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Coronary MR Imaging: Breath-hold Capability and Patterns, Coronary Artery Rest Periods, and ß-Blocker Use¹

¹ From the Department of Internal Medicine/Cardiology, German Heart Institute Berlin, Augustenburger Platz 1, 13353 Berlin, Germany (C.J., I.P., B.S., R.G., E.F., E.N.); Department of Cardiology, University of Freiburg, Freiburg, Germany (C.J.); and Department of Internal Medicine/Cardiology, University of Erlangen, Erlangen, Germany (S.A.). Received November 29, 2004; revision requested January 28, 2005; revision received March 11; accepted April 5; final version accepted May 17. Address correspondence to C.J. (e-mail: jahnke{at}dhzb.de).

	ABSTRACT

TOP ABSTRACT INTRODUCTION MATERIALS AND METHODS RESULTS DISCUSSION References

 
Purpose: To prospectively evaluate breath-hold capability and patterns, coronary artery rest periods, and ß-blocker use in coronary magnetic resonance (MR) imaging.

Materials and Methods: Ethics committee approval and informed consent were obtained. In 210 consecutive patients (mean age, 61.8 years ± 10.3 [standard deviation]; 146 men, 64 women), breath-hold patterns and maximal capability were assessed at expiration with dynamic navigator MR imaging (temporal resolution, 1 second). Left coronary artery (LCA) and right coronary artery (RCA) rest periods were determined at transverse cine imaging (steady-state free precession, retrospective gating, 40 phases per cycle). Before and after ß-blockade, rest periods were assessed in 25 additional patients (mean age, 61.4 years ± 7.1; 20 men, five women). Differences were tested within groups with paired Student t test and between groups with unpaired Student t test (continuous variables) and ² test (categoric variables). Pearson correlation was used to test the relationship between rest period and heart rate.

Results: Four distinct breath-hold patterns, characterized by diaphragmatic motion, were identified: pattern 1, steady plateau (55% of patients); 2, initial drift followed by plateau (12%); 3, continuous drift (19%); and 4, irregular, unsteady behavior (14%). Mean breath-hold capability with patterns 1 and 2 was 29 seconds ± 13 (range, 10–64 seconds). The rest period of LCA was longer than that of RCA (163 msec ± 75 vs 123 msec ± 60; P < .01) and began earlier in the cardiac cycle (521 msec ± 149 vs 540 msec ± 160; P < .01); In a minority of patients, LCA rest period began later (21%) or was shorter (14%). With no pharmacologic intervention, correlation between rest period duration and heart rate was weak (LCA, r = –0.52; RCA, r = –0.38; P < .01). However, ß-blockade significantly lowered heart rate (61.3 beats/min ± 7.2 vs 82.6 beats/min ± 12.5, P < .001) and increased rest duration (LCA, 201.8 msec ± 83.6 vs 111.8 msec ± 44.55; RCA, 134.8 msec ± 57.3 vs 83.1 msec ± 35.8; P < .001).

Conclusion: In 33% of patients (patterns 3 and 4), breath-hold pattern was unsuitable for high-spatial-resolution breath-hold MR imaging. LCA and RCA rest periods showed large variability in starting point and duration, with no correlation to heart rate.

© RSNA, 2006

	INTRODUCTION

TOP ABSTRACT INTRODUCTION MATERIALS AND METHODS RESULTS DISCUSSION References

 
Noninvasive coronary angiography offers great potential for the diagnosis of coronary artery disease (1–3). To improve reliable depiction of the entire coronary arterial tree, it is especially important to compensate for extensive vessel movement caused by respiration and cardiac contraction. The adverse effect of breathing-induced myocardial motion can be minimized by means of respiratory gating by using the magnetic resonance (MR) navigator technique (4,5). Results of previous studies have demonstrated that the respiration-induced movement of the heart is related to the motion of the diaphragm, which is dominated by a superior-inferior motion component (6). Thus, a reduction of image blurring can be achieved by using adaptive motion correction techniques. Alternatively, breath holding can be applied for both MR imaging (7–10) and multi–detector row computed tomography (CT) (11,12). For breath-hold coronary artery imaging, effective imaging durations are approximately 32–37 seconds for MR imaging (13,14) and 20 seconds for multi–detector row CT (3,15). Thus, the effectiveness of the breath-hold technique depends mainly on the breath-hold capability of the patient and the potential unintentional motion of the diaphragm during the breath-hold period (16,17).

