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ABSTRACT: To devise a method allowing real-time optimization of center frequency (CF) and shim for an interactive steady-state free-precession (SSFP) sequence by reformatting a previously acquired field map in the same orientation as the interactive acquisition.
Field maps were acquired in a rectangular parallel-piped phantom and a normal volunteer. An SSFP sequence was modified to communicate the current slice offset and rotation to an external program that reformatted the field map into the same plane, calculated the CF and shim offsets, and passed them back to the sequence. CF offsets as a function of position for the phantom were compared with the scanner prescan-determined offset.
In the phantom, the CF measurements agreed with the scanner-determined offsets. Bland-Altman analysis showed a bias of -14 Hz (field map - prescan) and limits of agreement of -28 to 0 Hz. In the volunteer there was a qualitative improvement in image quality when using the optimized center frequencies and shims.
The proposed method demonstrates how CF and shim can be optimized for any interactively positioned slice, resulting in reduced off-resonance artifacts.
Journal of Magnetic Resonance Imaging 05/2009; 29(5):1230-3. · 2.70 Impact Factor
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ABSTRACT: This paper presents work on interactive 2D projection magnetic resonance angiography, based on fresh blood imaging (FBI), which integrates navigation and triggering optimisation into a continuous fluoroscopic procedure. The technique was developed on a clinical 1.5-T MRI system and performed in five healthy volunteers. Initial feasibility study compared FBI projection angiograms with maximum intensity projection reformats from multi-slice, ECG-gated, 2D time-of-flight (TOF) in the lower peripheral arteries. A technical performance evaluation of 40 vessel segments showed that FBI generated angiograms of comparable diagnostic quality (P < 0.074) with fewer artefacts (P < 0.003). Quantitative vessel-to-background contrast measurements were higher in FBI (P < 0.014). The technique has potential application as an interactive vascular imaging tool in interventional or multi-location MRI examinations.
European Radiology 11/2008; 19(4):904-11. · 3.22 Impact Factor
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ABSTRACT: The mechanical properties of arterial walls have long been recognized to play an essential role in the development and progression of cardiovascular disease (CVD). Early detection of variations in the elastic modulus of arteries would help in monitoring patients at high cardiovascular risk stratifying them according to risk. An in vivo, non-invasive, high resolution MR-phase-contrast based method for the estimation of the time-dependent elastic modulus of healthy arteries was developed, validated in vitro by means of a thin walled silicon rubber tube integrated into an existing MR-compatible flow simulator and used on healthy volunteers. A comparison of the elastic modulus of the silicon tube measured from the MRI-based technique with direct measurements confirmed the method's capability. The repeatability of the method was assessed. Viscoelastic and inertial effects characterizing the dynamic response of arteries in vivo emerged from the comparison of the pressure waveform and the area variation curve over a period. For all the volunteers who took part in the study the elastic modulus was found to be in the range 50–250 kPa, to increase during the rising part of the cycle, and to decrease with decreasing pressure during the downstroke of systole and subsequent diastole.
Engineering in Medicine and Biology Society, 2008. EMBS 2008. 30th Annual International Conference of the IEEE; 09/2008
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ABSTRACT: A compact flow simulator for generating accurate pulsatile flow in a clinical magnetic resonance imaging (MRI) environment has been developed and integrated with a data acquisition (DAQ) system for recording scanner system activity and physiological waveforms. The flow simulator is relatively inexpensive, easy to construct and is controlled from a standard PC. The flow simulator is robust to repeated disassembly and reassembly (normalised cross-correlation 0.97) and generates accurate pulsatile flow (normalised cross-correlation 0.94). The DAQ system was used to monitor a standard MRI pulse sequence used in MR angiography and latent delays in the scanner gating subsystem.
Medical & Biological Engineering & Computing 05/2008; 46(4):399-406. · 1.88 Impact Factor
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ABSTRACT: The mechanical properties of arterial walls have long been recognized to play an essential role in the development and progression of cardiovascular disease (CVD). Early detection of variations in the elastic modulus of arteries would help in monitoring patients at high cardiovascular risk stratifying them according to risk. An in vivo, non-invasive, high resolution MR-phase-contrast based method for the estimation of the time-dependent elastic modulus of healthy arteries was developed, validated in vitro by means of a thin walled silicon rubber tube integrated into an existing MR-compatible flow simulator and used on healthy volunteers. A comparison of the elastic modulus of the silicon tube measured from the MRI-based technique with direct measurements confirmed the method's capability. The repeatability of the method was assessed. Viscoelastic and inertial effects characterizing the dynamic response of arteries in vivo emerged from the comparison of the pressure waveform and the area variation curve over a period. For all the volunteers who took part in the study the elastic modulus was found to be in the range 50-250 kPa, to increase during the rising part of the cycle, and to decrease with decreasing pressure during the downstroke of systole and subsequent diastole.
Conference proceedings: ... Annual International Conference of the IEEE Engineering in Medicine and Biology Society. IEEE Engineering in Medicine and Biology Society. Conference 02/2008; 2008:5569-72.
