Dark Blood Contrast-Enhanced Brain MRI Using Echo-uT1RESS

Abstract

Background: The widely used magnetization-prepared rapid gradient-echo (MPRAGE) sequence makes enhancing lesions and blood vessels appear bright after gadolinium administration. However, dark blood imaging using T1-weighted Sampling Perfection with Application optimized Contrast using different flip angle Evolution (T1 SPACE) can be advantageous since it improves the conspicuity of small metastases and leptomeningeal disease. As a potential alternative to T1 SPACE, we evaluated a new dark blood sequence called echo-uT₁RESS (unbalanced T1 Relaxation-Enhanced Steady-State).

Purpose: We compared the performance of echo-uT₁RESS with Dixon fid-uT₁RESS, MPRAGE, and T1 SPACE.

Study type: Retrospective, IRB approved.

Subjects/phantom: Phantom to assess flow properties of echo-uT₁RESS. Twenty-one patients (14 female, age range 35-82 years) with primary and secondary brain tumors.

Field strength/sequences: 3 Tesla/MPRAGE, T1 SPACE, Dixon fid-uT₁RESS, echo-uT₁RESS.

Assessment: Flow phantom signal vs. velocity as a function of flip angle and sequence. Qualitative image assessment on 4-point scale. Quantitative evaluation of tumor-to-brain contrast, apparent contrast-to-noise ratio (aCNR), and vessel-to-brain aCNR.

Statistical tests: Friedman and Mann-Whitney U tests. A P value <0.05 was considered statistically significant.

Results: In the phantom, echo-uT₁RESS showed greater flow-dependent signal loss than fid-uT₁RESS. In patients, blood vessels appeared bright with MPRAGE, gray with fid-uT₁RESS, and dark with T1 SPACE and echo-uT₁RESS. For MPRAGE, Dixon fid-uT₁RESS, echo-uT₁RESS, and T1 SPACE, respective tumor-to-brain contrast values were 0.6 ± 0.3, 1.3 ± 0.5, 1.0 ± 0.4, and 0.6 ± 0.4, while normalized aCNR values were 68.9 ± 50.9, 128.4 ± 59.2, 74.2 ± 42.1, and 99.4 ± 73.9.

Data conclusion: Volumetric dark blood contrast-enhanced brain MRI is feasible using echo-uT₁RESS. The dark blood effect was improved vs. fid-uT₁RESS, while both uT₁RESS versions provided better tumor-to-brain contrast than MPRAGE. Whereas T1 SPACE provided better tumor aSNR, echo-uT₁RESS provided better Weber contrast, lesion sharpness and a more consistent dark blood effect.

Evidence level: 3 TECHNICAL EFFICACY: Stage 1.

Keywords: brain tumor; contrast enhancement; dark blood MRI; fast imaging with steady‐state free precession; unbalanced T1 relaxation‐enhanced steady‐state.

Fig. 1.

Flow phantom signal versus velocity for fid-uT₁RESS and echo-uT₁RESS. Echo-uT₁RESS was more effective at suppressing flow signal for all tested velocities and excitation flip angles.

Fig. 2.

A right-sided acoustic neuroma (red arrow) is well shown by all pulse sequences after gadolinium administration. The right transverse sinus (blue arrow) appears bright with MPRAGE, gray with Dixon fid-uT₁RESS, and dark with water-excite echo-uT₁RESS.

Fig. 3.

A micro-metastasis (red arrow) is difficult to distinguish from a small blood vessel with MPRAGE but is conspicuous with both uT₁RESS versions. Water-excite echo-uT₁RESS provides better suppression of signal from superficial veins than Dixon fid-uT₁RESS.

Fig. 4.

A left-sided glomus jugulare tumor (red arrow) appears similarly bright to the contralateral jugular vein (blue arrow) with MPRAGE, whereas the jugular vein appears gray with Dixon fid-uT₁RESS and dark with water-excite echo-uT₁RESS.

Fig. 5.

Multiple small brain metastases are difficult to visualize with MPRAGE but are highly conspicuous with both uT₁RESS versions.

Fig. 6.

Multiple small brain metastases (red arrows) are seen with MPRAGE, echo-uT₁RESS and T1 SPACE, although a weakly enhancing lesion (orange arrow) in the posterior right temporal lobe is only visible with echo-uT₁RESS. Compared with echo-uT₁RESS, the margins of small lesions appear less distinct with T1 SPACE and there is inconsistent suppression of intravascular signal in some of the venous structures (blue arrows).

Fig. 7.

Large necrotic tumor (red arrow) is well seen with all sequences, although the tumor margins appear less sharp with T1 SPACE than echo-uT₁RESS. Intravascular signal is noted in the jugular vein and sigmoid sinus (blue arrow) with T1 SPACE, whereas these vessels appear uniformly dark with echo-uT₁RESS.