ABSTRACT
PURPOSE: To generate phase images with free of motion-induced artifact and susceptibility-induced distortion using 3D radial ultrashort TE (UTE) MRI.MATERIALS AND METHODS: The field map was theoretically derived by solving Laplace's equation with appropriate boundary conditions, and used to simulate the image distortion in conventional spin-warp MRI. Manufacturer's 3D radial imaging sequence was modified to acquire maximum number of radial spokes in a given time, by removing the spoiler gradient and sampling during both rampup and rampdown gradient. Spoke direction randomly jumps so that a readout gradient acts as a spoiling gradient for the previous spoke. The custom raw data was reconstructed using a homemade image reconstruction software, which is programmed using Python language. The method was applied to a phantom and in-vivo human brain and abdomen. The performance of UTE was compared with 3D GRE for phase mapping. Local phase mapping was compared with T₂* mapping using UTE.RESULTS: The phase map using UTE mimics true field-map, which was theoretically calculated, while that using 3D GRE revealed both motion-induced artifact and geometric distortion. Motion-free imaging is particularly crucial for application of phase mapping for abdomen MRI, which typically requires multiple breathold acquisitions. The air pockets, which are caught within the digestive pathway, induce spatially varying and large background field. T₂* map, that was calculated using UTE data, suffers from non-uniform T₂* value due to this background field, while does not appear in the local phase map of UTE data.CONCLUSION: Phase map generated using UTE mimicked the true field map even when non-zero susceptibility objects were present. Phase map generated by 3D GRE did not accurately mimic the true field map when non-zero susceptibility objects were present due to the significant field distortion as theoretically calculated. Nonetheless, UTE allows for phase maps to be free of susceptibility-induced distortion without the use of any post-processing protocols.
Subject(s)
Humans , Abdomen , Artifacts , Boidae , Brain , Image Processing, Computer-Assisted , Magnetic Resonance Imaging , MethodsABSTRACT
PURPOSE: Children born with single ventricle physiology demonstrate poor growth rate and suffer from malnutrition, which lead to increased morbidity and mortality in this population. We assume that an anabolic steroid, oxandrolone, will promote growth in these infants by improving myocardial energy utilization. The purpose of this paper is to study the efficacy of oxandrolone on myocardial energy consumption in these infants. MATERIALS AND METHODS: We modeled single ventricle physiology in a lamb by prenatally shunting the aorta to the pulmonary artery and then postnatally, we monitored cardiac energy utilization by quantitatively measuring the first order reaction rate constant, kf of the creatine-kinase reaction in the heart using magnetization transfer 31P magnetic resonance spectroscopy, home built 1H/31P transmit/receive double tuned coil, and transmit/receive switch. We also performed cine MRI to study the structure and dynamic function of the myocardium and the left ventricular chamber. The spectroscopy data were processed using home-developed python software, while cine data were analyzed using Argus software. RESULTS: We quantitatively measured both the first order reaction rate constant and ejection fraction in the control, shunted, and the oxandrolone-treated lambs. Both kf and ejection fraction were found to be more significantly reduced in the shunted lambs compared to the control lambs, and they are increased in oxandrolone-treated lambs. CONCLUSION: Some improvement was observed in both the first order reaction rate constant and ejection fraction for the lamb treated with oxandrolone in our preliminary study.