Michael Speidel PhD, Presenter: Nothing to Disclose

Brian Patrick Wilfley PhD, Abstract Co-Author: Nothing to Disclose

Josh Star-Lack PhD, Abstract Co-Author: Nothing to Disclose

Joseph Heanue PhD, Abstract Co-Author: Nothing to Disclose

Timothy Betts MS, Abstract Co-Author: Nothing to Disclose

Michael Scott Van Lysel PhD, Abstract Co-Author: Nothing to Disclose

To compare entrance exposure and large-area iodine signal-to-noise ratio (SNR) measured with the Scanning-Beam Digital X-ray (SBDX) prototype to that of a conventional interventional system.

Contrast, noise equivalent quanta (NEQ), and phantom entrance exposure were measured with the SBDX prototype (NexRay, Inc.) and a clinical II/CCD-based angiographic system (Philips H5000, MRC-200 x-ray tube). Phantoms were 23.3 to 35.0-cm thick acrylic with a 1-mm deep iohexol-equivalent disk placed at mid-thickness. The II/CCD system was operated with automatic exposure control. SBDX was operated from 70 kVp/14 kWp to 120 kVp/24 kWp with each phantom. SNR was calculated from disk contrast and NEQ(0), and exposure efficiency was calculated as squared SNR divided by phantom entrance exposure. A theoretical exposure efficiency dependent on primary contrast, scatter fraction, detection efficiency (DQE, grid transmission), beam geometry, and phantom transmission was evaluated for each system.

The SBDX SNR at 120 kVp was 88%, 69%, 72%, and 68% of the II/CCD SNR, respectively, for the 23.3, 28.0, 32.6, and 35.0 cm phantoms. The corresponding II/CCD techniques were 72, 79, 105, and 123 kVp. Comparing systems at equal kVp from thinnest to thickest phantom, SBDX entrance exposure was 3.3 to 9.4 R/min, the II/CCD entrance exposure was 36 to 117 R/min, and the SBDX SNR was 52% to 68% of the II/CCD value. Relative SBDX exposure efficiency ranged from 3.0x (23.3 cm) to 6.7x (32.6 cm). Theoretical predictions were in good agreement with measurements, and indicated that the higher SBDX exposure efficiency was primarily due to low x-ray scatter, a larger entrance field area, and higher overall detection efficiency. Measured scatter plus off-focus radiation fraction was 0.06 to 0.08 with SBDX, compared to 0.33 to 0.54 on the II/CCD system.

The SBDX prototype achieved a 3x to 7x increase in exposure efficiency when compared to conventional angiography. A scanning system with magnetically deflected focal spot and inverse beam geometry performs low scatter imaging at coronary angiographic frame rates, and has the potential to greatly reduce patient exposure for interventional cardiac procedures.

B.P.W.,J.S.,J.H.: Author was an employee of NexRay at the time the research was conducted.

Speidel, M, Wilfley, B, Star-Lack, J, Heanue, J, Betts, T, Van Lysel, M, Exposure Efficiency of the Scanning-Beam Digital X-ray Prototype Compared to a Wide-Beam Cardiac Angiographic System.  Radiological Society of North America 2005 Scientific Assembly and Annual Meeting, November 27 - December 2, 2005 ,Chicago IL. http://archive.rsna.org/2005/4412940.html