Robert Michael Lapp, Abstract Co-Author: Employee, VAMP GmbH, Erlangen, Germany

Dirk Ertel, Abstract Co-Author: Nothing to Disclose

Yiannis Kyriakou, Presenter: Nothing to Disclose

Willi A. Kalender PhD, Abstract Co-Author: Consultant, Siemens AG Founder, VAMP GmbH Scientific Advisor, VAMP GmbH Shareholder, VAMP GmbH

To reduce motion artifacts in non-gated dual-energy subtraction chest radiography by motion-free merging.

Dual-Energy chest radiography provides material selective information (soft tissue and bone images) for an improved differentiation of calcifications and lung nodules. The energy selective subtraction performed without ECG-gating results in motion induced artifacts which impairs diagnostic quality. Gated imaging is a logical solution but not routinely offered. We perform two individual measurements with low (60 kV) and high energy (120 kV) spectra. The low-energy image is acquired at the usual dose setting. To gain the high-energy information a series of images is made with an integral dose equivalent to a single conventional image. Both the low-energy image and the high-energy series are conducted at breath-hold so that only heart movement is present. The motion-free merging technique is introduced which combines motion-free areas of the series yielding low image noise and moving but nearly motion artifact free image regions. Finally, weighted logarithmic dual-energy subtraction is applied to the merged high-energy image and the low-energy standard image. Evaluations were performed with simulations and measurements using a C-arm system (Axiom Artis, Siemens AG, Germany) equipped with a digital radiography system using a flat-detector.

The merging approach conserves standard image noise levels in areas without cardiac motion while image noise in pericardial lung regions and in the heart is increased compared to standard images. Motion artifacts in the heart and in the lung areas close to the heart are significantly reduced in the material selective images when compared to a standard non-gated subtraction. The detectability of calcifications in direct heart vicinity in bone images was improved. A series of five projections was sufficient to provide a good synchronization at equivalent total dose.

The presented method is a practical way to reduce motion artifacts in dual energy subtraction radiography even when an ECG gating is not provided.

The method allows for dual-energy material selective images without motion artifacts for non-gated radiography systems.

Lapp, R, Ertel, D, Kyriakou, Y, Kalender, W, Reduction of Motion Artifacts in Non-gated Dual-energy Chest Radiography.  Radiological Society of North America 2007 Scientific Assembly and Annual Meeting, November 25 - November 30, 2007 ,Chicago IL. http://archive.rsna.org/2007/5008551.html