Blood pool agent strongly improves 3D magnetic resonance coronary angiography using an inversion pre-pulse

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.

Coronary magnetic resonance angiography

Coronary magnetic resonance angiography (MRA) is a powerful noninvasive technique with high soft-tissue contrast for the visualization of the coronary anatomy without X-ray exposure. Due to the small dimensions and tortuous nature of the coronary arteries, a high spatial resolution and sufficient volumetric coverage have to be obtained. However, this necessitates scanning times that are typically much longer than one cardiac cycle. By collecting image data during multiple RR intervals, one can successfully acquire coronary MR angiograms. However, constant cardiac contraction and relaxation, as well as respiratory motion, adversely affect image quality. Therefore, sophisticated motion-compensation strategies are needed. Furthermore, a high contrast between the coronary arteries and the surrounding tissue is mandatory. In the present article, challenges and solutions of coronary imaging are discussed, and results obtained in both healthy and diseased states are reviewed. This includes preliminary data obtained with state-of-the-art techniques such as steady-state free precession (SSFP), whole-heart imaging, intravascular contrast agents, coronary vessel wall imaging, and high-field imaging. Simultaneously, the utility of electron beam computed tomography (EBCT) and multidetector computed tomography (MDCT) for the visualization of the coronary arteries is discussed.

Fast 3D coronary artery contrast-enhanced magnetic resonance angiography with magnetization transfer contrast, fat suppression and parallel imaging as applied on an anthropomorphic moving heart phantom

A magnetic resonance sequence for high-resolution imaging of coronary arteries in a very short acquisition time is presented. The technique is based on fast low-angle shot and uses fat saturation and magnetization transfer contrast prepulses to improve image contrast. GeneRalized Autocalibrating Partially Parallel Acquisitions (GRAPPA) is implemented to shorten acquisition time. The sequence was tested on a moving anthropomorphic silicone heart phantom where the coronary arteries were filled with a gadolinium contrast agent solution, and imaging was performed at varying heart rates using GRAPPA. The clinical relevance of the phantom was validated by comparing the myocardial relaxation times of the phantom's homogeneous silicone cardiac wall to those of humans. Signal-to-noise ratio and contrast-to-noise ratio were higher when parallel imaging was used, possibly benefiting from the acquisition of one partition per heartbeat. Another advantage of parallel imaging for visualizing the coronary arteries is that the entire heart can be imaged within a few breath-holds.

SENSE or k-MAG to Accelerate Free Breathing Navigator-Guided Coronary MR Angiography

OBJECTIVE

The purpose of this study was to assess the relative merits of reducing the scanning time of navigator-guided (NAV) coronary MR angiography by including, both independently and in combination, two time-saving strategies: k-space weighted motion-adapted gating (k-MAG) and sensitivity encoding (SENSE, factor = 2).

SUBJECTS AND METHODS

Coronary arteries of 21 healthy subjects were imaged with four NAV MR angiography sequences: conventional NAV sequence, NAV with the addition of SENSE, NAV with the addition of k-MAG, and NAV with a combination of SENSE and k-MAG. All imaging parameters including the magnetization preparation schemes, prescribed spatial resolution, and acquisition duration per R-R interval were identical for all techniques. The total scanning time, navigator efficiency, visible length of the coronary artery, and subjective image quality were used as metrics for evaluating the performance of the techniques.

RESULTS

The results show that the addition of k-MAG to NAV coronary MR angiography (with or without SENSE) improved scan efficiency and decreased scanning time by an average of 17% without compromising the length of coronary artery visible or the image quality. The addition of SENSE to the NAV technique (with or without k-MAG) reduces the scanning time by an average of 50%.

CONCLUSION

While the average image quality of coronary arteries was unaffected by the addition of k-MAG to navigator techniques, there was a slight reduction in image quality scores for the navigator sequence with SENSE. Identification of the proximal coronary arteries was not hampered by the addition of k-MAG, SENSE, or both to the NAV coronary MR angiography sequence.

Comparison of Gradient-Echo and Steady-State Free Precession for Coronary Artery Magnetic Resonance Angiography Using a Gadolinium-Based Intravascular Contrast Agent

OBJECTIVES

Intravascular contrast agents may offer longer imaging times and better vessel visualization over conventional extravascular agents for magnetic resonance coronary angiography. The purpose of this study was to evaluate the effect of intravascular contrast (B-22956/1) on coronary visualization. Signal-to-noise ratio (SNR) and contrast-to-noise ratio (CNR) were compared in inversion-recovery (IR)-prepared FLASH (fast low-angle shot) and IR-trueFISP (true fast imaging with steady-state precession) sequences before and after contrast.

MATERIALS AND METHODS

Numeric simulations were performed to compare blood signals in IR-trueFISP and IR-FLASH sequences. Coronary imaging was performed in 15 swine.

RESULTS

Postcontrast CNR was improved 23% with breathhold IR-FLASH and 55% with breathhold IR-trueFISP as compared with precontrast trueFISP. With free-breathing, long TR IR-FLASH provided 131% and 55.8% higher SNR and 132% and 58.7% increased CNR compared with IR-FLASH with shorter TR and IR-trueFISP, respectively.

CONCLUSION

Intravascular contrast agents improve CNR and vessel visualization in coronary magnetic resonance angiography with IR-FLASH and IR-trueFISP.

Gadocoletic Acid Trisodium Salt (B22956/1)

RATIONALE AND OBJECTIVES

Inversion recovery, three-dimensional, gradient-recalled echo magnetic resonance coronary angiography (IR-3D-GRE-MRCA), performed after administration of an intravascular T1-relaxing agent with prolonged permanence in the blood, is one of the most promising approaches to noninvasive magnetic resonance imaging (MRI) of the coronaries. The aim of the present study was the evaluation of the physicochemical properties in solution, pharmacokinetics, elimination from the body, protein binding, and signal enhancement characteristics of gadocoletic acid trisodium salt (B22956/1), a candidate gadolinium-based MRI contrast agent for coronary angiography.

METHODS

The pharmacokinetics and elimination from the body of gadocoletate ion, the contrastographically active component of gadocoletic acid trisodium salt, was evaluated after intravenous administration in rats and monkeys, using for assays high-performance liquid chromatography, x-ray fluorescence, and inductively coupled plasma atomic emission spectrometry. The binding of the gadocoletate ion to animal and human serum albumin was studied by means of ultrafiltration. The imaging properties of blood outside coronary arteries after contrast agent administration were evaluated in cynomolgus monkeys (Macaca fascicularis) by measuring aortic signal-to-noise and contrast-to-noise ratios in lower body angiograms. The suitability of gadocoletic acid trisodium salt for achieving contrast-enhanced magnetic resonance coronary angiography (ceMRCA) was tested in Yucatan micropigs with an IR-3D-GRE sequence. All in vivo relaxation rate measurement and images were obtained using a 1.5 T Siemens Symphony scanner.

