Ashok Ramachandra

Publications of Ashok Ramachandra

• Adenosine-stress dynamic real-time myocardial perfusion CT and adenosine-stress first-pass dual-energy myocardial perfusion CT for the assessment of acute chest pain: Initial results.

  Authors: Markus Weininger, U Joseph Schoepf, Ashok Ramachandra, Christian Fink, Garrett W Rowe, Philip Costello, Thomas Henzler

  European journal of radiology. 12/2010;

  PURPOSE: Recent innovations in CT enable the evolution from mere morphologic imaging to dynamic and functional testing. We describe our initial experience performing myocardial stress perfusion CT inPURPOSE: Recent innovations in CT enable the evolution from mere morphologic imaging to dynamic and functional testing. We describe our initial experience performing myocardial stress perfusion CT in a clinical population with acute chest pain. METHODS AND MATERIALS: Myocardial stress perfusion CT was performed on twenty consecutive patients (15 men, 5 women; mean age 65±8 years) who presented with acute chest pain and were clinically referred for stress/rest SPECT and cardiac MRI. Prior to CT each patient was randomly assigned either to Group A or to Group B in a consecutive order (10 patients per group). Group A underwent adenosine-stress dynamic real-time myocardial perfusion CT using a novel "shuttle" mode on a 2nd generation dual-source CT. Group B underwent adenosine-stress first-pass dual-energy myocardial perfusion CT using the same CT scanner in dual-energy mode. Two experienced observers visually analyzed all CT perfusion studies. CT findings were compared with MRI and SPECT. RESULTS: In Group A 149/170 myocardial segments (88%) could be evaluated. Real-time perfusion CT (versus SPECT) had 86% (84%) sensitivity, 98% (92%) specificity, 94% (88%) positive predictive value, and 96% (92%) negative predictive value in comparison with perfusion MRI for the detection of myocardial perfusion defects. In Group B all myocardial segments were available for analysis. Compared with MRI, dual-energy myocardial perfusion CT (versus SPECT) had 93% (94%) sensitivity, 99% (98%) specificity, 92% (88%) positive predictive value, and 96% (94%) negative predictive value for detecting hypoperfused myocardial segments. CONCLUSION: Our results suggest the clinical feasibility of myocardial perfusion CT imaging in patients with acute chest pain. Compared to MRI and SPECT both, dynamic real-time perfusion CT and first-pass dual-energy perfusion CT showed good agreement for the detection of myocardial perfusion defects.

• Iterative image reconstruction techniques: Applications for cardiac CT.

  Authors: Matthias Renker, Ashok Ramachandra, U Joseph Schoepf, Rainer Raupach, Paul Apfaltrer, Garrett W Rowe, Sebastian Vogt, Thomas G Flohr, J Matthias Kerl, Ralf W Bauer, Christian Fink, Thomas Henzler

  Journal of cardiovascular computed tomography. 5(4):225-30.

  Traditional limitations of cardiac CT are related to image noise, blooming artifacts from calcifications and stents, and radiation exposure. We evaluated whether these limitations can be amelioratedTraditional limitations of cardiac CT are related to image noise, blooming artifacts from calcifications and stents, and radiation exposure. We evaluated whether these limitations can be ameliorated by the use of iterative reconstruction in image space (IRIS) instead of traditional filtered back projection (FBP) image reconstruction techniques. We compared image reconstruction with the use of IRIS with traditional FBP for their effect on image quality, noise, volume of heavy coronary artery calcifications, and stents as a measure of "blooming" artifacts, and radiation dose at cardiac CT. The radiation dose comparison was performed as a matched pair analysis, whereas all other comparisons were performed within the same group of patients. The subjective image quality of IRIS reconstructions was rated higher than FBP reconstructions. Image noise was lower with IRIS than with FBP. The volume of stents and heavy coronary artery calcifications measured lower in IRIS reconstructed series compared with FBP. Similar levels of image noise were achieved with 80/100 kVp of tube voltage with IRIS compared with 120 kVp and FBP, resulting in a 62% reduction in effective dose. Our preliminary experiences suggest that IRIS incrementally improves the CT evaluation of coronary arteries, especially in challenging scenarios. Substantial radiation reduction seems feasible without associated increases in image noise.