Elizabeth George MD, Abstract Co-Author: Nothing to Disclose

Michael Lally Steigner MD, Abstract Co-Author: Speaker, Toshiba Corporation

Antonios Antoniadis, Abstract Co-Author: Nothing to Disclose

Michael Hanley MD, Abstract Co-Author: Nothing to Disclose

Frank John Rybicki MD, PhD, Abstract Co-Author: Research Grant, Toshiba Corporation

Dimitris Mitsouras PhD, Presenter: Nothing to Disclose

Amir Imanzadeh MD, Abstract Co-Author: Nothing to Disclose

Kanako Kunishima Kumamaru MD, PhD, Abstract Co-Author: Nothing to Disclose

Yiannis M. Chatzizisis MD, Abstract Co-Author: Nothing to Disclose

Ruth M. Dunne MBBCh, Abstract Co-Author: Nothing to Disclose

Andreas Giannopoulos MD, Abstract Co-Author: Nothing to Disclose

A recently proposed sign at CTA, the “gravitational gradient” (GG), quantifies the antero-posterior inhomogeneity of luminal contrast enhancement under the hypothesis that it may signify slow flow in large vessels. We thoroughly investigated the GG in infrarenal AAA as a source of hemodynamic information and assessed its relevance with respect to rapid AAA growth.

The GG was measured in 67 consecutive pre-repair CTAs and used to classify patients as high (≥1.4) or normal (<1.4) GG (Figure). We compared the two groups for a) cardiovascular (CV) status, including ejection fraction; b) CTA scan and contrast delivery parameters, including timing; c) aortic and AAA geometry; d) characteristics of the blood flow patterns using computational fluid dynamics in 5 high and 5 matched normal GG patients; and e) AAA growth >0.4cm/yr in a 3-year period. We also assessed GG change in post-repair CTA available in 10 high GG patients.

18% of AAAs (n=12) exhibited a high GG≥1.4. A high GG was independent of patient CV status, CT scan/contrast delivery parameters, and AAA/aortic geometry (all p>0.05). The only significant differences between patients with high vs normal GG were a sudden drop in aortic enhancement between the renal arteries and aortic bifurcation (43±38 vs 10±39 HU drop, p<0.05; Figure), and all CFD-derived parameters, namely extent of retrograde flow or stasis (10±6% vs 2±2% luminal area affected, p<0.05, Figure), helicity (5±2 vs 12±5 m2/s2, p<0.05), and vorticity (72±25 vs 109±27 s-1, p<0.05). In the 10 high GG patients that underwent repair, both the high GG and sudden drop in aortic enhancement across the AAA resolved (pre vs post GG=1.9±0.5 vs 1.0±0.1, p<0.05; HU drop=42±42 vs 20±20, Figure). Finally, a high GG was associated with a relative risk of 2.7 (95% CI: 1.3-5.3, p<0.05) for AAA growth >0.4cm/yr.

Inhomogeneous luminal contrast enhancement in infrarenal AAA CTA as detected by the GG is associated with complex hemodynamic patterns and rapid aneurysm enlargement. Its potential use to detect patients at risk of rapid AAA growth and rupture should be further explored.

The Gravitational Gradient is a readily identifiable imaging sign in AAA CTA that is associated with disturbed blood flow patterns and clinically significant disease progression. It may have potential use in surveillance and elective repair algorithms toward reducing rupture rates.

George, E, Steigner, M, Antoniadis, A, Hanley, M, Rybicki, F, Mitsouras, D, Imanzadeh, A, Kumamaru, K, Chatzizisis, Y, Dunne, R, Giannopoulos, A, Gravitational Gradient (GG) in Abdominal Aortic Aneurysms (AAA) during CT Angiography (CTA) as a Sign of Disturbed Hemodynamics and Adverse Clinical Outcome.  Radiological Society of North America 2014 Scientific Assembly and Annual Meeting, - ,Chicago IL. http://archive.rsna.org/2014/14006966.html