Motion artifacts due to cardiac contraction can be minimized by performing data readout during periods of minimal coronary artery motion. In previous MR and multi–detector row CT coronary angiography studies, typical data acquisition windows ranged from 190 to 250 msec (3,11,13,15). However, considerable motion of the coronary arteries caused by cardiac contraction may still occur during the data acquisition period. Exact knowledge of the extent and timing of coronary arterial motion is important for image acquisition strategies within the limitations of a given technique. Thus, the purpose of our study was to prospectively evaluate individual breath-hold capability, breath-hold patterns, rest periods of the coronary arteries, and the use of ß-blocker medication for coronary MR imaging.

	MATERIALS AND METHODS

TOP ABSTRACT INTRODUCTION MATERIALS AND METHODS RESULTS DISCUSSION References

 
Subjects
The study was approved by the Charité and Virchow-Klinikum Ethics Committee. Written informed consent was given by all patients. Two-hundred ten consecutive patients referred for cardiac MR examinations (146 men, 64 women), with an average age of 61.8 years, were studied between January 2003 and September 2003. In all patients, cardiac MR imaging was performed for clinical indications (eg, left ventricular function, stress testing, scar imaging, cardiac anatomy). Patients with contraindications to MR imaging (noncompatible biometallic implants or claustrophobia) were not considered for study inclusion. As part of the study protocol, ß-blocker medication was stopped at least 24 hours prior to the MR examination in all patients. The pertinent medical history of the patients was recorded at the time of the examination (C.J., I.P.).

In addition to the 210 patients, another 25 consecutive patients (20 men, five women; mean age, 61 years ± 7 years [standard deviation]) were examined before and after the intravenous administration of a ß-blocker medication. Written informed consent was received from all patients. Patients with contraindications to the administration of metoprolol or an initial heart rate of less than 65 beats per minute were excluded from the study.

MR Imaging
All patients were examined in the supine position by using a 1.5-T whole-body MR system (Intera CV; Philips, Best, the Netherlands) that was equipped with a PowerTrak6000 gradient system (23 mT/m, 219-µsec rise time) and specifically designed software (release 9). A five-element cardiac synergy coil was used for signal reception. Cardiac synchronization was performed by using four electrodes placed on the left anterior hemithorax (vector electrocardiography), and imaging was triggered on the R wave of the electrocardiography examination (18). A rapid gradient-echo sequence as a multistack, multisection survey (steady-state free precession; repetition time msec/echo time msec, 4.0/1.3; flip angle, 55°) allowed for localization of the heart in the three standard planes (transverse, sagittal, and coronal).

Assessment of breath-hold capability and pattern.—Dynamic navigator MR imaging (ie, sequential imaging of one section with tracking of the diaphragm position; spatial resolution of 1 mm, temporal resolution of 500 msec), with the navigator positioned on the dome of the right hemidiaphragm, was performed in end expiration. Only the navigator display was used for further analyses; it continuously documented the position of the diaphragm during (a) free breathing, (b) the breath-hold command ("inhale—exhale—stop breathing"), and (c) the following breath-hold period. The navigator display allowed for the measurement of the maximal breath-hold capability and the assessment of diaphragmatic movement during breath holding (the breath-hold pattern). Breath-hold capability was defined as a period of continuous end-expiratory plateau position of the diaphragm, with a deviation of less than 3 mm. Directly before starting the measurement, patients were asked to hold their breath for as long as possible. Navigator MR imaging was repeated three times, and the longest breath-hold duration was chosen for analysis.

