Rationale and Objectives
To assess the validity and reliability of measuring mean aortic wall thickness (MAWT) of the ascending and descending aorta using cine steady-state free precession (SSFP) imaging compared to dark blood (DB) imaging.
Materials and Methods
DB and SSFP images of the thoracic aorta acquired at 1.5 T in 50 volunteers (26 women, 24 men; mean age: 50.2 ± 13.1 years) were used. MAWT was calculated on DB and SSFP images for the ascending and descending aorta at the level of the right pulmonary artery by two independent observers. Validity was assessed using Bland-Altman analysis, Passing-Bablok regression, and Spearman correlation. Reliability was assessed using Bland-Altman analysis and intraclass coefficients (ICCs).
Results
The mean MAWT of the ascending aorta on DB and SSFP images was 1.89 ± 0.21 mm and 1.87 ± 0.20 mm. The measurements for the descending aorta were 1.60 ± 0.22 and 1.63 ± 0.20 mm, respectively. Comparison of DB and SSFP measurements revealed a mean bias of 1.3% (95% limits of agreement (LOA): −7.9, 10.5%) for the ascending and of −2.1% (LOA: −10.5, 6.3%) for the descending aorta. The corresponding regression equation was y = 0.042 + 0.960 × ( r = 0.91; P < .0001) and y = 0.118 + 0.939 × ( r = 0.95; P < .0001), respectively. Intra- and interobserver variability showed a mean bias of less than 2.0% and LOA of less than ±15.0%. ICCs were greater than or equal to 0.85.
Conclusions
MAWT determination in the ascending and descending aorta using cine SSFP sequences is highly valid and reliable compared to DB imaging.
Determination of arterial wall thickness in different vascular territories has shown to be suitable for predicting patients’ risk for cardiovascular events . Arterial wall thickness depends on numerous physiologic and pathologic factors such as age, sex, blood pressure, smoking status, and on several metabolic markers . In recent years, magnetic resonance imaging (MRI) has become widely used for assessing arterial wall thickness. Wall thickness measurement is of particular interest not only in the carotid, coronary, and femoral arteries but also in the thoracic and abdominal aorta . Reference values are not available, and the effects of influencing factors are not yet fully understood.
The most widely used MR tool for imaging the aortic wall is the dark blood (DB) or black blood technique. DB imaging improves the visualization of the aortic wall by suppressing signal from intraluminal blood . However, cine steady-state free precession (SSFP) sequences are currently the basis for functional cardiac MRI and also enable visualization of the aortic wall. In routine cardiac examinations, cine SSFP sequences usually cover the thoracic aorta. Hence, they are potential candidates for measuring mean aortic wall thickness (MAWT) without extending examination time unduly but have not been validated for this purpose.
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Materials and methods
Study Population
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Imaging Protocol
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Table 1
Imaging Parameters of the Two Pulse Sequences Used
Sequence Parameter DB Sequence Cine SSFP Sequence Field of view (mm) 340 × 276 360 × 293 Pixel size 416 × 512 208 × 256 Slice thickness (mm) 4 6 TR/TE (ms) 2 R-R intervals/40.0 56.2/1.18 Flip angle (°) 180 68 Echo train length 23 1 Receiver bandwidth (kHz) 62.5 62.5 Turbo spin echo factor 14 - Scan time (m:s) 4:00 1:17 ECG synchronization Prospective Retrospective
ECG, electrocardiogram; SSFP, steady-state free precession; TE, echo time; TR, repetition time.
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Image Analysis and MAWT Measurement
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Statistical Analysis
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Results
MAWT of Ascending and Descending Aorta
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Validity Analysis
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Reliability Analysis
Intraobserver variability
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Table 2
Intraobserver Analysis for DB and SSFP Sequence
Observer 1 First vs. Second Session ICC (CI)DB sequenceMean bias; LOA (%) Ascending aorta −1.62; −14.43, 9.19 0.87 (0.78–0.94) Descending aorta −0.35; −7.29, 6.83 0.96 (0.93–0.98)SSFP sequence Ascending aorta 0.17; −5.56, 5.94 0.92 (0.91–0.96) Descending aorta −0.82; −8.44, 6.46 0.96 (0.92–0.98)
CI, confidence interval; DB, dark blood; ICC, intraclass correlation coefficient; LOA, limits of agreement; SSFP, steady-state free precession.
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Interobserver variability
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Table 3
Interobserver Analysis for DB and SSFP Sequence
Observer 1 vs. Observer 2 ICC (CI)DB sequenceMean bias; LOA (%) Ascending aorta −1.24; −13.43, 12.32 0.85 (0.76–0.90) Descending aorta 0.36; −8.15, 8.87 0.93 (0.90–0.94)SSFP sequence Ascending aorta −0.92; −8.65, 6.70 0.90 (0.85–0.93) Descending aorta −1.84; −11.07, 6.83 0.89 (0.83–0.94)
CI, confidence interval; DB, dark blood; ICC, intraclass correlation coefficient; LOA, limits of agreement; SSFP, steady-state free precession.
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Discussion
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Conclusion
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