Ultrasmall superparamagnetic iron oxide to enhance MRA of the renal and coronary arteries: studies in human patients

Preoperative Prediction of Axillary Lymph Node Metastasis in Breast Cancer Based on Intratumoral and Peritumoral DCE-MRI Radiomics Nomogram

Objective

To investigate the value of preoperative prediction of breast cancer axillary lymph node metastasis based on intratumoral and peritumoral dynamic contrast enhancement magnetic resonance imaging (DCE-MRI) radiomics nomogram. Material and Methods. In this study, a radiomics model was developed based on a training cohort involving 250 patients with breast cancer (BC) who had undergone axillary lymph node (ALN) dissection between June 2019 and January 2021. The intratumoral and peritumoral radiomics features were extracted from the second postcontrast images of DCE-MRI. Based on filtered radiomics features, the radiomics signature was built by using the least absolute shrinkage and selection operator method. The Support Vector Machines (SVM) learning algorithm was used to construct intratumoral, periatumoral, and intratumoral combined periatumoral models for predicting axillary lymph node metastasis (ALNM) in BC. Nomogram performance was determined by its discrimination, calibration, and clinical value. Multivariable logistic regression was adopted to establish a radiomics nomogram.

Results

The intratumoral combined peritumoral radiomics signature, which was composed of fifteen ALN status-related features, showed the best predictive performance and was associated with ALNM in both the training and validation cohorts (P < 0.001). The prediction efficiency of the intratumoral combined peritumoral radiomics model was higher than that of the intratumoral radiomics model and the peritumoral radiomics model. The AUCs of the training and verification cohorts were 0.867 and 0.785, respectively. The radiomics nomogram, which incorporated the radiomics signature, MR-reported ALN status, and MR-reported maximum diameter of the lesion, showed good calibration and discrimination in the training (AUC = 0.872) and validation cohorts (AUC = 0.863).

Conclusion

The intratumoral combined peritumoral radiomics model derived from DCE-MRI showed great predictive value for ALNM and may help to improve clinical decision-making for BC.

Improved coronary magnetic resonance angiography using gadobenate dimeglumine in pediatric congenital heart disease

BACKGROUND

CMRA in pediatrics remains challenging due to the smaller vessel size, high heart rates (HR), potential image degradation caused by limited patient cooperation and long acquisition times. High-relaxivity contrast agents have been shown to improve coronary imaging in adults, but limited data is available in children. We sought to investigate whether gadobenate dimeglumine (Gd-BOPTA) together with self-navigated inversion-prepared coronary magnetic resonance angiography (CMRA) sequence design improves coronary image quality in pediatric patients.

METHODS

Forty consecutive patients (mean age 6±2.8years; 73% males) were prospectively recruited for a 1.5-T MRI study under general anesthesia. Two electrocardiographic-triggered free breathing steady-state free precession (SSFP) angiography sequences (A and B) with isotropic spatial resolution (1.3mm³) were acquired using a recently developed image-based self-navigation technique. Sequence A was acquired prior to contrast administration using T2 magnetization preparation (T2prep). Sequence B was acquired 5-8min after a bolus of Gd-BOPTA with the T2prep replaced by an inversion recovery (IR) pulse to null the signal from the myocardium. Scan time, signal-to noise and contrast-to-noise ratios (SNR and CNR), vessel wall sharpness (VWS) and qualitative visual score for each sequence were compared.

RESULTS

Scan time was similar for both sequences (5.3±1.8 vs 5.2±1.5min, p=.532) and average heart rate (78±14.7 vs 78±14.5bpm, p=.443) remained constant throughout both acquisitions. Sequence B resulted in higher SNR (12.6±4.4 vs 31.1±7.4, p<.001) and CNR (9.0±1.8 vs 13.5±3.7, p<.001) and provided improved coronary visualization in all coronary territories (VWS A=0.53±0.07 vs B=0.56±0.07, p=.001; and visual scoring A=3.8±0.59 vs B=4.1±0.53, p<.001). The number of non-diagnostic coronary segments was lower for sequence B [A=42 (13.1%) segments vs B=33 (10.3%) segments; p=.002], and contrary to the pre-contrast sequence, never involved a proximal segment. These results were independent of the patients' age, body surface area and HR.

CONCLUSIONS

The use of Gd-BOPTA with a 3D IR SSFP CMRA sequence results in improved coronary visualization in small infants and young children with high HR within a clinically acceptable scan time.

Vascular Imaging With Ferumoxytol as a Contrast Agent

OBJECTIVE

Ferumoxytol is increasingly reported as an alternative to gadolinium-based contrast agents for MR angiography (MRA), particularly for patients with renal failure. This article summarizes more than 3 years of clinical experience with ferumoxytol-enhanced MRA for a range of indications and anatomic regions.

CONCLUSION

Ferumoxytol-enhanced MRA has many advantages including that it is safe for patients with renal failure and provides a lengthy plateau of vascular signal as a blood pool agent that allows longer navigated MRA sequences.

Contrast agents used in cardiovascular magnetic resonance imaging: current issues and future directions

Cardiovascular MRI is being increasingly used in the evaluation of ischemic heart disease, cardiac masses, complex congenital heart disease, and morphologic evaluation of the vascular anatomy throughout the body. Many and varied contrast media may be used to increase the sensitivity and specificity of detecting and evaluating various pathologies, and a knowledge of the different mechanisms of action, distributions and safety profiles of these agents is required for safe and effective imaging. This article reviews the currently available magnetic resonance (MR) contrast media, discusses the risks and benefits, and gives illustrated examples of current clinical applications in cardiovascular disease. A literature search covered the period 1990 to the present with the use of multiple databases including MEDLINE, PUBMED, SciSearch and Google Medical. All identified studies containing information relevant to the topic of cardiovascular MRI and cardiovascular MR contrast agents and their uses and properties were evaluated. Evaluation was limited to studies in English. The conclusions were that the use of contrast agents vastly increases the diagnostic yield, sensitivity and specificity of cardiovascular MRI in the non-invasive diagnosis of the full breadth of cardiovascular pathology. The use of contrast MRI for investigating ischemic heart disease, cardiac masses, and congenital heart disease and in angiography is now well established, and the referring physician, cardiologist, or radiologist requires an in-depth knowledge of the safety profiles and correct dosing of commonly prescribed contrast agents. As the number of MR contrast agents on the market continues to increase, knowledge of the basic mechanism of action is vital for keeping abreast of how new and emerging agents will affect clinical practice in the future.

Characterization of carotid artery plaques with USPIO-enhanced MRI: assessment of inflammation and vascularity as in vivo imaging biomarkers for plaque vulnerability

To evaluate ultra small superparamagnetic iron oxide particles (USPIO) enhanced magnetic resonance (MR) imaging for characterization of atherosclerotic carotid plaques by assessing vascularity and plaque inflammation, besides contrast-enhanced MR angiography (CE-MRA) of the carotid artery stenosis. Twelve patients with severe carotid artery stenosis, scheduled for endarterectomy, underwent MRI of the carotid artery bifurcation using SHU 555 C at a dose of 40 μmol Fe/kg BW. The MR imaging protocol comprised pre- and post-contrast T2*-w, a first-pass CE-MRA and dynamic T1-w sequences. For quantitative data analysis, the signal intensities (SI) were measured and SNR-data (SNR = SI(blood/plaque/bone marrow)/standard deviation(noise)) as well as ΔSI-data (SNR(post)-SNR(pre)) were calculated. In addition, two radiologists rated the diagnostic performance of first-pass MRA according to a four level decision scale. Staining of anti-dextran (SHU 555 C) and anti-CD68 (macrophages) was performed for immunohistological confirmation. Plaque sections with a T2*-w signal decline (intracellular USPIO accumulation in macrophages) showed significantly changes (mean -14%, 95% CI, -5 to -20%; P < 0.01) and corresponding plaque regions had significantly higher (15.15 ± 1.76 vs. 5.22 ± 1.50; P < 0.01) T1-w enhancement data (global estimation of vascularity). The first-pass MRA of the supra-aortal vessels provided images of diagnostic quality. Representative immunohistology sections revealed colocalization of dextran- and CD68-immunoreactive cells. USPIO-enhanced MRI is feasible for in vivo assessment of vascularity and macrophage content in atherosclerotic carotid plaques, determining an association of these potential imaging biomarkers of plaque vulnerability. Diagnostic MRA of the supra-aortal vessels can be imaged additionally with a single administration of SHU 555 C.

