Password Magazine — Issue 14: Healthcare

A healthy regard for better cardiac care

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+ The heart
+ Image processing
+ Imaging modalities
+ Useful links
+ More information

Genomics and other biomedical developments as well as progress in imaging technology are accelerating the build-up of knowledge about the origins and onset of disease and opening up new options for its detection and treatment. Cardiology is one of the areas being impacted by these changes. Volker Rasche looks at Philips' Cardio 2010 project and the role Philips is playing in shaping a world of improved cardiac care.

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The heart

The heart supplies the body with blood rich in oxygen, and pumps the returning blood back to the lungs where it is re-enriched with oxygen. The heart itself needs oxygen as well, which is supplied by the coronary arteries.

The formation of plaque in the coronary arteries is a major cause of heart disease. Two types can be distinguished: stable and unstable (vulnerable) plaque. Stable plaque is the progressive clogging of arteries by continuous deposition. Although potentially life-threatening, it is often detected in time, because patients develop functional complaints before acute myocardial events (ACE). The diagnosis is supported by various imaging modalities such as X-ray, MR, CT, US and ND (see sidebar Imaging modalities). Unstable plaque causes sudden rupture of early deposits from the artery walls. The resulting release of thrombolytic material causes blood clots, which can rapidly block the artery causing ACE or a heart attack. Unstable plaque is responsible for more than 50% of sudden cardiac deaths. Currently, unstable plaque is practically impossible to detect with imaging techniques, although research is being done to change this. Hopefully new techniques will also contribute to early disease assessment in the future, for example by the detection of molecular processes related to early deposits on the walls of blood vessels.

Other major types of heart disease include congestive heart failure (CHF, related to the blood pumping ability of the heart), and arrhythmias (abnormal heart rhythm) such as atrial fibrillation (AF). With increasing life expectancy and ACE survival rates, it can be expected that these diseases will become the most common forms of heart disease after coronary heart disease.

Image processing

Image processing is essential to convert raw imaging data into useful information for the physician.

Heart motion is an important complication in cardiac imaging, because the object changes location in subsequent images. Compensating for this, by accurate, patient-dependent and location-dependent modeling, is an important topic of research.

Several methods are being investigated to further automate the extraction of relevant information. A good example is a project to automatically render the 3-D structure of arteries from subsequent CT slices, and allow the artery to be followed by one movement of a computer mouse. This would help a physician to prepare an intervention, and help him or her navigate during the operation. Other projects aim at enhancing the capabilities of imaging modalities, allowing for example the walls and the inside of arteries to be distinguished in MR data, and hence visualize the formation of plaque, or to properly register time series for perfusion analysis or other dynamic phenomena.

Imaging modalities

Several image modalities exist, each having specific advantages and development issues.

X-ray imaging X-ray imaging is still the most widely used imaging technique. It provides a good spatial resolution (down to 0.2 millimetre) and is well suited to guide intervention. Its main limitation is the need for a contrast medium to enhance the contrast between arteries and surrounding tissue. This medium has to be injected directly into the artery, requiring an interventional procedure. Important current research work is focused on 3-D and 4-D (time-resolved 3-D) reconstruction, for example to obtain information on blood flow or temporal information over one cardiac cycle. Another technique is the development of iterative image-processing methods to calculate images from a limited amount of data. This minimizes the exposure of patients and physicians to radiation.

Magnetic Resonance (MR) imaging MR is rapidly gaining ground in cardiac diagnostics. Unlike X-ray, MR provides good contrast between different types of soft tissue, allowing the characterization of plaque, for example. MR is the only technique capable of providing all major cardiac diagnostic, anatomical and functional information, and is therefore an attractive option for a ‘one-stop shop’ solution. On the other hand, MR is currently limited by its poor spatial resolution and long acquisition times. Philips Research is addressing these issues, for example by using higher magnetic fields, dedicated detection coils for cardiac measurements and more efficient data acquisition strategies.

Nuclear Medicine imaging In Nuclear Medicine (NM) imaging, a contrast medium containing a low concentration of radioactive material is used. The nuclear radiation is detected by a camera and provide information on the perfusion of the heart muscle or its viability, for example. NM imaging is a form of molecular imaging, generating a bright signal (hot spot) at the location of the targeted process. It hardly provides any anatomical information. Other current limitations are the restricted spatial resolution and long acquisition times. Philips Research is currently targeting these limitations by investigating new detector and system concepts for improved sensitivity and spatial resolution, improved motion-compensated registration of NM images to CT for better correlation of the hot-spots to anatomical details, and by improved reconstruction techniques.

Ultrasound Ultrasound is rapidly developing for a broad range of medical applications (see Password 5, pp. 5-8). Besides visualizing structures, ultrasound is particularly suited to characterizing the functioning of organs by real-time imaging. Cardiac applications include the measurement of blood flow inside non-coronary vessels, and the motion of heart and non-coronary vessel walls. The latter can be used as an indicator of the seriousness of plaque deposition at a very early stage, as shown in a project by Philips Research. Further progress in 3-D and real-time imaging, and the development of dedicated algorithms will increase the role of ultrasound in cardiac diagnostics in the future.

Computed Tomography (CT) CT is a combination of X-ray imaging and computer processing that generates 3-D images of internal organs. Its strong point in cardiology is the fact that the entire heart including the heart chambers and the coronary arteries can be covered with reasonable spatial resolution within a few seconds by a single data acquisition. CT is a promising candidate for replacing invasive diagnostic coronary angiography by a non-invasive procedure. Currently, its main limitations are the limited temporal and spatial resolution. Philips Research is actively working on dedicated cardiac acquisition and reconstruction algorithms as well as new detector concepts to improve these points.

Useful links

+ Philips Medical Systems in Cardiology

For more information

Dr Volker Rasche
Principal Scientist at Philips Research Hamburg, Germany
Email: volker.rasche@philips.com