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Published online before print September 9, 2004, 10.1148/radiol.2332031545
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(Radiology 2004;233:567-573.)
© RSNA, 2004

Cardiac Imaging

MR Coronary Angiography with SH L 643 A: Initial Experience in Patients with Coronary Artery Disease1

Christoph U. Herborn, MD, Michaela Schmidt, RT, Oliver Bruder, MD, Eike Nagel, MD, Kohkan Shamsi, MD, PhD and Jörg Barkhausen, MD

1 From the Department of Diagnostic and Interventional Radiology, University Hospital Essen, Hufelandstrasse 55, 45122 Essen, Germany (C.U.H., J.B.); Siemens Medical Solutions, Erlangen, Germany (M.S.); Department of Cardiology, Elisabeth-Hospital, Essen, Germany (O.B.); Department of Cardiology, German Heart Institute, Berlin, Germany (E.N.); and Berlex, Montville, NJ (K.S.). Received September 24, 2003; revision requested December 5; revision received January 15, 2004; accepted February 17. Address correspondence to J.B. (e-mail: joerg.barkhausen@uni-essen.de).


   ABSTRACT
TOP
 ABSTRACT
INTRODUCTION
 MATERIALS AND METHODS
RESULTS
 DISCUSSION
 REFERENCES
 
PURPOSE: To prospectively assess the accuracy of breath-hold three-dimensional magnetic resonance (MR) coronary angiography with the gadolinium-based intravascular contrast agent SH L 643 A in patients with coronary artery disease.

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

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

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

© RSNA, 2004

Index terms: Arteries, stenosis or obstruction, 548.762, 548.763 • Coronary vessels, MR, 548.121413, 548.121416, 548.121419, 548.12142, 548.12143 • Magnetic resonance (MR), contrast media • Magnetic resonance (MR), vascular studies


   INTRODUCTION
TOP
 ABSTRACT
 INTRODUCTION
MATERIALS AND METHODS
RESULTS
 DISCUSSION
 REFERENCES
 
Coronary artery disease is the leading cause of death throughout the industrialized world and especially in the United States, where it accounted for more than 40% of deaths in 2002 (1). Since its clinical introduction nearly 50 years ago, invasive coronary artery angiography has been the reference standard for the diagnosis of coronary artery disease (2,3). Limitations inherent in conventional coronary angiography include a major complication rate of approximately 0.3%–1.1%, considerable radiation exposure, and excessive cost to health care systems (4,5). These drawbacks have promoted alternative imaging strategies. With the development of ultrafast magnetic resonance (MR) imaging sequences, MR angiography of the coronary arteries has recently become possible. The results of early studies with two-dimensional time-of-flight MR angiographic techniques were encouraging, but the method provided poor through-plane resolution. This shortcoming was addressed in the development of three-dimensional (3D) techniques with isotropic voxel size. Advantageous features of 3D imaging techniques are the acquisition of thinner sections, superior signal-to-noise ratio (SNR), and total coverage of the tortuous coronary arteries in a single volume (slab). Saturation effects, however, severely reduce contrast between blood and myocardium with 3D techniques (6). One method proposed for improving the quality of 3D MR coronary angiography is the use of T1-shortening contrast agents (7–9). Given the relatively brief intravascular residence time of extracellular gadolinium chelates and their rapid extravasation into the myocardium, the gadolinium-based contrast agents currently available for clinical use permit 3D MR coronary angiography only during the first arterial pass directly after intravenous application (10).

Recently, however, preclinical studies of several intravascular MR contrast agents were launched. These compounds remain in the blood longer than extracellular agents and undergo either no extravasation or almost none. At the same time, they have higher T1 relaxivities (11–14). Some of these new intravascular MR contrast agents have been shown to improve coronary artery depiction at MR angiography in animal studies and in preliminary clinical trials (15–18). SH L 643 A is a gadolinium-based macromolecular blood pool agent that improves coronary MR imaging both in animals and in healthy human volunteers (19,20). Therefore, the purpose of this study was to prospectively assess the accuracy of breath-hold 3D MR coronary angiography with use of the gadolinium-based intravascular contrast agent SH L 643 A in patients with coronary artery disease.


