Non-cryogenic anatomical imaging in ultra-low field regime: Hand MRI demonstration

Abstract

Ultra-low field (ULF) MRI with a pulsed prepolarization is a promising method with potential for applications where conventional high-, mid-, and low-field medical MRI cannot be used due to cost, weight, or other restrictions. Previously, successful ULF demonstrations of anatomical imaging were made using liquid helium-cooled SQUIDs and conducted inside a magnetically shielded room. The Larmor frequency for these demonstrations was ~ 3 kHz. In order to make ULF MRI more accessible, portable, and inexpensive, we have recently developed a non-cryogenic system. To eliminate the requirement for a magnetically shielded room and improve the detection sensitivity, we increased the frequency to 83.6 kHz. While the background noise at these frequencies is greatly reduced, this is still within the ULF regime and most of its advantages such as simplicity in magnetic field generation hardware, less stringent requirements for uniform fields etc., remaining. In this paper we demonstrate use of this system to image a human hand with up to 1.5 mm resolution. The signal-to-noise ratio was sufficient to reveal anatomical features within a scan time of less than 7 minutes. This prototype can be scaled up for constructing head and full body scanners, and work is in progress toward demonstration of head imaging.

Applications of optically detected MRI for enhanced contrast and penetration in metal

“…The spatially and temporally resolved flow information is essential for the many applications of porous metals. Combined with recent developments in anatomical imaging by Savukov and coworkers [39], optically detected MRI may have broad applications in many disciplines.…”

Non-cryogenic ultra-low field MRI of wrist–forearm area

“…To increase the volume for imaging we modified significantly our previous setup [24] used for the hand MRI. First of all, we increased the dimensions of the Bp electro-magnet to an ID of 160 mm and a depth of 190 mm.…”

“…To investigate the performance and noise of a ULF-MRI system with a pre-polarization coil and internal shield we developed a non-cryogenic pick-up coil based hand-MRI ULF scanner operating at 83.6 kHz [24]. We demonstrated hand-MRI imaging with 2×2 and 1.5×1.5 mm 2 resolutions acquired in less than 20 minutes.…”

“…Our new modified system for hand and arm imaging has many parts identical to those used in the previous setup [24], namely, the Bm and gradient coils, the gradient amplifiers, computer interface, but several parts such as the Bp coil, the switch for the Bp coil, the rf shield, and the pick-up coil were replaced. The sequence also was the same, although the sequence parameters were optimized for new conditions.…”

Spin damping in an rf atomic magnetometer

“…Recently, atomic magnetometers using optically-pumped alkali atoms have been shown to be more sensitive to radio-frequency magnetic fields than standard coil detection [3], particularly at low frequencies as is needed for low-field magnetic resonance [4][5][6][7][8] or nuclear quadrupole resonance [9]. Sensitivities as low as 0.2 fT/ √ Hz are gained at the expense of operating with a relatively narrow signal bandwidth, on the order of a half a kHz, or a correspondingly long alkali spin-spin relaxation time T 2 of about a millisecond [9].…”