Assessment of coronary artery rest periods.—The coronary artery rest periods were defined as a relative standstill of the corresponding coronary artery. The analysis was identical to a previously published procedure used for coronary MR angiography (19). In brief, a cine steady-state free precession MR study (retrospective gating, 40 phases per cardiac cycle) was conducted in the transverse orientation, with a geometry that resembled a conventional four-chamber view. This cine study was used to image the cross sections of the left circumflex artery—considered to be indicative of the most extensive movement of the left coronary artery (LCA)—and the right coronary artery (RCA) within the left and right atrioventricular groove, respectively. Regions of interest, or ROIs, were manually placed on the entire cross sections of the LCA and RCA to determine each rest period individually. The ROI size was equivalent to the size of the coronary artery in cross section. The ROIs were always placed by the same observer (C.J., with 3 years of experience in coronary MR imaging). The time during which the coronary artery cross section was completely within the ROI was defined as the rest period, which enabled measurement of its starting point and duration. Rest periods were usually identified during end systole and mid-diastole; the longer rest period was then chosen for the evaluation. In addition, the individual heart rate was recorded.

Influence of clinical parameters on breath-hold capability and rest periods.—The potential influence of age, left ventricular ejection fraction, any known chronic obstructive pulmonary disease (COPD), or a previous thoracotomy on breath-hold capability and coronary artery rest period duration was considered important. Thus, those factors were also considered in our analysis.

ß-Blocker Intervention Group
The study group of 25 additional patients without contraindications to MR imaging or the application of a ß-blocker was examined before and after the intravenous application of metoprolol tartrate (Beloc; Astra Zeneca, Wedel, Germany). The drug was injected in 2.5-mg fractions (maximal dose, 10 mg) until the heart rate was less than 60 beats per minute. Patients were observed for at least 2 hours after metoprolol administration. The MR imaging procedure performed was identical to that described for the first patient group. Before and after the intravenous administration of metoprolol, the characteristics of LCA and RCA rest periods in conjunction with the individual heart rate were measured.

To calculate whether ß-blockade would shorten total MR imaging duration, the following formula was used: relative imaging duration = ID_BB/ID₀ = (HB_BB · RP₀)/(HB₀ · RP_BB), where ID₀ and ID_BB are the imaging durations before and after ß-blocker administration, respectively, HB₀ and HB_BB are the heartbeat intervals before and after ß-blocker administration, respectively, and RP₀ and RP_BB are the rest period durations before and after ß-blocker administration (ie, the acquisition duration per heartbeat). This formula was based on the principle that imaging duration is proportional to the heartbeat interval and is inversely proportional to the acquisition duration per heartbeat, which is equivalent to the duration of the rest period of the coronary arteries. Longer heartbeat intervals result in longer imaging durations, whereas longer rest periods allow for longer data acquisition per heartbeat and, thus, shorten the total imaging duration.

Statistical Analysis
Statistical analysis was performed by using a statistical software package (SPSS, release 11.01; SPSS, Chicago, Ill). For all continuous parameters, results were given as the mean ± standard deviation. To detect statistically significant differences within a group, the paired Student t test was used for continuous variables. Differences between groups were tested by applying the unpaired Student t test for continuous variables and the ² test for categoric variables. Pearson correlation was used to test the relationship between coronary artery rest periods and individual heart rate and to analyze the correlation of age or left ventricular ejection fraction with breath-hold capability or coronary artery rest period durations. All tests were two-tailed, and P < .05 was considered to indicate a statistically significant difference.

	RESULTS

TOP ABSTRACT INTRODUCTION MATERIALS AND METHODS RESULTS DISCUSSION References

 
Patients demographics are given in Table 1.

Steady plateau.—In 115 (55%) of the 210 patients, there was a steady plateau of the diaphragm during breath holding, which was defined as a stable continuous end-expiratory position of the diaphragm, with a deviation of less than 3 mm, that started immediately after the breath-hold command (pattern 1, Fig 1a). The duration of the plateau phase was considered to be the breath-hold capability of the patient.