   MATERIALS AND METHODS
TOP
 ABSTRACT
 INTRODUCTION
 MATERIALS AND METHODS
RESULTS
 DISCUSSION
 REFERENCES
 
Patients
The study was approved by the institutional review board, and informed consent was obtained from all participants prior to their enrollment in the study. Within 3 months, we prospectively enrolled 12 patients who had coronary artery disease (seven men, five women; age range, 46–78 years; mean age, 61.3 years). Criteria for inclusion were as follows: for women, postmenopausal status; for both men and women, proved stenosis of at least one proximal coronary artery segment at conventional angiography, which had to have been performed no more than 4 weeks prior to SH L 643 A injection, as well as willingness to comply with the study procedures, and informed written consent. Exclusionary criteria consisted of the following: a history of anaphylactic reaction to any allergen, including drugs and contrast agents; pericardial effusion; arrhythmia; body weight of more than 100 kg; dialysis; or application of any contrast agent or performance of planned surgical intervention within 24 hours before or after SH L 643 A injection. In addition, patients who had undergone stent implantation or percutaneous transluminal coronary angioplasty or who were unable to remain recumbent for at least 45 minutes were excluded from the study. A physical examination was performed before and 6 and 24 hours after contrast material application. Urinalysis was performed, and blood samples were obtained for hematologic, coagulation, and chemical analyses. All samples were assessed at a central laboratory (Labor für Klinische Forschung, Kiel, Germany). One author (C.U.H.) reviewed all vital signs, electrocardiographic tracings, and laboratory reports and indicated clinically relevant changes according to a list of normal ranges provided by the central laboratory. Any adverse event that occurred within 24 hours after contrast agent administration was documented by the same author by using a standard case record template. Adverse events that were transient and required no special treatment or intervention and no alterations to laboratory testing were designated as mild. Moderate adverse events were experiences that indicated injury without long-term risk and that could be alleviated with simple therapeutic treatments and with laboratory test alterations. Severe adverse events were experiences that required therapeutic intervention. If hospitalization was required for treatment, the precipitating event was designated a serious adverse event. Serious adverse events included death, life-threatening adverse event requiring inpatient hospitalization or prolongation of existing hospitalization, and persistent or significant disability or incapacity.

Contrast Agent
The intravascular contrast agent SH L 643 A (Gadomer-17; Schering, Berlin, Germany) is a formulation of gadolinium chelates containing dendrimeric molecules with a molecular weight of about 17 kDa. The gadolinium concentration in this formulation is equimolar to that in most extracellular gadolinium-based preparations (0.5 mmol/mL). At a resonant frequency of 20 MHz, the relaxivity of this formulation in water and plasma is very high, at 17.4 and 18.9 L · mmol–1 · sec–1, respectively. After intravenous administration, SH L 643 A is distributed within the intravascular space and does not substantially extravasate to the interstitial space. The serum concentration profile is clearly dominated by the initial distribution phase, with a volume of distribution of 0.05 L ± 0.01 (standard deviation) per kilogram body weight and an elimination half-life of 0.21 hours ± 0.04. The total serum clearance is 1.54 mL · min–1 · kg–1 ± 0.22. SH L 643 A is eliminated quickly and in nonmetabolized form from the body through the kidneys by glomerular filtration. Within the first 4 hours after infusion, more than 80% of the injected dose is eliminated in urine. Fecal excretion is negligible.

MR Coronary Angiography
All imaging was performed on a 1.5-T MR imager (Magnetom Sonata; Siemens, Erlangen, Germany) equipped with a high-performance three-axis gradient system. Patients were placed in supine position, head first, within the bore of the magnet, and a phased-array torso coil with four active coil elements was used. After application of a transverse localizer sequence to identify the origin of the left and right coronary arteries, double oblique imaging sequences were applied along the axis of the vessel evaluated. All examinations were performed during deep inspiration and breath holding. Breath holding was monitored by using navigation echoes collected at the dome of the right side of the diaphragm with paired 90° and 180° pulses to ensure intraindividually comparable inspiration levels and to detect any motion of the diaphragm during imaging. For nonenhanced imaging of the coronary arteries, true fast imaging with steady-state precession (FISP) was used (Table 1).


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  		TABLE 1. Parameters of 3D MR Coronary Angiographic Sequences

 
For all contrast-enhanced examinations, SH L 643 A (0.1 mmol gadolinium per kilogram body weight) was injected via an 18-gauge plastic catheter in the left antecubital vein at an individually adjusted flow rate during a period of 40 seconds. In order to guarantee standardized administration of the agent, an automatic injector (Spectris; Medrad, Pittsburgh, Pa) was used. The dose was chosen according to findings in previous studies in which a gadolinium dose of 0.1 mmol/kg yielded high enhancement values during the equilibrium phase (21).

