Gilles Renault MD, PhD, Abstract Co-Author: Nothing to Disclose

Andre De Oliveira, Abstract Co-Author: Nothing to Disclose

Frederique Frouin, Abstract Co-Author: Nothing to Disclose

Alain Herment, Abstract Co-Author: Nothing to Disclose

Olivier Lucidarme MD,PhD, Presenter: Nothing to Disclose

Perfusion assessment using contrast enhanced ultrasound is of growing interest. However respiratory artifacts frequently prevent proper characterization and quantification of contrast uptake kinetics. Indeed, ongoing contrast uptake makes registration difficult and partial volume effects due to out-of-plane motion can appear. A strategy is proposed to minimize respiratory motion artifacts in ultrasound contrast imaging sequences, based on the assumption that respiratory motion and contrast uptake are statistically independent, thus enabling an a posteriori gating and parametric imaging.

To date, 12 nude mice with grafted Wilms tumor were studied. The transducer (15L8w, working at 14MHz) was mechanically fixed above the mice allowing them to breathe freely. Contrast ultrasound images were acquired after injection of 0.1ml of Sonovue using a Sequoia 512 device (Siemens). Dual images in CPS and fundamental modes were acquired at 25Hz over 20s. A respiratory component was estimated by independent component analysis on the fundamental sequence. Two subsets of frames corresponding to the minima and maxima of the respiratory cycle were created from the contrast enhanced CPS sequence. A bi-slice ultrasound perfusion sequence was created and processed using parametric imaging.

In all cases, respiratory cycle was identified with a frequency around 3.25 Hz, and frame selection was possible. An average of 40% of the original frames was kept for parametric imaging. Visual evaluation by clinicians showed that motion was clearly reduced, and region of interest measurements confirmed this result. Parametric analysis depicted typical contrast uptake patterns: an early vascular contrast uptake, a consecutive cortical enhancement and a late perfusion pattern in tumor areas.

This preliminary study showed that independent component analysis can be used as a tool to reduce respiratory motion artifacts, facilitating parametric imaging and quantification in small animal studies. Application of this methodology to human abdominal examinations (liver and kidneys) is under evaluation.

Renault, G, De Oliveira, A, Frouin, F, Herment, A, Lucidarme, O, Frame Selection Method for Respiratory Gating in Contrast Ultrasound Studies of Small Animals.  Radiological Society of North America 2005 Scientific Assembly and Annual Meeting, November 27 - December 2, 2005 ,Chicago IL. http://archive.rsna.org/2005/4412871.html