Browsing by Subject "Magnetic particle imaging (MPI)"

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Open Access
DC shift based image reconstruction for magnetic particle imaging
(IEEE, 2017) Sarıca, Damla; Demirel, Ömer Burak; Sarıtaş, Emine Ülkü
Magnetic Particle Imaging (MPI) is a new imaging technology that images the spatial distribution of iron oxide nanoparticles. Since the magnetic field strength that can be safely applied in MPI is limited, the field-of-view (FOV) must be divided into partial FOVs. Because the excitation magnetic field causes direct feedthrough on the receiver coil, the excitation frequency must be filtered out of the MPI signal. During this process, the nanoparticle signal at the same frequency is also lost, as a result of which each partial FOV experiences different levels of DC shift. In the standard MPI image reconstruction, these DC shifts are calculated from neighboring overlapping partial FOVs. Here, we propose a novel method that directly reconstructs the MPI image from the calculated DC shift values. Especially in the case of low bandwidth signal acquisitions, this method yields higher resolution images when compared to the standard method. The simulation results at various signal-to-noise ratios (SNR) show that the proposed method produces 6-8 dB increase in peak SNR and yields images that closely match the ideal image.
Open Access
Dynamic decoupling and noise analysis for simultaneous transmission and reception imaging
(2020-08) Taşdelen, Bilal
In simultaneous transmission and reception (STAR) MRI, along with the coupling of the excitation pulse to the received signal, noise, and undesired distortions (spurs) coming from the transmit chain also leak into the acquired signal and degrade image quality. The properties of this coupled noise and its relationship with the transmit ampliﬁer gain, transmit chain noise density, isolation performance, and imaging bandwidth are analyzed. The importance of achieving high isolation and careful selection of the corresponding parameters are demonstrated. A cancellation algorithm, together with a vector modulator, is used for transmit-receive isolation. With higher isolation, coupled transmit noise can be reduced to the point that the dominant noise source becomes acquisition noise, as in the case for pulsed MRI. Ampliﬁers with diﬀerent gain and noise properties are used in the experiments to verify the derived noise-transmit parameter relation. With the proposed technique, more than 80 dB isolation in the analog domain is achieved. The leakage noise and the spurs coupled from the transmit chain are reduced. It is shown that the transmit gain plays the most critical role in determining suﬃcient isolation, whereas the ampliﬁer noise ﬁgure does not contribute as much. Additionally, the active cancellation technique mentioned above is adapted to Magnetic Particle Imaging (MPI) for active cancellation of the direct-feedthrough. A signiﬁcant increase of up to 40 dB in detection sensitivity at the fundamental harmonic on an in-house Arbitrary Waveform Relaxometer (AWR) is demonstrated.