Pulmonary artery pulsatility and effect on vessel diameter assessment in magnetic resonance imaging

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Abstract

Background

Information about thoracic vascular sizes can crucially affect clinical decision-making in cardiovascular disease. A variety of imaging techniques such as catheter angiography, contrast enhanced computed tomography (CT) and cardiac magnetic resonance imaging (CMR) are routinely used to measure vascular diameters. Traditionally, CMR black blood sequences were the main anatomical tool for visualization of vascular anatomy and still are in many centers. More recently, the vessel diameters are measured on multiplanar reconstructions derived from static magnetic resonance angiography (MRA). This study was performed to investigate the variation of vessel diameter measurements on different CMR techniques with respect to their data acquisition scheme.

Methods

We recruited two groups of patients for this prospective study. One group included patients with repaired tetralogy of Fallot (TOF), with at least moderate pulmonary insufficiency and another group of patients who underwent CMR as part of a diagnostic work-up for arrhythmogenic right ventricular cardiomyopathy (ARVC). Additional images of the right pulmonary artery (RPA) were acquired in the double inversion recovery (DIR) black blood, cine steady state free precession (SSFP) and MRA. All images were reviewed by two CMR trained readers using the electronic caliper provided within the picture archiving and communication system package. The maximum diameter of each artery was recorded in millimeters with up to one decimal point. Paired t-tests and Bland–Altman plots were used for comparison of measurements between different sequences.

Results

A total of 52 patients were recruited for this study, 26 patients in the TOF group (15 males, age 12.55 ± 2.9) and 26 patients in the ARVC group (15 males, age 15.6 ± 2.3). In both groups, the RPA sizes were not significantly different between the DIR images and diastolic cine SSFP (p > 0.05). Measurements on DIR were significantly smaller than those made on systolic cine SSFP or MRA in both groups (p < 0.0001). Vessel diameters measured on systolic SSFP were significantly larger than measurements made on diastolic SSFP (p < 0.0001). There was no significant difference between vessel measurements on MRA and measurements on systolic cine SSFP (p = 0.44 for the TOF group and p = 0.79 for ARVC group). Measurements on the MRA datasets were significantly larger than those on diastolic SSFP images (p < 0.0001).

Conclusion

Black blood, white blood and MRA sequences are all reproducible CMR methods for the assessment of arterial diameters in children and adolescents. Measurements from systolic phase SSFP images are comparable to those from contrast-enhanced MRA. Therefore, the administration of contrast medium is not necessary in every case. Cine SSFP images offer the additional advantage over the other methods in such that both the largest and the smallest diameter of the vessel during the cardiac cycle can be assessed using this technique. This is even more relevant in highly pulsatile circulations, such as patients with repaired TOF and significant pulmonary insufficiency.

Introduction

Accurate information on vessel size can crucially affect clinical decision-making and interventional or surgical planning in cardiovascular disease. Depending on the clinical scenario, the concern may be vessel hypoplasia, narrowing or dilatation [1], [2], [3], [4], [5]. A variety of imaging techniques such as catheter angiography, contrast enhanced computed tomography (CT) and cardiovascular magnetic resonance imaging (CMR) are routinely used to measure vascular diameters. In CMR, black blood sequences were once the main anatomical tool for visualization of vascular anatomy and still are in some centers. More often, the vessel diameters are measured on multiplanar reconstructions (MPRs) derived from static contrast enhanced magnetic resonance angiography (MRA). The non-gated contrast enhanced MRA dataset provides a 3-dimensional approach allowing for coverage of multiple vessels in a single acquisition and possibility of post processing. The data acquisition is performed over a few cardiac cycles and as there is no electrocardiogram (ECG) gating, there is potential for blurring of the vessel wall due to vascular pulsatility during the cardiac cycle. Other ECG gated two-dimensional CMR imaging techniques with good anatomical detail and high blood-tissue differentiation are also utilized to measure the cross-section of a vessel. Few of such techniques including the cine steady state free precession (SSFP), acquire information throughout the entire cardiac cycle with the additional advantage of providing information on arterial pulsatility and allowing for measurement of the vessel diameter during systole and diastole. Some of these sequences such as most black blood sequences however, acquire images only during diastole. Another factor that can affect the vessel diameter measured on the two-dimensional CMR images is the imaging plane prescription. As a consequence, the results for arterial diameters derived from different CMR acquisitions may not be comparable, especially in regurgitant lesions with potentially increased vessel pulsatility due to increased flow. In theory, the cine SSFP images should provide the most accurate information about vessel diameter as they provide information about the vessel diameter during systole and diastole. The aim of the current study was to investigate the variation of vessel diameter measurements on different CMR techniques with respect to their data acquisition scheme. Various techniques were therefore applied in patient populations with presumed normal arterial tree and those with regurgitant lesions with presumed increased pulsatility due to increased flow.

Section snippets

Patient population

This is a prospective single-center cohort study. Following approval by the institutional research ethics board and written parental informed consent, two groups of patients were recruited for this study. Group 1 consisted of patients with repaired tetralogy of Fallot (TOF), with at least moderate pulmonary regurgitation based on prior CMR, who underwent a clinical CMR examination. Group 2 consisted of patients who underwent CMR as part of a diagnostic work-up for arrhythmogenic right

Results

Data analysis was performed in data sets of all recruited patients resulting in a total of 156 measurements. Detailed results are shown in Table 1.

The MRA measurements using FWHM technique were not statistically different from the MRA measurements obtained using the PACS preset window (p > 0.05). The measurements from the FWHM technique were used for the statistical analysis, except for intra- and inter-observer variability. The results for RPA measurements are summarized in Table 1 for the TOF

Discussion

Knowing the exact vessel size is important both in the case of enlarged arteries and when hypoplastic or stenotic arteries are a concern. Arterial dilatation is a concern in Marfan's syndrome [1], aortic aneurysm [2], [3] or when planning for percutaneous pulmonary valve replacement in TOF patients with significant pulmonary regurgitation and right ventricular dilatation [4]. The degree of arterial hypoplasia features in surgical decision-making, for example when pulmonary arteries are small in

Limitations

The most important limitation of this study is that no independent gold standard of the vessel size was available, since this was a clinical in situ study. In addition to differences between the sequences, variability was introduced by the subjectivity of the measurements carried out by human CMR readers. However, the aim for this study was to assess differences in arterial luminal diameter measurements based on different sequences in clinical practice, rather than in an artificial setting of

Conclusion

Black blood, white blood and MRA sequences are all reproducible CMR methods for the assessment of arterial diameters in children and adolescents. Measurements from systolic phase SSFP images are comparable to those from contrast-enhanced MRA. Therefore, the administration of contrast medium is not necessary in every case. Cine SSFP images offer the additional advantage over the other methods in such that both the largest and the smallest diameter of the vessel during the cardiac cycle can be

Conflict of interest

None.

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