Free-running cardiac magnetic resonance fingerprinting: Joint T1/T2 map and Cine imaging.

PURPOSE: To develop and evaluate a novel non-ECG triggered 2D magnetic resonance fingerprinting (MRF) sequence allowing for simultaneous myocardial T1 and T2 mapping and cardiac Cine imaging. METHODS: Cardiac MRF (cMRF) has been recently proposed to provide joint T1/T2 myocardial mapping by triggering the acquisition to mid-diastole and relying on a subject-dependent dictionary of MR signal evolutions to generate the maps. In this work, we propose a novel "free-running" (non-ECG triggered) cMRF framework for simultaneous myocardial T1 and T2 mapping and cardiac Cine imaging in a single scan. Free-running cMRF is based on a transient state bSSFP acquisition with tiny golden angle radial readouts, varying flip angle and multiple adiabatic inversion pulses. The acquired data is retrospectively gated into several cardiac phases, which are reconstructed with an approach that combines parallel imaging, low rank modelling and patch-based high-order tensor regularization. Free-running cMRF was evaluated in a standardized phantom and ten healthy subjects. Comparison with reference spin-echo, MOLLI, SASHA, T2-GRASE and Cine was performed. RESULTS: T1 and T2 values obtained with the proposed approach were in good agreement with reference phantom values (ICC(A,1) > 0.99). Reported values for myocardium septum T1 were 1043 ± 48 ms, 1150 ± 100 ms and 1160 ± 79 ms for MOLLI, SASHA and free-running cMRF respectively and for T2 of 51.7 ± 4.1 ms and 44.6 ± 4.1 ms for T2-GRASE and free-running cMRF respectively. Good agreement was observed between free-running cMRF and conventional Cine 2D ejection fraction (bias = -0.83%). CONCLUSION: The proposed free-running cardiac MRF approach allows for simultaneous assessment of myocardial T1 and T2 and Cine imaging in a single scan.

Cardiac Magnetic Resonance Fingerprinting: Technical Developments and Initial Clinical Validation.

PURPOSE OF REVIEW: Magnetic resonance imaging (MRI) has enabled non-invasive myocardial tissue characterization in a wide range of cardiovascular diseases by quantifying several tissue specific parameters such as T1, T2, and T2* relaxation times. Simultaneous assessment of these parameters has recently gained interest to potentially improve diagnostic accuracy and enable further understanding of the underlying disease. However, these quantitative maps are usually acquired sequentially and are not necessarily co-registered, making multi-parametric analysis challenging. Magnetic resonance fingerprinting (MRF) has been recently introduced to unify and streamline parametric mapping into a single simultaneous, multi-parametric, fully co-registered, and efficient scan. Feasibility of cardiac MRF has been demonstrated and initial clinical validation studies are ongoing. Provide an overview of the cardiac MRF framework, recent technical developments and initial undergoing clinical validation. RECENT FINDINGS: Cardiac MRF has enabled the acquisition of co-registered T1 and T2 maps in a single, efficient scan. Initial results demonstrate feasibility of cardiac MRF in healthy subjects and small patient cohorts. Current in vivo results show a small bias and comparable precision in T1 and T2 with respect to conventional clinical parametric mapping approaches. This bias may be explained by several confounding factors such as magnetization transfer and field inhomogeneities, which are currently not included in the cardiac MRF model. Initial clinical validation for cardiac MRF has demonstrated good reproducibility in healthy subjects and heart transplant patients, reduced artifacts in inflammatory cardiomyopathy patients and good differentiation between hypertrophic cardiomyopathy and healthy controls. Cardiac MRF has emerged as a novel technique for simultaneous, multi-parametric, and co-registered mapping of different tissue parameters. Initial efforts have focused on enabling T1, T2, and fat quantification; however this approach has the potential of enabling quantification of several other parameters (such as T2*, diffusion, perfusion, and flow) from a single scan. Initial results in healthy subjects and patients are promising, thus further clinical validation is now warranted.

Molecular imaging in cardiovascular diseases.

