Lara Mrak1, Christopher J. François1, Sonja Kinner1,2, and Mark L. Schiebler1
1Radiology, UW-Madison, Madison, WI, United States, 2University Hospital Essen, Essen, Germany
Synopsis
The size of the ascending aorta is of critical importance
for patient survival as it is directly related to the likelihood of aortic
dissection and risk of death. The
traditional imaging method that has been used for this measurement has been
computed tomography of the chest. With many more children and young adults now
being imaged with contrast enhanced magnetic resonance angiography examinations
(CE-MRA) , it is useful to know what the range of variability is for the normal
aorta on these exams. We present here age and sex specific values for nomograms of the ascending aorta derived from non-gated CE-MRA
examinations that are indexed to body surface area.Introduction
There is a progressive enlargement of the ascending aorta
with age. Males have larger ascending aortas than females. The size of the
normal aorta needs to be indexed to the patient’s body surface area m2 (BSA), as it is well known that larger individuals have larger aortas. Aortic
size nomogram tables have been developed that show the risk of complications from
aortic rupture based on size and the BSA. ( Ref 1). For example, an individual with a
BSA of 1.8 m2 with an ascending aorta larger than 5.0 cm has a risk of
complications from aortic dissection of 8%/year. (Ref 1)
Purpose
We sought to generate sex and age specific
nomograms
of the orthogonal and direct axial diameters of the
ascending aorta that are indexed to the BSA
from ungated contrast-enhanced magnetic resonance angiography (CE-MRA) exams.
Methods
This was a HIPAA compliant and
IRB approved retrospective study from a data set of over 113 CE-MRA
examinations initially performed for the primary evaluation of suspected pulmonary
embolism. The 113 subjects, (60 females: 53 males) were evenly distributed into the following age groups: (A) < 45 years; (B) 45-54; (C)
55-64; and (D) > 65 years. The CE-MRA exam was performed at 1.5T ( GE
Healthcare, Waukesha, WI) using a post
contrast ( gadobenate dimeglumine at 0.1mmol/kg, Bracco Diagnostics) fluoro-triggered, 3D elliptical-centric fast
SPGR sequence performed pre-, during-, and post-injection. (Ref 2) Axial (Ref 3) and double-oblique (orthogonal)(Ref 4)
measurements of the ascending aorta (AscA) diameter were performed directly on
a PACS workstation. Measurements were made at the level of the main right pulmonary
artery (Figures 1 and 2). One
investigator measured the AscA three times in all 113 patients and a second
investigator performed the same measurements three times in a subset of 21
patients. Inter- and intra-observer variability between measurements was quantified
using Bland-Altman analysis. Plots for the aortic dimensions were generated for
each age group and sex followed by the combined results for each sex plotting
the aortic dimensions indexed to BSA by age.
Results
We found the inter-observer variability to be 0.34mm ± 3.365 mm (2 SD) for the
axial measurements and 0.12 mm ±
3.13 (2 SD) for orthogonal measurements. While the intra-observer variability
was 0.20mm ± 2.81mm (2 SD) for axial measurements and 0.58mm
± 2.61 mm (2 SD) for
orthogonal measurements. The inter-test variability between
the axial and orthogonal measurements showed a bias of -0.60 mm ± 2.43 mm( 2 SD) (Figure 3). The combined nomogram for all of the females with AscA dimension mm /BSA m2 shows a R2 value of 0.21 (Figure 4), while the male indexed nomogram
shows a R2 value of 0.107 (Figure 5).
Discussion
We confirm the findings of
Bireley et al (Ref 4) showing that orthogonal measurements of the AscA
are less variable for a single observer than the direct axial measurements. As
expected, we found that males have larger AscA dimensions than women; even after
indexing to BSA. We show that there is good interobserver agreement as well as
reasonable intraobserver agreement for these measurements made free hand on the
PACS work station without the use of post processing to determine the aortic wall. These nomograms can serve
as a basis for determining the relative importance of an individual’s aortic
dimensions using non-gated breath hold CE-MRA examinations.
Disclosure
Cardiopulmonary MRA is an off label use of gadolinium based contrast agents.
Acknowledgements
The authors wish to thank GE
Healthcare, Bracco Diagnostics and the Departmental Research and Development
Fund.
References
1. Davies Ann Thorac
Surg 2006;81:169–77
2. Schiebler JMRI 2013; 38:914-925
3. Wolak JACC 2008;
1 (2): 200-208
4.
Bireley JMRI
2007; 26: 1480-1485