RESULTS

The fractional binding of gadocoletate ion at a concentration of 0.5 mM to serum albumin at the physiological concentration was 95%, 92%, 88%, and 86% for human, monkey, pig, and rat, respectively. In rats and monkeys, gadocoletate ion was excreted unmetabolized through the biliary and urinary routes. It was recovered with feces depending on the injected dose in percentages from 18% to 97%, providing evidence for a saturable biliary pathway. Plasma pharmacokinetics showed the complete elimination of gadocoletate ion within 24 hours after administration. In the monkey, the gadocoletate ion showed the pharmacokinetic behavior of a compound with partial vascular confinement and long plasma half-life, which may be ascribed to elevated binding to serum albumin. These properties manifested themselves in lower body angiograms with excellent image contrast between vessels and muscle. The slowly decaying aortic blood signal-to-noise and contrast-to-noise ratios over a 15-minute period is expected to allow 3-dimensional coronary angiography. The potential of gadocoletic acid trisodium salt for ceMRCA was also demonstrated in Yucatan micropigs. Elevated blood signal intensity and almost total myocardial signal suppression was maintained for almost 1 hour after administration, ie, for much longer than expected to be necessary for coronary angiography. During the whole period high resolution images of the right coronary artery could be obtained.

CONCLUSIONS

On the basis of the pharmacokinetic profile and imaging characteristics, gadocoletic acid trisodium salt shows promise as a MR contrast agent for coronary angiography.

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

OBJECTIVE

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

MATERIALS AND METHODS

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

RESULTS

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

CONCLUSION

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

Retrospective gating for mouse cardiac MRI

Cardiac MR imaging in small animals presents some difficulties due to shorter cardiac cycles and smaller dimensions than in human beings, but prospectively gated techniques have been successfully applied. As with human imaging, there may be certain applications in animal imaging for which retrospective gating is preferable to prospective gating. For example, cardiac imaging in multiple mice simultaneously is one such application. In this work we investigate the use of retrospective gating for cardiac imaging in a mouse. Using a three-dimensional imaging protocol, we show that image quality with retrospective gating is comparable to prospectively gated imaging. We conclude that retrospective gating is applicable for small animal cardiac MRI and show how it can be applied to the problem of cardiac MRI in multiple mice.

Magnetic resonance angiography of coronary arteries with a 3-dimensional magnetization-prepared true fast imaging with steady-state precession sequence compared with conventional coronary angiography

BACKGROUND

The aim of the study was to compare the detection of clinically significant coronary artery stenosis using a magnetic resonance 3-dimensional (3D) breath-hold true fast imaging with steady-state precession (trueFISP) sequence with conventional coronary angiography.

METHODS

Twenty-nine patients who were scheduled to undergo or had recently undergone diagnostic conventional coronary angiogram participated in this study. The left main, left anterior descending, left circumflex, and right coronary arteries were studied using the 3D breath-hold trueFISP technique. Each artery was imaged with 1 acquisition in 16 to 32 heartbeats. The image quality, vessel length, and presence or absence of stenosis were evaluated. A score of 1 to 3 (1 = noninterpretable, 2 = good, 3 = excellent) was used to assess image quality. The sensitivity, specificity, accuracy, positive predictive value, and negative predictive value of magnetic resonance angiography in detecting significant coronary artery stenosis (> 50% luminal narrowing) on conventional coronary angiogram were calculated.

RESULTS

Of 116 vessels, 108 were assessed in 29 patients. Twenty vessels that had image quality score of 1 were excluded from further evaluation. The mean lengths of vessels visualized were the following: left anterior descending 3.6 cm, left circumflex 3.4 cm, and right coronary 6.6 cm. The entire length of the left main coronary artery was visualized. For the visualized arterial segments, the sensitivity, specificity, accuracy, positive predictive value, and negative predictive value for detecting significant coronary artery stenosis were 92.8%, 95.3%, 95.0%, 68.4%, and 99.2%, respectively.

CONCLUSIONS

The 3D breath-hold trueFISP technique, which uses the endogenous contrast of blood, is potentially useful in ruling out significant coronary artery stenosis but not yet sensitive enough as a screening tool.

Coronary magnetic resonance imaging: visualization of the vessel lumen and the vessel wall and molecular imaging of arteriothrombosis

Coronary magnetic resonance (MR) imaging has dramatically emerged over the last decade. Technical improvements have enabled reliable visualization of the proximal and midportion of the coronary artery tree for exclusion of significant coronary artery disease. However, current technical developments focus also on direct visualization of the diseased coronary vessel wall and imaging of coronary plaque because plaques without stenoses are typically more vulnerable with higher risk of plaque rupture. Plaque rupture with subsequent thrombosis and vessel occlusion is the main cause of myocardial infarction. Very recently, the first success of molecular imaging in the coronary arteries has been demonstrated using a fibrin-specific contrast agent for selective visualization of coronary thrombosis. This demonstrates in general the high potential of molecular MR imaging in the field of coronary artery disease. In this review, we will address recent technical advances in coronary MR imaging, including visualization of the lumen and the vessel wall and molecular imaging of coronary arteriothrombosis. First results of these new approaches will be discussed.

Spiral coronary angiography using a blood pool agent

PURPOSE

To experimentally investigate the optimum dose of an iron-oxide-based blood pool agent for spiral coronary MR angiography (MRA), and the difference between single and multiple spiral excitations in each cardiac cycle.

MATERIALS AND METHODS

Images using single and triple spiral excitations in each cardiac cycle were obtained in late diastole of the left main coronary artery in eight pigs following an inversion prepulse. Measurements were obtained before and after injection of increasing doses of an iron oxide blood pool agent (Clariscan) corresponding to concentrations of 0.8, 2.2, and 3.9 mg Fe/kg BW. The signal-to-noise ratio (SNR) and contrast-to-noise ratio (CNR) were measured.

RESULTS

For 0.8 mg Fe/kg BW relative to precontrast values, a significant increase was observed for both one (SNR: 2.3, CNR: 3.8) and three (SNR: 1.4, CNR: 2.2) excitations (P < 0.01). When the dose was increased from 0.8 mg Fe/kg BW to 2.2 mg Fe/kg BW, only the SNR (P < 0.01) increased further. Significantly higher CNR (1.6-1.8) and SNR (1.4-1.6) values were seen for one excitation relative to three excitations at all concentrations (P < 0.05).