View larger version (86K): [in this window] [in a new window] [Download PPT slide]   Figure 1a: Navigator display of breath-hold patterns shows position of diaphragm (red dots) by depicting liver-lung interface during free breathing and subsequent breath-hold period at end expiration. Distance between two vertical blue lines is 1 second. (a) Steady plateau position of diaphragm throughout breath hold, with no deviation. (b) At start of breath hold, diaphragm initially drifted to end expiration; immediately after, plateau phase with minimal diaphragm movement (2-mm deviation) was recorded. (c) During breath hold, diaphragm continuously drifted to end expiration, rendering depiction of a period of minimal diaphragm movement impossible (19% of patients). (d) Completely irregular and unsteady diaphragm movement during breath hold; thus, a period of minimal diaphragm movement could not be determined.

View larger version (70K): [in this window] [in a new window] [Download PPT slide]   Figure 1b: Navigator display of breath-hold patterns shows position of diaphragm (red dots) by depicting liver-lung interface during free breathing and subsequent breath-hold period at end expiration. Distance between two vertical blue lines is 1 second. (a) Steady plateau position of diaphragm throughout breath hold, with no deviation. (b) At start of breath hold, diaphragm initially drifted to end expiration; immediately after, plateau phase with minimal diaphragm movement (2-mm deviation) was recorded. (c) During breath hold, diaphragm continuously drifted to end expiration, rendering depiction of a period of minimal diaphragm movement impossible (19% of patients). (d) Completely irregular and unsteady diaphragm movement during breath hold; thus, a period of minimal diaphragm movement could not be determined.

View larger version (83K): [in this window] [in a new window] [Download PPT slide]   Figure 1c: Navigator display of breath-hold patterns shows position of diaphragm (red dots) by depicting liver-lung interface during free breathing and subsequent breath-hold period at end expiration. Distance between two vertical blue lines is 1 second. (a) Steady plateau position of diaphragm throughout breath hold, with no deviation. (b) At start of breath hold, diaphragm initially drifted to end expiration; immediately after, plateau phase with minimal diaphragm movement (2-mm deviation) was recorded. (c) During breath hold, diaphragm continuously drifted to end expiration, rendering depiction of a period of minimal diaphragm movement impossible (19% of patients). (d) Completely irregular and unsteady diaphragm movement during breath hold; thus, a period of minimal diaphragm movement could not be determined.

View larger version (70K): [in this window] [in a new window] [Download PPT slide]   Figure 1d: Navigator display of breath-hold patterns shows position of diaphragm (red dots) by depicting liver-lung interface during free breathing and subsequent breath-hold period at end expiration. Distance between two vertical blue lines is 1 second. (a) Steady plateau position of diaphragm throughout breath hold, with no deviation. (b) At start of breath hold, diaphragm initially drifted to end expiration; immediately after, plateau phase with minimal diaphragm movement (2-mm deviation) was recorded. (c) During breath hold, diaphragm continuously drifted to end expiration, rendering depiction of a period of minimal diaphragm movement impossible (19% of patients). (d) Completely irregular and unsteady diaphragm movement during breath hold; thus, a period of minimal diaphragm movement could not be determined.

View larger version (29K): [in this window] [in a new window] [Download PPT slide]   Figure 2: Histogram of breath-hold capability in 141 patients shows leftward shift to shorter breath-hold durations in comparison with the normal distribution with the same mean and standard deviation, mainly resulting from the exceptionally good breath-hold capability (60 seconds) of 14 patients alone.

On average, the rest period of the LCA was significantly longer and started significantly earlier in the cardiac cycle in comparison with that of the RCA (Table 2); the duration of the rest periods showed a wide range of variability for both coronary arteries. In a minority of patients, the rest period of the LCA started later (45 [21%] of 210 patients) or was shorter (29 [14%] of 210 patients; Fig 3) than that of the RCA.