Imaging stem cells implanted in infarcted myocardium

Stem cell-based cellular cardiomyoplasty represents a promising therapy for myocardial infarction. Noninvasive imaging techniques would allow the evaluation of survival, migration, and differentiation status of implanted stem cells in the same subject over time. This review describes methods for cell visualization using several corresponding noninvasive imaging modalities, including magnetic resonance imaging, positron emission tomography, single-photon emission computed tomography, and bioluminescent imaging. Reporter-based cell visualization is compared with direct cell labeling for short- and long-term cell tracking.

Effect of Field Strengths on Magnetic Resonance Angiography

OBJECTIVES

We sought to compare the intravascular enhancement of an ultrasmall superparamagnetic iron oxide (USPIO) blood-pool contrast agent to gadopentetate dimeglumine for contrast-enhanced magnetic resonance angiography (CE-MRA) at field strengths of 1.5 and 3.0 T in rabbits.

MATERIALS AND METHODS

CE-MRA at 1.5 and 3.0 T was performed at several time points (50 seconds and 5, 10, 20, and 30 minutes) after the manual intravenous injection of 40 micromol Fe/kg body weight of an USPIO (SH U 555 C; Schering AG, Berlin, Germany) and 100 micromol/kg body weight gadopentetate dimeglumine (Magnevist; Schering AG, Berlin, Germany). MRA was performed with comparable acquisition parameters at both field strengths (Turbo-gradient sequence; 1.5 T: TR/TE/alpha: 5.5/1.7 milliseconds/40 degrees ; 3.0 T: TR/TE/alpha: 5.1/1.8 milliseconds/40 degrees ) on clinical imaging systems (both: Gyroscan Intera, Philips Medical Systems, Best, The Netherlands). At either field strength, 6 rabbits were studied with both contrast agents (n = 24 in total). Signal-to-noise ratio (SNR) and contrast-to-noise ratio (CNR) were calculated from signal intensity measurements in the abdominal aorta.

RESULTS

Compared with 1.5 T, the SNR and CNR of gadopentetate dimeglumine significantly increased at 3.0 T by a factor of 2.2 and 2.3, respectively (P <or= 0.01), measured 50 seconds after intravenous injection. SNR and CNR of SH U 555 C, measured 50 seconds after intravenous injection, did not change significantly with increasing field strength (P >or= 0.05). At both field strength and either time point, CNR and SNR of SH U 555 C were significantly higher compared with gadopentetate dimeglumine at 3.0 T (P <or= 0.01).

CONCLUSIONS

SNR and CNR of gadopentetate dimeglumine significantly increased with increasing field strength. No SNR or CNR gain was observed for SH U 555 C. However, blood-pool MRA with SH U 555 C is feasible at 3.0 T. Compared with gadopentetate dimeglumine, SNR and CNR of SH U 555 C were significantly higher from 5 to 30 minutes at both field strengths (P <or= 0.01).

Ferumoxtran-10-enhanced MR imaging of the bone marrow before and after conditioning therapy in patients with non-Hodgkin lymphomas

To quantify permeability changes of the "blood-bone marrow barrier" (BMB) and to detect malignant bone marrow infiltrations before and after conditioning therapy for subsequent leukapheresis using ferumoxtran-10-enhanced magnetic resonance (MR) imaging. Twenty-two patients with malignant non-Hodgkin lymphomas (NHL), including 9 patients (group A) before and 13 patients (group B) after conditioning therapy, underwent MR of the spine before and after infusion of ferumoxtran-10 (0.045 mmol Fe/kg BW). Pulse sequences comprised dynamic T1-GE and pre- and post-contrast T1-SE and STIR sequences. Dynamic deltaSI-data were correlated with the quantity of mobilized CD34+ cells. In addition, the number of focal bone marrow lesions was compared before and after ferumoxtran-10 administration. Dynamic deltaSI-data were higher in group B than in group A, indicating an increased BMB permeability after conditioning therapy. However, deltaSI-data did not correlate with the quantity of mobilized CD34+ cells. Ferumoxtran-10-enhanced STIR images demonstrated a significant signal decline of the normal, non-neoplastic bone marrow and a significantly increased detection of focal neoplastic lesions compared to pre-contrast images (P<0.05). Ferumoxtran-10 depicted the bone marrow response to conditioning therapy by an increase in BMB-permeability, which, however, did not correlate with the number of mobilized CD34+ cells. Ferumoxtran-10 improved the detection of focal bone marrow lesions significantly (P<0.05).

Free-breathing, three-dimensional coronary artery magnetic resonance angiography: comparison of sequences

PURPOSE

To compare six free-breathing, three-dimensional, magnetization-prepared coronary magnetic resonance angiography (MRA) sequences.

MATERIALS AND METHODS

Six bright-blood sequences were evaluated: Cartesian segmented gradient echo (C-SGE), radial SGE (R-SGE), spiral SGE (S-SGE), spiral gradient echo (S-GE), Cartesian steady-state free precession (C-SSFP), and radial SSFP (R-SSFP). The right coronary artery (RCA) was imaged in 10 healthy volunteers using all six sequences in randomized order. Images were evaluated by two observers with respect to signal-to-noise ratio (SNR), contrast-to-noise ratio (CNR), visible vessel length, vessel edge sharpness, and vessel diameter.

RESULTS

C-SSFP depicted RCA over the longest distance with high vessel sharpness, good SNR, and excellent background suppression. S-GE provided best SNR and CNR in proximal segments, but more vessel blurring and poorer background suppression, resulting in poor visualization of distal segments. R-SSFP images showed good background suppression and best vessel sharpness, but only moderate SNR. C-SGE provided good SNR and reasonable CNR, but lowest vessel sharpness. S-SGE and R-SGE visualized the RCA over the smallest distance, mostly due to vessel blurring and low SNR, respectively.

CONCLUSION

Overall, Cartesian SSFP provided the best image quality with excellent vessel sharpness, visualization of long vessel segments, and good SNR and CNR.