UNLABELLED: Cardiovascular diseases remain the leading cause of morbidity and mortality in industrialized and developing countries. In clinical practice, the in-vivo identification of atherosclerotic lesions, which can lead to complications such as heart attack or stroke, remains difficult. Imaging techniques provide the reference standard for the detection of clinically significant atherosclerotic changes in the coronary and carotid arteries. The assessment of the luminal narrowing is feasible, while the differentiation of stable and potentially unstable or vulnerable atherosclerotic plaques is currently not possible using non-invasive imaging. With high spatial resolution and high soft tissue contrast, magnetic resonance imaging (MRI) is a suitable method for the evaluation of the thin arterial wall. In clinical practice, native MRI of the vessel wall already allows the differentiation and characterization of components of atherosclerotic plaques in the carotid arteries and the aorta. Additional diagnostic information can be gained by the use of non-specific MRI contrast agents. With the development of targeted molecular probes, that highlight specific molecules or cells, pathological processes can be visualized at a molecular level with high spatial resolution. In this review article, the development of pathophysiological changes leading to the development of the arterial wall are introduced and discussed. Additionally, principles of contrast enhanced imaging with non-specific contrast agents and molecular probes will be discussed and latest developments in the field of molecular imaging of the vascular wall will be introduced. KEY POINTS: Molecular magnetic resonance imaging has great potential to improve the in vivo characterization of atherosclerotic plaques. Based on the molecular information is feasible to enable a better differentiation of stable and unstable (vulnerable) atherosclerotic plaques.

Molecular imaging in cardiovascular diseases.

Cardiovascular diseases remain the leading cause of morbidity and mortality in industrialized and developing countries. In clinical practice, the in-vivo identification of atherosclerotic lesions, which can lead to complications such as heart attack or stroke, remains difficult. Imaging techniques provide the reference standard for the detection of clinically significant atherosclerotic changes in the coronary and carotid arteries. The assessment of the luminal narrowing is feasible, while the differentiation of stable and potentially unstable or vulnerable atherosclerotic plaques is currently not possible using non-invasive imaging. With high spatial resolution and high soft tissue contrast, magnetic resonance imaging (MRI) is a suitable method for the evaluation of the thin arterial wall. In clinical practice, native MRI of the vessel wall already allows the differentiation and characterization of components of atherosclerotic plaques in the carotid arteries and the aorta. Additional diagnostic information can be gained by the use of non-specific MRI contrast agents. With the development of targeted molecular probes, that highlight specific molecules or cells, pathological processes can be visualized at a molecular level with high spatial resolution. In this review article, the development of pathophysiological changes leading to the development of the arterial wall are introduced and discussed. Additionally, principles of contrast enhanced imaging with non-specific contrast agents and molecular probes will be discussed and latest developments in the field of molecular imaging of the vascular wall will be introduced.

Detection of intracoronary thrombus by magnetic resonance imaging in patients with acute myocardial infarction.

BACKGROUND: Persistent intracoronary thrombus after plaque rupture is associated with an increased risk of subsequent myocardial infarction and mortality. Coronary thrombus is usually visualized invasively by x-ray coronary angiography. Non-contrast-enhanced T1-weighted magnetic resonance (MR) imaging has been useful for direct imaging of carotid thrombus and intraplaque hemorrhage by taking advantage of the short T1 of methemoglobin present in acute thrombus and intraplaque hemorrhage. The aim of this study was to investigate the use of non-contrast-enhanced MR for direct thrombus imaging (MRDTI) in patients with acute myocardial infarction. METHODS AND RESULTS: Eighteen patients (14 men; age, 61±9 years) underwent MRDTI within 24 to 72 hours of presenting with an acute coronary syndrome before invasive x-ray coronary angiography; MRDTI was performed with a T1-weighted, 3-dimensional, inversion-recovery black-blood gradient-echo sequence without contrast administration. Ten patients were found to have intracoronary thrombus on x-ray coronary angiography (left anterior descending, 4; left circumflex, 2; right coronary artery, 4; and right coronary artery-posterior descending artery, 1), and 8 had no visible thrombus. We found that MRDTI correctly identified thrombus in 9 of 10 patients (sensitivity, 91%; posterior descending artery thrombus not detected) and correctly classified the control group in 7 of 8 patients without thrombus formation (specificity, 88%). The contrast-to-noise ratio was significantly greater in coronary segments containing thrombus (n=10) compared with those without visible thrombus (n=131; mean contrast-to-noise ratio, 15.9 versus 2.6; P<0.001). CONCLUSION: Use of MRDTI allows selective visualization of coronary thrombus in a patient population with a high probability of intracoronary thrombosis.

