MR-guided sclerotherapy of low-flow vascular malformations using T₂-weighted interrupted bSSFP (T₂W-iSSFP): Comparison of pulse sequences for visualization and needle guidance

Purpose: Image-guided treatment of low-flow vascular (venous or lymphatic) malformations presents a challenging visualization problem, regardless of the imaging modality being used for guidance. The purpose of this study was to employ a new magnetic resonance imaging (MRI) sequence, T₂-weighted interrupted balanced steady-state free precession (T₂W-iSSFP), for real-time image guidance of needle insertion. Materials and Methods: T₂W-iSSFP uses variable flip angle balanced steady-state free precession (bSSFP, a.k.a. SSFP) to establish T₂-weighting and fat suppression. Swine (n = 3) and patients (n = 4, three female, all with venous malformations) were enrolled in the assessment. T₂-weighted turbo spin echo (T₂-TSE) with spectral adiabatic inversion recovery (SPAIR), SPAIR-T₂-TSE or T₂-TSE for short, was used as the reference. T₂-weighted half Fourier acquired single shot turbo spin echo (T₂-HASTE) with SPAIR (SPAIR-T₂-HASTE, T₂-HASTE for short), fat saturated bSSFP (FS-SSFP), and T₂W-iSSFP were imaged. Numeric metrics, namely, contrast-to-noise ratio (CNR) efficiency (CNR divided by the square root of acquisition time) and local sharpness (the reciprocal of edge width), were used to assess image quality. MR-guided sclerotherapy was performed on the same patients using real-time T₂W-iSSFP to guide needle insertion. Results: Comparing the visualization of needles in the images of swine, the local sharpness (mm^-1) was: 0.21 ± 0.06 (T₂-HASTE), 0.48 ± 0.02 (FS-SSFP), and 0.49 ± 0.03 (T₂W-iSSFP). T₂W-iSSFP is higher than T₂-HASTE (P < 0.001). For the patient images, their CNR efficiencies were: 797 ± 66 (T₂-HASTE), 281 ± 44 (FS-SSFP), and 860 ± 29 (T₂W-iSSFP). T₂W-iSSFP is higher than FS-SSFP (P < 0.02). The frame rate of T₂W-iSSFP was 2.5-3.5 frames per second. All MR-guided sclerotherapy procedures were successful, with all needles (six punctures) placed in the targets. Conclusion: T₂W-iSSFP provides effective lesion identification and needle visualization. This new pulse sequence can be used for MR-guided sclerotherapy of low-flow vascular malformations. It may have potential use in other MR-guided procedures where heavily T₂-weighted real-time images are needed.