Contrast-enhanced MR coronary angiography was started during the early arterial phase (ie, 20 seconds after initiation of contrast agent administration). Imaging was repeated continuously for a total acquisition time of 30 minutes. An inversion-recovery–prepared 3D segmented gradient-echo sequence (fast low-angle shot) was used. The inversion-recovery preparatory pulse was used to suppress the myocardial signal after contrast agent administration and to maximize blood-myocardium contrast. Inversion times for maximal blood-myocardium contrast at contrast-enhanced imaging were individually determined for each examination by using an inversion time scout sequence (22) and varied from 180 to 240 msec for all examinations. The imaging planes were arranged along the main axis of the vessel that was to be examined. The time window of acquisition per R-R interval was less than or equal to 140 msec and was adapted to the heart rate of each patient, as was the delay between the QRS complex and the initiation of data collection in diastole. All heartbeats were detected; the software we used provides no algorithm for the detection of extrasystole or arrhythmia. The flip angle was constant for nonenhanced and contrast-enhanced imaging. For both true FISP and the inversion-recovery–prepared 3D segmented gradient-echo sequence, centric k-space ordering was used. The parameters for nonenhanced and contrast-enhanced imaging are specified in Table 1. Section thickness, number of sections, slab thickness, voxel size, acquisition time, and phase-encoding steps per heartbeat are given as minimum or maximum values because the parameters were individually adjusted, depending on the heart rate and the breath holding capabilities of each patient.

According to the study protocol, each imaging session started with the left main coronary and the left anterior descending arteries to gain comparable data sets. Subsequently, the right coronary artery was imaged. There was no dedicated acquisition for the left circumflex coronary artery. Electrocardiographic tracings were recorded during the entire examination, and the pulse rate, arterial blood pressure, and oxygen saturation were measured automatically (MR 9500; MR Equipment, Bay Shore, NY) every 5 minutes until the end of the MR examination.

Acquisition and Analysis of Conventional Angiograms
All conventional coronary angiographic examinations were performed with multiple projections by using a standard angiographic unit (Hicor; Siemens, Erlangen, Germany). Diagnostic left and right coronary angiograms were obtained by using the Judkins technique. For each projection, a bolus of 15–25 mL of iodinated contrast material (iohexol, Accupaque; Amersham, Oslo, Norway) was manually injected. Significant coronary artery disease was defined as a reduction of 50% or more in the luminal diameter of a major epicardial artery (23). Each coronary vessel was assessed by a cardiologist (O.B., with 4 years of experience in the interpretation of conventional coronary angiograms), and the reduction in luminal diameter for each lesion (<50%, ≥50%, or occlusion) was reported.

MR Coronary Angiographic Analysis and Statistical Analysis
To prevent any recognition bias, all patient-related data on images were masked. SNR was measured by one author (C.U.H.) within the first 3 cm of the left anterior descending artery, with equally sized (size range, 20–40 pixels) and locally adapted regions of interest, by using the equation SIcor/SDn, where SIcor is signal intensity in the coronary artery and SDn is the standard deviation of noise obtained from signal intensity measurement in a circular region of interest in the air outside the patient. Blood-myocardium CNR was calculated in the same manner by placing the region of interest in myocardium adjacent to the vessel evaluated and by using the formula (SIcor – SImyo)/SDn, where SImyo is the signal intensity of myocardium. Image quality was assessed in consensus by a radiologist and a cardiologist (C.U.H., with 3 years of experience, and O.B., with 2 years of experience, respectively, in MR coronary angiography). A four-point Likert-type scale was used to score image quality as follows: 1, nondiagnostic quality (no signal intensity enhancement in vessel lumen); 2, moderate diagnostic quality (inhomogeneous signal intensity enhancement in vessel lumen, incomplete delineation of vessel border, evaluation possible with low diagnostic confidence); 3, good visualization (good and almost completely homogeneous signal intensity enhancement in vessel lumen, incomplete delineation of vessel border, evaluation possible with satisfactory diagnostic confidence); and 4, excellent visualization (superb and completely homogeneous signal intensity enhancement in vessel lumen, optimal delineation of vessel border, evaluation possible with high diagnostic confidence). Statistical comparison of nonenhanced and contrast-enhanced MR coronary angiographic data was based on a paired bidirectional Student t test of no difference versus difference, with a P value of less than .05 considered to indicate significant difference. Maximum reduction of luminal diameter for each lesion (<50%, ≥50%, or occlusion) was assessed in consensus by two experienced readers (C.U.H. and J.B., each with 4 years of experience with MR coronary angiography) by using the MR angiograms. Nonenhanced and contrast-enhanced MR angiograms were evaluated in random order by both readers. MR angiograms were compared with conventional angiograms of the left main coronary artery, proximal and middle left anterior descending artery, proximal circumflex coronary artery, and proximal and middle right coronary artery, segment by segment, to calculate the sensitivity and specificity of MR angiography for depiction of substantial coronary artery stenosis. Nonenhanced and contrast-enhanced MR angiograms were compared for SNR, CNR, and overall image quality. Accuracy was determined as the percentage of segments that were correctly classified. All measurements were noted on an electronic data sheet (Excel 2002; Microsoft, Redmond, Wash) and subjected to statistical analysis by using statistical software (SPSS, version 12.0 [2003]; SPSS, Chicago, Ill).


