Myocardial Stress Perfusion with a Novel Dual-Source CT Scanner – Technical Update and Initial Clinical Experience F. Bamberg 1 , K. Nikolaou 1 , A. Becker 2 , E. Klotz 3 , B. Schmidt 3 , T. Flohr 3 1 Department of Clinical Radiology, University Hospitals Munich, Munich, Germany 2 Department of Medicine I, University Hospitals Munich, Munich, Germany 3 Siemens Healthcare, Forchheim, Germany Correspondence to: Konstantin Nikolaou Department of Clinical Radiology, University Hospitals Munich, Munich, Germany Tel: +49 89 7095 3620; Fax: +49 89 7095 8832; E-mail: konstantin.nikolaou@med.uni-muenchen.de Key words: Myocardial perfusion imaging, contrast computed tomograpy, cardiac CT. Summary Traditionally, myocardial perfusion imaging by CT has been hampered by limited detector size and stability of Hounsfield Units in moving cardiac acquisition modes. In the present article, we describe the technical principles of a novel, dynamic heart shuttle scan acquisition using a second generation dual source CT system (SOMATOM Definition Flash, Siemens Healthcare, Forchheim, Germany). With simultaneous injection of iodinated con- trast agent, this protocol allows for sequential assessment of myocardial enhancement with reasonable radiation exposure of less than 10 mSv. We also present the case of a 69-year-old male patient who underwent dynamic CT-based myocardial perfusion imaging to determine the hemodynamic relevance of a stenosis in the left anterior descending coronary artery. Introduction – technical Up to now, cardiac perfusion imaging with CT systems was extremely challenging. This was because of several issues and limitations. On one hand, the achievable scan range was limited by the detector width (typically not more than 4 cm). On the other hand, the stability of CT Hounsfield numbers (HU) in cardiac acquisition and reconstruction modes was insufficient for (semi-) quanti- tative perfusion imaging. To fulfil the key pre-requisite of cardiac imaging, which is the highest temporal resolution, 180°-based reconstruction techniques are typically used. Doing so, a temporal resolution of half of the rotation time is achieved for single source CT systems, and of a quarter of the rotation time for dual source systems. Unfortunately, this cardiac CT-specific reconstruction does not have 360° symmetry, which is the optimal setting to obtain stable HU values. This is not really a limitation for dynamic scanning, if the data were always acquired from the same angular positions such as for Electron- Beam CT Systems with triggered acquisition. The partial reconstruction variations are always in the same location and cancel out in a dynamic analysis. In continuously rotating CT system, however, this condition is not ful- filled. The angular position of data acquisition depends on the correlation between heart rate and rotation time, which leads to variable and unpredictable artefacts in the images. Studies have shown (1) [Primak, McCollough, Med. Physics, 2008], that the magnitude of those artefacts (i.e. the change of HU numbers during dynamic acqui- sition) is in the same range as the expected myocardial enhancement. In summary, for dynamic contrast enhanced CT examination of the heart, the discussed limitations with regard to both scan coverage and HU variations have to be overcome first to assess myocardial perfusion with CT techniques. Methods – technical Scans were performed on a second generation dual source CT system: SOMATOM Definition Flash (Siemens Healthcare, Forchheim, Germany). For the dynamic acquisition, a newly developed heart shuttle scan mode was used (see Fig. 1). Data are alternatingly acquired at two table positions in ECG-triggered mode using end- systolic timing; the tables move forward and backward between the two positions with a table acceleration of 300 mm/s 2 . With a detector width of 38 mm, and a 10% overlap between both scan ranges, the scan coverage of this acquisition technique is 73 mm, which is sufficient to cover the complete myocardium in endsystolic extension. Endsystolic triggering was chosen, because it has several advantages: extrasystolic events do not require special control handling; the volume of the left ventricle is smaller; the total amount of intraventricular contrast is 2/2009 n IMAGING DECISIONS