Schar, Nezafat, Stuber, Boesiger, Kozerke. Tailoring transient balanced gradient echo coronary MRA at 3T. Proc Fourteenth Scientific Meeting of Int Soc Magn Reson Med 370. 2006.
Publications
2006
Caplan LR, Manning WJ. Brain Embolism. Taylor & Francis; 2006. p. 348.
The only source to fully cover every aspect of brain embolism, this guide analyzes the causes, symptoms, diagnosis, and management of this disorder-providing a detailed overview of major topics pertinent to embolism including donor sources, recipient sites, embolic material, recipient brain supply arteries, vascular and brain pathology, and the treatment of cardiac and arterial sources. Clearly guiding readers through key anatomical structures, diagnostic developments, therapeutic advances, and best practices in clinical care, this source will serve as a must-have desk reference for any clinician in the field.
Nezafat R, Thompson R, Derbyshire A, McVeigh E. Partial field-of-view spiral phase-contrast imaging using complex difference processing. Magn Reson Med. 2006;56(3):676–80.
Rapid flow imaging was achieved with a partial field of view (pFOV) spiral motion-encoded technique. The FOV and the acquisition time were reduced by a factor of 2 by undersampling k-space. The pFOV spiral k-space trajectory aliased signals from outside a circular ring whose radius was inversely proportional to the distance between adjacent spirals in k-space. In this study the FOV was adjusted so that all of the moving spins were located inside the inner half circle of the full FOV. Complex subtraction of two differentially flow-encoded images was used to remove the spurious phase sources and provide an accurate measurement of flow. The complex subtraction process also serves to eliminate aliasing artifacts that are generated by static tissue from outside the reduced FOV. Experiments in a flow phantom and volunteers showed that the flow estimates obtained by pFOV spiral motion encoding are in good agreement with the estimates reconstructed using complex difference processing.
Nezafat R, Stuber M, Ouwerkerk R, Gharib A, Desai M, Pettigrew R. B1-insensitive T2 preparation for improved coronary magnetic resonance angiography at 3 T. Magn Reson Med. 2006;55(4):858–64.
At 3 T, the effective wavelength of the RF field is comparable to the dimension of the human body, resulting in B1 standing wave effects and extra variations in phase. This effect is accompanied by an increase in B0 field inhomogeneity compared to 1.5 T. This combination results in nonuniform magnetization preparation by the composite MLEV weighted T2 preparation (T2 Prep) sequence used for coronary magnetic resonance angiography (MRA). A new adiabatic refocusing T2 Prep sequence is presented in which the magnetization is tipped into the transverse plane with a hard RF pulse and refocused using a pair of adiabatic fast-passage RF pulses. The isochromats are subsequently returned to the longitudinal axis using a hard RF pulse. Numerical simulations predict an excellent suppression of artifacts originating from B1 inhomogeneity while achieving good contrast enhancement between coronary arteries and surrounding tissue. This was confirmed by an in vivo study, in which coronary MR angiograms were obtained without a T2 Prep, with an MLEV weighted T2 Prep and the proposed adiabatic T2 Prep. Improved quantitative and qualitative coronary MRA image measurement was achieved using the adiabatic T2 Prep at 3 T.
2005
Nezafat R Kellman P, Stehning C Nezafat R, AM G, MY D, RG W, RI P, ER M, M S. Improved spatial-temporal resolution MR coronary blood flow imaging at 3T. J Cardiovasc Magn Reson 7(1) 199. 2005.
Nezafat R Kellman P, R O, AM G, MY D, RG W, RI P, ER M, M S. Blood pool signal loss in the presence of field inhomogeneity at 3T coronary imaging. Biomedical Engineering Society Annual Fall Meeting. 2005.
Nezafat R Kellman P, RB T, ER M. Partial field of view phase contrast MR imaging. Biomedical Engineering Society Annual Fall Meeting. 2005.
Nezafat R Kellman P, R O, AM G, RI P, ER M, M S. B1 Insensitive T2 preparation sequence for coronary imaging at 3T. Proc Thirteenth Scientific Meeting of Int Soc Magn Reson Med 2794. 2005.
Stehning C Nezafat R, Nezafat R Kellman P, AM G, MY D, RG W, RI P, ER M, M S. Dual navigators for time-resolved MR coronary blood flow imaging at 3T during free breathing. Proc Thirteenth Scientific Meeting of Int Soc Magn Reson Med 1616. 2005.
Nezafat R, Kellman P, Derbyshire A, McVeigh E. Real-time blood flow imaging using autocalibrated spiral sensitivity encoding. Magn Reson Med. 2005;54(6):1557–61.
A novel spiral phase contrast (PC) technique was developed for high temporal resolution imaging of blood flow without cardiac gating. An autocalibrated spiral sensitivity encoding (SENSE) method is introduced and used to reconstruct PC images. Numerical simulations and a flow phantom study were performed to validate the technique. To study the accuracy of the flow measurement in vivo, a high-resolution cardiac experiment was performed and a subset of undersampled SENSE reconstructed data were reconstructed. Good agreement between the velocity measurement from the fully-sampled and undersampled data was achieved. Real-time experiments were performed to measure blood velocity in the ascending aorta and aortic valve, and during a Valsalva maneuver. The results demonstrate the potential of this technique for real-time flow imaging.