View larger version (23K): [in this window] [in a new window] [Download PPT slide]   Figure 3a: Scatter plots of (a) starting point and (b) duration of RCA and LCA rest period in 210 patients. Black line is line of identity. (a) In the majority of patients, LCA rest period started earlier, with corresponding data points located below the line of identity; in 45 patients (21%), LCA rest period began later. The two clusters of data points correspond to end-systolic and mid-diastolic rest periods. (b) In most patients, LCA rest period was longer (data points above line of identity); in 29 patients (14%), LCA rest period was shorter.

View larger version (25K): [in this window] [in a new window] [Download PPT slide]   Figure 3b: Scatter plots of (a) starting point and (b) duration of RCA and LCA rest period in 210 patients. Black line is line of identity. (a) In the majority of patients, LCA rest period started earlier, with corresponding data points located below the line of identity; in 45 patients (21%), LCA rest period began later. The two clusters of data points correspond to end-systolic and mid-diastolic rest periods. (b) In most patients, LCA rest period was longer (data points above line of identity); in 29 patients (14%), LCA rest period was shorter.

View larger version (24K): [in this window] [in a new window] [Download PPT slide]   Figure 4a: (a,b) Scatter plot of rest period duration of (a) LCA and (b) RCA plotted against individual heart rate. Only weak linear correlation was found for the LCA, as well as for the RCA. Dashed lines are heart rate limits for patient subgroups. The tendency for longer rest periods in patients with lower heart rates and for shorter rest periods with higher heart rates can be appreciated. However, the majority of patients with heart rates of 60–90 beats per minute showed no obvious correlation between heart rate and rest period duration. (c,d) Box-and-whisker plots show relationship between individual heart rate and duration of (c) LCA and (d) RCA rest periods. If heart rate was less than 60 beats per minute, LCA and RCA rest periods were significantly prolonged (*) (P < .01). If heart rate was more than 90 beats per minute, a tendency toward shorter rest periods was recognized.

View larger version (26K): [in this window] [in a new window] [Download PPT slide]   Figure 4b: (a,b) Scatter plot of rest period duration of (a) LCA and (b) RCA plotted against individual heart rate. Only weak linear correlation was found for the LCA, as well as for the RCA. Dashed lines are heart rate limits for patient subgroups. The tendency for longer rest periods in patients with lower heart rates and for shorter rest periods with higher heart rates can be appreciated. However, the majority of patients with heart rates of 60–90 beats per minute showed no obvious correlation between heart rate and rest period duration. (c,d) Box-and-whisker plots show relationship between individual heart rate and duration of (c) LCA and (d) RCA rest periods. If heart rate was less than 60 beats per minute, LCA and RCA rest periods were significantly prolonged (*) (P < .01). If heart rate was more than 90 beats per minute, a tendency toward shorter rest periods was recognized.

View larger version (14K): [in this window] [in a new window] [Download PPT slide]   Figure 4c: (a,b) Scatter plot of rest period duration of (a) LCA and (b) RCA plotted against individual heart rate. Only weak linear correlation was found for the LCA, as well as for the RCA. Dashed lines are heart rate limits for patient subgroups. The tendency for longer rest periods in patients with lower heart rates and for shorter rest periods with higher heart rates can be appreciated. However, the majority of patients with heart rates of 60–90 beats per minute showed no obvious correlation between heart rate and rest period duration. (c,d) Box-and-whisker plots show relationship between individual heart rate and duration of (c) LCA and (d) RCA rest periods. If heart rate was less than 60 beats per minute, LCA and RCA rest periods were significantly prolonged (*) (P < .01). If heart rate was more than 90 beats per minute, a tendency toward shorter rest periods was recognized.

View larger version (15K): [in this window] [in a new window] [Download PPT slide]   Figure 4d: (a,b) Scatter plot of rest period duration of (a) LCA and (b) RCA plotted against individual heart rate. Only weak linear correlation was found for the LCA, as well as for the RCA. Dashed lines are heart rate limits for patient subgroups. The tendency for longer rest periods in patients with lower heart rates and for shorter rest periods with higher heart rates can be appreciated. However, the majority of patients with heart rates of 60–90 beats per minute showed no obvious correlation between heart rate and rest period duration. (c,d) Box-and-whisker plots show relationship between individual heart rate and duration of (c) LCA and (d) RCA rest periods. If heart rate was less than 60 beats per minute, LCA and RCA rest periods were significantly prolonged (*) (P < .01). If heart rate was more than 90 beats per minute, a tendency toward shorter rest periods was recognized.

