Compressed-sensing motion compensation (CosMo): a joint prospective-retrospective respiratory navigator for coronary MRI.

Prospective right hemidiaphragm navigator (NAV) is commonly used in free-breathing coronary MRI. The NAV results in an increase in acquisition time to allow for resampling of the motion-corrupted k-space data. In this study, we are presenting a joint prospective-retrospective NAV motion compensation algorithm called compressed-sensing motion compensation (CosMo). The inner k-space region is acquired using a prospective NAV; for the outer k-space, a NAV is only used to reject the motion-corrupted data without reacquiring them. Subsequently, those unfilled k-space lines are retrospectively estimated using compressed sensing reconstruction. We imaged right coronary artery in nine healthy adult subjects. An undersampling probability map and sidelobe-to-peak ratio were calculated to study the pattern of undersampling, generated by NAV. Right coronary artery images were then retrospectively reconstructed using compressed-sensing motion compensation for gating windows between 3 and 10 mm and compared with the ones fully acquired within the gating windows. Qualitative imaging score and quantitative vessel sharpness were calculated for each reconstruction. The probability map and sidelobe-to-peak ratio show that the NAV generates a random undersampling k-space pattern. There were no statistically significant differences between the vessel sharpness and subjective score of the two reconstructions. Compressed-sensing motion compensation could be an alternative motion compensation technique for free-breathing coronary MRI that can be used to reduce scan time.

Tracking and characterization of fragments in a beating heart using 3D ultrasound for interventional guidance.

Fragments generated by explosions and similar incidents can become trapped in a patient's heart chambers, potentially causing disruption of cardiac function. The conventional approach to removing such foreign bodies is through open heart surgery, which comes with high perioperative risk and long recovery times. We thus advocate a minimally invasive surgical approach through the use of 3D transesophageal echocardiography (TEE) and a flexible robotic end effector. In a phantom study, we use 3D TEE to track a foreign body in a beating heart, and propose a modified normalized cross-correlation method for improved accuracy and robustness of the tracking, with mean RMS errors of 2.3 mm. Motion analysis of the foreign body trajectory indicates very high speeds and accelerations, which render unfeasible a robotic retrieval method based on following the tracked trajectory. Instead, a probability map of the locus of the foreign body shows that the fragment tends to occupy only a small sub-volume of the ventricle, suggesting a retrieval strategy based on moving the robot end effector to the position with the highest spatial probability in order to maximize the possibility of capture.

A method for measuring the accuracy of multi-modal image fusion system for catheter-based cardiac interventions using a novel motion enabled targeting phantom.

Targeted stem cell therapy offers great potential for the repair of infarcted cardiac tissue following heart attack. Safe delivery of stem-cells via catheter based interventions remains a challenge. A multi-modal image fusion approach has been considered for safe targeting of myocardial infarct border zones. In this paper we present an apparatus and method for measuring the accuracy of catheter-based injections using a multi-modal image fusion system. We also present results of the accuracy of our image fusion system under varying levels of cardio-respiratory motion.

Fast and accurate calibration of an X-ray imager to an electromagnetic tracking system for interventional cardiac procedures.

Cardiovascular disease affects millions of Americans each year. Interventional guidance systems are being developed as treatment options for some of the more delicate procedures, including targeted stem cell therapy. As advanced systems for such types of interventional guidance are being developed, electromagnetic (EM) tracking is coming in demand to perform navigation. To use this EM tracking technology, a calibration is necessary to register the tracker to the imaging system. In this paper we investigate the calibration of an X-ray imaging system to EM tracking. Two specially designed calibration phantoms have been designed for this purpose, each having a rigidly attached EM sensor. From a clinical usability point-of-view, we propose to divide this calibration problem into two steps: i) in initial calibration of the EM sensor to the phantom design using an EM tracked needle to trace out grooves in the phantom surface and ii) segmentation from X-ray images and 3D reconstruction of beads embedded in the phantom in a known geometric pattern. Combining these two steps yields and X-ray-to-EM calibration accuracy of less than 1 mm when overlaying an EM tracked needle on X-ray images.

Self-selected resistance training intensity in novice weightlifters.

The purpose of this study was to determine the intensity of self-selected weightlifting exercise in untrained men and women. Thirteen men (age = 19.5 +/- 1.9, height = 70.0 +/- 2.4 in., weight = 174 +/- 20.1 lb, % fat = 14.3 +/- 6.7) and 17 women (age =18.7 +/- 1.0, height = 64.9 +/- 2.3 in., weight = 135.4 +/- 22.8 lb, % fat= 23.4 +/- 4.7) who were novice lifters completed seated bench press, leg extension, seated back row, military press, and biceps curl. Following self-selection trials, subjects' 1 repetition maximum (1RM) was assessed for each lift. Results showed that for both genders, self-selected loads were all below 60% 1RM. All lift intensities were similar for men and women (range = 42-57% 1RM). Repetitions completed and rating of perceived exertion responses were not different between gender. Results show that subjects do not select a lifting intensity sufficient to induce hypertrophic responses and subsequent strength increases.