive evaluation of pulmonary embolism and deep venous thrombosis in a single exam. The introduction of parallel imaging has substantially improved the spatial and temporal resolution of pulmonary MR angiography. By combining time-resolved pulmonary perfusion MRI with high-resolution pulmonary MRA a sensitivity and specificity of over 90% is achievable, which is comparable to the accuracy of CTA. Thus, for certain patient groups, such as patients with contraindications to iodinated contrast media and young women with a low clinical probability for pulmonary embolism, MRI can be considered as a first-line imaging tool for the assessment of pulmonary embolism.

Magnetic resonance imaging of acute pulmonary embolism

Pulmonary embolism (PE) is a very common and potentially life-threatening disease. In comparison with CT, the clinical relevance of magnetic resonance imaging (MRI) for the assessment of PE is low. Nevertheless, as there are some potential advantages of MRI over CT (e.g. radiation free method, better safety profile of MR contrast media, capability of functional imaging). In certain patient, groups MRI might therefore be considered as a valuable alternative in the assessment of suspected PE. This article reviews the relevant MRI techniques for the evaluation of PE and gives an overview of the current literature for contrast-enhanced MR angiography of PE.

Contrast-enhanced magnetic resonance imaging of central nervous system tumors: agents, mechanisms, and applications

Brain tumors are one of the most common neoplasms in young adults and are associated with a high mortality and disability rate. Magnetic resonance imaging (MRI) is widely accepted to be the most sensitive imaging modality in the assessment of cerebral neoplasms. Because the detection, characterization, and exact delineation of brain tumors require a high lesion contrast that depends on the signal of the lesion in relation to the surrounding tissue, contrast media is given routinely. Anatomical and functional, contrast agent-based MRI techniques allow for a better differential diagnosis, grading, and especially therapy decision, planing, and follow-up. In this article, the basics of contrast enhancement of brain tumors will be reviewed. The underlying pathology of a disrupted blood-brain barrier and drug influences will be discussed. An overview of the currently available contrast media and the influences of dosage, field strength, and application on the tumor tissue contrast will be given. Challenging, contrast-enhanced, functional imaging techniques, such as perfusion MRI and dynamic contrast-enhanced MRI, are presented both from the technical side and the clinical experience in the assessment of brain tumors. The advantages over conventional, anatomical MRI techniques will be discussed as well as possible pitfalls and drawbacks.