Temporally flexible artifact suppression high field  SSFP images using Golden Angle incremented linear combination Steady-state Free Precession (LCSSFP) in DESPOT1/2 images
H. Douglas Morris1 and J. Andrew Derbyshire2

1NIH Mouse Imaging Facility, National Institutes of Health, Bethesda, MD, United States, 2Functional MRI Facility, National Institutes of Health, Bethesda, MD, United States


Rapid imaging of endogenously labeled neuroprogenitor cells in the rat brain is shown using high-field MRI and efficient Steady-State Free Precession sequences. A RF-phase cycle progression based on the Golden Angle is used to produce Linear Combination SSFP (LCSSFP) images without banding artifacts. The method yields high resolution images with few global distortions suitable for cell tracking and calculating relaxation images.


MRI is an excellent tool for cell tracking via magnetic micro-particles. It is possible to track individual single cells via magnetic particles greater than 1 micron diameter using high resolution MR microscopy. This technique relies on the magnetic field distortion of the particle to produce a local artifact in the image many times larger that the particle itself.[1] Consequently, cells can be tracked in tissue in 3D and in vivo. In vivo cell labeling techniques are possible using in situ label reservoirs.[2] High concentrations of the magnetic label in the sub-ventricular zone will label neuroprogenitor cells yet generate global magnetic field distortions in high-SNR efficiency techniques such as steady-state free precession (SSFP).[3] The field artifacts can be suppressed by a weighted linear combination of SSFP images with RF cycling (LCSSFP).[4] Quantitative relaxation imaging of labeled tissues is possible using a LCSSP corrected version of the DESPOT method. [5] We describe a technique based on the Golden Angle to parse the offset bandwidth without a fixed set of acquisitions as applied to the LCSSFP technique. Using the Golden angle increment in the RF phase, the banding artifacts do not appear in the same position twice no matter how long the cycle is projected forward. This is analogous to the use of Golden Angle selected projections in back-projection MRI.[6] We demonstrate the utility of this method for rapidly obtaining MR DESPOT images of a rat brain labeled with micron-sized magnetic particles.


MR images were acquired on a Bruker Avance III 14.1T NMR spectrometer with microimaging apparatus (Bruker Biospin, Inc., Billerica MA, USA) using a standard Avance RF III console, Micro-5 gradients (G=1.5 T/m, SR=2500 T/m/s) and 25 mm ID SAW RF coil. The 3D SSFP imaging parameters are TR/TE=2.0/1.0ms, pulse angle 20° or 60°, 1 NEX, FOV 30x18x13 mm, 512x340x168 for a resolution of 50x50x75 µm, with a total acquisition time of 1minute 45 seconds per image. The LCSSFP images were formed by the complex summation of the individual images with a minimum of 3 phase precession sequences. The minimum time required for each LCSSFP image is 3 times that of a single SSFP image. Six-week-old Sprague-Dawley rats (Charles River Laboratories, Inc., Wilmington, MA) were stereotactically injected with 1.4x108 MPIOs (Bangs Laboratories, Inc., Fishers, IN). Two-weeks post injection, animals were transcardially perfused with PBS followed by 10% buffered formalin solution. Intact brains were removed and stored in PBS.


Figure 1 shows representative saggital and transverse slices for a conventional SSFP (A) and LCSSFP (B) sequences through the midplane of a normal rat brain. Figure 1A images demonstrates the banding artifact observed in SSFP images where the high concentration of magnetic particles in the ventricles produce local field gradients and move the resonant frequency out of the passband for the pulse sequence. Figure 1B images are formed of three separate SSFP images with different RF pulse phase progression cycles: (0-0-0-0), (0-137.51-275.02-52.53), and (0-275.02-190.04-105.06). The acquired images are squared, summed, and scaled. The banding artifacts are greatly reduced in the brain tissue away from the large distortions of the high concentration of magnetic particles in the ventricles and produces a high quality image. DESPOT1 or DESPOT2 analysis is performed on the resultant two excitation angle images. Figure 1C is a R1 map calculated image. Total acquisition time is approximately 10:30s.


High-resolution (50x50x75 µm) images of a rat brain injected with iron oxide particles were acquired using SSFP sequence at 14T under 2 minutes. Field artifacts were successfully suppressed using golden angle LCSSFP with 3 phase cycles, with a 3-fold increase in acquisition time. SNR and artifact suppression can be enhanced by incremented the phase cycles and acquiring the additional images independently due to the Golden Angle (GA) progression. The sliding window nature of the GA can be exploited to provide rapid MR microscopy for investigating the position of magnetic particles in the rodent brain even with local field distortions. The resultant images use DEPOT1/2 relaxation analysis to create R1/R2 maps in addition to cell tracking images.


We acknowledge the support of NIH, NINDS, NIMH, and the NIH Mouse Imaging Facility and their staff.


1) Shapiro et al. MRI detection of single particles for cellular imaging. Proc Natl Acad Sci USA 101(30) 10901-6 (2004).

2) Sumner et al. In vivo labeling of adult neural progenitors for MRI with micron sized particles of iron oxide: Quantitation of labeled cell phenotype. Neuroimage 44(3) 671-8 (2009)

3) A. Opplelt et al. FISP: eine neue schenell Pulssequenxae fur die Kernspintomographie., Electromedica 54, 15-18 (1986).

4) SS Vasanawala et al. Linear Combination Steady-State Free Precession MRI, Magn Reson Med 43(1), 82-90 (2000).

5) Deoni et. al. Rapid Combined T1 and T2 Mapping Using Gradient Recalled Acquisition in the Steady State, Magn Reson Med 49(3), 515-526(2003).

6) Winkelmann et al. An optimal radial profile order based on the Golden Ratio for time-resolved MRI. IEEE Trans Med Imag 26(1), 68-76 (2007).


Saggital and Transverse mid-plane images of rat brain and R1 map. (A) SSFP image with single phase cycle. (B) GA-LCSSFP image with three phase cycles and (C ) R1 image from DESPOT1.

Proc. Intl. Soc. Mag. Reson. Med. 24 (2016)