CONCLUSION

At low concentrations, an iron oxide blood pool agent can increase SNR and CNR significantly with both single excitation and triple excitations using an inversion-prepared spiral acquisition scheme. At higher concentrations, T2* effects reduce image quality.

Improved three-dimensional free-breathing coronary magnetic resonance angiography using gadocoletic acid (B-22956) for intravascular contrast enhancement

PURPOSE

To evaluate gadocoletic acid (B-22956), a gadolinium-based paramagnetic blood pool agent, for contrast-enhanced coronary magnetic resonance angiography (MRA) in a Phase I clinical trial, and to compare the findings with those obtained using a standard noncontrast T2 preparation sequence.

MATERIALS AND METHODS

The left coronary system was imaged in 12 healthy volunteers before B-22956 application and 5 (N = 11) and 45 (N = 7) minutes after application of 0.075 mmol/kg of body weight (BW) of B-22956. Additionally, imaging of the right coronary system was performed 23 minutes after B-22956 application (N = 6). A three-dimensional gradient echo sequence with T2 preparation (precontrast) or inversion recovery (IR) pulse (postcontrast) with real-time navigator correction was used. Assessment of the left and right coronary systems was performed qualitatively (a 4-point visual score for image quality) and quantitatively in terms of signal-to-noise ratio (SNR), contrast-to-noise ratio (CNR), vessel sharpness, visible vessel length, maximal luminal diameter, and the number of visible side branches.

RESULTS

Significant (P < 0.01) increases in SNR (+42%) and CNR (+86%) were noted five minutes after B-22956 application, compared to precontrast T2 preparation values. A significant increase in CNR (+40%, P < 0.05) was also noted 45 minutes postcontrast. Vessels (left anterior descending artery (LAD), left coronary circumflex (LCx), and right coronary artery (RCA)) were also significantly (P < 0.05) sharper on postcontrast images. Significant increases in vessel length were noted for the LAD (P < 0.05) and LCx and RCA (both P < 0.01), while significantly more side branches were noted for the LAD and RCA (both P < 0.05) when compared to precontrast T2 preparation values.

CONCLUSION

The use of the intravascular contrast agent B-22956 substantially improves both objective and subjective parameters of image quality on high-resolution three-dimensional coronary MRA. The increase in SNR, CNR, and vessel sharpness minimizes current limitations of coronary artery visualization with high-resolution coronary MRA.

Coronary artery magnetic resonance angiography

Coronary magnetic resonance angiography (coronary MRA) continues to advance rapidly from both a technical and clinical perspective. Coronary MRA has benefited directly from improvements in spatial resolution, contrast definition, and advances in motion correction, which have furthered its routine use in evaluating coronary artery bypass grafts and anomalous coronary arteries. Work in refining the techniques for more accurate identification of coronary artery disease (CAD) continues, with advances in navigator-gated and breath-hold motion correction techniques, novel k-space strategies (e.g., spiral and radial k-space filling), development and application of intravascular contrast agents, and imaging at higher field strengths. Ultimately, these developments may lead to the routine application of coronary MRA as a screening tool for CAD. This article reviews the development of coronary MRA, discusses the requirements and tools necessary for optimal visualization of the coronary arteries, and describes the application of coronary MRA to acquired and congenital CAD.

Clinical utility of computed tomography and magnetic resonance techniques for noninvasive coronary angiography

OBJECTIVE

The purpose of this study was to provide a comprehensive review of the literature relating to electron beam angiography (EBA), magnetic resonance angiography, and spiral computed tomography, currently the three most promising noninvasive methods to visualize obstructions in the coronary tree.

BACKGROUND

Given the high costs and invasiveness of coronary angiography, there is increased interest in noninvasive coronary angiography, which has made great strides to become a clinically useful tool to augment conventional coronary angiography (CCA).

METHODS

MEDLINE searches were performed to include all articles related to noninvasive angiography utilizing either magnetic resonance imaging (MRI), multi-row detector spiral computed tomography (MDCT), and electron beam tomography (EBT). Weighted analysis was performed to define the published sensitivity and specificity for each technique.

RESULTS

Electron beam angiography (EBA) provides an overall sensitivity of 87% and specificity of 91% for the detection of obstructive coronary artery disease (CAD). Four-level MDCT data demonstrated an overall sensitivity of 59% and specificity of 89%, with higher accuracy in two recent studies of 16-level detector devices. Magnetic resonance angiography demonstrated sensitivity for detection of obstructive CAD of 77% and specificity of 71%.

CONCLUSIONS

Noninvasive coronary angiography is a rapidly developing technique and currently not an alternative to CCA in all cases. All three methods are currently used clinically in certain centers with appropriate expertise. Selective use should prove both cost-effective and provide a safer, less-invasive method for patients to determine the need for medical versus revascularization therapy.

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.

Three-dimensional navigator coronary MRA with the aid of a blood pool agent in pigs: Improved image quality with inclusion of the contrast agent first-pass

PURPOSE

To evaluate the effect of including the first-pass of a blood pool agent (BPA) on the image quality of three-dimensional navigator coronary MRA.

MATERIALS AND METHODS

A pig model was used to perform: 1) T1 simulation of the BPA, based on actual blood samples, and 2) BPA-enhanced three-dimensional navigator coronary MRA, with or without inclusion of the first-pass of the BPA. The acquisitions with inclusion of the first-pass were timed with the use of a test bolus. The acquisitions without first-pass were started one minute after bolus injection (steady-state). A gradient echo acquisition technique with centric k-space sampling was applied. Comparison of both acquisitions was based on determination of contrast-to-noise ratio (CNR), signal-to-noise ratio (SNR), and vessel length.

RESULTS

T1 simulation shows a distinct T1 reduction during first-pass (to a level below 50 msec), increasing to 190 msec during steady-state. Images obtained with first-pass inclusion showed improved CNR (8.6 +/- 1.7 vs. 4.5 +/- 1.8), SNR (11.9 +/- 1.6 vs. 7.4 +/- 2.0), and vessel length (99.2 +/- 10.9 mm vs. 60.5 +/- 21.8 mm) as compared to the acquisitions during steady-state only (all: P< 0.05).

CONCLUSION

The image quality of three-dimensional navigator coronary MRA combined with a gadolinium BPA in pigs is improved when starting the image acquisition during first-pass of the bolus.

