Stopping Heart Attacks

“Joint cardiac and respiratory motion correction and super-resolution in coronary PET/CT”

Sonal Ambwani (PhD’11)
Prof. W.Clem Karl, Dr. Ahmet Tawakol (Mass. General Hospital), Dr. Homer Pien (Mass. General Hospital)

Funding: Bernard M. Gordon Center for Subsurface Sensing & Imaging Systems (CenSSIS)

Background: Coronary artery diseases(CAD) such as Atherosclerosis is the leading cause of mortality in industrialized nations. It is characterized by chronic inflammation and plaque formation in the arterial walls due to the deposition of activated macrophage white blood cells, low-density lipoproteins, and calcium. If not properly diagnosed and treated, this plaque can lead to severe complications resulting in myocardial infarction. Cardiac catheterization is the current gold standard for assessing the severity of coronary artery stenosis, but this technique provides no information about the physiological state of the coronary walls. Non-invasive techniques such as cardiac computed tomography (CT) provides information on both stenosis and plaque composition, but yields no insight on the degree of inflammation. Positron emission tomography (PET) has been shown to have the potential of imaging inflammation in large and static blood vessels such as the carotid artery in the neck. However, PET images of the heart have severe blurring induced by the presence of cardiac and respiratory motion during the 15-20 minutes of PET acquisition. Figure 1. illustrates the PET/CT cardiac imaging problem.

PET image (left); corresponding CT image with coronary plaque in the box (middle); fused PET/CT image demonstrating the loss of resolution in PET (right)

PET image (left); corresponding CT image with coronary plaque in the box (middle); fused PET/CT image demonstrating the loss of resolution in PET (right)

Description: The overall aim of this research project is to allow direct, non-invasive imaging of developing coronary plaques. This goal can be accomplished by enabling high resolution, high signal-to-noise (SNR) imaging of coronary artery inflammation through PET-CT. This is achieved by jointly compensating for both cardiac and respiratory motion and performing super-resolution reconstruction of the PET. X-ray CT images are taken in a breath-hold state. Thus, they are used to provide respiration free cardiac motion information. It is safe to assume that the PET and CT volumes are in perfect alignment. This cardiac motion information is then incorporated in a unified PET reconstruction functional which jointly estimates the residual respiratory motion, corrects for both phase-aligned cardiac and respiratory motion and provides a super-resolved estimate of the PET reconstruction. A key feature of this approach is that we make use of all available data which leads to the preservation of SNR. We have termed our technique as Data-domain Cardiac Shape Tracking and Adjustment for Respiration of D-CSTAR.

From left to right: Reference image with plaque lesion indicated by arrow; conventional PET reconstruction result with no motion correction; “motion-frozen” method result that ignores respiration; “dual-gated” method result that involves discarding data; D-CSTAR result

From left to right: Reference image with plaque lesion indicated by arrow; conventional PET reconstruction result with no motion correction; “motion-frozen” method result that ignores respiration; “dual-gated” method result that involves discarding data; D-CSTAR result

Results: The experiments have been performed on the Extended Cardiac Torso (XCAT) generated cardiac CT and PET activity phantoms. In Figure 2 and 3 we present the comparison of the D-CSTAR approach with the conventional PET reconstruction and two of the methods proposed previously in literature. The proposed D-CSTAR method has proved to outperform these methods both qualitatively and quantitatively in reconstructing a well defined, localized lesion.

Line profiles through the red cross section shown in results above (D-CSTAR, motion frozen and dual-gated methods).

Line profiles through the red cross section shown in the results above.

Publications:

S. Ambwani, S. Cho, W.C. Karl, A. Tawakol, and H. Pien, “A feasibility study of joint respiratory and cardiac motion correction for coronary PET/CT imaging,” Biomedical Imaging: From Nano to Macro, 2009. ISBI ’09. IEEE International Symposium on, pp. 935 –938, Jun. 2009.

S. Ambwani, W.C. Karl, A. Tawakol, and H. Pien, ” Joint cardiac and respiratory motion correction and super-resolution in coronary PET/CT”, submitted to ISBI’11.