   RESULTS
TOP
 ABSTRACT
 INTRODUCTION
 MATERIALS AND METHODS
RESULTS
DISCUSSION
 REFERENCES
 
MR coronary angiography with the intravascular contrast agent SH L 643 A (including both nonenhanced and contrast-enhanced imaging) was successfully completed in all patients. Compared with baseline values previous to the MR examination, no significant changes in pulse rate, arterial blood pressure, oxygen saturation, or laboratory values were observed after administration of SH L 643 A. Neither acute nor late-phase adverse effects were observed in the study cohort.

SNR Measurements
Overall results of SNR measurements between 2 and 4 minutes after injection of SH L 643 A, as well as separate calculations for individual segments of the left and right coronary arteries, are summarized in Table 2. No statistically significant differences in SNR were found between nonenhanced and contrast-enhanced MR angiograms (25.2 ± 11.4 vs 29.5 ± 9.8; P > .3).


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  		TABLE 2. Comparison of SNR and CNR Measurements on Nonenhanced and Contrast-enhanced MR Coronary Angiograms

 
CNR Measurements
Compared with that measured on nonenhanced MR angiograms, CNR for coronary arteries versus myocardium was significantly improved on MR angiograms acquired 2–4 minutes after injection of SH L 643 A (9.8 ± 5.1 vs 23.0 ± 8.7; P < .01). CNR parameters and corresponding P values are specified in Table 2. CNR improvement is visible in Figure 1, in which the left coronary artery in a 56-year-old male patient can readily be evaluated after injection of SH L 643 A, whereas the vessel is hardly assessable on the nonenhanced image. CNR increased immediately after contrast agent application and reached the maximum within 1–3 minutes after injection. Thereafter, CNR decreased, but it remained slightly elevated 30 minutes after administration of SH L 643 A.



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  		Figure 1. Coronary angiograms in 56-year-old man with coronary artery disease. A, Oblique nonenhanced MR angiogram acquired with true FISP sequence poorly depicts left coronary artery system. B, Oblique contrast-enhanced MR angiogram acquired with 3D breath-hold fast low-angle shot 2 minutes after intravenous injection of SH L 643 A shows considerable increase in blood-to-myocardium CNR, which allows delineation of left main coronary and left anterior descending arteries and side branches. C, Left anterior oblique conventional angiogram obtained with manual injection of 12 mL iohexol shows stenosis greater than 50% at level of left coronary artery bifurcation (arrow). Stenosis was also correctly assessed on B.

 
Image Quality
The overall image quality score significantly improved from a mean of 2.0 ± 0.9 on the nonenhanced images to 2.9 ± 0.9 (P < .01) on the contrast-enhanced images acquired 2–4 minutes after contrast agent injection and assessed by using the four-point Likert-type scale. Separate analysis for individual coronary artery segments revealed that the most substantial improvement occurred in the depiction of the left main and left anterior descending coronary arteries (Table 3).


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  		TABLE 3. Comparison of Overall Image Quality and Quality of Coronary Artery Depiction on Nonenhanced versus Contrast-enhanced MR Angiograms

 
Coronary Artery Assessment
The number of coronary artery segments for which depiction was nondiagnostic was significantly decreased on contrast-enhanced images, from 27 (38%) to seven (10%) of 72 (P < .05), compared with the number of such segments on nonenhanced images.

