Image quality and diagnostic accuracy of unenhanced SSFP MR angiography compared with conventional contrast-enhanced MR angiography for the assessment of thoracic aortic diseases

The purpose of this study was to determine the image quality and diagnostic accuracy of three-dimensional (3D) unenhanced steady state free precession (SSFP) magnetic resonance angiography (MRA) for the evaluation of thoracic aortic diseases. Fifty consecutive patients with known or suspected thoracic aortic disease underwent free-breathing ECG-gated unenhanced SSFP MRA with non-selective radiofrequency excitation and contrast-enhanced (CE) MRA of the thorax at 1.5 T. Two readers independently evaluated the two datasets for image quality in the aortic root, ascending aorta, aortic arch, descending aorta, and origins of supra-aortic arteries, and for abnormal findings. Signal-to-noise ratio (SNR) and contrast-to-noise ratio (CNR) were determined for both datasets. Sensitivity, specificity, and diagnostic accuracy of unenhanced SSFP MRA for the diagnosis of aortic abnormalities were determined. Abnormal aortic findings, including aneurysm (n = 47), coarctation (n = 14), dissection (n = 12), aortic graft (n = 6), intramural hematoma (n = 11), mural thrombus in the aortic arch (n = 1), and penetrating aortic ulcer (n = 9), were confidently detected on both datasets. Sensitivity, specificity, and diagnostic accuracy of SSFP MRA for the detection of aortic disease were 100% with CE-MRA serving as a reference standard. Image quality of the aortic root was significantly higher on SSFP MRA (P < 0.001) with no significant difference for other aortic segments (P > 0.05). SNR and CNR values were higher for all segments on SSFP MRA (P < 0.01). Our results suggest that free-breathing navigator-gated 3D SSFP MRA with non-selective radiofrequency excitation is a promising technique that provides high image quality and diagnostic accuracy for the assessment of thoracic aortic disease without the need for intravenous contrast material

Haridimos Tsoukas : understanding organizational change via philosophy and complexity

Haridimos (“Hari”) Tsoukas is a Greek organizational theorist whose work has been influential in introducing and popularizing a holistic, process-based conception of organizational change. Traditional accounts of change assume that entities (including organizations) are by nature static and only undergo change after external force is applied. In contrast, Tsoukas maintains that change is ever-present in the social world and that change itself is the intrinsic basis for organizing. As such for Tsoukas, organizations are not static entities but ongoing processes of organizing, embedded within social nexuses of practices and discourses, which are constantly mutating. He identifies two main sources of organizational change: (i) the world being an open-system and (ii) the reflexive agent. The assumptions and conclusions underlying his work have been strongly influenced by interpretative, phenomenological, and process philosophy, as well as complexity theory. To acquaint the reader with his ideas and work, the chapter is structured as follows: first it will describe Tsoukas’ background, secondly it will summarize his key contributions to understanding organizational change, and thirdly it will discuss new insights from his work and it will conclude with his work’s legacies and unfinished business