Towards Fast Diffusion-Sensitized MR Imaging of the Eye and Orbit with High Anatomic Fidelity: Combining a Segmented RARE variant with Inner Volume Imaging
Katharina Paul1, Till Huelnhagen1, Oliver Stachs2, and Thoralf Niendorf1,3

1Berlin Ultrahigh Field Facility (B.U.F.F), Max Delbrück Center for Molecular Medicine in the Helmholtz Association (MDC), Berlin, Germany, 2Department of Ophthalmology, University Medicine Rostock, Rostock, Germany, 3Experimental and Clinical Research Center, a joint cooperation between the Charité Medical Faculty and the Max-Delbrueck-Center for Molecular Medicine in the Helmholtz Association, Berlin, Germany


Diffusion-weighted imaging of the eye and orbit is an emerging MRI application to provide guidance during diagnostic assessment and treatment of ophthalmological diseases. It has been shown that RARE based diffusion-sensitized imaging (ms-RARE) provides images free of geometric distortions. Though, artifacts induced by involuntary eye motion remain a concern. Applying inner volume imaging (IVI) offers the possibility to shorten acquisition times by reducing the number of acquired phase encoding lines. This study examines the applicability of IVI in conjunction with ms-RARE with the goal to reduce the propensity to bulk eye motion in diffusion-sensitized ophthalmic imaging.


MRI of the spatial arrangements of the eye segments and their masses is an emerging application increasingly used in (pre)-clinical imaging and diagnostic radiology [1-5]. Diffusion‑weighted MRI (DWI) probes self-diffusion of water in tissue on a microscopic level and holds the promise to enhance the diagnostic accuracy over anatomic ophthalmic imaging [6]. Diffusion-sensitized segmented split-echo rapid acquisition with relaxation enhancement (ms-RARE) imaging provides high-spatial resolution images of the eye, orbit and Nervus opticus at 3.0 T and 7.0 T [7]. Geometric distortions that are observed for EPI-DWI approaches even at lower field strengths are offset by DWI using ms-RARE, but artifacts induced by involuntary eye motion remain a concern. Inner volume imaging (IVI) [8] is particularly suited for ophthalmic imaging since the field of view (FOV) can be conveniently adjusted to the target region. This study examines the applicability of IVI in conjunction with ms-RARE with the goal to shorten acquisition time and to reduce the propensity to bulk eye motion in diffusion-sensitized ophthalmic imaging.


In vivo studies in healthy volunteers (n=3) were performed on a 3.0 T whole body MR system (Siemens Healthcare, Erlangen, Germany). Informed written consent was obtained from each volunteer prior to the study in compliance with the local institutional review board guidelines. IVI was realized by applying the excitation radiofrequency pulse selectively in phase encoding direction. Diffusion-sensitized ms-RARE (Figure 1) was conducted using: TR=3300ms, TE=46ms, receiver bandwidth=263kHz, ESP=6.6ms, spatial resolution=(0.5x0.5x5)mm3, six b-values ranging from 0 to 500s/mm2. Full FOV imaging ((140x140)mm2, acquisition matrix 256x256, acquisition time 58s per b-value) was performed in comparison to a 50% reduced FOV acquisition (140x70)mm2, acquisition matrix 256x128, acquisition time 31 s per b-value). To further tailor the FOV to the target region, the FOV was reduced to (120x48)mm2 with an acquisition matrix of 192x78 resulting in an in-plane spatial resolution of (0.6x0.6)mm2 and an acquisition time of 21s per b-value. Apparent diffusion coefficient maps were generated by fitting the data points obtained for a series of b-values to a linear decay after taking the logarithm of the signal intensity.


The anatomical images (b=0s/mm2) (Figure2a-c) demonstrate that IVI allows adjustment of the FOV to the eye and the orbit without folding artifacts. For the full FOV configuration phase encoding was set L-R to circumvent folding artifacts; for the reduced FOV set-up it could be changed to A-P which better fits the target anatomy. Simultaneously, the acquisition time was reduced by a factor of two for the 50% FOV configuration. The reduction in signal-to-noise ratio (SNR) for ms-RARE with IVI did not impede diagnostic image quality of the morphological images. ADC mapping free of geometric distortion was feasible for all FOV configurations (Figure2d-f). For strong diffusion weighting the SNR was further lowered generating a higher noise level in the ADC maps obtained for reduced FOV acquisition. Despite of this confinement no diagnostic information was lost since the complete bulbus was well displayed.


Reducing the FOV along the phase encoding direction is beneficial for ocular MRI but also for optic nerve imaging where only a narrow region is in the focus of interest. Imaging the eye and the orbit involves strategies to reduce involuntary motion including application of a triggering scheme dictating fixing and relaxing periods or asking the volunteer to avoid blinking by fixing the view on a fixation cross. Both strategies benefit from shorter acquisition times ultimately resulting in better image quality and enhanced volunteer comfort. The proposed IVI technique is restricted to single-slice acquisitions. Incorporating ZOOM imaging [9] offers means for multi-slice imaging. Replacing the current Cartesian sampling pattern by radial views – preferably PROPELLER [10] – promises to further reduce the susceptibility of diffusion-weighted ms-RARE to motion and hence would relax the demands of volunteer cooperation.


This study demonstrates that diffusion-sensitized ms-RARE in conjunction with inner volume imaging provides distortion-free images of the eye and orbit. At the same time acquisition time is drastically shortened compared to the traditional full FOV ms-RARE approach without compromising diagnostic value. The relaxed time constraints of IVI ms-RARE reduce the propensity of conventional ms-RARE to eye motion. This benefit is very instrumental en route to fast and robust high-spatial resolution DWI of the eye and the orbit with high anatomic fidelity for the diagnosis, therapy planning and treatment response monitoring of ocular and orbital diseases.


No acknowledgement found.


[1] Mafee et al, Neuroimag Clin N Am 2005,15:23; [2] Apushkin et al, Neuroimag Clin N Am 2005,15:49; [3] Sepahdari et al, AJNR 2012,33:314; [4] Beenakker et al, NMR Biomed 2013,26:1864; [5] Graessl et al, Invest Radiol 2014,49:260; [6] Norris et al, NMR Biomed 1994,7:304; [7] Paul et al, Invest Radiol 2015,50:309; [8] Feinberg et al, Radiology 1985,156:743; [9] Wheeler-Kingshott et al, Magn Reson Med 2002,47:24; [10] Pipe, Magn Reson Med 199, 42:963.


Basic scheme of the diffusion-sensitized ms-RARE sequence. The dephasing frequency encoding gradient is unbalanced. After the third refocusing pulse, both the odd (E1) and the even (E2) echoes are generated for the first time. These data are acquired without phase encoding and serve as navigator signal.

Anatomical images (a-c) and ADC maps (d-f) of a healthy volunteer for a full FOV configuration (top), a corresponding reduced FOV acquisition (middle) and a further adjusted geometric set-up (bottom). White arrows indicate phase encoding direction. All ADC maps exhibit the same scaling.

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