High spatial resolution and high contrast visualization of brain arteries and veins: impact of blood pool contrast agent and water-selective excitation imaging at 3T.

PURPOSE: To investigate a blood pool contrast agent and water-selective excitation imaging at 3 T for high spatial and high contrast imaging of brain vessels including the veins. METHODS AND RESULTS: 48 clinical patients (47 ± 18 years old) were included. Based on clinical findings, twenty-four patients received a single dose of standard extracellular Gadoterate-meglumine (Dotarem®) and 24 received the blood pool contrast agent Gadofosveset (Vasovist®). After finishing routine MR protocols, all patients were investigated with two high spatial resolution (0.15 mm (3) voxel size) gradient echo sequences in random order in the equilibrium phase (steady-state) as approved by the review board: A standard RF-spoiled gradient-echo sequence (HR-SS, TR/TE 5.1/2.3 msec, FA 30°) and a fat-suppressed gradient-echo sequence with water-selective excitation (HR-FS, 1331 binominal-pulse, TR/TE 8.8/3.8 msec, FA 30°). The images were subjectively assessed (image quality with vessel contrast, artifacts, depiction of lesions) by two investigators and contrast-to-noise ratios (CNR) were compared using the Student's t-test. The image quality and CNR in the HR-FS were significantly superior compared to the HR-SS for both contrast agents (p < 0.05). The CNR was also improved when using the blood pool agent but only to a minor extent while the subjective image quality was similar for both contrast agents. CONCLUSION: The utilized sequence with water-selective excitation improved image quality and CNR properties in high spatial resolution imaging of brain arteries and veins. The used blood pool contrast agent improved the CNR only to a minor extent over the extracellular contrast agent.

[MR imaging of lymph nodes using Gadofluorine M: feasibility in a swine model at 1.5 and 3T]. / MR-Bildgebung von Lymphknoten mit Gadofluorine M in einem Schweinemodell bei 1,5 and 3T.

PURPOSE: To investigate the potential of Gadofluorine M for targeted lymph node imaging in a human size animal model and on a clinical MR scanner at 1.5 and 3 T. MATERIALS AND METHODS: Pelvic and cervical lymph nodes in a swine model were investigated prior to and 24 hours after intravenous administration of 50 micromol/kg body weight Gadofluorine M, an experimental contrast agent. MR imaging was carried out on clinical 1.5 T and 3 T whole-body MR systems using clinically available coils and T 1-weighted sequences. The signal-to-noise ratio (SNR) and contrast-to-noise ratio (CNR) with respect to the surrounding tissue were assessed and compared using the Student's t-test. The Gd concentration in the lymph nodes (n = 43) was measured post mortem by Inductively Coupled Plasma-Atomic Emission Spectroscopy (ICP-AES). RESULTS: Gadofluorine M allowed for high signal and high contrast visualization of lymph nodes in all stations on post-contrast images with a significantly increased SNR and CNR (SNR pelvic lymph nodes post vs. pre: 46 +/- 7 vs.14 +/- 3, SNR cervical lymph nodes post vs. pre: 105 +/- 64 vs. 32 +/- 21; CNR pelvic lymph node vs. muscle post vs. pre 28 +/- 5 vs. 0.2 +/- 0.5, CNR cervical lymph node vs. muscle post vs. pre 76 +/- 53 vs. 11 +/- 15, p < 0.05 for all comparisons). The SNR and CNR in the pelvis were further improved using 3 T compared to 1.5 T scanners (SNR lymph nodes 3 T vs. 1.5 T 84 +/- 6 vs. 46 +/- 7, CNR lymph node vs. muscle 3 T vs. 1.5 T 53 +/- 9 vs. 28 +/- 5 respectively, p < 0.05). A high concentration of Gd in the lymph nodes was found (149 +/- 25 mmol Gd/L). CONCLUSION: Gadofluorine M accumulates in the lymph nodes and allows for selective targeted high contrast MR imaging of lymph node tissue in a large animal model using clinically available MR imaging techniques. 3 T further improves SNR and CNR compared to 1.5 T.

