Exercise stress cardiac magnetic resonance.

摘要

This work presents the development and validation of a new cardiac stress imaging modality combining treadmill exercise stress testing with cardiac magnetic resonance imaging (exercise CMR). CMR offers several distinct advantages over standard stress imaging modalities. It has higher spatial resolution compared to nuclear scintigraphy without exposure to ionizing radiation, provides better contrast-to-noise than echocardiography, and offers comprehensive diagnostic information by combining stress cardiac function, stress myocardial perfusion, and myocardial viability.;The first step was to test the concept feasibility, combining cardiac wall motion and myocardial perfusion obtained immediately post-exercise with myocardial viability at rest. The feasibility testing was successfully performed in 20 healthy subjects using a partially MRI-compatible treadmill located in the corner of the MRI room. However, several technical challenges including image artifacts and temporal resolution, accuracy of 12-lead electrocardiogram (ECG) monitoring, and the need for a fully MRI-compatible treadmill were identified.;Another aspect of exercise CMR to be considered is 12-lead ECG monitoring inside the MRI room, which is required both during treadmill exercise and recovery. Although the ECG is known to be non-diagnostic within the bore of any high-field magnet due to the magnetohydrodynamic (MHD) effect, the magnetic field threshold below which accurate ECG monitoring is feasible inside the MRI room but outside of the magnet bore was determined. It was shown that reliable ECG measurements could be obtained within the ST segment at magnetic field strengths below approximately 70 mT measured at the aortic arch. This corresponded to approximately 80 cm from the bore entrance for the Siemens 1.5T Avanto system, but could be extrapolated to any other system knowing the magnetic field plot. Based on this threshold, it was shown that accurate 12-lead ECG monitoring is feasible during treadmill exercise immediately adjacent to the magnet and during supine recovery from exercise on the MRI patient table.;Next, the feasibility of exercise CMR for accurate diagnosis of ischemia was investigated in 43 patients with known or suspected coronary artery disease who were referred for treadmill nuclear imaging. Both exercise CMR and nuclear data were obtained while exercising the patient only once. It was shown that exercise CMR could accurately detect coronary artery disease compared to coronary angiography as the gold standard, and preliminary results indicated favorable accuracy compared to nuclear stress imaging. However, the sample size would need to be increased in order to draw statistical conclusions. Successfully demonstrating that exercise CMR is diagnostically and prognostically superior to nuclear stress imaging in a larger clinical trial could have a significant impact on clinical practice and potentially change the current standard of cardiac stress testing.;Although these preliminary studies were conducted using the partially MRI-compatible treadmill in the corner of the MRI room, this would be impractical as a standard clinical stress imaging modality. It was necessary to minimize the time between end of exercise and imaging in order to capture rapidly resolving exercise-induced cardiac wall motion abnormalities, necessitating treadmill placement beside the MRI table. Requiring the patient to walk from a treadmill positioned any distance from the MRI table would create a potential safety concern since patients may become lightheaded and subject to falling immediately following maximal exercise. Furthermore, there was risk of operator error in moving the treadmill too close to the magnet, and the entire setup in the corner of the room would not be possible at higher field strengths such as 3T. Therefore, a fully MRI-compatible water hydraulic treadmill was developed, which could be positioned immediately adjacent to the MRI table. This thesis presents all aspects pertaining to the development and testing of the feedback control system for continuous control of treadmill speed and elevation inside the MRI room. (Abstract shortened by UMI.)