Comparison between Gd-DTPA and several bisamide derivatives as potential MRI contrast agents

Four neutral gadolinium complexes of diethylenetriaminepentaacetic acid (DTPA)-bisamide derivatives have been synthesized and characterized. Their potential application as tissue-specific and low-osmolarity MRI contrast agents has been evaluated by in vitro and in vivo experiments. Their measured relaxivities in D(2)O, bovine serum albumin and human serum transferrin solutions showed favorable relaxation ability. In vivo studies have proven that Gd(DTPA-BDMA), Gd(DTPA-BIN), and Gd(cyclic-DTPA-1,2-pn) could be promising liver-specific MRI contrast agents and Gd(DTPA-BDMA), and Gd(cyclic-DTPA-1,2-pn) have favorable renal excretion capability. Among them, Gd(cyclic-DTPA-1,2-pn) is a more powerful hepatic contrast agent and Gd(DTPA-BIN) provides the stable imaging contrast for several hours. They also show a lower toxicity.

Improved MR coronary angiography with use of a new rapid clearance blood pool contrast agent in pigs

PURPOSE

To evaluate in an animal model the potential for clinical use of a new rapid clearance blood pool contrast agent to improve free-breathing and breath-hold magnetic resonance (MR) coronary angiography.

MATERIALS AND METHODS

Free-breathing and breath-hold MR coronary angiography were performed in a pig model (n = 9) (a) without use of a contrast agent; (b) with P792 (Guerbet Research, Aulnay Sous Bois, France), a monodisperse monogadolinated macromolecular compound that acts as a blood pool contrast agent with rapid clearance properties; and (c) with an extravascular gadolinium-based contrast agent. This resulted in six imaging options, which were compared in terms of contrast-to-noise ratio (CNR), signal-to-noise ratio, and vessel length measurements by using the Student t test.

RESULTS

Use of P792 improved CNR and visible vessel length significantly with both MR respiratory motion correction approaches, as compared with nonenhanced MR imaging (P <.05). CNR was improved by 76% (from 5.0 to 8.6) with the free-breathing approach and by 34% (from 6.2 to 8.2) with the breath-hold approach. Visible vessel length was increased by 27% (from 79.7 to 99.2 mm) with the free-breathing approach and by 90% (from 48.2 to 86.5 mm) with the breath-hold approach. The P792-enhanced free-breathing approach allowed more distal visualization of the coronary arteries than did the P792-enhanced breath-hold approach (P <.05). Use of the extravascular contrast agent did not improve image quality significantly when compared with that of nonenhanced MR images.

CONCLUSION

Use of P792 improves coronary artery MR imaging in conjunction with free-breathing and breath-hold approaches.

Improvement of image quality of non-invasive coronary artery imaging with magnetic resonance by the use of the intravascular contrast agent Clariscan (NC100150 injection) in patients with coronary artery disease

PURPOSE

To assess the feasibility of Clariscan, an intravascular contrast agent, for free breathing, navigator assisted, high resolution, three-dimensional-magnetic resonance coronary angiography (MRCA) in patients, as extracellular contrast agents are unfavorable for the improvement of image quality.

MATERIALS AND METHODS

MRCA was performed in 10 patients with known coronary artery disease (CAD) with (1-5 mg Fe/kg body weight) and without contrast agent.

RESULTS

Compared to unenhanced images, Clariscan did not improve signal-to-noise (SNR) or contrast-to-noise ratios (CNR) compared to fat or myocardium in the proximal parts of the coronary arteries. However, when analyzing the peripheral parts (>4 cm from origin), CNR(fat) and CNR(myo) improved up to a factor of 1.81 and 5.85, respectively, at a dose of 3 mg Fe/kg body weight, while SNR did not reach statistical significance. The visible length of the coronary arteries was improved from 49 +/- 18 mm to 73 +/- 33 mm. The proximal diameter was reduced from 3.6 +/- 0.8mm to 3.2 +/- 0.8 mm, representing more closely the diameter of 3.1 +/- 0.7 mm measured by quantitative coronary angiography. Of 11 significant stenoses (>50%), eight were identified in the enhanced compared to six in the unenhanced images.

CONCLUSION

The use of Clariscan at a dose of 2-3 mg Fe/kg body weight improves image quality of three-dimensional-MRCA, especially in the peripheral segments, and, thus, the diagnostic accuracy for the detection of CAD.

Coronary MR angiography clinical applications and potential for imaging coronary artery disease

Over the past decade, CMRA has emerged as a unique clinical imaging tool with applications in selected populations. Patients with suspected coronary artery anomalies and patients with Kawasaki disease and coronary aneurysms are among those for whom CMRA has demonstrated clinical usefulness. For assessment of patients with atherosclerotic CAD, CMRA is useful for detection of patency of bypass grafts. At centers with appropriate expertise and resources, CMRA also appears to be of value for exclusion of severe proximal multivessel CAD in selected patients. Data from multicenter trials will continue to define the clinical role of CMRA, particularly as it relates to assessment of CAD. Future developments and enhancements of CMRA promise better lumen and coronary artery wall imaging. This may become the new target in noninvasive evaluation of CAD.

Cardiac MR imaging

There has been tremendous progress for MR imaging depiction of cardiac morphology and function. Further advances toward achieving faster acquisition with real-time imaging, higher resolution for plaque imaging, and quantitative analysis are taking place at a rapid pace.

Two- and three-dimensional MR coronary angiography with intraarterial injections of contrast agent in dogs: a feasibility study

Magnetic resonance (MR) images of coronary arteries were acquired with an inversion recovery-prepared technique after intraarterial injection of contrast material in five dogs. Real-time two-dimensional projection images were obtained with a temporal resolution of 3 frames per second. Three-dimensional electrocardiographically triggered high-spatial-resolution images were obtained with a fraction of the contrast agent required for intravenous injections. Background tissues were adequately suppressed in all images. On the basis of this experimental data, the optimal contrast agent concentration for two-dimensional real-time projection imaging was 6%. This preliminary work shows that contrast material-enhanced MR angiography with intraarterial injections is feasible with the proposed techniques.

