A fast field-cycling MRI relaxometer for physical contrasts design and pre-clinical studies in small animals

Abstract

We present a fast field-cycling NMR relaxometer with added magnetic resonance imaging capabilities. The instrument operates at a maximum proton Larmor frequency of 5 MHz for a sample volume of 35 mL. The magnetic field homogeneity across the sample is 1400 ppm. The main field is generated with a notch-coil electromagnet of own design, fed with a current whose stability is 220 ppm. We show that images of reasonable quality can still be produced under such conditions. The machine is being designed for concept testing of the involved instrumentation and specific contrast agents aimed for field-cycling magnetic resonance imaging applications. The general performance of the prototype was tested through localized relaxometry experiments, T 1 -dispersion weighted images, temperature maps and T 1 -weighted images at different magnetic field intensities. We introduce the concept of positive and negative contrast depending on the use of pre-polarized or nonpolarized sequences. The system is being improved for pre-clinical studies in small animals.

Fast iron oxide-induced low-field magnetic resonance imaging

“…All the experiments were performed using a low-field FFC-MRI relaxometer developed in our laboratory [20]. The maximum detection field (B D ) was 125 mT (5 MHz for protons Larmor frequency) with a magnetic field homogeneity of 1400 ppm (measured within a sample volume of 35 ml).…”

“…Typical image acquisition time of the order of minutes in fast field-cycling MRI (FFC-MRI) represents a clear disadvantage in comparison with standard high-field MRI [18,20]. This fact limits the time-dependent study of certain processes, restricting the access to functional images.…”

Joint multi‐field T1 quantification for fast field‐cycling MRI

“…This approach, also referred to as delta relaxation enhanced MR (dreMR), has auspicious applications for the detection and quantification of contrast agents with increased specificity and sensitivity 9,13‐15 . Several systems were also developed to access the endogenous dispersion of tissues in the low‐field regime 16‐20 . Recently, a whole‐body FFC scanner approved for clinical imaging studies was reported, capable of reaching any field from 50 µT to 0.2T 21 .…”

“… 9 , 13 , 14 , 15 Several systems were also developed to access the endogenous dispersion of tissues in the low‐field regime. 16 , 17 , 18 , 19 , 20 Recently, a whole‐body FFC scanner approved for clinical imaging studies was reported, capable of reaching any field from 50 µT to 0.2T. 21 Controlled variations of the magnetic field with this single resistive magnet design allow for multi‐field quantification over a wide range of field strength while retaining image quality down to ultra‐low fields.…”

Joint multi-field T$_1$ quantification for fast field-cycling MRI

“…This approach, also referred to as delta relaxation enhanced MR (dreMR), has auspicious applications for the detection and quantification of contrast agents with increased specificity and sensitivity [9,13,14,15]. Several systems were also developed to access the endogenous T 1 dispersion of tissues in the low-field regime [16,17,18,19,20].…”