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Vessel wall MRI of the thoracic aorta: correlation to histology and transesophageal ultrasound. Preliminary results.

PURPOSE
To visualise the vessel wall of the descending thoracic aorta using magnetic resonance imaging. To evaluate the diagnostic potential of tailored T1-weighted sequences with contrast enhancement to assess systemic atherosclerotic disease.


METHODS
This study was performed on a clinical 1.5 Tesla scanner using a gradient strength of 30 mT/m and the phased array spine coil. A cadaver was examined to optimise a magnetic resonance imaging (MRI) protocol to evaluate atherosclerotic aortic wall disease. The acquired MR images were compared to gross specimens and histology. Subsequently seven patients who had undergone transesophageal ultrasound (TEU) with detailed assessment of the descending thoracic aorta were examined with MRI. The optimised protocol included untriggered and fat suppressed T2-weighted turbo spin echo sequences and ECG-triggered and fat suppressed T1-weighted spin echo sequences before and after iv administration of Gd-DTPA. Findings of the MR images were compared to the results of TEU. Contrast enhancement measurements were performed in normal and thickened vessel wall segments.


RESULTS
For the cadaver study a good correlation of the degree of vessel wall thickening and the extent of plaque imaged with the applied MR protocol was found. Tissue characterisation was limited due to post mortem changes. In vivo ECG-triggered T1-weighted images showed good correlation to TEU in terms of vessel wall thickness and plaque extension as verified by means of consensus reading. Differentiation of the plaque components fat, calcium and fibrous tissue was possible. In thickened aortic wall segments and fibrous caps a mean contrast enhancement of 50.4 % +/- 23.5 % was measurable while normal wall segments showed an enhancement of 6.7 % +/- 3.1 %. The difference of contrast enhancement was highly significant (p < 0.0001).


CONCLUSION
Using fat suppressed T1-weighted sequences with contrast enhancement the extent of atherosclerotic vessel wall changes can be demonstrated. The suggested MR protocol contains a high potential for diagnosis and follow-up of therapy of atherosclerotic disease of the descending thoracic aorta.