Markus Holotta MSc, Presenter: Nothing to Disclose

Christian Kremser PhD, Abstract Co-Author: Nothing to Disclose

Rainer Schulze MSc, Abstract Co-Author: Nothing to Disclose

Martin Reiner, Abstract Co-Author: Nothing to Disclose

Regina Esterhammer MD, Abstract Co-Author: Nothing to Disclose

Pavle Torbica, Abstract Co-Author: Nothing to Disclose

Werner R. Jaschke MD, PhD, Abstract Co-Author: Nothing to Disclose

In the present study we evaluated the applicability of a line-detector based photoacoustic tomography (PAT) system to visualize anatomical details of explanted mouse hearts and to detect myocardial infarctions. Results were compared to magnetic resonance images.

Mice with myocardial infarction induced by ligation of the descending branch of the left coronary artery (LAD) were sacrificed after different time periods (1, 2, 3 and 5 days). The hearts were excised and examined by PAT and a clinical 1.5T whole body MRI system (Siemens Avanto) using a standard small loop coil. 3 different hearts for each time period were used. For PAT, the hearts were scanned by a nanosecond pulsed laser using a wavelength of 750 nm. We used a Mach-Zehnder interferometer based photoacoustic setup for the detection of ultrasonic waves emitted from the sample. PAT of the mouse heart required approximately 1.5 hours. Spatial resolution of the current PAT instrumentation is < 100 µm. The MR imaging protocol included 3D T1 weighted gradient echo sequences and 3D T2 weighted TSE sequences with a pixel spacing of 195 µm x 195 µm x 600 µm.

Comparable anatomical details of the heart, like papillary muscles and valves, could be visualized by PAT and MRI. Myocardial infarction was demonstrated by both imaging modalities with comparable image quality and contrast after 2 days and beyond. Ischemic areas were demonstrated as low absorbing areas by PAT. Infarct size corresponded well in PAT and MRI. Comparison of 3 fresh and fixed hearts revealed that in fresh hearts small vessels gave a better signal than in fixed hearts in photoacoustic imaging. This might be due to the degradation of the main absorbing component, hemoglobin, by formaldehyde. These vessels were not visible on MR images.

In the present work we could show that PAT is capable of imaging cardiac anatomy and detecting pathological changes in a heart muscle such as myocardial infarction. In this study, small vessels were clearly seen on PAT, but not on MR images. Due to the high optical absorption of hemoglobin PAT has great potential in the visualization of small myocardial vessels.

PAT is a promising imaging technique with various fields of applications. The use of non-ionizing radiation and low-cost equipment predestine this modality for the application in clinical practice.

Holotta, M, Kremser, C, Schulze, R, Reiner, M, Esterhammer, R, Torbica, P, Jaschke, W, Ex Vivo Photoacoustic Imaging of Myocardial Infarction in Mouse Hearts.  Radiological Society of North America 2011 Scientific Assembly and Annual Meeting, November 26 - December 2, 2011 ,Chicago IL. http://archive.rsna.org/2011/11034570.html