Flow-targeted inversion-prepared b-TFE coronary MR angiography: initial results in patients.

PURPOSE: Visualization of coronary blood flow in the right and left coronary system in volunteers and patients by means of a modified inversion-prepared bright-blood coronary magnetic resonance angiography (cMRA) sequence. MATERIALS AND METHODS: cMRA was performed in 14 healthy volunteers and 19 patients on a 1.5 Tesla MR system using a free-breathing 3D balanced turbo field echo (b-TFE) sequence with radial k-space sampling. For magnetization preparation a slab selective and a 2D selective inversion pulse were used for the right and left coronary system, respectively. cMRA images were evaluated in terms of clinically relevant stenoses (< 50 %) and compared to conventional catheter angiography. Signal was measured in the coronary arteries (coro), the aorta (ao) and in the epicardial fat (fat) to determine SNR and CNR. In addition, maximal visible vessel length, and vessel border definition were analyzed. RESULTS: The use of a selective inversion pre-pulse allowed direct visualization of the coronary blood flow in the right and left coronary system. The measured SNR and CNR, vessel length, and vessel sharpness in volunteers (SNR coro: 28.3 +/- 5.0; SNR ao: 37.6 +/- 8.4; CNR coro-fat: 25.3 +/- 4.5; LAD: 128.0 cm +/- 8.8; RCA: 74.6 cm +/- 12.4; Sharpness: 66.6 % +/- 4.8) were slightly increased compared to those in patients (SNR coro: 24.1 +/- 3.8; SNR ao: 33.8 +/- 11.4; CNR coro-fat: 19.9 +/- 3.3; LAD: 112.5 cm +/- 13.8; RCA: 69.6 cm +/- 16.6; Sharpness: 58.9 % +/- 7.9; n.s.). In the patient study the assessment of 42 coronary segments lead to correct identification of 10 clinically relevant stenoses. CONCLUSION: The modification of a previously published inversion-prepared cMRA sequence allowed direct visualization of the coronary blood flow in the right as well as in the left coronary system. In addition, this sequence proved to be highly sensitive regarding the assessment of clinically relevant stenotic lesions.

Whole-heart coronary magnetic resonance angiography: value for the detection of coronary artery stenoses in comparison to multislice computed tomography angiography.

BACKGROUND: Coronary magnetic resonance imaging and computed tomography are being discussed as alternatives to catheter angiography in the detection of coronary artery disease. Yet, only few comparative validations have been performed. PURPOSE: To compare steady-state free precession whole heart coronary magnetic resonance imaging (MRI) with multidetector coronary computed tomography angiography (CTA) for the detection of coronary artery disease using catheter angiography as the standard of reference. MATERIAL AND METHODS: Twenty patients with known CAD were examined with navigator (NAV) gated and corrected free-breathing 3D balanced gradient echo whole heart coronary MRI and coronary CTA. Subjective overall image quality (4 point scale, 1 = excellent), visibility of vessel segments and accuracy for the detection of significant coronary stenoses (>50%) were compared to coronary x-ray angiography by two blinded readers. RESULTS: Median of subjective image quality was 3 for coronary MRI and 2 for coronary CTA. Of a total of 209 segments, 67 segments (32%) had to be excluded from the evaluation by coronary MRI (61 due to insufficient image quality and 6 due to stent artifacts). For coronary CTA, 31 segments (15%) had to be excluded from the evaluation (12 due to insufficient image quality, 15 due to severe calcifications superimposing the vessel lumen and 4 due to stent artifacts. Segment based values for the detection of >/=50% diameter coronary x-ray angiographic stenoses were: specificity: MRI 88%, CTA 95%; sensitivity: MRI 82%, CTA 84%; diagnostic accuracy: MRI 87%, CTA 93%; positive predictive value: MRI 68%, CTA 77% and negative predictive value: MRI 94%, CTA 95%. CONCLUSION: Coronary WH-MRI was inferior to coronary CTA regarding image quality and number of evaluable segments but both had similar diagnostic value for the detection and exclusion of CAD when only evaluable segments were included.