Eleven patients (5%) had COPD. Comparing patients with COPD with those without COPD, no significant differences for rest period duration were found. However, patients with COPD had a significantly shorter breath-hold capability (21 seconds ± 9 vs 29 seconds ± 12, P = .043).

Twenty-three percent of all patients (48 of 210 patients) had undergone previous thoracotomy owing to aortocoronary bypass surgery (44 patients) or cardiac valve surgery (four patients) without an assured phrenicus lesion. No significant differences between patients who had and those who had not undergone previous thoracotomy were found for breath-hold capability, breath-hold patterns, or starting points and durations of the LCA and RCA rest period.

ß-Blocker Intervention Group
Before ß-blockade, the 25 patients in the intervention group demonstrated results that were similar to those in the main patient population (Table 3). After ß-blockade (mean dose of metoprolol, 7.7 mg ± 3.1), individual heart rate decreased significantly, the duration of the coronary artery rest periods increased significantly, and the starting points were found to occur significantly later in the cardiac cycle (Table 3). The calculation of whether ß-blockade would shorten total MR imaging duration showed that a reduction of total imaging time of 27% for the LCA and 19% for the RCA could be achieved with ß-blockade during MR imaging (Table 3).

	DISCUSSION

TOP ABSTRACT INTRODUCTION MATERIALS AND METHODS RESULTS DISCUSSION References

A major determinant for the quality and accuracy of noninvasive coronary angiography is the effective suppression of cardiac motion, which is optimally achieved by acquiring image data during the cardiac rest period. Again, we observed a large variability concerning the starting point and the duration of coronary artery rest periods. To date, only limited data on coronary artery rest periods are available; in addition, the study populations that have been considered previously consisted predominantly of healthy volunteers or of a small number of patients only (21–23). In agreement with our results, these investigators showed that the mean rest period of the LCA is longer and starts earlier during the cardiac cycle than the rest period of the RCA. Whereas periods of minimal cardiac motion were frequently observed in systole and diastole, in general it has been advised that one should acquire coronary image data during mid-diastole (2,9,24). In the present study, a total of 26% of patients demonstrated a longer coronary artery rest period during end systole than during mid-diastole. This observation highlights the need to adapt the time point for coronary MR imaging within the heartbeat interval to the patient's individual rest period in order to obtain optimal image quality (21). Since approximately 20% of the patients in our study showed an atypical behavior of the coronary artery rest periods, with a shorter or later rest period of the LCA compared with the RCA, each motion component needs to be determined individually.

Interestingly, when the whole patient population was considered, a weak linear correlation between heart rate and rest period duration was found. However, it is noteworthy that two findings give a hint for a limited relationship between the rest period duration and the individual heart rate: First, patients with heart rates of less than 60 beats per minute demonstrated significantly prolonged rest periods (for both LCA and RCA) when compared with the majority of patients, who demonstrated heart rates that ranged from 60 to 90 beats per minute. Second, when considering the individual patient only, the initially determined rest period duration can be significantly prolonged by the application of a ß-blocker. However, apart from patients with very low heart rates, the patient's individual heart rate does not reliably predict the actual duration of the coronary artery rest period.

The effect of our results on imaging strategies for MR imaging or multi–detector row CT, however, is considerably different. Since with MR imaging the acquisition duration per heartbeat can be changed over a wide range in very small steps (several milliseconds), most users of MR imaging might rather decrease the acquisition duration per heartbeat to the previously determined rest period and prolong imaging time. In contrast, most users of multi–detector row CT might rather increase the rest period of the coronary artery with the use of ß-blockers. Although no obvious correlation was found between heart rate and coronary artery rest periods, within the same patient a significant effect of ß-blockade on rest period durations was demonstrated.