First-pass and equilibrium-MRA of the aortoiliac region with a superparamagnetic iron oxide blood pool MR contrast agent (SH U 555 C): results of a human pilot study

The purpose of this study was to study different doses for first-pass and equilibrium phase MRA of aortoiliac vessels with a superparamagnetic iron oxide (SPIO) intravascular MR contrast agent (SH U 555 C) after single i.v. bolus injection. Sixteen healthy volunteers were prospectively enrolled into this single-blind, placebo-controlled clinical trial. SHU 555 C was injected as an i.v. bolus at stepwise increased dose levels of 5, 10, 20 and 40 micromol Fe/kg bodyweight (b.w.) corresponding to injection volumes of 0.01, 0.02, 0.04 and 0.08 ml/kg b.w. Serial high-resolution three-dimensional MRA of the aortoiliac vessels was acquired during first-pass and equilibrium, at 6 min intervals up to 42 min after contrast application using a breath-hold three-dimensional FLASH sequence on a 1.5 T scanner. Intravascular enhancement was calculated within the abdominal aorta and the inferior vena cava and a statistical analysis for significant differences in vessel enhancement was performed during the bolus and equilibrium phases. The visibility of vessels was ranked and effects of potential artifacts on image quality were graded for each time point and dose group. SH U 555 C showed a dose-dependent intravascular enhancement during the observation period (42 min). The highest dose of 40 micromol Fe/kg b.w. revealed the highest image quality during first-pass and equilibrium phases. The intravascular enhancement in the aorta increased dose-dependently from 5 to 40 micromol kg b.w. during first-pass and equilibrium phases (p<0.05). Intravascular signal inhomogeneities were observed at lower doses and decreased with increasing doses. First-pass MRA was diagnostic at doses of 10, 20 and 40 micromol Fe/kg b.w. For equilibrium MRA, a dose of 40 micromol Fe/kg b.w. was considered to be diagnostic. SH U 555 C proved to be a contrast agent with a high T1-effect suitable for both first-pass MRA comparable to gadolinium-enhanced MRA and high resolution equilibrium MRA up to 42 min post-injection (p.i.).

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.

The utility of superparamagnetic contrast agents in MRI: theoretical consideration and applications in the cardiovascular system

This review will discuss the in vivo physical chemical relaxation properties of superparamagnetic iron oxide particles. Various parameters such as size, magnetization, compartmentalization and water exchange effects and how these alter the behavior of the iron oxide particles in an in vitro vs an in vivo situation with special reference to the cardiovascular system will be exemplified. Furthermore, applications using iron oxide particles for vascular, perfusion and viability imaging as well as assessment of the inflammatory status of a given tissue will be discussed.

Magnetic resonance molecular imaging with nanoparticles

Molecular imaging agents are extending the potential of noninvasive medical diagnosis from basic gross anatomic descriptions to complicated phenotypic characterizations based on the recognition of unique cell surface biochemical signatures. Although originally the purview of nuclear medicine, molecular imaging is now a prominent feature of most clinically relevant imaging modalities, in particular magnetic resonance (MR) imaging. MR nanoparticulate agents afford the opportunity not only for targeted diagnostic studies but also for image-monitored site-specific therapeutic delivery, much like the "magic bullet" envisioned by Paul Erhlich 100 years ago. Combining high-resolution MR molecular imaging with drug delivery will facilitate verification and quantification of treatment (ie, rational targeted therapy) and will offer new clinical approaches to many diseases.

Comparison of the Iron Oxide-Based Blood-Pool Contrast Medium VSOP-C184 With Gadopentetate Dimeglumine for First-Pass Magnetic Resonance Angiography of the Aorta and Renal Arteries in Pigs

RATIONALE AND OBJECTIVES

VSOP-C184 at a dose of 0.045 mmol Fe/kg has been shown to be an efficient blood pool contrast medium for equilibrium magnetic resonance angiography (MRA) that can be administered as a bolus. The present study was performed to determine whether VSOP-C184 is also suitable for first-pass MRA.

MATERIALS AND METHODS

Fifteen MRA examinations at 1.5 T were performed in minipigs using a fast 3D fast low-angle shot (FLASH) sequence (repetition time = 4.5 ms, echo time = 1.7 ms, excitation angle = 25 degrees, matrix 256, body phased-array coil). The citrate-stabilized iron oxide preparation VSOP-C184 was investigated (total particle diameter: 7.0 +/- 0.15 nm; core size: 4 nm) and compared with gadopentetate dimeglumine (Gd-DTPA). The following doses were tested: VSOP-C184: 0.015, 0.025, and 0.035 mmol Fe/kg; Gd-DTPA: 0.1 and 0.2 mmol Gd/kg; n = 3 examinations/dose. Data were analyzed quantitatively (signal enhancement (ENH) and vessel edge definition (VED)) and qualitatively.

RESULTS

First-pass MRA using the 3 doses of VSOP-C184 yielded the following ENH: aorta: 9.4 +/- 2.6; 12.31 +/- 1.2; 16.53 +/- 1.7; renal arteries: 7.6 +/- 2.2; 9.9 +/- 1.0; 13.2 +/- 0.5. The values for the 2 doses of Gd-DTPA were aorta: 12.9 +/- 1.0; 16.8 +/- 2.2; renal arteries: 11.2 +/- 1.23; 11.3 +/- 1.7. VED for the 3 doses of VSOP-C184 was aorta: 106.3 +/- 31.0; 135.3 +/- 58.8; 141.3 +/- 71.0; renal arteries: 102.2 +/- 24.3; 146.8 +/- 63.0; 126.9 +/- 37.6 and for the 2 doses of Gd-DTPA, aorta: 157.2 +/- 47.8; 164.2 +/- 36.8; renal arteries: 165.9 +/- 30.4; 170.3 +/- 38.2 respectively. The differences between VSOP-C184 and Gd-DTPA are clinically not relevant and statistically not significant (p > or = .05). Qualitative evaluation of image quality, contrast, and delineation of vessels showed the results obtained with VSOP-C184 at doses of 0.025 and 0.035 mmol Fe/kg to be similar to those of Gd-DTPA at 0.1 and 0.2 mmol Gd/kg.

CONCLUSION

VSOP-C184 is suitable for first-pass MRA at doses of 0.025 and 0.035 mmol Fe/kg and thus, in addition to its blood pool characteristics, allows for selective visualization of the arteries without interfering venous signal.

Myocardial Perfusion and MR Angiography of Chest with SH U 555 C: Results of Placebo-controlled Clinical Phase I Study

PURPOSE

To evaluate SH U 555 C for contrast material-enhanced three-dimensional magnetic resonance (MR) angiography of the chest and myocardial perfusion.

MATERIALS AND METHODS

For chest MR angiography, SH U 555 C was intravenously injected at four doses (5, 10, 20, and 40 micromol iron [Fe] per kilogram of body weight) into three healthy volunteers per dose group, and placebo (saline) was injected into one additional volunteer per dose group (16 subjects). With a body phased-array coil, serial high-spatial-resolution breath-hold three-dimensional MR angiography of the chest was performed at baseline, first pass, and 6, 12, 18, 24, 30, 36, and 42 minutes after injection. SH U 555 C (40 micromol Fe/kg) was injected into four additional volunteers to evaluate cardiac perfusion. Signal intensity (SI) was measured in vessels, cardiac chambers, and myocardium to calculate relative SI changes during time. Analysis of variance for multiple comparisons was applied for statistical analysis. Two readers assessed image quality. Subjects were monitored for side effects (cardiovascular reactions) for 24 hours.

RESULTS

SH U 555 C showed a dose-dependent increase in SI enhancement during first pass and equilibrium phase. SH U 555 C showed dose-dependent increase (range, 259% +/- 160 [SD] at 5 micromol Fe/kg to 907% +/- 370 at 40 micromol Fe/kg) for thoracic aorta during first pass. Intravascular SI did not significantly decrease with time during equilibrium phase within arterial and venous vessels. Image quality remained stable and was diagnostic for highest dose group to 30 minutes, with good to excellent contrast even in smaller blood vessels. For cardiac perfusion, SH U 555 C showed peak enhancement during first pass through right and left ventricles, as well as stable SI during equilibrium phase within cardiac chambers and myocardium. Peak enhancement during first pass was limited due to susceptibility effects, which were more pronounced in right ventricle than in left. Contrast agent was well tolerated, and no cardiovascular reactions occurred.