Molecular coronary MR imaging of human thrombi using EP-2104R, a fibrin-targeted contrast agent: experimental study in a swine model.

PURPOSE: The aim of this study was to investigate the use of a fibrin-specific contrast agent (EP-2104R, EPIX Pharmaceuticals, Lexington, Massachusetts, USA) for targeted molecular magnetic resonance (MR) imaging of human clot material removed from patients in a model of coronary thrombosis in swine. MATERIALS AND METHODS: Freshly ex vivo engineered clots from human blood and human in situ developed clots removed from patients were delivered into the coronary arteries of nine domestic swine. For MR imaging a navigator-gated, free-breathing, cardiac-triggered 3D inversion recovery black-blood gradient echo sequence was performed prior to clot delivery (baseline), after clot delivery but prior to contrast media administration, and two hours after systemic (i.v.) injection of 4 micromol/kg EP-2104R. MR images were analyzed by two investigators and the contrast-to-noise ratio and Gadolinium (Gd) concentration in the clots were assessed. RESULTS: On baseline images and prior to contrast media application no thrombi were visible. Post contrast administration all 10 coronary emboli (five ex vivo engineered clots and five human clots removed from patients) were selectively visualized as white spots with a mean contrast-to-noise ratio to the blood pool and the surrounding tissue of >12 and a mean Gd concentration of >100 microM. CONCLUSION: Molecular MR imaging using the fibrin-targeted contrast agent EP-2104R allows selective visualization of human clot material in a model of coronary thrombosis in swine.

Analysis of residual coronary artery motion for breath hold and navigator approaches using real-time coronary MRI.

Coronary artery MRI methods utilize breath holds, or diaphragmatic navigators, to compensate for respiratory motion. To increase image quality and navigator (NAV) gating efficiency, slice tracking is used, with more sophisticated affine motion models recently introduced. This study assesses the extent of remaining coronary artery motion in free breathing NAV and single and multi breath hold coronary artery MRI. Additionally, the effect of the NAV gating window size was examined. To visualize and measure the respiratory induced motion, an image containing a coronary artery cross section was acquired at each heartbeat. The amount of residual coronary artery displacement was used as a direct measure for the performance of the respiratory motion correction method. Free breathing studies with motion compensation (slice tracking with 5 mm gating window) had a similar amount of residual motion (0.76+/-0.17 mm) as a single breath hold (0.52+/-0.20 mm) and were superior to multiple breath holds (1.22+/-0.60 mm). Affine NAV methods allowed for larger gating windows ( approximately 10 mm windows) with similar residual motion (0.74+/-0.17 mm). In this healthy adult cohort (N=10), free-breathing NAV methods offered respiratory motion suppression similar to a single breath hold.

Inversion prepared coronary MR angiography: direct visualization of coronary blood flow.

PURPOSE: Visualization of coronary blood flow by means of a slice-selective inversion pre-pulse in concert with bright-blood coronary MRA. MATERIALS AND METHODS: Coronary magnetic resonance angiography (MRA) of the right coronary artery (RCA) was performed in eight healthy adult subjects on a 1.5 Tesla MR system (Gyroscan ACS-NT, Philips Medical Systems, Best, NL) using a free-breathing navigator-gated and cardiac-triggered 3D steady-state free-precession (SSFP) sequence with radial k-space sampling. Imaging was performed with and without a slice-selective inversion pre-pulse, which was positioned along the main axis of the coronary artery but perpendicular to the imaging volume. Objective image quality parameters such as SNR, CNR, maximal visible vessel length, and vessel border definition were analyzed. RESULTS: In contrast to conventional bright-blood 3D coronary MRA, the selective inversion pre-pulse provided a direct measure of coronary blood flow. In addition, CNR between the RCA and right ventricular blood pool was increased and the vessels had a tendency towards better delineation. Blood SNR and CNR between right coronary blood and epicardial fat were comparable in both sequences. CONCLUSION: The combination of a free-breathing navigator-gated and cardiac-triggered 3D SSFP sequence with a slice-selective inversion pre-pulse allows for direct and directional visualization of coronary blood flow with the additional benefit of improved contrast between coronary and right ventricular blood pool.

