Dual-source CT coronary angiography in patients with atrial fibrillation: Comparison with single-source CT

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Abstract

Objective

To evaluate the performance of dual-source computed tomography (DSCT) for the visualization of the coronary arteries in a population with atrial fibrillation (AF) compared to single-source CT (SSCT) and to explore the impact of patients’ heart rate (HR) on image quality (IQ) and reconstruction timing.

Methods

Thirty consecutive patients (11 male, 19 female; 69.0 ± 9.2 years old) with suspected coronary artery disease and permanent AF were examined on a DSCT scanner (120 kV, 400 mAs/rot, 0.33 s rotation time, 64 × 0.6 mm collimation, pitch 0.20–0.28, Siemens Somatom Definition). Patients were divided into two groups: low and medium HR group (HR  80 bpm, n = 14) and high HR group (HR > 80 bpm, n = 16). Five of the patients also underwent conventional coronary angiography (CAG). The raw data from both tube detector arrays were reconstructed as DSCT data using a routine algorithm (temporal resolution of 83 ms). The raw data from one tube detector array was reconstructed separately on the same system using a routine single source algorithm (temporal resolution of 83–165 ms) and defined as virtual SSCT data. Image quality was assessed using a four-point grading scale from excellent (1) to non-assessable (4).

Results

IQ of the DSCT data was significantly better than that of the virtual SSCT data (mean score 1.33 ± 0.61 vs. 1.80 ± 1.02; Z = −8.755, P = 0.000). 98.6% of the segments shown in DSCT were diagnostic, compared with 89.9% of the segments in virtual SSCT, χ2 = 32.595, P = 0.000. In DSCT group, IQ of low HR group was also better than that of high HR group, although the difference was not as big (mean score 1.25 ± 0.52 vs. 1.38 ± 0.66; Z = −2.227, P = 0.026). The mean HR of low HR group and high HR group were 67.4 ± 8.5 beats per minute (bpm) and 94.2 ± 8.8 bpm (t = −8.499, P = 0.000). The range of the variation of HR was higher in high HR group than in low HR group (mean difference between maximum and minimum HR 79.5 ± 21.0 vs. 49.9 ± 21.1 bpm; t = −3.845, P = 0.001). In 23 (77%) patients optimal IQ was achieved within one phase for all three main arteries. In low HR group, the optimal phase was distributed evenly between diastole and systole; but in high HR group, the optimal phase shifted to systole in most cases (92%). In five cases these results were compared to CAG results to look for the ability to identify stenosis with a diameter reduction of more than 50% of the lumen. With DSCT it was possible to diagnose 20 of 21 stenosis and 48 of 49 non-stenosed vessel segments correctly. With SSCT 19 of 21 stenosis and 45 of 49 non-stenosed vessel segments were diagnosed correctly according to CAG.

Conclusion

Due to its high temporal resolution, DSCT provides images of full diagnostic image quality in patients with AF, which otherwise would be excluded from CT examinations. The number of assessable segments for DSCT is still somewhat less than in non-AF patients, but in opposition to SSCT still valid for routine diagnostic imaging. Patients’ HR had impact on IQ and reconstruction timing.

Introduction

Recent advances in multi-slice computed tomography (MSCT) technology have improved the quality of non-invasive coronary artery imaging. Investigators reported improved results in visualization of the coronary arteries and diagnosis of coronary artery disease in a selected population of patients [1], [2], [3], [4], [5], [6], [7]. One limitation of MSCT coronary angiography is that irregular heart rates prevent adequate visualization and evaluation of the coronary arteries, and patients with atrial fibrillation (AF) are usually excluded from scanning [1], [4], [6], [8], [9], [10].

Atrial fibrillation (AF) is the most common arrhythmia in elderly persons worldwide [11]. The prevalence of AF increases with age. In the Framingham study it’s prevalence doubles with each advancing decade of age, from 2% at age 60–69 years to almost 9% at age 80–89 years [12]. The most frequently associated cardiac conditions are hypertension (28.9%), atherosclerotic cardiovascular disease (24.7%) and rheumatic heart disease (17.5%) [13]. AF is a significant marker for both a higher incidence of stroke and death [14]. Non-rheumatic AF is associated with approximately a three to fivefold increase in risk for stroke after adjusting for other risk factors [15].

The recently introduced dual-source CT (DSCT) scanner is characterized by two x-ray tubes and two corresponding detectors mounted onto the rotating gantry with an angular offset of 90° [16] The new scanner system offers a high temporal resolution of 83 ms in a mono-segment reconstruction mode, which is a major difference from single-source CT (SSCT) systems that rely on multi-segment reconstruction techniques to improve temporal resolution [17]. However, the latter approach relies on a complete periodicity of heart motion, limiting its use in patients with variable heart rates.

A first feasibility study has shown promising results with DSCT in AF patients for coronary artery imaging [18]. Since AF patients are now included for CTA, it is the intend of the authors to assess the difference between SSCT and DSCT to find out if the differences in exclusion and inclusion are reasonable, as well as to find out what special implications it has to scan AF patients and to give a first hint what the best approach is to scan such patients, since there has been not much experience with AF patients due to the former exclusion. In addition to that, the purpose of this study is to explore the impact of patients’ heart rate (HR) on image quality (IQ) and reconstruction timing, so to find out what time window and HR are most suitable for these patients.

Section snippets

Patients

Between January 2007 and January 2008, 30 consecutive patients (11 male, 19 female; mean age 69.0 ± 9.2 years; age range 45–83 years) with suspected coronary artery disease and permanent AF underwent non-invasive DSCT coronary angiography. Exclusion criteria were allergic to iodine-containing contrast medium, renal insufficiency (serum creatinine > 1.5 mg/dl), pregnancy, respiratory impairment, unstable clinical status, marked heart failure, and previous bypass surgery. Patients were divided into

Results

The DSCT protocol was well tolerated by all patients, and all were able to hold their breath during data acquisition. IQ of the DSCT data was significantly better than that of the virtual SSCT data (mean score 1.33 ± 0.61 vs. 1.80 ± 1.02; Wilcoxon test Z = −8.755, P = 0.000). Of a total of 436 coronary segments that were present in our patients, 98.6% (430/436) of the segments shown in DSCT were diagnostic, compared with 89.9% (392/436) of the segments in virtual SSCT, χ2 = 32.595, P = 0.000 (see Table 1;

Discussion

Irregular heart rates are known as limitations of CT coronary angiography [20]. This is because at irregular heart rates, the temporal variability of the diastolic phase is increased between contiguous heart cycles, which create motion artifacts due to the inaccurate location of temporal windows, the lack of data, or both. This demands high temporal resolution of the CT scanner for accurate image reconstructions. Main purpose of this study is to evaluate the recent development of not excluding

Conclusion

In summary, due to its high temporal resolution, DSCT provides images of full diagnostic image quality in patients with AF, which otherwise would be excluded from CT examinations. The number of assessable segments for DSCT is still somewhat less than in non-AF patients, but in opposition to SSCT still valid for routine diagnostic imaging. Patients’ HR had impact on IQ and reconstruction timing.

Conflict of the interest statement

None.

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