Vipul Ravindra Sheth MD, PhD, Presenter: Nothing to Disclose

Qun He MEng, Abstract Co-Author: Nothing to Disclose

Graeme M. Bydder MBChB, Abstract Co-Author: Nothing to Disclose

Jody Corey-Bloom, Abstract Co-Author: Nothing to Disclose

Jiang Du PhD, Abstract Co-Author: Nothing to Disclose

Myelin is a lamellar membranous structure essential for proper function of the nervous system. In this study we aimed to image and quantify myelin in volunteers and patients with multiple sclerosis (MS) using ultrashort echo time (UTE) sequences on a clinical 3T scanner.

The protons in myelin itself have very short T2s and are not detected with clinical sequences. We have implemented a 2D adiabatic inversion recovery prepared dual echo UTE (IR-dUTE) acquisition with a TE of 8 μs to detect signals from these protons. An adiabatic inversion pulse was used to invert and null the long T2 components in white matter. The ultrashort T2 components are not inverted due to fast relaxation, and are detected by subsequent UTE data acquisition. Residual signals from other long T2 signals (e.g., gray matter) are suppressed via subtraction of the 2nd image from the first one, providing selective depiction of the ultrashort T2* components in white matter. The IR-dUTE sequence was applied to ten healthy volunteers and 12 MS patients using the following parameters: 24 cm FOV, 5 mm slice, 125 kHz bandwidth, 60°, 1500 ms TR, 420 ms TI, TE=8 μs and 2.2 ms, recon matrix=256X256, 6.5 min scan time. T2* was quantified with two interleaved 4-echo UTE acquisitions (TEs = 0.008/2.2/4.4/6.6 ms, 0.2/3.3/5.5/7.7 ms). T2* was quantified via mono-exponential fitting of the IR-UTE signal decay.

High contrast was achieved for myelin both in healthy volunteers and MS patients. Myelinated areas of white matter appeared high signal on IR-dUTE images and areas of presumed myelin loss appeared low signal. Myelin showed an ultrashort T2* of 0.2-0.5 ms. These results suggest that the IR-UTE sequence can generate high contrast images of myelin, and allow direct assessment of myelin loss and changes in its tissue properties via T2* measurement. Further validation will be performed via IR-UTE imaging of white matter specimens before and after D2O exchange (little or no change in IR-UTE signal would show that myelin is selectively directed).

The 2D IR-dUTE sequence can directly image and quantify the ultrashort T2* components in white matter of the brain in a clinical setting. There is significantly loss of the ultrashort T2* components, consistent with myelin loss in MS patients.

Direct imaging and quantification of myelin may significantly advance the study of white matter diseases, including MS.

Sheth, V, He, Q, Bydder, G, Corey-Bloom, J, Du, J, In Vivo Imaging of Myelin Using Ultrashort Echo Time (UTE) Sequences at 3T.  Radiological Society of North America 2014 Scientific Assembly and Annual Meeting, - ,Chicago IL. http://archive.rsna.org/2014/14008410.html