[Technical aspects of MR coronary angiography]. / Technische Aspekte der MR-Koronarangiographie.

Within the past several years, MR angiography (MRA) has experienced major technological improvements. Whereas the contrast enhanced MRA of non-coronary vessels has become established in routine clinical diagnostics, MR coronary angiography still represents technical challenges to the MR scientists and clinical investigators. To allow diagnostic quality MR coronary angiography, precise and reliable visualization of small tortuous vessels moving at fast speed is necessary. This article reviews the basic principles of MRA with special consideration to MR coronary artery imaging.

Impact of bulk cardiac motion on right coronary MR angiography and vessel wall imaging.

The purpose of this study was to investigate the impact of in-plane coronary artery motion on coronary magnetic resonance angiography (MRA) and coronary MR vessel wall imaging. Free-breathing, navigator-gated, 3D-segmented k-space turbo field echo ((TFE)/echo-planar imaging (EPI)) coronary MRA and 2D fast spin-echo coronary vessel wall imaging of the right coronary artery (RCA) were performed in 15 healthy adult subjects. Images were acquired at two different diastolic time periods in each subject: 1) during a subject-specific diastasis period (in-plane velocity <4 cm/second) identified from analysis of in-plane coronary artery motion, and 2) using a diastolic trigger delay based on a previously implemented heart-rate-dependent empirical formula. RCA vessel wall imaging was only feasible with subject-specific middiastolic acquisition, while the coronary wall could not be identified with the heart-rate-dependent formula. For coronary MRA, RCA border definition was improved by 13% (P < 0.001) with the use of subject-specific trigger delay (vs. heart-rate-dependent delay). Subject-specific middiastolic image acquisition improves 3D TFE/EPI coronary MRA, and is critical for RCA vessel wall imaging.

3D coronary vessel wall imaging utilizing a local inversion technique with spiral image acquisition.

Current 2D black blood coronary vessel wall imaging suffers from a relatively limited coverage of the coronary artery tree. Hence, a 3D approach facilitating more extensive coverage would be desirable. The straightforward combination of a 3D-acquisition technique together with a dual inversion prepulse can decrease the effectiveness of the black blood preparation. To minimize artifacts from insufficiently suppressed blood signal of the nearby blood pools, and to reduce residual respiratory motion artifacts from the chest wall, a novel local inversion technique was implemented. The combination of a nonselective inversion prepulse with a 2D selective local inversion prepulse allowed for suppression of unwanted signal outside a user-defined region of interest. Among 10 subjects evaluated using a 3D-spiral readout, the local inversion pulse effectively suppressed signal from ventricular blood, myocardium, and chest wall tissue in all cases. The coronary vessel wall could be visualized within the entire imaging volume.

Direct comparison of 3D spiral vs. Cartesian gradient-echo coronary magnetic resonance angiography.