Performance of a new gadolinium-based intravascular contrast agent in free-breathing inversion-recovery 3D coronary MRA

In three-dimensional (3D) coronary magnetic resonance angiography (MRA), the in-flow contrast between the coronary blood and the surrounding myocardium is attenuated as compared to thin-slab two-dimensional (2D) techniques. The application of a gadolinium (Gd)-based intravascular contrast agent may provide an additional source of signal and contrast by reducing T(1blood) and supporting the visualization of more distal or branching segments of the coronary arterial tree. In six healthy adults, the left coronary artery (LCA) system was imaged pre- and postcontrast with a 0.075-mmol/kg bodyweight dose of the intravascular contrast agent B-22956. For imaging, an optimized free-breathing, navigator-gated and -corrected 3D inversion recovery (IR) sequence was used. For comparison, state-of-the-art baseline 3D coronary MRA with T(2) preparation for non-exogenous contrast enhancement was acquired. The combination of IR 3D coronary MRA, sophisticated navigator technology, and B-22956 allowed for an extensive visualization of the LCA system. Postcontrast, a significant increase in both the signal-to-noise ratio (SNR; 46%, P < 0.05) and contrast-to-noise ratio (CNR; 160%, P < 0.01) was observed, while vessel sharpness of the left anterior descending (LAD) artery and the left coronary circumflex (LCX) were improved by 20% (P < 0.05) and 18% (P < 0.05), respectively.

Multislice breath-hold spiral magnetic resonance coronary angiography in patients with coronary artery disease: effect of intravascular contrast medium

PURPOSE

First, to apply a breath-hold multislice 2D spiral magnetic resonance (MR) approach in patients acquiring within 16 heartbeats (acquisition window, 116 msec) a 10-mm-thick stack of four slices (resolution, 1.3 x 1.3 mm(2)); and second, to evaluate the effect of an intravascular Fe-based contrast medium (CM) on a signal-to-noise ratio (SNR) and a contrast-to-noise ratio (CNR).

MATERIALS AND METHODS

In each patient one or two coronary arteries were imaged prior to and following cumulative doses of 0.25, 0.5, and 0.75 mg of Fe/kg of body weight (bw) of an intravascular CM (CLARISCAN trade mark, Nycomed-Amersham, Princeton, NJ, USA) containing ultrasmall superparamagnetic iron oxide (USPIO) particles.

RESULTS

On precontrast maximum intensity projection (MIP) images generated from the stack of slices, 10 and 11 stenoses of 12 stenoses confirmed by coronary angiography were detected by readers 1 and 2, respectively. SNR and CNR in the coronary arteries peaked at 0.50 mg of Fe/kg of bw, yielding a slight increase of 15.5% and 18.4%, respectively (P < 0.05 vs. precontrast), which did not improve detection of coronary artery stenoses.

CONCLUSION

The presented multislice spiral approach allows display of coronary anatomy in MIP formats for convenient display of coronary stenoses. The pulse sequence did not benefit from an intravascular USPIO-based CM, since little improvement in SNR and CNR was achieved.

Navigator-gated free-breathing three-dimensional balanced fast field echo (TrueFISP) coronary magnetic resonance angiography

RATIONALE AND OBJECTIVES

Recent developments of MR imaging equipment enabled high-quality steady state-free-precession (Balanced FFE, True-FISP) MR-imaging with a substantial 'T2 like' contrast, resulting in a high signal intensity of the blood-pool without the application of exogenous contrast agents. It is hypothesized that Balanced-FFE may be valuable for contrast enhancement in 3D free-breathing coronary MRA.

MATERIALS AND METHODS

Navigator-gated free-breathing cardiac triggered coronary MRA was performed in 10 healthy adult subjects and three patients with radiograph defined coronary artery disease using a segmented k-space 3D Balanced FFE imaging sequence.

RESULTS

High contrast-to-noise ratio between the blood-pool and the myocardium (29 +/- 8) and long segment visualization of both coronary arteries could be obtained in about 5 minutes during free breathing using the present navigator-gated Balanced-FFE coronary MRA approach. First patient results demonstrated successful display of coronary artery stenoses.

CONCLUSION

Balanced FFE offers a potential alternative for endogenous contrast enhancement in navigator-gated free-breathing 3D coronary MRA. The obtained results together with the relatively short scanning time warrant further studies in larger patient collectives.

"Soap-Bubble" visualization and quantitative analysis of 3D coronary magnetic resonance angiograms

In order to compare coronary magnetic resonance angiography (MRA) data obtained with different scanning methodologies, adequate visualization and presentation of the coronary MRA data need to be ensured. Furthermore, an objective quantitative comparison between images acquired with different scanning methods is desirable. To address this need, a software tool ("Soap-Bubble") that facilitates visualization and quantitative comparison of 3D volume targeted coronary MRA data was developed. In the present implementation, the user interactively specifies a curved subvolume (enclosed in the 3D coronary MRA data set) that closely encompasses the coronary arterial segments. With a 3D Delaunay triangulation and a parallel projection, this enables the simultaneous display of multiple coronary segments in one 2D representation. For objective quantitative analysis, frequently explored quantitative parameters such as signal-to-noise ratio (SNR); contrast-to-noise ratio (CNR); and vessel length, sharpness, and diameter can be assessed. The present tool supports visualization and objective, quantitative comparisons of coronary MRA data obtained with different scanning methods. The first results obtained in healthy adults and in patients with coronary artery disease are presented.

Comparison of contrast-enhanced breath-hold and free-breathing respiratory-gated imaging in three-dimensional magnetic resonance coronary angiography

Suppression of respiratory motion is one of the major challenges of magnetic resonance (MR) coronary angiography. Two approaches to compensate for respiratory motion have often been proposed: breath-hold (BH) and free-breathing respiratory-gated (FBRG) imaging. So far, however, these approaches have never been directly compared. MR coronary angiography was performed in 32 patients with suspected coronary artery disease. MR data were acquired using contrast-enhanced BH and FBRG 3-dimensional MR coronary angiographic techniques. MR images were compared with regard to image quality using quantitative parameters and with regard to accuracy for stenosis detection in the proximal and mid-coronary segments in comparison to x-ray angiography. With regard to image quality, BH was superior to FBRG. Signal-to-noise ratio was 29.1 +/- 10.7 for BH versus 18.8 +/- 9.7 for FBRG (p <0.05) and contrast-to-noise was 18.0 +/- 7.4 for BH versus 11.3 +/- 7.9 for FBRG (p </=0.05). One hundered seventy-one of 224 coronary artery segments (76%) were evaluable in BH compared with 155 of 224 in FBRG (69%). In the evaluable segments, BH demonstrated a sensitivity of 87% (26 of 30 stenoses detected) and specificity of 92% (129 of 141 nonstenotic segments correctly identified), whereas FBRG showed a sensitivity of 60% (15 of 25) and specificity of 89% (115 of 130). Overall accuracy was 91% (155 of 171) for BH and 84% (130 of 155) for FBRG. Sensitivity was significantly higher for BH (p = 0.0320), whereas specificity and overall accuracy were not significantly different. Thus, contrast-enhanced BH MR coronary angiography compares favorably to FBRG imaging with regard to image quality and detection of coronary stenoses.