CONCLUSION

SH U 555 C bolus injected at highest dose of 40 micromol Fe/kg has capability for depiction at first-pass MR angiography and for cardiac perfusion.

Macromolecular contrast medium (feruglose) versus small molecular contrast medium (gadopentetate) enhanced magnetic resonance imaging: differentiation of benign and malignant breast lesions

RATIONALE AND OBJECTIVES

To compare the diagnostic performance of the blood pool agent feruglose and the standard extracellular contrast agent gadopentetate in their abilities to differentiate benign and malignant breast tumors.

PATIENTS AND METHODS

Fourteen women, aged 35-77 years (mean, 55 years), with 19 breast lesions underwent dynamic fast field echo 14/1/30 degrees (TR/TE/alpha) magnetic resonance imaging of the breast after bolus injection of feruglose (Clariscan; Amersham Health, Amersham, UK: dose, 2 mg Fe/kg) and an additional, comparative gadopentetate (dose, 0.2 mmol gadolinium/kg)-enhanced fast field echo 10/4/30 degrees (TR/TE/alpha) magnetic resonance study within 1-11 days (mean, 4.8 days) before or after the feruglose study. All breast tumors were surgically excised within 1-6 days (mean, 2.5 days) after completion of the magnetic resonance studies. Data were analyzed by measuring quantitative enhancement data and qualitatively by categorizations of the shape of the tumor enhancement curves. Group differences between quantitative data of the two contrast agents and between benign and malignant tumors were evaluated using a two-tailed paired-sample t test. Differences in curve type distribution between benign and malignant tumors were tested with the chi2 test.

RESULTS

Histopathology showed a spectrum of 10 benign and nine malignant breast lesions: five mastopathies, two fibroadenomas, two chronic inflammations, and one papillomatosis, as well as five invasive ductal carcinomas and four invasive lobular carcinomas. Substantial differences were observed between feruglose- and gadopentetate-enhanced images: the mean tumor deltaSI(%) peak enhancement and wash-in rate were significantly higher for gadopentetate- as compared with feruglose-enhanced images (P < .05). Using either contrast agent, morphologic enhancement characteristics showed a considerable overlap between benign and malignant breast lesions. However, the kinetic enhancement profiles of benign and malignant lesions were significantly different based on feruglose-enhanced data (chi2 = 9.017; P = .0027) but not gadopentetate-enhanced data (chi2 = 2.239; P = .3264).

CONCLUSION

Compared with gadopentetate, the new blood pool agent feruglose provided an improved characterization of the evaluated breast lesions; however, at the cost of weaker overall tumor enhancement.

First-pass contrast-enhanced magnetic resonance angiography in humans using ferumoxytol, a novel ultrasmall superparamagnetic iron oxide (USPIO)-based blood pool agent

PURPOSE

To evaluate the feasibility of first-pass contrast-enhanced magnetic resonance angiography (MRA) using ferumoxytol in humans.

MATERIALS AND METHODS

First-pass and equilibrium phase MRA were performed using ferumoxytol in one healthy volunteer and 11 patients with a fast three-dimensional spoiled gradient recalled (SPGR) pulse sequence. The examined vessels included carotid arteries, thoracic aorta, abdominal aorta, and peripheral arteries. A dose of either 71.6 micromol Fe/kg (n = 9), or 35.8 micromol Fe/kg (n = 3) was used. Based on a phantom study, the agent with initial concentration of 537.2 micromol Fe/mL was diluted by either four-fold (134.3 micromol Fe/mL) or eight-fold (67.1 micromol Fe/mL) for first-pass MRA.

RESULTS

All subjects completed their studies without adverse events. First-pass MRA showed selective arterial enhancement, with both arterial and venous enhancement on delayed acquisitions. Selective venous enhancement could be obtained by subtraction of arterial phase images from equilibrium phase images. The findings in ferumoxytol MRA were consistent with the results of original vascular tests.

CONCLUSION

Our preliminary experience supports the feasibility of first-pass MRA with ferumoxytol. Satisfactory arterial enhancement during first-pass imaging is obtained with injection of diluted contrast agent. With ferumoxytol, arteries and veins can be selectively depicted in a single exam.

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

PURPOSE

To assess SH L 643A for three-dimensional breath-hold and respiratory-gated magnetic resonance (MR) imaging in the depiction of coronary arteries.

MATERIALS AND METHODS

Twelve healthy male volunteers underwent either three-dimensional breath-hold (n = 6) or respiratory-gated (n = 6) coronary MR angiography before and after intravenous injection of 0.1 mmol SH L 643A per kilogram of body weight. For nonenhanced and contrast material-enhanced examinations, signal-to-noise ratio (SNR) and contrast-to-noise ratio (CNR) measurements were obtained. Image quality was assessed in consensus with a five-point scale. Statistical analysis of nonenhanced and contrast-enhanced images was based on a two-tailed paired Student t test. A P value at the.05 significance level was used.

RESULTS

Overall statistically significant improvement in CNR was observed after administration of SH L 643A compared with that on nonenhanced images (8.7 +/- 5.3 [SD] vs 23.6 +/- 7.2, P <.01). While SNR of contrast-enhanced images showed improvement over that of nonenhanced images, the difference was not statistically significant (25.4 +/- 0.8 vs 30.2 +/- 16.8, P >.2). Image quality improved from a mean of 3.1 +/- 0.8 for nonenhanced images to 4.0 +/- 0.8 (P <.01) for contrast-enhanced images.

CONCLUSION

SH L 643A causes significant improvement of the blood-myocardium contrast enhancement at coronary MR angiography compared with that with nonenhanced sequences.

3DVIEWNIX-AVS: a software package for the separate visualization of arteries and veins in CE-MRA images

Our earlier study developed a computerized method, based on fuzzy connected object delineation principles and algorithms, for artery and vein separation in contrast enhanced Magnetic Resonance Angiography (CE-MRA) images. This paper reports its current development-a software package-for routine clinical use. The software package, termed 3DVIEWNIX-AVS, consists of the following major operational parts: (1) converting data from DICOM3 to 3DVIEWNIX format, (2) previewing slices and creating VOI and MIP Shell, (3) segmenting vessel, (4) separating artery and vein, (5) shell rendering vascular structures and creating animations. This package has been applied to EPIX Medical Inc's CE-MRA data (AngioMark MS-325). One hundred and thirty-five original CE-MRA data sets (of 52 patients) from 6 hospitals have been processed. In all case studies, unified parameter settings produce correct artery-vein separation. The current package is running on a Pentium PC under Linux and the total computation time per study is about 3 min. The strengths of this software package are (1) minimal user interaction, (2) minimal anatomic knowledge requirements on human vascular system, (3) clinically required speed, (4) free entry to any operational stages, (5) reproducible, reliable, high quality of results, and (6) cost effective computer implementation. To date, it seems to be the only software package (using an image processing approach) available for artery and vein separation of the human vascular system for routine use in a clinical setting.

Gadobenate dimeglumine-enhanced magnetic resonance angiography of the pelvic arteries

RATIONALE AND OBJECTIVES

To evaluate 4 doses of gadobenate dimeglumine (Gd-BOPTA) for contrast-enhanced magnetic resonance angiography (CE-MRA) of the pelvic arteries and to compare CE-MRA with unenhanced time-of-flight MRA (2D-TOF-MRA).