With conventional coronary angiography used as the reference standard, the sensitivity and specificity of nonenhanced MR angiography performed with the steady-state sequence for detection of substantial coronary artery stenosis were 63% and 96%, respectively, whereas the contrast-enhanced MR examination had a significantly higher sensitivity of 80% (P < .04) and an almost unchanged specificity of 93% (Figs 1, 2). Accuracy for detection of substantial coronary artery stenosis on true FISP images was 78%, compared with 87% on fast low-angle shot images acquired after injection of SH L 643 A (P = .042).



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  		Figure 2. Coronary angiograms in 61-year-old woman with coronary artery disease. A, Right anterior oblique conventional angiogram; B, oblique nonenhanced true FISP MR angiogram; and, C, oblique contrast-enhanced 3D fast low-angle shot MR angiogram show stenosis greater than 50% in the right coronary artery (arrow).

 

   DISCUSSION
TOP
 ABSTRACT
 INTRODUCTION
 MATERIALS AND METHODS
RESULTS
 DISCUSSION
REFERENCES
 
To our knowledge, this is the first study in which nonenhanced and contrast-enhanced MR coronary angiography were compared with conventional angiography as the reference standard by using the intravascular gadolinium-based MR contrast agent SH L 643 A in patients with substantial coronary artery disease. We found a considerable overall improvement in image quality and CNR, with a good sensitivity and high specificity for detection of relevant disease, by using the new intravascular agent SH L 643 A. Besides its excellent tolerability, SH L 643 A at a gadolinium dose of 0.1 mmol/kg allowed continuous coronary artery imaging for 30 minutes and coverage of the proximal and middle coronary artery tree after a single injection. SH L 643 A combines prolonged intravascular retention with strong T1 relaxivity and thus seems to be well suited for breath-hold 3D MR coronary angiography. Breath-hold MR coronary angiography with SH L 643 A did not result in statistically significant SNR changes, however—a fact that reflects the influence of the inversion pulse on SNR measurements at contrast-enhanced imaging.

Data acquisition at MR coronary angiography with 3D gradient echoes is performed during the late diastolic phase, when cardiac motion is negligible, and the technique thus provides a relatively low efficacy with regard to SNR per segment investigated. Furthermore, considerable magnetization recovery between each acquisition cycle leads to poor contrast between blood and myocardium and prevents clear identification and confident assessment of native coronary arteries. To overcome these limitations, alternative MR techniques were devised to suppress the myocardial signal by using T2 weighting (24–26), magnetization transfer (27,28), or steady state preparatory pulses at contrast-enhanced MR coronary angiography (7,15,29). Fast imaging techniques with steady-state precession (eg, true FISP, balanced fast field echo) have become clinically available. Inherent in these techniques is a complex interaction between T2 and T1 relaxivity that improves contrast between blood and myocardium, which in turn leads to good delineation of coronary arteries (30,31). The results of our study, however, demonstrate that coronary artery–myocardium CNR and image quality can be further improved with the use of contrast-enhanced inversion-recovery– prepared imaging, compared with CNR and image quality provided by the 3D steady-state precession technique. Moreover, sensitivity and specificity for the detection of substantial coronary artery disease were clearly improved with contrast-enhanced imaging. These findings suggest that intravascular contrast agents should be used for examinations in which the coronary arteries cannot be sufficiently assessed with nonenhanced MR imaging or with currently available extracellular compounds.

In addition, SH L 643 A would allow for a two-stage cardiac examination: With an initial fast bolus injection, cardiac perfusion might be assessed, whereas a second injection might be used for evaluation of coronary arteries. Recently, Gerber et al (32) showed in an animal model that SH L 643 A provided more prolonged differentiation of ischemic myocardium from remote myocardium than that provided by an extracellular contrast agent (gadopentetate dimeglumine).