While 3D thin-slab coronary magnetic resonance angiography (MRA) has traditionally been performed using a Cartesian acquisition scheme, spiral k-space data acquisition offers several potential advantages. However, these strategies have not been directly compared in the same subjects using similar methodologies. Thus, in the present study a comparison was made between 3D coronary MRA using Cartesian segmented k-space gradient-echo and spiral k-space data acquisition schemes. In both approaches the same spatial resolution was used and data were acquired during free breathing using navigator gating and prospective slice tracking. Magnetization preparation (T(2) preparation and fat suppression) was applied to increase the contrast. For spiral imaging two different examinations were performed, using one or two spiral interleaves, during each R-R interval. Spiral acquisitions were found to be superior to the Cartesian scheme with respect to the signal-to-noise ratio (SNR) and contrast-to-noise-ratio (CNR) (both P < 0.001) and image quality. The single spiral per R-R interval acquisition had the same total scan duration as the Cartesian acquisition, but the single spiral had the best image quality and a 2.6-fold increase in SNR. The double-interleaf spiral approach showed a 50% reduction in scanning time, a 1.8-fold increase in SNR, and similar image quality when compared to the standard Cartesian approach. Spiral 3D coronary MRA appears to be preferable to the Cartesian scheme. The increase in SNR may be "traded" for either shorter scanning times using multiple consecutive spiral interleaves, or for enhanced spatial resolution.

The impact of navigator timing parameters and navigator spatial resolution on 3D coronary magnetic resonance angiography.

The impact of navigator spatial resolution and navigator evaluation time on image quality in free-breathing navigator-gated 3D coronary magnetic resonance angiography (MRA), including real-time motion correction, was investigated in a moving phantom. Objective image quality parameters signal-to-noise ratio (SNR) and vessel sharpness were compared. It was found that for improved mage quality a short navigator evaluation time is of crucial importance. Navigator spatial resolution showed minimal influence on image quality.

In vivo magnetic resonance imaging of experimental thrombosis in a rabbit model.

The process of atherosclerotic plaque disruption has been difficult to monitor because of the lack of an animal model and the limited ability to directly visualize the plaque and overlying thrombus in vivo. Our aim was to validate in vivo magnetic resonance imaging (MRI) of the thrombus formation after pharmacological triggering of plaque disruption in the modified Constantinides animal model of plaque disruption. Atherosclerosis was induced in 9 New Zealand White male rabbits (3 kg) with aortic balloon endothelial injury followed by a high cholesterol (1%) diet for 8 weeks. After baseline (pretrigger) MRI, the rabbits underwent pharmacological triggering with Russell's viper venom and histamine, followed by another MRI 48 hours later. Contiguous cross-sectional T2-weighted fast spin echo images of the abdominal aorta were compared by histopathology. In all animals, aortic wall thickening was present on the pretrigger MRI. On MRIs performed 48 hours after triggering, a histologically confirmed intraluminal thrombus was visualized in 6 (67%) of the 9 animals. MRI data correlated with the histopathology regarding aortic wall thickness (R=0.77, P<0.0005), thrombus size (R=0.82, P<0.0001), thrombus length (R=0.86, P<0.005), and anatomic location (R=0.98, P<0.0001). In vivo, MRI reliably determines the presence, location, and size of the thrombus in this animal model of atherosclerosis and plaque disruption. The combination of in vivo MRI and the modified Constantinides animal model could be an important research tool for our understanding of the pathogenesis of acute coronary syndromes.

Motion artifact reduction and vessel enhancement for free-breathing navigator-gated coronary MRA using 3D k-space reordering.

Breathing-induced bulk motion of the myocardium during data acquisition may cause severe image artifacts in coronary magnetic resonance angiography (MRA). Current motion compensation strategies include breath-holding or free-breathing MR navigator gating and tracking techniques. Navigator-based techniques have been further refined by the applications of sophisticated 2D k-space reordering techniques. A further improvement in image quality and a reduction of relative scanning duration may be expected from a 3D k-space reordering scheme. Therefore, a 3D k-space reordered acquisition scheme including a 3D navigator gated and corrected segmented k-space gradient echo imaging sequence for coronary MRA was implemented. This new zonal motion-adapted acquisition and reordering technique (ZMART) was developed on the basis of a numerical simulation of the Bloch equations. The technique was implemented on a commercial 1.5T MR system, and first phantom and in vivo experiments were performed. Consistent with the results of the theoretical findings, the results obtained in the phantom studies demonstrate a significant reduction of motion artifacts when compared to conventional (non-k-space reordered) gating techniques. Preliminary in vivo findings also compare favorably with the phantom experiments and theoretical considerations. Magn Reson Med 45:645-652, 2001.