METHODS

A multicenter Phase II dose-finding study was performed in 136 patients with Gd-BOPTA doses of 0.025, 0.05, 0.1, and 0.2 mmol/kg bodyweight. Evaluation of CE-MRA images and comparison with 2D-TOF-MRA images was performed onsite and by 2 blinded offsite reviewers in terms of subjective image quality, number of lesions detected, and confidence in lesion characterization.

RESULTS

Significant (P < 0.05) improvements over unenhanced findings were observed for CE-MRA at all dose levels. For reviewer 1 and the onsite investigators, the overall image quality increased up to a dose of 0.1 mmol/kg and then plateaued. For reviewer 2, increased image quality was noted up to a dose of 0.2 mmol/kg. Significant (P < 0.005) increases in diagnostic confidence on CE-MRA versus unenhanced MRA was observed for all dose groups by reviewer 1 and the onsite investigators and for the 0.1 and 0.2 mmol/kg dose groups by reviewer 2. No serious adverse events were recorded that were attributable to the study drug and no trends in laboratory parameters, vital signs, or electrocardiogram recordings were observed.

CONCLUSIONS

Gadobenate dimeglumine-enhanced MRA is safe and significantly more effective than unenhanced 2D-TOF-MRA for imaging the pelvic arteries. A dose of 0.1 mmol/kg appears the most appropriate dose for subsequent Phase III clinical evaluation.

Multicenter phase-II trial of safety and efficacy of NC100150 for steady-state contrast-enhanced peripheral magnetic resonance angiography

The aim of this study was to test the safety and efficacy of NC100150 injection for steady-state contrast-enhanced peripheral MR angiography in a multicentre phase-II trial. Thirty-three patients underwent steady-state NC100150 enhanced MR angiography (5 mg Fe/kg body weight) of the aortoiliac and femoropopliteal arteries. Safety assessment consisted of pre- and post-injection (2, 24 and 72 h) monitoring of vital signs, physical examination as well as laboratory and electrocardiographic parameters. To determine sensitivity and specificity for detection of haemodynamically significant stenoses (HSS; >50% reduction of luminal diameter) MR angiograms were compared with intra-arterial digital subtraction angiography (IA DSA), which was considered the standard of reference. In 33 patients a mean of 12.8 ml NC100150 was injected. Eleven patients reported 13 mild and 2 moderate adverse events. Five mild and one moderate adverse event were considered due to NC100150 injection. There were no significant changes in vital signs, laboratory or electrocardiographic parameters. Sensitivity and specificity (in percent) for detection of HSS were 87 and 64, 56 and 76, and 75 and 84, for iliac, femoral and popliteal arteries, respectively. NC100150 high-resolution steady-state MR angiography can be performed safely and is feasible for the detection of peripheral arterial HSS, but is as yet not a clinically useful alternative to conventional gadolinium-enhanced MR angiography.

Cardiac MRI: recent progress and continued challenges

Cardiac MRI continues to develop and advance. MRI accurately depicts cardiac structure, function, perfusion, and myocardial viability with an overall capacity unmatched by any other single imaging modality. MRI is an accepted and widely utilized tool for cardiovascular research. Its clinical use has been limited, but is increasing because of its proven clinical efficacy, the proliferation of cardiac-capable MRI systems, and the development of improved pulse sequences. The following article reviews the landmark developments in this field, with an emphasis on recent progress in the evaluation of ischemic or acquired heart disease.

Influence of blood-pool contrast media on MR imaging and flow measurements in the presence of pulmonary arterial stents in swine

PURPOSE

To compare the effects of various stents on magnetic resonance (MR) imaging flow volume measurements and to determine the value of a blood-pool MR imaging contrast medium in assessment of vascular stents.

MATERIALS AND METHODS

In 11 pigs, six nitinol stents (Memotherm), four platinum stents (NuMed), and one elgiloy stent (Wallstent) were placed in the main pulmonary artery under x-ray fluoroscopic guidance. MR imaging was performed 3 months after stent placement before and after injection of NC100150 contrast medium. Blood flow volumes were assessed with velocity-encoded cine MR imaging through and next to the stent. The signal-to-noise ratio and width of susceptibility artifacts of the stents also were determined. Measurements were analyzed with the paired Student t test and Bland-Altman test, where appropriate.

RESULTS

Blood flow volumes measured through the nitinol and platinum stents disclosed no significant difference between velocity-encoded cine MR imaging measurements through and next to the stent. On cine MR images, small susceptibility artifacts were observed around the nitinol and platinum stents. Signal-to-noise ratio in the stent lumen was reduced in nitinol and platinum stents when compared with that next to the stent. The elgiloy stent produced severe susceptibility artifacts, making measurement of flow volumes impossible. NC100150 injection caused no significant effect on flow volume measurements. It improved the signal-to-noise ratio of the pulmonary arterial lumen outside and, to a lesser extent, inside the stent.

CONCLUSION

Assessment of morphology and flow volumes through nitinol and platinum stents is feasible with MR imaging. Blood-pool contrast media provide persistent signal enhancement in the pulmonary artery and, to a lesser extent, in the lumina of nitinol and platinum stents.

Blood pool contrast-enhanced MRI detects suppression of microvascular permeability in early postinfarction reperfusion after nicorandil therapy

Nicorandil is an adenosine triphosphate-sensitive potassium channel opener with a nitrate-like effect. It is approved for clinical use in Europe and Japan as an antianginal drug. The purpose of this investigation was to assess the acute effects of nicorandil therapy on microvascular injury using the blood pool MR contrast medium, NC100150 injection (Clariscan). Microvascular injury was produced in 24 rats using 45 min of coronary occlusion / 3 hr reperfusion. Nicorandil was infused at 15 min of occlusion and during reperfusion. Control animals received a saline solution. MR imaging was used to characterize microvascular permeability, quantify the extent of microvascular injury, LV volume, and wall thickness. Hyperenhancement at 30 min after administration of 0.05 mmol/kg Clariscan mapped the extent of ischemia-induced loss of microvascular integrity. The accumulation of Clariscan in the injured region was significantly suppressed in nicorandil compared to control rats. Nicorandil reduced the extent of microvascular injury from 44 +/- 2% to 18 +/- 2% (P < 0.01) and true infarction size from 29 +/- 2% to 12 +/- 1%. The extent of the hyperenhanced region correlated with the true size of area at risk at autopsy. On spin-echo MRI during end-diastole, nicorandil reduced LV end-diastolic volume and preserved wall thickness in remote myocardium; both parameters are markers of LV dilatation caused by acute infarction (remodeling). In conclusion, blood pool contrast-enhanced MRI has the potential to depict and quantify the extent of microvascular permeability and injury. Nicorandil suppressed microvascular permeability, reduced infarction size, and improved LV function in early postinfarction reperfusion.

Coronary MR angiography: experimental results with a monomer-stabilized blood pool contrast medium

PURPOSE

To evaluate the signal-enhancing characteristics of monomer-coated very small superparamagnetic iron oxide (SPIO) particles used as a blood pool contrast medium for magnetic resonance (MR) angiography in the coronary arteries.

MATERIALS AND METHODS

The particles used in this study were coated with citrate as the monomer (VSOP-C91). The particles have a total diameter of 7 nm and show the following relaxivities at 0.47 T: T1, 19 L/mmol. sec(-1); T2, 29 L/mmol. sec(-1). Fifteen cardiac MR examinations were performed at 1.5 T in five pigs. Images were acquired from immediately to 35 minutes (equilibrium phase) after intravenous injection of gadopentetate dimeglumine, gadobenate dimeglumine, and the very small SPIO particles (n = 5 for each substance).

