A conventional cardiac catheterization system uses a point x-ray source to project an x-ray beam through the patient onto a large-area detector. NovaRay’s system has an inverse geometry, which consists of a large-area scanning x-ray source and a small-area detector. The scanning x-ray source projects a rapid sequence of narrow x-ray beams through the patient and onto a small-area, high efficiency detector. The system acquires a series of overlapping small-field-of-view images that are combined electronically to generate the full image.

A major advantage of inverse geometry is its inherent scatter reduction. A conventional system has a large-area detector close to the patient’s chest and, therefore, a large amount of scatter radiation reaches the detector. To address this problem, a conventional system incorporates a grid—a parallel arrangement of thin lead-foil strips—between the patient and the detector, to reduce the amount of scatter radiation reaching the detector. Due to the thickness of the lead-foil strips, approximately 30% of the image radiation is absorbed in the scatter-reduction grid, reducing image quality. Because this grid is an imperfect device, typically as much scatter radiation as image radiation reaches the detector. The scatter radiation is noise that lowers the signal-to-noise ratio and reduces image quality.

NovaRay’s system has a small-area detector at a large distance from the patient. With this geometry, very few of the x-ray photons scattered randomly off the patient strike the detector. With much less scattered radiation, there is a significant reduction in the noise source that reduces image quality in a conventional system. By eliminating the need for a scatter-reduction grid, NovaRay also avoids the associated loss of image radiation.

The NovaRay inverse geometry also spreads the incident radiation over a larger area of the patient’s skin. The point x-ray source of a conventional system concentrates the radiation where it enters the patient’s skin. With NovaRay’s distributed x-ray source, x-ray radiation is diffused where it enters the patient’s skin, spreading radiation over approximately double the area of a conventional system, cutting skin radiation exposure by 50% and reducing the possibility of radiation injury.

Inverse geometry also allows for open patient access. The large-area detector in a conventional system must be kept close to the patient’s chest for optimum image quality. This arrangement is claustrophobic for the patient and restricts access of the clinical staff to the patient. In contrast, the NovaRay detector is approximately one meter away from the patient, allowing easy patient access at all times.