Proximal Thoracic Aortic Diameter Measurements at CT: Repeatability and Reproducibility According to Measurement Method
OBJECTIVES: To determine the variability in CT measurements of proximal thoracic aortic diameters obtained using double-oblique short axis and semiautomatic centerline analysis techniques.
METHODS: Institutional review board approval, with waiver of informed consent, was obtained for this HIPAA-compliant, retrospective study. Cardiac gated thoracic aortic CT scans were evaluated in 25 patients. Maximum aortic diameter measurements at the annulus, sinuses, sinotubular junction and ascending aorta were generated using double-oblique short axis and semiautomatic centerline analysis techniques.
Intraobserver and interobserver variability and variability between techniques were assessed using the Wilcoxon signed rank test, Spearman’s correlation coefficients and Bland-Altman plots.
RESULTS: Mean intraobserver diameter differences using double oblique views ranged from -0.3 to 0.6 mm. The 95 % confidence interval for difference in diameters was ±2.4 to ±5.1 mm for radiologist #1 and ±2.6 to ±5.2 mm for radiologist #2, depending on location. Mean intraobserver diameter differences using centerline analysis ranged from 0.2 to 2.3 mm, and the 95 % confidence interval for difference in diameters was ±2.0 to ±4.6 mm, depending on location. Significant interobserver differences were seen for both double oblique views and centerline analysis. Measurements obtained using the two methods were strongly correlated (r = 0.81-0.99), although they were consistently larger using centerline analysis (95 % confidence interval, ±1.8 to ±3.2 mm).
CONCLUSIONS: Although viagra measurement variability of the proximal thoracicaorta was generally low using double oblique and centerline analysis techniques, differences of up to approximately 5 mm in diameter occurred within the 95 % confidence interval. Neither technique was clearly more reliable than the other.
PMID: 22864960
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See also:
Comparison of Aortic Root Measurements in Patients Undergoing Transapical Aortic Valve Implantation (TA-AVI) Using Three-Dimensional Rotational Angiography (3D-RA) and Multislice Computed Tomography (MSCT): Differences and Variability.
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The aim of the study is to determine the variability in CT measurements of proximal thoracic aortic diameters obtained using double-oblique short axis and semiautomatic centerline analysis techniques.
» Is the sample size of 25 patients (14 with aneurysmal disease) adequate to determine agreement between techniques (double oblique and centerline method).
JC: We believe that the group is on the small side, which may create a bias as described below.
» Among the 25 patients there were some that also had TEE and were selected for future correlation with CT. Should these patients have been included in the analysis of this study?
JC: Not really. It probably wasn’t even necessary to mention that those patients had a TEE at all.
» What is the significance of utilizing retrospective gating rather than prospective gating for this study?
JC: It has a significant impact in the radiation dose to the patient. The benefit obtained from ecg-gating the studies is still debatable from a clinical point of view. Furthermore, 12 out of 37 patients were not included due to motion artifact which we believe (although we have no ways of knowing for sure) were probably due to poor gating/mis-registration.
» Routine scanning of the abdominal aorta was performed in all patients with a first time aortic scan and this was given as the reason to use retrospective gating. Should this practice be performed adopted in clinical practice?
JC: This is also debatable. While the risk factors are the same for thoracic and abdominal aortic disease, the benefit weighted against the large radiation dose does not seem to justify this imaging protocol. Maybe screening the abdomen with US?
» What landmarks are used to determine proximal, mid ascending aorta?
JC: None where given in the paper. The convention is the PA crossing as a landmark. It is important to mention all of these details when assessing reliability.
» Which measurements should be reported at the sinus level (cusp to commissure, largest cusp to cusp or both) and which is more clinically relevant (the ACC guidelines refer to the widest cusp diameter usually at the mid-level)?
JC: Great question! We don’t know if there is a clinically relevant answer out there.
» Repeat measurements were made after at least 2 weeks for intra-observer variability. Is this adequate to avoid recall bias in a small sample and should there be more detail about the method of repeat measurement?
JC: The fact that the cohort was so small, makes the possibility of recall bias even stronger. More detail on how this was prevented should have been given (randomizing the order of patients when reviewing them, etc.).
» Is there a reason why the measurements by the centerline analysis were consistently larger than the double oblique’s?
JC: We are guessing that it had to do with the tortuosity of the vessels and how difficult it is for the semi-automated algorithms to find a true perpendicular axis to flow. In essence, it is impossible to make a diameter smaller than what it truly is, only larger.
» Both techniques had occasional outliers >5 mm (clinically significant) and it is suggested that this may be due to abnormalities in the contour of the z axis of the ascending aorta. What suggestions can be made to avoid this error?
JC: A healthy dose of obsessive-compulsiveness.