RESULTS

Immediately after administration of gadopentetate dimeglumine, gadobenate dimeglumine, and the very small SPIO particles, respectively, increases in the signal-to-noise ratio in blood were 94%, 103%, and 102% and in myocardium were 83%, 83%, and 29% (P <.05, very small SPIO particles versus the low-molecular-weight gadolinium-based compounds). Differences in the blood-to-myocardium contrast-to-noise ratio and visualization of the coronary arteries and their branches were also significant.

CONCLUSION

VSOP-C91 significantly improves visualization of the coronary arteries at MR angiography from immediately to 35 minutes after injection.

Superparamagnetic iron oxide MION as a contrast agent for sodium MRI in myocardial infarction

An intravascular iron-based contrast agent was used as a sodium (23Na) MRI T2 relaxant in an effort to suppress the blood signal from the ventricular cavities in normal and infarcted canine myocardium in vivo. 23Na MRI signal decreases in blood were attributed to decreases in the fast (T2f) and slow (T2s) transverse relaxation components, which were quantified as a function of dose and MRI echo time (TE). In vivo 23Na MRI signal decreases up to 65% were noted in ventricular blood when imaging under dose and TE conditions of 10 mg/kg body weight and 5 ms, respectively. Contrast injection followed by subsequent 23Na MRI in canine myocardial infarction led to a clear delineation of the location of the injured tissue, as identified by postmortem triphenyltetrazolium chloride staining, and to an improvement in the contrast-to-noise ratio between the blood in the ventricular chamber and the infarcted tissue that was as high as 3.3-fold in the postcontrast images in comparison to the precontrast images.

Gadolinium-enhanced, vessel-tracking, two-dimensional coronary MR angiography: single-dose arterial-phase vs. delayed-phase imaging

The purposes of our study were to investigate the benefits of using a single dose of an extracellular contrast agent for coronary magnetic resonance angiography (CMRA) and to determine the relative benefits of arterial-phase vs. delayed-phase image acquisition. The right coronary artery was imaged in 10 healthy adults using a breath-hold, two-dimensional fast gradient echo pulse sequence designed for vessel tracking (multiphase, multislice image acquisition). Pre- and postcontrast CMRA was performed. Postcontrast imaging consisted of arterial- and delayed-phase CMRA following a 15 mL bolus (single dose) of contrast media and of delayed-phase imaging following a cumulative 45 mL contrast dose (triple dose). Contrast-enhanced CMRA provided a significantly higher (P < 0.001) signal-to-noise ratio (SNR) and contrast-to-noise ratio (CNR) than noncontrast CMRA. CNR was highest for single-dose arterial-phase CMRA (13.1 +/- 4.5) and triple-dose delayed-phase CMRA (13.0 +/- 4.8), followed by single-dose delayed-phase CMRA (8.4 +/- 3.5) and noncontrast CMRA (4.2 +/- 1.8). Single-dose arterial-phase CMRA provided the best visualization of the distal right coronary artery and was preferred for blinded physician assessments. We concluded that utilization of a single dose of extracellular contrast media improves CMRA, especially if timed for arterial-phase imaging. J. Magn. Reson. Imaging 2001;13:682-689.

Contrast-enhanced MR imaging of coronary arteries: comparison of intra- and extravascular contrast agents in swine

PURPOSE

To compare the efficacy of an intravascular contrast agent, gadomer-17, in improving magnetic resonance (MR) imaging of coronary arteries with that of an extravascular agent, gadopentetate dimeglumine, in pigs.

MATERIALS AND METHODS

Eight pigs underwent imaging after three injections: 0.20 mmol of gadopentetate dimeglumine per kilogram of body weight and 0.05 and 0.10 mmol/kg gadomer-17. Coronary images were acquired repeatedly after each injection by using an inversion-recovery-prepared segmented three-dimensional sequence with either breath holding (n = 4) or respiratory gating (n = 4). Coronary artery-to-myocardium contrast-to-noise ratios (CNRs) were compared between injections.

RESULTS

At breath-hold imaging, substantial CNR improvement over precontrast images was observed in images acquired during the first pass of gadopentetate dimeglumine in coronary arteries and up to 6 and 10 minutes after 0.05 and 0.10 mmol/kg of gadomer-17 injections, respectively. The CNR with 0.10 mmol/kg of gadomer-17 was 20% (P <.05) higher than that with gadopentetate dimeglumine at first-pass imaging. At respiratory-gated imaging, significant CNR improvement (P <.05) over precontrast images was observed in images acquired up to 10, 30, and 50 minutes after gadopentetate dimeglumine and both gadomer-17 injections, respectively. The CNR on the first images obtained after 0.10 mmol/kg gadomer-17 injection was 168% (P <.05) higher than that on the images obtained after gadopentetate dimeglumine injection.

CONCLUSION

Gadomer-17 provided greater and more persistent CNR improvements than did gadopentetate dimeglumine; further evaluation of its utility for coronary imaging in humans is warranted.

Blood pool MR contrast agents for cardiovascular imaging

Currently available magnetic resonance (MR) contrast agents are not confined to the intravascular space because of their small molecular size. These agents produce peak vascular enhancement for only a short period. Conversely, blood pool agents have longer intravascular residence time and higher relaxivity. Therefore these agents provide MR angiography with flexibility, versatility, and accuracy. With blood pool agents, the timing of contrast injection becomes less significant because the optimal imaging window is in tens of minutes rather than seconds. In addition, larger anatomic regions can be imaged optimally. Preliminary evidence appears to support the notion that blood pool agents may play a diagnostic role in coronary, peripheral, and pulmonary angiography. Besides their ability to increase vascular contrast, blood pool agents provide physiologic information, including rate of entry, rate of accumulation, and rate of elimination. MR imaging with blood pool agents also have proven to be of significant value in the assessments of myocardial perfusion and microvascular permeability. In anticipation of broad clinical use, blood pool agents are currently being evaluated in human trails. Examples include gadolinium-chelate that binds in vivo to albumin to form blood pool agents and ultrasmall superparamagnetic iron oxide particles. This review discusses the applications of MR blood pool agents in the cardiovascular system. J. Magn. Reson. Imaging 2000;12:890-898.

Evaluation of nonperfused myocardial ischemia with MRI and an intravascular USPIO contrast agent in an ex vivo pig model

The ultrasmall superparamagnetic iron oxide (USPIO) preparation NC100150 Injection (Clariscan; Nycomed Imaging, Oslo, Norway) was tested for its ability to delineate nonperfused myocardium under steady-state conditions. An experimental animal model of focal myocardial ischemia induced by ligation of the distal part of the left anterior descending artery was used. The contrast agent was administered in four doses: 0, 4, 8, and 12 mg Fe/kg body weight. Magnetic resonance examination ex vivo, including T1-, T2-, and T2*-weighted sequences, was performed. Nonperfused myocardium was determined by fluorescein. The best delineation of nonperfused myocardium was found with a T1-weighted inversion recovery/turbo spin-echo sequence and doses of 4 and 8 mg Fe/kg body weight, where 95% of the volume was discernible at the dose of 4 mg Fe/kg body weight. The results suggest that steady-state imaging by T1-weighted sequence with the use of NC100150 Injection to delineate nonperfused myocardium is feasible. J. Magn. Reson. Imaging 2000;12:866-872.