In addition, longer rest periods were generally found for heart rates below 60 beats per minute. This explains the observation by users of multi–detector row CT that image artifacts can be substantially reduced by lowering heart rate below this threshold (3). Clearly, a disadvantage of ß-blockade is the prolongation of imaging time—and, consequently, breath-hold duration—if a given number of heartbeats is used for data acquisition. However, since the prolongation of rest period per heartbeat can be used to acquire the complete data set in fewer heartbeats, the net effect of ß-blockade may be advantageous. Our data support this view; in addition, we could show that imaging duration for coronary MR imaging can be shortened by 27% for the LCA and 19% for the RCA during ß-blockade. Thus, we recommend the routine use of ß-blockers for coronary MR angiography. Yet, it is noteworthy that the heart rate of the patient is not predictive of the absolute duration of the coronary artery rest period. In addition, lowering the heart rate below 60 beats per minute does not guarantee a rest period of 200 msec or more, which is required for most coronary multi–detector row CT angiography protocols.

In multi–detector row CT, data acquisition need not be synchronized to the cardiac cycle. Instead, image reconstruction is correlated to the simultaneously recorded electrocardiogram, and it is retrospectively possible to obtain images at any desired instant in the cardiac cycle. In addition, overall scanning duration is not or is only minimally influenced by the heart rate of the patient (since no alterations or only slight alterations in pitch—that is, table feed per rotation—are made depending on the heart rate). Overall scanning duration is typically approximately 20 seconds or less (3,15) and, thus, is within the average breath-hold duration capability observed in the present study. However, a stable diaphragmatic position without drift is necessary, so the variability in breath-hold patterns we observed raises some concern. As far as the position of the coronary artery rest period is concerned, multi–detector row CT imaging offers some flexibility because it is possible to retrospectively account for the individual situation and minimize motion artifacts by reconstructing data sets at arbitrary time points in the cardiac cycle until the optimal phase for each coronary artery has been found. However, this process can be time consuming and, therefore, a priori knowledge of favorable cardiac phases, such as was obtained in this study, can be extremely helpful. Also, some multi–detector row CT manufacturers provide scanning tools that reduce tube current—and thus, x-ray exposure—during predefined parts of the cardiac cycle deemed unlikely to contribute to image reconstruction (25). Again, a priori knowledge of the cardiac phase that will display the least coronary artery motion may thus be advantageous.

While measurements of breath-holding parameters and coronary motion can readily be performed on current MR systems, however, similar techniques are not yet developed for multi–detector row CT.

Our study had limitations. In our study, we used two-dimensional cine imaging of the midportion of the respective coronary artery for determination of the coronary artery rest periods. A three-dimensional approach with coverage of the main course of the epicardial arteries allowing the detection of their complex motion pattern might be advantageous. In addition, further studies are needed to evaluate the effect of the four different breath-hold patterns on image quality.

In conclusion, in 33% of patients, breath-hold imaging may be problematic due to continuous drift or irregular motion of the diaphragm during breath holding. In all patients, breath-hold capability and diaphragmatic pattern should be individually determined to select the imaging strategy, and the time point and duration of the rest period of the LCA and RCA need to be determined individually. Use of ß-blockade is recommended in most patients for non-invasive coronary artery imaging with MR and multi–detector row CT.

	FOOTNOTES

 

Abbreviations: COPD = chronic obstructive pulmonary disease • LCA = left coronary artery • RCA = right coronary artery

Author contributions: Guarantors of integrity of entire study, C.J., E.N.; study concepts/study design or data acquisition or data analysis/interpretation, all authors; manuscript drafting or manuscript revision for important intellectual content, all authors; manuscript final version approval, all authors; literature research, C.J., S.A., B.S.; clinical studies, C.J., I.P., B.S., R.G.; statistical analysis, C.J., I.P.; and manuscript editing, all authors

Authors stated no financial relationship to disclose.

	References

TOP ABSTRACT INTRODUCTION MATERIALS AND METHODS RESULTS DISCUSSION References

 

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