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Non-invasive Diagnostics of Cardiovascular Disease
MRI methods are effective for the monitoring of infarction progression and healing, and for follow up of revascularization or coronary bypass procedures during patient recovery. However, when it is necessary to assess if surgery was successful and blood flow to previously ischemic area(s) has been restored, MRI is not suitable for use in surgical rooms due to the bulkiness and cost of equipment.
There are several techniques, collectively called angiography, used for post-operative monitoring of blood flow through large and medium size vessels. These include X-ray, ultrasonography, and fluorescent imaging of a flow tracer dye called indocyanine green (ICG).
However none of these methods is capable of providing information on tissue oxygenation, the true index of adequate blood supply, which depends not only on blood flow but also on oxygen demand of cardiac tissue.
In collaboration with the NRC-IBD Spectroscopy Group, the Cardiac Studies Group has developed a new method to monitor tissue oxygenation using near-infrared (NIR) spectroscopic imaging. The technique allows acquisition of 2-dimentional maps of the heart surface showing the distribution of oxygenated and deoxygenated hemoglobin (Hb, vascular blood) and myoglobin (Mb, cardiac cells), which directly depends on average tissue oxygen content.
The major advantage of using NIR range (650-1050 nm) is the significant depth of light penetration into the tissue (ca. 10 mm). Unlike visible light that penetrates ca. 1 mm, NIR provides considerable depth of interrogation (subepicardium).
Figure 1 shows a typical set of images obtained from a pig heart in vivo during temporary blockage (called occlusion or ligation) of large left anterior descending artery (LAD).
Figure 1
Detection of cardiac ischemia in vivo by near-infrared spectroscopic (NIRS) imaging
Occlusion results in deoxygenation of the affected area (called the area at risk) indicating insufficient blood supply while occlusion release restores oxygenation of the previously ischemic area. Blood flow deficit (ischemia) can also be detected with NIR flow tracer, indocyanine green (ICG, ~800 nm absorbance peak), which penetrates slower in the affected area (Fig. 2).
Figure 2
Representative ICG maps showing its wash-in and wash-out during LAD occlusion and reflow
On the 5th and 6th frames (8-10 s) in each of 3 sets red areas correspond to well perfused portions of the hearts while blue areas correspond to poorly perfused portions.
In addition, mapping of the surface temperature with a thermal camera also reveals areas of reduced blood flow, which appear as regions of reduced temperature (Fig. 3). NIR and thermal imaging are well suited for intraoperative applications, e.g., during coronary bypass surgery.
Figure 3
Thermal maps of pig heart in vivo during LAD occlusion and reflow
Related Information
Read more about Non-invasive Diagnostics of Cardiovascular Disease:
- Cardiac Energetics and Ion Channels
- Cardiac Ischemia and Infarction
- Myocardial Preservation
- Stem Cells