Passive catheter tracking using MRI: comparison of conventional and magnetization-prepared FLASH

PURPOSE

To compare a magnetization-prepared gradient-echo (GRE) sequence with a conventional GRE sequence for visualizing contrast agent-filled catheters.

MATERIALS AND METHODS

Passive visualization of endovascular catheters using MRI was compared between two imaging sequences: 1) inversion recovery (IR)-fast low angle shot (FLASH), and 2) conventional FLASH. Two-dimensional projection images of the catheters filled with 4% diluted contrast agent in a phantom and the aorta of swine were obtained with each sequence with a temporal resolution of two frames per second. We compared background suppression and catheter visibility using the catheter-to-background signal ratio and the ratings of two radiologists.

RESULTS

In the phantom, IR-FLASH allowed for a 200% increase in catheter-to-background ratio (p < 0.01) and improved depiction of catheters over conventional FLASH. In swine, the IR-FLASH images showed a statistically significant improvement of 80% (p < 0.001) over conventional FLASH in all comparisons of the catheter-to-background signal ratio, and an improvement of 160% (p < 0.05) in comparison with the radiologists' observations.

CONCLUSION

This study shows that IR-FLASH is a better technique for passive tracking of contrast agent-filled catheters than conventional FLASH.

A direct comparison of noninvasive coronary angiography by electron beam tomography and navigator-echo-based magnetic resonance imaging for the detection of restenosis following coronary angioplasty

RATIONALE AND OBJECTIVES

To compare electron beam tomography (EBT) with MR imaging (MRI) for detection of restenosis after coronary angioplasty (PTCA).

METHODS

One hundred eighteen patients after PTCA were investigated. By EBT, 50 axial images were acquired (3-mm slice thickness, 120-160 mL radiographic contrast agent). MRI was performed using respiratory-gated sequences (24-48 cross-sections, 2-mm slice thickness, 20 mL Gd-DTPA). EBT and MRI images were evaluated concerning high-grade post-PTCA restenosis (> or = 70%) and validated against coronary angiography.

RESULTS

In EBT, 28 patients and in MRI, 31 patients were not evaluable. In the remaining patients, sensitivity for restenosis detection was 90% in EBT (17/19) and 73% in MRI (11/15; P = 0.370). In EBT, specificity was significantly higher (66% vs. 49%, P = 0.043). Overall accuracy was 71% for EBT and 53% for MRI (P = 0.014).

CONCLUSIONS

For the detection of high-grade restenosis after PTCA, EBT demonstrated significantly higher accuracy than MRI.

MRA of the lower extremities in patients with pulmonary embolism using a blood pool contrast agent: initial experience

PURPOSE

To evaluate the feasibility of blood pool contrast-enhanced magnetic resonance angiography (MRA) to visualize the arterial and venous vessel tree and to detect deep venous thrombosis (DVT) of the lower extremities.

MATERIALS AND METHODS

Nine consecutive patients with pulmonary embolism (mean age = 46 +/- 9) were randomized to various doses of NC100150 (between 0.75 and 6 mg of Fe/kg of body weight). A T1-weighted (T1W) 3D gradient recalled echo (GRE) sequence (TE = 2.0 msec, TR = 5.0 msec) was used. Two observers blinded to the dose of contrast agent assessed image quality, contrast attenuation, and appearance of thrombi.

RESULTS

Qualitative assessment of overall MRA image quality and semiquantitative vessel scoring revealed good to excellent delineation of venous and arterial vessel segments independent of the dose of NC100150. However, quantitative region of interest analysis revealed a significantly higher signal-to-noise ratio (SNR) in the high-dose group than in the mid- and low-dose groups of NC100150 (P < 0.01). Between dose groups, the SNR was independent of vessel type (artery or vein) and vessel segment localization (proximal or distal). All seven venous thrombi (mean length = 7.2 +/- 0.95 cm) were characterized by a very low signal intensity (SI), which was only 16.6 +/- 7% of the SI in adjacent venous segments (P < 0.0001).

CONCLUSION

High-quality MR angiograms of the lower extremities can be obtained using low concentrations of NC100150 in combination with a strong T1W 3D GRE sequence. The obvious delineation of venous thrombi suggests that this technique may be potentially used as a noninvasive "one-stop shopping" tool in the evaluation of thromboembolic disease.

Coronary magnetic resonance angiography: experimental evaluation of the new rapid clearance blood pool contrast medium P792

The signal-enhancing characteristics of a new monodisperse monogadolinated macromolecular MR contrast medium (P792) were evaluated for magnetic resonance angiography (MRA) of the coronary arteries. A total of 15 cardiac examinations were performed in pigs at 1.5 T using a 3D gradient-echo sequence. Images were acquired during breath-hold before and up to 35 min after IV injection of Gd-DTPA (0.3 mmol Gd/kg), Gd-BOPTA (0.2 mmol Gd/kg), and P792 (13 micromol Gd/kg). An increase in the signal-to-noise ratio (SNR) of 97% +/- 17%, 108% +/- 37%, and 109% +/- 31% in coronary arteries and of 82% +/- 19%, 82% +/- 24%, and 28% +/- 18% in myocardium, respectively, was measured during the first postcontrast acquisition. The blood-to-myocardium signal-difference-to-noise ratio (SDNR) was significantly higher for P792 than for the other Gd compounds (P <.05) for up to 15 min after injection. Qualitative assessment showed that visualization of the coronary arteries and their branches was significantly better for P792 compared to the low-molecular Gd compounds (P <.05). The blood pool contrast medium P792 is well suited for MRA of the coronary arteries.

Accelerated coronary MRA by simultaneous acquisition of multiple 3D stacks

The implementation and first in vivo results of a novel coronary magnetic resonance angiography (MRA) protocol allowing simultaneous acquisition of multiple geometrically independent 3D imaging stacks are presented. Each imaging stack is acquired in a separate cardiac phase using an individual magnetization preparation and navigator-based gating and prospective motion correction. Each stack covers one of the main coronary vessels. Thus, an improvement of scan efficiency was achieved, which was used in this study to reduce total scan time at standard image quality. Experiments performed in healthy volunteers and in patients using a two-stack approach yielded a total scan time reduction of 50% with an image quality equivalent to standard single-stack coronary MRA.

