A portable single‐sided magnet system for remote NMR measurements of pulmonary function

Abstract

In this work, we report initial results from a light-weight, low field magnetic resonance device designed to make relative pulmonary density measurements at the bedside. The development of this device necessarily involves special considerations for the magnet, RF and data acquisition schemes as well as a careful analysis of what is needed to provide useful information in the ICU. A homogeneous field region is created remotely from the surface of the magnet such that when the magnet is placed against the chest, an NMR signal is measured from a small volume in the lung. In order to achieve portability, one must trade off field strength and therefore spatial resolution. We report initial measurements from a ping-pong ball size region in the lung as a function of lung volume. As expected, we measured decreased signal at larger lung volumes since lung density decreases with increasing lung volume. Using a CPMG sequence with ΔTE=3.5 ms and a 20 echo train, a signal to noise ratio ~1100 was obtained from an 8.8mT planar magnet after signal averaging for 43 s. This is the first demonstration of NMR measurements made on a human lung with a light-weight planar NMR device. We argue that very low spatial resolution measurements of different lobar lung regions will provide useful diagnostic information for clinicians treating Acute Respiratory Distress Syndrome as clinicians want to avoid ventilator pressures that cause either lung over distension (too much pressure) or lung collapse (too little pressure).

Operational Amplifiers Revisited for Low Field Magnetic Resonance Relaxation Time Measurement Electronics

“…A typical system of off the shelf components may consist of a ZHL-3A+ power amplifier from Mini-Circuits (US$229) fed to the input to an nmrservice.de transcoupler (duplexer) that operates from 0.7 to 1 MHz (US$735) and the return signal amplified using a Mini-Circuits ZFL-500LN (US$93) giving a cost of more than US$1000. Advances in permanent magnet technology has seen report of applications of low field unilateral magnets below 20 mT corresponding to frequencies below 1 MHz [7]. In this work we demonstrate that the current generation of operational amplifiers, in the form of a simple inverting design, can effectively provide the power and preamplifiers in this frequency range and at a fraction of the cost of commercial components.…”

NMR CAPIBarA: Proof of Principle of a Low-Field Unilateral Magnetic Resonance System for Monitoring of the Placenta during Pregnancy

“…Figure 2b shows the top view of the magnet array. Unlike Dabaghyan et al [16], who made use of a solenoid to interrogate a large sample volume, a planar coil was produced using a milled 75 μm FR4 Printed Circuit Board (PCB) with 5 turns at a line width of 2 mm, with 1mm spacing between tracks, inner and outer coil lengths of 82 mm and 105 mm, respectively, and inner and outer coil widths of 40 mm and 67 mm, respectively, with an epoxy resin coating applied post-production. The coil is also visible in Figure 2b.…”

“…In an article by Dabaghyan et al [16], the authors presented a unilateral magnet design which, like the NMR MoUSE, provides a B 0 parallel with the surface of the magnet. Their magnet was constructed from two rectangular arrays of 240 small NdFeB magnets, around 400 mm between centers with a saddle point at around 80 mm above the magnet surface and with a field strength at this point of 10 mT (note that this is more than an order of magnitude smaller than the 0.25 T and above of the profile NMR-MoUSE family).…”

Deep neural-network based optimization for the design of a multi-element surface magnet for MRI applications

“…There are two broad classes of optimization target fields: one which consists of a linear static magnetic field gradient perpendicular to the surface of the magnet [ 28 , 32 , 33 , 35 , 41 , 45 , 49 ] or a localized ‘sweet spot’ consisting of a ROI in which the magnetic field is relatively homogeneous in all three dimensions [ 29 , 30 , 34 , 42 , 43 , 48 , 50 ]. In the next section we will use the EA model we developed to find an optimized magnet design solution by varying the relative positions of the individual permanent cubic magnets.…”