Purpose Point‐of‐care MRI requires operation outside of Faraday shielded rooms normally used to block image‐degrading electromagnetic interference (EMI). To address this, we introduce the EDITER method (External Dynamic InTerference Estimation and Removal), an external sensor‐based method to retrospectively remove image artifacts from time‐varying external interference sources. Theory and Methods The method acquires data from multiple EMI detectors (tuned receive coils as well as untuned electrodes placed on the body) simultaneously with the primary MR coil during and between image data acquisition. We calculate impulse response functions dynamically that map the data from the detectors to the time varying artifacts then remove the transformed detected EMI from the MR data. Performance of the EDITER algorithm was assessed in phantom and in vivo imaging experiments in an 80 mT portable brain MRI in a controlled EMI environment and with an open 47.5 mT MRI scanner in an uncontrolled EMI setting. Results In the controlled setting, the effectiveness of the EDITER technique was demonstrated for specific types of introduced EMI sources with up to a 97% reduction of structured EMI and up to 76% reduction of broadband EMI in phantom experiments. In the uncontrolled EMI experiments, we demonstrate EMI reductions of up to 99% using an electrode and pick‐up coil in vivo. We demonstrate up to a nine‐fold improvement in image SNR with the method. Conclusion The EDITER technique is a flexible and robust method to improve image quality in portable MRI systems with minimal passive shielding and could reduce the reliance of MRI on shielded rooms and allow for truly portable MRI.

BackgroundThe meniscus plays a crucial role in knee joint stability, load transmission, and stress distribution. Meniscal tears are the most common reported knee injuries, and the current standard treatment for meniscal deficiency is meniscal allograft transplantation. A major limitation of this approach is that meniscal allografts do not have the capacity to remodel and maintain tissue homeostasis due to a lack of cellular infiltration. The purpose of this study was to provide a new method for enhanced cellular infiltration in meniscal allografts.MethodsTwenty medial menisci were collected from cadaveric human sources and split into five experimental groups: (1) control native menisci, (2) decellularized menisci, (3) decellularized menisci seeded with human adipose-derived stem cells (hASC), (4) decellularized needle-punched menisci, and (5) decellularized needle-punched menisci seeded with hASC. All experimental allografts were decellularized using a combined method with trypsin EDTA and peracetic acid. Needle punching (1-mm spacing, 28 G microneedle) was utilized to improve porosity of the allograft. Samples were recellularized with hASC at a density of 250 k/g of tissue. After 28 days of in vitro culture, menisci were analyzed for mechanical, biochemical, and histological characteristics.ResultsMenisci maintained structural integrity and material properties (compressive equilibrium and dynamic moduli) throughout preparations. Increased DNA content was observed in the needle-punched menisci but not in the samples without needle punching. Histology confirmed these results, showing enhanced cellular infiltration in needle-punched samples.ConclusionsThe enhanced infiltration achieved in this study could help meniscal allografts better remodel post-surgery. The integration of autologous adipose-derived stem cells could improve long-term efficacy of meniscal transplantation procedures by helping to maintain the meniscus in vivo.

Purpose To perform B1+$$ {B}_1^{+} $$‐selective excitation using the Bloch–Siegert shift for spatial localization. Theory and Methods A B1+$$ {B}_1^{+} $$‐selective excitation is produced by an radiofrequency (RF) pulse consisting of two summed component pulses: an off‐resonant pulse that induces a B1+$$ {B}_1^{+} $$‐dependent Bloch–Siegert frequency shift and a frequency‐selective excitation pulse. The passband of the pulse can be tailored by adjusting the frequency content of the frequency‐selective pulse, as in conventional B0$$ {B}_0 $$ gradient‐localized excitation. Fine magnetization profile control is achieved by using the Shinnar–Le Roux algorithm to design the frequency‐selective excitation pulse. Simulations analyzed the pulses' robustness to off‐resonance, their suitability for multi‐echo spin echo pulse sequences, and how their performance compares to that of rotating‐frame selective excitation pulses. The pulses were evaluated experimentally on a 47.5 mT MRI scanner using an RF gradient transmit coil. Multiphoton resonances produced by the pulses were characterized and their distribution across B1+$$ {B}_1^{+} $$ predicted. Results With correction for varying B1+$$ {B}_1^{+} $$ across the desired profile, the proposed pulses produced selective excitation with the specified profile characteristics. The pulses were robust against off‐resonance and RF amplifier distortion, and suitable for multi‐echo pulse sequences. Experimental profiles closely matched simulated patterns. Conclusion The Bloch–Siegert shift can be used to perform B0$$ {B}_0 $$‐gradient‐free selective excitation, enabling the excitation of slices or slabs in RF gradient‐encoded MRI.

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Point of care MRI requires operation outside of an MR shielded room where electromagnetic interference can degrade image quality. To address this, we demonstrate a self-calibrated generalized dynamic model to retrospectively remove time-varying external interference. The method uses data acquired from multiple Electromagnetic Interference (EMI) detectors simultaneous with the primary MR coil. We test the approach both in a controlled EMI setting on an 80mT Halbach scanner and an uncontrolled real-world EMI setting on a 47.5mT permanent magnet open MRI system.