Contrast-enhanced coronary MR angiography: relationship between coronary artery delineation and blood T1

Contrast-enhanced coronary angiography has become an important technique for magnetic resonance (MR) coronary artery imaging. However, the relationship between the quality of the coronary artery images and blood T1 has not yet been fully explored. In this paper, we assessed this relationship in an animal model by using a prototypical blood pool agent. With accumulated injections of this agent, the blood T1 would be maintained at different levels. The measured blood T1 values in vivo were 147 +/- 3, 82 +/- 6, 48 +/- 4, 40 +/- 3, and 30 +/- 8 msec (N = 7). Fixed and variable flip angle schemes were used in coronary artery imaging. The signal to noise ratios (SNR) of coronary arteries were measured and the image quality was assessed. It was found that blood T1 less than 80 msec might be desired. No statistically significant difference was observed between two flip angle schemes. There was better vessel definition using variable flip angle at blood T1 lower than 50 msec. Understanding this relationship may be beneficial to optimizing image protocol and/or design of blood pool contrast agents for contrast-enhanced coronary angiography.

Navigator Echo-Based Respiratory Gating for Three-Dimensional MR Coronary Angiography: Reduction of Scan Time Using a Slice Interpolation Technique

PURPOSE

The aim of the study was to compare a conventional respiratory-gated 3D MR coronary angiographic technique (conventional MRCA) with a respiratory-gated 3D MR coronary angiographic technique that includes a slice interpolation technique (slice interpolation MRCA). Both MRCA techniques were compared based on the quality of visualization of the coronary arteries and the diagnostic accuracy in identifying hemodynamically significant coronary artery stenoses.

METHOD

Forty patients with known proximal coronary artery stenosis after conventional CA were examined on a 1.5 T scanner, that is, 20 patients with each sequence. A 6 point grading system (0 = worst quality, 5 = best quality) was used to evaluate and compare the image quality. The length and proximal diameter of the depicted coronary arteries were measured. Detection of coronary artery stenoses was compared with that obtained by conventional CA by two blinded readers.

RESULTS

With the slice interpolation technique, the average scan time of the entire heart was reduced by approximately 40%. With use of conventional MRCA, 69% of all proximal and middle coronary artery segments were visualized with a sufficient image quality; with the slice interpolation technique, 79% of these segments were depicted adequately. For the assessment of stenoses, sensitivity was 71% and specificity was 53% for conventional MRCA and 72 and 60% for slice interpolation MRCA, respectively. These differences in sensitivity and specificity were statistically not significant.

CONCLUSION

The application of a slice interpolation technique reduces the scan time, maintains a comparable sensitivity and specificity for the assessment of coronary artery stenoses, and increases the number of completely identified coronary artery segments compared with the conventional technique.

Coronary arteries: magnetization-prepared contrast-enhanced three-dimensional volume-targeted breath-hold MR angiography

A volume-targeted contrast agent-enhanced breath-hold coronary magnetic resonance angiographic technique was optimized and evaluated in 16 volunteers. Substantial increases in coronary signal-to-noise ratio, contrast-to-noise ratio, lengths of depiction, and vessel sharpness were observed on enhanced images. The imaging approach with two 20-mL injections of contrast agent covers the left and right coronary arteries in two breath holds and is a promising method for coronary imaging.

Measurement of the gadopentetate dimeglumine partition coefficient in human myocardium in vivo: normal distribution and elevation in acute and chronic infarction

PURPOSE

To establish a method for measuring the partition coefficient (lambda) of gadopentetate dimeglumine in humans in vivo, evaluate the spatial and intersubject variation in the lambda of normal myocardium, and compare these values on a regional basis with lambda values of acute and chronic infarcted myocardium.

MATERIALS AND METHODS

Twelve healthy subjects and patients with acute (n = 5) or chronic (n = 5) myocardial infarction underwent magnetic resonance imaging at 1.5 T. Look-Locker images were acquired at four short-axis levels to measure myocardial and blood longitudinal relaxation time at baseline and after a 30-40-minute infusion of gadopentetate dimeglumine. lambda was calculated as DeltaR1(M)/DeltaR1(B, )where M = myocardium, and B = blood.

RESULTS

The magnitude of the estimated lambda in normal myocardium was uniform over the entire myocardium at 0.56 mL/g +/- 0.10 (SD). The lambda values in patients with acute (0.91 mL/g +/- 0.11, P <.001) or chronic (lambda = 0.78 mL/g +/- 0.09, P <.001) infarction were significantly elevated, as compared with those in healthy subjects. A 20% elevation in lambda, as compared with the mean value of a corresponding normal circumferential segment, allowed identification of chronically (sensitivity, 88%; specificity, 96%) or acutely (sensitivity, 100%; specificity, 98%) infarcted segments.

CONCLUSION

Quantification of the lambda in vivo allows differentiation between normal and acutely or chronically infarcted myocardium, with high sensitivity and specificity.

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.

Three-dimensional high-resolution fast spin-echo coronary magnetic resonance angiography

Due to SNR constraints, current "bright-blood" 3D coronary MRA approaches still suffer from limited spatial resolution when compared to conventional x-ray coronary angiography. Recent 2D fast spin-echo black-blood techniques maximize signal for coronary MRA at no loss in image spatial resolution. This suggests that the extension of black-blood coronary MRA with a 3D imaging technique would allow for a further signal increase, which may be traded for an improved spatial resolution. Therefore, a dual-inversion 3D fast spin-echo imaging sequence and real-time navigator technology were combined for high-resolution free-breathing black-blood coronary MRA. In-plane image resolution below 400 microm was obtained. Magn Reson Med 45:206-211, 2001.

Noninvasive detection of coronary artery stenosis using contrast-enhanced three-dimensional breath-hold magnetic resonance coronary angiography

OBJECTIVES

The purpose of this study was to evaluate a contrast-enhanced three-dimensional (3D) breath-hold magnetic resonance (MR) technique for detection of coronary artery stenoses.

BACKGROUND

The accuracy of previously published MR coronary angiography protocols varies widely. Recently, coronary artery imaging using T1-shortening contrast agent has become possible, but so far there are no data concerning its clinical application.

