14 August 2016
The accumulation of fat in arteries is a major factor in cardiovascular disease, but monitoring the composition and growth of such deposits inside the body is very difficult. Now, researchers in the US and China have created an intravascular catheter probe that produces accurate, detailed images of fat deposits inside arteries for the first time1.
The excessive build-up of lipids (fat molecules) and fibrous material inside artery walls is known as atherosclerosis. These deposits, called plaques, commonly have a lipid core with a fibrous outer layer, and can grow to either block the artery or rupture suddenly resulting in acute heart failure and death. The precise imaging of different stages of arterial plaques is crucial to identify those most likely to rupture.
Intravascular photoacoustic (IVPA) imaging techniques show promise for this purpose. IVPA works by sending out light from a fast-pulsing laser. Tissue molecules respond to the light stimulation by emitting ultrasound signals that vary depending on their composition. These signals are then analysed to create three-dimensional images showing the location and composition of tissues inside the body.
Now, Ji-Xin Cheng and co-workers at Purdue University in the US, in collaboration with scientists in China, have designed a new IVPA probe capable of imaging artery walls at an appropriate depth and speed to achieve high-resolution pictures of plaques for the first time.
“We designed our probe to allow the light and sound waves to follow the same path throughout the imaging process,” says Cheng. “This ‘collinear’ design means we can see through the entire blood vessel wall, because the penetration depth is enhanced by the overlapping optical and sound waves.”
In previous designs, the emitted light and resulting sound waves crossed paths, distorting the final image and misrepresenting depth, exact plaque location and tissue composition. The accuracy and detail provided by the new probe greatly improves on previous versions, and works at fifty times the speed of existing IVPA probes.
“We trialled our probe using ‘dummy’ fat deposits – namely butter and pig fat – and the clarity and detail of the picture allowed us to differentiate between them,” says Cheng. “Further imaging of pig and human arteries ex vivo [outside the body] provided detailed images of the lipid core and fibrous outer layers of plaques.”
The researchers believe their new design could benefit not just cardiovascular disease monitoring, but prove useful in other applications such as intramuscular imaging. Further work is needed before the probe will be commercially available.
- Cao, Y., Hui, J., Kole, A., Wang, P., Yu, Q. et al. High-sensitivity intravascular photoacoustic imaging of lipid-laden plaque with a collinear catheter design. Nature Scientific Reports (2016). | article