Comparison of Gadomer-17 and gadopentetate dimeglumine for differentiation of benign from malignant breast tumors with MR imaging

RATIONALE AND OBJECTIVES

This study compared gadopentetate dimeglumine (molecular weight, 0.5 kD), a standard contrast medium, and Gadomer-17 (apparent molecular weight, approximately 35 kD), a new, clinically applicable, large-molecular contrast medium, with respect to their microvascular characterizations of experimentally induced breast tumors at magnetic resonance (MR) imaging.

MATERIALS AND METHODS

A spectrum of breast tumors, benign through highly malignant, was induced in Sprague-Dawley rats (n = 30) by intraperitoneal administration of N-ethyl-N-nitrosourea (ENU), a potent carcinogen. All animals underwent three-dimensional spoiled gradient-recalled MR imaging, with precontrast imaging and dynamic postcontrast imaging after injection of gadopentetate dimeglumine (0.1 mmol/kg) and Gadomer-17 (0.03 mmol/kg), administered in a random order at a 24-hour interval. Several microvascular parameters were compared: the endothelial transfer coefficient (K(PS)), a measure of microvascular permeability; the fractional plasma volume (fPV), and the plasma equivalent volume. Each MR imaging parameter was correlated with histopathologic findings.

RESULTS

With Gadomer-17, the mean values for K(PS) and fPV were significantly greater in carcinomas than in fibroadenomas (P < .004 and .04, respectively). With gadopentetate dimeglumine, the mean values for fPV and PEV were significantly greater in carcinomas (P <. 004 and .02, respectively). Because of the high variability within both fibroadenoma and carcinoma groups, however, there were no significant correlations between K(PS), fPV, or PEV and histopathologic tumor grade as indicated by the Scarff-Bloom-Richardson score, for either agent.

CONCLUSION

Although the K(PS) and fPV estimates obtained from dynamic MR imaging data with Gadomer-17 enhancement offer some potential for characterizing breast tumors, none of the quantitative microvascular parameters derived with either agent were significantly correlated with histopathologic tumor grade.

Deep venous thrombosis and consecutive pulmonary embolism as the first sign of an ovarian cancer: MR angiography using an intravascular contrast agent (CLARISCAN)

We describe a case of progressive deep venous thrombosis and chest pain studied by contrast-enhanced magnetic resonance (MR) angiography with the new intravascular contrast medium CLARISCAN (NC100150 Injection). Combined MR venography and angiography demonstrated pelvic vein thrombosis and consecutive pulmonary embolism caused by a large abdominal tumor, diagnosed as an ovarian cancer after surgery. The potential role of an intravascular contrast medium for studying the vascular system in multiple regions of the body within a single examination without the need for bolus timing is discussed. J. Magn. Reson. Imaging 2000;12:497-500.

Value of navigator echo magnetic resonance angiography in detecting occlusion/patency of arterial and venous, single and sequential coronary bypass grafts

Aim of our work was to validate magnetic resonance angiography (MRA) in detecting occlusion/patency of coronary artery bypass grafts. Twenty patients with previous history of bypass surgery and recurrent episodes of chest pain were enrolled. Two patients could not be studied (claustrophobia, erratic breathing). Thus, 18 patients with 51 bypasses were examined using a navigator echo sequence: 21 arterial grafts (six sequential) and 30 saphenous vein grafts (five sequential). All patients had undergone contrast conventional angiography 3-15 days before MRA. The magnetic resonance (MR) data set was analyzed by two independent readers blinded to the results of conventional angiography (occlusion of 12 of 51 grafts). At magnetic resonance, two bypasses of the posterior descending artery, patent at conventional angiography, could not be visualized because of imaging slab malpositioning. Interobserver concordance was 96% (47/49). Magnetic resonance and conventional angiography provided identical answers in 47 out of 49 (96%) of the examined grafts. Eleven out of 12 occluded grafts and 36 out of 37 patent grafts were correctly identified with MR. As far as occlusion is concerned, the sensitivity of MR was 91%, the specificity 97%. To summarize, a 30 min outpatient MR examination is highly reliable in determining occlusion/patency of arterial and venous, single and sequential bypasses.

MR contrast media for myocardial viability, microvascular integrity and perfusion

Cardiovascular imaging requires an appreciation of rapidly evolving MR imaging sequences as well as careful utilization of intravascular, extracellular and intracellular MR contrast media. At the present time, clinical studies are restricted to the use of extracellular MR contrast media. MR imaging has the potential to noninvasively measure multiple parameters of the cardiovascular system in a single imaging session. Recent advances in fast and ultrafast MR imaging have considerably enhanced the capability of this technique, beyond the assessment of left ventricular wall motion and morphology into visualization of the coronary arteries and measurement of blood flow. During the course of the last several years, multiple strategies for imaging viable myocardium have been developed and validated using MR contrast media. Contrast enhanced dynamic MR imaging provides information regarding microvascular integrity and perfusion. Because these information can be provided noninvasively by MR imaging, repeated measurements can be performed in longitudinal studies to monitor the progression or regression of myocardial injury. Similar studies are needed to examine the effects of newly developed cardioprotective therapeutics. Development of suitable intravascular MR contrast medium may be essential for visualization of the coronary arteries and interventional therapies. MR imaging may emerge as one-stop-shop for evaluating the heart and coronary system. This capability will make MR imaging cost-effective in the first decade of this millennium.

Three-dimensional, navigator-echo MR coronary angiography in detecting stenoses of the major epicardial vessels, with conventional coronary angiography as the standard of reference

PURPOSE

To test three-dimensional (3D), navigator-echo magnetic resonance (MR) coronary angiography in detecting stenoses of the coronary arteries.

MATERIALS AND METHODS

Forty-two patients (age range, 50-79 years) underwent MR coronary angiography (1.5 T). A navigator-echo sequence was used. Two or three 15% overlapped transverse slabs were acquired. Data were analyzed by readers blinded to conventional coronary angiographic results. On conventional coronary angiograms, coronary arterial stenoses of 50% or greater narrowing were considered significant. On MR coronary angiograms, the major coronary vessels were subdivided into proximal (within 5 cm) and distal (beyond 5 cm) segments, except for the left main vessel. Stenoses of 50% or greater were identified on reformatted multiplanar MR coronary angiograms.

RESULTS

Three MR coronary angiographic examinations were aborted because of patient claustrophobia; 39 of 39 left main, 117 of 117 proximal, and 78 of 117 distal segments were visualized. MR coronary angiography showed a sensitivity of 82% (95% CI: 73%, 91%) and a specificity of 89% (95% CI: 85%, 94%) in overall stenoses identification, of 90% (95% CI: 81%, 99%) and 90% (95% CI: 83%, 96%) for proximal segments, and of 68% (95% CI: 50%, 86%) and 81% (95% CI: 71%, 92%) for distal segments, respectively.

CONCLUSION

Navigator-echo, 3D MR coronary angiography is a promising sequence for assessing coronary arterial stenoses, but further improvements are required for distal segments.

Three-dimensional cardiac cine magnetic resonance imaging with an ultrasmall superparamagnetic iron oxide blood pool agent (NC100150)

The purpose of this study was to assess image quality of three-dimensional (3D) cardiac cine magnetic resonance (MR) imaging before and after administration of a T1-shortening ultrasmall superparamagnetic iron oxide blood pool agent (NC100150). 3D cardiac cine MR imaging was performed in 13 volunteers using a radiofrequency-spoiled cardiac-gated 3D cine gradient-echo sequence with short repetition and echo times. Compared with precontrast images, postcontrast images showed no enhancement in fat and skeletal muscle, moderate enhancement in myocardium, and significant enhancement in ventricular cavity. After contrast injection, the signal ratio of the ventricular chamber to the myocardium significantly increased, and dramatic improvements were seen in the quality of the cineangiographic images and the depiction of cardiac valves. This quantitative study has shown that 3D cardiac cine MR imaging using a blood pool agent provided MR ventriculography and cineangiography with excellent image quality.

