Clinical evaluation of white matter lesions on 3D inversion recovery ultrashort echo time MRI in multiple sclerosis

Abstract

Background: We clinically evaluated the quality of white matter lesions (WML) of the cerebrum on 3D inversion recovery ultrashort echo time (IR-UTE) magnetic resonance imaging (MRI) in multiple sclerosis (MS) patients.

Methods: Forty-nine patients with MS were included in this study. A 3T MRI scanner was used. Two radiologists (readers) evaluated the quality of WML on IR-UTE images using a three-point Likert scale (1-good quality, 2-moderate quality, 3-insufficient quality). They also rated other WML-related factors potentially influencing WML quality using another three-point Likert scale (1-no/minor impact, 2-moderate impact, 3-high impact). Another reader rated the presence of WML on IR-UTE to evaluate the diagnostic value (right/false positive and false negative) of IR-UTE in detecting WML. Signal intensity ratios (SIRs) derived from WML signal intensities and WML sizes were also determined and analyzed.

Results: Two hundred and seventy-five MS lesions were evaluated. 87% of the lesions were rated Likert 1 on IR-UTE (P<0.01). WML rated Likert 2 and 3 presented near the grey matter (GM) in 58% of the cases (n=21), with 14 lesions being ≤2 mm (P=0.03). 62.5% of the WML rated Likert 2/3 were in the temporal lobe (P=0.02). The mean SIR of WML on IR-UTE was 1.14±0.22, while the mean SIR on fluid-attenuated inversion recovery (FLAIR) was 6.97±1.88. There was no significant correlation of SIRs between IR-UTE and FLAIR (R=0.14, P=0.245). 92.4% of the WML were correctly detected on IR-UTE (n=254). 19 out of the 21 false positive/negative rated WML were located near the GM or in the temporal lobe. WML presented 7.7% smaller in mean on IR-UTE compared to FLAIR. Factors affecting WML quality with a moderate or high impact (Likert 2 and 3) were not found.

Conclusions: Most WML are clearly detectable on IR-UTE sequences. The main limitations are WML in the temporal lobe and near the GM.

Keywords: Multiple sclerosis; brain; diagnostics; magnetic resonance imaging (MRI); white matter.

Figure 1

Principle of the 3D IR-UTE sequence for myelin imaging. (A) 3D IR-UTE sequence diagram, (B) the cones sampling strategy, (C) the myelin imaging contrast mechanism. The pulse sequence employs a long adiabatic inversion pulse to invert the longitudinal magnetization of WM_L, followed by a short rectangular pulse excitation and cones sampling with a minimal TE of 32 µs. The spiral trajectories are distributed along each cones for efficient sampling of the 3D k-space. The multi-spokes are sampled when the inverted longitudinal magnetization of WM_L approaches the nulling point. The residual long T2 signals are suppressed by subtracting the second echo from the first one, creating excellent contrast for myelin. IR-UTE, inversion recovery ultrashort echo time; WM_L, long T2 whiter matter; TE, echo time; DAW, data acquisition window; FID, free induction decay; Gx,y,z, gradient; N_sp, number of spokes; RF, radio frequency; TR, repetition time.

Figure 2

Examples of WML on 3D IR-UTE (A,C,E) and 3D FLAIR (B,D,F). (A,B) Show a lesion near the GM that is clearly to distinguish on both sequences (white arrow), while images (C,D) present a small lesion near the GM of under 2 mm (black arrow), which is not sufficient to detect on 3D IR-UTE. (E,F) Show a clearly identifiable periventricular WML (white arrowhead). WML, white matter lesion; IR-UTE, inversion recovery ultrashort echo time; FLAIR, fluid-attenuated inversion recovery; GM, grey matter.

Figure 3

Whole brain image on 3D IR-UTE (A) and 3D FLAIR (B). A WML in the right frontal lobe is shown (white arrow). IR-UTE, inversion recovery ultrashort echo time; FLAIR, fluid-attenuated inversion recovery; WML, white matter lesion.