Trends in Cardiovascular Imaging: The Heart in 3D

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3D-Heart.jpg - 3D Heart
View from the inside: Sketch of the live volumetric imaging (LVI) intracardiac catheter, now in development.
Source: RTI International

The 3D revolution hasn’t just taken over Hollywood. Access to volumetric 3D imaging of the heart is changing the way interventional procedures are performed, particularly in patients with challenging and complicated anatomy. Meanwhile, the rapid adoption of 3D transesophageal echocardiography is a result of its usefulness to surgeons, but what will be its ultimate role?

The next wave in 3D

Cardiac catheterization is the standard for assessing anatomy and physiology in congenital heart disease (CHD), and fixed projection angiography is typically used to guide congenital cardiovascular interventions. There are drawbacks, however, to the effectiveness of fixed projection angiography, including limitations in soft tissue visualization and imprecise characterization of segmental branch pulmonary arteries, coronary arteries and other complex structures.

“Understanding...three-dimensional anatomy becomes absolutely key in performing these procedures appropriately.”

Jamil Aboulhosn, MD, director of the Ahmanson/UCLA Congenital Heart Disease Center

Enter rotational angiography, which has advanced cardiac catheterization by enhancing imaging. In contrast to fixed projection 2D angiography, rotational angiography swings the camera 240 degrees around the patient over four seconds at 30 frames/second during expiratory breath-hold, according to Thomas E. Fagan, MD, of Children’s Hospital Colorado in Aurora.

“With one angiogram, by viewing these structures in such different projections, we start to gain a lot more information depending on the type of structure,” says Fagan.

Studies have shown the technique provides diagnostic quality imaging without increasing contrast or radiation exposure (JACC Cardiovasc Imaging 2010;3:1149-57). It can aid clinicians by revealing the relationship between adjacent structures and helps when carrying out procedures with a risk of serious complications.

Fagan breaks rotational angiography down into three modalities, the first being a single, standard 2D angiogram. The 2D x-ray projection images from the rotational angiogram can then be reconstructed into a 3D image volume set, similar to a CT scanner. The third modality is multiplanar reformatting, which is the simultaneous display of 2D image slices from several orientations simultaneously, allowing the user to scroll through the reconstructed volume one slice at a time.

Recently, Fagan and colleagues evaluated the overall diagnostic utility of all three rotational angiography modalities. A pair of reviewers assigned to each modality subjectively rated the utility compared with standard angiograms, and in more than 60 percent of cases, more information was gained using rotational angiography. In 80 percent of cases, it was at least as useful as the standard.

Next steps involve looking at those 20 percent of cases where there was no added benefit and determining when the technology should be applied. There are also some limitations with temporal distortions caused by cardiac motion. Logistically, having the camera in motion requires forethought when setting up a procedure. “You’ve got a very large piece of equipment moving very quickly around a patient,” says Fagan, which means extra care must be taken to make sure people along with cables, tubes and other equipment don’t interfere with the camera’s movement.

The 3D roadmap

3D rotational angiography, CT or MR images can be integrated with fluoroscopy to provide a roadmap to help interventionalists. “Once you bring [the 3D image in] and you step on the fluoro, the 3D image will appear right over the structures that we intend to work with,” says Fagan.

Jamil Aboulhosn, MD, director of the Ahmanson/UCLA Congenital Heart Disease Center, and colleagues have been pushing the envelope on the utilization of 3D overlays, and he explains the leap in technology is akin to the advancement in video games from pixelated Pac-Man in the 1980s to the realistic 3D games of today.

These 3D techniques are invaluable in cases of patients with unusual anatomy such as an upside-down heart or in people born with single ventricle defects. “For all of these things, traditional imaging and assumptions are challenged,” says Aboulhosn. “Understanding roadmaps and three dimensional anatomy becomes absolutely key in performing these procedures appropriately.”

Without the overlay, performing cath lab procedures can be like guiding a wire through shadows and shades of grey. Bringing in a 3D model is similar to dropping the roadmap