3D MR angiography of the entire aorta: modified application of the body-phased array coil for a single-shot technique

OBJECTIVE

Evaluation of different contrast-enhanced MR angiography imaging protocols for visualization of the entire aorta in breath-hold technique.

METHODS AND PATIENTS

Three different CE (0.15 mmol/kg) MRA protocols were evaluated by phantom and patient studies: (1) two separate MRA with conventional application of the body-phased array coil; (2) a single-shot MRA with modified application of the body-phased array coil; (3) a single-shot MRA with the body coil. Duplex sonography, CTA and DSA were used as standard of reference.

RESULTS

In all examinations the entire aorta could be visualized. The best SNR was acquired with protocol (1). The SNR of protocol (2) was reduced if the sagittal body diameter of the patient was greater than 20 cm and decreased significantly with diameters over 30 cm. By the use of protocol (3) the SNR was notably poor. The quality scored for the visualization of the entire aorta was 97.5% (protocol 1); 92.5% (protocol 2); and 80.0% (protocol 3).

CONCLUSION

In most cases the modified application of the body-phased array coil allows the imaging of the entire aorta as a single-shot 3D CE MRA in diagnostic quality.

MR angiography with superparamagnetic iron oxide: feasibility study

Magnetic resonance (MR) angiography with blood-pool superparamagnetic iron oxide (SPIO) particles was evaluated in the whole-body vascular system. In 12 adult patients, three-dimensional fast imaging with steady-state precession was performed in successive steps from the lungs to the calves before and after a standard dose for liver imaging (15 mumol of iron per kilogram of body weight) of AMI-25. On SPIO-enhanced MR angiograms, visualization of the pulmonary arterial, whole-body, and lower extremity venous systems was graded as good or sufficient in all patients, and femoral vein thrombosis was clearly demonstrated in one patient.

Coronary MRA--a clinical experience in Europe

This review concentrates on contributions from European centers to magnetic resonance (MR) imaging of the coronary arteries. Coronary MR angiography has developed rapidly over the last 10 years, and there has been considerable interaction between Europe and the United States in the technical and clinical developments during this time. The major problems of coronary imaging have been gradually overcome with the combined use of respiratory and cardiac gating, as well as three-dimensional imaging. The ultrafast techniques such as spiral and echoplanar methods are likely to play a larger role in the future, and flow measurements are becoming possible. The next millennium should see the adoption of these techniques into routine clinical practice to allow the safe non-invasive diagnosis of coronary artery disease.J. Magn. Reson. Imaging 1999;10:721-727.

Characterization of t1 relaxation and blood-myocardial contrast enhancement of NC100150 injection in cardiac MRI

A new ultrasmall superparamagnetic iron oxide (Clariscan; NC100150 Injection) was studied in domestic farm pigs. The T1 effects were characterized for blood and myocardium and the blood-myocardial contrast was measured in T1-weighted cine images. The contrast-to-noise ratio (CNR) and signal-to-noise ratio (SNR) were measured at baseline and contrast doses of 1 and 5 mg Fe/kg body weight (bw) at end diastole and late systole. The T1 values for blood and myocardium were reduced by 97 and 43%, respectively, from baseline to 5 mg Fe/kg bw. The CNR was significantly improved with contrast at end diastole and late systole. The maximum improvement shown was 202% at 5 mg Fe/kg bw in late systole. The percent SNR enhancement was significantly higher in blood than myocardium at late systole. NC100150 Injection is an effective T1 shortening agent and can be used to improve blood-myocardial contrast in cine images of the heart. J. Magn. Reson. Imaging 1999;10:784-789.

High-resolution magnetic resonance angiography of the mouse brain: application to murine focal cerebral ischemia models

Three-dimensional time-of-flight high-resolution magnetic resonance angiography was applied to visualize the cerebral vasculature of the mouse brain. In normal mice, angiograms of good quality, showing the essential details of the arterial cerebrovascular anatomy, could be obtained in only 2.5 min without the use of contrast agents. Signals from slowly flowing blood, e.g., in veins, could also be detected after administration of a blood pool contrast agent. The technique was applied to mouse models of permanent and transient brain ischemia, involving the occlusion of the middle cerebral artery. High-resolution magnetic resonance angiography proved to be a very useful tool for verifying the success of the occlusion in these models.

Blood pool contrast agents for cardiovascular MR imaging

The distribution and elimination of contrast agents is mainly determined by their size. First-pass perfusion with the use of blood pool contrast agents (BPCAs) and/or rapid clearance blood-pool-like contrast agents may allow quantitative myocardial perfusion evaluation in patients. This requires contrast bolus injection with a very fast injection speed. A major profit from BPCAs is expected for magnetic resonance angiography (MRA). The persistent signal-enhancing effects of BPCAs allow for a longer acquisition time window, which may be used to increase both the signal-to-noise ratio and/or image resolution. This is of paramount importance for coronary imaging, in which high-resolution imaging is desired. Moreover, the improved acquisition time window can be used to make multiple scans after one contrast injection. The role of ultrasmall paramagnetic iron oxide particles (USPIOs) for MRA is not clear yet, as they are limited by T2* effects at higher doses. Several safety aspects have to be taken into account before BPCAs are applied in humans, for whom toxicity caused by the injection speed is a concern.

Contrast-enhanced MR angiography of the carotid bifurcation

With contrast-enhanced MR angiographic techniques, a T1-shortening contrast agent is injected into the blood stream. Imaging during the first pass of the contrast agent permits acquisition of a high-contrast MR angiogram. Scan parameters such as flip angle, repetition time, echo time, and scan duration, and injection parameters, such as dose and rate, must be carefully chosen to achieve maximum contrast between blood vessels and stationary tissues. A critical parameter affecting image quality is the timing of the acquisition relative to the injection. If the collection of the center of k-space does not coincide with peak arterial concentration, artifacts, reduced SNR, and venous enhancement may result. Several techniques have been developed to address the timing issue. Post-processing techniques such as subtracting a pre-contrast image from a post-contrast angiogram can be used to improve image quality. Intravascular contrast agents that may also lead to improved image quality are currently being developed.

Magnetic resonance perfusion imaging in ischemic heart disease

This review explores the present status of contrast media available for myocardial perfusion studies, the magnetic resonance (MR) sequences adapted to multi-slice first-pass acquisitions, and the issue of myocardial perfusion quantification. To date, only low molecular weight paramagnetic gadolinium chelates have been used in clinical protocols for myocardial perfusion. With the availability of fast MR acquisition techniques to follow the first-pass distribution of the contrast agent in the myocardium, the bolus tracking technique represents the more widely used protocol in MR perfusion studies. On T1-weighted imaging, the ischemic zone appears with a delayed and lower signal enhancement compared with normally perfused myocardium. Visual analysis of the image series can be greatly improved by image post-processing to obtain relative myocardial perfusion maps. With an intravascular tracer, myocardial kinetics are in theory easier to analyze in terms of perfusion. In experimental studies, different intravascular or blood pool MR contrast agents have been tested to measure quantitative perfusion parameters. If a simple flow-limited kinetic model is developed with MR contrast agents, one important clinical application will be the evaluation of the functional consequence of coronary stenoses, ie, non-invasive evaluation of the coronary reserve.