METHODS

Magnetic resonance coronary angiography was performed in 50 patients with suspected coronary artery disease. Magnetic resonance data acquisition using an ultrafast 3D gradient-echo sequence lasted over 32 heartbeats within one single breath-hold. Twenty milliliters of gadopentetate dimeglumine was injected at a flow rate of 1 ml/s for two successive studies covering the main coronary arteries in single-oblique planes. Stenosis assessment by MR was compared with significant (diameter stenosis > 50%) stenoses on X-ray angiography. Evaluation was limited to the proximal and mid-coronary artery segments.

RESULTS

Two hundred sixty-eight of 350 artery segments (76.6%) could be evaluated. Left circumflex coronary artery was only evaluable in 50% of cases by MR. In the evaluable segments, 48 of 56 stenoses and 193 of 212 nonstenotic segments were correctly classified by MR. On a patient basis, MR correctly identified 34 of 36 patients with and 8 of 14 patients without significant coronary stenoses as demonstrated by X-ray angiography (sensitivity 94.4%, specificity 57.1%).

CONCLUSIONS

Oblique projection contrast-enhanced MR coronary angiograms obtained within one single breath-hold permit identification of patients with coronary stenoses in the proximal and mid segments of the major coronary arteries with satisfactory accuracy.

Repeated 3D coronary MR angiography with navigator echo gating: technical quality and consistency of image interpretation

The purpose of this study was to evaluate the technical quality of 3D coronary MR angiography (CMRA) with navigator echo and the consistency of image interpretation in repeated imaging sessions. Fourteen subjects underwent CMRA, 10 of whom were imaged twice. The coronary arteries (96 segments) were analyzed twice for hemodynamically significant stenoses. Signal-to-noise and contrast-to-noise ratios varied considerably between the two imagings. Fat saturation was poor or satisfactory in 37%; in 15% of the slabs, the severity of artifacts was moderate; and the overall quality was good to excellent in only 42% of the imagings. The intraobserver reproducibility was good (kappa = 0.54), but the consistency of interpretation for repeated CMRA was only satisfactory (kappa = 0.43). Sensitivities of 84 and 84% and specificities of 70 and 62% were obtained for the two readings. Although the reproducibility of image reading is good, 3D CMRA with navigator echo provides only fair technical consistency, and the frequently compromised image quality impairs the clinical utility of this technique.

Contrast agent-enhanced, free-breathing, three-dimensional coronary magnetic resonance angiography

For free-breathing, high-resolution, three-dimensional coronary magnetic resonance angiography (MRA), the use of intravascular contrast agents may be helpful for contrast enhancement between coronary blood and myocardium. In six patients, 0.1 mmol/kg of the intravascular contrast agent MS-325/AngioMARK was given intravenously followed by double-oblique, free-breathing, three-dimensional inversion-recovery coronary MRA with real-time navigator gating and motion correction. Contrast-enhanced, three-dimensional coronary MRA images were compared with images obtained with a T2 prepulse (T2Prep) without exogenous contrast. The contrast-enhanced images demonstrated a 69% improvement in the contrast-to-noise ratio (6.6 +/- 1.1 vs. 11.1 +/- 2.5; P < 0.01) compared with the T2Prep approach. By using the intravascular agent, extensive portions (> 80 mm) of the native left and right coronary system could be displayed consistently with sub-millimeter in-plane resolution. The intravascular contrast agent, MS-325/AngioMARK, leads to a considerable enhancement of the blood/muscle contrast for coronary MRA compared with T2Prep techniques. The clinical value of the agent remains to be defined in a larger patient series. J. Magn. Reson. Imaging 1999;10:790-799.

Contrast-enhanced coronary MRA

Coronary angiography with magnetic resonance imaging (MRI) has long been a goal for bringing cardiac MRI into clinical use for diagnosis of coronary artery disease. In this paper, the fundamental problems of respiratory and cardiac motion, signal-to-noise ratio, and contrast-to-noise ratio are discussed in reference to implications for coronary imaging strategies. Various methods that have been proposed to improve signal-to-noise and contrast-to-noise ratios in MR coronary imaging are presented with an emphasis on the role of T1-shortening contrast agents, both extracellular and intravascular. Although much progress has been made in recent years in techniques for imaging the coronary arteries, ultimate clinical success remains unproved. Success will depend on synergistic developments in MR acquisition techniques, respiratory compensation methods, post-processing techniques, and contrast agents to develop a workable solution for reliable coronary imaging across a wide range of patients. J. Magn. Reson. Imaging 1999;10:703-708.

Evaluation of coronary artery bypass grafts by magnetic resonance imaging

Magnetic resonance (MR) angiography and flow mapping have the potential to become a major noninvasive diagnostic tool for the assessment of coronary artery bypass graft morphology and function. Several MR sequences, such as conventional non-respiratory compensated methods, and phase contrast cine flow sequences have been reported for the evaluation of bypass graft patency. However the visualization of different graft segments and the detection of graft stenosis remains difficult. Recent advances in MR coronary angiography and flow mapping are volume coronary angiongraphy with targeted scans, navigator gated angiography, contrast-enhanced angiography, and breath-hold or navigator gated flow sequences. Future approaches, such as navigator gated fast MR techniques resulting in high-resolution angiography in combination with breath-hold MR flow mapping with high temporal resolution, might allow a comprehensive evaluation of bypass graft stenosis and function. This review article will address the major issues concerning the MR evaluation of bypass grafts.

Improved coronary artery definition with T2-weighted, free-breathing, three-dimensional coronary MRA

BACKGROUND

Three-dimensional (3D) navigator-gated and prospectively corrected free-breathing coronary magnetic resonance angiography (MRA) allows for submillimeter image resolution but suffers from poor contrast between coronary blood and myocardium. Data collected over >100 ms/heart beat are also susceptible to bulk cardiac and respiratory motion. To address these problems, we examined the effect of a T2 preparation prepulse (T2prep) for myocardial suppression and a shortened acquisition window on coronary definition.

METHODS AND RESULTS

Eight healthy adult subjects and 5 patients with confirmed coronary artery disease (CAD) underwent free-breathing 3D MRA with and without T2prep and with 120- and 60-ms data-acquisition windows. The T2prep resulted in a 123% (P<0. 001) increase in contrast-to-noise ratio (CNR). Coronary edge definition was improved by 33% (P<0.001). Acquisition window shortening from 120 to 60 ms resulted in better vessel definition (11%; P<0.001). Among patients with CAD, there was a good correspondence with disease.

CONCLUSIONS

Free-breathing, T2prep, 3D coronary MRA with a shorter acquisition window resulted in improved CNR and better coronary artery definition, allowing the assessment of coronary disease. This approach offers the potential for free-breathing, noninvasive assessment of the major coronary arteries.