Several other new intravascular contrast agents have been evaluated for contrast-enhanced MR coronary angiography, both in preclinical studies and in studies performed in healthy volunteers. The group of intravascular contrast agents includes superparamagnetic iron oxide particles, or SPIOs, and gadolinium molecules with or without albumin binding. The use of albumin-binding gadolinium-based compounds such as MS-325 or B-22956 resulted in substantial CNR enhancement of the coronary arteries in healthy humans (17,33), as did the application of the rapid-clearance blood pool agent P792 (Vistarem; Guerbet, Aulnay-sous-Bois, France) in swine (34). Iron oxide particles such as NC100150 (35), SH U 555 C (36), and very small superparamagnetic iron oxide particles, or VSOPs (37,38), also have the capability to strongly increase the blood signal and thus have been evaluated for use at MR angiography and at MR coronary angiography, respectively. Encouraging results have been reported in preclinical studies of these compounds. The use of iron oxide agents may be problematic, however, because of the inherent signal intensity decrease they produce with T2- and T2*-shortening effects. Furthermore, iron oxide compounds have a relatively long pharmacologic half-life and accumulate in the spleen and liver, which may impair subsequent MR examinations of these organs.

The majority of studies of MR imaging in coronary arteries have been conducted by using 3D free-breathing navigator-gated and -corrected techniques (24,25,39). In comparison with breath-hold MR coronary angiography, MR coronary angiography with respiratory gating has the advantages of higher spatial resolution, coverage of larger anatomic volumes, and better SNR. Nevertheless, a strict separation of the techniques for MR coronary angiography does not seem appropriate. In this study, navigator echoes were used to monitor breath holding in each patient to allow optimized data acquisition. Given the long period of breath holding in patients with coronary artery disease (in some patients, >30 seconds), free-breathing navigator-gated sequences might appear to have been more suitable. Yet, none of our study participants had to cancel the examination for breath-hold reasons. Short acquisitions with breath holding might provide better depiction of arteries in patients in whom free-breathing navigator-gated MR coronary angiography fails to provide images of sufficient diagnostic quality. Given the intravascular disposition of the contrast agent, repetitive imaging with both techniques is conceivable.

In two large studies, each performed in more than 100 patients, investigators compared nonenhanced free-breathing navigator-gated and -corrected MR coronary angiography with conventional coronary angiography and reported high sensitivities and specificities for the detection of relevant coronary artery disease (39,40). Nevertheless, approximately one-third of all resultant images were not assessable, because of impaired image quality. In these cases, the use of a breath-hold sequence and the administration of an intravascular contrast agent might be an attractive alternative and might result in a reduction in the number of nondiagnostic examinations.

Our current study has some deficits. First and foremost, this was a study in a relatively small number of patients without prior coronary artery interventions (eg, coronary artery stent implantation). The criterion that all study participants must have undergone conventional coronary angiography prior to MR coronary angiography may have further reduced the number of eligible patients. Given the small study population, we did not perform a statistical power analysis or an analysis for sex- or age-related differences between cohorts. Furthermore, the consensus readout might be a major limitation of our study, as separate results would have made an interobserver comparison possible. Hence, differences in the nonenhanced and contrast-enhanced sequences might have become even clearer. In addition, the calculation of CNR values might call into question whether a separate evaluation of image quality was necessary. An objective assessment, however, appeared attractive and underscored significant qualitative differences between nonenhanced and contrast-enhanced images. Finally, a comparison between free-breathing respiratory-gated MR coronary angiography and the described breath-hold technique would have been attractive with regard to differences between the two methods in spatial resolution and quantitative parameters (20).

In conclusion, the use of the intravascular contrast agent SH L 643 A in conjunction with an inversion-recovery 3D MR angiographic technique, in direct comparison with conventional angiography, improves depiction and assessment of the coronary arteries in patients with substantial coronary artery disease.


   FOOTNOTES
 
Abbreviations: CNR = contrast-to-noise ratio, FISP = fast imaging with steady-state precession, SNR = signal-to-noise ratio, 3D = three-dimensional

Author contributions: Guarantor of integrity of entire study, K.S.; study concepts and design, C.U.H., J.B., E.N., K.S.; literature research, C.U.H., O.B.; clinical studies, C.U.H., O.B.; data acquisition, M.S., C.U.H., J.B.; data analysis/interpretation, C.U.H., O.B., J.B.; statistical analysis, C.U.H.; manuscript definition of intellectual content, C.U.H., J.B., K.S.; manuscript revision/review, J.B., E.N., K.S.; manuscript preparation, editing, and final version approval C.U.H.


   REFERENCES
TOP
 ABSTRACT
 INTRODUCTION
 MATERIALS AND METHODS
RESULTS
 DISCUSSION
 REFERENCES
 

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